Flexible display device

Abstract

The present disclosure relates to a flexible display apparatus, and according to an aspect of the present disclosure, the flexible display apparatus includes a display panel including a folding area and a non-folding area, a back plate disposed under the display panel and supporting the display panel, a bottom plate disposed under the back plate and including a plurality of grooves to correspond to the folding area, and a plurality of nano spiral structures disposed to correspond to the plurality of grooves. Accordingly, the flexible display apparatus forms a groove pattern in the bottom plate and includes a nano spiral structure in each of the plurality of grooves to effectively alleviate folding stress and reduce visibility of the pattern, ultimately can improve appearance quality.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2021-0184600, filed on December 22, 2021, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. Technical Field

[0003] This disclosure relates to a flexible display device, and more specifically, to a flexible display device in which the pattern of the substrate is not visible from the outside, while maintaining high folding characteristics and high reliability, so as to have excellent appearance quality. Background Technology

[0004] In recent years, with the advent of the information age, the field of display technology, which visually expresses electrical information signals, has developed rapidly. In response, various display devices with superior performance characteristics (such as thinness, light weight, and low power consumption) have been developed. Specific examples of such display devices include liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), and organic light-emitting diodes (OLEDs).

[0005] Meanwhile, efforts continue to diversify the shape and size of display devices. For example, display devices with various shapes are being developed, such as curved display devices with curved surfaces or flexible display devices that maintain their display performance even when bent or folded. Flexible display devices use flexible substrates for their display panels, allowing support members such as back plates or base plates to be positioned below the display panel to prevent sagging and protect it from foreign objects and external impacts. Summary of the Invention

[0006] In the back panel and / or base plate used in flexible display devices, an opening pattern is formed in the folding area to ensure folding characteristics. However, the problem in this case is that the opening pattern is visible to the user, which degrades the appearance quality.

[0007] Therefore, the purpose of this disclosure is to provide a flexible display device with excellent appearance quality by minimizing the visibility of the pattern of the support member to the user while maintaining high foldability and reliability.

[0008] The purpose of this disclosure is not limited to the purposes mentioned above, and other purposes not mentioned above will be clearly understood by those skilled in the art from the following description.

[0009] According to one aspect of this disclosure, a flexible display device includes: a display panel including a folded region and a non-folded region; a back plate disposed below the display panel and supporting the display panel; a bottom plate disposed below the back plate and including a plurality of grooves corresponding to the folded region; and a plurality of nanospiral structures configured to correspond to the plurality of grooves.

[0010] Further details of exemplary embodiments are included in the detailed description and accompanying drawings.

[0011] According to an exemplary embodiment of this disclosure, the flexible display device forms a groove pattern in a substrate instead of an open pattern, and includes a nano-helical structure in each of the plurality of grooves to effectively reduce folding stress and decrease the visibility of the pattern. Therefore, the appearance quality can be improved.

[0012] The effects of this disclosure are not limited to those exemplified above, and many more different effects are included in this specification. Attached Figure Description

[0013] The above and other aspects, features and other advantages of this disclosure will become clearer from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0014] Figure 1 This is a schematic plan view of a flexible display device according to an exemplary embodiment of the present disclosure;

[0015] Figure 2 It is along Figure 1 A schematic cross-sectional view of line II;

[0016] Figure 3 This is a schematic plan view of the base plate in a flexible display device according to an exemplary embodiment of the present disclosure;

[0017] Figure 4 It is a view used to illustrate the properties of nano-helical structures arranged by a magnetic or electric field;

[0018] Figure 5A This is an enlarged cross-sectional view showing the state in which the arrangement of the nano-helical structures is deformed;

[0019] Figure 5B This is an enlarged cross-sectional view showing the restored arrangement of the nano-helical structures;

[0020] Figures 6 to 9 This is a schematic cross-sectional process diagram illustrating a method for manufacturing a substrate in a flexible display device according to an exemplary embodiment of the present disclosure;

[0021] Figure 10It is an SEM image of the surface of the infill material in the base plate of Example 1;

[0022] Figure 11 It is a photograph showing the visibility of the groove pattern on the base plate according to Example 1;

[0023] Figure 12 This is a photograph showing the visibility of the groove pattern on the base plate according to Comparative Example 1;

[0024] Figure 13 This is a photograph showing the visibility of the groove pattern on the base plate according to Comparative Example 2;

[0025] Figure 14 This is a photograph showing the visibility of the groove pattern on the base plate according to Comparative Example 3;

[0026] Figure 15 These are photographs showing the visibility of patterns in Comparative Example 1 and Example 1 based on the presence of a magnetic field;

[0027] Figure 16 The photograph shows the visibility and degree of restoration of the groove pattern on the base plate according to Example 5;

[0028] Figure 17 The photographs show the visibility and degree of restoration of the groove pattern on the base plate according to Example 1; and

[0029] Figure 18 The photograph shows the visibility and degree of restoration of the groove pattern on the base plate according to Example 6. Detailed Implementation

[0030] Please refer to the following and appendix. Figure 1 The advantages and features of this disclosure, as well as methods for achieving these advantages and features, will become clear from the exemplary embodiments described in detail herein. However, this disclosure is not limited to the exemplary embodiments disclosed herein, but will be implemented in various forms. Exemplary embodiments are provided by way of example only to enable those skilled in the art to fully understand the disclosure and scope of this disclosure. Therefore, this disclosure will be limited only by the scope of the appended claims.

[0031] The shapes, dimensions, ratios, angles, numbers, etc., shown in the accompanying drawings used to describe exemplary embodiments of this disclosure are merely examples, and this disclosure is not limited thereto. Throughout the specification, the same reference numerals generally denote the same elements. Furthermore, in the following description of this disclosure, detailed descriptions of known related technologies may be omitted to avoid unnecessarily obscuring the subject matter of this disclosure. Terms used herein, such as “comprising,” “having,” and “consisting of,” are generally intended to allow for the addition of additional components, unless these terms are used in conjunction with the term “only.” Unless otherwise expressly stated, any reference to the singular may include the plural form.

[0032] Even without explicit explanation, components are interpreted as including the normal tolerance range.

[0033] When using terms such as “on top of,” “above,” “below,” and “adjacent to” to describe the positional relationship between two parts, one or more parts may be located between the two parts, unless these terms are used with the terms “immediately adjacent” or “directly.”

[0034] When an element or layer is placed "on" another element or layer, it can be directly on the other layer or another element, or there can be intermediate elements or layers in between.

[0035] 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 another. Therefore, the first component mentioned below can be the second component in the technical concept of this disclosure.

[0036] Throughout the specification, the same reference numerals generally denote the same elements.

[0037] For ease of description, the dimensions and thickness of each component shown in the accompanying drawings are illustrated, and this disclosure is not limited to the dimensions and thickness of the components shown.

[0038] The features of the various embodiments of this disclosure may be combined or integrated in part or in whole, and may be interlocked and operated in technically different ways, and the embodiments may be carried out independently or in relation to each other.

[0039] In the following, a flexible display device according to an exemplary embodiment of the present disclosure will be described in detail with reference to the accompanying drawings.

[0040] Figure 1 This is a schematic plan view of a flexible display device according to an exemplary embodiment of the present disclosure. Figure 2 It is along Figure 1 A schematic cross-sectional view taken from line II. Figure 3This is a schematic plan view of the base plate in a flexible display device according to an exemplary embodiment of the present disclosure.

[0041] Reference Figure 1 and Figure 3 The flexible display device 100 according to an exemplary embodiment of the present disclosure includes a base plate 110, an adhesive layer Adh, a back plate 120, a display panel 130, an optical control layer 140, and a cover member 150. Hereinafter, for ease of description, the flexible display device according to the exemplary embodiment of the present disclosure will be described assuming it to be an organic light-emitting display device, but is not limited thereto.

[0042] Display panel 130 includes a display area DA and a non-display area NDA. Furthermore, the display panel includes a folding area FA and non-folding areas NFA1 and NFA2. Display panel 130 can be divided into display area DA and non-display area NDA depending on whether an image is displayed, and can also be divided into folding area FA and non-folding area NFA depending on whether it is foldable. Therefore, a portion of display panel 130 can be both display area DA and folding area FA, and another portion of display panel 130 can be both non-display area NDA and non-folding area NFA.

[0043] The display area DA is the region in which multiple pixels are configured to actually display an image. Within the display area DA, multiple pixels, including the emitting area for displaying the image, thin-film transistors for driving the pixels, and capacitors can be configured. A pixel can include multiple subpixels SP. A subpixel SP is the smallest unit for configuring the display area, and each subpixel SP can be configured to emit light of a specific wavelength band. For example, each of the subpixels SP can be configured to emit red, green, blue, or white light.

[0044] The non-display area NDA is configured to surround the display area DA. The non-display area NDA is the area in which no image is actually displayed, and various wiring and driver ICs for driving the pixels and driving elements set in the display area DA are located therein.

[0045] As described above, the display panel 130 can be defined as a foldable region FA and non-foldable regions NFA1 and NFA2, depending on whether it is foldable. The display panel 130 includes a foldable region FA and non-foldable regions NFA1 and NFA2 in addition to the foldable region. The foldable region FA is the area that folds when the flexible display device 100 is folded, and it folds according to a specific radius of curvature relative to the folding axis. For example, the folding axis of the foldable region FA can be formed in the X-axis direction, and the non-foldable regions NFA1 and NFA2 can extend from the foldable region FA in the Y-axis direction perpendicular to the folding axis. When the foldable region FA is folded relative to the folding axis, the foldable region FA can form a part of a circle or an ellipse. In this case, the radius of curvature of the foldable region FA can refer to the radius of the circle or ellipse formed by the foldable region FA.

[0046] The non-folding regions NFA1 and NFA2 are areas that do not fold when the flexible display device 100 is folded. That is, when the flexible display device 100 is folded, the non-folding regions NFA1 and NFA2 remain flat. The non-folding regions NFA1 and NFA2 can be located on either side of the folding region FA. In other words, the non-folding regions NFA1 and NFA2 can be regions extending in the Y-axis direction relative to the folding axis. In this case, the folding region FA can be defined between the non-folding regions NFA1 and NFA2. Furthermore, when the flexible display device 100 is folded relative to the folding axis, the non-folding regions NFA1 and NFA2 can overlap each other.

[0047] The display panel 130 may include a flexible substrate and display elements.

[0048] The flexible substrate supports various components of the display panel 130. The flexible substrate can be a flexible plastic substrate. For example, the plastic substrate can be a polymer material selected from polyimide, polyamide-imide, polyethersulfone, polyethylene terephthalate, and polycarbonate, but is not limited thereto.

[0049] Driving thin-film transistors (TFTs) for driving display elements can be disposed on a flexible substrate. The TFTs can be disposed in each of a plurality of pixel regions. For example, a driving TFT includes a gate electrode, an active layer, a source electrode, and a drain electrode. The driving TFT may also include a gate insulating layer that insulates the gate electrode from the active layer and an interlayer insulating layer that insulates the gate electrode from the source and drain electrodes.

[0050] A planarization layer can be disposed on the driving thin-film transistor to planarize the upper surface, and a display element is disposed on the planarization layer. The display element can be an organic light-emitting diode (OLED). An OLED can include an anode, a cathode, and an organic light-emitting layer disposed between the anode and cathode. In an OLED, holes injected from the anode and electrons injected from the cathode couple on the organic light-emitting layer to emit light. The emitted light can be used to display an image.

[0051] An optical control layer 140 can be disposed on the display element. The optical control layer 140 uniformly transmits light emitted from the display panel 130 without reducing brightness, thereby improving luminous efficiency. Furthermore, the optical control layer 140 absorbs external light to minimize the reduction in visibility and contrast caused by external light reflection. For example, the optical control layer 140 can be a polarizing film, but is not limited to this.

[0052] Cover member 150 is disposed on optical control layer 140. Cover member 150 protects display panel 130 from external impacts and scratches. Therefore, cover member 150 can be formed of a transparent material with excellent impact resistance and scratch resistance. In addition, cover member 150 protects display panel 130 from moisture or foreign matter that penetrates from the outside.

[0053] For example, the cover member 150 may be a film formed of polymers such as polyimide, polyamide-imide, polyethylene terephthalate, polymethyl methacrylate, polypropylene glycol, and polycarbonate. A decorative film is disposed beneath the cover member 150, or a decorative pattern may be formed on the lower surface of the cover member 150 to correspond to the non-display area. The decorative film or pattern prevents components such as wiring disposed in the non-display area NDA from being visible to the outside. Furthermore, the decorative film or pattern also serves to suppress light leakage through the side surfaces of the flexible display device 100.

[0054] When the flexible display device 100 is folded or bent, the flexible display panel 130 may have difficulty maintaining its intended shape and may be susceptible to external stimuli. Therefore, various types of support members can be provided on the rear surface of the display panel 130. For example, a back plate 120 and a base plate 110 can be provided on the rear surface of the display panel 130.

[0055] The plastic flexible substrate is thin, which may cause the display panel 130 to sag during folding or bending, and to compensate for this, a back plate 120 may be disposed on the rear surface of the display panel 130.

[0056] The backsheet 120 can be formed of a plastic material to support the flexible substrate and maintain high foldability. For example, the backsheet 120 can be selected from polyethylene terephthalate film, polycarbonate, polyimide film, or polyamide-imide film, but is not limited thereto. As another example, the backsheet 120 can be a foldable metal foil with excellent rigidity. For example, the backsheet 120 can be a metal foil including metals such as stainless steel (SUS), Invar alloy, aluminum, or magnesium, but is not limited thereto.

[0057] A base plate 110 is disposed below the back plate 120 to supplement the rigidity of the flexible substrate and the back plate 120. For example, the base plate 110 can be formed of a metallic material such as stainless steel (SUS), Invar alloy, aluminum, or magnesium. Such a metallic material has higher strength than a plastic material, which allows for further improvement in the durability of the flexible display device 100. Furthermore, when the base plate is formed of a metallic material, it has the advantage that the thickness is kept thinner than that of a plastic material to allow for folding, and rigidity and impact resistance are ensured.

[0058] The base plate 110 includes a plurality of grooves G. The plurality of grooves G can be formed on the upper surface of the base plate 110 to correspond to the folding region FA. That is, the plurality of grooves G are recessed from the upper surface of the base plate 110 toward the lower surface. When the flexible display device 100 is folded, stress is concentrated in the folding region FA. The plurality of grooves G can disperse the stress concentrated in the folding region FA during folding. As described above, since the plurality of grooves G are formed at positions corresponding to the folding region FA, it is advantageous that the flexible display device 100 has excellent foldability and reliability.

[0059] Each of the plurality of grooves G can be formed to extend elongatedly along a direction parallel to the folding axis. That is, each of the plurality of grooves G can be formed to extend along the same X-axis direction as the folding axis. Therefore, each of the plurality of grooves G can be formed parallel to the folding axis and has a strip shape in a planar view. In other words, each of the plurality of grooves G has a long axis in the same X-axis direction as the folding axis and a short axis in the Y-axis direction perpendicular to the X-axis direction. In this case, rigidity increases along the long axis and flexibility increases along the short axis, which is beneficial for ensuring foldability.

[0060] Reference Figure 3 Multiple grooves G are spaced apart from each other at specific intervals to be formed as islands in a plan view. When the multiple grooves G are spaced apart as islands and do not extend along the folding axis, stretchability can be maintained at a high level. Although in Figure 2 and Figure 3For ease of description, multiple grooves are shown in four rows, but this is not a limitation. Furthermore, the multiple grooves G formed as island structures can be arranged in a zigzag pattern, which further reduces folding stress and helps ensure reliability.

[0061] If necessary, each of the plurality of recesses G may optionally extend continuously across the display area DA into the non-display area in the same X-axis direction as the folding axis without being disconnected.

[0062] Although the cross-sectional shape of each of the plurality of grooves G is rectangular in the accompanying drawings, it is not limited thereto. The cross-sectional shape of each of the plurality of grooves G can be formed in various shapes, such as polygonal shapes other than semi-circular or quadrilateral shapes.

[0063] In related technologies, in order to disperse the folding stress concentrated in the folding area, an opening pattern, i.e., multiple holes, is formed on the base plate. In this case, the folding stress is dispersed to meet folding reliability, but the increased visibility of the opening pattern deteriorates the appearance quality.

[0064] According to an exemplary embodiment of this disclosure, the flexible display device 100 forms grooves on the upper surface of the base plate 110, thereby reducing the visibility of the pattern and improving the appearance quality. Specifically, a plurality of grooves G are formed at a predetermined depth from the upper surface of the base plate 110 in the thickness direction (Z-axis). Therefore, the user's recognition of the plurality of grooves G formed in the folded area FA is reduced, thus improving the appearance quality.

[0065] Multiple grooves G can be formed by removing a portion of the material forming the base plate 110. For example, multiple grooves G can be formed by known methods such as photolithography, laser etching, or plasma etching, but are not limited thereto.

[0066] Filler 111 in each of the plurality of grooves G.

[0067] When multiple grooves G are formed in the base plate 110 overlapping the folding area FA, stress during folding is dispersed, improving foldability. However, steps are formed, reducing flatness. Therefore, the stress irregularity during folding leads to problems such as component separation or breakage, resulting in unsatisfactory folding reliability and limiting the realization of flexible display devices with large curvatures. Furthermore, reduced flatness in the folding area FA causes distortion of the image displayed in the folding area FA, thus degrading display quality.

[0068] Therefore, the plurality of grooves G are filled with filler 111 to reduce steps and minimize the reduction in flatness. At least a portion of each of the plurality of grooves G is filled with filler 111. The thickness of the filler 111 filling the plurality of grooves G can be adjusted as needed. For example, to reduce the visibility of steps and groove patterns and to maintain high folding reliability, the filler 111 in the plurality of grooves G is filled to a depth equal to or greater than 0.5 times the depth of each of the plurality of grooves, but is not limited thereto.

[0069] For example, filler 111 can be a soft polymer or a welding material.

[0070] For example, filler 111 is a polymer that can be cured by heat or UV light, and is selected from, but not limited to, acrylic resins, polyurethane resins and silicone resins.

[0071] For example, the soldering material can be formed from liquid solder or solder paste, wherein conductive particles are uniformly dispersed in a binder resin. For example, the binder resin can be selected from epoxy resins, polyurethane-based resins, acrylic resins, silicone-based resins, phenol-based resins, melamine-based resins, alkyd-based resins, urea-formaldehyde resins, and unsaturated polyester resins. For example, the conductive particles can be selected from tin and alloys of one or more metals selected from silver, copper, lead, bismuth, zinc, and indium.

[0072] Reference Figure 3 Multiple nano-helical structures 112 are disposed on the filler 111. The nano-helical structures 112 minimize the reduction in flatness by filling the steps caused by the multiple grooves G without reducing foldability, making the multiple groove (G) pattern invisible from the outside of the flexible display device 100. Therefore, the appearance quality of the flexible display device is improved.

[0073] The nanospiral structure 112 has a spring or coil shape and a complex shape compared to other three-dimensional nanostructures such as nanorods, nanowires, or nanotubes. The nanospiral structure is arranged on the filler 111 such that the recognition of the multiple grooves G formed on the substrate 110 from the outside of the flexible display device 100 can be reduced more effectively.

[0074] Multiple nanospiral structures 112 are disposed on the filler 111 corresponding to each of the multiple grooves G. Each of the multiple nanospiral structures 112 is disposed in each of the multiple grooves G. Each of the multiple nanospiral structures 112 is disposed from the upper surface of the filler 111 toward the thickness direction of the base plate 110, i.e., the Z-axis direction. Therefore, each of the multiple nanospiral structures 112 is disposed from the upper surface of the filler 111 toward the lower surface of the back plate 120.

[0075] Reference Figure 2 and Figure 3 The nano-spiral structures 112 are arranged in a zigzag pattern on the filler 111 in each of the plurality of grooves G. That is, the plurality of nano-spiral structures 112 are arranged in a zigzag pattern on the filler 111 in each of the plurality of grooves G in both the X-axis and Y-axis directions. As described above, when the plurality of nano-spiral structures 112 are arranged in a zigzag pattern, the step filling effect is maximized while maintaining high foldability to minimize the recognition of the groove pattern, but this is not a limitation. If the degree of recognition of the multiple groove (G) patterns is not so high, the plurality of nano-spiral structures 112 can be randomly arranged or regularly arranged along lines.

[0076] Unlike typical nanostructures, nanohelical structures possess the following characteristic: when a magnetic or electric field is applied, the nanohelical structures align in a regular direction. Therefore, multiple nanohelical structures 112 are regularly arranged in the thickness direction (Z-axis direction) of the substrate 110. In the following text, reference will be made to... Figure 4 , Figure 5A and Figure 5B Describe in detail the physical properties of the nano-helical structure 112. Figure 4 It is a view used to illustrate the properties of nanospiral structures arranged by a magnetic or electric field. Figure 5A This is an enlarged cross-sectional view showing the state in which the arrangement of the nano-helical structures is deformed. Figure 5B This is an enlarged cross-sectional view showing the restored state of the nano-helical structure arrangement.

[0077] Reference Figure 4 When a magnetic or electric field is applied, the nanohelical structure 112 aligns regularly in a single direction. When a magnetic or electric field is applied, the nanohelical structure 112 aligns within the applied field. For example, when a magnetic field is applied to the nanohelical structure 112, the nanohelical structure aligns from the N pole to the S pole. As another example, when an electric field is applied to the nanohelical structure 112, the nanohelical structure 112 aligns in a direction from the positive end (+) to the negative end (-).

[0078] Although the regular arrangement of the nanohelical structure 112 is disrupted by the external environment, the nanohelical structure will readjust to its regular arrangement if an electric or magnetic field is applied. (See reference...) Figure 5A When using the flexible display device 100, the multiple nano-helical structures 112 regularly arranged in each of the multiple grooves G may be disrupted. In this case, when a magnetic field is applied from the outside via wireless charging, such as Figure 5B As shown, multiple nano-helical structures 112 can be arranged regularly. That is, when the flexible display device 100 is used, even if the nano-helical structures 112 are disrupted, they can be restored to their original arrangement by an external magnetic field. Therefore, the appearance quality is always maintained at a high level.

[0079] For example, the nanospiral structure 112 may include, but is not limited to, one or more materials selected from zinc oxide, magnesium oxide, and carbon nanotubes. Zinc oxide is readily fabricated into the nanospiral structure 112 and exhibits excellent dispersibility. Furthermore, the zinc oxide nanospiral structure 112 has the advantage of excellent responsiveness to external magnetic fields and excellent alignment recovery. For reference, although the nanospiral structure 112 including magnesium oxide may reduce the visibility of the groove pattern, the defect rate is relatively high when fabricating the nanospiral structure 112, resulting in relatively low magnetic susceptibility. Although the nanospiral structure 112 including carbon nanotubes may reduce the visibility of the groove pattern and has a relatively low defect rate when fabricating the nanospiral structure 112, its magnetic susceptibility and dispersibility are relatively low. Therefore, the nanospiral structure 112 including zinc oxide is likely most desirable for easily arranging the nanospiral structure 112, reducing pattern visibility, and maintaining high appearance quality over a long period.

[0080] For example, the average length of the nanospiral structure 112 can be from 3 μm to 13 μm, and preferably from 7 μm to 10 μm. In this case, it is susceptible to the influence of an external magnetic field, making it easy to arrange the nanospiral structure 112 in a regular manner, and exhibiting excellent restoring force when the arrangement is deformed. Therefore, the visibility of the groove pattern is further reduced, and the appearance quality is further improved.

[0081] For example, the nanospiral structure 112 can be fabricated by various known methods such as melt spinning, methods for growing the nanospiral structure 112 on a substrate, and fabrication methods using templates. Desiredly, the nanospiral structure 112 can be fabricated by melt spinning, which has the advantage of easily controlling the thickness or length of the nanospiral structure 112 and enabling large-scale production. Specifically, melt spinning is performed by melting, spinning, and cooling materials such as zinc oxide, magnesium oxide, and carbon nanotubes. The spun nanostructure has a linear shape. If the spun nanostructure is rapidly cooled, the spun nanostructure is coiled into a spring shape, thereby obtaining a nanospiral structure. At this time, the rotational speed of the wheel from which the spinning material is spun, the cooling rate, and the rotational radius of the wheel are controlled to obtain the desired thickness and length.

[0082] For example, the weight ratio of the filler 111 to the nanospiral structure 112 in each of the plurality of grooves G can be from 90:10 to 99:1. Desiredly, the weight ratio of the filler 111 to the nanospiral structure 112 in each of the plurality of grooves G can be from 97:3 to 93:7 or from 96:4 to 93:7. Within this range, due to the inclusion of the nanospiral structure 112, the effect of reducing the visibility of the groove pattern is more excellent, and the resilience is also excellent, resulting in excellent appearance quality.

[0083] An adhesive layer Addh is disposed between the base plate 110 and the back plate 120. The adhesive layer Addh bonds the base plate 110 and the back plate 120. Furthermore, the adhesive layer Addh is filled in the empty spaces of the plurality of grooves G to be filled in the steps. Therefore, the adhesive layer Addh is positioned to be in direct contact with the filler 111 and the plurality of nano-helical structures 112. The adhesive layer Addh can be selected from, but is not limited to, optically transparent adhesives (OCA), optically transparent resins (OCR), and pressure-sensitive adhesives (PSA).

[0084] To ensure foldability, a low-modulus adhesive is used to form the adhesive layer. In this case, the problem is that the multiple groove patterns are more clearly visible from the outside of the flexible display device. According to an exemplary embodiment of this disclosure, in each of the multiple grooves G, the filler 111 and the multiple nano-helical structures 112 are configured such that, although the adhesive layer Adh is formed of a low-modulus adhesive, the visibility of the multiple groove (G) patterns is minimized. Therefore, according to an exemplary embodiment of this disclosure, a flexible display device 100 with excellent foldability and reliability, as well as excellent appearance quality, can be provided.

[0085] In the following text, reference will be made to Figures 6 to 9 A method for manufacturing a base plate according to an exemplary embodiment of the present invention is described. Figures 6 to 9 This is a schematic cross-sectional process diagram illustrating a method for manufacturing a substrate in a flexible display device according to an exemplary embodiment of the present disclosure.

[0086] First, a base plate 110' is fabricated, and a plurality of grooves G are formed in the region corresponding to the folded region FA. As described above, the plurality of grooves G can be formed by a method selected from photolithography, laser etching, and plasma etching processes.

[0087] Next, each of the plurality of grooves G is filled with filler 111. Specifically, a mask on which an opening pattern corresponding to the plurality of grooves G is formed is placed over the base plate 110', and filler 111 is filled into the plurality of grooves G and cured. For example, filler 111 may be a polymer, liquid solder, or solder paste that is cured by heat or light. As another example, filler 111 may be formed by a microspot welding process that locally applies liquid solder or solder paste to selected areas.

[0088] Next, a magnetic or electric field is applied to a magnetic reactive membrane 190 comprising a plurality of protrusions 191 to attach the nanospiral structures 112 to each of the protrusions 191. The plurality of nanospiral structures 112, fabricated by melt spinning, are randomly arranged and have electromagnetic connectivity. Therefore, a magnetic reactive membrane 190 is used to arrange the plurality of nanospiral structures 112 in a specific region in a regular pattern. The magnetic reactive membrane 190 comprises a plurality of protrusions 191. When an electric or magnetic field is applied to the magnetic reactive membrane 190, the nanospiral structures 112 attach to each protrusion 191 through electromagnetic interaction.

[0089] The magnetic reactive film 190 is a film comprising a magnetic material. For example, the magnetic reactive film 190 may be a plastic film in which iron-based magnetic particles are dispersed. Specifically, the magnetic reactive film 190 may be a polysiloxane film in which carbonyl iron particles are dispersed. Carbonyl iron is a magnetic material, such that the magnetic reactive film 190 comprising carbonyl iron is magnetically reactive. When no external magnetic field is applied, the protrusions 191 do not protrude from the surface of the magnetic reactive film 190, but are folded to contact the magnetic reactive film 190. When a magnetic field is applied to the magnetic reactive film 190, an electric dipole is formed at the end of the protrusion 191, such that... Figure 8 As shown, protrusion 191 is deformed into an upright structure perpendicular to the surface of magnetic reactive film 190, with the direction being the same as the direction of the applied magnetic field. Nano-helical structures 112 are attached to each of the protrusions 191 of magnetic reactive film 190 by the induced magnetic field between the electric dipoles formed in protrusion 191 and nano-helical structures 112.

[0090] Next, the nanospiral structures 112 attached to each of the plurality of protrusions 191 are transferred to the filler 111. After the magnetic reactive film 190 with the nanospiral structures 112 attached is placed on the substrate 110, the nanospiral structures 112 attached to the plurality of protrusions 191 are transferred to the filler 111. When the magnetic field applied to the magnetic reactive film 190 with the nanospiral structures 112 attached is removed after the magnetic reactive film 190 is placed at the desired position, the nanospiral structures 112 are transferred to the filler 111.

[0091] At this time, in order to minimize the recognition of the multiple grooves G from the outside of the flexible display device 100, the nanospiral structure 112 can be transferred to the filler 111 filling each of the multiple grooves G to be arranged in a zigzag pattern. Simultaneously, the nanospiral structure 112 is disposed on the filler 111 by selectively attaching and transferring the nanospiral structure 112 at the protrusions 191 formed on the magnetic reactive film 190. Therefore, the distribution and shape of the protrusions 191 formed in the magnetic reactive film 190 can be formed to correspond to the desired arrangement of the nanospiral structure 112.

[0092] Next, an electric or magnetic field is applied to the substrate 110, causing the nano-helical structures 112 to align in a single direction. (Refer to the above.) Figure 4 The nanospiral structure 112 exhibits a characteristic of aligning in a single direction when an electric or magnetic field is applied. Therefore, after transferring the nanospiral structure 112 onto the filler 111, an electric or magnetic field is applied in the thickness direction of the substrate 110 to align multiple nanospiral structures in that direction. This step can be omitted if the nanospiral structure 112 remains in a sufficiently regular alignment after transferring it onto the filler 111 using the magnetic reactive membrane 190.

[0093] The substrate 110 manufactured as described above has the advantage of excellent appearance quality because the filler 111 and multiple nano-helical structures 112 are filled in multiple grooves G. Therefore, the shapes of the multiple grooves G formed in the substrate 110 are not visible to the user, while maintaining high foldability and reliability of the flexible display device 100.

[0094] The effects of this disclosure will be described in more detail below with reference to examples and comparative examples. However, while the following examples are provided to illustrate this disclosure, its scope is not limited thereto.

[0095] [Example 1]

[0096] Multiple grooves are formed in a metal substrate. Silicone-based resin is filled in each of the grooves. Zinc oxide nanospiral structures (average length 9 μm) are transferred onto the filler using a magnetic reactive film. At this point, the weight ratio of the filler to the nanospiral structures is controlled to be 98:2. Figure 10 This is a SEM image showing the zinc oxide nanospiral structure on the surface of the filler transferred to the substrate according to Example 1. (Refer to...) Figure 10 This confirmed that the zinc oxide nanospiral structure was uniformly transferred to the surface of the filler. Next, an electric field was applied along the thickness direction of the metal substrate to align the nanospiral structure in that direction. This resulted in structures with... Figure 2 and Figure 3The base plate of the structure shown is manufactured using this process.

[0097] [Example 2]

[0098] Except that the weight ratio of filler to nanospiral structure is changed to 96:4, the base plate is manufactured using the same method as in Example 1.

[0099] [Example 3]

[0100] Except that the weight ratio of filler to nanospiral structure is changed to 94:6, the base plate is manufactured using the same method as in Example 1.

[0101] [Example 4]

[0102] Except that the weight ratio of filler to nanospiral structure is changed to 92:8, the base plate is manufactured using the same method as in Example 1.

[0103] [Example 5]

[0104] The substrate was fabricated using the same method as in Example 1, except that a zinc oxide nanospiral structure with an average length of 5 μm was used.

[0105] [Example 6]

[0106] The substrate was fabricated using the same method as in Example 1, except that a zinc oxide nanospiral structure with an average length of 11 μm was used.

[0107] [Comparative Example 1]

[0108] Except that the nanospiral structure is not provided on the filler, the base plate is manufactured by the same method as in Example 1. That is, the base plate according to Comparative Example 1 is formed such that only the filler is filled in each of the plurality of grooves.

[0109] [Comparative Example 2]

[0110] Except that the substrate is manufactured by the same method as in Example 1, except that a silicon-based resin in which silver (Ag) nanoparticles (with a diameter of 100 nm to 200 nm) are dispersed is filled in each of the multiple grooves and the nanospiral structure is not arranged on the filler. In this case, the weight ratio of silicon-based resin to silver nanoparticles is controlled to be 98:2.

[0111] [Comparative Example 3]

[0112] Except that the substrate is manufactured using the same method as in Example 1, except that a silicon-based resin in which silver (Ag) nanowires (300 nm to 500 nm in length) are dispersed is filled in each of the multiple grooves and the nanospiral structures are not arranged on the filler. In this case, the weight ratio of silicon-based resin to silver nanowires is controlled to be 98:2.

[0113] [Experimental Example 1]

[0114] The visibility of the patterns on the substrates prepared according to Example 1 and Comparative Examples 1 to 3 to the user was evaluated. The visibility of the patterns was evaluated as follows: a sample was prepared by laminating a display panel onto the substrate; a contour map of the surface of the display panel was optically obtained using an Optimap surface analysis device; and then the height deviation was measured based on the contour map. A greater height deviation indicates greater pattern visibility.

[0115] The results are shown in Table 1 and... Figures 11 to 14 The Chinese side indicated that...

[0116] Figure 11 It is a photograph showing the visibility of the groove pattern on the base plate according to Example 1, and Figure 12 This is a photograph showing the visibility of the groove pattern on the base plate according to Comparative Example 1. Figure 13 The photograph shows the visibility of the groove pattern on the base plate according to Comparative Example 2, and Figure 14 The table shows photographs illustrating the visibility of the groove pattern on the base plate according to Comparative Example 3. In the table, the degree to which the pattern on the base plate is identifiable is expressed numerically, and this means that the higher the value, the lower the appearance quality.

[0117] [Table 1]

[0118] Comparative Example 1 Comparative Example 2 Comparative Example 3 Example 1 Pattern visibility 1.77 1.45 1.41 0.94

[0119] Also refer to Table 1 and Figures 11 to 14 This confirms that the groove pattern in Example 1 is almost invisible compared to Comparative Examples 1 to 3. Specifically, in Example 1, the visibility is reduced by half compared to Comparative Example 1, where only silicone resin is filled in each of the plurality of grooves. This demonstrates that the appearance quality of the display device is significantly improved when a nano-spiral structure is disposed on the filler. In Comparative Example 2, where silicone resin with dispersed silver nanoparticles is filled, the visibility is lower than that of Comparative Example 1, but the shape of the groove is still visible. Furthermore, in Comparative Example 3, where silicone resin with dispersed silver nanowires is filled, the visibility of the groove shape is lower than that of the groove shape in Comparative Example 1, but the appearance quality is not as good as that of Example 1.

[0120] [Experimental Example 2]

[0121] The visibility, dent feature, and recovery of the patterns on the substrates prepared according to Examples 1 through 4 were evaluated for the user. Pattern visibility was measured in the same manner as in Experimental Example 1. The results are shown in Table 2 and... Figure 15The indentation characteristics were evaluated as follows: the sample surface was scratched with a pencil at a 45-degree angle and a speed of 300 mm / min while a 500 g load was applied, and the surface was then visually observed for scratching. The degree of recovery was evaluated to determine how much of the nanospiral arrangement was restored by an external magnetic field when the arrangement was deformed, and the degree of recovery was calculated using Equation 1 below.

[0122] [Equation 1]

[0123] degree of recovery = M1 - M2

[0124] In Equation 1, M1 refers to the visibility of the pattern in a zero magnetic field state where there is no influence from the magnetic field, and M2 refers to the visibility of the pattern after the sample has been exposed to a magnetic field of a specific amplitude for one hour.

[0125] Figure 15 The photograph shows the visibility of the patterns in Comparative Example 1 and Example 1 based on the presence of a magnetic field. Figure 15 (a) is a photograph showing the visibility of the sample of Comparative Example 1 in which the nanospiral structure was not transferred to the filler. Figure 15 (b) is a photograph showing the visibility of the pattern in the zero magnetic field state of Example 1. Figure 15 (c) is a photograph showing the visibility of the pattern after a magnetic field is applied to the sample of Example 1.

[0126] First, through comparison Figure 15 (a) and Figure 15 (b) confirms that after transferring the nanospiral structure onto the filler, the visibility of the groove pattern is reduced, and the visibility of the pattern in Comparative Example 1 is 1.7, while the visibility of the pattern in Example 1 is 0.9, which reduces the visibility of the pattern by half.

[0127] By comparison Figure 15 (b) and Figure 15 (c) confirms that when a magnetic field of 100 emu is applied to the sample of Example 1 for one hour, the visibility of the pattern is further reduced, specifically from 0.9 to 0.8. This means that it is related to the magnetic susceptibility of the nanospiral structure, and that when the arrangement of the nanospiral structure is deformed, in response to the external magnetic field, the nanospiral structure realigns in a single direction. That is, according to the exemplary embodiment of this disclosure, although the arrangement of the nanospiral structure is deformed due to repeated folding or unfolding of the flexible display device, the nanospiral structure rearranges in a single direction if a magnetic field is applied from the outside via wireless charging. Therefore, high appearance quality can be maintained for a long time.

[0128] Table 2 below summarizes the indentation characteristics, pattern visibility, and restitution based on the weight ratio of the nanospiral structure.

[0129] [Table 2]

[0130]

[0131] Referring to Table 2, it was confirmed that in Example 3, with a filler-to-nanospiral structure ratio of 94:6, all dent features, pattern visibility, and restitution were excellent. In Example 1, with a filler-to-nanospiral structure ratio of 98:2, the high ratio of the lower-strength filler resulted in the lowest dent features. The low ratio of the nanospiral structures further confirmed that the restitution obtained from the external magnetic field was relatively low. Meanwhile, in Example 4, with the highest ratio of nanospiral structures, the dent features were the best, but the pattern visibility increased slightly due to the interaction between the nanospiral structures. Furthermore, the restitution was slightly reduced compared to Example 3. However, the pattern visibility was much lower than in Comparative Example 1, which helps improve the appearance quality, and the substrate of Example 4 can be advantageously used when improved dent features and appearance quality are required.

[0132] [Experiment Example 3]

[0133] To determine the restitution rate based on the amplitude of the externally applied magnetic field, the restitution rate was measured by varying the amplitude of the magnetic field relative to the samples in Examples 1 to 4. The restitution rate was calculated using Equation 1, the same as in Experimental Example 2. The results are shown in Table 3 below.

[0134] [Table 3]

[0135]

[0136] Referring to Table 3, it was confirmed that in each of Examples 1 to 4, the higher the strength of the externally applied magnetic field, the higher the refractive index. Furthermore, as described above in Experimental Example 2, it was confirmed that Example 3, with a filler-to-nanohylocereus ratio of 96:4, exhibited the best refractive index. It was further confirmed that, compared to Examples 1 to 3, Example 4, with the highest ratio of nanohelical structures, showed a reduced refractive index due to the interactions between the nanohelical structures.

[0137] [Experiment Example 4]

[0138] The pattern visibility and restitution of the substrates prepared according to Examples 1, 5, and 6 were evaluated. The results are shown in Table 4 and... Figures 16 to 18 The Chinese side indicated that... Figure 16 (a) is a photograph showing the visibility of the pattern on the base plate according to Example 5, and Figure 16(b) is a photograph showing the degree of restoration. Figure 17 (a) is a photograph showing the visibility of the groove pattern on the base plate according to Example 1, and Figure 17 (b) is a photograph showing the degree of restoration. Figure 18 (a) is a photograph showing the visibility of the groove pattern on the base plate according to Example 6, and Figure 18 (b) is a photograph showing the degree of restoration.

[0139] [Table 4]

[0140] Comparative Example 1 Example 5 Example 1 Example 6 Average length of nanohelical structure - 5μm 9μm 11μm Pattern visibility 1.77 0.97 0.93 0.95 Recovery rate (100 EMU, one hour) - 0.09 0.13 0.10

[0141] Referring to Table 4, it was confirmed that the pattern visibility was significantly reduced compared to Comparative Example 1, which did not include the nanospiral structure, regardless of the average length of the nanospiral structure. Furthermore, referring to... Figures 16 to 18 This demonstrates that in each of Examples 1, 5, and 6, the visibility of the pattern further decreases when an external magnetic field is applied, resulting in excellent restitution relative to the external magnetic field. Specifically, it is demonstrated that in Example 1, where the average length of the nanospiral structure is 9 μm, the pattern exhibits the lowest visibility and the best restitution in the zero magnetic field state.

[0142] Exemplary embodiments of this disclosure can also be described as follows:

[0143] According to one aspect of this disclosure, a flexible display device includes: a display panel including a folded region and a non-folded region; a back plate disposed below the display panel and supporting the display panel; a bottom plate disposed below the back plate and including a plurality of grooves corresponding to the folded region; and a plurality of nanospiral structures configured to correspond to the plurality of grooves.

[0144] When a magnetic or electric field is applied, multiple nanospiral structures can align in a single direction.

[0145] Multiple nanohelical structures may include one or more selected from zinc oxide, magnesium oxide and carbon nanotubes.

[0146] The average length of multiple nanospiral structures can range from 3 μm to 13 μm.

[0147] The flexible display device may also include fillers in at least some of the multiple recesses, wherein multiple nanospiral structures may be disposed on the fillers.

[0148] The weight ratio of the filler to the nanospiral structure in at least some of the multiple grooves can be from 90:10 to 99:1.

[0149] Each of the multiple nanospiral structures can be arranged so that it points from the upper surface of the filler to the lower surface of the backing plate.

[0150] Multiple nanospiral structures can be arranged in a zigzag pattern on the filler.

[0151] The flexible display device may also include an adhesive layer disposed between a base plate and a back plate, wherein the adhesive layer may be configured to be in direct contact with the filler and multiple nano-helical structures and to cover multiple grooves.

[0152] The filler may include a soft polymer or a welding material.

[0153] Multiple grooves can be recessed from the upper surface of the base plate toward the lower surface.

[0154] Each of the multiple grooves can extend parallel to the folding axis.

[0155] Multiple grooves can be arranged in a zigzag pattern in the folded area.

[0156] While exemplary embodiments of this disclosure have been described in detail with reference to the accompanying drawings, this disclosure is not limited thereto and may be embodied in many different forms without departing from the technical concept of this disclosure. Therefore, the exemplary embodiments of this disclosure are provided for illustrative purposes only and are not intended to limit the technical concept of this disclosure. The scope of the technical concept of this disclosure is not limited thereto. Therefore, it should be understood that the above exemplary embodiments are illustrative in all respects and do not limit this disclosure. The scope of protection of this disclosure should be interpreted based on the appended claims, and all technical concepts within their equivalent scope should be interpreted as falling within the scope of this disclosure.

Claims

1. A flexible display device, comprising: The display panel includes a folding area and a non-folding area; A back panel, which is disposed below the display panel and supports the display panel; A base plate is disposed below the back plate and includes a plurality of grooves corresponding to the folding area; as well as Multiple nanospiral structures are configured to correspond to the multiple grooves. When a magnetic or electric field is applied, the multiple nano-helical structures are arranged in a single direction.

2. The flexible display device according to claim 1, wherein, The plurality of nanohelical structures include one or more selected from zinc oxide, magnesium oxide and carbon nanotubes.

3. The flexible display device according to claim 1, wherein, The average length of the plurality of nanospiral structures is 3 μm to 13 μm.

4. The flexible display device according to claim 1, further comprising: A filler material is used to fill at least some of the plurality of grooves. The plurality of nano-helical structures are disposed on the filler.

5. The flexible display device according to claim 4, wherein, The weight ratio of the filler to the nanospiral structure in at least some of the plurality of grooves is from 90:10 to 99:

1.

6. The flexible display device according to claim 4, wherein, Each of the plurality of nanospiral structures is arranged such that it points from the upper surface of the filler to the lower surface of the backing plate.

7. The flexible display device according to claim 6, wherein, The multiple nanospiral structures are arranged in a zigzag pattern on the filler.

8. The flexible display device according to claim 4, further comprising: An adhesive layer is disposed between the base plate and the back plate. The adhesive layer is configured to be in direct contact with the filler and the plurality of nanospiral structures, and to cover the plurality of grooves.

9. The flexible display device according to claim 4, wherein, The filler includes a soft polymer or a welding material.

10. The flexible display device according to claim 1, wherein, The plurality of grooves are recessed from the upper surface of the base plate toward the lower surface.

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

12. The flexible display device according to claim 1, wherein, The plurality of grooves are arranged in a zigzag pattern in the folded area.

Images