Flexible display device

Abstract

The present invention relates to a flexible display device, and more specifically, comprises a display panel, a back plate disposed below the display panel, and a plate bottom disposed below the back plate, wherein the back plate comprises a base substrate and a hard coating layer disposed on at least one surface of the base substrate. The flexible display device according to the present invention provides excellent rigidity and improved compression characteristics without including a shock-absorbing layer or a plate top, and provides the effect of improving the durability of the flexible display device by reinforcing the rigidity of the folding part.

Description

Technology Field

[0001] The present invention relates to a flexible display device, and more specifically, to a flexible display device having excellent rigidity and durability and improved compression characteristics. Background Technology

[0002] With the recent entry into the information age, the field of displays, which visually represent electrical information signals, has developed rapidly. In response to this, various display devices with excellent performance characteristics such as thinness, lightness, and low power consumption are being developed. Specific examples of such display devices include Liquid Crystal Displays (LCDs), Plasma Display Panel Devices (PDPs), Field Emission Display Devices (FEDs), and Organic Light Emitting Display Devices (OLEDs).

[0003] Meanwhile, efforts to diversify the shape and size of display devices are continuing. For example, display devices with various shapes are continuously being developed, such as curved display devices with curved surfaces and flexible display devices that can maintain their display performance even when bent or folded. The display panel of a flexible display device uses a flexible substrate, and a support member, such as a back plate, is placed at the bottom of the display panel to prevent sagging and to protect the display panel from external foreign matter and impact. The problem to be solved

[0004] Since the back plate is a thin film, using it alone as a support member results in insufficient rigidity. Therefore, various durability reinforcement layers, such as a plate top, plate bottom, and shock-absorbing layer, are combined and used on the back surface of the back plate. Specifically, to simultaneously satisfy rigidity and impact resistance, a combination of a plate top, plate bottom, and a silicone-based shock-absorbing layer is used on the lower part of the back plate, or a combination of a silicone-based shock-absorbing layer and a plate bottom is used. Although rigidity and impact resistance can be secured, there is a problem where folding characteristics deteriorate as the thickness of the flexible display device increases, and there are limitations in reducing the radius of curvature.

[0005] Accordingly, when the plate top or shock-absorbing layer is removed to reduce the radius of curvature, rigidity is reduced, and defects such as dents or punctures occur on the surface during folding. In particular, the folding area is more vulnerable to durability because greater stress is applied during folding.

[0006] In addition, to improve folding characteristics, an opening pattern is formed on the bottom of the plate to correspond to the folding area; however, when the top of the plate is removed, the opening pattern becomes visible to the user, which causes a problem of degraded appearance quality.

[0007] Accordingly, the problem that the present invention aims to solve is to provide a flexible display device with excellent rigidity without including a plate top or a shock-absorbing layer.

[0008] Another problem that the present invention aims to solve is to provide a flexible display device with excellent durability that minimizes dent or puncture defects without including a plate top or shock-absorbing layer, and reduces the difference in rigidity between the folding area and the non-folding area.

[0009] The problems of the present invention are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0010] A flexible display device according to one embodiment of the present invention includes a display panel, a back plate disposed below the display panel, and a plate bottom disposed below the back plate, wherein the back plate includes a base substrate and a hard coating layer disposed on at least one surface of the base substrate.

[0011] Specific details of other embodiments are included in the detailed description and drawings. Effects of the invention

[0012] The flexible display device of the present invention includes a hard coating layer on at least one surface of the back plate, thereby providing the effect of excellent rigidity even without including a plate top or a shock-absorbing layer.

[0013] In addition, the flexible display device of the present invention can minimize the occurrence of dents or punctures when folded, even though it does not include a plate top or a shock-absorbing layer.

[0014] In addition, the flexible display device of the present invention provides the effect of excellent durability by reducing the difference in rigidity between the folding area and the non-folding area.

[0015] In addition, the flexible display device of the present invention does not include a plate top or a shock-absorbing layer, so its structure is simple and can contribute to increased productivity by simplifying the manufacturing process.

[0016] In addition, since the flexible display device of the present invention does not include a plate top or a shock-absorbing layer, an adhesive layer for bonding them is also not required, and accordingly, the thickness of the flexible display device can be slimmed down. In addition, as the thickness is reduced, the radius of curvature can be reduced while maintaining high folding characteristics.

[0017] The effects according to the present invention are not limited to those exemplified above, and a wider variety of effects are included within the present invention. Brief explanation of the drawing

[0018] FIG. 1 is a plan view of a flexible display device according to one embodiment of the present invention. Figure 2 is a cross-sectional view along I-I' of Figure 1. FIG. 3 is a cross-sectional view of a flexible display device according to another embodiment of the present invention. FIG. 4 is a plan view of a flexible display device according to another embodiment of the present invention. Figure 5 is a cross-sectional view according to II-II' of Figure 4. FIG. 6 is a cross-sectional view of a flexible display device when it is bent according to another embodiment of the present invention. Specific details for implementing the invention

[0019] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims.

[0020] Shapes, areas, ratios, angles, numbers, etc. disclosed in the drawings for explaining embodiments of the present invention are exemplary, and therefore the present invention is not limited to the depicted details. Throughout the specification, the same reference numerals refer to the same components. Furthermore, in describing the present invention, if it is determined that a detailed description of related prior art may unnecessarily obscure the essence of the present invention, such detailed description is omitted. Where terms such as "includes," "has," or "is made up" are used in the present invention, other parts may be added unless "only" is used. When a component is expressed in the singular, it includes cases where it is included in the plural unless specifically stated otherwise.

[0021] In interpreting the components, they are interpreted to include a margin of error even in the absence of a separate explicit statement.

[0022] In the case of describing a positional relationship, for example, when the positional relationship between two parts is described using expressions such as 'on,' 'upper,' 'lower,' or 'next to,' one or more other parts may be located between the two parts unless 'immediately' or 'directly' is used.

[0023] When an element or layer is referred to as "on" another element or layer, it includes cases where another layer or element is placed directly on top of or in between.

[0024] Additionally, terms such as first, second, etc. are used to describe various components, but these components are not limited by these terms. These terms are used merely to distinguish one component from another. Accordingly, the first component mentioned below may be the second component within the technical scope of the present invention.

[0025] Throughout the specification, the same reference numerals refer to the same components.

[0026] The area and thickness of each component shown in the drawings are illustrated for convenience of explanation, and the present invention is not necessarily limited to the area and thickness of the illustrated components.

[0027] The features of each of the various embodiments of the present invention may be combined or combined with one another, either partially or wholly, and may technically enable various interlocking and operation. Each embodiment may be implemented independently of one another or may be implemented together in an associated relationship.

[0028] The present invention will be described below with reference to the drawings.

[0029] FIG. 1 is a plan view of a flexible display device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view along I-I' of FIG. 1. Referring to FIG. 1 and FIG. 2 together, a flexible display device (100) according to an embodiment of the present invention includes a display panel (130), a back plate (120), a plate bottom (110), a first adhesive layer (ADH1), a second adhesive layer (ADH2), an optical control layer (140), a deco layer (150), and a cover member (160). The back plate (120) includes a base substrate (121) and a hard coating layer (122).

[0030] Hereinafter, a flexible display device (100) according to one embodiment of the present invention will be described for each component.

[0031] The flexible display device (100) can be divided into a folding area (FA) and a non-folding area (NFA1, NFA2) depending on whether it is folded or not. The folding area (FA) is an area that is folded when the flexible display device (100) is folded, and can be folded according to a specific radius of curvature with respect to the folding axis. For example, the folding axis of the folding area (FA) can be formed in the X-axis direction, and the non-folding area (NFA1, NFA2) can be extended from the folding area (FA) in the Y-axis direction perpendicular to the folding axis. When the folding area (FA) is folded with respect to the folding axis, the folding area (FA) can form a part of a circle or an ellipse. In this case, the radius of curvature of the folding area (FA) refers to the radius of the circle or ellipse formed by the folding area (FA).

[0032] The non-folding areas (NFA1, NFA2) are areas that are not folded when the flexible display device (100) is folded. That is, the non-folding areas (NFA1, NFA2) maintain a flat state when the flexible display device (100) is folded. The non-folding areas (NFA1, NFA2) may be located on both sides of the folding area (FA). That is, the non-folding areas (NFA1, NFA2) may be areas extended in the Y-axis direction with respect to the folding axis. In this case, the folding area (FA) may be defined between the non-folding areas (NFA1, NFA2). Additionally, when the flexible display device (100) is folded with respect to the folding axis, the non-folding areas (NFA1, NFA2) may overlap each other.

[0033] When the upper surface on which an image is displayed in the flexible display device (100) is defined as the display surface and the lower surface of the flexible display device (100), which is the opposite side of the display surface, is defined as the back surface, the folding area (FA1) can be folded in a selected manner among an out-folding method in which the display surface of the flexible display device (100) is folded so that it is exposed to the outside, or an in-folding method in which the display surfaces of the flexible display device (100) are folded so that they face each other.

[0034] The display panel (130) displays an image. For example, the display panel (130) may be a liquid crystal display panel that displays an image by controlling the light transmittance of the liquid crystal. As another example, the display panel (130) may be an organic light-emitting display panel that includes an organic light-emitting layer and displays an image using light emitted from it. For convenience of explanation, the following description uses the case where the display panel is an organic light-emitting display panel as an example, but is not limited thereto.

[0035] The display panel (130) may include a flexible substrate (131) and an organic light-emitting element (132).

[0036] The flexible substrate (131) includes a display area (DA) and a non-display area (NDA).

[0037] The display area (DA) is an area where a plurality of pixels are arranged to substantially display an image. In the display area (DA), a plurality of pixels including light-emitting regions for displaying an image, and thin-film transistors, capacitors, etc. for driving the pixels may be arranged. A single pixel may include a plurality of subpixels (SP). A subpixel (SP) is the minimum unit constituting the display area (DA), and each subpixel (SP) may be configured to emit light of a specific wavelength band. For example, each subpixel (SP) may be configured to emit red, green, blue, or white light.

[0038] The non-display area (NDA) is positioned to surround the display area (DA). The non-display area (NDA) is an area where images are not substantially displayed, and various wiring, driving ICs, etc., are arranged thereto to drive the pixels and driving elements placed in the display area (DA).

[0039] The flexible substrate (131) supports various elements constituting the display panel (130). The flexible substrate (131) may be a plastic substrate having flexibility. For example, the plastic substrate may be selected from polyimide, polyethersulfone, polyethylene terephthalate, and polycarbonate, but is not limited thereto. In the case of a plastic substrate, since the barrier properties against moisture or oxygen are relatively weak, it may have a structure in which a plastic film and an inorganic film are laminated to compensate for this. For example, the flexible substrate (131) may be a multilayer structure in which a first polyimide film, an inorganic film, and a second polyimide film are sequentially laminated.

[0040] An organic light-emitting element (132) is placed on a flexible substrate (131). The organic light-emitting element (132) may include an anode, a cathode, and an organic light-emitting layer placed between them. In the organic light-emitting element (132), holes injected from the anode and electrons injected from the cathode combine in the organic light-emitting layer to emit light. An image can be displayed using the light emitted in this way.

[0041] A driving thin-film transistor for driving the organic light-emitting element (132) may be disposed between the flexible substrate (131) and the organic light-emitting element (132). The driving thin-film transistor may be disposed in each of a plurality of sub-pixel (SP) regions. For example, the driving thin-film transistor may include a gate electrode, an active layer, a source electrode, and a drain electrode. Specifically, for example, an active layer may be disposed on the flexible substrate (131), and a gate insulating layer may be disposed on the active layer to insulate the active layer from the gate electrode. Additionally, an interlayer insulating layer may be disposed on the flexible substrate (131) to insulate the gate electrode from the source electrode and the drain electrode. A source electrode and a drain electrode, respectively in contact with the active layer, may be formed on the interlayer insulating layer. A planarization layer may be disposed between the thin-film transistor and the organic light-emitting element (132). The planarization layer planarizes the top of the thin-film transistor. The planarization layer may include a contact hole for electrically connecting the thin-film transistor and the anode.

[0042] When the flexible display panel (130) is folded or bent, it may be difficult to maintain its shape in a constant form and may be vulnerable to external stimuli.

[0043] Accordingly, various types of support members may be placed on the back surface of the display panel (130). For example, a back plate (120) and a plate bottom (110) may be placed on the back surface of the display panel (130).

[0044] When using a flexible substrate (131) made of plastic material, the thickness is thin, so sagging of the display panel (130) may occur during folding or bending, and to compensate for this, a back plate (120) may be placed on the back of the display panel (130).

[0045] A first adhesive layer (ADH1) is disposed between the back plate (120) and the display panel (130). The first adhesive layer (ADH1) bonds the back plate (120) and the display panel (130). The first adhesive layer (ADH1) may be selected from optical clear adhesive (OCA), optical clear resin (OCR), pressure sensitive adhesive (PSA), etc., but is not limited thereto.

[0046] The back plate (120) includes a base substrate (121) and a hard coating layer (122). The base substrate (121) supports the flexible substrate (131) so that it does not sag. A plastic film may be used as the base substrate (121) to support the flexible substrate (131) while maintaining high folding characteristics. For example, the plastic film may be selected from a polyethylene terephthalate film, a polyimide film, or a polyamideimide film.

[0047] Polyimide films or polyamideimide films do not exhibit cloudiness when folded and have excellent mechanical rigidity. Accordingly, it is easy to implement a flexible display device with a larger curvature. Polyethylene terephthalate films are relatively inexpensive, but polyethylene terephthalate films lack rigidity compared to polyimide or polyamideimide films. However, as described below, rigidity can be supplemented by forming a hard coating layer (122) on one side of the polyethylene terephthalate film. In particular, polyethylene terephthalate has excellent solubility in solvents compared to polyimide or polyamideimide. Accordingly, the hard coating layer (122) can be formed thicker on the polyethylene terephthalate film compared to the polyimide film or polyamideimide film, thereby supplementing rigidity.

[0048] For example, the thickness of the base substrate (121) may be 40 μm to 80 μm. Within this range, the flexible substrate (131) can be supported while maintaining high folding characteristics.

[0049] A hard coating layer (122) is placed on the lower surface of the base substrate (121). The hard coating layer (122) improves the rigidity of the base substrate (121). Accordingly, the rigidity of the flexible display device (100) can be maintained at a high level without placing a plate top or shock-absorbing layer on the lower part of the back plate (120).

[0050] The hard coating layer (122) can be formed to come into direct contact with the base substrate (121) through a known coating method without using an adhesive member such as a light-transparent adhesive. For example, the hard coating layer (122) can be formed on the base substrate (121) by a known method such as a slit coating method, a bar coating method, an immersion coating method, a spin coating method, a dispensing method, or a screen printing method.

[0051] The thickness of the hard coating layer (122) may be 30㎛ to 60㎛ or 40㎛ to 50㎛. If the thickness of the hard coating layer (122) is less than 30㎛, the effect of improving the strength of the flexible display device (100) is insufficient, and the recovery force against pressure of the flexible display device (100) may be reduced. In addition, if the thickness of the hard coating layer (122) exceeds 60㎛, the folding characteristics may be degraded. In addition, in order to form the hard coating layer (122) with a thickness of 60㎛ or more, the proportion of silicone-based resin in the hard coat composition must be increased. However, when the proportion of silicone-based resin increases, the proportion of solvent decreases relatively, and the hard coating layer formed with such a hard coat composition has reduced adhesion to the base substrate. Accordingly, there may be a problem in that the hard coating layer lifts from the base substrate and cracks occur during folding. For reference, polyethylene terephthalate has excellent solubility in solvents compared to polyimide or polyamideimide. Accordingly, when the thickness of the hard coating layer is formed thickly to 50㎛ to 60㎛, a polyethylene terephthalate film can be used as the base substrate to ensure adhesion between the base substrate (121) and the hard coating layer (122).

[0052] The hard coating layer (122) includes a silicone-based resin. The silicone-based resin has excellent impact resistance and recovery properties against pressure. Accordingly, the mechanical properties of the flexible display device (100), such as durability and impact resistance, can be greatly improved.

[0053] For example, silicone-based resins can be formed from epoxy-modified silicone polymers.

[0054] Specifically, for example, the silicone resin can be formed from epoxy-modified siloxane oligomers having different epoxy equivalents. For example, the silicone resin can be formed by polymerizing a hard coat composition comprising a first epoxy-modified siloxane oligomer and a second epoxy-modified siloxane oligomer having a different epoxy equivalent. In this case, there is an advantage of better recovery characteristics against pressure, folding characteristics, and durability of the flexible display device (100).

[0055] The hard coat composition may further include one or more types selected from urethane acrylate-based linkers, acrylate-based linkers, and epoxy-based linkers. When additional linkers are included, the compression recovery characteristics of the flexible display device (100) can be improved, while the folding characteristics can be maintained at a high level without deterioration.

[0056] In addition, the hard coat composition may further include an initiator capable of curing the hard coat composition through optical and chemical reactions.

[0057] Additionally, the epoxy equivalent of the epoxy-modified siloxane oligomer can be adjusted depending on the type of base substrate (121). For example, polyethylene terephthalate film as the base substrate (121) has the advantage of being inexpensive and easy to obtain, but its mechanical properties are relatively lower compared to polyimide film or polyamideimide film. Accordingly, when using polyethylene terephthalate film as the base substrate, a hard coating layer (122) can be formed with an epoxy-modified siloxane oligomer having a relatively large epoxy equivalent to compensate for the mechanical properties.

[0058] Additionally, when forming a hard coating layer (122) by mixing the first epoxy-modified siloxane oligomer and the second epoxy-modified siloxane oligomer, the difference in epoxy equivalents between the first epoxy-modified siloxane oligomer and the second epoxy-modified siloxane oligomer may vary depending on the type of base substrate (121). When a polyethylene terephthalate film is used as the base substrate (121), as described above, it is preferable that the epoxy equivalents of the first and second epoxy-modified siloxane oligomers be high to compensate for mechanical properties. Accordingly, when a polyethylene terephthalate film is used, the difference in epoxy equivalents between the first epoxy-modified siloxane oligomer and the second epoxy-modified siloxane oligomer may be smaller than when a polyimide film or a polyamideimide film is used as the base substrate (121).

[0059] A plate bottom (110) is positioned below a back plate (120). A second adhesive layer (ADH2) is positioned between the back plate (120) and the plate bottom (110). That is, the second adhesive layer (ADH2) is positioned between the hard coating layer (122) of the back plate (120) and the plate bottom (110). The second adhesive layer (ADH2) bonds the back plate (120) and the plate bottom (110). The second adhesive layer (ADH2) may be selected from optical clear adhesive (OCA), optical clear resin (OCR), pressure sensitive adhesive (PSA), etc., but is not limited thereto.

[0060] The plate bottom (110) is positioned below the back plate (120) to reinforce the rigidity of the flexible substrate (131), which is formed of plastic material, and the back plate (120). For example, the plate bottom (110) may be formed of a metal material such as stainless steel (SUS), Invar, aluminum, or magnesium. Since these metal materials have higher strength compared to plastic materials, they can further improve the durability of the flexible display device (100).

[0061] At least one opening pattern can be formed in the plate bottom (110) corresponding to the folding area (FA) of the flexible display device (100). The opening pattern allows the plate bottom (110) of the folding area (FA) to be easily folded and can effectively relieve stress applied to the plate bottom (110) during folding. In addition, it can improve the folding characteristics of the flexible display device (100) by facilitating restoration after folding. The opening pattern can be formed in the folding area (FA) with different shapes or different spacing. For example, the opening pattern can have a rectangular, rhombus, or circular shape.

[0062] In conventional flexible display devices, a plate top or shock-absorbing layer is placed between the plate bottom and the back plate. In the flexible display device (100) of the present invention, a hard coating layer (122) formed on a base substrate (121) can serve as the plate top or shock-absorbing layer. Accordingly, the flexible display device (100) has the advantage of excellent mechanical properties such as durability, compression recovery, and impact resistance, even without having a plate top or shock-absorbing layer.

[0063] An optical control layer (140) is disposed on the display panel (130). The optical control layer (140) can uniformly transmit light emitted from the display panel (130) to the outside without reducing the brightness of the flexible display device (100), and can improve display quality by absorbing or reflecting external light. For example, the optical control layer (140) may be a polarizing film, but is not limited thereto.

[0064] The optical control layer (140) can be bonded to the upper part of the display panel (130) by a light-transparent adhesive or a pressure-sensitive adhesive.

[0065] A deco layer (150) may be disposed on the optical control layer (140). The deco layer (150) may be bonded onto the optical control layer (140) by a light-transparent adhesive or a pressure-sensitive adhesive. The deco layer (150) includes a deco pattern formed of a light-absorbing material and an overcoat layer formed of a transparent resin. For example, the deco pattern may be formed of a light-absorbing metal, carbon black, black resin, etc. The deco pattern is formed to overlap with the non-display area (NDA) of the display panel (130). Accordingly, the deco layer (150) prevents components such as wiring placed in the non-display area (NDA) from being visible to the outside. In addition, the deco layer (150) functions to prevent light leakage from the side portion of the flexible display device (100). The deco pattern may be disposed adjacent to the lower surface of the cover member (160). However, not limited thereto, the deco pattern may be positioned below the deco layer (150) and arranged adjacent to the optical control layer (140). The overcoat layer covers the step difference caused by the deco pattern to flatten the surface on which the deco pattern is formed. For example, the overcoat layer may include one or more types selected from acrylic resin, epoxy resin, siloxane resin, urethane resin, etc., but is not limited thereto.

[0066] A cover member (160) is placed on a deco layer (150). The cover member (160) protects the display panel (130) from being damaged by external impact or from being degraded by moisture, oxygen, or foreign matter entering from the outside. The cover member (160) may be bonded onto the deco layer (150) by a light-transparent adhesive or a pressure-sensitive adhesive.

[0067] The cover member (160) may be formed from a material that is transparent and has excellent impact resistance and scratch resistance. For example, the cover member (160) may be a film made of a polymer such as polyimide, polyamideimide, polyethylene terephthalate, polymethyl methacrylate, polypropylene glycol, or polycarbonate. As another example, the cover member (160) may be a film made of an optically isotropic polymer such as a cycloolefin (co)polymer, optically isotropic polycarbonate, or optically isotropic polymethyl methacrylate. As yet another example, the cover member (160) may be formed from chemically strengthened thin glass.

[0068] In addition, various functional layers, such as an external light reflection reduction layer, a UV blocking layer, and a hard coating layer, may be disposed on the cover member (160). Also, if the cover member (160) is formed of thin glass, a protective film to prevent shattering may be disposed on the cover member (160).

[0069] A flexible display device (100) according to one embodiment of the present invention includes a back plate (120) having a hard coating layer (122) containing a silicone-based resin formed on the lower part of a base substrate (121). Accordingly, even without including a plate top or a shock-absorbing layer, the occurrence of compression or perforation during folding can be minimized.

[0070] In addition, the hard coating layer (122) prevents the pattern formed on the plate bottom (110) corresponding to the folding area (FA) from being visible outside the flexible display device (100).

[0071] In addition, the flexible display device (100) of the present invention provides the effect of excellent durability by reducing the difference in rigidity between the folding area (FA) and the non-folding area (NFA1, NFA2) of the plate bottom (110).

[0072] In addition, the flexible display device (100) of the present invention does not include a plate top or a shock-absorbing layer, so the structure is simple and the manufacturing process can be simplified, which can contribute to improving productivity.

[0073] In addition, since the flexible display device (100) of the present invention does not include a plate top or a shock-absorbing layer, an adhesive layer for bonding them is also not required, and the thickness of the flexible display device (100) can be slimmed down. In this way, as the thickness of the flexible display device (100) is reduced, the radius of curvature can be reduced while maintaining high folding characteristics.

[0074] For example, the flexible display device (100) according to the present invention may be implemented as a flexible display device with a large curvature, wherein the radius of curvature of the folding area (FA) is 3R or less, and furthermore, 1.5R or less. In this specification, a radius of curvature of 1R means that the radius of the curved surface of the folding area (FA) is 1mm when folded.

[0075] FIG. 3 is a cross-sectional view of a flexible display device according to another embodiment of the present invention. Since the flexible display device (200) shown in FIG. 3 is substantially identical to the flexible display device (100) shown in FIG. 1 and FIG. 2 except for the placement position of the hard coating layer, a redundant description is omitted.

[0076] Referring to FIG. 3, a hard coating layer (222) is placed on top of a base substrate (221). A first adhesive layer (ADH1) is placed between the hard coating layer (222) of the back plate (220) and the display panel (130). Accordingly, the hard coating layer (222) of the back plate (220) and the display panel (130) are bonded by the first adhesive layer (ADH1). A second adhesive layer (ADH2) is placed between the base substrate (221) of the back plate (220) and the plate bottom (110). Accordingly, the base substrate (221) and the plate bottom (110) are bonded by the second adhesive layer (ADH2).

[0077] As illustrated in FIG. 3, when a hard coating layer (222) is placed on top of a base substrate (221), the compression recovery in the folding area (FA) and non-folding area (NFA1, NFA2) of the flexible display device (200) is further improved and perforation defects can be further minimized. Accordingly, a flexible display device (200) having superior durability can be provided.

[0078] The plate bottom (110) includes an opening pattern corresponding to the folding area (FA) to facilitate folding, in which case the impact strength of the folding area (FA) is lower than the impact strength of the non-folding area (NFA1, NFA2). As such, the difference in strength between the folding area (FA) and the non-folding area (NFA1, NFA2) may limit the improvement of durability. When a hard coating layer (222) is placed on the upper part of the base substrate (221), the impact strength in the folding area (FA) can be further improved, thereby reducing the difference in impact strength between the folding area (FA) and the non-folding area (NFA1, NFA2) and improving durability.

[0079] FIGS. 4 to 6 are drawings for explaining a flexible display device according to another embodiment of the present invention. FIG. 4 is a plan view of a flexible display device according to another embodiment of the present invention. FIG. 5 is a cross-sectional view along II-II' of FIG. 4. FIG. 6 is a cross-sectional view of a flexible display device according to another embodiment of the present invention when it is bent.

[0080] The flexible display device (300) illustrated in FIGS. 4 to 6 is substantially the same as the flexible display device (200) illustrated in FIG. 3, except that the flexible substrate has a bending allowable area and further includes an auxiliary back plate, a third adhesive layer, and a fourth adhesive layer, so a redundant description is omitted.

[0081] Referring to FIGS. 4 through 6, the flexible substrate (331) may have at least one bending-allowing region (BA) capable of bending. For example, the flexible substrate (331) includes a display area (DA), a first non-display area (NDA1), a bending-allowing region (BA), and a second non-display area (NDA2). The first non-display area (NDA1) is positioned to surround the four corners of the display area (DA). The first non-display area (NDA1) surrounding at least one of the four corners of the display area (DA) may be extended outwardly to form the bending-allowing region (BA) and the second non-display area (NDA2). In FIG. 4, for convenience of explanation, one side of the first non-display area (NDA1) surrounding one of the four corners of the display area (DA) is shown as extended, but is not limited thereto.

[0082] A bending allowable area (BA) may be arranged extending from one side of a first non-display area (NDA1). The bending allowable area (BA) is an area where the flexible substrate (331) is bent. The first non-display area (NDA1) may be a substantially flat portion, and the bending allowable area (BA) may be bent at a constant bending angle from the first non-display area (NDA1). In this way, as a portion of the non-display area is bent toward the back of the flexible substrate (331), the bezel area may be reduced.

[0083] The second non-display area (NDA2) may be positioned extending from one side of the bending allowance area (BA). That is, the bending allowance area (BA) is positioned between the first non-display area (NDA1) and the second non-display area (NDA2).

[0084] An auxiliary back plate (370) is disposed on the lower surface of a flexible substrate (331) corresponding to a second non-display area (NDA2). The auxiliary back plate (370) is disposed on the same surface as the back plate (220). The auxiliary back plate (370) is disposed spaced apart from the back plate (220). The auxiliary back plate (370) can be formed using the same material as the back plate (220) and by the same process. Accordingly, the auxiliary back plate (370) may have a structure in which the same layer formed of the same material as the back plate (220) is stacked.

[0085] For example, the auxiliary back plate (370) includes an auxiliary base substrate (371) and an auxiliary hard coating layer (372). The auxiliary base substrate (371) is formed of the same material as the base substrate (221) of the back plate (220). The auxiliary hard coating layer (372) is formed of the same material as the hard coating layer (222) of the back plate (220). Although FIG. 5 shows the auxiliary hard coating layer (372) disposed on the upper surface of the auxiliary base substrate (371), it is not limited thereto. If the back plate (220) has a structure in which the hard coating layer (222) is disposed below the base substrate (221), the auxiliary back plate (370) may also have a structure in which the auxiliary hard coating layer (372) is disposed below the auxiliary base substrate (371) in the same way.

[0086] Referring to FIG. 5, a third adhesive layer (ADH3) may be disposed between the auxiliary back plate (370) and the flexible substrate (331) in the second non-display area (NDA2). The third adhesive layer (ADH3) is disposed between the flexible substrate (331) and the auxiliary hard coating layer (372) to bond the flexible substrate (331) and the auxiliary back plate (370). The third adhesive layer (ADH3) may be the same as the second adhesive layer (ADH2). The third adhesive layer (ADH3) may be selected from, but is not limited to, an optical clear adhesive (OCA), an optical clear resin (OCR), a pressure sensitive adhesive (PSA), etc.

[0087] Referring further to FIG. 5, a fourth adhesive layer (ADH4) may be disposed on the lower part of the auxiliary back plate (370). The fourth adhesive layer (ADH4) is disposed to be in contact with the base substrate (371) of the auxiliary back plate (370). The fourth adhesive layer (ADH4) may be the same as the first adhesive layer (ADH1). The fourth adhesive layer (ADH4) may be selected from optical clear adhesive (OCA), optical clear resin (OCR), pressure sensitive adhesive (PSA), etc., but is not limited thereto.

[0088] Hereinafter, the case in which the flexible substrate (331) is bent will be described in detail with reference to FIG. 6.

[0089] Referring to FIG. 6, as the bending allowable area (BA) is bent, the second non-display area (NDA2) of the flexible substrate (331) is positioned on the back surface of the flexible substrate (331) so as to overlap the first non-display area (NDA1) of the flexible substrate (331). The second non-display area (NDA2) may also be positioned to overlap at least a portion of the display area (DA) as well as the first non-display area (NDA1) of the flexible substrate (331).

[0090] For example, the bending allowable area (BA) can be bent toward the back of the flexible substrate (331) such that the second non-display area (NDA2) of the flexible substrate (331) overlaps with at least a portion of the first non-display area (NDA1). Accordingly, the second non-display area (NDA2) is positioned to face the lower surface of the plate bottom (110). Additionally, when the bending allowable area (BA) is bent, an auxiliary back plate (370) is positioned on the lower part of the plate bottom (110) that overlaps with the first non-display area (NDA1). The auxiliary back plate (370) and the plate bottom (110) are bonded together by a fourth adhesive layer (ADH4).

[0091] Specifically, for example, a fourth adhesive layer (ADH4) is disposed on the lower part of the plate bottom (110) that overlaps the first non-display area (NDA1). An auxiliary base substrate (371) is disposed on the lower part of the fourth adhesive layer (ADH4). An auxiliary hard coating layer (372) is disposed on the lower part of the auxiliary base substrate (371). Additionally, a third adhesive layer (ADH3) is disposed on the lower part of the auxiliary hard coating layer (372). When the bending allowable area (BA) is bent, the end of the second non-display area (NDA2) of the flexible substrate (331) is disposed to overlap the auxiliary hard coating layer (372). At this time, the second non-display area (NDA2) of the flexible substrate (331) may be a substantially flat area. The second non-display area (NDA2) of the flexible substrate (331) and the auxiliary hard coating layer (372) are bonded by a third adhesive layer disposed between them.

[0092] In this way, as a portion of the non-display area where the driving IC, etc. is placed is bent toward the back of the flexible substrate (331), the bezel area of ​​the flexible display device (300) can be reduced. Additionally, as an auxiliary back plate (370) including an auxiliary base substrate (371) and an auxiliary hard coating layer (372) is placed on the flexible substrate (331) corresponding to the second non-display area (NDA2), the occurrence of dents or punctures during bending can be minimized, and the display panel (130) can be stably supported.

[0093] The effects of the present invention described above will be explained in more detail below through examples and comparative examples. However, the following examples are for illustrative purposes only and do not limit the scope of the present invention.

[0094] [Example 1]

[0095] First, a polyimide film with a thickness of 50 μm was prepared. Next, a hard coat composition was prepared comprising two types of epoxy-modified siloxane oligomers with different epoxy equivalents and an initiator. Next, the hard coat composition was applied onto the polyimide film and cured to form a hard coating layer with a thickness of 40 μm. A flexible display device having a structure as shown in FIG. 2 was manufactured including the back plate prepared in this manner.

[0096] [Example 2]

[0097] A flexible display device having the structure shown in FIG. 3 was manufactured in the same manner as in Example 1, except that the position of the hard coating layer was changed so that the polyimide film was placed at the bottom and the hard coating layer was placed at the top.

[0098] [Example 3]

[0099] A flexible display device having the same structure as Example 1 was manufactured, except that a polyethylene terephthalate film with a thickness of 50 μm was used as the base substrate instead of a polyimide film in Example 1.

[0100] [Example 4]

[0101] A flexible display device having the same structure as Example 2 was manufactured, except that a polyethylene terephthalate film with a thickness of 50 μm was used as the base substrate instead of a polyimide film in Example 2.

[0102] [Comparative Example 1]

[0103] A flexible display device was manufactured in the same manner as in Example 1, except that the formation of the hard coating layer in Example 1 was omitted and a back plate consisting only of a polyimide film with a thickness of 50 μm was used.

[0104] [Comparative Example 2]

[0105] A flexible display device was manufactured in the same manner as in Example 3, except that the formation of the hard coating layer in Example 3 was omitted and a backplate consisting only of a polyethylene terephthalate film with a thickness of 50 μm was used.

[0106] [Experimental Example]

[0107] The indentation characteristics, puncture strength, and pattern transferability of the flexible display device manufactured as described above were evaluated.

[0108] 1. Indentation characteristics

[0109] First, a load of 300 gf was applied to the specimens according to Examples 1 to 4 and Comparative Examples 1 to 2, and the specimens were pressed with a pencil for 1 minute, then left for 24 hours. After 24 hours, the presence of scratches and indentations was observed visually. The results are listed in Table 1 below.

[0110] 2. Punching strength

[0111] The puncture strength of each flexible display device was measured using a texture analyzer. Specifically, the maximum puncture load was measured by pressing the folding area with a puncture probe (2 mm diameter, stainless steel) while increasing the force applied to the specimen. The maximum puncture load was determined as the load at which damage, such as bright spots or dark spots, occurred on the display panel. The results are listed in Table 1 below.

[0112] 3. Whether mouth opening pattern is transferred

[0113] After storing the flexible display device for 10 days under conditions of 60°C and 90% relative humidity, the visibility of the opening pattern formed on the bottom of the plate was evaluated visually under a 700lx fluorescent lamp. The degree of visibility of the pattern was judged as weak, weak, medium, medium-strong, or strong. The results are listed in Table 1 below.

[0114] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Pressure characteristics H-2H H-2H H-2H H-2H H-2H H-2H Drilling strength (Kgf) 5 5.5 5.5 5.5 3.5 3.5 Whether the opening pattern is transferred approximately approximately approximately approximately middle river

[0115] Referring to Table 1 above, it can be seen that the flexible display device according to Examples 1 to 4 of the present invention maintains high compression characteristics, while the perforation strength in the folding area, where the strength is relatively lower due to the opening pattern, is significantly improved compared to Comparative Example 1 and Comparative Example 2.

[0116] In addition, it can be confirmed that the degree to which the opening pattern is visible in the flexible display device according to Examples 1 to 4 is weaker compared to Comparative Examples 1 and 2 as a hard coating layer is formed on the base substrate of the back plate.

[0117] In various embodiments of the present invention, the flexible display device can be described as follows.

[0118] A flexible display device according to one embodiment of the present invention includes a display panel, a back plate disposed below the display panel, and a plate bottom disposed below the back plate, wherein the back plate includes a base substrate and a hard coating layer disposed on at least one surface of the base substrate.

[0119] According to another feature of the present invention, the base substrate may be selected from a polyethylene terephthalate film, a polyimide film, or a polyamideimide film.

[0120] According to another feature of the present invention, the hard coating layer may include a silicone-based resin.

[0121] According to another feature of the present invention, the silicone resin can be formed from an epoxy-modified siloxane oligomer.

[0122] According to another feature of the present invention, a silicone-based resin may be formed by polymerizing a composition comprising a first epoxy-modified siloxane oligomer and a second epoxy-modified siloxane oligomer having an epoxy equivalent different from that of the first epoxy-modified siloxane oligomer.

[0123] According to another feature of the present invention, the composition may further include one or more selected from urethane acrylate-based linkers, acrylate-based linkers, and epoxy-based linkers.

[0124] According to another feature of the present invention, the thickness of the hard coating layer may be 30㎛ to 60㎛.

[0125] According to another feature of the present invention, it may further include a first adhesive layer disposed between a back plate and a plate bottom to bond the back plate and the plate bottom, and a second adhesive layer disposed between a back plate and a display panel to bond the back plate and the display panel.

[0126] According to another feature of the present invention, the flexible display device includes a folding area and a non-folding area, and the plate bottom may have an opening pattern formed to correspond to the folding area.

[0127] According to another feature of the present invention, a display panel comprises a flexible substrate and a device layer on the flexible substrate, wherein the flexible substrate comprises a display area, a first non-display area surrounding the display area, a bending allowable area extending from the first non-display area, and a second non-display area extending from one side of the bending allowable area, and the bending allowable area can be bent toward the back surface of the flexible substrate such that the second non-display area of ​​the flexible substrate overlaps with at least a portion of the first non-display area.

[0128] According to another feature of the present invention, an auxiliary back plate may be further included that is positioned at the bottom of the plate to correspond to a first non-display area.

[0129] According to another feature of the present invention, an auxiliary back plate may be disposed on the same surface as the back plate and spaced apart from one side of the back plate.

[0130] According to another feature of the present invention, the auxiliary back plate may include an auxiliary base substrate and an auxiliary hard coating layer disposed on the upper or lower surface of the auxiliary base substrate.

[0131] According to another feature of the present invention, the auxiliary base substrate may be made of the same material as the base substrate, and the auxiliary hard coating layer may be made of the same material as the hard coating layer.

[0132] According to another feature of the present invention, the bending allowable area is bent toward the back surface of the flexible substrate, and the second non-display area of ​​the flexible substrate may be positioned to overlap with at least a part of the auxiliary back plate.

[0133] According to another feature of the present invention, it may further include a third adhesive layer disposed between a flexible substrate and an auxiliary back plate to bond the flexible substrate and the auxiliary back plate, and a fourth adhesive layer disposed between an auxiliary back plate and a plate bottom to bond the auxiliary back plate and the plate bottom.

[0134] Although embodiments of the present invention have been described in more detail with reference to the attached drawings, the present invention is not necessarily limited to these embodiments and may be modified in various ways within the scope of the technical spirit of the present invention. Accordingly, the embodiments disclosed in the present invention are intended to explain, not to limit, the technical spirit of the present invention, and the scope of the technical spirit of the present invention is not limited by these embodiments. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. The scope of protection of the present invention shall be interpreted by the claims below, and all technical spirits within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention. Explanation of the symbols

[0135] 100, 200, 300: Flexible display device 110: Plate Bottom 120, 220: Backplate 121, 221: Base entry 122, 222: Hard coating layer 130, 330: Display panel 140: Optical control layer 150: Decor layer 160: Cover missing 370: Auxiliary backplate 371: Auxiliary base material 372: Auxiliary hard coating layer ADH1: First adhesive layer ADH2: Second adhesive layer ADH3: Third adhesive layer ADH4: 4th adhesive layer FA: Folding area NFA1, NFA2: Non-folding area DA: Display area NDA: Non-display area NDA1: 1st Non-display Area NDA2: Second non-display area BA: Bending Allowed Area

Claims

Claim 1 A flexible display device comprising: a display panel; a cover member disposed on the display panel and having a functional layer or a protective film disposed on at least one surface; a back plate disposed below the display panel; and a plate bottom disposed below the back plate, wherein the back plate comprises a base substrate and a hard coating layer disposed on the upper or lower surface of the base substrate. Claim 2 A flexible display device according to claim 1, wherein the base substrate is selected from a polyethylene terephthalate film, a polyimide film, or a polyamideimide film. Claim 3 A flexible display device according to claim 1, wherein the hard coating layer comprises a silicone-based resin. Claim 4 In paragraph 3, the flexible display device wherein the silicone-based resin is formed from an epoxy-modified siloxane oligomer. Claim 5 A flexible display device according to claim 4, wherein the silicone-based resin is formed by polymerizing a composition comprising a first epoxy-modified siloxane oligomer and a second epoxy-modified siloxane oligomer having an epoxy equivalent different from that of the first epoxy-modified siloxane oligomer. Claim 6 A flexible display device according to claim 5, wherein the composition further comprises one or more types selected from urethane acrylate-based linkers, acrylate-based linkers, and epoxy-based linkers. Claim 7 In claim 5, the thickness of the hard coating layer is 30㎛ to 60㎛, flexible display device. Claim 8 A flexible display device according to claim 1, further comprising a first adhesive layer disposed between the back plate and the plate bottom to bond the back plate and the plate bottom, and a second adhesive layer disposed between the back plate and the display panel to bond the back plate and the display panel. Claim 9 In claim 1, the flexible display device comprises a folding area and a non-folding area, and the plate bottom has an opening pattern formed to correspond to the folding area. Claim 10 A flexible display device according to claim 1, wherein the display panel comprises a flexible substrate and a device layer on the flexible substrate, and the flexible substrate comprises a display area, a first non-display area surrounding the display area, a bending allowable area extending from the first non-display area, and a second non-display area extending from one side of the bending allowable area, wherein the bending allowable area is bent toward the back surface of the flexible substrate such that the second non-display area of ​​the flexible substrate overlaps with at least a portion of the first non-display area. Claim 11 A flexible display device according to claim 10, further comprising an auxiliary back plate disposed at the bottom of the plate to correspond to the first non-display area. Claim 12 In claim 11, the auxiliary back plate is disposed on the same surface as the back plate and is spaced apart from one side of the back plate, forming a flexible display device. Claim 13 A flexible display device according to claim 11, wherein the auxiliary back plate comprises an auxiliary base substrate and an auxiliary hard coating layer disposed on the upper or lower surface of the auxiliary base substrate. Claim 14 A flexible display device according to claim 13, wherein the auxiliary base substrate is made of the same material as the base substrate, and the auxiliary hard coating layer is made of the same material as the hard coating layer. Claim 15 A flexible display device according to claim 11, wherein the bending allowable area is bent toward the back surface of the flexible substrate, and the second non-display area of ​​the flexible substrate is positioned to overlap with at least a portion of the auxiliary back plate. Claim 16 A flexible display device according to claim 11, further comprising a third adhesive layer disposed between the flexible substrate and the auxiliary back plate to bond the flexible substrate and the auxiliary back plate, and a fourth adhesive layer disposed between the auxiliary back plate and the plate bottom to bond the auxiliary back plate and the plate bottom.

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