Abstract:
Embodiments relate to a foldable display apparatus including a hinge providing supporting for a bending area of a flexible display panel. The flexible display panel includes a first flat display area and a second flat display area at both sides of a bending display area. A first rear cover provides support for the first flat display area and has a first edge. A second rear cover provides support for the second flat display area and has having a second edge facing the first edge and parallel to the first edge. The hinge includes rear hinge covers longitudinally extending parallel to the first edge and the second edge, and elastic axis members coupling the plurality of rear hinge covers in an interlocking and rotatable manner. The elastic axis members are deformed as the rear hinge covers make a relative movement by bending of the hinge.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Republic of Korea Patent Application No. 10-2015-0123275 filed on Aug. 31, 2015, which is hereby incorporated by reference as if fully set forth herein. 
     BACKGROUND 
     Field of the Disclosure 
     Embodiments of the present invention relate to a foldable display apparatus, and more particularly, to a foldable display apparatus which is bent with a predetermined curvature or unfolded into a flat state. 
     Discussion of the Related Art 
     Generally, display devices using flat display panels such as liquid crystal display device, plasma display device, organic light emitting display device, electrophoretic display device and electro-wetting display device are applied to notebook computers, portable electronic devices, televisions or monitors. 
     With the increasing demand for a large-sized screen in the portable electronic devices, an apparatus with a large-sized display area using a flat display panel has been developed and commercialized. Especially, a foldable display apparatus or rollable display apparatus using advantages of a flexible display panel capable of being bent or fold, which allows ease of portability and large-sized display area, has been attracted great attentions as a next generation technology. The foldable display apparatus may be applied in various fields of television and monitor as well as mobile devices of mobile communication terminal, electronic notebook, electronic book, PMP (portable multimedia player), navigation, UMPC (ultra mobile PC), mobile phone, smart phone and tablet PC (personal computer). 
     In a conventional foldable display apparatus, when a pair of supporters is rotated, a flexible display panel is folded by a detachment of an adhesive member attached to the supporter so that it is possible to reduce a bending stress occurring when the flexible display panel is folded. 
     However, if the flexible display panel of the related art foldable display apparatus is repetitively folded and unfolded, the flexible display panel may become bent for a process of attaching the flexible display panel to the supporter by the use of adhesiveness of the adhesive member or detaching the flexible display panel from the supporter, thereby lowering reliability of the flexible display panel. 
     SUMMARY 
     Embodiments relate to a foldable display apparatus including a flexible display panel, a first rear cover, a second rear cover, and a hinge. The flexible display panel includes a first flat display area, a second flat display area and a bending display area between the first flat display area and the second flat display area. The first rear cover provides support for the first flat display area and has a first edge. The second rear cover provides support for the second flat display area and has a second edge facing the first edge in an unfolded state of the foldable display apparatus. The hinge is between the first rear cover and the second rear cover. The hinge supports the bending display area and includes a plurality of rear hinge members and a plurality of elastic axis members. The rear hinge members are between the first edge and the second edge. The rear hinge covers interlock with each other in the unfolded state and is rotated around each other from the unfolded state into a folded state. The elastic axis members couple the plurality of rear hinge covers, the first edge and the second edge. The elastic axis members are deformed as the rear hinge members are rotated around each other by bending of the flexible display panel. 
     In one embodiment, deformation of the elastic axis members in the folded state of the foldable display apparatus is greater than deformation of the elastic axis members in the unfolded state. 
     In one embodiment, the rear hinge members include a first rear hinge member, a second rear hinge member, and a third rear hinge member. The first rear hinge member is coupled to the first edge via a first elastic axis member of the plurality of elastic axis members. The second rear hinge member is coupled to the second edge via a second elastic axis member of the plurality of elastic axis members. The third rear hinge member is coupled between the first rear hinge member and the second rear hinge member. 
     In one embodiment, the first rear hinge member includes first inner connection protrusions with holes for receiving the first axis member and the first edge comprises first cover protrusions with holes for receiving the first elastic axis member. The second rear hinge member includes second inner connection protrusions with holes for receiving the second axis member and the second edge comprises second cover protrusions with holes for receiving the second elastic axis member. 
     In one embodiment, the foldable display apparatus further includes a fourth rear hinge member and a fifth rear hinge member. The fourth rear hinge member is coupled to the third rear hinge member via a third elastic axis member of the plurality of elastic axis members. The fourth rear hinge member is coupled to the first rear hinge member via the fourth elastic axis member. The fifth rear hinge member is coupled to the third rear hinge member via a fifth elastic member. The fifth rear hinge member is coupled to the second rear hinge member via a sixth elastic axis member. 
     In one embodiment, each of a subset of the plurality of the rear hinge members includes a first supporting bar and a first rotation axis portion. The first supporting bar extends parallel to the first edge or the second edge and has an upper surface providing support for a portion of the bending display area. The first rotation axis portion has a first inner portion protrusion inserted into first protrusion insertion space in another rear hinge member as the hinge is unbent. The first inner portion protrusion is retracted from the first protrusion insertion space as the hinge is bent. 
     In one embodiment, each of the subset of the plurality of the rear hinge members includes a second supporting bar and a second rotation axis portion. The second supporting bar extends parallel to the first edge or the second edge. The second rotation axis portion is at an opposite longitudinal side of the first rotation axis portion. The second rotation axis portion has a second inner portion protrusion inserted into second protrusion insertion space in the other rear hinge member as the hinge is unbent. The second inner portion protrusion is retracted from the second protrusion insertion space as the hinge is bent. 
     In one embodiment, each of the subset of the rear hinge member includes outer connection protrusions with holes for receiving one of the elastic axis members, and inner connection protrusions with holes for receiving another of the elastic axis members. 
     In one embodiment, an inner connection protrusion of one of the rear hinge members is placed between (i) two of a plurality of cover protrusions extending from the first edge or (ii) two of a plurality of cover protrusions of another rear hinge member. 
     In one embodiment, each of the cover protrusions has a hole for receiving the other of the elastic axis members. 
     In one embodiment, each of the subset of the rear hinge member further includes a plurality of central supporting bars between the first and second supporting bars, the outer connection protrusions and the inner connection protrusions attached to the central supporting bars. 
     In one embodiment, the rear hinge member includes a center rear hinge member in a middle of the hinge. Both lateral sides of the center rear hinge member are formed with protrusion insertion space to receive support sidewalls extending from two of the subset of rear hinge members adjacent to the center rear hinge member. 
     In one embodiment, each of the plurality of rear hinge members, the first edge and the second edge have a same length. 
     In one embodiment, the foldable display apparatus further includes a panel supporting frame between (i) the flexible display panel and (ii) surfaces of the first rear cover, the second rear cover and the hinge. The panel supporting frame guides folding or unfolding of the bending display area. 
     In one embodiment, the panel support frame includes a first supporting member, a second supporting member and a bending member between the first supporting member and the second supporting member. 
     In one embodiment, the bending member includes a patterned surface facing the hinge and a smooth surface facing the bending display area. The patterned surface includes grooves extending parallel to the first and second edges. 
     In one embodiment, the bending member includes a first outer protrusion overlapping with a portion of the first supporting member and a second outer protrusion overlapping with a portion of the second supporting member. Bosses from the portions of the first and second supporting members extend through the bending member. 
     In one embodiment, the foldable display apparatus further includes screws inserted into the bosses to secure the bending member to the first and second supporting members. The bosses are aligned along a line parallel to the first and second edges to guide bending of the panel supporting member. 
     In one embodiment, the first supporting member includes a first line of bosses for coupling to the first rear cover. The second supporting member includes a second line of bosses for coupling to the second rear cover. 
     In one embodiment, each of the plurality of rear hinge members has a first surface providing support for the bending display area and a second surface at an opposite side of the first surface. An increase in a first distance between two first surfaces of adjacent rear hinge members is different than an increase of a second distance between two second surfaces of the adjacent rear hinge members when the rear hinge members are rotated from the unfolded state into a folded state. 
     Embodiments also relate to folding or unfolding of a foldable display apparatus. A hinge between a first rear cover provides support for a first flat display area of a flexible display panel and a second rear cover provides support for a second flat display area of the flexible display panel. The hinge is bent to fold the foldable display apparatus. The hinge provides support for a bending area of the flexible display panel between the first and second flat display area. When the hinge is bent, deformation of a plurality of elastic axis members coupling a plurality of rear hinge members of the hinge in an interlocking manner in an unfolded state is increased, and the rear hinge members are rotated around each other from the unfolded state. The hinge is unbent to unfold the foldable display from a folded state. When the hinge is unbent, deformation of the plurality of elastic axis members is decreased, and the rear hinge members are rotated around each other from the folded state. 
     In one embodiment, bending of the hinge causes inserting of an inner portion protrusion of one of the rear hinge members into protrusion insertion space of another of the rear hinge members. The inner portion protrusion laterally extending from the one of the rear hinge members. 
     In one embodiment, unbending of the hinge causes retracting of the inner portion protrusion of one of the rear hinge members from protrusion insertion space of another of the rear hinge members. 
     In one embodiment, bending of the hinge includes bending a bending member of a panel supporting frame between the flexible display panel and surfaces of the first rear cover, the second rear cover and the hinge. 
     It is to be understood that both the foregoing general description and the following detailed description of embodiments of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of embodiments of the invention. In the drawings: 
         FIG. 1  is a perspective view of a foldable display apparatus according to one embodiment. 
         FIG. 2  is an exploded perspective view illustrating a foldable display apparatus of  FIG. 1  according to one embodiment. 
         FIG. 3  is an exploded perspective view illustrating structures of first and second rear covers and a hinge of  FIG. 2 , according to one embodiment. 
         FIG. 4  is a cross sectional view taken along line I-I′ of  FIG. 2 , according to one embodiment. 
         FIG. 5  is a cross sectional view taken along line II-IP of  FIG. 2 , according to one embodiment. 
         FIG. 6  illustrates a first rear hinge of  FIG. 3 , according to one embodiment. 
         FIG. 7  illustrates a second rear hinge cover of  FIG. 3 , according to one embodiment. 
         FIG. 8  illustrates a third rear hinge cover of  FIG. 3 , according to one embodiment. 
         FIG. 9  illustrates first to sixth elastic axis members shown in  FIG. 3 . 
         FIG. 10A  is a rear perspective view illustrating an unfolded state of the foldable display apparatus according to one embodiment. 
         FIG. 10B  is a cross sectional view taken along line of  FIG. 10A . 
         FIG. 10C  is a cross sectional view taken along line IV-IV′ of  FIG. 10A . 
         FIG. 11A  is a rear perspective view illustrating the foldable display apparatus in a half-folded state according to one embodiment. 
         FIG. 11B  is a cross sectional view taken along line V-V′ of  FIG. 11A . 
         FIG. 11C  is a cross sectional view taken along line VI-VI′ of  FIG. 11A . 
         FIG. 12A  is a rear perspective view illustrating the foldable display apparatus in a folding state according to one embodiment. 
         FIG. 12B  is a cross sectional view taken along line VII-VII′ of  FIG. 12A . 
         FIG. 12C  is a cross sectional view taken along line VIII-VIII′ of  FIG. 12A . 
         FIG. 13  is an exploded perspective view illustrating a foldable display apparatus according to another embodiment. 
         FIG. 14  is a rear perspective view illustrating a panel supporting frame of  FIG. 13 . 
         FIG. 15  is a cross sectional view taken along line IX-IX′ of  FIG. 14 . 
         FIG. 16  illustrates a panel supporting frame in a folded state according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     Terms disclosed in this specification should be understood as follows. 
     The term of a singular expression should be understood to include a multiple expression as well as the singular expression if there is no specific definition in the context. The terms such as “the first” and “the second” are used only to differentiate one element from other elements. Thus, a scope of claims is not limited by these terms. Also, it should be understood that the term such as “include” or “have” does not preclude existence or possibility of one or more features, numbers, steps, operations, elements, parts or their combinations. It should be understood that the term “at least one” includes all combinations related with any one item. For example, “at least one among a first element, a second element and a third element” may include all combinations of two or more elements selected from the first, second and third elements as well as each element of the first, second and third elements. Also, if it is mentioned that a first element is positioned “on or above” a second element, it should be understood that the first and second elements may be brought into contact with each other, or a third element may be interposed between the first and second elements. 
     Hereinafter, a foldable display apparatus according to the embodiment of the present invention will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Also, in the following description of the present invention, if detailed description of elements or functions known in respect of the present invention is determined to make the subject matter of the present invention unnecessarily obscure, the detailed description will be omitted. 
       FIG. 1  schematically illustrates a foldable display apparatus according to the embodiment of the present invention.  FIG. 2  is an exploded perspective view illustrating a foldable display apparatus according to one embodiment of the present invention. 
     Referring to  FIGS. 1 and 2 , the foldable display apparatus according to one embodiment of the present invention may include a flexible display panel  100 , a first rear cover  200 , a second rear cover  300 , a hinge  400  and a front cover  500 . 
     The flexible display panel  100  may be a flexible organic light emitting display panel, a flexible electrophoretic display panel or a flexible electro-wetting display panel. 
     The flexible display panel  100  may include a display area  112  for displaying an image by a pixel array provided with a plurality of pixels. The display area  112  may include a first display area DA 1 , a second display area DA 2  and a bending display area BDA. 
     The first display area DA 1  may be defined with a first area of the flexible display panel  100  positioned at one side of the bending display area BDA in the display area  112 , and the second display area DA 2  may be defined with a second area of the flexible display panel  100  positioned at the other side of the bending display area BDA in the display area  112 . 
     When the flexible display panel  100  is unfolded into the flat state, the first display area DA 1 , the second display area DA 2  and the bending display area BDA constitute one display area  112  to provide a relatively large screen. 
     If the flexible display panel  100  is bent in accordance with a predetermined curvature with respect to the bending display area BDA, an image is not displayed on the display area  112 . 
     Additionally, the foldable display apparatus according to one embodiment of the present invention may further include a driving integrated circuit  120  and a flexible circuit film  130 . 
     The driving integrated circuit  120  is attached to a chip mounting area prepared in the flexible display panel  100  by a chip bonding process. The driving integrated circuit  120  drives the pixels formed in the display area  112  on the basis of data signal and pixel driving signal supplied through a display pad portion to display an image. Additionally, the driving integrated circuit  120  is mounted on the flexible circuit film  130 , and is connected with the pixel array. 
     The flexible circuit film  130  is attached to the display pad portion prepared in the flexible display panel  100  by a film attachment process. The flexible circuit film  130  transmits various power and signals supplied from a system driver (not shown) to the driving integrated circuit  120 . The flexible circuit film  130  may be formed of TCP (Tape Carrier Package), COF (Chip On Flexible Board or Chip On Film), or FPC (Flexible Printed Circuit). Herein, one end of the flexible circuit film  130  is attached to the display pad portion, and the other end of the flexible circuit film  130  is connected with the system driver provided in a receiving space of the second rear cover  200 . 
     A rear surface of the flexible display panel  100  may be supported by a flexible supporting plate  140 . 
     The flexible display panel  100  is maintained in the flat state by the use of flexible supporting plate  140  which is attached to the entire rear surface of the flexible display panel  100 . The flexible supporting plate  140  may be formed of a plastic material, for example, any one of PI(Polyimide), PET(Polyethyleneterephthalate), PEN(Polyethylenapthanate), PC(Polycarbonate), PNB(Polynorborneen) and PES(Polyethersulfone). Herein, it is possible to omit the flexible supporting plate  140 . 
     Additionally, the foldable display apparatus according to one embodiment may further include a touch screen (not shown) for a user interface by a user&#39;s touch. The touch screen may be attached to the flexible display panel  100 , or may be provided inside the flexible display panel  100  for a process of forming the pixel array. 
     The foldable display apparatus according to one embodiment of the present invention may further include a signal applying portion (not shown) extending from an edge of the flexible display panel  100  so as to have a predetermined width and length instead of the flexible circuit film  130 , wherein the signal applying portion (not shown) may be connected with the driving system. In this case, the flexible circuit film  130  is omitted. 
     The first rear cover  200  receives and supports one side of the flexible display panel  100  corresponding to the first display area DA 1  of the flexible display panel  100 . The first rear cover  200  is rotatably connected with one side of the hinge  400 . 
     The second rear cover  300  receives and supports the other side of the flexible display panel  100  corresponding to the second display area DA 2  of the flexible display panel  100 . The second rear cover  300  is rotatably connected with the other side of the hinge  400 . 
     The hinge  400  is connected between the first rear cover  200  and the second rear cover  300 . The hinge  400  serves as a rotation axis for folding or unfolding of the bending display area BDA of the flexible display panel  100 . Especially, the hinge  400  guides the folding and unfolding of the flexible display panel  100  with respect to the bending display area BDA, and supports the bending display area BDA of the flexible display panel  100  which is unfolded in the flat state or folded in accordance with a predetermined curvature. 
     The hinge  400  supports the bending display area BDA of the flexible display panel  100  through a plurality of rear hinge covers engaged by an elastic axis member and connected with an inner side of the first rear cover  200  and an inner side of the second rear cover  300 . The hinge  400  enables the flexible display panel  100  to fold or unfold without bending by a change of interval between each of the plurality of rear hinge covers. 
     When the flexile display panel  100  is folded with respect to the bending display area BDA, each of the plurality of rear hinge covers is rotated so as to have a maximum large interval within a range enabling to engage the plurality of rear hinge covers in accordance with a bending-shape change of the elastic axis member so that the bending display area BDA of the flexible display panel  100  is folded with the predetermined curvature without bending the first and second display areas DA 1  and DA 2  of the flexible display panel  100 . 
     When the flexible display panel  100  is unfolded, the plurality of rear hinge covers are rotated to be engaged in accordance with the elastic restoring force of the elastic axis member whose bending shape is changed, and are concentrated so that the bending display area BDA of the flexible display panel  100  is supported, and the entire area of the flexible display panel  100  is unfolded in the flat state. In this case, the flexible display panel  100  may be unfolded into the flat state by the elastic restoring force of the elastic axis members. 
     Except the rear hinge cover positioned in the center, the plurality of rear hinge covers may be symmetric with respect to the rear hinge cover positioned in the center. 
     The front cover  500 , which is connected with the first and second rear covers  200  and  300 , covers a front edge of the flexible display panel  100 . The front cover  500  according to one example may include a front upper cover  510 , a front lower cover  520  and a pair of front central covers  530 . 
     The front upper cover  510  is connected with the first rear cover  200  to cover the front edge adjacent to the first display area DA 1  of the flexible display panel  100 . That is, the front upper cover  510  covers only upper side and left and right sides of the first display area DA 1  except the first display area DA 1  and the bending display area BDA adjacent to the first display area DA 1 . The front upper cover  510  may be formed of a hard material. 
     The front lower cover  520  may be connected with the second rear cover  300  to cover the front edge adjacent to the second display area DA 2  of the flexible display panel  100 . That is, the front lower cover  520  covers only lower side and left and right sides of the second display area DA 2  except the second display area DA 2  and the bending display area BDA adjacent to the second display area DA 2 . The front lower cover  620  may be formed of a hard material. 
     The pair of front central covers  530  may be connected between the front upper cover  510  and the front lower cover  520  to cover the front edge adjacent to the bending display area BDA of the flexible display panel  100 . That is, the pair of front central covers  530  cover only the left and right sides of the bending display area BDA. The pair of front central covers  530  may be formed of a soft material or a soft material with wrinkles. In this case, each of the front upper cover  510  and the front lower cover  520  and the connection portion between the front central covers  530  of one pair may overlap with each other so as to improve formability and adhesiveness. 
     In the foldable display apparatus according to one example, the interval between each of the plurality of rear hinge covers engaged with each other is changed according to the folding or unfolded state of the flexible display panel  100 , whereby the flexible display panel  100  is folded or unfolded without bending. Also, in case of the foldable display apparatus according to one example of the present invention, the flexible display panel  100  is unfolded in the flat state in accordance with the elastic restoring force of the plurality of elastic axis members so that it is possible to improve user&#39;s ease for the unfolding of the flexible display panel  100 . 
       FIG. 3  is an exploded perspective view illustrating the first and second rear covers and the hinge shown in  FIG. 2 .  FIG. 4  is a cross sectional view along I-I′ of  FIG. 2 .  FIG. 5  is a cross sectional view along II-II′ of  FIG. 2 . 
     Referring to  FIGS. 2 to 5 , the first rear cover  200  according to one example receives and supports one side of the flexible display panel  100 . The first rear cover  200  according to one example may include a first edge  231 , a first bottom portion  210 , a first sidewall  220 , a first panel supporting portion  230 , a pair of first portion protrusions  240  and a plurality of first cover protrusions  250 . 
     The first bottom portion  210  covers a rear surface of one side of the flexible display panel  100 . 
     The first sidewall  220  is vertically provided at lateral sides of the first bottom portion  210  connected with one side of the hinge  400  except an inner lateral side of the first bottom portion  210  to surround first area lateral sides of the flexible display panel  100  supported on the first bottom portion  210 . The first sidewall  220  protects each lateral side of the flexible display panel  100  from an external shock. 
     The first panel supporting portion  230  is vertically provided in the inner lateral side of the first bottom portion  210  connected with one side of the hinge  400  to support the flexible display panel  100 . A height from the first bottom portion  210  to the first panel supporting portion  230  is lower than a height of the first sidewall  220 . In one embodiment, the height of an upper surface of the first panel supporting portion  230  is lower than the height of the upper surface of the first side wall  220 . The difference in the height of the upper surface of the first panel supporting portion  230  and the upper surface of the first side wall is equal to the thickness of the flexible display panel  100 . Additionally, the upper surface of the first panel supporting portion  230  may be connected with a predetermined portion of a rear surface of the first display area DA 1  of the flexible display panel  100  adjacent to the bending display area BDA of the flexible display panel  100  by the use of adhesive member (not shown) such as adhesive or double-sided tape. 
     The pair of first portion protrusions  240  may protrude from the first sidewall  220  confronting one side of the hinge  400  toward the hinge  400 . That is, each of the first portion protrusions  240  of one pair is provided at a predetermined distance (D) from an upper surface of the first sidewall  220 , and each of the first portion protrusions  240  of one pair protrudes from an inner lateral side of the first sidewall  220  facing a first direction (X) toward the hinge  400  to have a predetermined length in the first direction (X). Accordingly, a stepped portion is prepared between the first sidewall  220  and each of the first portion protrusions  240  of one pair. Additionally, a protruding end in each of the first portion protrusions  240  of one pair directly confronting the hinge  400  may have a cross section with a curved-line surface for smooth connection and rotation with the hinge  400 , for example, a semicircle-shaped cross section. 
     The plurality of first cover protrusions  250  are provided at fixed intervals in a lateral side of the first panel supporting portion  230 , and more particularly, an inner sidewall  232  of the first panel supporting portion  230  directly confronting one side of the hinge  400 . That is, the plurality of first cover protrusions  250  protrude from the inner sidewall  232  of the first panel supporting portion  230  toward the hinge  400  so as to have a predetermined length in the first direction (X). Each of the plurality of first cover protrusions  250  has a first axis supporting hole  252  prepared in the center thereof. 
     The second rear cover  300  according to one example receives and supports the other side of the flexible display panel  100 . The second rear cover  300  may include a second bottom portion  310 , a second sidewall  320 , a second panel supporting portion  330 , a second edge  331 , a pair of second portion protrusions  340  and a plurality of second cover protrusions  350 . The second rear cover  300  is symmetric in structure to the first rear cover  200  with respect to the hinge  400 . 
     The second bottom portion  310  covers a rear surface of the other side of the flexible display panel  100 . 
     The second sidewall  320  is vertically provided at lateral sides of the second bottom portion  310  connected with the other side of the hinge  400  except an inner lateral side of the second bottom portion  310  to surround second area lateral sides of the flexible display panel  100  supported on the second bottom portion  310 . The second sidewall  320  protects each lateral side of the flexible display panel  100  from an external shock. 
     The second panel supporting portion  330  is vertically provided in the inner lateral side of the second bottom portion  310  connected with the other side of the hinge  400  to support the flexible display panel  100 . A height from the second bottom portion  310  to the second panel supporting portion  330  is lower than a height of the second sidewall  320 . In one embodiment, the height of an upper surface of the second panel supporting portion  330  is lower than the height of the upper surface of the second side wall  320 . The difference in the height of the upper surface of the second panel supporting portion  330  and the upper surface of the second side wall is equal to the thickness of the flexible display panel  100 . Additionally, the upper surface of the second panel supporting portion  330  may be connected with a predetermined portion of a rear surface of the second display area DA 2  of the flexible display panel  100  adjacent to the bending display area BDA of the flexible display panel  100  by the use of adhesive member (not shown) such as adhesive or double-sided tape. 
     The pair of second portion protrusions  340  may protrude from the second sidewall  320  confronting the other side of the hinge  400  toward the hinge  400 . That is, each of the second portion protrusions  340  of one pair is provided at a predetermined distance (D) from an upper surface of the second sidewall  320 , and each of the second portion protrusions  340  of one pair protrudes from an inner lateral side of the second sidewall  320  facing the first direction (X) toward the hinge  400  to have a predetermined length in the first direction (X). Accordingly, a stepped portion is prepared between the second sidewall  320  and each of the second portion protrusions  340  of one pair. Additionally, a protruding end in each of the second portion protrusions  340  of one pair directly confronting the hinge  400  may have a cross section with a curved-line surface for smooth connection and rotation with the hinge  400 , for example, a semicircle-shaped cross section. 
     The plurality of second cover protrusions  350  are provided at fixed intervals in a lateral side of the second panel supporting portion  330 , and more particularly, an inner sidewall  332  of the second panel supporting portion  330  directly confronting the other side of the hinge  400 . That is, the plurality of second cover protrusions  350  protrude from the inner sidewall  332  of the second panel supporting portion  330  toward the hinge  400  so as to have a predetermined length in the first direction (X). Each of the plurality of second cover protrusions  350  has a second axis supporting hole  352  prepared in the center thereof. 
     The hinge  400  according to one example may include a first rear hinge cover  410 , a second rear hinge cover  420  and a third rear hinge cover  430 . 
     The first rear hinge cover  410  is rotatably connected with the first rear cover  200  by a first elastic axis member  410   a . As shown in  FIGS. 4 to 6 , the first rear hinge cover  410  according to one example may include a first lower supporting bar  411 , a pair of first edge sidewalls  412 , a first central supporting bar  413 , a first upper supporting bar  414 , a plurality of first outer connection protrusions  415 , a plurality of first inner connection protrusions  416  and a pair of first rotation axes  417 . 
     The first lower supporting bar  411  is prepared in a rectangular shape whose length is the same as the length of the first edge  231  of the first rear cover  200 . 
     The pair of first edge sidewalls  412  is provided to have a predetermined height in both sides of the first lower supporting bar  411 . The pair of first edge sidewalls  412  may have a third axis supporting hole  412   a  into which the first elastic axis member  410   a  is inserted. 
     The first central supporting bar  413  is vertically prepared in an upper surface of the first lower supporting bar  411 . The first central supporting bar  413  may be vertically prepared in an outer side of the first lower supporting bar  411  adjacent to the second rear cover  300 . 
     The first upper supporting bar  414  is prepared in an upper surface of each of the first central supporting bar  413  and the pair of first edge sidewalls  412  while being overlapped with the first lower supporting bar  411 . Accordingly, the first central supporting bar  413 , the first upper supporting bar  414  and the remaining central portions of the first lower supporting bar  411  except both sides of the first lower supporting bar  411  may have a cross section of ‘[’ shape. 
     The plurality of first outer connection protrusions  415  are provided at fixed intervals along a length direction (Y) of the first central supporting bar  413 , wherein each of the plurality of first outer connection protrusions  415  protrudes toward the first rear cover  200  so as to have a predetermined length in the first direction (X) from an outer surface of the first central supporting bar  413 . In this case, the plurality of first outer connection protrusions  415  alternates with the plurality of first cover protrusions  250  prepared in the first rear cover  200 , whereby the first rear hinge cover  410  has a plurality of first outer insertion spaces  413   a , wherein each of the plurality of first outer insertion spaces  413   a  is prepared between each of the plurality of first outer connection protrusions  415 . 
     Each of the plurality of first outer connection protrusions  415  is inserted into the space between each of the plurality of first cover protrusions  250  in the first rear cover  200 . That is, each of the plurality of first outer connection protrusions  415  is inserted into the space between each of the plurality of first cover protrusions  250 , and each of the plurality of first cover protrusions  250  is inserted into the space between each of the plurality of first outer insertion spaces  413   a . Accordingly, the plurality of first outer connection protrusions  415  are engaged with the plurality of first cover protrusions  250 , wherein the plurality of first outer connection protrusions  415  alternate with the plurality of first cover protrusions  250 . 
     Each of the plurality of first outer connection protrusions  415  has a fourth axis supporting hole  415   a  overlapped with the third axis supporting hole  412   a.    
     The plurality of first inner connection protrusions  416  are provided at fixed intervals along the length direction (Y) of the first central supporting bar  413 , wherein each of the plurality of first inner connection protrusions  416  protrudes toward the second rear cover  300  so as to have a predetermined length in the first direction (X) from an inner surface of the first central supporting bar  413 . Each of the plurality of first inner connection protrusions  416  has a fifth axis supporting hole  416   a . With respect to the length direction (Y) of the first central supporting bar  413 , a first inner insertion space  413   b  is prepared between each of the plurality of first inner connection protrusions  416 . 
     Each of the plurality of first inner connection protrusions  416  is prepared between each of the plurality of first outer connection protrusions  415 . That is, the plurality of first outer connection protrusions  415  and the plurality of first inner connection protrusions  416 , which alternate with each other, are provided in a zigzag pattern with the first central supporting bar  413  provided in-between. 
     The pair of first rotation axes  417  is prepared at both sides of the first upper supporting bar  414 , wherein the pair of first rotation axes  417  serve as a rotation axis for the first rear hinge cover  410 . Each of the first rotation axes  417  included in one pair according to one example may include a first supporting sidewall  417   a , a first outer portion protrusion  417   b  and a first inner portion protrusion  417   c.    
     The first supporting sidewall  417   a  is vertically prepared in an upper surface of the first upper supporting bar  414 . The first supporting sidewall  417   a  supports the first outer portion protrusion  417   b  and the first inner portion protrusion  417   c.    
     The first outer portion protrusion  417   b , which overlaps with the upper surface of the first upper supporting bar  414 , protrudes to have a predetermined length from an upper outer surface of the first supporting sidewall  417   a . In this case, the first outer portion protrusion  417   b  has a protruding length which is not protruding out of a vertical line VL vertically extending from an outer short side of the first lower supporting bar  411 , and also overlaps with an upper surface of the first upper supporting bar  414 . Additionally, a protruding end of the first outer portion protrusion  417   b  may have a cross section with a curved-line surface for smooth connection and rotation with the adjacent first rear cover  200 , for example, a semicircle-shaped cross section. 
     The first outer portion protrusion  417   b  is overlapped with the upper surface of the first upper supporting bar  414  by the first supporting sidewall  417   a , and is also provided at a predetermined distance from the upper surface of the first upper supporting bar  414  so that a first protrusion insertion space  417   d  is prepared between the first outer portion protrusion  417   b  and the first upper supporting bar  414  being overlapped with each other. That is, the first outer portion protrusion  417   b  and the first upper supporting bar  414  are provided in parallel with the first protrusion insertion space  417   d  provided in-between. When the first portion protrusion  240  prepared in the first rear cover  200  is inserted into the first protrusion insertion space  417   d , the first rear hinge cover  410  is engaged and connected with the first rear cover  200 . 
     The first inner portion protrusion  417   c  protrudes from an inner surface of the first supporting sidewall  417   a , wherein the first inner portion protrusion  417   c  has a predetermined length whose direction is in opposition to the protruding direction of the first outer portion protrusion  417   b  while being parallel to the upper surface of the first upper supporting bar  414 . A protruding length of the first inner portion protrusion  417   c  from the first supporting sidewall  417   a  may be the same as a protruding length of the first outer portion protrusion  417   b  from the first supporting sidewall  417   a . The first inner portion protrusion  417   c  is engaged and connected with the third rear hinge cover  430 . Additionally, a protruding end of the first inner portion protrusion  417   c  may have a cross section with a curved-line surface for smooth connection and rotation with the third rear hinge cover  430 , for example, a semicircle-shaped cross section. 
     Referring once again to  FIGS. 2 to 5 , the second rear hinge cover  420  is rotatably connected with the second rear cover  300  by the second elastic axis member  420   a . As shown in  FIGS. 4, 5 and 7 , the second rear hinge cover  420  according to one example may include a second lower supporting bar  421 , a pair of second edge sidewalls  422 , a second central supporting bar  423 , a second upper supporting bar  424 , a plurality of second outer connection protrusions  425 , a plurality of second inner connection protrusions  426  and a pair of second rotation axes  427 . The second rear hinge cover  420  is symmetric to the first rear hinge cover  410  with respect to the third rear hinge cover  430 , whereby a detailed description for the same parts will be omitted, and a brief description for the second rear hinge cover  420  will be shown as follows. 
     The second lower supporting bar  421  is prepared in a rectangular shape whose length is the same as a second side  331  of the second rear cover  300 . The pair of second edge sidewalls  422  may be provided in both sides of the second lower supporting bar  421 , and the pair of second edge sidewalls  422  may have a sixth axis supporting hole  422   a  into which the second elastic axis member  420   a  is inserted. The second central supporting bar  423  is vertically prepared in an upper surface of the second lower supporting bar  421 . The second upper supporting bar  424  is prepared in an upper surface of each of the second central supporting bar  423  and the pair of second edge sidewalls  422  while being overlapped with the second lower supporting bar  421 . Accordingly, the second central supporting bar  423 , the second upper supporting bar  424  and the remaining central portions of the second lower supporting bar  421  except both sides of the second lower supporting bar  421  may have a cross section of ‘]’ shape. 
     The plurality of second outer connection protrusions  425  protrude from the outer surface of the second central supporting bar  423  toward the second rear cover  300 . In this case, the plurality of second outer connection protrusions  425  alternate with the plurality of second cover protrusions  350  prepared in the second rear cover  300 , whereby the second rear hinge cover  420  has a plurality of second outer insertion spaces  423   a , wherein each of the plurality of second outer insertion spaces  423   a  is prepared between each of the plurality of second outer connection protrusions  425 . 
     Each of the plurality of second outer connection protrusions  425  is inserted into the space between each of the plurality of second cover protrusions  350  in the second rear cover  300 . That is, each of the plurality of second outer connection protrusions  425  is inserted into the space between each of the plurality of second cover protrusions  350 , and each of the plurality of second cover protrusions  350  is inserted into each of the plurality of second outer insertion spaces  423   a . Accordingly, the plurality of second outer connection protrusions  425  are engaged with the plurality of second cover protrusions  350 , wherein the plurality of second outer connection protrusions  425  alternate with the plurality of second cover protrusions  350 . 
     Each of the plurality of second outer connection protrusions  425  has a seventh axis supporting hole  425   a  overlapped with the sixth axis supporting hole  422   a.    
     The plurality of second inner connection protrusions  426  protrude from the inner surface of the second central supporting bar  423  toward the first rear cover  200 . Each of the plurality of second inner connection protrusions  426  has an eighth axis supporting hole  426   a . With respect to the length direction (Y) of the second central supporting bar  423 , a second inner insertion space  423   b  is prepared between each of the plurality of second inner connection protrusions  426 . Accordingly, the plurality of second outer connection protrusions  425  and the plurality of second inner connection protrusions  426 , which alternate with each other, are provided in a zigzag pattern with the second central supporting bar  423  provided in-between. 
     The pair of second rotation axes  427  is prepared at both sides of the second upper supporting bar  424 , wherein the pair of second rotation axes  427  serve as a rotation axis for the second rear hinge cover  420 . Each of the second rotation axes  427  included in one pair according to one example may include a second supporting sidewall  427   a , a second outer portion protrusion  427   b  and a second inner portion protrusion  427   c.    
     The second supporting sidewall  427   a  is vertically prepared in an upper surface of the second upper supporting bar  424 . 
     The second outer portion protrusion  427   b , which is overlapped with the upper surface of the second upper supporting bar  424 , protrudes to have a predetermined length from an upper outer surface of the second supporting sidewall  427   a . A protruding end of the second outer portion protrusion  427   b  may have a cross section with a curved-line surface for smooth connection and rotation with the adjacent second rear cover  300 , for example, a semicircle-shaped cross section. In this case, the second outer portion protrusion  427   b  has a protruding length which is not protruding out of a vertical line VL vertically extending from an outer short side of the second lower supporting bar  421 , and is also overlapped with an upper surface of the second upper supporting bar  424 . 
     The second outer portion protrusion  427   b  is overlapped with the upper surface of the second upper supporting bar  424  by the second supporting sidewall  427   a , and is also provided at a predetermined distance from the upper surface of the second upper supporting bar  424  so that a second protrusion insertion space  427   d  is prepared between the second outer portion protrusion  427   b  and the second upper supporting bar  424  being overlapped with each other. That is, the second outer portion protrusion  427   b  and the second upper supporting bar  424  are provided in parallel with the second protrusion insertion space  427   d  provided in-between. According as the second portion protrusion  340  prepared in the second rear cover  300  is inserted into the second protrusion insertion space  427   d , the second rear hinge cover  420  is engaged and connected with the second rear cover  300 . 
     The second inner portion protrusion  427   c  protrudes from an inner surface of the second supporting sidewall  427   a , wherein the second inner portion protrusion  427   c  has a predetermined length whose direction is in opposition to the protruding direction of the second outer portion protrusion  427   b  while being parallel to the upper surface of the second upper supporting bar  424 . Additionally, a protruding end of the second inner portion protrusion  427   c  may have a cross section with a curved-line surface for smooth connection and rotation with the third rear hinge cover  430 , for example, a semicircle-shaped cross section. 
     Referring once again to  FIGS. 2 to 5 , the third rear hinge cover  420  is provided between the first and second rear hinge covers  410  and  420 , whereby the first and second rear hinge covers  410  and  420  are rotatably supported by the third and fourth elastic axis members  430   a  and  430   b . The third rear hinge cover  430  is a rear surface central hinge cover, wherein the third rear hinge cover  430  serves as a folding reference axis when the flexible display panel  100  is folded. The first rear hinge cover  410  and the second rear hinge cover  420  are folded with respect to the third rear hinge cover  430 . As shown in  FIGS. 4, 5 and 8 , the third rear hinge cover  430  according to one example may include a third lower supporting bar  431 , a pair of third edge sidewalls  432 , a third central supporting bar  433 , a third upper supporting bar  434 , a pair of third outer connection protrusion  435 , a plurality of third inner connection protrusions  436  and a pair of third rotation axes  437 . 
     The third lower supporting bar  431  is prepared in a rectangular shape whose length is the same as those of the first and second rear hinge bars  411  and  421 . 
     The pair of third edge sidewalls  432  is provided to have a predetermined height in both sides of the third lower supporting bar  431 . The pair of third edge sidewalls  432  may have ninth and tenth axis supporting holes  432   a  and  432   b  into which the third and fourth elastic axis members  430   a  and  430   b  are respectively inserted. In this case, the ninth axis supporting hole  432   a  passes through the outer side of each of the third edge sidewalls  432  of one pair in a length direction (Y) of the third lower supporting bar  431 , and the tenth axis supporting hole  432   b  passes through the inner side of each of the third edge sidewalls  432  of one pair in the length direction (Y) of the third lower supporting bar  431 . 
     The third central supporting bar  433  is vertically prepared in the center of an upper surface of the third lower supporting bar  431 . 
     The third upper supporting bar  434  is prepared in the upper surface of each of the third central supporting bar  433  and the pair of third edge sidewalls  432  while being overlapped with the third lower supporting bar  431 . Accordingly, the third central supporting bar  433 , the third upper supporting bar  434  and the remaining central portions of the third lower supporting bar  431  except both sides of the third lower supporting bar  431  may have a cross section of ‘I’ shape. 
     The plurality of third outer connection protrusions  435  are provided at fixed intervals along the length direction (Y) of the third central supporting bar  433 , wherein each of the plurality of third outer connection protrusions  435  protrudes toward the first rear cover  200  so as to have a predetermined length in the first direction (X) from an outer surface of the third central supporting bar  433 . In this case, the plurality of third outer connection protrusions  435  alternate with the plurality of first inner connection protrusions  416  prepared in the first rear hinge cover  410 , whereby the third rear hinge cover  430  has a plurality of third outer insertion spaces  433   a , wherein each of the plurality of third outer insertion spaces  433   a  is prepared between each of the plurality of third outer connection protrusions  435 . 
     Each of the plurality of third outer connection protrusions  435  is inserted into each of the plurality of first inner insertion spaces  413   b  prepared in the first rear hinge cover  410 . That is, each of the plurality of third outer connection protrusions  435  is inserted into the space between each of the plurality of first inner connection protrusions  416 , and each of the plurality of first inner connection protrusions  416  is inserted into each of the plurality of third outer insertion spaces  433   a . Accordingly, the plurality of third outer connection protrusions  435  are engaged with the plurality of first inner connection protrusions  416 , wherein the plurality of third outer connection protrusions  435  alternate with the plurality of first inner connection protrusions  416 . 
     Each of the plurality of third outer connection protrusions  435  may have an eleventh axis supporting hole (not shown) overlapped with the ninth axis supporting hole  432   a.    
     The plurality of third inner connection protrusions  436  are provided at fixed intervals along the length direction (Y) of the third central supporting bar  433 , wherein each of the plurality of third inner connection protrusions  436  protrudes toward the second rear cover  300  so as to have a predetermined length in the first direction (X) from an inner surface of the third central supporting bar  433 . Each of the plurality of third inner connection protrusions  436  has a twelfth axis supporting hole  436   a . With respect to the length direction (Y) of the third central supporting bar  433 , a third inner insertion space  433   b  is prepared between each of the plurality of third inner connection protrusions  436 . 
     Each of the plurality of third inner connection protrusions  436  is prepared between each of the plurality of third outer connection protrusions  435 . That is, the plurality of third outer connection protrusions  435  and the plurality of third inner connection protrusions  436 , which alternate with each other, are provided in a zigzag pattern with the third central supporting bar  433  provided in-between. 
     The pair of third rotation axes  437  is prepared at both sides of the third upper supporting bar  434 , wherein the pair of third rotation axes  437  serve as a rotation axis for each of the first and second rear hinge covers  410  and  420 . Each of the third rotation axes  437  included in one pair according to one example may include a third supporting sidewall  437   a , a third outer portion protrusion  437   b  and a third inner portion protrusion  437   c.    
     The third supporting sidewall  437   a  is vertically prepared in the center of an upper surface of the third upper supporting bar  434  to support the third outer portion protrusion  437   b  and the third inner portion protrusion  437   c.    
     The third outer portion protrusion  437   b , which is overlapped with the upper surface of the third upper supporting bar  434 , protrudes to have a predetermined length from an upper outer surface of the third supporting sidewall  437   a . In this case, the third outer portion protrusion  437   b  has a protruding length which is not protruding out of a vertical line VL vertically extending from an outer short side of the third lower supporting bar  431 , and is also overlapped with an upper surface of the third upper supporting bar  434 . Additionally, a protruding end of the third outer portion protrusion  437   b  may have a cross section with a curved-line surface for smooth connection and rotation with the first rear hinge cover  410 , for example, a semicircle-shaped cross section. 
     The third outer portion protrusion  437   b  is overlapped with the upper surface of the third upper supporting bar  434  by the third supporting sidewall  437   a , and is also provided at a predetermined distance from the upper surface of the third upper supporting bar  434  so that a third protrusion insertion space  437   d  is prepared between the third outer portion protrusion  437   b  and the third upper supporting bar  434  being overlapped with each other. That is, the third outer portion protrusion  437   b  and the third upper supporting bar  434  are provided in parallel with the third protrusion insertion space  437   d  provided in-between. According as the first inner portion protrusion  417   c  prepared in the first rear hinge cover  410  is inserted into the third protrusion insertion space  437   d , the third rear hinge cover  430  is engaged and connected with the first rear hinge cover  410 . 
     The third inner portion protrusion  437   c , which is overlapped with the upper surface of the third upper supporting bar  434 , protrudes to have a predetermined length from an upper inner surface of the third supporting sidewall  437   a . In this case, the third inner portion protrusion  437   c  has a protruding length which is not protruding out of a vertical line VL vertically extending from an inner short side of the third lower supporting bar  431 , and is also overlapped with an upper surface of the third upper supporting bar  434 . Additionally, a protruding end of the third inner portion protrusion  437   c  may have a cross section with a curved-line surface for smooth connection and rotation with the second rear hinge cover  420 , for example, a semicircle-shaped cross section. 
     The third inner portion protrusion  437   c  is overlapped with the upper surface of the third upper supporting bar  434  by the third supporting sidewall  437   a , and is also provided at a predetermined distance from the upper surface of the third upper supporting bar  434  so that a fourth protrusion insertion space  437   e  is prepared between the third inner portion protrusion  437   c  and the third upper supporting bar  434  being overlapped with each other. That is, the third inner portion protrusion  437   c  and the third upper supporting bar  434  are provided in parallel with the fourth protrusion insertion space  437   e  provided in-between. According as the second inner portion protrusion  427   c  prepared in the second rear hinge cover  410  is inserted into the fourth protrusion insertion space  437   e , the third rear hinge cover  430  is engaged and connected with the second rear hinge cover  420 . 
     Additionally, the hinge  400  according to one example may further include a fourth rear hinge cover  440  and a fifth rear hinge cover  450 . 
     The fourth rear hinge cover  440  is rotatably connected between the first rear hinge cover  410  and the third rear hinge cover  430 . For example, the fourth rear hinge cover  440  is rotatably connected with the first rear hinge cover  410  by the fifth elastic axis member  440   a , and is also rotatably connected with the third rear hinge cover  430  by the third elastic axis member  430   a . In the same manner as the first rear hinge cover  410  shown in  FIG. 6 , the fourth rear hinge cover  440  may include a first lower supporting bar  411 , a pair of first edge sidewalls  412 , a first central supporting bar  413 , a first upper supporting bar  414 , a plurality of first outer connection protrusions  415 , a plurality of first inner connection protrusions  416  and a pair of first rotation axes  417 , whereby the same reference numbers will be used throughout the drawings to refer to the same or like parts, and a detailed description for the same parts will be omitted. 
     Each of a plurality of first outer connection protrusions  415  prepared in the fourth rear hinge cover  440  is inserted into each first inner insertion space  413   b  provided between each of the plurality of first inner connection protrusions  416  prepared in the first rear hinge cover  410 . Accordingly, the plurality of first outer connection protrusions  415  prepared in the fourth rear hinge cover  440  are engaged with the plurality of first inner connection protrusions  416  prepared in the first rear hinge cover  410 , wherein the plurality of first outer connection protrusions  415  prepared in the fourth rear hinge cover  440  alternate with the plurality of first inner connection protrusions  416  prepared in the first rear hinge cover  410 . 
     Each of a plurality of first inner connection protrusions  416  prepared in the fourth rear hinge cover  440  is inserted into each third outer insertion space  433   a  provided between each of the plurality of third outer connection protrusions  435  prepared in the third rear hinge cover  430 . Accordingly, the plurality of first inner connection protrusions  416  prepared in the fourth rear hinge cover  440  are engaged with the plurality of third outer connection protrusions  435  prepared in the third rear hinge cover  430 , wherein the plurality of first inner connection protrusions  416  prepared in the fourth rear hinge cover  440  alternate with the plurality of third outer connection protrusions  435  prepared in the third rear hinge cover  430 . 
     A pair of first rotation axes  417  prepared in the fourth rear hinge cover  440  may include a first outer portion protrusion  417   b , a first inner portion protrusion  417   c  and a first protrusion insertion space  417   d.    
     The first outer portion protrusion  417   b  of the fourth rear hinge cover  440  is overlapped in an up-and-down direction with and also connected with the first inner portion protrusion  417   c  of the first rear hinge cover  410 . That is, the first inner portion protrusion  417   c  of the first rear hinge cover  410  is inserted into the first protrusion insertion space  417   d  of the fourth rear hinge cover  440  so that the first outer portion protrusion  417   b  of the fourth rear hinge cover  440  is overlapped in an up-and-down direction with the first inner portion protrusion  417   c  of the first rear hinge cover  410 , whereby the fourth rear hinge cover  440  is engaged and connected with the first rear hinge cover  410 . 
     When the first inner portion protrusion  417   c  of the fourth rear hinge cover  440  is inserted into the third protrusion insertion space  437   d  of the third rear hinge cover  430 , the first inner portion protrusion  417   c  of the fourth rear hinge cover  440  is overlapped in an up-and-down direction with the third outer portion protrusion  437   b  of the third rear hinge cover  430 , whereby the fourth rear hinge cover  440  is engaged and connected with the third rear hinge cover  430 . 
     The fifth rear hinge cover  450  is rotatably connected between the second rear hinge cover  420  and the third rear hinge cover  430 . For example, the fifth rear hinge cover  450  is rotatably connected with the second rear hinge cover  420  by the sixth elastic axis member  450   a , and is also rotatably connected with the third rear hinge cover  430  by the fourth elastic axis member  430   b . In the same manner as the second rear hinge cover  420  shown in  FIG. 7 , the fifth rear hinge cover  450  may include a second lower supporting bar  421 , a pair of second edge sidewalls  422 , a second central supporting bar  423 , a second upper supporting bar  424 , a plurality of second outer connection protrusions  425 , a plurality of second inner connection protrusions  426  and a pair of second rotation axes  427 , whereby the same reference numbers will be used throughout the drawings to refer to the same or like parts, and a detailed description for the same parts will be omitted. 
     Each of a plurality of second outer connection protrusions  425  prepared in the fifth rear hinge cover  450  is inserted into each second inner insertion space  423   b  provided between each of the plurality of second inner connection protrusions  426  prepared in the second rear hinge cover  420 . Accordingly, the plurality of second outer connection protrusions  425  prepared in the fifth rear hinge cover  450  are engaged with the plurality of second inner connection protrusions  426  prepared in the second rear hinge cover  420 , wherein the plurality of second outer connection protrusions  425  prepared in the fifth rear hinge cover  450  alternate with the plurality of second inner connection protrusions  426  prepared in the second rear hinge cover  420 . 
     Each of a plurality of second inner connection protrusions  426  prepared in the fifth rear hinge cover  450  is inserted into each third inner insertion space  433   b  provided between each of the plurality of third inner connection protrusions  436  prepared in the third rear hinge cover  430 . Accordingly, the plurality of second inner connection protrusions  426  prepared in the fifth rear hinge cover  450  are engaged with the plurality of third inner connection protrusions  436  prepared in the third rear hinge cover  430 , wherein the plurality of second inner connection protrusions  426  prepared in the fifth rear hinge cover  450  alternate with the plurality of third inner connection protrusions  436  prepared in the third rear hinge cover  430 . 
     A pair of second rotation axes  427  prepared in the fifth rear hinge cover  450  may include a second outer portion protrusion  427   b , a second inner portion protrusion  427   c  and a second protrusion insertion space  427   d.    
     The first outer portion protrusion  427   b  of the fifth rear hinge cover  450  is overlapped in an up-and-down direction with and also connected with the second inner portion protrusion  427   c  of the second rear hinge cover  420 . That is, the second inner portion protrusion  427   c  of the second rear hinge cover  420  is inserted into the second protrusion insertion space  427   d  of the fifth rear hinge cover  450  so that the second outer portion protrusion  427   b  of the fifth rear hinge cover  450  is overlapped in an up-and-down direction with the second inner portion protrusion  427   c  of the second rear hinge cover  420 , whereby the fifth rear hinge cover  450  is engaged and connected with the second rear hinge cover  420 . 
     According as the second inner portion protrusion  427   c  of the fifth rear hinge cover  450  is inserted into the fourth protrusion insertion space  437   e  of the third rear hinge cover  430 , the second inner portion protrusion  427   c  of the fifth rear hinge cover  450  is overlapped in an up-and-down direction with the third inner portion protrusion  437   c  of the third rear hinge cover  430 , whereby the fifth rear hinge cover  450  is engaged and connected with the third rear hinge cover  430 . 
       FIG. 9  illustrates the first to sixth elastic axis members shown in  FIG. 3 , which shows the changed states of the first to sixth elastic axis members in accordance with the folding of the flexible display panel. 
     Referring to  FIG. 9  in connection with  FIGS. 3 to 5 , each of the first to sixth elastic axis members  410   a ,  420   a ,  430   a ,  430   b ,  440   a  and  450   a  according to one example may be an elastic body with an elastic restoring force, for example, coil spring. 
     The first elastic axis member  410   a  is alternately inserted between the first rear cover  200  and the first rear hinge cover  410 . That is, after the first elastic axis member  410   a  is inserted into the third axis supporting hole  412  prepared in the first rear hinge cover  410 , the first elastic axis member  410   a  is alternately inserted into the plurality of first axis supporting holes  252  prepared in the first rear cover  200  and the plurality of fourth axis supporting holes  415   a  prepared in the first rear hinge cover  410  to support the first rear cover  200  and the first rear hinge cover  410 . 
     When the flexible display panel  100  is folded, the first elastic axis member  410  is changed to the zigzag shape between the first rear cover  200  and the first rear hinge cover  410  in accordance with the rotation angle of each of the first rear cover  200  and the first rear hinge cover  410 , whereby the first rear cover  200  and the first rear hinge cover  410  are rotated without separation. When the flexible display panel  100  is unfolded, the first elastic axis member  410   a  provides the elastic restoring force to the first rear cover  200  and the first rear hinge cover  410 , whereby the plurality of first outer connection protrusions  415  prepared in the first rear hinge cover  410  and the plurality of first cover protrusions  240  prepared in the first rear cover  200  are engaged and rotated without separation. 
     The fifth elastic axis member  440   a  is alternately inserted between the fourth rear hinge cover  440  and the first rear hinge cover  410 . That is, after the fifth elastic axis member  440   a  is inserted into the third axis supporting hole  412   a  prepared in the fourth rear hinge cover  440 , the fifth elastic axis member  440   a  is alternately inserted into the plurality of fifth axis supporting holes  416   a  prepared in the first rear hinge cover  410  and the plurality of fourth axis supporting holes  415   a  prepared in the fourth rear hinge cover  440  to support the fourth rear hinge cover  440  and the first rear hinge cover  410 . 
     When the flexible display panel  100  is folded, the fifth elastic axis member  440   a  is changed to the zigzag shape between the fourth rear hinge cover  440  and the first rear hinge cover  410  in accordance with the rotation angle of each of the fourth rear hinge cover  440  and the first rear hinge cover  410 , whereby the fourth rear hinge cover  440  and the first rear hinge cover  410  are rotated without separation. When the flexible display panel  100  is unfolded, the fifth elastic axis member  440   a  provides an elastic restoring force to the fourth rear hinge cover  440  and the first rear hinge cover  410 , whereby the plurality of first inner connection protrusions  416  prepared in the first rear hinge cover  410  and the plurality of first outer connection protrusions  415  prepared in the fourth rear hinge cover  440  are engaged and rotated without separation. 
     The sixth elastic axis member  450   a  is alternately inserted between the fifth rear hinge cover  450  and the second rear hinge cover  420 . That is, after the sixth elastic axis member  450   a  is inserted into the sixth axis supporting hole  422   a  prepared in the fifth rear hinge cover  450 , the sixth elastic axis member  450   a  is alternately inserted into the plurality of eighth axis supporting holes  426   a  prepared in the second rear hinge cover  420  and the plurality of seventh axis supporting holes  425   a  prepared in the fifth rear hinge cover  450  to support the fifth rear hinge cover  450  and the second rear hinge cover  420 . 
     When the flexible display panel  100  is folded, the sixth elastic axis member  450   a  is changed to a zigzag shape between the fifth rear hinge cover  450  and the second rear hinge cover  420  in accordance with the rotation angle of each of the fifth rear hinge cover  450  and the second rear hinge cover  420 , whereby the fifth rear hinge cover  450  and the second rear hinge cover  420  are rotated without separation. When the flexible display panel  100  is unfolded, the sixth elastic axis member  450   a  provides an elastic restoring force to the fifth rear hinge cover  450  and the second rear hinge cover  420 , whereby the plurality of second outer connection protrusions  426  prepared in the second rear hinge cover  420  and the plurality of second inner connection protrusions  425  prepared in the fifth rear hinge cover  450  are engaged and rotated without separation. 
     The third elastic axis member  430   a  is alternately inserted between the third rear hinge cover  430  and the fourth rear hinge cover  440 . That is, after the third elastic axis member  430   a  is inserted into the ninth axis supporting hole  432   a  prepared in the third rear hinge cover  430 , the third elastic axis member  430   a  is alternately inserted into the plurality of fifth axis supporting holes  416   a  prepared in the fourth rear hinge cover  440  and the plurality of eleventh axis supporting holes (not shown) prepared in the third rear hinge cover  430  to support the fourth rear hinge cover  440  and the third rear hinge cover  430 . 
     When the flexible display panel  100  is folded, the third elastic axis member  430   a  is changed to a zigzag shape between the fourth rear hinge cover  440  and the third rear hinge cover  430  in accordance with the rotation angle of each of the fourth rear hinge cover  440  and the third rear hinge cover  430 , whereby the fourth rear hinge cover  440  and the third rear hinge cover  430  are rotated without separation. When the flexible display panel  100  is unfolded, the third elastic axis member  430   a  provides an elastic restoring force to the fourth rear hinge cover  440  and the third rear hinge cover  430 , whereby the plurality of third outer connection protrusions  435  prepared in the third rear hinge cover  430  and the plurality of first inner connection protrusions  416  prepared in the fourth rear hinge cover  440  are engaged and rotated without separation. 
     The fourth elastic axis member  430   b  is alternately inserted between the third rear hinge cover  430  and the fifth rear hinge cover  450 . That is, after the fourth elastic axis member  430   b  is inserted into the tenth axis supporting hole  432   b  prepared in the third rear hinge cover  430 , the fourth elastic axis member  430   b  is alternately inserted into the plurality of eighth axis supporting holes  426   a  prepared in the fifth rear hinge cover  450  and the plurality of twelfth axis supporting holes  436   a  prepared in the third rear hinge cover  430  to support the fifth rear hinge cover  450  and the third rear hinge cover  430 . 
     When the flexible display panel  100  is folded, the fourth elastic axis member  430   b  is changed to a zigzag shape between the fifth rear hinge cover  450  and the third rear hinge cover  430  in accordance with the rotation angle of each of the fifth rear hinge cover  450  and the third rear hinge cover  430 , whereby the fifth rear hinge cover  450  and the third rear hinge cover  430  are rotated without separation. When the flexible display panel  100  is unfolded, the fourth elastic axis member  430   b  provides an elastic restoring force to the fifth rear hinge cover  450  and the third rear hinge cover  430 , whereby the plurality of third inner connection protrusions  436  prepared in the third rear hinge cover  430  and the plurality of second outer connection protrusions  426  prepared in the fifth rear hinge cover  450  are engaged and rotated without separation. 
       FIG. 10A  is a rear perspective view illustrating the unfolded state of the foldable display apparatus according to one embodiment of the present invention.  FIG. 10B  is a cross sectional view along of  FIG. 10A .  FIG. 10C  is a cross sectional view along IV-IV′ of  FIG. 10A . Hereinafter, the unfolded state of the foldable display apparatus according to one embodiment of the present invention will be described with reference to  FIGS. 10A, 10B and 10C . 
     As shown in  FIG. 10A , in case of the foldable display apparatus according to one embodiment of the present invention, when the first and second rear covers  200  and  300  are unfolded, the first and second display area and the bending display area of the flexible display panel are unfolded by the elastic restoring force of each of the first to sixth elastic axis members  410   a ,  420   a ,  430   a ,  430   b ,  440   a  and  450   a  of the hinge  400  to realize a large-sized screen. 
     As shown in  FIG. 10B , when the first and second rear covers  200  and  300  are unfolded, the portion protrusions  240 ,  340 ,  417   b ,  417   c ,  427   b ,  427   c ,  437   b  and  437   c  prepared in the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450  and the first and second rear covers  200  and  300  are overlapped with each other, and are engaged in an up-and-down direction. Accordingly, the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450  are supported by the first portion protrusion  240  of the first rear cover  200  and the second portion protrusion  340  of the second rear cover  300 , whereby the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450  are maintained in the flat state. Thus, both sides of the bending display area BDA defined in the flexible display panel  100  are supported by the connection protrusions  417   b ,  427   b  and  437   b  prepared in the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450  to maintain the flat state. 
     As shown in  FIG. 10C , when the first and second rear covers  200  and  300  are unfolded, the connection protrusions  250 ,  350 ,  415 ,  425 ,  426 ,  435  and  436  prepared in the first and second rear covers  200  and  300  and the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450  are alternately engaged by the elastic restoring force of the first to sixth elastic axis members  410   a ,  420   a ,  430   a ,  430   b ,  440   a  and  450   a . Accordingly, the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450  are supported by the first cover protrusion  250  of the first rear cover  200  and the second cover protrusion  350  of the second rear cover  300  to maintain the flat state. Thus, the central portion of the bending display area BDA defined in the flexible display panel  100 , except both sides of the bending display area BDA, is supported by the upper supporting bars  414 ,  424  and  434  of the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450  shown in  FIGS. 6 to 8  to maintain the flat state. 
       FIG. 11A  is a rear perspective view illustrating the foldable display apparatus in a half-folded state according to one embodiment of the present invention.  FIG. 11B  is a cross sectional view along V-V′ of  FIG. 11A .  FIG. 11C  is a cross sectional view along VI-VI′ of  FIG. 11A  Hereinafter, the half-folding state of the foldable display apparatus according to one embodiment of the present invention will be described in detail as follows. 
     As shown in  FIG. 11A , in case of the foldable display apparatus according to one embodiment of the present invention, if the first and second rear covers  200  and  300  are rotated to face with each other, the first to sixth elastic axis members  410   a ,  420   a ,  430   a ,  43   b ,  440   a  and  450   a  are changed to the zigzag shape in accordance to the rotation angle of each of the first and second rear covers  200  and  300 , whereby the first and fourth rear hinge covers  410  and  440  are rotated in a first rotation direction with respect to a rotation axis of the third rear hinge cover  430 , and the second and fifth rear hinge covers  420  and  450  are rotated in a second rotation direction which is opposite to the first rotation direction. Thus, according as the interval between each of the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450  is gradually increased, the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450  are spaced apart from each other in a curve shape to form a bending guide surface. Accordingly, the bending display area BDA of the flexible display panel is folded with a predetermined curvature along the bending guide surface. 
     As shown in  FIG. 11B , when the first and second rear covers  200  and  300  are half-folded, the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450  are respectively rotated in accordance with the shape change of the first to sixth elastic axis members  410   a ,  420   a ,  430   a ,  430   b ,  440   a  and  450   a . At this time, under the condition that each of the protrusions  240 ,  340 ,  417   c  and  427   c  prepared in the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450  and the first and second rear covers  200  and  300  is used as a rotation axis RA, the first and fourth rear hinge covers  410  and  440  are rotated in a first rotation direction with respect to a rotation central axis of the third rear hinge cover  430 , and the second and fifth rear hinge covers  420  and  450  are rotated in a second rotation direction with respect to a rotation central axis of the third rear hinge cover  430 . Thus, the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450  are spaced apart from each other in a curve shape to form a bending guide surface of the curved shape. Accordingly, the bending display area BDA of the flexible display panel is folded with a predetermined curvature along the bending guide surface. 
     As shown in  FIG. 11C , when the first and second rear covers  200  and  300  are half-folded, the connection protrusions  250 ,  350 ,  415 ,  425 ,  426 ,  435  and  436  prepared in the first and second rear covers  200  and  300  and the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450  are alternately spaced from each other in accordance with the shape change of the first to sixth elastic axis members  410   a ,  420   a ,  430   a ,  430   b ,  440   a  and  450   a . Accordingly, the upper supporting bars  414 ,  424  and  434  of the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450  shown in  FIGS. 6 to 8  are spaced apart from each other in a curve shape to form a bending guide surface of the curved shape. Accordingly, the bending display area BDA of the flexible display panel is folded with a predetermined curvature along the bending guide surface. 
       FIG. 12A  is a rear perspective view illustrating the folding state of the foldable display apparatus according to one embodiment of the present invention.  FIG. 12B  is a cross sectional view along VII-VII′ of  FIG. 12A .  FIG. 12C  is a cross sectional view along VIII-VIII′ of  FIG. 12A . Hereinafter, the folding state of the foldable display device according to one embodiment of the present invention will be described as follows. 
     As shown in  FIG. 12A , in case of the foldable display apparatus according to one embodiment of the present invention, when the first and second rear covers  200  and  300  are additionally rotated and folded, the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450  are spaced from each other at maximum in accordance with the additional change of zigzag shape of the first to sixth elastic axis members  410   a ,  420   a ,  430   a ,  430   b ,  440   a  and  450   a  to form a bending guide surface of a curved shape. Thus, the bending display area of the flexible display panel is folded with a predetermined curvature along the bending guide surface. 
     As shown in  FIG. 12B , when the first and second rear covers  200  and  300  are folded, the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450  are rotated at maximum in accordance with the additional shape change of the first to sixth elastic axis members  410   a ,  420   a ,  430   a ,  430   b ,  440   a  and  450   a  of the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450 . At this time, under the condition that each of the portion protrusions  240 ,  340 ,  417   c  and  427   c  is used as a rotation axis RA, the first and fourth rear hinge covers  410  and  440  are rotated in a first rotation direction with respect to a rotation central axis of the third rear hinge cover  430 , and the second and fifth rear hinge covers  420  and  450  are rotated in a second rotation direction with respect to a rotation central axis of the third rear hinge cover  430 . Accordingly, the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450  are spaced from each other at maximum to form a bending guide surface of a curved shape. Thus, the bending display area of the flexible display panel is folded with a predetermined curvature along the bending guide surface. 
     As shown in  FIG. 12C , when the first and second rear covers  200  and  300  are folded, the connection protrusions  250 ,  350 ,  415 ,  425 ,  426 ,  435  and  436  are spaced at maximum from each other in accordance with the shape change of the first to sixth elastic axis members  410   a ,  420   a ,  430   a ,  430   b ,  440   a  and  450   a . Accordingly, in case of the central portion of the bending display area BDA except both sides of the bending display area BDA defined in the flexible display panel  100 , the upper supporting bars  414 ,  424  and  434  of the first to fifth rear hinge covers  410 ,  420 ,  430 ,  440  and  450  shown in  FIGS. 6 to 8  are spaced from each other to form a bending guide surface of a curved shape. Thus, the bending display area of the flexible display panel is folded with a predetermined curvature along the bending guide surface. 
     Meanwhile, the flexible display panel  100 , which is folded with the curvature set in accordance with the folding of the first and second rear covers  200  and  300 , is semiautomatically unfolded in the flat state in accordance with the elastic restoring force of the first to sixth elastic axis members  410   a ,  420   a ,  430   a ,  430   b ,  440   a  and  450   a  which are changed from a zigzag type to a straight-line shape when the first and second rear covers  200  and  300  are unfolded. 
     In the foldable display apparatus according to one embodiment of the present invention, when the flexible display panel is folded, the interval between each of the plurality of rear hinge covers is changed in accordance with the shape change of the elastic axis member, whereby the bending guide surface of the curved line shape is formed so that it is possible to prevent the flexible display panel from being bent when the flexible display panel is folded or unfolded, thereby improving reliability of the flexible display panel. 
       FIG. 13  is an exploded perspective view illustrating a foldable display apparatus according to another embodiment. The embodiment of  FIG. 13  additionally providing a panel supporting frame.  FIG. 14  is a rear perspective view of a panel supporting frame shown in  FIG. 13 .  FIG. 15  is a cross sectional view along IX-IX′ of  FIG. 1 . Hereinafter, only the structure relating the panel supporting frame will be described in detail as follows. 
     Referring to  FIGS. 13 to 15 , the panel supporting frame  600  according to one example is connected with first and second areas of the aforementioned flexible display panel  100  to support a bending display area BDA. The panel supporting frame  600  according to one example is received in first and second rear covers  200  and  300 . That is, the panel supporting frame  600  is connected with a rear side of the flexible display panel  100 , wherein the panel supporting frame  600  guides folding and unfolding of the flexible display panel  100  with respect to the bending display area BDA. To this end, the panel supporting frame  600  according to one example may include a bending member  611  and first and second supporting members  613  and  615 . 
     The bending member  611  supports the bending display area BDA of the flexible display panel  100 . The bending member  611  guides the bending display area BDA of the flexible display panel  100  to be bent with a predetermined curvature. The bending member  611  is not physically connected with the flexible display panel  100  by the use of adhesive member (not shown) such as adhesive or double-sided tape. The bending member  611  serves as a supporter for supporting a panel bending portion overlapped with the bending display area BDA of the flexible display panel  100 . To this end, the bending member  611  may include any one material or two or more materials of soft materials, for example, rubber, silicon, polyurethane and polyvinyl chloride. 
     The bending member  611  according to one example may include a body  611   a , a first outer protrusion  611   b  and a second outer protrusion  611   c.    
     The body  611   a  is overlapped with the bending display area BDA of the flexible display panel  100 , wherein the body  611   a  supports the bending display area BDA of the flexible display panel  100  or guides the bending of the bending display area BDA. The body  611   a  according to one example may include a bending portion (A) and first and second bending buffers (B 1 , B 2 ). 
     The bending portion (A) is defined with the center of the body  611   a , and is overlapped with the bending display area BDA of the flexible display panel  100 . The bending portion (A) is formed of a soft material so that the bending portion (A) is bent in accordance with the bending of the bending display area BDA. A length of the bending portion (A) may be set to be identical to a length of the bending display area BDA defined in the flexible display panel  100  with respect to a length direction (X) of the flexible display panel  100 , or may be set in accordance with the bending curvature of the bending display area BDA. For example, a first length of the bending portion (A) is set in accordance with a folded radius circumference. A maximum length of the bending portion (A) is set to be 30% or more than 30% of the radius circumference so as to provide the smooth curvature, and also set to be less than 180% of the radius circumference so as to maintain hardness of the bending member  611 , preferably. 
     The first and second bending buffers (B 1 , B 2 ) are bending buffer areas, wherein the first and second bending buffers (B 1 , B 2 ) are prepared in both sides of the bending portion (A) while being in parallel to each other. The first and second bending buffers (B 1 , B 2 ) may be overlapped with inner sides of display areas (DA 1 , DA 2 ) being in contact with the bending display area BDA of the flexible display panel  100 . The first bending buffer (B 1 ) is prepared at one side of the body  11   a , that is, one side of the bending portion (A), and the second bending buffer (B 2 ) is prepared at the other side of the body  11   a , that is, the other side of the bending portion (A). In this case, a second length of each of the first and second bending buffers (B 1 , B 2 ) is set within a range of 10%˜70% of the length of the bending portion (A) so as to maintain hardness of the bending member  611 , preferably. Each of the first and second bending buffers (B 1 , B 2 ) is formed of a soft material so that it is possible to maintain the smooth curvature of the bending display area BDA when the flexible display panel  100  is bent. 
     The first outer protrusion  611   b  is prepared at one side of the body  611   a , and is overlapped with the first supporting member  613 . The first outer protrusion  611   b  according to one example, which protrudes toward the first supporting member  13 , has a predetermined length from one side of the body  611   a , and more particularly, a lower portion of a first long side of the body  611   a , and then the protruding first outer protrusion  611   b  is overlapped with the inner side of the first supporting member  613 . 
     The second outer protrusion  611   c  is prepared at the other side of the body  611   a . With the body  11   a  provided between the first outer protrusion  611   b  and the second outer protrusion  611   c , the second outer protrusion  611   c  is provided in parallel to the first outer protrusion  611   b , and is overlapped with the second supporting member  15 . The second outer protrusion  11   c  according to one example, which protrudes toward the second supporting member  615 , has a predetermined length from the other side of the body  611   a , and more particularly, a lower portion of a second long side of the body  611   a , and then the protruding second outer protrusion  611   c  is overlapped with the inner side of the second supporting member  615 . 
     Additionally, the bending member  611  according to the first embodiment of the present invention may further include a length compensation pattern  611   d  prepared in a lower surface of the body  611   a  in opposite to an upper surface of the body  611   a , wherein the upper surface of the body  611   a  directly confronts the flexible display panel  100 . 
     The length compensation pattern  611   d  may be an uneven pattern with a plurality of hollows in the lower surface of the body  11   a , wherein the plurality of hollows included in the uneven pattern may be provided at fixed intervals along a length direction X (or a short-side direction) of the body  611   a  while being in parallel to a width direction Y (or a long-side direction) of the body  611   a . The uneven pattern  611   d  according to one example may include a plurality of slits, wherein each of the slits may have a predetermined width, and the plurality of slits included in the uneven pattern  611   d  may be provided in parallel to the long side of the body  611   a  and are provided in the lower surface of the bending portion (A). The length compensation pattern  611   d  compensates for a length change through a change of interval between the adjacent slits when the flexible display panel  100  is repetitively folded or unfolded so that it is possible to prevent the bending display area BDA of the flexible display panel  100  from being wrinkled, and to make the bending display area BDA of the flexible display panel  100  be bent with the predetermined curvature. A width and depth of each of the slits may be set in accordance with the bending curvature of the bending display area BDA. 
     Additionally, the length compensation pattern  611   d  may be prepared in the upper surface of the body  611   a , that is, a supporting surface of the body  611   a  for supporting the bending display area BDA of the flexible display panel  100 . In this case, the uneven pattern may cause a sense of difference on a touch for the flexible display panel  100 . Accordingly, the length compensation pattern  611   d  is prepared in the lower surface of the body  611   a , preferably. 
     The first supporting member  613 , which is connected with one side of the bending member  11 , supports the first display area (DA 1 ) of the flexible display panel  100 . The inner lateral side of the first supporting member  613  and one side of the bending member  611  are overlapped with each other, and are physically connected with each other as one body. Also, the first supporting member  613  is physically connected with a first panel rear portion of the flexible display panel  100  overlapped with the first display area (DA 1 ) of the flexible display panel  100 , whereby the first panel rear portion is maintained in the flat state. To this end, the first supporting member  613  is formed of a hard material whose hardness is relatively higher than that of the bending member  611 , for example, plastic material or metal material. 
     The first supporting member  613  according to one example may include a first base plate  613   a  and a first inner protrusion  613   b.    
     The first base plate  613   a  is overlapped with the first display area (DA 1 ) of the flexible display panel  100 , wherein the first base plate  613   a  supports the first panel rear portion of the flexible display panel  100 . In this case, the first base plate  613   a  may be physically connected with the first panel rear portion by the use of adhesive member (not shown). An inner lateral side of the first base plate  613   a  which directly confronts the first outer protrusion  611   b  of the bending member  611  is physically connected with a lateral side of the first outer protrusion  611   b.    
     The first inner protrusion  613   b  is prepared at an inner lateral side of the first base plate  613   a , overlapped with the first outer protrusion  611   b  of the bending member  611 , and physically connected with the upper surface of the first outer protrusion  611   b  and one lateral side of the body  611   a . The first inner protrusion  613   b , which protrudes toward the bending member  611 , has a predetermined length from the inner lateral side of the first base plate  613   a , and more particularly, an upper portion of an inner short side of the first base plate  613   a , and then the protruding first inner protrusion  613   b  is overlapped with the first outer protrusion  611   b  of the bending member  611 . In this case, the first inner protrusion  613   b  and the first outer protrusion  611   b  may have the same length. A length in each of the first inner protrusion  613   b  and the first outer protrusion  611   b  may be set to be 10% or more than 10% of the length of the bending portion (A) so as to secure a sufficient attachment area (or bonding area) between the bending member  611  and the first supporting member  613 , and also to prevent a separation even in a repetitive folding. 
     The first supporting member  613  according to one example may further include first and second rounding portion (R 1 , R 2 ) prepared at corners of the first inner protrusion  613   b  connected with the bending member  611 . 
     The first rounding portion (R 1 ) is prepared with a predetermined curvature at the corner between the first base plate  613   a  and the first inner protrusion  613   b . The first second rounding portion (R 2 ) is prepared with a predetermined curvature at the corner of the first inner protrusion  613   b  corresponding to the corner between the body  611   a  of the bending member  611  and the first outer protrusion  611   b . The first and second rounding portions (R 1 , R 2 ) increase the attachment area between the bending member  611  and the first supporting member  613  to enhance an adhesive strength between the bending member  611  and the first supporting member  613 . 
     The second supporting member  615 , which is connected with the other side of the bending member  611 , supports the second display area (DA 2 ) of the flexible display panel  100 . The inner lateral side of the second supporting member  615  and the other side of the bending member  611  are overlapped with each other, and are physically connected with each other as one body. Also, the second supporting member  615  is physically connected with a second panel rear portion of the flexible display panel  100  overlapped with the second display area (DA 2 ) of the flexible display panel  100 , whereby the second panel rear portion is maintained in the flat state. To this end, the second supporting member  615  may be formed of the same hard material as that of the first supporting member  613 , and the second supporting member  615  may be symmetrical to the first supporting member  613  with respect to the center of the bending portion (A). 
     The second supporting member  615  according to one example may include a second base plate  615   a  and a second inner protrusion  615   b.    
     The second base plate  615   a  is overlapped with the second display area (DA 2 ) of the flexible display panel  100 , wherein the second base plate  615   a  supports the second panel rear portion of the flexible display panel  100 . In this case, the second base plate  615   a  may be physically connected with the second panel rear portion by the use of adhesive member (not shown). An inner lateral side of the second base plate  615   a  which directly confronts the second outer protrusion  611   c  of the bending member  611  is physically connected with a lateral side of the second outer protrusion  611   c.    
     The second inner protrusion  615   b  is prepared at an inner lateral side of the second base plate  615   a , overlapped with the second outer protrusion  611   c  of the bending member  611 , and physically connected with the upper surface of the second outer protrusion  611   c  and the other side of the body  611   a . The second inner protrusion  615   b , which protrudes toward the bending member  611 , has a predetermined length from the inner lateral side of the second base plate  615   a , and more particularly, an upper portion of an inner short side of the second base plate  615   a , and then the protruding second inner protrusion  615   b  is overlapped with the second outer protrusion  611   c  of the bending member  611 . In this case, the second inner protrusion  615   b  and the second outer protrusion  611   c  may have the same length. 
     The first supporting member  615  according to one example may further include third and fourth rounding portions (R 3 , R 4 ) prepared at corners of the second inner protrusion  615   b  connected with the bending member  611 . 
     The third rounding portion (R 3 ) is prepared with a predetermined curvature at the corner between the second base plate  615   a  and the second inner protrusion  615   b . The fourth rounding portion (R 4 ) is prepared with a predetermined curvature at the corner of the second inner protrusion  615   b  corresponding to the corner between the body  611   a  of the bending member  611  and the second outer protrusion  611   c . The third and fourth rounding portions (R 3 , R 4 ) increase the attachment area between the bending member  611  and the second supporting member  615  formed of the different materials to enhance an adhesive strength between the bending member  611  and the second supporting member  615 . 
     Additionally, the panel supporting frame  600  according to the first embodiment of the present invention may further include a plurality of first to fourth bosses  613   c ,  615   c ,  613   d  and  615   d.    
     The first boss  613   c  protrudes out of the first supporting member  613  and supports one side of the bending member  611 . That is, the plurality of first bosses  613   c , which pass through the first outer protrusion  611   b  of the bending member  611 , are provided at fixed intervals in the lower surface of the first inner protrusion  613   b . The plurality of first bosses  613   c  protrude out of the lower surface of the first outer protrusion  611   b , wherein each of the plurality of first bosses  613   c  may have a cylinder shape. Each of the plurality of first bosses  613   c  may include a screw hole prepared in the center at its lower end. According as the plurality of first bosses  613   c  vertically penetrate through the first outer protrusion  611   b  of the bending member  611 , each of the plurality of first bosses  613   c  serves as a folding reference point to make the bending member  611  and/or first supporting member  613  folded without twists when the panel supporting frame  610  is folded. Also, each of the plurality of first bosses  613   c  is connected with the first panel supporting portion  230  of the first rear cover  200  by a coupling member (not shown) such as a screw coupled with the screw hole, whereby the inner lateral side of the first supporting member  613  is connected with the first panel supporting portion  230  of the first rear cover  200 . To this end, the first panel supporting portion  230  of the first rear cover  200  is provided with a plurality of first screw through holes  262  overlapped with the plurality of first bosses  613   c.    
     The second boss  615   c  protrudes out of the second supporting member  615  and supports the other side of the bending member  611 . That is, the plurality of second bosses  615   c , which pass through the second outer protrusion  611   c  of the bending member  611 , are provided at fixed intervals in the lower surface of the second inner protrusion  615   b . The plurality of second bosses  615   c  protrude out of the lower surface of the second outer protrusion  611   c , wherein each of the plurality of second bosses  615   c  may have a cylinder shape. Each of the plurality of second bosses  615   c  may include a screw hole prepared in the center at its lower end. According as the plurality of second bosses  615   c  vertically penetrate through the second outer protrusion  611   c  of the bending member  611 , each of the plurality of second bosses  615   c  serves as a folding reference point to make the bending member  611  and/or second supporting member  615  folded without twists when the panel supporting frame  610  is folded. Also, each of the plurality of second bosses  615   c  is connected with the second panel supporting portion  330  of the second rear cover  300  by a coupling member (not shown) such as a screw coupled with the screw hole, whereby the inner lateral side of the second supporting member  615  is connected with the second panel supporting portion  330  of the second rear cover  300 . To this end, the second panel supporting portion  330  of the second rear cover  300  is provided with a plurality of second screw through holes  362  overlapped with the plurality of second bosses  615   c.    
     The plurality of third bosses  613   d  protrude from the first supporting member  613 . That is, the plurality of third bosses  613   d  are vertically prepared at fixed intervals from the lower portion of the outer lateral side of the first base plate  613   a . Each of the plurality of third bosses  613   d  may have a cylinder shape. Each of the plurality of third bosses  613   d  may include a screw hole prepared in the center at its lower end. Each of the plurality of third bosses  613   d  is connected with the first bottom portion  210  of the first rear cover  200  by a coupling member (not shown) such as a screw coupled with the screw hole, whereby the outer lateral side of the first supporting member  613  is connected with the first bottom portion  210  of the first rear cover  200 . To this end, the first bottom portion  210  of the first rear cover  200  is provided with a plurality of third screw through holes  264  overlapped with the plurality of third bosses  613   d.    
     The plurality of fourth bosses  615   d  protrude from the second supporting member  615 . That is, the plurality of fourth bosses  615   d  are vertically prepared at fixed intervals from the lower surface of the outer lateral side of the second base plate  615   a . Each of the plurality of fourth bosses  615   d  may have a cylinder shape. Each of the plurality of fourth bosses  615   d  may include a screw hole prepared in the center at its lower end. Each of the plurality of fourth bosses  615   d  is connected with the second bottom portion  310  of the second rear cover  300  by a coupling member (not shown) such as a screw coupled with the screw hole, whereby the outer lateral side of the second supporting member  615  is connected with the second bottom portion  310  of the second rear cover  300 . To this end, the second bottom portion  310  of the second rear cover  300  is provided with a plurality of fourth screw through holes  364  overlapped with the plurality of fourth bosses  615   d.    
     The bending member  611  and the first and second supporting member  613  and  615  may be formed as one body by an insert injection method or double injection method using both soft and hard materials. Accordingly, in case of the panel supporting frame  600  according to the embodiment of the present invention, the first and second supporting members  613  and  615  formed of the hard material are overlapped with and connected with both sides of the bending member  611  formed of the soft material, thereby providing a soft material portion M 1 , a heterogeneous material portion M 2  and a hard material portion M 3 . 
     The soft material portion M 1  is a single material portion defined by the body  611   a  of the bending member  611 , wherein the soft material portion M 1  for supporting the bending display area BDA of the flexible display panel  100  is bent in accordance with the bending of the bending display area BDA. 
     The heterogeneous material portion M 2  corresponds to a combined portion of the soft material and the hard material, that is, an overlapped portion between the bending member  611  and each of the first and second supporting members  613  and  615 . The heterogeneous material portion M 2  minimizes a sense of difference in the touch on the boundary between the soft material and the hard material, and also increases an attachment area between the soft material and the hard material to enhance formability and adhesiveness between the soft material and the hard material. 
     The hard material portion M 3  is a single material portion defined by the base plates  613   a  and  615   a  of the first and second supporting members  613  and  615 , wherein the hard material portion M 3  secures hardness of the flexible display panel  100  and maintains flatness of the flexible display panel  100 . 
     In case of the panel supporting frame  600  according to one embodiment of the present invention, the attachment area between the bending member  611  and the supporting members  613  and  615  is largely increased owing to the connection portion formed by overlapping and connecting the bending member  611  of the soft material and each of the first and supporting member  613  and  615  of the hard material, whereby it is possible to prevent the bending member  611  and the supporting members  613  and  615  from being separated from each other even in case of the repetitive folding and unfolding. Also, the panel supporting frame  600  according to one embodiment of the present invention is physically connected with the lower surface of the flexible display panel  100  so that it is possible to maintain hardness of the flexible display panel  100 , to stably protect the flexible display panel  100  even when the flexible display panel  100  is repetitively folded, to maintain the bending curvature of the bending display area BDA when the flexible display panel  100  is folded, and to maintain the flexible display panel  100  in the flat state by the stable supporting of the bending display area BDA when the flexible display panel  100  is unfolded. The panel supporting frame  600  according to one embodiment of the present invention is physically connected with and formed as one body with the lower surface of the flexible display panel  100  except the bending display area BDA so that it is possible to facilitate a transfer of the flexible display panel  100 , and to improve an assembly between the flexible display panel  100  and the housing. 
       FIG. 16  shows a folding state of the panel supporting frame according to one embodiment of the present invention. 
     Referring to  FIG. 16 , in case of the panel supporting frame  600  according to one embodiment of the present invention, the first and second supporting members  613  and  615  of the hard material are respectively overlapped with and connected with both sides of the bending member  611  of the soft material, whereby the flexible display panel  100  is bent in an inside bending method through the bending of the bending member  611 . In this case, the inside bending method indicates that the first and second display areas DA 1  and DA 2  directly confront each other when the flexible display panel  100  is folded. For example, according as the first and second rear covers  200  and  300  are folded, the second supporting member  615  is folded onto the first supporting member  613  by the inside bending of the bending member  611  so that the bending display area BDA of the flexible display panel  100  is bent with the predetermined curvature, and the first and second display areas DA 1  and DA 2  of the flexible display panel  100  directly confront each other. 
     The bosses  613   c  and  615   c  prepared in the first and second supporting members  613  and  615  make the flexible display panel  100  folded without twists when the flexible display panel  100  is folded. When the flexible display panel  100  is folded, the interval between the adjacent slits prepared in the length compensation pattern  611   d  of the bending member  611  is increased in accordance with a tensile force occurring in the lower surface of the bending member  611  so that a length change of the bending member  611  is compensated, and thus the bending display area BDA of the flexible display panel  100  is bent in accordance with the smooth curvature without wrinkles. 
     Accordingly, the foldable display apparatus according to another embodiment of the present invention may have the same effect as that of the foldable display apparatus according to one embodiment of the present invention. Especially, the panel supporting frame  600  for supporting the flexible display panel  100  is connected with the first and second rear covers  200  and  300  so that it is possible to minimize a sense of difference in the touch on the display areas DA 1  and DA 2  and the bending display area BDA of the flexible display panel  100 , to reinforce hardness of the flexible display panel  100  by the use of panel supporting frame  600 , and also to maintain the flat state of the bending display area BDA in the folded flexible display panel. 
     According to the present invention, the flexile display panel is folded and unfolded without bending according as the interval between each of the plurality of rear hinge covers engaged and connected with each other is changed in accordance with the folding or unfolded state of the flexible display panel to improve reliability of the flexible display panel. 
     Also, the folded flexible display panel is unfolded in the flat state according to the elastic restoring force of the plurality of elastic axis members so that it is possible to improve a user&#39;s ease for folding and unfolding processes of the flexible display panel. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.