KR20210010029A - Protecting film for cover window of flexible display device, cover window and flexible display device comprising the same - Google Patents

Abstract

The present invention relates to: a protecting film for a cover window of a flexible display device in which a first hard coating layer comprising 3 parts by weight or less of inorganic particles relative to 100 parts by weight of a binder resin, a second hard coating layer comprising 10 to 45 parts by weight of inorganic particles relative to 100 parts by weight of the binder resin, and a light-transmitting substrate are sequentially stacked; and the cover window for the flexible display device comprising the same; and the flexible display device comprising the same.

Description

Protective film for cover windows of flexible display devices, cover windows and display devices including them {PROTECTING FILM FOR COVER WINDOW OF FLEXIBLE DISPLAY DEVICE, COVER WINDOW AND FLEXIBLE DISPLAY DEVICE COMPRISING THE SAME}

The present invention relates to a protective film for a cover window of a flexible display device, a cover window including the same, and a display device.

Recently, as the demand for display devices that input, manipulate, and display information on a touch screen such as televisions, computers, mobile communication terminals, smartphones, vehicle navigation systems, and cash dispensers has increased, flat displays are being applied to more diverse purposes. ) In addition, recently, a flexible display that can be bent or folded has been released.

Such a cover window for a flexible display is a layer applied to the outermost side of a flexible display, and needs excellent flexibility in order to exhibit high hardness and scratch resistance and at the same time satisfy characteristics such as bender, foldable, and rollable. Generally, in order to satisfy such high hardness, glass is used as a cover panel.

However, when using glass as a cover panel, the hardness is excellent, but the impact resistance is lowered and it is fragile when an impact occurs, and there is a risk for the user to handle it due to the occurrence of fragments. There is a need for a protective film that can improve impact resistance.

However, when the conventional protective film is excellent in scratch resistance and hardness characteristics, there is a problem in that the flexibility is lowered and thus dynamic folding and static folding are deteriorated.In addition, when the bending property is excellent, scratch resistance There is a problem that the properties and hardness properties are deteriorated. Therefore, there is a need for a protective film having excellent scratch resistance and hardness properties and excellent flexibility.

The present invention satisfies the balance of physical properties of flexibility, high hardness and scratch resistance at the same time, in particular, almost no damage to the film even by repeated bending or folding operation, improves the impact resistance of the glass panel, and the glass panel Provides a protective film for a cover window of a flexible display device that prevents scattering when broken.

In addition, the present invention includes the protective film, and exhibits flexibility, flexibility, high hardness, scratch resistance, and high transparency, and in particular, there is little damage to the film even by repeated bending or folding operation, so that it is bent, flexible, and rollable. Or, a cover window of a flexible display device that can be easily applied to a foldable mobile device or a display device is provided.

In addition, the present invention provides a flexible display device including the cover window.

In the present specification, a first hard coating layer comprising 3 parts by weight or less of inorganic particles relative to 100 parts by weight of the first binder resin; A second hard coating layer comprising 10 to 45 parts by weight of inorganic particles relative to 100 parts by weight of the binder resin; And a light-transmitting substrate; are sequentially stacked, and a thickness ratio of the first hard coating layer and the second hard coating layer is 10:90 to 40:60, providing a protective film for a cover window of a flexible display device.

In addition, the present specification provides a cover window for a flexible display device including a protective film for a cover window of the flexible display device.

In addition, the present specification provides a flexible display device including a cover window of the flexible display device.

Hereinafter, a protective film for a cover window of a flexible display device according to a specific embodiment of the present invention, a cover window of a flexible display device including the same, and a flexible display device will be described in more detail.

In the present specification, "flexible" refers to a state having a degree of flexibility that does not cause cracks of 3 mm or more in length when wound around a cylindrical mandrel having a diameter of 8 mm or less, and thus this The flexible plastic film of the present invention can be applied as a cover film for a bendable, flexible, rollable, or foldable display.

In the present specification, "(meth)acrylate" is meant to include both acrylate or methacrylate.

In the present specification, the "light-transmitting substrate" means a substrate having a light transmittance of 50% or more in a visible light region, for example, 380 to 780 nm.

According to an embodiment of the present invention, a first hard coating layer comprising 3 parts by weight or less of inorganic particles relative to 100 parts by weight of a binder resin; A second hard coating layer comprising 10 to 45 parts by weight of inorganic particles relative to 100 parts by weight of the binder resin; And a light-transmitting substrate; are sequentially stacked, and a thickness ratio of the first hard coating layer and the second hard coating layer is 10:90 to 40:60, and a protective film for a cover window of a flexible display device may be provided.

The present inventors have conducted research on an optical laminate applicable to a protective film for a cover window of a flexible display device, and in an optical laminate having a two-layered hard coating layer on one side of a light-transmitting substrate, in contact with the light-transmitting substrate. The lower hard coating layer (hereinafter referred to as the second hard coating layer) is thicker than the upper hard coating layer (hereinafter referred to as the first hard coating layer), and for example, the thickness ratio of the first and second hard coating layers is higher. 10:90 to 40:60, and the second hard coating layer contains inorganic particles in a specific amount, while the first hard coating layer contains almost no inorganic particles, while having high hardness and excellent scratch resistance When wound around a mandrel having a diameter of 8 mm or less, cracks did not occur, so it was confirmed that it can be used as a protective film for a cover window of a flexible display device, and the invention was completed.

In addition, the protective film for the cover window of such a flexible display device is realized to satisfy the physical property balance of flexibility and high hardness at the same time, and at the same time exhibits excellent scratch resistance and high hardness characteristics. It was confirmed through an experiment that it could be easily applied to a bendable, flexible, rollable, or foldable mobile device, or a display device due to almost no damage, and the invention was completed.

As described above, physical properties such as bending durability, scratch resistance, and high hardness of the protective film for a cover window of the flexible display device are components included in the first hard coating layer and the second hard coating layer, in particular, a component of a binder resin. And, it may be according to whether the inorganic particles are included in the binder resin and the content thereof. In addition, the above-described physical properties may also be related to the thickness ratio of the first hard coating layer and the second hard coating layer.

A two-layer hard coating layer may be formed on the light-transmitting substrate included in the protective film for the cover window of the flexible display device, and as described above, a second hard coating layer is formed on the light-transmitting substrate, and 2 A first hard coating layer is formed on the hard coating layer, and the protective film may sequentially include a first hard coating layer, a second hard coating layer, and a substrate. As the protective film includes a light-transmitting substrate and a two-layer hard coating layer, excellent bendability, hardness, and scratch resistance may be simultaneously realized. In addition, according to this structure, the balance of flexibility, scratch resistance, and high hardness can be satisfied at the same time, and damage to the internal structure can be prevented even by repeated bending or folding operations, and also excellent mechanical properties and heat resistance. It may have optical properties such as high transparency.

In the above-described two-layered hard coating layer, the second hard coating layer, which is a lower layer, is 100 parts by weight of a binder resin, and 10 to 45 parts by weight of inorganic particles, 10 to 40 parts by weight, 15 to 35 parts by weight, based on 100 parts by weight of the binder resin, Or 20 to 30 parts by weight. Meanwhile, the upper layer includes 100 parts by weight of the binder resin, and 3 parts by weight or less, 1 part by weight or less, or 0.1 parts by weight or less, or substantially no inorganic particles based on 100 parts by weight of the binder resin. May not.

The inorganic particles may serve to improve the hardness of the hard coating layer, but when inorganic particles are present on the surface of the hard coating layer due to a somewhat weak interaction with the binder resin, scratch resistance is lowered due to surface roughness. Can be.

Therefore, in order to improve the scratch resistance of the protective film for the cover window of the flexible display device according to the embodiment, the first hard coating layer, which is an upper layer, is 3 parts by weight or less, 1 part by weight or less, 0.1 parts by weight compared to 100 parts by weight of the binder resin. It may contain less than a part by weight, or may not contain substantially inorganic particles. When the first hard coating layer contains more than 3 parts by weight of inorganic particles compared to 100 parts by weight of the binder resin, the scratch resistance of the protective film is lowered, making it easy for external impacts. Scratch Can occur.

On the other hand, in order to improve the hardness of the protective film for a cover window of the flexible display device, the second hard coating layer, which is a lower layer, contains 10 to 45 parts by weight, 10 to 40 parts by weight, and 15 to 40 parts by weight of inorganic particles based on 100 parts by weight of the binder resin. It may contain 35 parts by weight, 20 to 30 parts by weight. Accordingly, the protective film satisfies the balance of physical properties of flexibility and high hardness at the same time, and can prevent damage to the internal structure even by repeated bending or folding operations, and at the same time, excellent mechanical properties, heat resistance, and high transparency, etc. It can have the optical properties of.

When too few inorganic particles are included in the second hard coating layer, sufficient hardness cannot be achieved, and when too many inorganic particles are included There is a problem in that the coating film becomes brittle and the bending characteristics are deteriorated.

The inorganic particles include, for example, silica, aluminum oxide, zirconia, titania, zinc oxide, germanium oxide, indium oxide, tin oxide, indium tin oxide, antimony oxide, cerium oxide, etc.; Metal fluoride particles formed of magnesium fluoride, sodium fluoride, or the like; Metal sulfide particles; Metal nitride particles; And it may be at least one selected from the group consisting of metal particles.

In addition, the diameter of the inorganic particles may be 1 to 300 nm, 10 to 200 nm, or 30 to 100 nm.

The protective film for the cover window of the flexible display device according to the above embodiment simultaneously satisfies the balance of properties of flexibility, high hardness, and scratch resistance, and prevents damage to the internal structure even by repeated bending or folding operations. , It can have optical properties such as high transparency along with high mechanical properties and heat resistance. In addition, the physical property balance and excellent optical properties may be related to the thickness of the first hard coating layer and the second hard coating layer.

In the above-described two-layered hard coating layer, the first hard coating layer, which is an upper layer, may be thinner than the second hard coating layer, which is a lower layer, and specifically, the thickness ratio of the first hard coating layer and the second hard coating layer is 10:90. To 40:60, 15:85 to 35:65, or 20:80 to 30:70. If the thickness ratio of the first hard coating layer and the second hard coating layer is less than 10:90 Scratch resistance may be deteriorated, and if it exceeds 40:60, there is a problem in that bending characteristics are deteriorated.

On the other hand, the thickness of the first hard coating layer is 1㎛ to 10㎛, It may be 1 to 9㎛, or 2 to 7㎛. When the thickness of the first hard coating layer is too thick, the bending properties may be deteriorated, and when the first hard coating layer is too thin, there is a problem in that scratch resistance is deteriorated.

The thickness of the second hard coating layer is 1㎛ to 10㎛, 2 to 9㎛, Or it may be 3 to 8㎛. When the thickness of the second hard coating layer is too thick, the bending properties may be deteriorated, and when the second hard coating layer is too thin, there is a problem in that the film hardness is decreased.

Meanwhile, the total thickness of the first hard coating layer and the second hard coating layer may be 2 to 15 μm, 3 to 14 μm, or 4 to 13 μm. When the sum of the total thicknesses of the first hard coating layer and the second hard coating layer is excessively large, crack resistance and durability for repeated bending or folding operation may be deteriorated. On the other hand, when the sum of the total thicknesses described above becomes excessively thin, the hardness may be lowered, so that scratches may occur due to external impact.

Meanwhile, due to the specific composition and structure of the protective film for a cover window of the flexible display device described above, durability against repeated bending or folding operations applied to the protective film is also excellent.

Specifically, cracks may not occur when a gap of 4 mm is placed in the middle of the protective film for a cover window of the flexible display device, and when both sides of the protective film are folded and unfolded at 90 degrees with respect to the bottom surface and repeated 100,000 times at room temperature. . Repeating the folding and unfolding of 4mm in the middle of the protective film may be, for example, a bending test performed around a rod having a diameter of 4mm on the protective film.

In addition, the protective film for a cover window of the flexible display device may have a pencil hardness measured on the surface of the first hard coating layer of H or more based on a 750 g load.

In addition, the protective film for a cover window of the flexible display device may have a water contact angle of 105° or more on the surface of the first hard coating layer. When the protective film is used for a display surface in a touch panel, the first hard coating layer may function as a touch surface. Since the protective film has a water contact angle of 105° or more, the touch panel can be freely operated by sliding a finger or a pen on the touch surface.

Meanwhile, the protective film for a cover window of the flexible display device of the embodiment has a light transmittance of 90.0% or more, 92.0% or more, or 94.0% or more, and a haze of 1.0% or less, or 0.7% or less with respect to light in a wavelength range of 550 nm. , Or 0.5% or less.

The protective film for a cover window of the flexible display device of the embodiment includes a hard coating layer that has high hardness and can secure durability against repeated bending or folding operations, and this feature of the hard coating layer is included in the hard coating layer. Composition of the binder resin and as described above It may be related to the presence or absence of inorganic particles and their content.

Specifically, the binder resin included in the first hard coating layer and the second hard coating layer may include a multifunctional (meth)acrylate-based compound. The polyfunctional (meth)acrylate-based compound may be, for example, a polyfunctional (meth)acrylate-based monomer, a polyfunctional (meth)acrylate-based oligomer, or a mixture thereof. Specifically, the first hard coating layer and the second hard coating layer may include the same polyfunctional (meth)acrylate-based compound, or may include different polyfunctional (meth)acrylate-based compounds. At this time, as described above, the binder resin of the first hard coating layer contains 3 parts by weight or less, 1 part by weight or less, 0.1 parts by weight or less, or substantially does not contain inorganic particles based on 100 parts by weight of the binder resin. The second hard coating layer may contain 10 to 45 parts by weight, 10 to 40 parts by weight, 15 to 35 parts by weight, and 20 to 30 parts by weight of inorganic particles, based on 100 parts by weight of the binder resin.

Specifically, the multifunctional (meth) acrylate-based compound has 2 to 10 (meth) acrylate functional groups, and the weight average molecular weight is 50 to 2,000 g/mol, 10 to 1,000 g/mol, or 100 to 700 g/ mol, and an acrylate equivalent weight may be 50 to 1000 g/mol, 100 to 900 g/mol, or 150 to 800 g/mol.

In addition, the first hard coating layer and the second hard coating layer, based on 100 parts by weight of the binder resin, 50 parts by weight or more, 60 parts by weight to 100 parts by weight, or 70 parts by weight of the polyfunctional (meth) acrylate compound It may contain parts by weight to 95 parts by weight, and thus, the flexibility of the hard coating layer including the binder resin may be improved.

Further, the polyfunctional (meth)acrylate-based compound is composed of ethylene oxide, propylene oxide, urethane, caprolactone, epoxy and ester. It may be denatured with one or more selected from the group. Specifically, the polyfunctional (meth)acrylate-based compound has excellent flexibility and can impart flexibility to the hard coating layer using it, and furthermore, the above-described modified polyfunctional (meth)acrylate-based oligomer has improved flexibility. And, in the case of the hard coating layer using this, curling characteristics and flexibility may increase.

The polyfunctional (meth)acrylate oligomer has an acrylate functional group There are 2 to 10, the weight average molecular weight may be 200 to 2,000 g/mol, 200 to 1,000 g/mol, or 200 to 500 g/mol, and the acrylate equivalent weight is 100 to 1000 g/mol, It may be 200 to 900 g/mol, or 300 to 800 g/mol. The (meth)acrylate-based oligomer is not limited thereto, but may include, for example, one or more functional groups selected from the group consisting of urethane, epoxy, ether, alkylene oxide, and ester.

On the other hand, the polyfunctional (meth)acrylate-based monomer has an acrylate functional group There are 2 to 6, Weight average molecular weight 50 to 600 g/mol, 50 to 500 g/mol, or 50 to 300 g/mol. In addition, the polyfunctional (meth) acrylate monomer has an acrylate equivalent weight It may be 50 to 300 g/mol, 70 to 250 gmol, or 100 to 200 g/mol. The polyfunctional (meth)acrylate-based monomer is not limited thereto, but trimethylolpropane triacrylate (TMPTA), trimethylolpropaneethoxy triacrylate (TMPEOTA), glycerin propoxylated triacrylate (GPTA), Pentaerythritol tetraacrylate (PETA), dipentaerythritol hexaacrylate (DPHA), and the like.

The first hard coating layer may further include one or more additives selected from the group consisting of a fluorine-based additive, a silicone-based additive, and a fluorine-silicone-based additive. The additives may improve finger sliding properties, stain resistance and wipeability against stains. In the first hard coating layer, 0.5 to 5 parts by weight, 1 to 4 parts by weight, or 2 to 3 parts by weight of the additive may be included with respect to 100 parts by weight of the binder resin. remind If the content of the additive is too small, finger sliding properties, stain resistance, and wipeability against stains may be deteriorated, and if the content of the additive is too high, the content of other components may be reduced, thereby reducing strength and scratch resistance.

The fluorine-based additive is not limited thereto, but may be a fluoropolyether, a fluoropolyalkyl, or a mixture thereof. In addition, the silicone additive is not limited thereto, but may be a silicone resin modified with various organic groups such as polyether, alkyl, acrylic, and epoxy.

In addition, the fluorine-silicone-based additive is not limited thereto, but may be a polydialkylsiloxane-based polymer in which at least one silicon is substituted with one or more fluorine, for example, a siloxane-fluoropolyalkyl-based compound.

On the other hand, the protective film for the cover window of the flexible display device has excellent optical properties and satisfies the balance of physical properties of flexibility, high hardness, and high scratch resistance in order to realize the above-described characteristics, and can be applied to the internal structure by repeated bending or folding operations. It is preferable to include a light-transmitting substrate capable of preventing damage to occur. In this case, the light-transmitting substrate refers to a substrate having a light transmittance of 50% or more in a visible light region, for example, 380 to 780 nm.

Specifically, the yellow index of the light-transmitting substrate measured based on the standard of ASTM D1925 is 4.5 or less or 3.8 or less, and the haze of the light-transmitting substrate measured based on the standard of ASTM D1003 is 1.1% or less, or 0.4 to 0.8% It may be, and thus may have colorless and transparent optical properties.

The type of the light-transmitting substrate is not limited as long as it satisfies the above-described characteristics, but more specific examples include polyimide (PI), polyimideamide, polyetherimide (PEI), and polyethylene. Terephthalate (PET), polyethylenenaphthalate (PEN), polyetheretherketon (PEEK), cyclic olefin polymer (COP), polyacrylate (PAC), polymethyl It may include one or more selected from the group consisting of methacrylate (polymethylmethacrylate, PMMA), and triacetylcellulose (TAC).

In addition, the thickness of the light-transmitting substrate may be 5 to 150 μm, 10 to 130 μm, or 20 to 100 μm. When the thickness of the light-transmitting substrate is too thin, it may be broken or curled during the coating layer forming process, and it may be difficult to achieve high hardness. On the other hand, if the thickness is too thick, the flexibility may be poor and it may be difficult to form a flexible film.

Meanwhile, in the protective film for a cover window of the flexible display device, a second hard coating layer is formed by applying and photocuring a coating composition for forming a second hard coating layer on at least one surface of the light-transmitting substrate, and forming a second hard coating layer on the second hard coating layer. 1 It can be provided by applying a coating composition for forming a hard coating layer and photocuring.

The method of applying the coating composition is not particularly limited as long as it can be used in the technical field to which the present technology belongs, and for example, bar coating method, knife coating method, roll coating method, blade coating method, die coating method, microgravure coating Method, comma coating method, slot die coating method, lip coating method, solution casting method, etc. can be used.

Between the light-transmitting substrate and the second hard coating layer, between the first hard coating layer and the second hard coating layer, or on the first hard coating layer, a plastic resin film, an adhesive film, a release film, a conductive film, a conductive layer, a liquid crystal layer , A coating layer, a cured resin layer, a non-conductive film, a metal mesh layer or a patterned metal layer such as a layer, film, or film may further include one or more.

For example, a conductive antistatic layer is first formed on the light-transmitting substrate, and then a second hard coating layer is formed thereon to provide an anti-static function, or a low refractive index layer is formed on the first hard coating layer. It can also be introduced to implement a low reflection function.

In addition, the layer, film, or film may be in any form of a single layer, a double layer, or a laminated type. The layer, film, or film may be laminated on the coating layer by lamination of a freestanding film using an adhesive or an adhesive film, or coating, vapor deposition, sputtering, etc., but the present invention It is not limited thereto.

Meanwhile, the first and second hard coating layers include photoinitiators, organic solvents, surfactants, UV absorbers, UV stabilizers, anti-yellowing agents, leveling agents, antifouling agents, dyes for improving color values, in addition to the binder resin and inorganic fine particles. Ingredients commonly used in the technical field to which the present invention pertains may be further included. In addition, the content can be variously adjusted within a range that does not deteriorate the physical properties of the hard coating layer, so it is not particularly limited, but may be included in, for example, about 0.01 to about 30 parts by weight based on 100 parts by weight of the hard coating layer. .

The surfactant may be a 1 to 2 functional fluorine-based acrylate, a fluorine-based surfactant, or a silicone-based surfactant. At this time, the surfactant may be included in a form dispersed or crosslinked in the hard coating layer.

In addition, a UV absorber or a UV stabilizer may be included as the additive, and the UV absorber may include a benzophenone compound, a benzotriazole compound, or a triazine compound, and the UV stabilizer is tetramethylpi And peridine (tetramethyl piperidine).

As the photoinitiator, 1-hydroxy-cyclohexyl-phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2-hydroxy-1-[4-(2-hydroxyethoxy )Phenyl]-2-methyl-1-propanone, methylbenzoylformate, α,α-dimethoxy-α-phenylacetophenone, 2-benzoyl-2-(dimethylamino)-1-[4-(4- Morpholinyl)phenyl]-1-butanone, 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone diphenyl (2,4, 6-trimethylbenzoyl)-phosphine oxide, or bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, but is not limited thereto. In addition, currently marketed products include Irgacure 184, Irgacure 500, Irgacure 651, Irgacure 369, Irgacure 907, Darocur 1173, Darocur MBF, Irgacure 819, Darocur TPO, Irgacure 907, and Esacure KIP 100F. These photoinitiators may be used alone or in combination of two or more different types.

Examples of the organic solvent include alcohol solvents such as methanol, ethanol, isopropyl alcohol, butanol, 2-methoxyethanol, 2-ethoxyethanol, and alkoxy alcohol solvents such as 1-methoxy-2-propanol, acetone, and methyl. Ketone solvents such as ethyl ketone, methyl isobutyl ketone, methyl propyl ketone, cyclohexanone, propylene glycol monopropyl ether, propylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, Ether solvents such as diethylene glycol monomethyl ether, diethyl glycol monoethyl ether, diethyl glycol monopropyl ether, diethyl glycol monobutyl ether, diethylene glycol-2-ethylhexyl ether, benzene, toluene, xylene and The same aromatic solvent may be used alone or in combination.

Meanwhile, according to another embodiment of the invention, A cover window for a flexible display device including a protective film for a cover window of the flexible display device according to the embodiment may be provided.

The cover window for the flexible display device includes: a glass cover having a thickness of 30 μm to 200 μm; And it may include a protective film, specifically, the protective film may be located on the glass cover.

The glass cover It may have a transparent characteristic, and thus, light output from the display panel inside the flexible display device may be transmitted. In addition, the glass cover may have high hardness and excellent scratch resistance, but may be fragile due to low impact resistance. The glass cover may include, for example, glass having a refractive index (eg, a refractive index of 1.65 or more), but is not limited thereto.

However, the cover window for a flexible display device according to another embodiment includes a protective film for a cover window of the flexible display device, and in particular, by forming the protective film on the glass panel, the impact resistance of the glass panel In addition, it is possible to prevent the occurrence of scratches or imprints due to external impact, and prevent scattering when the glass panel is broken, thereby preventing danger in handling by the user.

Specifically, the glass cover may have a thickness of 30 µm to 200 µm, 40 to 180 µm, or 50 to 150 µm, and if the thickness is too thin, there is a problem that hardness characteristics are deteriorated, Too thick There is a problem in that the bending properties are deteriorated.

The cover window for the flexible display device may further include an adhesive layer. The adhesive layer may be disposed between the glass panel and the protective film. The adhesive layer may attach the glass panel and the protective film by pressure (pressing force) at room temperature.

The adhesive layer may be implemented as an adhesive or an adhesive film, and is not particularly limited as long as it is known in the art. Meanwhile, the adhesive film is not particularly limited as long as it is known in the art, but a double-sided adhesive film such as an optically clear adhesive (OCA) film may be used.

Meanwhile, according to another embodiment of the present invention, a flexible display device including a cover window of the flexible display device according to the embodiment may be provided.

The flexible display device is a curved, bendable, flexible, rollable, or foldable mobile communication terminal, a touch panel of a smartphone, a tablet PC, and a wearable. It can include both devices and various displays. According to various embodiments, the wearable device is an accessory type (e.g., a watch, a ring, a bracelet, an anklet, a necklace, glasses, contact lens, or a head-mounted-device (HMD)), a fabric, or an integrated clothing ( For example, it may include at least one of an electronic clothing), a body-attached type (eg, a skin pad or tattoo), or a living body type (eg, an implantable circuit).

The flexible display device may include a display panel and a cover window. In addition, the cover window may include a glass cover and a protective film, and may further include an adhesive layer between the glass cover and the protective film.

Meanwhile, the flexible display device may be, for example, a liquid crystal display (LCD) device, a light emitting diode (LED) display device, an organic light emitting diode (OLED) display device, a microelectromechanical system (MEMS) display device, or a rollable display device. It can be (rollable display or foldable display).

For example, in the organic light emitting diode (OLED) display device, a cover window of the flexible organic light emitting diode display device may be located at an outer portion in a direction in which light or a screen exits, and a cathode that provides electrons, An electron transport layer, an emission layer, a hole transport layer, and an anode providing holes may be sequentially formed. In addition, the organic light emitting diode (OLED) display may further include a hole injection layer (HIL) and an electron injection layer (EIL).

In order for the organic light-emitting diode (OLED) display to function and operate as a flexible display, the cathode and anode electrodes, and each component may be used as a material having a predetermined elasticity.

Another example of the flexible display device may be a rollable display or foldable display.

Meanwhile, the rollable display device may have various structures depending on the application field and specific shape, and includes, for example, a cover window, a touch panel, a polarizing plate, a barrier film, a light emitting device (OLED device, etc.), a transparent substrate, etc. It can be a structure.

According to the present invention, while simultaneously satisfying the balance of physical properties of flexibility, high hardness, and scratch resistance, there is almost no damage to the film even by repeated bending or folding operation, improving the impact resistance of the glass panel, and When this is broken, a protective film for a cover window of a flexible display device that prevents scattering may be provided.

In addition, the cover window and the flexible display device including the protective film for the cover window of the flexible display device exhibit flexibility, bendability, high hardness, scratch resistance, and high transparency, and in particular, film even by repeated bending or folding operation. Since the damage of the device is little, it can be usefully applied to bendable, flexible, rollable, or foldable mobile devices, display devices, front panels of various instrument panels, and display parts.

1 is an experimental example It schematically shows how to perform the bending durability test of 3.

Hereinafter, the functions and effects of the invention will be described in more detail through specific embodiments of the invention. However, these embodiments are only presented as examples of the invention, and the scope of the invention is not determined thereby.

[ Manufacturing example : Preparation of coating solution for hard coating layer formation]

Manufacturing example 1-1

Multifunctional acrylate compound MF001 (manufacturer: Daiichi Kogyo Seiyaku, 5--6 functional, ethylene oxide modified) 100g, fluorine additive RS-537 (manufacturer: DIC) 2g, photoinitiator I184 (manufacturer: Ciba) 2g and solvent A coating solution for forming a first hard coat layer was prepared by mixing 100 g of phosphorus methyl isobutyl ketone.

Manufacturing example 1-2

Multifunctional acrylate compound CN9013 (manufacturer: Sartomer, 9-functional, urethane modified) 100g, fluorine-based additive RS-537 (manufacturer: DIC) 2g, photoinitiator I907 (manufacturer: Ciba) 2g, and methyl isobutyl as a solvent 100 g of ketone was mixed to prepare a coating solution for forming the first hard coating layer.

Manufacturing example 1-3

Polyfunctional acrylate-based compound trimethylolpropane triacrylate (manufacturer: Cytec, weight average molecular weight: 296 g/mol, acrylate group equivalent: 99 g/mol) 100 g, fluorine-based additive RS-537 (manufacturer: DIC) 2 g , 2g of a photoinitiator I184 (manufacturer: Ciba) and 100g of methyl isobutyl ketone as a solvent were mixed to prepare a coating solution for forming a first hard coat layer.

Manufacturing example 1-4

Multifunctional acrylate compound MF001 (manufacturer: Daiichi Kogyo Seiyaku, 5--6 functional, ethylene oxide modified) 100g, fluorine additive RS-537 (manufacturer: DIC) 2g, inorganic particles MEK-AC-4130Y (silicasol) , Manufacturer: Nissan Chemical, diameter: 50nm, solid content 30%) 67g, photoinitiator I184 (manufacturer: Ciba) 2g, and a solvent, methyl isobutyl ketone 100g was mixed to prepare a coating solution for forming a first hard coat layer.

Manufacturing example 2-1

Polyfunctional acrylate compound trimethylolpropane triacrylate (manufacturer: Cytec, weight average molecular weight: 296 g/mol, acrylate group equivalent: 99 g/mol) 50 g, polyfunctional acrylate compound PS4040 (manufacturer: Miwon , Weight average molecular weight: 1300g/mol, acrylate group equivalent: 325, tetrafunctional, ester modified) 50g, inorganic particles MEK-AC-4130Y (silica sol, manufacturer: Nissan Chemical, diameter: 50nm, solid content 30%) 67g , 2 g of I184 (manufacturer: Ciba) as a photoinitiator, and 100 g of methyl isobutyl ketone as a solvent were mixed to prepare a coating solution for forming a second hard coating layer.

Manufacturing example 2-2

Trimethylolpropane triacrylate as a polyfunctional acrylate compound (manufacturer: Cytec, weight average molecular weight: 296 g/mol, acrylate group equivalent: 99 g/mol) 50 g, M244, a polyfunctional acrylate compound (manufacturer: Miwon , Weight average molecular weight: 468g/mol, acrylate group equivalent: 234g/mol, bifunctional, epoxy modified) 50g, inorganic particles MEK-AC-4130Y (silica sol, manufacturer: Nissan Chemical, diameter: 50nm, solid content 30% ) 67g, a photoinitiator of I184 (manufacturer: Ciba) 2g, and a solvent of methyl isobutyl ketone 100g were mixed to prepare a coating solution for forming a second hard coating layer.

Manufacturing example 2-3

Polyfunctional acrylate compound trimethylolpropane triacrylate (manufacturer: Cytec, weight average molecular weight: 296 g/mol, acrylate group equivalent: 99 g/mol) 50 g, polyfunctional acrylate compound PS4040 (manufacturer: Miwon , Weight average molecular weight: 1300 g/mol, acrylate group equivalent: 325, tetrafunctional, ester modified) 50 g, inorganic particles MEK-AC-2140Z (silica sol, manufacturer: Nissan Chemical, diameter: 12 nm, solid content 40%) 112.5 g, a photoinitiator of I184 (manufacturer: Ciba) 2 g, and a solvent of methyl isobutyl ketone 100 g were mixed to prepare a coating solution for forming a second hard coat layer.

Manufacturing example 2-4

Polyfunctional acrylate compound trimethylolpropane triacrylate (manufacturer: Cytec, weight average molecular weight: 296 g/mol, acrylate group equivalent: 99 g/mol) 50 g, polyfunctional acrylate compound PS4040 (manufacturer: Miwon , Weight average molecular weight: 1300 g/mol, acrylate group equivalent: 325, tetrafunctional, ester modified) 50 g, inorganic particles MEK-AC-2140Z (silica sol, manufacturer: Nissan Chemical, diameter: 12 nm, solid content 40%) 125 g , 2g of the photoinitiator I184 (manufacturer: Ciba) and 100g of methyl isobutyl ketone as a solvent were mixed to prepare a coating solution for forming a second hard coat layer.

Manufacturing example 2-5

Polyfunctional acrylate compound pentaerythritol triacrylate (manufacturer: Kyoeisha, weight average molecular weight: 298 g/mol, acrylate group equivalent: 100 g/mol) 100 g, inorganic particles MEK-AC-2140Z (silicasol, manufacturer: Nissan Chemical, diameter: 12 nm, solid content 40%) 125g, photoinitiator I184 (manufacturer: Ciba) 2g, solvent methyl isobutyl ketone 100g was mixed to prepare a coating solution for forming a second hard coating layer.

[ Example And Comparative example : Flexible Cover of display device For windows Protective film]

A coating solution for forming a second hard coating layer described in Table 1 below was applied to one surface of a light-transmitting base polyethylene terephthalate film, respectively, by a bar coating method, and dried at 60° C. for 2 minutes in an air atmosphere. Photocured with a mercury lamp (light quantity: 100mJ/cm2) in a nitrogen atmosphere to prepare a second hard coating layer.

Thereafter, on the second hard coating layer, each of the agents listed in Table 1 1 The coating solution for forming a hard coating layer was applied by a bar coating method and dried at 60° C. for 2 minutes in an air atmosphere. Photo-cured with a mercury lamp (light quantity: 200mJ/cm2) in a nitrogen atmosphere to prepare a first hard coating layer to prepare an optical laminate (protective film).

After the curing was completed, the thickness of the first hard coating layer and the second hard coating layer and the thickness of the polyethylene terephthalate film were measured using a digital micrometer, and the results are shown in Table 1 below.

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 1st hard coating layer Coating liquid Manufacturing Example 1-1 Manufacturing Example 1-1 Manufacturing Example 1-2 Manufacturing Example 1-1 Manufacturing Example 1-3 Manufacturing Example 1-4 Manufacturing Example 1-1 - Manufacturing Example 1-1 Manufacturing Example 1-1 Thickness (㎛) 2 1.5 3 2 5 2 5 - 2 2 2nd hard coating layer Coating liquid Manufacturing Example 2-1 Manufacturing Example 2-2 Manufacturing Example 2-2 Manufacturing Example 2-3 - Manufacturing Example 2-2 Manufacturing Example 2-2 Manufacturing Example 2-1 Manufacturing Example 2-4 Manufacturing Example 2-5 Thickness (㎛) 5 6 10 5 - 5 3 5 5 5 Light-transmitting substrate thickness (㎛) 75 100 75 75 75 75 75 75 75 75

<Experimental example : Flexible Cover of display device For windows Measurement of physical properties of protective film>

Experimental example 1: pencil hardness

Examples and Comparative Examples For the first hard coating layer of each protective film, a maximum of no scratches after reciprocating three times at an angle of 45 degrees and a load of 750 g according to the measurement standard JIS K5400-5-4 using a pencil hardness meter. The hardness was checked.

Experimental example 2: Flexibility Test

According to the method of measurement standard JIS K5600-5-1, for each of the protective films of Examples and Comparative Examples, the minimum diameter at which cracks of 3 mm or more in length did not occur after being wound around a cylindrical mandrel of various diameters were measured.

Experimental example 3: bending durability test

1 is a view schematically showing a method of performing a bending durability and bending stability test for a protective film according to an embodiment of the present invention.

Each of the cover windows of Examples and Comparative Examples was cut, but laser cut was performed to a size of 80 x 140 mm to minimize microcracks at the edge. Place the laser-cut film on the measuring equipment so that the gap between the folds is 4mm, and at room temperature, fold and unfold both sides of the film 90 degrees with respect to the bottom surface in a continuous operation (the film folding speed is once per 1.5 seconds). Repeated 10,000 times.

After removing the film after repeating 10,000 times, it was observed whether or not a crack of 3 mm or more occurred. When no cracks occurred, bending 10,000 times and observing the occurrence of cracks were repeated to measure the maximum number of repetitions in which no cracks occurred. If the crack did not occur until 100,000 times of repetition, it was judged as good, and if a crack occurred, it was judged as bad.

Experimental example 4: Scratch resistance evaluation

Examples and Comparative Examples For the hard coating layer formed on the front surface of each of the protective films, a load of 500 gf was applied to the steel wool (#0000) and reciprocated 100 times at a speed of 30 rpm to measure the surface of the hard coating film. If one or less scratches of 1 cm or less observed with the naked eye were observed, it was judged as good, and if more than one scratch was observed, it was judged as bad.

Experimental example 5: transmittance and Haze

For each of the protective films of Examples and Comparative Examples, transmittance and haze were measured using a spectrophotometer (device name: COH-400).

The measurement results of the physical properties for Examples and Comparative Examples are shown in Table 2 below.

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Pencil hardness 2H 2H 2H 2H 2H 2H 2H H 2H 3H Flexibility (mm) 6 5 6 8 12 6 10 4 10 16 Bending durability Good Good Good Good Bad Good Bad Good Bad Bad Scratch resistance Good Good Good Good Good Bad Good Bad Good Good Transmittance (%) 92.0 92.1 92.0 92.1 92.2 92.0 92.1 92.2 92.1 92.0 Haze (%) 0.3 0.4 0.3 0.3 0.3 0.3 0.4 0.3 0.3 0.3

As shown in Table 2, the protective film for the cover window of the flexible display device of the embodiments exhibits high hardness and satisfies sufficient flexibility at the same time and exhibits excellent scratch resistance, and optical properties related to transmittance and haze. It has been confirmed that the film is hardly damaged even by repeated bending or folding operation, so that it can be easily applied to a bendable, flexible, rollable, or foldable mobile device, or a display device.

On the contrary, the protective films of the comparative examples did not have relatively low scratch resistance or exhibited bending durability enough to be used as a protective film of a flexible display device, unlike the examples.

Specifically, Comparative Example 1 including only the first hard coating layer, Comparative Example 3 in which the first hard coating layer is thicker than the second hard coating layer, and 50 parts by weight of nano silica in the second hard coating layer based on 100 parts by weight of the binder resin In the case of Comparative Examples 5 and 6 including parts, it was confirmed that the bending durability did not show enough to be used as a protective film for a flexible display device.

On the other hand, in the case of Comparative Example 2 containing more than 3 parts by weight of nano silica in the first hard coating layer compared to 100 parts by weight of the binder resin, and Comparative Example 4 including only the second hard coating layer, it was confirmed that low scratch resistance was exhibited. .

Claims (16)

A first hard coating layer comprising 3 parts by weight or less of inorganic particles relative to 100 parts by weight of the binder resin;
A second hard coating layer comprising 10 to 45 parts by weight of inorganic particles relative to 100 parts by weight of the binder resin; And
Light-transmitting substrate; are sequentially stacked,
A protective film for a cover window of a flexible display device, wherein a thickness ratio of the first hard coating layer and the second hard coating layer is 10:90 to 40:60.
The method of claim 1,
A protective film for a cover window of a flexible display device that does not cause cracks when the cover window is folded and unfolded at 90 degrees with respect to the bottom surface at a distance of 4 mm in the middle of the cover window and is repeated 100,000 times at room temperature.
The method of claim 1,
The first hard coating layer has a pencil hardness of H or more under a load of 750 g, a protective film for a cover window of a flexible display device.
The method of claim 1,
A protective film for a cover window of a flexible display device having a water contact angle of 105° or more on the surface of the first hard coating layer.
The method of claim 1,
A protective film for a cover window of a flexible display device having a transmittance of 90.0% or more with respect to light in a wavelength range of 550 nm and a haze value of 1.0% or less.
The method of claim 1,
The thickness of the first hard coating layer is 1㎛ to 10㎛, the protective film for the cover window of the flexible display device.
The method of claim 1,
The thickness of the second hard coating layer is 1㎛ to 10㎛, the protective film for the cover window of the flexible display device.
The method of claim 1,
The total thickness of the first hard coating layer and the second hard coating layer is 2 to 15㎛, the protective film for the cover window of the flexible display device.
The method of claim 1,
The binder resin included in the first hard coating layer and the second hard coating layer comprises a multifunctional (meth)acrylate-based compound, a protective film for a cover window of a flexible display device.
The method of claim 9,
The first hard coating layer and the second hard coating layer, based on 100 parts by weight of the binder resin, containing 50 parts by weight or more of the polyfunctional (meth) acrylate-based compound, a protective film for a cover window of a flexible display device.
The method of claim 9,
The polyfunctional (meth)acrylate-based compound is selected from the group consisting of ethylene oxide, propylene oxide, urethane, caprolactone, epoxy, and ester. A protective film for a cover window of a flexible display device, modified with one or more types.
The method of claim 1,
The first hard coating layer further comprises at least one additive selected from the group consisting of a fluorine-based additive, a silicon-based additive, and a fluorine-silicone-based additive. A protective film for a cover window of a flexible display device.
The method of claim 1,
The light-transmitting substrate is polyimide (PI), polyimideamide, polyetherimide (PEI), polyethylene terephtalate (PET), polyethylene naphthalate (PEN), polyether ether. Ketone (polyetheretherketon, PEEK), cyclic olefin polymer (COP), polyacrylate (PAC), polymethylmethacrylate (PMMA), and triacetylcellulose (TAC) A protective film for a cover window of a flexible display device comprising at least one selected from the group.
A cover window for a flexible display device, comprising a protective film for a cover window of the flexible display device of claim 1.
The method of claim 14,
A glass cover having a thickness of 30 μm to 200 μm; And the protective film; including, a cover window for a flexible display device.
A display device comprising the cover window for the flexible display device of claim 14.

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