Flexible display device

Abstract

The present disclosure relates to a flexible display device, and the flexible display device according to an exemplary embodiment of the present disclosure includes: a display panel including a folding area and a non-folding area; and a back plate including a base layer supporting the display panel below the display panel and including a plurality of grooves corresponding to the folding area on the bottom surface; and a filler filled in at least a portion of the plurality of grooves, and the filler includes metal fiber. According to an exemplary embodiment of the present disclosure, components such as a top plate, a bottom plate, and a damping layer are not included, but mechanical properties such as impact resistance are met and the thickness of the display device is minimized, so that the folding characteristics and reliability are significantly improved. Therefore, a flexible display device having a greater curvature than that of the prior art can be easily realized.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the priority of Korean Patent Application No. 10-2020-0175076 filed in the Korean Intellectual Property Office on December 15, 2020, the disclosure of which is incorporated herein by reference. Technical Field

[0003] The present disclosure relates to a flexible display device, and more particularly, to a flexible display device having excellent mechanical properties, improved appearance quality, and improved folding reliability. Background Art

[0004] In recent years, with the advent of the information age, the display field that visually represents electrical information signals has developed rapidly, and in response to this, various display devices having excellent properties such as thin thickness, light weight, and low power consumption have been developed. Specific examples of such display devices include liquid crystal display (LCD) devices, plasma display panel (PDP) devices, field emission display (FED) devices, organic light emitting display (OLED) devices, etc.

[0005] Meanwhile, efforts are continuing to diversify the shapes and sizes of display devices. For example, display devices having various shapes, such as a curved display device having a curved surface or a flexible display device that maintains its display performance even in a bent or folded state, are being continuously developed. The display panel of the flexible display device uses a flexible substrate so that a supporting member such as a backplane is disposed below the display panel to suppress sagging of the display panel and protect the display panel from foreign matter and impact from the outside. Summary of the invention

[0006] The supporting member of the prior art is composed of a back plate and a plate assembly including a top plate and a bottom plate, and is provided with an adhesive layer for bonding the various layers. As a result, the thickness of the supporting member is thick, so that the stress applied to the supporting member during the folding process is large, which reduces the folding reliability.

[0007] In addition, in order to achieve the desired curvature, an opening pattern is formed in at least a partial area of ​​the back plate and / or the plate assembly. However, there is a problem that the opening pattern is visible to the user, which deteriorates the appearance quality. In addition, even if a damping layer having a foam structure is provided at the lowermost portion to ensure impact resistance, defects may be caused due to depression or perforation of the surface during the folding process.

[0008] Therefore, an object to be achieved by the present disclosure is to provide a flexible display device including a back plate, which significantly reduces the thickness of the display device while maintaining high rigidity.

[0009] Another object to be achieved by the present disclosure is to provide a flexible display device having excellent folding reliability and impact resistance and excellent appearance quality with a higher curvature compared to the prior art.

[0010] Still another object to be achieved by the present disclosure is to provide a flexible display device which reduces visibility of a pattern formed in a folding area and disperses stress concentrated on an engraved pattern portion during folding to suppress cracking or plastic deformation during repeated folding.

[0011] The purpose of the present disclosure is not limited to the above-mentioned purpose, and those skilled in the art can clearly understand other purposes not mentioned above through the following description.

[0012] According to one aspect of the present disclosure, a flexible display device includes: a display panel, the display panel including a folding area and a non-folding area; a back plate, the back plate including a base layer supporting the display panel below the display panel and including a plurality of grooves corresponding to the folding area on a bottom surface; and a filler filled in at least a portion of the plurality of grooves, and the filler includes metal fiber.

[0013] Additional details of example embodiments are included in the detailed description and the accompanying drawings.

[0014] According to an exemplary embodiment of the present disclosure, a flexible display device forms a groove pattern instead of an opening pattern in a back panel to effectively relieve folding stress and reduce visibility of a pattern, thereby improving appearance quality.

[0015] Further, according to the present disclosure, metal fibers are filled in the plurality of grooves to disperse the stress concentrated on the relief pattern unit during the folding process and improve the rigidity of the back plate. In addition, the plurality of grooves are filled with metal fibers, so that the folding stress is effectively relieved, and deformation such as fracture or plastic deformation is not caused even during repeated folding, thereby providing high reliability.

[0016] Further, according to the present disclosure, components such as a top plate, a bottom plate, and a damping layer configured together with a back plate in the prior art are omitted, so that the thickness of the display device can be significantly reduced. Therefore, compared with the prior art, a flexible display device that satisfies folding reliability and mechanical properties such as impact resistance and has a larger curvature can be realized. In addition, the damping layer is omitted, so that the defect problem caused by depression or perforation of the surface during the folding process can be minimized.

[0017] The effects according to the present disclosure are not limited to the above-exemplified contents, and more various effects are included in this specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and other aspects, features and other advantages of the present disclosure will be more clearly understood from the following detailed description in conjunction with the accompanying drawings, in which:

[0019] Figure 1 is a schematic plan view of a flexible display device according to an exemplary embodiment of the present disclosure;

[0020] Figure 2 is along Figure 1 A schematic cross-sectional view of line II';

[0021] Figure 3 is a schematic plan view of a bottom surface of a back plate in a flexible display device according to an exemplary embodiment of the present disclosure;

[0022] 4A to 4F is a schematic cross-sectional process diagram for illustrating a method for manufacturing a backplane in a flexible display device according to an exemplary embodiment of the present disclosure;

[0023] Figure 5 is a schematic cross-sectional view of a flexible display device according to another exemplary embodiment of the present disclosure;

[0024] Figure 6 is a diagram showing a folding simulation result of a back plate according to the present disclosure;

[0025] Figure 7 is a diagram showing a folding simulation result of a back plate according to the prior art; and

[0026] Figure 8 is a diagram showing a folding simulation result of another back plate according to the prior art. DETAILED DESCRIPTION

[0027] By referring to the exemplary embodiments described in detail below in conjunction with the accompanying drawings, the advantages and features of the present disclosure and the methods for achieving these advantages and features will become clear. However, the present disclosure is not limited to the exemplary embodiments disclosed herein, but will be implemented in various forms. The exemplary embodiments are provided only as examples to enable those skilled in the art to fully understand the disclosure of the present disclosure and the scope of the present disclosure. Therefore, the present disclosure will only be limited by the scope of the appended claims.

[0028] The shapes, sizes, ratios, angles, quantities, etc. used to describe the exemplary embodiments of the present disclosure shown in the accompanying drawings are merely examples, and the present disclosure is not limited thereto. Throughout the specification, the same reference numerals generally represent the same elements. In addition, in the following description of the present disclosure, detailed descriptions of known prior art may be omitted to avoid unnecessarily obscuring the subject matter of the present disclosure. Terms such as "including", "having" and "consisting of..." used herein are generally intended to allow the addition of other components unless these terms are used together with the term "only". Unless otherwise expressly stated, any reference to the singular may include the plural.

[0029] Even if not explicitly stated, the components are interpreted as including ordinary error ranges.

[0030] When terms such as “on,” “above,” “below,” and “near” are used to describe the positional relationship between two components, one or more components may be located between the two components unless these terms are used together with the term “immediately” or “directly.”

[0031] When one element or layer is disposed “on” another element or layer, a third layer or element may be directly interposed on the other element or between them.

[0032] Although the terms "first", "second", etc. are used to describe various components, these components are not limited by these terms. These terms are only used to distinguish one component from other components. Therefore, the first component mentioned below can be the second component in the technical concept of the present disclosure.

[0033] Throughout the specification, like reference numerals generally refer to like elements.

[0034] The size and thickness of each component shown in the drawings are shown for convenience of description, and the present disclosure is not limited to the size and thickness of the components shown.

[0035] The features of the various embodiments of the present disclosure may be partially or entirely bonded or combined with each other, and may be technically related and operated with each other in various ways, and the embodiments may be performed independently or in association with each other.

[0036] Hereinafter, a flexible display device according to exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0037] Figure 1 is a schematic plan view of a flexible display device according to an exemplary embodiment of the present disclosure. Figure 2 is along Figure 1 Schematic cross-sectional view along line II'.

[0038] refer to Figure 1 and Figure 2, the flexible display device 100 according to an exemplary embodiment of the present disclosure includes a back plate 110, a display panel 120, and a cover member 130. Hereinafter, for convenience of description, it will be described by assuming that the flexible display device according to an exemplary embodiment of the present disclosure is an organic light emitting display device, but is not limited thereto.

[0039] The display panel 120 includes a display area DA and a non-display area NDA. In addition, the display panel 110 includes a folding area FA and non-folding areas NFA1 and NFA2. The display panel 120 can be divided into a display area DA and a non-display area NDA according to whether an image is displayed, and can be divided into a folding area FA and a non-folding area NFA according to whether it is foldable. Therefore, a part of the display panel 120 may be the display area DA and the folding area FA, and another part of the display panel 120 may be the non-display area NDA and the non-folding area NFA.

[0040] 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 may be arranged, and the plurality of pixels include a light-emitting area for displaying an image, a thin film transistor for driving the pixel, a capacitor, etc. A pixel may include a plurality of sub-pixels SP. The sub-pixel SP is the smallest unit constituting the display area, and each sub-pixel SP may be configured to emit light of a specific wavelength band. For example, each sub-pixel SP may be configured to emit red light, green light, blue light, or white light.

[0041] The non-display area NDA is provided to surround the display area DA. The non-display area NDA is a region where no image is substantially displayed and various wirings, a driving IC, etc. for driving pixels and driving elements provided in the display area DA are provided.

[0042] As described above, the display panel 120 may be defined as a folding area FA and non-folding areas NFA1 and NFA2, depending on whether it is foldable. The display panel 120 includes a foldable folding area FA and non-folding areas NFA1 and NFA2 other than the folding area. The folding area FA is an area that is folded when the flexible display device 100 is folded and may be folded according to a specific radius of curvature relative to a folding axis. For example, the folding axis of the folding area FA may be formed in the X-axis direction, and the non-folding areas NFA1 and NFA2 may extend from the folding area FA in the Y-axis direction perpendicular to the folding axis. When the folding area FA is folded relative to the folding axis, the folding area FA may form a part of a circle or an ellipse. At this time, the radius of curvature of the folding area FA may refer to the radius of the circle or ellipse formed by the folding area FA.

[0043] The non-folding areas NFA1 and NFA2 are areas that are not folded when the flexible display device 100 is folded. That is, when the flexible display device 100 is folded, the non-folding areas NFA1 and NFA2 remain in a flat state. The non-folding areas NFA1 and NFA2 may be located on both sides of the folding area FA. That is, the non-folding areas NFA1 and NFA2 may be areas extending in the Y-axis direction relative to the folding axis. At this time, the folding area FA may be defined between the non-folding areas NFA1 and NFA2. Further, when the flexible display device 100 is folded relative to the folding axis, the non-folding areas NFA1 and NFA2 may overlap each other.

[0044] The display panel 120 includes a flexible substrate 121 and a display element 122 .

[0045] The flexible substrate 121 supports various elements constituting the display panel 120. The flexible substrate 121 may be a plastic substrate having flexibility. For example, the plastic substrate may be a polymer material selected from polyimide, polyamideimide, polyethersulfone, polyethylene terephthalate, and polycarbonate, without being limited thereto.

[0046] The plastic substrate has relatively weak barrier properties to moisture or oxygen, so to compensate for this, the plastic substrate may have a structure in which a plastic film and an inorganic layer are stacked. For example, the flexible substrate 121 may have a multilayer structure in which a first plastic film, an inorganic layer, and a second plastic film are sequentially stacked, without being limited thereto.

[0047] The flexible substrate 121 has excellent folding characteristics, but is thin and has lower rigidity than a glass substrate or a metal substrate, so it is difficult to maintain a constant shape during folding, and thus, sagging may occur. Therefore, in order to support the flexible substrate 121 and improve impact resistance, a back plate 110 is provided below the display panel 120.

[0048] The back plate 110 is disposed under the display panel 120 to support the display panel 120 and protect the display panel 120 from moisture or foreign matter infiltrated from the outside and external impact. The back plate 110 will be described in more detail below.

[0049] A driving thin film transistor for driving the display element 122 may be provided on the flexible substrate 121. The driving thin film transistor may be provided in each of the plurality of pixel regions. For example, the driving thin film transistor includes a gate, an active layer, a source electrode, and a drain electrode. The driving thin film transistor may further include a gate insulating layer for insulating the gate from the active layer and an interlayer insulating layer for insulating the gate from the source electrode and the drain electrode.

[0050] A planarization layer may be disposed on the driving thin film transistor to planarize an upper surface.

[0051] The display element 122 may be disposed on the planarization layer. The display element 122 may be an organic light emitting diode. The organic light emitting diode may include an anode, a cathode, and an organic light emitting layer disposed therebetween. In the organic light emitting diode, holes injected from the anode and electrons injected from the cathode are coupled on the organic light emitting layer to emit light. The emitted light as described above may be used to display an image.

[0052] The cover member 130 is disposed on the display element 122. The cover member 130 protects the display panel 120 from external impacts and scratches. Therefore, the cover member 130 may be formed of a transparent material having excellent impact resistance and scratch resistance. In addition, the cover member 130 protects the display panel 120 from moisture infiltrating from the outside. When moisture infiltrates from the outside, the display panel 120 deteriorates, and thus the display quality may be reduced.

[0053] For example, the cover member 130 may be a film formed of a polymer such as polyimide, polyamideimide, polyethylene terephthalate, polymethyl methacrylate, polypropylene glycol, or polycarbonate. As another example, the cover member may be a film formed of an optically isotropic polymer such as cycloolefin (co)polymer, optically isotropic polycarbonate, or optically isotropic polymethyl methacrylate.

[0054] In addition, the cover member 130 may have a multi-layer structure in which various functional layers are stacked. For example, the cover member 130 may include various functional layers such as an external light reflection reducing layer, a UV blocking layer, or a hard coating layer.

[0055] In the following, we will refer to Figure 3 The back plate 110 is described in more detail. Figure 3 is a schematic plan view of a bottom surface of a back panel in a flexible display device according to an exemplary embodiment of the present disclosure.

[0056] For reference Figure 2 and Figure 3 , the back plate 110 is disposed below the display panel 120. That is, the back plate 110 is disposed on the back side of the flexible substrate 121 to suppress sagging or deformation of the flexible substrate 121 and protect the display panel 120 from external impact or foreign matter.

[0057] The back plate 110 may be bonded to the display panel 120 through the adhesive layer Adh. That is, the back plate 110 is attached to the back surface of the flexible substrate 121 through the adhesive layer Adh.

[0058] The back sheet 110 includes a base layer 111 , a filler 112 , and a conductive adhesive layer 113 .

[0059] The base layer 111 is used to substantially support the display panel 120. The base layer 111 may be a foldable plate having excellent rigidity. The base layer 111 may be formed of a material having greater rigidity than the flexible substrate 121 to support the display panel 120.

[0060] For example, the base layer 111 may be a metal plate including a metal such as stainless steel (SUS), invar, aluminum or magnesium. The metal plate has excellent rigidity and impact resistance and excellent restoring force. When the back plate 110 is formed of a metal material having excellent rigidity as described above, even if its thickness is reduced, mechanical properties such as the required rigidity can be maintained to firmly support the display panel 120. Therefore, compared with the back plate formed by the polymer material of the prior art, the thickness can be significantly reduced. The thickness of the back plate 110 is minimized to reduce the stress applied to the back plate 110 or the display panel 120 during the folding process, so that the folding reliability can be improved and the folding characteristics can be improved. In addition, a flexible display device having a greater curvature than the prior art can be realized, and further, a multi-foldable display device or a rollable display device can also be realized. In addition, the base layer 111 formed of the metal material as described above has excellent restoring force, so that even in the repeated folding process, deformation such as plastic deformation will not be caused, thereby improving the appearance defects.

[0061] For example, the thickness of the base layer 111 may be 90 μm to 220 μm. When the thickness of the base layer 111 is less than 90 μm, the base layer is so thin that the base layer cannot effectively support the display panel 120 that is about to sag. In addition, when the thickness of the base layer 111 is greater than 220 μm, the thickness of the back plate 110 is so large that when the flexible display device 100 is folded, the stress applied to the display panel 120 increases, which may cause cracks. In addition, the restoring force is reduced, resulting in plastic deformation, which may fail to meet the folding reliability.

[0062] The base layer 111 includes a plurality of grooves G. Although Figure 2 and Figure 3 In the figure, for the convenience of description, it is shown that four grooves are formed, but it is not limited thereto.

[0063] A plurality of grooves G may be formed on the bottom surface of the base layer 111 to correspond to the folding area FA. That is, the plurality of grooves G are recessed from the bottom surface of the base layer 111 toward the top surface. When the flexible display device 100 is folded, stress is concentrated on the folding area FA. The plurality of grooves G may disperse the stress concentrated on the folding area FA during the folding process. As described above, since the plurality of grooves G are formed in a position corresponding to the folding area FA, there are advantages that the flexible display device 100 is easy to fold and has excellent restoring force.

[0064] refer to Figure 3, each of the plurality of grooves G may be formed to extend long in a direction parallel to the folding axis. That is, each of the plurality of grooves G may be formed to extend long in the X-axis direction which is the same as the folding axis. Therefore, each of the plurality of grooves G may be formed in a rod shape parallel to the folding axis in a plan view.

[0065] Each of the plurality of grooves G may continuously extend to the non-display area along the X-axis direction which is the same as the folding axis without interruption on the display area DA, without being limited thereto.

[0066] Despite Figure 2 and Figure 3 The cross-sectional shape of each of the plurality of grooves G is shown as a quadrilateral, but the cross-sectional shape of each of the plurality of grooves G is not limited thereto. The cross-sectional shape of each of the plurality of grooves G may be formed into various shapes, such as a polygon, in addition to a semicircular or quadrilateral shape.

[0067] In the prior art, in order to disperse the folding stress concentrated on the folding area, an opening pattern, that is, a plurality of holes, is formed on the base layer. In this case, the folding stress is dispersed to meet the folding reliability, but the visibility of the opening pattern increases, so that the appearance quality is deteriorated.

[0068] The flexible display device 100 according to an exemplary embodiment of the present disclosure forms grooves on the bottom surface of the base layer 111, thereby reducing the visibility of the pattern to improve the appearance quality. That is, a plurality of grooves G are formed at a predetermined depth from the bottom surface of the base layer 111 along the thickness direction (Z axis) of the base layer 111. Therefore, the plurality of grooves G formed in the folding area FA are not visible to the user, so that the appearance quality can be improved.

[0069] For example, the depth of each of the plurality of grooves G may be 10 μm to 40 μm or 20 μm to 30 μm, and within this range, the visibility of the plurality of grooves G is reduced, so that the appearance quality is improved. In addition, the stress concentrated on the folding area FA during the folding process is effectively dispersed, so that the folding characteristics can be improved.

[0070] The plurality of grooves G may be formed by removing a portion of a material forming the base layer 111. For example, the plurality of grooves G may be formed by a known method such as photolithography, laser etching, or plasma etching, without being limited thereto.

[0071] The filler 112 is filled in at least a portion of the plurality of grooves. For example, the filler 112 is filled in each of the plurality of grooves.

[0072] When a plurality of grooves G are formed on the base layer 111 overlapping the folding area FA, stress is dispersed during the folding process, thereby improving the folding characteristics. However, a step is formed and the flatness of the back plate 110 and the flexible display device 100 is degraded. Therefore, problems such as component separation or component breakage are caused due to uneven stress during the folding process, so that the folding reliability cannot be satisfied or the realization of a flexible display device with a large curvature is limited. Further, when the flatness of the folding area FA is degraded, the image displayed in the folding area FA is distorted, causing the display quality to degrade.

[0073] Therefore, the filler 112 is formed to fill in the plurality of grooves G. The filler 112 includes metal fibers. Therefore, the stress more concentrated on the folding area FA (specifically, in the grooves G) during the folding process can be more effectively dispersed. Therefore, the folding characteristics are improved, so that the flexible display device 100 with a greater curvature can be easily realized.

[0074] When the filler 112 is not filled in the plurality of grooves G, stress is concentrated on the embossed pattern portion recessed from the surface, thereby possibly causing cracks during repeated folding. Therefore, folding reliability is not satisfied and improvement of the curvature of the flexible display device may be limited.

[0075] In the prior art, in order to improve the folding characteristics without making the opening pattern visible, a soft material such as silicone resin (e.g., PDMS) or acrylic resin is filled in the opening of the opening pattern. However, in this case, there is a problem that plastic deformation is easily caused due to repeated folding.

[0076] The filler 112 of the present disclosure includes metal fibers. For example, the metal fibers may include one or more metals selected from stainless steel, titanium, and aluminum. Such metal materials are not prone to plastic deformation and have excellent rigidity.

[0077] For example, the plurality of grooves G may be filled with metallic yarn or metal fiber sheets. That is, the filler 112 may be formed of metallic yarn or metal fiber sheets.

[0078] For example, the metal wire may be processed to have a predetermined thickness and length by stretching the metal fiber. For example, the metal wire may be formed by stretching a single metal fiber. As another example, the metal wire may have a twisted structure by twisting a single metal fiber in a predetermined direction, or may have a twisted structure by twisting a plurality of metal fibers.

[0079] The metal wire is filled in each of the plurality of grooves G to form a structure in which the metal fibers are randomly entangled. Since the metal fibers are randomly entangled, an irregular network structure is formed. Therefore, the filler 112 filled in each of the plurality of grooves G is formed to have a porous structure including a plurality of holes. The filler 112 has elasticity due to the above-mentioned structural characteristics. Therefore, the metal wire is stretched along the folding direction (Y-axis direction) during the folding process and the stress is evenly dispersed without concentration. Due to the structural characteristics, the restoring force is excellent, and deformation is not easily caused even during repeated folding, so the durability is excellent.

[0080] For example, the diameter of the metal wire may be 5 μm to 15 μm. Within this range, the metal wire may be easily filled in each of the plurality of grooves G and have excellent elasticity to effectively disperse stress concentrated on the folding area FA during the folding process.

[0081] As another example, the metal wire may be a yarn in which a polymer coating is formed on the surface of the metal wire, or a mixed yarn in which the metal wire and the polymer fiber are mixed. The polymer coating and the polymer fiber may be formed of a polymer such as polyester or nylon, without being limited thereto.

[0082] The metal fiber sheet may be formed by randomly or regularly entangled and stacked metal fibers to form a film. For example, the metal fiber sheet may be a nonwoven fabric sheet or a fabric sheet formed of metal fibers.

[0083] A nonwoven sheet is formed of randomly tangled metal sheets, but a woven sheet may be formed of regularly tangled metal sheets. Specifically, the woven sheet may be formed by crossing and weaving metal fibers divided into vertical (warp) lines and horizontal (weft) lines, and the woven sheet has a structure in which the metal fibers are arranged in a grid form.

[0084] The nonwoven fabric sheet and the fabric sheet as described above are formed by randomly or regularly entangled metal fibers to have a porous structure including a plurality of holes. Therefore, the filler 112 formed by filling a plurality of grooves G with the nonwoven fabric sheet or the fabric sheet has elasticity. Therefore, the nonwoven fabric sheet and the fabric sheet are stretched along the folding direction (Y-axis direction) during the folding process, so that the stress can be evenly dispersed without being concentrated. Due to this structural feature, the restoring force is excellent, and deformation is not easily caused even during repeated folding, so the durability is excellent.

[0085] The nonwoven fabric sheet and the fabric sheet may further include a polymer coating or polymer fibers. The polymer coating may be formed to coat the metal fibers constituting the sheet. Further, the polymer fibers are entangled with the metal fibers to form a woven structure. As another example, the nonwoven fabric sheet or the fabric sheet may be a sheet formed by immersing the nonwoven fabric sheet or the fabric sheet in a polymer to fill a plurality of holes. Here, the polymer may be selected from polyester, nylon, etc., but is not limited thereto.

[0086] When the plurality of grooves G are filled with metal wires or metal fiber sheets as described above, the back plate 110 can maintain high mechanical strength by the high rigidity of the metal material. In addition, as described above, the metal wires or metal fiber sheets formed by metal fibers have excellent elasticity due to structural characteristics. Therefore, in the filler 112 formed by filling the metal wires or metal fiber sheets, the metal fibers in the filler 112 extend along the folding direction during the folding process. Therefore, during the folding process, the stress can be evenly dispersed without being concentrated on the folding area FA. In addition, the filler 112 formed by the metal fibers due to the elastic characteristics can minimize the rupture or plastic deformation of the back plate 110 caused by repeated folding.

[0087] At the same time, the filler 112 can be attached to the plurality of grooves G by the adhesive layer 113. The conductive adhesive layer 113 can join the filler 112 to the plurality of grooves G to fix them. The conductive adhesive layer 113 can be disposed on the innermost surface of the plurality of grooves G. Therefore, the upper surface of the filler 112 is joined to the groove G by the conductive adhesive layer 113, so that the filler 112 can be fixed to the groove G without deviation during the folding process. In addition, the side surface of the filler 112 is not fixed by the conductive adhesive layer 113, so that the metal fiber in the filler 112 can be easily stretched along the folding direction during the folding process. Thus, the stress concentrated on the embossed pattern portion during the folding process can be more effectively dispersed.

[0088] For example, the conductive adhesive layer 113 may be formed of a solder paste in which conductive particles are uniformly dispersed in a binder resin.

[0089] For example, the binder resin may be selected from epoxy-based resins, urethane-based resins, acrylic resins, silicon-based resins, phenol-based resins, melamine-based resins, alkyd-based resins, urea resins, unsaturated polyester resins, and the like.

[0090] For example, the conductive particles may be selected from alloys of tin and one or more metals selected from silver, copper, lead, bismuth, zinc, and indium.

[0091] When heat is applied to the conductive particles, the conductive particles melt and fuse to allow the filler 112 to be bonded to the plurality of grooves G. As shown in FIG.

[0092] In the following, reference will be made to 4A to 4FA method for forming the filling material 112 in the plurality of grooves G is described in more detail. 4A to 4F Detailed description is provided for explaining a method for manufacturing a back panel in a flexible display device according to an exemplary embodiment of the present disclosure.

[0093] First, a base layer 111 having a plurality of grooves G formed thereon is prepared.

[0094] Reference Figure 4A , a plurality of grooves G are formed on the bottom surface of the base layer 111 corresponding to the folding area FA. As described above, the plurality of grooves G may be formed by a method selected from photolithography, laser etching, and plasma etching processes.

[0095] Next, a releasable adhesive layer 150 is formed on the bottom surface of the base layer 111 .

[0096] Reference Figure 4B , the peelable adhesive layer 150 is selectively formed on the bottom surface of the base layer 111. The peelable adhesive layer 150 is formed on the bottom surface of the base layer 111 except for the plurality of grooves G. That is, the peelable adhesive layer 150 is not formed in the plurality of grooves G. The peelable adhesive layer 150 can be formed using an adhesive that can be removed from the base material by reducing adhesion as needed. For example, the peelable adhesive layer 150 can be formed by applying a reprocessable optically transparent adhesive or a water stripping solution released by water dissolution. For example, the reprocessable optically transparent adhesive can be an optically transparent adhesive whose adhesion changes according to heat, light or pressure, without being limited thereto.

[0097] Next, solder paste 113 ′ is applied on the bottom surface of the base layer 111 .

[0098] refer to Figure 4C , the solder paste 113' is applied on the entire bottom surface of the base layer 111. Unlike the peelable adhesive layer 150, the solder paste 113' is also applied to the inside of the plurality of grooves G. After applying the solder paste 113', an annealing process may be selectively further included as needed.

[0099] Next, metal fibers are filled in the plurality of grooves G and welded to form the filler 112 .

[0100] refer to Figure 4DFirst, metal fibers are filled in the plurality of grooves G. For example, a metal fiber sheet is laminated on the bottom surface of the base layer 111 corresponding to the folding area FA to fill the metal fibers in the plurality of grooves G. Specifically, lamination is performed by joining the metal fiber sheet on the bottom surface of the base layer 111 and then pressing them using a lamination roller. When the metal fiber sheet joined to the base layer 111 is pressed using the lamination roller, the metal fibers are filled in the plurality of grooves to form the fillers 112.

[0101] Next, the filler 112 is joined into the plurality of grooves G using a welding process.

[0102] refer to Figure 4E , after forming the filler 112, a welding process is performed, and the filler 112 is fixed to the plurality of grooves G without deviating from the plurality of grooves G. The conductive particles in the solder paste 113' are melted and fused by the welding process to form a conductive adhesive layer 113. Therefore, the top surface of the filler 112 in contact with the solder paste 113' is welded and fixed in the plurality of grooves G. For example, the welding process is performed by heating at a temperature of 140°C to 230°C for 30 seconds to 50 minutes. If the heating unit melts the conductive particles, the heating unit is not particularly limited. The melted conductive particles are fused to form the conductive adhesive layer 113, and therefore, the filler 112 can be firmly bonded to the plurality of grooves G through the conductive adhesive layer 113.

[0103] Next, the removable adhesive layer 150 and the conductive adhesive layer 113 laminated on the surface thereof are removed.

[0104] As described above, the peelable adhesive layer 150 may be removed from the base material by reducing the adhesiveness as needed. Therefore, the peelable adhesive layer 150 and the conductive adhesive layer 113 laminated on the surface thereof may be removed together by reducing the adhesiveness of the peelable adhesive layer 150. For example, the peelable adhesive layer 150 formed by applying a water stripping solution includes a material that dissolves when moisture is applied, so that the adhesiveness may be reduced. As described above, the peelable adhesive layer 150 and the conductive adhesive layer 113 laminated on the surface thereof are removed by reducing the adhesiveness of the peelable adhesive layer 150 to produce a substrate having a structure such as Figure 4F The back plate 110 of the structure shown.

[0105] 4A to 4FThe manufacturing process of the back plate 110 shown in is exemplary and is not limited thereto. As another example, the back plate 110 can be manufactured by a micro spot welding process. According to the micro spot welding process, solder paste is locally applied in selected areas to perform welding. For example, after preparing a base layer 111 formed with a plurality of grooves G, solder paste is applied in each of the plurality of grooves G, and then metal fibers are filled therein to perform welding, thereby manufacturing the back plate 110. According to this method, the solder paste is not applied on the entire bottom surface of the base layer 111, but is locally applied in necessary areas, namely, in the plurality of grooves G. Thus, the back plate 110 can be omitted. Figure 4B The formation process of the peelable adhesive layer 150 is shown in FIG. Figure 4F The removal process of the peelable adhesive layer 150 and the conductive adhesive layer 113 is shown.

[0106] The back plate 110 supporting the display panel 120 in the flexible display device 100 according to the exemplary embodiment of the present disclosure includes a base layer 111, the base layer 111 includes a plurality of grooves G on the bottom surface and corresponding to the folding area FA and a filler 112 filled in the plurality of grooves G. The filler 112 includes metal fibers. According to the present disclosure, a plurality of grooves G are formed in the base layer 111 instead of an opening pattern passing through the base layer 111, thereby reducing the visibility of the pattern and having excellent appearance quality. In addition, the base layer 111 is formed of a material having excellent rigidity so that the mechanical strength is excellent, and the plurality of grooves G are formed so that the stress concentrated on the folding area FA during the folding process can be uniformly dispersed. In addition, the filler 112 including metal fibers is filled in the plurality of grooves G, and the metal fibers have excellent elasticity and recovery properties, so that they are stretched in the folding direction during the folding process and restored to their original state during the unfolding process. Therefore, a flexible display device 100 having excellent folding characteristics and reliability can be provided. Furthermore, even if the flexible display device is repeatedly folded, it is not easily broken or plastically deformed due to the high elasticity of the metal fibers, thereby achieving excellent durability.

[0107] In the flexible display device of the prior art, a board assembly including a top plate and a bottom plate is additionally provided below the back plate, and a damping layer is further provided in the board assembly as needed to compensate for impact resistance, so the thickness of the flexible display device is quite large. Therefore, it is difficult to realize a flexible display device with a larger curvature. In addition, the damping layer is formed of a soft and flexible material such as PDMS, so in the flexible display device of the prior art having the damping layer, defects are easily generated due to depression or perforation during folding.

[0108] However, in the back plate 110 according to the present disclosure, the folding characteristics are significantly improved while maintaining high mechanical rigidity, so that no plate assembly or damping layer is required. Therefore, the thickness of the flexible display device 100 is significantly reduced, so that even if the curvature is implemented to be greater than that of the prior art, the folding reliability can be satisfied.

[0109] For example, the flexible display device 100 according to the present disclosure may be implemented as a flexible display device including a large curvature of the folding area FA having a curvature of 3R or less (further, 1.5R or less). In addition, even if the curvature increases, the folding reliability is satisfied, thereby being implemented as a multi-foldable display device. In this specification, the curvature radius 1R means that the radius of the curved surface of the folding area during the folding process is 1 mm.

[0110] Figure 5 is a schematic cross-sectional view of a flexible display device according to another exemplary embodiment of the present disclosure. Figure 5 , a flexible display device 200 according to another exemplary embodiment of the present disclosure includes a backplane 210, a display panel 120, and a cover member 130, and the backplane 210 includes a base layer 211, a filler 212, and a conductive adhesive layer 213. Figure 2 Compared with the flexible display device 100 shown in FIG. Figure 5 Other components of the flexible display device 200 shown in FIG. 2 are substantially the same except for the shapes of the plurality of grooves G, the filler 212 , and the conductive adhesive layer 213 , and thus redundant descriptions will be omitted.

[0111] refer to Figure 5 , a plurality of grooves G are formed on the bottom surface of the base layer 211 corresponding to the folding area FA. Each of the plurality of grooves G is recessed from the bottom surface of the base layer 211 toward the top surface. At this time, each of the plurality of grooves G may be formed to have a semicircular cross-sectional shape. That is, each of the plurality of grooves G is formed so that the gradient gradually decreases from the bottom surface to the top surface of the base layer 111.

[0112] When the plurality of grooves G are formed to have a semicircular shape, Figure 2 Compared with the flexible display device shown in FIG. 1 , the visibility of the pattern can be further reduced. Therefore, a flexible display device 200 having a more excellent appearance quality can be provided.

[0113] In addition, when the plurality of grooves G are formed to have a semicircular shape, the cross-sectional area of ​​the grooves G gradually increases toward the bottom surface of the base layer 211. Thus, the stress concentrated on the folding area FA when the flexible display device 200 is folded can be more effectively dispersed. Therefore, a flexible display device having a higher curvature while satisfying folding reliability can be easily realized.

[0114] Since the plurality of grooves G are formed to have a semicircular shape, the filler 212 is also filled to have a semicircular shape corresponding to the plurality of grooves G.

[0115] Furthermore, the conductive adhesive layer 213 bonding the filler 212 to the groove G may also be formed to have a shape with a curvature.

[0116] As described above, since the plurality of grooves G, the filler 212, and the conductive adhesive layer 213 are respectively formed to have curvatures, the visibility of the pattern is further reduced, so that the appearance quality of the flexible display device 200 can be improved. In addition, the folding stress when the flexible display device is folded is more favorably dispersed, so that the folding characteristics of the flexible display device 200 can be further improved. Specifically, even if the stress is more concentrated on the portion where the plurality of grooves G are formed during the folding process, the conductive adhesive layer 213 has a curvature. Figure 5 The back plate 110 of the structure shown can also disperse the stress concentrated on the portion of the groove G more effectively.

[0117] Therefore, according to Figure 5 The exemplary embodiment shown can more easily realize Figure 2 The flexible display device 100 shown has a greater curvature.

[0118] Figures 6 to 8 It is a simulation diagram showing the stress distribution when the half module of the backplane of the present disclosure or the prior art is folded inward with a curvature radius of 3R. The simulation results are represented in different grayscales according to the degree of stress applied to the backplane, and as the stress increases, they are represented in the order of black, dark gray, and light gray.

[0119] first, Figure 6 is a diagram showing the folding simulation results of the back panel according to the present disclosure. Specifically, Figure 6 The simulation results of a back plate having a structure in which a plurality of grooves are formed corresponding to the folded regions of a base layer formed of a stainless steel material and metal fiber sheets are filled in the plurality of grooves are shown.

[0120] refer to Figure 6 , the back panel according to the present disclosure generally uniformly shows black in the folding area, so the stress applied to the back panel during the folding process is small and uniformly dispersed, so it can be understood that the stress difference applied to each position is small.

[0121] Figure 7 is a folding simulation result of a back plate according to the prior art, in which a plurality of grooves are formed in the folding area of ​​the back plate similar to the present disclosure, but fillers are not filled in the plurality of grooves. Figure 7, when the filler is not formed in the plurality of grooves, it is understood that the protrusions between the plurality of grooves are represented by black, but the folding area is represented by dark gray and light gray as a whole. This means that the stress applied to the folding area is large and the difference in stress applied according to the position is significant. In addition, it is understood that the formation of the plurality of grooves causes the stress to be particularly concentrated on the embossed pattern portion having a relatively small thickness.

[0122] Figure 8 The folding simulation results of a back panel with silicone as filler instead of metal fiber sheets in multiple grooves are shown. Figure 8 , the entire folding area is represented by dark gray and black, but in the folding area with a larger radius of curvature, it is confirmed as the area represented by light gray. Therefore, when multiple grooves are filled with silicone, it is confirmed that the multiple grooves are not filled with fillers. Figure 7 Compared with the back plate of the present invention, the stress is slightly relieved and uniform. However, compared with the present disclosure in which a plurality of grooves are filled with metal fibers, it is confirmed that the relief and dispersion of the stress are not significant.

[0123] In summary, in the flexible display device according to the present disclosure, the backplane includes a base layer, the base layer includes a plurality of grooves on the bottom surface and corresponding to the folding area, and a filler filled in at least a portion of the plurality of grooves and including metal fibers. Thus, the stress concentrated on the folding area during the folding process is reduced and the stress is evenly dispersed in the folding area, thereby providing excellent folding characteristics and reliability.

[0124] Exemplary embodiments of the present disclosure may also be described as follows:

[0125] According to one aspect of the present disclosure, a flexible display device includes a display panel and a back panel, wherein the display panel includes a folding area and a non-folding area, the back panel includes a base layer supporting the display panel below the display panel and including a plurality of grooves on a bottom surface corresponding to the folding area, and a filler filled in at least a portion of the plurality of grooves, wherein the filler includes metal fibers.

[0126] The thickness of the base layer may be 90 μm to 220 μm.

[0127] The base layer may be formed of one or more metals selected from stainless steel (SUS), Invar, aluminum, and magnesium.

[0128] The plurality of grooves may be recessed from the bottom surface toward the top surface of the base layer.

[0129] Each of the plurality of grooves may extend parallel to the fold axis.

[0130] A depth of each of the plurality of grooves may be 10 μm to 40 μm.

[0131] The plurality of grooves may be formed to have a quadrangular shape or a semicircular shape.

[0132] The metal fibers may be metal wires or metal fiber sheets.

[0133] The metal fibers may include one or more metals selected from stainless steel, titanium, and aluminum.

[0134] The diameter of the metal wire may be 5 μm to 15 μm.

[0135] The metal fiber sheet may include a structure in which metal fibers are arranged in a grid pattern.

[0136] The metal fiber sheet may be a nonwoven fabric sheet or a fabric sheet including metal fibers.

[0137] The filler may be attached to each of the plurality of grooves by the conductive adhesive layer.

[0138] A top surface of the filler may be welded to each of the plurality of recesses through the conductive adhesive layer.

[0139] The radius of curvature of the folding area may be 3R or less.

[0140] Although the exemplary embodiments of the present disclosure have been described in detail with reference to the accompanying drawings, the present disclosure is not limited thereto, but can be implemented in a variety of different forms without departing from the technical concept of the present disclosure. Therefore, the exemplary embodiments of the present disclosure are provided for illustrative purposes only and are not intended to limit the technical concept of the present disclosure. The scope of the technical concept of the present disclosure is not limited thereto. Therefore, it should be understood that the above exemplary embodiments are exemplary in all aspects and do not limit the present disclosure. The scope of protection of the present disclosure should be interpreted based on the following claims, and all technical concepts within the equivalent scope thereof should be understood to fall within the scope of protection of the present disclosure.

Claims

1. A flexible display device, comprising: A display panel, the display panel comprising a folding area and a non-folding area; as well as a backplane, the backplane comprising a base layer and a filler, the base layer supporting the display panel below the display panel and comprising a plurality of grooves corresponding to the folding area on a bottom surface, the filler being filled in at least a portion of the plurality of grooves, Wherein, the filler comprises metal fibers, wherein a top surface of the filler is welded to each of the plurality of grooves through a conductive adhesive layer, and at least a portion of a side surface of the filler is not fixed by the conductive adhesive layer, wherein the plurality of grooves and the filler are formed to have a semicircular shape, and the conductive adhesive layer is formed to have a curvature, and Wherein, the metal fiber is a metal wire or a metal fiber sheet.

2. The flexible display device according to claim 1, wherein: The base layer has a thickness of 90 μm to 220 μm.

3. The flexible display device according to claim 1, wherein: The base layer is formed of one or more metals selected from stainless steel (SUS), invar, aluminum, and magnesium.

4. The flexible display device according to claim 1, wherein: The plurality of grooves are recessed from the bottom surface toward a top surface of the base layer.

5. The flexible display device according to claim 1, wherein: Each of the plurality of grooves extends parallel to the folding axis.

6. The flexible display device according to claim 1, wherein: Each of the plurality of grooves has a depth of 10 μm to 40 μm.

7. The flexible display device according to claim 1, wherein: The metal fiber includes one or more metals selected from stainless steel, titanium and aluminum.

8. The flexible display device according to claim 1, wherein: The metal wire has a diameter of 5 μm to 15 μm.

9. The flexible display device according to claim 1, wherein: The metal fiber sheet includes a structure in which the metal fibers are arranged in a grid pattern.

10. The flexible display device according to claim 1, wherein: The metal fiber sheet is a nonwoven fabric sheet or a fabric sheet including the metal fibers.

11. The flexible display device according to claim 1, wherein: The curvature radius of the folding area is less than 3R.

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