KR20200133670A - Cover window for flexible display device and flexible display device - Google Patents

Abstract

The present invention relates to a cover window of a flexible display device and a flexible display device including the same. The flexible display device comprises: a light-transmitting substrate; and a first hard coating layer and a second hard coating layer respectively formed on both surfaces of the light-transmitting substrate, wherein the ratio of the amide C=O peak to the ester C=O peak is in a predetermined range in the IR spectrum for each of the first hard coating layer and the second hard coating layer.

Description

Cover window and display device of a flexible display device {COVER WINDOW FOR FLEXIBLE DISPLAY DEVICE AND FLEXIBLE DISPLAY DEVICE}

The present invention relates to a cover window and a display device of a flexible display device.

With the recent development of mobile devices such as smartphones and tablet PCs, thinner and slimmer display substrates are required. Glass or tempered glass is generally used as a material having excellent mechanical properties for a display window or front panel of such a mobile device. However, the glass causes a high weight of the mobile device due to its own weight, and there is a problem of damage due to external impact.

Accordingly, plastic resins are being studied as a material that can replace glass. Plastic resin films are lightweight and less likely to break, so they are suitable for the trend of pursuing lighter mobile devices. In particular, in order to achieve a film having properties of high hardness and abrasion resistance, a film in which a hard coating layer made of a plastic resin is coated on a supporting substrate has been proposed.

As a method of improving the surface hardness of the hard coating layer, a method of increasing the thickness of the hard coating layer may be considered. In order to secure a surface hardness that can replace glass, it is necessary to implement a certain thickness of the hard coating layer. However, as the thickness of the hard coating layer increases, the surface hardness may increase, but it is practically applicable because wrinkles and curls increase due to the curing shrinkage of the hard coating layer, and cracks or peeling of the hard coating layer are likely to occur. Is not easy.

Meanwhile, a display in which a part of a display device is curved or flexibly bent for aesthetic and functional reasons has recently attracted attention, and this trend is particularly prominent in mobile devices such as smartphones and tablet PCs. However, since glass is not suitable for use as a cover plate to protect such a flexible display, it needs to be replaced with plastic resin. However, for this purpose, it is difficult to manufacture a film having sufficient flexibility while exhibiting a high hardness of a glass level.

The present invention exhibits high hardness while realizing to satisfy the physical property balance of flexibility and high hardness at the same time, and in particular, there is almost no damage to the film even by repeated bending or folding operation, so a bendable, flexible, rollable, or foldable mobile device Or, a cover window of a flexible display device that can be easily applied to a display device is provided.

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

In the present specification, a light-transmitting substrate or a polymer substrate; And a first hard coating layer and a second hard coating layer formed on both sides of the light-transmitting substrate or the polymer substrate, respectively, and the ratio of the ester C=O peak to the amide C=O peak in the IR spectrum for the first hard coating layer Is 0.8 or less, and the ratio of the ester C=O peak to the amide C=O peak in the IR spectrum for the second hard coating layer is greater than 0.8, providing a cover window of a flexible display device.

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

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

In the present specification, "flexible" means a state having a degree of flexibility that does not cause cracks of 3 mm or more in length when wound on a cylindrical mandrel having a diameter of 3 mm, and thus the present invention The flexible plastic film of is applicable 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.

The light-transmitting substrate may have a transmittance of 50% or more, or a transmittance of 50% to 99.9% at a wavelength of 300 nm or more, or 400 nm to 800 nm.

According to one embodiment of the invention, a light-transmitting substrate or a polymer substrate; And a first hard coating layer and a second hard coating layer formed on both sides of the light-transmitting substrate or the polymer substrate, respectively, and the ratio of the ester C=O peak to the amide C=O peak in the IR spectrum for the first hard coating layer A cover window of a flexible display device having a ratio of 0.8 or less and an amide C=O peak to an ester C=O peak of more than 0.8 in the IR spectrum for the second hard coating layer may be provided.

The present inventors conducted a study on an optical laminate applicable to a flexible display device having a thinner thickness, and the ratio of the ester C=O peak to the amide C=O peak in the IR spectrum on the light-transmitting substrate or the polymer substrate was The laminate structure in which the first hard coating layer of 0.8 or less and the second hard coating layer with the ratio of the ester C=O peak to the amide C=O peak in the IR spectrum exceeds 0.8 has high hardness and has a mandrel of 3 mm in diameter. ), the invention was completed after confirming that it could be used as a cover window of a flexible display device because no cracks occurred when wound around the device.

In addition, the cover window of such a flexible display device exhibits high hardness while realizing to satisfy the balance of flexibility and high hardness at the same time. In particular, the film is hardly damaged even by repetitive bending or folding, so it is possible to bendable, flexible, and rollable. , Or a foldable mobile device, or a display device, it was confirmed through an experiment that the invention was completed.

Since the cover window of the flexible display device may have physical properties that can replace tempered glass, etc., it may not be broken by pressure or force applied from the outside, but may also have a property of sufficient bending and folding. .

As described above, physical properties such as bending durability and surface hardness of the cover window of the flexible display device are obtained by forming each of the first and second hard coating layers having the above characteristics on the light-transmitting substrate or the polymer substrate. will be.

The ratio of the intensity of the amide C=O peak (about 1690 cm ^-1 ) to the intensity of the ester C=O peak (about 1724 cm ^-1 ) in the IR spectrum for the hard coating layer is contained in the binder resin included in the hard coating layer. It is related to the type and content of urethane acrylate. Specifically, the ratio may be related to the molecular weight of the binder resin included in the hard coating layer, this ratio may be related to the toughness and flexibility of the hard coating layer, and also the detailed structure or detailed repeating unit of the hard coating layer It may also be related to characteristics such as the type of, or the size or ratio of a detailed structure or a detailed repeating unit.

In the IR spectrum for the first hard coating layer, the ratio of the ester C=O peak to the amide C=O peak may be 0.8 or less, or 0.5 to 0.8, or 0.600 to 0.800, or 0.650 to 0.750.

As the ratio of the ester C=O peak to the amide C=O peak in the IR spectrum for the first hard coating layer is within the above-described range, the first hard coating layer has excellent bending durability while maintaining high hardness, In particular, it may have excellent bending durability under conditions such as low temperature and high temperature/high humidity.

For example, when the ratio of the ester C=O peak to the amide C=O peak in the IR spectrum for the first hard coating layer in the cover window of the flexible display device exceeds 0.8, the surface hardness is at the side of the first hard coating layer. The measured surface pencil hardness may be lowered to 4H or less based on 750 g, and curls of the coating film may not be maintained when configured with the second hard coating layer.

Meanwhile, in the IR spectrum for the second hard coating layer, the ratio of the ester C=O peak to the amide C=O peak may be greater than 0.8, or 0.820 to 1.500, or 0.825 to 1.200, or 0.830 to 1.100.

As the ratio of the ester C=O peak to the amide C=O peak in the IR spectrum for the second hard coating layer is in the above-described range, the second hard coating layer has excellent flexibility and improves bending durability. It may have, and when configured with the above-described first hard coating layer, it may have a characteristic of maintaining the curl of the coating film.

For example, if the ratio of the ester C=O peak to the amide C=O peak in the IR spectrum for the second hard coating layer in the cover window of the flexible display device is less than 0.8, when configured with the first hard coating layer Bending durability (5mm, room temperature) may be reduced, especially at low temperatures. In addition, when configured with the first hard coating, the curl of the coating film may not be maintained.

In the cover window of the flexible display device, the first hard coating layer may be located in a direction toward the outside with the light-transmitting substrate as a center, and the second hard coating layer may be located in a direction toward the inside of the flexible display device. have.

That is, the first hard coating layer and the second hard coating layer having different characteristics may be formed on both sides of the light-transmitting substrate included in the cover window of the flexible display device, respectively, but the curl is good and the hardness is maintained. While bending durability is excellent. In particular, it has excellent bending durability at low temperature and high temperature/high humidity.

In addition, according to this structure, it is possible to satisfy the balance of physical properties of flexibility and high hardness at the same time, and prevent damage to the internal structure even by repeated bending or folding operations. In addition, excellent mechanical properties, heat resistance, and high transparency are provided. It can have optical properties.

On the contrary, hard coating layers having the same characteristics are formed on both sides of the light-transmitting substrate, or ester C=O peak versus amide C=O in the IR spectrum for each of the first and second hard coating layers described above. If the ratio of the peak is not satisfied, curl may occur in the cover window of the flexible display device, and the cover window of the flexible display device may be sufficient, so that it may be difficult to implement a bending durability characteristic.

The cover window of the flexible display device may have a surface pencil hardness measured from the side of the first hard coating layer of 5H or more based on a 750g load, When a hard coating layer having a pencil hardness of 5H or more is applied together under a load of 750 g and wound around a mandrel having a diameter of 3 mm, cracks may not occur.

In addition, due to the structure of the cover window of the flexible display device described above, it is excellent in durability against repetitive bending or folding operations applied under low temperature conditions, and durability against repetitive bending or folding operations applied under high temperature and high humidity conditions. Is also excellent.

More specifically, cracks may not occur in 50,000 bending durability tests performed on a 5mm diameter rod at a temperature of -20°C for the cover window of the flexible display device.

In addition, cracks may not occur in a bending durability test of 100,000 times performed around a rod having a diameter of 5 mm at a temperature of 60° C. and 90 RH% for the cover window of the flexible display device.

As described above, as it has high durability against repeated bending or folding operation applied under low temperature conditions or high temperature/high humidity conditions, cracking of the hard coating layer under severe conditions of the product to which the cover window having the hard coating layer is applied. Can be prevented.

In addition, the cover window of the flexible display device has high surface hardness and high durability against repeated bending even at room temperature. Specifically, the cover window of the flexible display device may have a surface pencil hardness of 5H or more based on 750g measured from the side of the first hard coating layer, and a rod having a diameter of 2mm at a temperature of room temperature (25°C) for the cover window of the flexible display device. Cracks may not occur in the 200,000 bending durability tests performed around.

Meanwhile, the cover window of the flexible display device according to the embodiment may have a light transmittance of 90.0% or more and a haze of 1.0% or less, or 0.7% or less, or 0.5% or less.

Meanwhile, in order to realize the above-described characteristics, the cover window of the flexible display device has excellent optical properties, satisfies the balance of physical properties of flexibility and high hardness at the same time, and prevents damage to the internal structure even by repeated bending or folding operations. It is preferable to include a light-transmitting substrate capable of.

More 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 %, and thus may have colorless and transparent optical properties.

In addition, the light-transmitting substrate has an Elastic Modulus of 5 GPa or more, or 5 to 10 GPa, measured by applying a strain rate of 12.5 mm/min to a sample having a thickness of 50 ± 2 μm. In this way, it can have excellent mechanical properties and high elasticity and thermal resistance.

The kind of the light-transmitting substrate is not limited as long as it satisfies the above-described properties, but, for example, a glass substrate is used, or a polyimide, polyamide, polyamideimide, or mixture thereof, or a copolymer thereof It is possible to use a polymer substrate containing .

As described above, flexibility can be secured in a film or optical laminate having a generally thin thickness, but it is not easy to secure durability against repeated bending or folding operations while securing high surface strength.

On the contrary, the cover window of the flexible display device of the embodiment includes a hard coating layer capable of securing durability against repeated bending or folding while having high hardness together with the light-transmitting substrate of the above-described characteristics, as described above. Can have features.

Specifically, the hard coating layer may include a binder resin.

A specific example of the binder resin is not limited, for example, it may be a polymer or copolymer of monomer(s) having a photocurable reactive group, and specifically, a (meth)acrylate-based monomer or oligomer, a vinyl-based monomer or oligomer, etc. It may be a polymer or a copolymer formed from.

For example, the binder resin may include a polymer or copolymer of 1 to 6 functional (meth)acrylate-based monomers.

The 1 to 6 functional acrylate monomers or oligomers are trimethylolpropane triacrylate (TMPTA), trimethylolpropane ethoxy triacrylate (TMPEOTA), glycerin propoxylated triacrylate (GPTA), pentaerythritol tetra Acrylate (PETA), dipentaerythritol hexaacrylate (DPHA), and the like. The 1 to 6 functional acrylate monomers or oligomers may be used alone or in combination of different types.

The (meth)acrylate-based monomer or oligomer or vinyl-based monomer or oligomer has a weight average molecular weight (Mw) of about 200 to about 2,000 g/mol, or about 200 to about 1,000 g/mol, or about 200 to about 500 g May be in the range of /mol.

The 1 to 6 functional acrylate monomers have an acrylate equivalent weight in the range of about 50 to about 300 g/mol, or about 50 to about 200 g/mol, or about 50 to about 150 g/mol. I can.

In addition, the binder resin may include a crosslinked copolymer of a 1 to 6 functional acrylate monomer and a 7 to 20 functional urethane acrylate monomer or oligomer.

The 7 to 20 functional urethane acrylate monomer or oligomer is crosslinked and polymerized with the 1 to 6 functional acrylate monomer or oligomer to form a copolymer, and the coating layer formed after curing has high hardness, flexibility, and impact resistance. Can be given. The 7 to 20 functional urethane acrylate monomers or oligomers may be used alone or in combination of different types.

The crosslinked copolymer is the 1 to 6 functional acrylate monomer or oligomer and 7 to 20 functional urethane acrylate monomer or oligomer is about 1: 9 to about 5: 5, preferably about 1: 9 to about It may be crosslinked polymerization at a weight ratio of 4: 6, more preferably about 1: 9 to about 3.5: 6.5. By including a crosslinked copolymer in which 1 to 6 functional acrylate monomers or oligomers and 7 to 20 functional urethane acrylate monomers or oligomers are crosslinked in the weight ratio, it exhibits sufficient flexibility and achieves good physical properties of high hardness can do.

The 7 to 20 functional urethane acrylate oligomer has a weight average molecular weight in the range of about 2,000 to about 8,000 g/mol, or about 3,000 to about 6,000 g/mol, or about 3,000 to about 5,000 g/mol, the coating layer It may be desirable for optimization of physical properties.

Meanwhile, as described above, the ratio of the intensity of the amide C=O peak (about 1690 cm ^-1 ) to the intensity of the ester C=O peak (about 1724 cm ^-1 ) in the IR spectrum for the hard coating layer is It is related to the type and content of urethane acrylate contained in the included binder resin. Specifically, the ratio may be related to the molecular weight of the binder resin included in the hard coating layer, this ratio may be related to the toughness and flexibility of the hard coating layer, and also the detailed structure or detailed repeating unit of the hard coating layer It may also be related to characteristics such as the type of, or the size or ratio of a detailed structure or a detailed repeating unit.

Accordingly, the ratio of the ester C=O peak to the amide C=O peak in the IR spectrum for the first hard coating layer is 0.8 or less, and the ester C=O peak versus the amide C= in the IR spectrum for the second hard coating layer. The ratio of the O peak may be greater than 0.8, and to satisfy this, the first hard coating layer is a binder including a cured product between a (meth)acrylic polymer and a (meth)acrylate compound having a weight average molecular weight of 10,000 to 200,000 It may include a resin and fine inorganic particles dispersed in the binder resin.

In the IR spectrum for the first hard coating layer, the ratio of the ester C=O peak to the amide C=O peak is relatively high.The binder resin is a (meth)acrylic polymer having a weight average molecular weight of 10,000 to 200,000. It may be due to inclusion.

In addition, the feature is that the binder resin included in the first hard coating layer contains a polyfunctional (meth)acrylate compound in a predetermined amount together with a (meth)acrylic polymer having a weight average molecular weight of 10,000 to 200,000. It may be according.

For example, the binder resin contained in the first hard coating layer contains 50 to 85% by weight of an advantageous portion from the 8 to 12 functional (meth)acrylate compound, and has a weight average molecular weight of 10,000 to 200,000 (meth) ) It may satisfy the above-described properties, including 5 to 40% by weight of the portion derived from the acrylic polymer.

More specifically, the binder resin included in the first hard coating layer is from 5 to 40% by weight of a (meth)acrylic polymer having a weight average molecular weight of 10,000 to 200,000; 50 to 85% by weight of an 8 to 12 functional (meth)acrylate compound; And 1 to 6 functional (meth) acrylate compound 5 to 40% by weight; It may include a copolymer formed from a mixture containing.

Accordingly, a binder resin derived from a (meth)acrylate compound and the binder satisfying the condition that the ratio of the ester C=O peak to the amide C=O peak in the IR spectrum for the second hard coating layer exceeds 0.8. It may contain fine inorganic particles dispersed in the resin.

More specifically, the binder resin contained in the second hard coating layer is 8 to 12 functional (meth) acrylate compound 40 to 85% by weight; And 1 to 6 functional (meth) acrylate compound 15 to 60% by weight; It may include a copolymer formed from a mixture containing.

Due to the above-described difference, the ratio of the ester C=O peak to the amide C=O peak in the IR spectrum for each of the first and second hard coating layers may vary.

In addition, the hard coating layer may include fine inorganic particles dispersed in the binder resin.

The inorganic particles may be, for example, metal atoms such as silica, aluminum, titanium, zinc, or oxides or nitrides thereof, and may each independently use silica fine particles, aluminum oxide particles, titanium oxide particles, or zinc oxide particles. have.

The fine inorganic particles may have an average radius of 100 nm or less, or 5 to 100 nm.

The hard coating layer may include two or more types of fine inorganic particles having an average radius different from that of the binder resin. In this case, the two or more kinds of inorganic particles may include first inorganic particles having an average radius of 20 to 35 nm and second inorganic particles having an average radius of 40 to 130 nm.

The average radius of each of the first inorganic particles and the second inorganic particles can be determined through a commonly known method, for example, measuring the radius of individual particles identified in electron micrographs (SEM, TEM, etc.) of the hard coating layer. It may be calculated and derived, or may be an average radius of inorganic particles calculated through an X-ray scattering experiment.

Meanwhile, the content of the fine inorganic particles included in the hard coating layer is not largely limited, but preferably the hard coating layer contains 40 to 100 parts by weight, or 30 to 100 parts by weight of the fine inorganic particles relative to 100 parts by weight of the binder resin. can do. That is, the first hard coating layer includes 30 to 100 parts by weight of the fine inorganic particles relative to 100 parts by weight of the binder resin, and the second hard coating layer includes 30 to 100 parts by weight of the fine inorganic particles relative to 100 parts by weight of the binder resin. can do.

When the content of the fine inorganic particles included in the hard coating layer is too small, the hardness of the hard coating layer may be lowered. In addition, when the content of the fine inorganic particles included in the hard coating layer is too high, the hardness may increase, but the flexibility of the cover window may be greatly reduced or durability against repeated bending or folding operations may also decrease.

The cover window of the flexible display device satisfies the balance of physical properties of flexibility and high hardness at the same time even in a thin thickness range compared to other previously known optical laminates, and prevents damage to the internal structure even by repeated bending or folding operations. It can have high mechanical properties, heat resistance, and optical properties such as high transparency.

More specifically, the light-transmitting substrate may have a thickness of 5 μm to 100 μm, a thickness of 10 μm to 80 μm, or a thickness of 20 μm to 60 μm. If the thickness of the substrate is less than 5 μm, 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, when the thickness exceeds 100 μm, the flexibility may be poor, making it difficult to form a flexible film.

The hard coating layer may have a thickness of 1 μm to 20 μm, or 3 μm to 15 μm. When the thickness of the hard coating layer is excessively large, the flexibility of the cover window of the flexible display device or durability against repeated bending or folding operations may be deteriorated.

Meanwhile, the cover window of the flexible display device may be provided by applying the coating composition for forming the hard coating layer on at least one surface of the light-transmitting substrate 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.

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 between the upper surface of the hard coating layer or the light-transmitting substrate or the polymer substrate and the hard coating layer Or it may further include one or more layers, films, or films such as a patterned metal layer.

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

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.

On the other hand, the hard coating layer, in addition to the binder resin, inorganic fine particles, etc., photoinitiators, organic solvents, surfactants, UV absorbers, UV stabilizers, anti-yellowing agents, leveling agents, antifouling agents, dyes for improving color values, etc. Ingredients commonly used in the field may be further included. In addition, the content may 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 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 includes a curved, bendable, flexible, rollable, or foldable mobile communication terminal, a touch panel of a smartphone or tablet PC, and It includes all kinds of displays.

An example of the flexible display device may be a flexible light emitting device display device.

For example, in the organic light emitting diode (OLED) display, a cover window of the flexible display device may be located at an outer portion in a direction in which light or a screen exits, and a cathode providing electrons, an electron transport layer 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, in addition to using the polymer film as a cover window, the cathode and anode electrodes, and each component are made of a material having a predetermined elasticity. Can be used.

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

The rollable display device may have a variety of structures depending on the application field and specific shape, and includes, for example, a cover plastic window, a touch panel, a polarizing plate, a barrier film, a light-emitting device (OLED device, etc.), a transparent substrate, etc. Can be

According to the present invention, it exhibits high hardness while realizing to satisfy the physical property balance of flexibility and high hardness at the same time, and in particular, there is almost no damage to the film even by repeated bending or folding operation, so it is a bendable, flexible, rollable, or foldable mobile A cover window and a flexible display device of a flexible display device that can be easily applied to a device or a display device may be provided.

Since the cover window of the flexible display device may have physical properties that can replace tempered glass, etc., it is not only not broken by pressure or force applied from the outside, but also has a property of sufficient bending and folding. , Flexibility, flexibility, high hardness, scratch resistance, and high transparency, and the film is less damaged even in repetitive, continuous bending or folding for a long time, so it is bendable, flexible, rollable, or foldable. (foldable) It can be usefully applied to mobile devices, display devices, front panels of various instrument panels, and displays.

1 shows the IR spectrum of the hard coating layer obtained in each of Preparation Example 1-1, Preparation 1-2, and Preparation 1-5.
Figure 2 schematically shows a method of performing the bending durability and bending stability tests of Experimental Examples 7 and 8.

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.

[Production Example: Preparation of a coating solution for forming a hard coating layer]

Manufacturing Example 1-1

Trimethylolpropane triacrylate (TMPTA, manufacturer: Cytec, Mw = 296 g/mol, acrylate group equivalent = 99 g/mol) 20 g, a trifunctional acrylate compound, MU9800 (manufacturer: Miwon, Mw=3500g/mol, acrylate group equivalent=389g/mol) 30g, MU9020, a 10-functional urethane acrylate compound (Manufacturer: Miwon, Mw=4500 g/mol, acrylate group equivalent=450g/mol) 30g, SMP-250AP (Acrylic polymer, manufacturer: Gongyeongsa, acrylate group equivalent = 240~260g/mol, weight average molecular weight (Mw): 37,000), an acrylate polymer compound, is propylene glycol monomethyl ether (Propylene glycol monomethyl) ether) dissolved in 50% by weight of a binder solution, 1 g of a photoinitiator Irgacure 184 (manufacturer: Ciba), and 20 g of methyl ethyl ketone (MEK) were mixed to prepare an acrylate solution.

60 g of a solution in which silica particles S1 (average particle diameter of 20 nm, surface modified with methacrylate silane coupling agent) are dispersed in 50% by weight in n-butyl acetate and silica particles S2 (average A coating solution for forming a hard coating layer was prepared by mixing 100 g of a solution having a particle diameter of 40 nm and a 30% by weight solution of methyl ethyl ketone (MEK) having a surface modified with an acrylate silane coupling agent.

Preparation Examples 1-2 to 1-7

A coating solution for forming a hard coating layer was prepared in the same manner as in Preparation Example 1-1, except that the content of the components used as shown in Table 1 below was adjusted.

Manufacturing Example 2-1

9-functional urethane acrylate compound MU9800 (manufacturer: Miwon, Mw=3500 g/mol, acrylate group equivalent = 389 g/mol) 30 g, 10-functional urethane compound MU9020 (manufacturer: Miwon, Mw=4500 g/ mol, acrylate group equivalent = 450 g/mol) 40 g, trifunctional urethane acrylate compound PU340 (manufacturer: Miwon, Mw = 2400 g/mol, acrylate group equivalent = 800 g/mol), 30 g, photoinitiator Irgacure 184 ( Manufacturer: Ciba) 1g, methyl ethyl ketone (MEK) 40g was mixed to prepare an acrylate solution.

60 g of a solution in which silica particles S1 (average particle diameter of 20 nm, surface modified with methacrylate silane coupling agent) are dispersed in 50% by weight in n-butyl acetate and silica particles S2 (average A coating solution for forming a hard coating layer was prepared by mixing 100 g of a solution having a particle diameter of 40 nm and a 30% by weight solution of methyl ethyl ketone (MEK) having a surface modified with an acrylate silane coupling agent.

manufacturer,
product name Manufacturing example
1-1 Preparation Example 1-2 Manufacturing Example 1-3 Manufacturing example
1-4 Manufacturing Example 1-5 Preparation Example 1-6 Manufacturing Example 1-7 Manufacturing example
2-1 Acrylate compound/polymer
(Unit: g) TMPTA 20 10 10 20 30 50 MU9800 30 30 30 30 30 40 30 30 MU9020 30 40 30 30 40 10 20 40 SMP-250AP 20 20 30 20 50 PU340 30 Inorganic fine particles* (unit: g) S1 30 30 30 30 30 30 30 30 S2 30 30 30 30 30 30 30 30 Photoinitiator Irgacure 184 One One One One One One One One Organic solvent MEK 20 20 10 20 40 40 40 40

* In Table 1, the content of inorganic fine particles is expressed as the net weight of only inorganic fine particles excluding the solvent according to the weight% of the inorganic fine particles dispersed in the solvent.

[Examples and Comparative Examples: Cover Window of a Flexible Display Device]

On both sides of a 50 μm-thick polyimide substrate (product name: A-50-D, manufacturer: Kolon Industries, modulus (UTM measurement: 6.1 GPa)), the coating solution for forming a hard coating layer shown in Table 2 below was applied by a bar coating method. Then, it was dried in an air atmosphere for 2 minutes at 90° C. Photocured with a metal halide lamp having a wavelength of 290 to 320 nm (light quantity: 200 mJ/cm2) to prepare an optical laminate After curing was completed, the coating layers formed on both sides of the coating layer were formed. The thickness was 10 μm each.

At this time, FT-IR (Fourier-transform infrared spectroscopy; FTS 3000) was performed on each of the hard coating layers formed on one surface of the polyimide substrate using the coating solution for forming the hard coating layer of Preparation Examples 1-1 to 2-1. Using the ATR (attenuated total reflectance) IR mode condition, the absorbance was measured with a resolution of 4 cm ^-1 and a scan number of 64 in a wavenumber range of 650 to 4000 cm ^-1 , and the measurement result The ratio of the intensity of the amide C=O peak (about 1690 cm ^-1 ) to the intensity of the ester C=O peak (about 1724 cm ^-1 ) was obtained from.

division Manufacturing example
1-1 Preparation Example 1-2 Manufacturing Example 1-3 Manufacturing example
1-4 Manufacturing Example 1-5 Preparation Example 1-6 Manufacturing Example 1-7 Manufacturing example
2-1 Ratio of amide C=O peak to ester C=O peak in IR spectrum 0.654 0.736 0.748 0.675 0.399 0.352 0.874 0.834

<Experimental Example: Measurement of physical properties of an optical laminate>

Experimental Example 1: Pencil hardness

Examples and Comparative Examples For the hard coating layer formed on the front surface of each cover window, using a pencil hardness measuring machine, according to the measurement standard JIS K5400-5-4, a load of 750 g and a reciprocation of 45 degrees three times at an angle of 45 degrees, and no scratches. The maximum hardness was confirmed.

Experimental Example 2: Transmittance and Haze

The transmittance and haze were measured using a spectrophotometer (device name: COH-400) for each of the cover windows of Examples and Comparative Examples.

Experimental Example 3: Flexion Test

According to the method of measurement standard JIS K5600-5-1, the cover windows of each of the Examples and Comparative Examples were wound around cylindrical mandrels of various diameters, and then the minimum diameter at which cracks did not occur was measured.

Experimental Example 4: Coating layer adhesion

Examples and Comparative Examples For the entire surface of the hard coating layer formed on the front surface of each cover window, scratches were made to form 100 grids within the size of 1cm * 1cm ~ 2cm * 2cm using a cutter knife, and Nichiban Tape (CT-24 ) To perform a peel test after attaching. Peeling tests were performed twice on the same side, and adhesion was evaluated from 5B (no peeling) to 0B (front peeling) according to the peeled level (5B good).

-5B (no peeling)

-4B (1~5 grids with peeled parts)

-3B (6 to 15 grids with peeled parts)

-2B (16-35 grids with detached parts)

-1B (36~50 grids with detached parts)

-0B (more than 51 grids with detached parts)

Experimental Example 5: Evaluation of scratch resistance

Examples and Comparative Examples With respect to the hard coating layer formed on the front surface of each of the cover windows, a load of 500 gf was applied to the steel wool (#0000) and reciprocated 500 times at a speed of 30 rpm to measure the surface of the hard coating film. When one or less scratches of 1 cm or less observed with the naked eye were observed, it was judged as good.

Experimental Example 6: bending durability test

2 is a diagram schematically showing a method of performing a bending durability and bending stability test on a film according to an embodiment of the present invention.

Each film of Examples and Comparative Examples was cut, but was laser cut to a size of 80 x 140 mm to minimize microcracks at the edge. Place the laser cut film on the measuring equipment and make the gap between the folds at 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 (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 (OK, NG). 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.

(Temperature and humidity conditions)

1) Room temperature: 25℃

2) Low temperature: -20℃

3) High temperature/high humidity: 60℃ / 90 RH%

The measurement results of the physical properties for Examples and Comparative Examples are shown in Table 3 below.

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 1st hard coating layer Manufacturing Example 1-1 Manufacturing Example 1-2 Manufacturing Example 1-3 Manufacturing Example 1-4 Manufacturing Example 1-5 Preparation Example 1-6 Manufacturing Example 1-7 2nd hard coating layer Manufacturing Example 2-1 Manufacturing Example 2-1 Manufacturing Example 2-1 Manufacturing Example 2-1 Manufacturing Example 2-1 Manufacturing Example 2-1 Manufacturing Example 2-1 Transmittance (%) 91.9 91.7 92.1 91.9 91.9 92.0 91.8 Haze (%) 0.50 0.40 0.36 0.65 0.50 0.40 0.40 Attaching the coating layer OK OK OK OK OK OK OK Scratch resistance Good Good Good Good Good Good Good Pencil hardness 6H 7H 6H 7H 6H 8H 3H Flexion test 2mm 2mm 2mm 2mm 4mm 6mm 3mm Bending durability (25℃, 5mm) 100,000 times
Ok 100,000 times
Ok 100,000 times
Ok 100,000 times
Ok 100,000 times
Ok NG 100,000 times
Ok Bending durability (100,000 times, 25℃, 2mm) 100,000 times Ok 100,000 times Ok 100,000 times
Ok 100,000 times
Ok 100,000 times
Ok NG 100,000 times
Ok Bending durability (200,000 times, 25℃, 2mm) 200,000 times Ok 200,000 times Ok 200,000 times
Ok 200,000 times
Ok NG NG 200,000 times
Ok Low temperature bending durability (-20℃, 5mm) 50,000 times OK 50,000 times OK 50,000 times
OK 50,000 times
OK NG NG NG High temperature/high humidity durability (60℃,90 RH%) 5mm) 100,000 times Ok 100,000 times Ok 100,000 times
Ok 100,000 times
Ok NG NG 100,000 times
Ok

As shown in Table 3, the cover window of the flexible display device of the embodiments exhibits a high hardness as well as satisfies sufficient flexibility while exhibiting a high hardness of a glass level, and exhibits high hardness. It has been confirmed that it can be easily applied to a bendable, flexible, rollable, or foldable mobile device, or a display device.

On the contrary, the cover windows of the comparative examples did not have a relatively low surface hardness, unlike the examples, or did not exhibit bending durability enough to be used as a cover window of a flexible display device.

Claims (15)

Light-transmitting substrate; And a first hard coating layer and a second hard coating layer respectively formed on both sides of the light-transmitting substrate,
In the IR spectrum for the first hard coating layer, the ratio of the ester C = O peak to the amide C = O peak is 0.8 or less,
In the IR spectrum for the second hard coating layer, the ratio of the ester C = O peak to the amide C = O peak is greater than 0.8,
Cover window of a flexible display device.
The method of claim 1,
A cover window of a flexible display device, wherein a ratio of an amide C=O peak to an ester C=O peak in an IR spectrum for the first hard coating layer is 0.500 to 0.800.
The method of claim 1,
A cover window of a flexible display device, wherein a ratio of an ester C=O peak to an amide C=O peak in an IR spectrum for the second hard coating layer is 0.820 to 1.500.
The method of claim 1,
A cover window of a flexible display device that does not cause cracks in 50,000 bending durability tests conducted around a 5mm diameter rod at a temperature of -20℃.
The method of claim 1,
Cover window of a flexible display device that does not cause cracks in a bending durability test of 100,000 times performed around a 5mm diameter rod at a temperature of 60℃ and 90RH%.
The method of claim 1,
The surface pencil hardness measured from the side of the first hard coating layer is 5H or more based on 750g,
A cover window of a flexible display device that does not cause cracks in a bending durability test of 200,000 times performed around a rod having a diameter of 2 mm at a temperature of 25°C.
The method of claim 1,
The cover window of the flexible display device, wherein the elastic modulus of the light-transmitting substrate measured by applying a strain rate of 12.5 mm/min is 5 GPa or more.
The method of claim 7,
The light-transmitting substrate includes one or more polymers selected from the group consisting of polyimide, polyamide, and polyamideimide. Cover window of a flexible display device.
The method of claim 1,
A cover window of a flexible display device having a transmittance of 90.0% or more with respect to light in a wavelength region of 550 nm and a haze value of 1.00% or less.
The method of claim 1,
The light-transmitting substrate has a thickness of 5 to 100 μm,
Each of the first and second hard coating layers has a thickness of 1 to 20 μm. A cover window of a flexible display device.
The method of claim 1,
The first hard coating layer comprises a binder resin including a cured product between a (meth)acrylic polymer and a (meth)acrylate compound having a weight average molecular weight of 10,000 to 200,000 and fine inorganic particles dispersed in the binder resin,
The second hard coating layer comprises a binder resin derived from a (meth)acrylate compound and fine inorganic particles dispersed in the binder resin,
Cover window of a flexible display device.
The method of claim 11,
The binder resin included in the first hard coating layer is 5 to 40% by weight of a (meth)acrylic polymer having a weight average molecular weight of 10,000 to 200,000; 50 to 85% by weight of an 8 to 12 functional (meth)acrylate compound; And 1 to 6 functional (meth) acrylate compound 5 to 40% by weight; comprising a copolymer formed from a mixture comprising,
Cover window of a flexible display device.
The method of claim 11,
The binder resin contained in the second hard coating layer is from 40 to 85% by weight of an 8 to 12 functional (meth)acrylate compound; And 1 to 6 functional (meth) acrylate compound 15 to 60% by weight; comprising a copolymer formed from a mixture comprising,
Cover window of a flexible display device.
The method of claim 11,
The first hard coating layer includes 30 to 100 parts by weight of the fine inorganic particles relative to 100 parts by weight of the binder resin,
The second hard coating layer includes 30 to 100 parts by weight of the fine inorganic particles relative to 100 parts by weight of the binder resin,
Cover window of a flexible display device.
A flexible display device including a cover window of the flexible display device of claim 1.

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