Patent Publication Number: US-10334750-B2

Title: Flexible frame and flexible display unit having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Pursuant to 35 U.S.C. § 119(a), this application claims the benefit of earlier filing date and right of priority to Korean Application No. 10-2017-0144868, filed on Nov. 1, 2017, the contents of which are hereby incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to a flexible frame configured to be elastically deformable between a flat state and a bent state at a maximum curvature, and a flexible display unit having the same. 
     2. Description of the Related Art 
     A portable electronic device (hereinafter, mobile terminal) such as a communication terminal, a multimedia device, a portable computer, a game machine, and a photographing apparatus has a display for displaying image information. The mobile terminal may have a folding structure that can be folded to a smaller size for convenience of carrying. In this type of mobile terminal, two bodies are connected by a folding structure (for example, a hinge portion). 
     Displays in the related art have a non-foldable structure, and thus a structure in which a display is disposed over two whole bodies that are foldably connected to each other cannot be implemented. Therefore, a substantially large screen cannot be applied to a mobile terminal with a folding structure. 
     However, in recent years, as a flexible display capable of bending has been developed, research has been carried out to apply a flexible display to a mobile terminal having a folding structure. In this case, a flexible display may be disposed over two whole bodies across a folding structure, thereby implementing a large screen. However, even with a flexible display capable of bending, the flexible display itself may be broken when it is completely bent (i.e., bent angularly), and thus a structure capable of limiting a curvature radius of the flexible display when folding the mobile terminal is required. 
     In order to allow the flexible display to be bent at a preset curvature, a structure in which a flexible frame is laminated with a flexible display is used. However, flexible frames developed until now has only a structure in which one portion thereof can be curved at a specific curvature, but a structure in which two adjacent portions are connected smoothly while being configured to allow bending at different maximum curvatures has not been proposed. 
     In particular, when the two adjacent portions have different curvatures, a breakage of the flexible display may occur due to a change in curvature at the boundary. Therefore, studies on a flexible frame capable of smoothly connecting two adjacent portions having different curvatures have been carried out. 
     On the other hand, stainless steel is generally used as the flexible frame. However, stainless steel is not an optimal material from the viewpoint of restoration because the yield strain is not so large. In particular, in the case of a flexible frame made of stainless steel, when the flexible display is bent, it may not be flattened again, thereby causing a problem in which a surface of the flexible display undulates like a wave. 
     In addition, when an impact is applied to the flexible display in case where the flexible frame is formed of a metal material, the flexible frame may not absorb the impact, thereby causing a problem in which the flexible display is damaged. 
     SUMMARY OF THE INVENTION 
     A first object of the present disclosure is to provide a flexible frame laminated with a flexible display to bend two adjacent portions of the flexible display at different maximum curvatures in accordance with shape deformation. 
     A second object of the present disclosure is to provide a design method capable of adjusting a degree of bending and a repulsive force of the flexible frame. 
     A third object of the present disclosure is to provide a flexible frame capable of smoothly connecting two adjacent portions having different curvatures of a flexible display. 
     A fourth object of the present disclosure is to provide a flexible frame capable of restoring a flexible display to a flat state even when the bending and restoration of the flexible display are repeated, thereby allowing the flexible display to be flattened all the time. 
     A fifth object of the present disclosure is to provide a laminated structure of a flexible display and a flexible frame capable of absorbing an impact applied to the flexible display. 
     In order to accomplish the first object of the present disclosure, a flexible frame may be provided with a flexible region, and the flexible region may include a first flexible portion having first holes formed repeatedly and bendable up to a state having a maximum first curvature; and a second flexible portion having second holes formed repeatedly in parallel to the first holes, and bendable up to a state having a maximum second curvature, wherein a total area occupied by the first holes per unit area in the first flexible portion is larger than a total area occupied by the second holes per unit area in the second flexible portion, so that the first curvature is larger than the second curvature. 
     The first holes may be repeatedly formed along a widthwise direction and a lengthwise direction of the flexible region which intersect with each other, wherein the second holes are repeatedly formed along the widthwise direction and the lengthwise direction of the flexible region which intersect each other. 
     The first holes may be arranged in a zigzag form while partially overlapping each other along the lengthwise direction of the flexible region, wherein the second holes are arranged in a zigzag form while partially overlapping each other along the lengthwise direction of the flexible region. 
     A length of each overlapped portion of the first holes may be longer than a length of each overlapped portion of the second holes. 
     The first holes and the second holes respectively may include a plurality of holes having the same size and spaced apart from one another at preset intervals. 
     The first holes and the second holes may further include respectively another hole having at least one of a size and a spaced interval different from those of the plurality of holes. 
     The second object of the present disclosure may be accomplished by adjusting a total area occupied by holes per unit area in each flexible portion. 
     The third object of the present disclosure may be accomplished by a connecting portion having third holes formed repeatedly between the first flexible portion and the second flexible portion in parallel to the first and second holes. 
     A total area occupied by the third holes per unit area in the connecting portion may be smaller than the total area occupied by the first holes per unit area in the first flexible portion and larger than the total area occupied by the second holes per unit area in the second flexible portion. 
     A length of each of the third holes may be shorter than a length of the first hole and longer than a length of the second hole. 
     The length of each of the third holes may gradually decrease from the first flexible portion toward the second flexible portion. 
     The third holes may be arranged in a zigzag form while partially overlapping each other along the lengthwise direction of the flexible region, and wherein a length of each overlapped portion of the third holes may be shorter than a length of each overlapped portion of the first holes and longer than a length of each overlapped portion of the second holes. 
     A length of each overlapped portion of the third holes may gradually decrease from the first flexible portion toward the second flexible portion. 
     The third object of the present disclosure may be accomplished by a boundary portion having fourth holes formed repeatedly between the second flexible portion and a rigid portion, the rigid portion located on one side of the second flexible portion. 
     A total area occupied by the fourth holes per unit area in the boundary portion is smaller than the total area occupied by the second holes per unit area in the second flexible portion. 
     A length of each of the fourth holes may be shorter than a length of the second hole. 
     A length of a hole of the fourth holes, the hole adjacent to the rigid portion, may be shorter than a length of another hole of the fourth holes, the another hole adjacent to the second flexible portion. 
     The fourth holes may be arranged in a zigzag form while partially overlapping each other along the lengthwise direction of the flexible region, wherein a length of each overlapped portion of the fourth holes is shorter than a length of each overlapped portion of the second holes. 
     In order to accomplish the fourth object of the present disclosure, a flexible display unit of the present disclosure may include a flexible display formed to be elastically deformed; and a flexible frame coupled to a rear surface of the flexible display, wherein the flexible frame includes a flexible portion in which first holes are repeatedly formed to be bendable up to a state having a maximum first curvature; and a rigid portion disposed on at least one side of the flexible portion, and the flexible frame is formed of a titanium material. 
     When the flexible display is deformed, an interval between the first holes may be enlarged or reduced to apply a restoring force to the flexible display. 
     An adhesive portion may be disposed between the flexible display and the flexible frame, and a part of the adhesive portion may be exposed rearward through the first holes. 
     In order to accomplish the fifth object of the present disclosure, the flexible display unit of the present disclosure may include an adhesive portion disposed on a rear surface of the flexible display; and a silicon portion disposed between the adhesive portion and the flexible frame, wherein the silicon portion includes a first portion disposed on the flexible portion and the rigid portion; and a second portion filled in the first holes. 
     The second portion may form the same plane as the rear surface of the flexible frame. 
     The silicon portion may be integrally formed with the flexible frame by insert injection. 
     Alternatively, the flexible display unit of the present disclosure may further include an adhesive portion disposed between the flexible display and the flexible frame; and a silicon portion filled in the first holes. 
     The silicon portion may be brought into contact with a part of the adhesive portion exposed through the first holes. 
     The silicon portion may form the same plane as the rear surface of the flexible frame. 
     The silicon portion may be integrally formed with the flexible frame by insert injection. 
     On the other hand, the present disclosure may include a flexible display formed to be elastically deformed; and a flexible frame coupled to a rear surface of the flexible display, wherein the flexible frame includes a first flexible portion in which first holes are repeatedly formed to be bendable up to a state having a maximum first curvature; a second flexible portion in which second holes parallel to the first holes are repeatedly formed on one side of the first flexible portion, and configured to be bendable up to a state having a maximum second curvature; and a third flexible portion in which third holes parallel to the first holes are repeatedly formed on the other side of the first flexible portion, and configured to be bendable up to a state having a maximum third curvature; and wherein the first curvature is at least two times the second and third curvatures. 
     Moreover, the present disclosure discloses a mobile terminal, including a terminal body formed of an elastically deformable material, a flexible display unit coupled to one surface of the terminal body and configured to be elastically deformable together with the terminal body; and magnet portions provided at both ends of the terminal body disposed to face each other in a state where the first to third flexible portions are bent at the first to third curvatures, respectively, to exert attractive forces on each other. 
     The effects of the present disclosure obtained through the above-mentioned solution are as follows. 
     First, a total area occupied by the first holes per unit area in the first flexible portion is designed to be larger than a total area occupied by the second holes per unit area in the second flexible portion, thereby implementing a flexible frame that is bendable at a larger curvature in the first flexible portion than the second flexible portion. Therefore, the flexible frame may be laminated with a flexible display, thereby implementing a flexible display unit in which two adjacent portions are bent at different maximum curvatures. 
     Second, since a repulsive force to be restored increases as increasing a degree of bending, and a total area occupied by the holes per unit area in each flexible portion may be adjusted to adjust a degree of bending and a repulsive force of the flexible display unit. 
     Third, a connecting portion may be formed between two flexible portions that is bendable at different maximum curvatures or a boundary portion may be formed between a flexible portion and a rigid portion, thereby implementing a flexible display unit in which two adjacent portions having different curvatures are connected smoothly. 
     Fourth, when titanium having a lower yield strength compared to stainless steel but having a predetermined level of yield strength and a large yield strain is used for a flexible frame, the flexible display may be restored to a flat state all the time, thereby preventing the phenomenon of undulating like a wave. Therefore, the reliability of the flexible display unit can be improved. 
     Fifth, since a silicon portion may be provided between the flexible display and the flexible frame to elastically support the flexible display, thereby absorbing an impact transmitted to the flexible display at a predetermined level. Moreover, since the silicon portion is filled in the holes of the flexible frame, a restoring force of the silicon portion may be added to a restoring force of the flexible frame itself, thereby increasing a total restoring force. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
       In the drawings: 
         FIG. 1  is a view showing an example of a flexible frame of the present disclosure; 
         FIG. 2  is a conceptual view showing a state in which each flexible portion of the flexible frame shown in  FIG. 1  is bent at a maximum curvature; 
         FIG. 3  is a conceptual view showing a Y direction area change of the flexible frame shown in  FIG. 1 ; 
         FIG. 4  is an enlarged view of a flexible region shown in  FIG. 1 ; 
         FIG. 5  is an enlarged view of a first flexible portion shown in  FIG. 4 ; 
         FIG. 6  is a conceptual view for explaining an X direction arrangement form of holes applied to the first flexible portion shown in  FIG. 5 ; 
         FIG. 7  is a conceptual view for explaining an X direction arrangement form of holes applied to the first flexible portion shown in  FIG. 5 ; 
         FIG. 8  is a conceptual view for explaining that the first flexible portion shown in  FIG. 5  can have a symmetrical shape with respect to the X and Y axes; 
         FIG. 9  is an enlarged view of a connecting portion shown in  FIG. 4 ; 
         FIG. 10  is a conceptual view showing an example of a boundary portion shown in  FIG. 4 ; 
         FIG. 11  is a conceptual view showing another example of a boundary portion shown in  FIG. 4 ; 
         FIG. 12  is a conceptual view showing an example of a flexible display unit having a flexible frame according to the present disclosure; 
         FIG. 13  is a conceptual view showing another example of a flexible display unit having a flexible frame according to the present disclosure; 
         FIG. 14  is a conceptual view showing still another example of a flexible display unit having a flexible frame according to the present disclosure; 
         FIG. 15  is a conceptual diagram for explaining a restoring mechanism of a flexible display unit by combining a flexible display with a flexible frame according to the present disclosure; 
         FIG. 16  is a conceptual view illustrating an example of a mobile terminal to which a flexible display unit having the flexible frame shown in  FIG. 1  is applied; 
         FIG. 17  is a view showing another example of a flexible frame of the present disclosure; 
         FIG. 18  is a conceptual view showing a state in which a flexible portion of the flexible frame shown in  FIG. 17  is bent at a maximum curvature; 
         FIG. 19  is a conceptual view showing a Y direction area change of the flexible frame shown in  FIG. 17 ; 
         FIG. 20  is an enlarged view of a flexible region shown in  FIG. 17 ; 
         FIG. 21  is a conceptual view illustrating an example of a mobile terminal to which a flexible display unit having the flexible frame shown in  FIG. 17  is applied; 
         FIG. 22  is a conceptual view showing an example of a mobile terminal to which a flexible display unit having another example of the flexible frame of the present disclosure is applied; and 
         FIG. 23  is a conceptual view showing still another example of a flexible frame of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, a flexible frame according to the present invention and a flexible display unit having the same will be described in detail with reference to the drawings. 
     In describing the embodiments disclosed herein, moreover, the detailed description will be omitted when a specific description for publicly known technologies to which the invention pertains is judged to obscure the gist of the present invention. 
     The accompanying drawings are used to help easily understand various technical features and it should be understood that the embodiments presented herein are not limited by the accompanying drawings. As such, the present disclosure should be construed to extend to any alterations, equivalents and substitutes in addition to those which are particularly set out in the accompanying drawings. 
     In the following description, a singular representation may include a plural representation as far as it represents a definitely different meaning from the context. 
       FIG. 1  is a view showing an example of a flexible frame  100  of the present disclosure, and  FIG. 2  is a conceptual view showing a state in which each flexible portion of the flexible frame  100  shown in  FIG. 1  is bent at a maximum curvature, and  FIG. 3  is a conceptual view showing a Y direction area change of the flexible frame  100  shown in  FIG. 1 , and  FIG. 4  is an enlarged view of a flexible region  110  shown in  FIG. 1 . 
     In the following description, the X direction corresponds to a widthwise direction of the flexible frame  100 , and the Y direction corresponds to a lengthwise direction of the flexible frame  100 . 
     Referring to  FIGS. 1 to 4 , the flexible frame  100  includes the flexible region  110  that is bendable at least at a maximum curvature. The flexible region  110  may include flexible portions that is bendable at different maximum curvatures. The flexible portions may be sequentially disposed along one direction (Y direction in the drawing) of the flexible frame  100 , so that the flexible frame  100  can be bent with respect to one direction. 
     In this example, the flexible region  110  includes a first flexible portion  111  that is bendable up to a state having a maximum first curvature and a second flexible portion  112  that is bendable up to a state having a maximum second curvature. As shown in the drawing, two second flexible portions  112  may be provided, and disposed on both sides of the first flexible portion  111  in the Y direction. 
     First holes  111 ′ are repeatedly formed on the first flexible portion  111  to implement the bending of the first flexible portion  111 . In other words, flexibility may be generated on the first flexible portion  111  due to the first holes  111 ′, and the first flexible portion  111  may be bent up to a state having the maximum first curvature. 
     The first holes  111 ′ are repeatedly formed along the X and Y directions intersecting each other. The first holes  111 ′ are elongated in the X direction. 
     Similarly, second holes  112 ′ are repeatedly formed on the second flexible portion  112  to implement the bending of the second flexible portion  112 . In other words, flexibility may be generated on the first flexible portion  112  due to the first holes  112 ′, and the first flexible portion  112  may be bent up to a state having the maximum first curvature. Here, the second curvature has a curvature different from the first curvature. 
     The second holes  112 ′ are formed parallel to the first holes  111 ′ so that the second flexible portion  112  can be bent with respect to the Y direction together with the first flexible portion  111 . The second holes  112 ′ are respectively formed in a repetitive manner along the X and Y directions intersecting each other. The second holes  112 ′ are extended in an elongated manner in the X direction. 
     In this example, the first curvature is greater than the second curvature. In other words, the first flexible portion  111  is configured to be more bendable than the second flexible portion  112 . Therefore, while the first and second flexible portions  111 ,  112  are bent at the first and second curvatures, respectively, a repulsive force acting on the first flexible portion  111  is greater than that acting on the second flexible portion  112 . 
     In  FIG. 2 , it is shown that the first and second flexible portions  111 ,  112  are bent to the maximum. Since the reciprocal of the curvature is a curvature radius, a curvature radius (R 1 ) of the first flexible portion  111  is smaller than a curvature radius (R 2 ) of the second flexible portion  112  in this state. The center (O) of the curvature radius (R 1 ) of the first flexible portion  111  is located in an inner space formed by the folding of the flexible frame  100 , and the center (O′, O″) of the curvature radius of the second flexible portion  112  is located in an outer space formed by the folding of the flexible frame  100 . 
     A rigid portion  120  is disposed on one side of each second flexible portion  112  in the Y direction. The rigid portion  120 , as a portion that is hardly bent by an external force, may be formed in a plane. The rigid portion  120  is not formed with holes intended to implement bending. 
     As described above, the rigid portion  120  and the first flexible portion  111  are disposed on both sides of the second flexible portion  112  in the Y direction. In a state where the first and second flexible portions  111 ,  112  are bent to the maximum, the rigid portions  120  are arranged to face each other. 
     Referring to  FIG. 3 , the larger a total area occupied by the holes per unit area (or a particular area) of the flexible portion, the more flexible the flexible portion becomes. In other words, the smaller a total area occupied by an inherently rigid material per unit area of the flexible portion, the more flexible the flexible portion becomes. It means that a maximum curvature of the flexible portion can be adjusted by changing a total area occupied by the holes per unit area of the flexible portion at design time. 
     In this manner, a total area occupied by the first holes  111 ′ per unit area in the first flexible portion  111  is greater than a total area occupied by the second flexible portions  111  per unit area in the second flexible portion  111  so that the first flexible portion  111  is more bendable than the second flexible portion  112 . 
     As described above, the second flexible portion  112  is disposed on both sides of the first flexible portion  111 , respectively, in the Y direction, and the rigid portion  120  is provided on one side of each second flexible portion  112  in the Y direction. 
     A connecting portion  113  for smoothly connecting the first flexible portion  111  and the second flexible portion  112  is formed between the first flexible portion  111  and the second flexible portion  112 . Similarly, a boundary portion  114  for smoothly connecting the first flexible portion  112  and the second flexible portion  120  is formed between them. 
     In other words, the rigid portion  120 , the boundary portion  114 , the second flexible portion  112 , the connecting portion  113 , the first flexible portion  111 , the connecting portion  113 , the second flexible portion  112 , the boundary portion  114 , and the rigid portion  120  are sequentially arranged on the flexible frame  100 . 
     Hereinafter, each of the portions will be described in more detail. 
     For reference, only the first flexible portion  111  and the second flexible portion  112  are formed in such a manner that a total area occupied by the first holes  111 ′ per unit area is larger than a total area occupied by the second holes  112 ′, but there is substantially no difference in the arrangement of the first hole  111 ′ and the second hole  112 ′. Therefore, the description of the first flexible portion  111  with reference to  FIGS. 5 to 8  below may be applied as it is to the second flexible portion  112  as it is. 
       FIG. 5  is an enlarged view of the first flexible portion  111  shown in  FIG. 4 . 
     Referring to  FIG. 5 , the first holes  111 ′ formed in the first flexible portion  111  are repeatedly formed along the X and Y directions intersecting each other. The first holes  111 ′ formed in the first flexible portion  111  are formed in an elongated manner in the X direction so that the first flexible portion  111  is bendable with respect to the Y direction. 
     The first holes  111 ′ may be formed in a recessed shape at both end portions of the flexible frame  100  in the X direction. The first holes  111 ′ having such a shape may be formed one by one along the Y direction. 
     The first holes  111 ′ are arranged in a zigzag manner while partially overlapping each other along the Y direction. As shown in the drawing, the first holes  111 ′ arranged along the X direction are disposed directly in the Y direction above or below a region between the first holes  111 ′ arranged along the X direction (a region where an inherent material of the rigid flexible frame  100  remains, hereinafter referred to as a “link”). 
     As described above, the second holes  112 ′ having the same shape as the first holes  111 ′ formed on the first flexible portion  111  may be also formed on the second flexible portion  112 . However, a length of a mutually overlapping portion between the second holes  112 ′ is designed to be shorter than that of a mutually overlapping portion between the first holes  111 ′. 
     A repulsive force per unit area of the link may be calculated by the following equation. 
     
       
         
           
             T 
             = 
             
               
                 θ 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   GJ 
                   ′ 
                 
               
               l 
             
           
         
       
     
     T=Repulsive force (Torque) (Nm) 
     l=Length (m) where holes are overlapped along the Y direction 
     G=Modulus of rigidity (N/m2) 
     J′=Polar moment of inertia (m4) 
     θ=Bent angle per link (radians) 
     
       
         
           
             θ 
             = 
             
               
                 Θ 
                 ⁡ 
                 
                   ( 
                   Total 
                   ) 
                 
               
               n 
             
           
         
       
     
     n=Number of links formed along the Y direction 
     Θ(Total)=Angle bent to the maximum (radians) 
     In other words, as an overlapping length of the holes increases along the Y direction, a repulsive force decreases, and as a bent angle of per link increases, a repulsive force increases. 
     As a result of the simulation, a bent angle per link in the first flexible portion  111  is overwhelmingly larger than a bent angle per link in the second flexible portion  112  (approximately 20 times), and thus it can be seen that a larger repulsive force acts on the first flexible portion  111  though a length where the holes are overlapped along the Y direction is shorter in the first flexible portion  111 . 
     On the other hand, since the links are arranged along the X direction, the repulsive force increases in proportion to a number of the arranged links. In this example, since the number of links arranged in the X direction is the same for both the first flexible portion  111  and the second flexible portion  112 , it can be seen that there is no great influence on the mutual comparison of the repulsive forces is. 
       FIG. 6  is a conceptual view for explaining the X direction arrangement of the first holes  111 ′ applied to the first flexible portion  111  shown in  FIG. 5 . 
     Referring to  FIG. 6A , the first holes  111 ′ may include a plurality of holes  111 ′ a  arranged at preset intervals along the X direction while having the same width (X direction). 
     As shown in the drawing, each of the plurality of holes  111 ′ a  may have a width (A) and may be spaced apart from each other with a spacing interval (B) therebetween. As described above, the plurality of holes  111 ′ a  may have a repeated shape according to a constant reference (width and spacing interval). 
     In some embodiments, the flexible portions may include perforations to allow for bending of the frame which do not correspond to fully defined holes or openings. For example, a perforation may correspond to a puncture in a particular pattern where the material of the flexible frame is punctured or cut to allow for flexing of the frame at the puncture or cut location. The perforation may not correspond to any material removed from the frame, and the material of the frame may be left attached where the puncture or cut is located. Other embodiments may include a combination of an opening or a hole where material of the frame is actually removed (or formed to not include such portions) along with a perforation or cut of the material adjacent to the opening or hole. In other embodiments, an opening or hole may have a concave portion, where the material of the frame juts into the opening or hole area to define a “dent” in the opening or hole. It will be appreciated that all of these various embodiments are considered in this disclosure and may be combinable with any other configuration discussed herein. 
     Referring to  FIG. 6B , the first holes  111 ′ may further include a hole  111 ′ b  that is different in at least one of width and spacing interval from the plurality of holes  111 ′ a.    
     As shown in the drawing, at least one hole  111 ′ b  that is different in at least one of width and spacing from the plurality of holes  111 ′ a  may be added between the plurality of holes  111 ′ a  having a width (A) and being spaced apart from each other with a spacing interval (B) therebetween. The added hole  111 ′ b  has a width (A′), and the width (A′) has a value smaller or larger than the width (A). Furthermore, a spacing interval (B′) between the added hole  111 ′ b  and one of the plurality of holes  111 ′ a  repeatedly disposed adjacent thereto according to a predetermined reference has a value smaller or larger than the spacing distance (B). 
     In this drawing, it is seen that a hole  111 ′ b  having a left-right spacing interval (B′) and a width (A′) is added between a plurality of holes  111 ′ a  repeatedly arranged according to a predetermined reference. The left and right spacing intervals may be of course set differently from each other. 
     By adding the holes described above, the maximum curvature or repulsive force of the first flexible portion  111  may be adjusted. For example, when the spacing interval (B′) is increased beyond the spacing interval (B) or the width (A′) is reduced from the width (A), the maximum curvature of the first flexible portion  111  may be reduced, and accordingly the repulsive force acting thereon may be reduced. On the contrary, when the spacing interval (B′) is reduced from the spacing interval (B) or the width (A′) is increased beyond the width (A), the maximum curvature of the first flexible portion  111  may be increased, and accordingly the repulsive force acting thereon may be increased. 
       FIG. 7  is a conceptual view for explaining the Y direction arrangement of the first holes  111 ′ applied to the first flexible portion  111  shown in  FIG. 5 . 
     Referring to  FIG. 7A , the first holes  111 ′ may include a plurality of holes  111 ′ c  arranged at preset intervals along the Y direction while having the same length (Y direction). 
     As shown in the drawing, each of the plurality of holes  111 ′ c  may have a length (C) and may be spaced apart from each other with a spacing interval (D) therebetween. As described above, the plurality of holes  111 ′ c  may have a repeated shape according to a constant reference (length and spacing interval). 
     Referring to  FIG. 7B , the first holes  111 ′ may further include a hole  111 ′ d  that is different in at least one of length and spacing interval from the plurality of holes  111 ′ c.    
     As shown in the drawing, a hole  111 ′ d  that is different in at least one of length and spacing interval from the plurality of holes  111 ′ c  may be added between the plurality of holes  111 ′ c  having a length (C) and being spaced apart from each other with a spacing interval (D) therebetween. The added hole  111 ′ d  has a length (C′) and the length C′ has a value smaller or larger than the length (C). Furthermore, a spacing interval (D′) between the added hole  111 ′ d  and one of the plurality of holes  111 ′ c  repeatedly disposed adjacent thereto according to a predetermined reference has a value smaller or larger than the spacing distance (D). 
     In this drawing, it is seen that a hole  111 ′ d  having a left-right spacing interval (D′) and a length (C′) is added between a plurality of holes  111 ′ c  repeatedly arranged according to a predetermined reference. The left and right spacing intervals may be of course set differently from each other. 
     By adding the holes described above, the maximum curvature or repulsive force acting on the first flexible portion  111  may be adjusted. For example, when the spacing interval (D′) is increased beyond the spacing interval (D) or the length (C′) is reduced from the length (C), the maximum curvature of the first flexible portion  111  may be reduced, and accordingly the repulsive force acting thereon may be reduced. On the contrary, when the spacing interval (D′) is reduced from the spacing interval (D) or the length (C′) is increased beyond the length (C), the maximum curvature of the first flexible portion  111  may be increased, and accordingly the repulsive force acting thereon may be increased. 
     In summary, the first and second holes  111 ′,  112 ′ include a plurality of holes arranged at the same size and at predetermined intervals. Here, the same size denotes that the width (X direction) and the length (Y direction) are the same. In some cases, a hole that is different in at least one of size or spacing interval from the plurality of holes may be added between the plurality of holes. 
       FIG. 8  is a conceptual view for explaining that the first flexible portion shown in  FIG. 5  can have a symmetrical shape with respect to the X and Y axes. 
     Referring to  FIG. 8 , the first flexible portion  111  may have a symmetrical shape with respect to an axis (X-axis) in the X direction passing through the center. Accordingly, in a state where the first flexible portion  111  is bent with respect to the Y direction, the first flexible portion  111  may have a symmetrical shape about the X-axis. 
     Similarly, the first flexible portion  111  may have a symmetrical shape with respect to an axis (Y-axis) in the Y direction passing through the center. Accordingly, in a state where the first flexible portion  111  is bent with respect to the Y direction, the first flexible portion  111  may maintain a uniform shape in the X direction. 
     When the first flexible portion  111  and the second flexible portion  112  are formed successively as the first flexible portion  111  and the second flexible portion  112  are configured to be bendable at different maximum curvatures, the flexible frame  100  may be damaged due to a change of curvature at the boundary. Hereinafter, a structure in which adjacent first and second flexible portions  111 ,  112  having different curvatures can be smoothly connected will be described. 
       FIG. 9  is an enlarged view of a connecting portion  113  shown in  FIG. 4 . 
     Referring to  FIG. 9 , the connecting portion  113  for smoothly connecting the first flexible portion  111  and the second flexible portion  112  is formed between the first flexible portion  111  and the second flexible portion  112 . Third holes  113 ′ parallel to the first and second holes  111 ′,  112 ′ are repeatedly formed on the connecting portion  113  so that the connecting portion  113  can be bent in the Y direction. The first holes  113 ′ are formed in an elongated manner in the X direction. 
     A degree of bending of the connecting portion  113  may be adjusted by changing a total area occupied by the third holes  113 ′ per unit area of the connecting portion  113  as described above with respect to the first and second flexible portions  111 ,  112 . 
     The connecting portion  113  is configured to be less bendable than the first flexible portion  111  and more bendable than the second flexible portion  112 . To this end, a total area occupied by the third holes  113 ′ per unit area in the connecting portion  113  is set to be smaller than a total area occupied by the first holes  111 ′ per unit area in the first flexible portion  111 , and larger than a total area occupied by the second holes  112 ′ per unit area in the flexible portion  112 . 
     For this purpose, a length of each of the third holes  113 ′ may be set to be smaller than that of the first holes  111 ′ and greater than that of the second holes  112 ′. Alternatively, a spacing interval between the third holes  113 ′ may be set to be larger than that between the first holes  111 ′ and smaller than that between the second holes  112 ′. 
     The third holes  113 ′ are arranged in a zigzag manner while partially overlapping each other along the Y direction. As shown in the drawing, the third holes  113 ′ arranged along the X direction are disposed in the Y direction directly above or below a region between the third holes  113 ′ arranged along the X direction (a region where an inherent material of the rigid flexible frame  100  remains). 
     Here, a length of a mutually overlapping portion between the third holes  113 ′ along the Y direction is set to be smaller than that of a mutually overlapping portion between the first holes  111 ′ and larger than that of a mutually overlapping portion between the second holes  112 ′. 
     The connecting portion  113  may be configured such that a degree of bending gradually decreases from the first flexible portion  111  to the second flexible portion  112 . In this case, a maximum curvature at one end portion of the connecting portion  113  adjacent to the first flexible portion  111  may be set to be larger than that at the other end portion of the connecting portion  113  adjacent to the second flexible portion  112 . In other words, the maximum curvature at one end portion of the connecting portion  113  may be set to be smaller than the first curvature, and the maximum curvature at the other end portion of the connecting portion  113  may be set to be larger than the second curvature. 
     For this purpose, a length of each of the third holes  113 ′ may be set to gradually decrease from the first flexible portion  111  to the second flexible portion  112 . Here, a degree of reduction of the length of the third holes  113 ′ may have a constant value (a). Alternatively, an interval spaced between the third holes  113 ′ may be set to gradually increase from the first flexible portion  111  to the second flexible portion  112 . Here, a degree of increase in the spacing interval between the third holes  113 ′ may have a constant value. 
     Moreover, a length of a mutually overlapping portion between the third holes  113 ′ may be set to gradually decrease from the first flexible portion  111  to the second flexible portion  112  in the Y direction. 
     Similarly to the connecting portion  113  for smoothly connecting the first flexible portion  111  and the second flexible portion  112 , a boundary portion  114  is provided even between the second flexible portion  112  and the rigid portion  120 . Hereinafter, a structure in which adjacent second flexible portion  112  and rigid portion  120  having different curvatures can be smoothly connected will be described. 
       FIG. 10  is a conceptual view showing an example of the boundary portion  114  shown in  FIG. 4 . 
     Referring to  FIG. 10 , the connecting portion  114  for smoothly connecting the second flexible portion  112  and the rigid portion  120  is formed between them. The fourth holes  114 ′ are repeatedly formed on the boundary portion  114  so that the boundary portion  114  can be bent in the Y direction. The fourth holes  114 ′ may be extended in an elongated manner in the X direction and disposed in parallel with the second holes  112 ′. 
     A degree of bending of the boundary portion  114  may be adjusted by changing a total area occupied by the fourth holes  114 ′ per unit area of the boundary portion  114  as described above with respect to the connecting portion  113 . 
     The boundary portion  114  is configured to be less bendable than second flexible portion  112 . For this purpose, a total area occupied by the fourth holes  114 ′ per unit area in the boundary portion  114  is set to be smaller than a total area occupied by the second holes  112 ′ per unit area in the second flexible portion  112 . 
     For this purpose, a length of each of the fourth holes  114 ′ may be set to be smaller than that of the second holes  112 ′. Alternatively, a spacing interval between the fourth holes  114 ′ may be set to be larger than that between the second holes  112 ′. 
     The fourth holes  114 ′ may be arranged in a zigzag manner while partially overlapping each other along the Y direction. As shown in the drawing, the fourth holes  114 ′ arranged along the X direction are disposed in the Y direction directly above or below a region between the fourth holes  114 ′ arranged along the X direction (a region where an inherent material of the rigid flexible frame  100  remains). 
     Here, a length of a mutually overlapping portion between the fourth holes  114 ′ along the Y direction is set to be smaller than that of a mutually overlapping portion of the second holes  112 ′. 
     A maximum curvature at one end portion of the boundary portion  114  adjacent to the second flexible portion  112  may be set to be larger than that at the other end portion of the boundary portion  114  adjacent to the rigid portion  120 . In other words, the maximum curvature at one end portion of the boundary portion  114  may be set to be smaller than the second curvature, and the maximum curvature at the other end portion of the boundary portion  114  may be set to be larger than zero. 
     For this purpose, a length of a hole adjacent to the second flexible portion  112  among the fourth holes  114 ′ may be set to be larger than that of a hole adjacent to the rigid portion  120 . Alternatively, a spacing interval between the fourth holes  114 ′ in a portion adjacent to the second flexible portion  112  may be set to be smaller than that between the fourth holes  114 ′ in a portion adjacent to the rigid portion  120 . 
       FIG. 11  is a conceptual view showing another example of the boundary portion  114  shown in  FIG. 4 . 
     Referring to  FIG. 11 , similarly to the previous example, the fourth holes  214 ′ are repeatedly formed on the boundary portion  214  so that the boundary portion  214  can be bent in the Y direction. The fourth holes  214 ′ may be extended in an elongated manner in the X direction and disposed in parallel with the second holes  212 ′. 
     The boundary portion  214  is configured to be less bendable than second flexible portion  212 . For this purpose, a total area occupied by the fourth holes  214 ′ per unit area in the boundary portion  214  is set to be smaller than a total area occupied by the second holes  212 ′ per unit area in the second flexible portion  212 . 
     However, the fourth holes  214 ′ for implementing this may be randomly arranged. In other words, the fourth holes  214 ′ may be randomly arranged under the condition that a total area occupied by the fourth holes  214 ′ per unit area in the boundary section  214  is set to be smaller than a total area occupied by the second holes  212 ′ per unit area in the second flexible portion  212 . 
     A maximum curvature at one end portion of the boundary portion  214  adjacent to the second flexible portion  212  may be set to be larger than that at the other end portion of the boundary portion  214  adjacent to the rigid portion  220 . In other words, the maximum curvature at one end portion of the boundary portion  214  may be set to be smaller than the second curvature, and the maximum curvature at the other end portion of the boundary portion  214  may be set to be larger than zero. 
     For this purpose, a total area occupied by the fourth holes  214 ′ per unit area at one end portion of the boundary portion  214  adjacent to the second flexible portion  212  may be set to be greater than a total area occupied by the fourth holes  214 ′ per unit area at the other end portion of the boundary portion  214  adjacent to the rigid portion  220 . In other words, a degree of bending of the boundary portion  214  may be adjusted in such a manner that a total area occupied by an inherent rigid material per unit area of the boundary portion  214  is greater at one end portion than at the other end portion of the boundary portion  214 . 
       FIG. 12  is a conceptual view showing an example of a flexible display unit  10  having the flexible frame  100  of the present disclosure. 
     Referring to  FIG. 12 , the flexible display unit  10  is formed in an elastically deformable manner, and includes a flexible display  11  and the foregoing flexible frame  100 . 
     The flexible display  11  is formed to be elastically deformable by an external force. The flexible display  11  may be configured to allow a touch input. 
     The flexible frame  100  is coupled to a rear surface of the flexible display  11 . The flexible display  11  is disposed to cover the rigid portion  120  and the flexible region  110  of the flexible frame  100 . Therefore, when the flexible region  110  is bent, the flexible display  11  is also bent, and when the flexible region  110  is restored, the flexible display  11  is also restored. 
     At least one or more flexible portions may be provided in the flexible region  110 . When a plurality of flexible portions are provided, they may be configured to be bendable up to a state having different maximum curvatures. 
     Various laminated structures may be applied to the flexible display  11  and the flexible frame  100 . For example, as shown in  FIG. 12 , the flexible display  11  and the flexible frame  100  may be coupled by a bonding portion  12  interposed therebetween. For the bonding portion  12 , an OCA (optically clear adhesive) may be used. In the above structure, a part of the bonding portion  12  is exposed through holes formed on the flexible portion in a rearward direction, that is, onto a rear surface of the flexible frame  100 . 
     According to the above structure, it is advantageous in that a laminated structure of the flexible display  11  and the flexible frame  100  may be implemented at a low cost, and a thickness of the flexible display unit  10  can be made slim. 
       FIG. 13  is a conceptual view showing another example of a flexible display unit  20  having the flexible frame  100  of the present disclosure. 
     Referring to  FIG. 13 , a bonding portion  22  is attached to a rear surface of the flexible display  21 . For the bonding portion  22 , an OCA (optically clear adhesive) may be used. 
     Between the bonding portion  22  and the flexible frame  100 , a silicon portion  23  with an elastically deformable material is disposed. The silicon portion  23  includes a first portion  23   a  disposed on the flexible region  110  and the rigid portion  120  and a second portion  23   b  filled between the holes  110 ′. Here, the first portion  23   a  and the second portion  23   b  are integrally formed. 
     The first portion  23   a  of the silicon portion  23  is provided between the flexible display  21  and the flexible frame  100  to elastically support the flexible display  21 . Therefore, an impact transmitted to the flexible display  21  may be absorbed to a determined level by the first portion  23   a.    
     The second portion  23   b  is exposed through the holes  110 ′ of the flexible region  110  in a rearward region, that is, onto a rear surface of the flexible frame  100 . As shown in the drawing, the second portion  23   b  may form the same plane as the rear surface of the flexible frame  100 . 
     The silicon portion  23  may be integrally formed with the flexible frame  100  by insert injection. The silicon part  23  is formed integrally with the flexible frame  100 , thereby allowing the silicon portion  23  to increase a restoring force of the flexible frame  100  itself. In other words, in this laminated structure, a restoring force of the flexible portion  100  acts on a restoring force of the silicon portion  23  at the same time. Therefore, this laminated structure has a larger restoring force compared to the laminated structure shown in  FIG. 12 . 
     In addition, the silicon portion  23  is configured to prevent the flexible frame  100  from being deformed by repeated bending. Therefore, according to this laminated structure, the reliability of the flexible frame  100  may be improved. 
       FIG. 14  is a conceptual view showing still another example of a flexible display unit  30  having the flexible frame  100  of the present disclosure. 
     Referring to  FIG. 14 , the flexible display  31  and the flexible frame  100  may be coupled by a bonding portion  32  interposed therebetween. For the bonding portion  32 , an OCA (optically clear adhesive) may be used. 
     The holes  110 ′ of the flexible region  110  are filled with a silicon portion  33  with an elastically deformable material. As shown in the drawing, the silicon portion  33  may be bought into contact with a portion of the bonding portion  32  exposed through the holes  110 ′. The silicon portion  33  may form the same plane as the rear surface of the flexible frame  100 . 
     The silicon portion  33  may be integrally formed with the flexible frame  100  by insert injection. In other words, the silicon portion  33  may be filled between the holes  110 ′. 
     The silicon part  33  is formed integrally with the flexible frame  100 , thereby allowing the silicon portion  33  to increase a restoring force of the flexible frame  100  itself. In other words, in this laminated structure, a restoring force of the flexible portion  100  acts on a restoring force of the silicon portion  33  at the same time. Therefore, this laminated structure has a larger restoring force compared to the laminated structure shown in  FIG. 12 . 
     Moreover, this laminated structure has an advantage capable of reducing a thickness of the silicon portion (the first portion  23   a  in  FIG. 13 ) disposed on the flexible region  110  and the rigid portion  120 . Therefore, when the present flexible display unit  30  is designed to have the same height as that of the flexible display unit  20  shown in  FIG. 13 , a thickness of the flexible frame  100  may be made thicker. Therefore, the present laminated structure has an advantage in that a yield strain of the flexible frame  100  compared to the laminated structure shown in  FIG. 13  can be increased. 
     For reference, the laminated structures illustrated in  FIGS. 12 to 14  may be applicable not only to the flexible frame  100  shown in  FIG. 1  but also to various modified examples of the flexible frame. For example, the present laminated structures may be applicable to a flexible frame  400  (refer to  FIG. 18 ) which will be described later. 
       FIG. 15  is a conceptual view for explaining a restoring mechanism of the flexible display unit  10  by the lamination of the flexible frame  100  and the flexible display  11  of the present disclosure. 
     In this drawing, as illustrated in  FIGS. 1 to 11 , the second flexible portion  112  is formed on both sides of the first flexible portion  111  to form the flexible region  110 . The first flexible portion  111  is configured to be bendable up to a state having a maximum first curvature by the first holes  111 ′ repeatedly formed, and the second flexible portion  112  is configured to be bendable up to a state having a maximum second curvature by the second holes  112 ′ repeatedly formed. Here, the first curvature is set to be larger than the second curvature. In other words, a first curvature radius of the first flexible portion  111  is smaller than a second curvature radius of the second flexible portion  112  in a state where the first and second flexible portions  111 ,  112  are bent to the maximum. 
     Referring to  FIG. 15A , in a first state where no external force is applied, a interval between the first holes  111 ′ and an interval between the second holes  112 ′ are maintained constant in an unchanged manner. In the first state, the flexible frame  100  is disposed flat, and the flexible display  11  laminated therewith is also disposed flat. In other words, in the first state, the flexible display unit  10  is disposed flat. 
     Referring to  FIG. 15B , a spacing interval between the first and second holes  111 ′,  112 ′ is extended or reduced in a second state in which the flexible display unit  10  is bent to the maximum by an external force. The flexible frame  100  and the flexible display  11  are laminated with each other and an entire length of the flexible frame  100  is not changed, and thus when there is a portion where a spacing interval between the holes is extended, a portion where the spacing interval between the holes is reduced occurs. 
     As a result, a restoring force is generated due to a property that the first and second holes  111 ′,  112 ′, which are extended or reduced, return to an original spacing interval in the flexible frame  100 . By the restoring force, the flexible display unit  10  returns to the first state. 
     Specifically, a spacing interval between the first holes  111 ′ formed on the first flexible portion  111  is increased, and a restoring force for decreasing the spacing interval between the first holes  111 ′ is generated in the first flexible portion  111 . A spacing interval between the second holes  112 ′ formed on the second flexible portion  112  is decreased, and a restoring force for increasing the spacing interval between the second holes  112 ′ is generated in the second flexible portion  112 . 
     The flexible frame  100  is preferably configured to have greater elasticity than the flexible display  11 . According to this, when the flexible frame  100  is bent, a restoring force of the flexible display  11  itself is added to a restoring force of the flexible frame  100 , thereby improving a restoring force of the flexible display unit  10 . 
     On the other hand, the first curvature is preferably designed to be twice or more the second curvature. In other words, a second curvature radius of the second flexible portion  112  is preferably designed to be twice or more than a first curvature radius of the first flexible portion  111  in a state where the first and second flexible portions  111 ,  112  are bent to the maximum. 
     Hereinafter, it will be described which material is suitable for use in the flexible frame  100 . 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                 Yield  
                 Elastic  
                 Yield  
                   
               
               
                 Type 
                 strength 
                 modulus 
                 strain 
                 Thickness 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Beta Titanium 
                  850 MPa 
                 80 
                 0.01063 
                 0.3 mm 
               
               
                 Titanium Gr2 
                  850 MPa 
                 110 
                 0.00773 
                 0.3 mm 
               
               
                 STS 301 EH 
                 1275 MPa 
                 200 
                 0.006375 
                 0.3 mm 
               
               
                   
               
            
           
         
       
     
     The above table shows a yield strength and a yield strain of titanium and stainless steel. 
     The relationship between stress and strain seen in a particular material may be represented by a stress-strain curve of the material. The material has a unique stress-strain curve, where the slope denotes a modulus of elasticity. 
     Yield strength refers to a force capable of withstanding until a material is no longer restored when applying a force to the material. Yield strain refers to a strain at yield strength. Furthermore, an area under the stress-strain curve up to a yield point denotes a restoring force. Therefore, it is seen that as the area increases, a restoring force of the material increases. 
     In order to allow the flexible frame  100  to withstand repeated bending and restoration, it is preferable that the flexible frame  100  is made of a material having a predetermined level of yield strength and a high yield strain and restoring force. 
     As can be seen from the table, stainless steel has a high yield strength but a small yield strain, and thus is not suitable for being applied to the flexible frame  100  in which bending and restoring are repeated. On the contrary, it can be seen that titanium has a yield strength lower than that of stainless steel but has a predetermined level of yield strength and a high yield strain. Accordingly, when the flexible frame  100  is formed of a titanium material, it may be bent without breakage, thereby implementing a restorable characteristic. 
     Various titanium materials such as Beta Titanium and Titanium Gr2 may be used to make the flexible frame  100 . Titanium Gr2 is a good choice when looking for relatively inexpensive titanium with a high yield strength and restoring force compared to stainless steel. 
     In addition, stainless steel is a ferromagnet, which can affect surrounding electronic components, while titanium does not have magnetic properties and thus is more suitable for use in an electronic device such as mobile terminal  1000  in which electronic components are integrated. 
       FIG. 16  is a conceptual view showing an example of a mobile terminal  1000  to which the flexible display unit  10  having the flexible frame  100  shown in  FIG. 1  is applied. 
     Referring to  FIG. 16 , the mobile terminal  1000  includes a first body  1100  and a second body  1200  that are configured to be relatively movable. The first body  1100  and the second body  1200  may have the same size. 
       FIG. 16A  shows a first state in which the first body  1100  and the second body  1200  are arranged in parallel, and  FIG. 16B  shows a second state in which the second body  1200  is folded over the first body  1100 . The mobile terminal  1000  is configured to freely modify its form from a first state to a second state, or from a second state to a first state. 
     In order to implement this, the first body  1100  and the second body  1200  may be respectively connected to the hinge portion  1300 , and configured to be rotatable with respect to the hinge portion  1300 . 
     Referring to  FIG. 16A , the flexible display unit  10  is disposed on one surface of the first body  1100  and on one surface of the second body  1200 . In other words, the flexible display unit  10  is disposed over the first body  1100  and the second body  1200 , thereby implementing a large screen. The flexible display unit  10  is disposed to cover the hinge portion  1300 . 
     The first flexible portion  111  of the flexible frame  100  is disposed to cover the hinge portion  1300 , and the second flexible portion  112  is disposed to cover the end portions of the first body  1100  and the second body  1200 . The first flexible portion  111  may be formed in the middle portion of the flexible frame  100 . The rigid portion  120  is disposed to cover the first body  1100  and the second body  1200  to support the flexible display  11  in a flat state. 
     Referring to  FIG. 16B , when the second body  1200  is folded over the first body  1100 , the flexible display unit  10  is bent by an external force. The first flexible portion  111  is bent at a first curvature, the second flexible portion  112  is bent at a second curvature, and the rigid portions  120  are arranged to face each other. Accordingly, the portions of the flexible display  11  supported by the rigid portion  120  are arranged to face each other. 
     The center of a curvature radius of the first flexible portion  111  is located in an inner space formed by the folding of the flexible frame  100  and the center of a curvature radius of the second flexible portion  112  is located in an outer space formed by the folding of the flexible frame  100 , and thus the flexible frame  100  is bent in a shape as shown in  FIG. 16B . Considering such a shape change, recessed spaces  1100 ′,  1200 ′ in which a part of the flexible display unit  10  corresponding to the first and second flexible portions  111 ,  112  can be received may be formed in the first and second bodies  1100 ,  1200 . 
     As shown in the drawing, the recessed spaces  1100 ′,  1200 ′ may be configured to be blocked by mechanically interlocking the first and second bodies  1100  and  1200  with the hinge portion  1300  in the first state shown in  FIG. 16A . In other words, the recessed spaces  1100 ′,  1200 ′ may be formed only in the second state shown in  FIG. 16B . 
     On the other hand, in the second state shown in  FIG. 16B , the first and second bodies  1100 ,  1200  are subjected to a force to return to the first state shown in  FIG. 16A  by a restoring force of the flexible display unit  10 . Accordingly, in order to maintain the second state shown in  FIG. 16B , the first body  1100  and the second body  1200  may be provided with magnet portions  1400 ′,  1400  which exert attractive forces on each other. 
     The magnet portions  1400 ′,  1400 ′ may be disposed at each end portion of the first and second bodies  1100 ,  1200  to face each other in a folded state. The attractive force exerted by the magnet portions  1400 ′,  1400  is set to be larger than a restoring force of the flexible display unit  10 . Therefore, the mobile terminal  1000  cannot return to the state of  FIG. 16A  only by a restoring force of the flexible display unit  10 . 
     However, when a force for moving the first body  1100  and the second body  1200  away from each other is (instantaneously) applied, and a sum force of the force and a restoring force of the flexible display unit  10  is larger than an attractive force of the magnet portions  1400 ′  1400 , the mobile terminal  1000  can be returned to the state of  FIG. 16A  only by the restoring force of the flexible display unit  10  thereafter. 
     Hereinafter, various other examples will be described in order to show that the flexible frame  100  can have various forms. 
       FIG. 17  is a view showing another example of a flexible frame  400  of the present disclosure, and  FIG. 18  is a conceptual view showing a state in which each flexible portion of the flexible frame  400  shown in  FIG. 17  is bent at a maximum curvature, and  FIG. 19  is a conceptual view showing a Y direction area change of the flexible frame  400  shown in  FIG. 17 , and  FIG. 20  is an enlarged view of a flexible region  410  shown in  FIG. 17 . 
     Referring to  FIGS. 17 to 20 , the flexible frame  400  includes a flexible portion  411 , a first rigid portion  420 ′ and a second rigid portion  420 ″ disposed on both sides of the flexible portion  411 , a first boundary portion  412 ′ disposed between the flexible portion  411  and the first rigid portion  420 ′ and a second boundary portion  412 ″ disposed between the flexible portion  411  and the second rigid portion  420 ″. Here, the flexible portion  411  and the first and second boundary portions  412 ′,  412 ″ form the flexible region  410 . 
     The flexible region  410  is configured to be bent with respect to the Y direction. Here, the X direction corresponds to a widthwise direction of the flexible frame  400 , and the Y direction corresponds to a lengthwise direction of the flexible frame  400 . 
     The flexible portion  411  is configured to be bendable up to a state having a maximum first curvature. First holes  411 ′ are repeatedly formed on the flexible portion  411  to implement the bending of the flexible portion  411 . In other words, flexibility may be generated on the flexible portion  411  due to the first holes  411 ′, and the flexible portion  411  may be bent up to a state having the maximum first curvature. 
     The first holes  411 ′ are repeatedly formed along the X and Y directions intersecting each other. The first holes  411 ′ are extended in an elongated manner in the X direction. 
     First and second rigid portions  420 ′,  420 ″ are respectively disposed on both sides of the flexible portion  411  in the Y direction. The first and second rigid pots  420 ′,  420 ″ may be formed in a plane that is hardly bent by an external force. Intentional holes are not formed on the first and second rigid portions  420 ′,  420 ″ to implement bending. In a state where the flexible portion  411  is bent to the maximum, the first and second rigid portions  420 ′,  420 ″ are arranged to face each other. 
     Between the flexible portion  411  and the first rigid portion  420 ′, and between the flexible portion  411  and the second rigid portion  420 ″, first and second boundary portions  412 ′,  412 ″ for smoothly connecting them are respectively formed. The second and third holes  412 ′,  412 ″ are formed on the first and second boundary portions  412 ′,  412 ″ so that the first and second boundary portions  412 ′,  412 ″ are bendable with respect to the Y direction. The second and third holes  412 ′,  412 ″ may be extended in an elongated manner in the X direction and disposed in parallel with the first holes  411 ′. 
     A degree of bending of the first and second boundary portions  412 ′,  412 ″ may be achieved by changing a total area occupied by the second and third holes  412 ′,  412 ″ per unit area of the first and second boundary portions  412 ′,  412 ″. 
     The first and second boundary portions  412 ′,  412 ″ are configured to be less bendable than the flexible portions  411 . For this purpose, a total area occupied by the second and third holes  412 ′,  412 ″ per unit area in the first and second boundary portion  412 ′,  412 ″ is set to be smaller than a total area occupied by the first holes  411 ′ per unit area in the flexible portion  411 . 
     For this purpose, a length of each of the second and third holes  412 ′,  412 ″ may be set to be smaller than that of the first holes  411 ′. Alternatively, a spacing interval between the second and third holes  412 ′,  412 ″ may be set to be larger than that between the first holes  411 ′. 
     The second and third holes  412 ′,  412 ″ may be arranged in a zigzag manner while partially overlapping each other along the Y direction. As shown in the drawing, the second and third holes  412 ′,  412 ″ arranged along the X direction are disposed in the Y direction directly above or below a region between the second and third holes  412 ′,  412 ″ arranged along the X direction (a region where an inherent material of the rigid flexible frame  400  remains). 
     Here, a length of a mutually overlapping portion between the second and third holes  412 ′,  412 ″ along the Y direction is set to be smaller than that of a mutually overlapping portion of the first holes  411 ′. 
     A maximum curvature at one end portion of the first and second boundary portions  412 ′,  412 ″ adjacent to the flexible portion  411  may be set to be greater than a maximum curvature at the other end portion of the first and second bound portions  412 ′,  412 ″ adjacent to the first and second rigid portions  420 ′,  420 ″. In other words, the maximum curvature at one end portion of the first and second boundary portions  412 ′,  412 ″ may be set to be smaller than the first curvature, and the maximum curvature at the other end portion of the first and second boundary portions  412 ′,  412 ″ may be set to be greater than zero. 
     To this end, a length of a hole adjacent to the flexible portion  411  of among the second and third holes  412 ′,  412 ″ may be set to be larger than that of a hole adjacent to the first and second rigid portions  420 ′,  420 ″. Alternatively, a spacing interval between the second and third holes  412 ′,  412 ″ at a portion adjacent to the flexible portion  411  may be set to be smaller than that between the second and third holes  412 ′,  412 ″ at a portion adjacent to the first and second rigid portions  420 ′,  420 ″. 
     Alternatively, the second and third holes  412 ′,  412 ″ may be randomly arranged under the condition that a total area occupied by the second and third holes  412 ′,  412 ″ per unit area in the first and second boundary portions  412 ′,  412 ″ is set to be smaller than a total area occupied by the first holes  411 ′ per unit area in the flexible portion  411 . 
       FIG. 18  shows a view in which the flexible portion  411  is bent to the maximum. As shown in the drawing, the center of a curvature radius of the flexible portion  411  is located in an inner space formed by the folding of the flexible frame  400 . 
       FIG. 21  is a conceptual view showing an example of a mobile terminal  2000  to which the flexible display unit  40  having the flexible frame  400  shown in  FIG. 17  is applied. 
     The flexible display unit  40  is formed in an elastically deformable manner, and includes a flexible display  41  and the foregoing flexible frame  400 . The flexible display  41  and the flexible frame  400  may be coupled to each other by a laminated structure described above in  FIGS. 12 to 14 . 
       FIG. 21A  shows a first state in which the flexible display unit  40  is folded flat on one surface of the terminal body  2100 , and  FIG. 21B  shows a second state in which the flexible display unit  40  is folded so that part thereof is disposed on the other surface of the terminal body  2100 . The flexible display unit  40  is configured to freely modify its form from a first state to a second state, or from a second state to a first state. 
     In order to implement this, the first rigid portion  420 ′ is configured to be attached onto one surface of the terminal body  2100 , and the first boundary portion  412 ′, the flexible portion  411 , the second boundary portion  412 ″, and the second rigid portion  420 ″ are configured to be detachable from the terminal body  2100 . 
     A round portion  2100 ′ is formed at one end portion of the terminal body  2100  to guide the modification of its shape such that the first boundary portion  412 ′, the flexible portion  411  and the second boundary portion  412 ″ can be bent in a corresponding manner to the round portion  2100 ′. A degree of bending, namely, a curvature, of the round portion  2100 ′, is preferably set to be equal to or smaller than a first curvature which is the maximum curvature at which the flexible portion  411  can be bent. 
     When the first boundary portion  412 ′, the flexible portion  411  and the second boundary portion  412 ″ are bent in a corresponding manner to the round portion  2100 ′, the second rigid portion  420 ″ is disposed to cover the other surface of the terminal body  2100 . A recess portion  2100 ″ capable of accommodating a portion of the flexible display unit  40  corresponding to the second rigid portion  420 ″ may be formed on the other surface of the terminal body  2100 . In a state where a portion of the flexible display unit  10  corresponding to the second rigid portion  120  is accommodated in the recess portion  2100 ″, an upper surface of the one portion may form the same plane as the other surface of the terminal body  2100 . 
     On the other hand, in the second state shown in  FIG. 21B , the flexible display unit  40  is subjected to a force of returning to the first state shown in  FIG. 21A  by a restoring force of the flexible frame  400 . Accordingly, in order to maintain the second state shown in  FIG. 21B , one end portion of the flexible display unit  40  and the terminal body  2100  may be provided with magnet portions  42 ,  2200  which exert attractive forces on each other. 
     The magnet portions  42 ,  2200  are provided on the other side of the second rigid portion  420 ′ and the terminal body  2100  so that the flexible display unit  40  can be dispose to face each other in a folded state. The attractive force exerted by the magnet portions  42 ,  2200  is set to be larger than a restoring force of the flexible display unit  40 . Therefore, the flexible display unit  40  cannot return to the state of  FIG. 21A  only by a restoring force of the flexible display unit  40 . 
     However, when a force for detaching the second rigid portion  420 ″ from the other side of the terminal body is (instantaneously) applied by a user, and a sum force of the force and a restoring force of the flexible display unit  40  is larger than an attractive force due to the magnet portions  42 ,  2200 , the flexible display unit  40  can be returned to the state of  FIG. 21A  only by the restoring force of the flexible display unit  40  thereafter. 
       FIG. 22  is a conceptual view showing an example of a mobile terminal  3000  to which a flexible display unit  50  having another example of the flexible frame  500  of the present disclosure is applied. 
     Referring to  FIG. 22A , the flexible frame  500  of the present example may be provided with two flexible regions  510 ′,  510 ″. The flexible region  510 ′ at an upper portion of the drawing is the same as a structure of the flexible frame  100  shown above in  FIG. 1 , and the flexible region  510 ″ at a lower portion of the drawing is the same as a structure of the flexible frame  400  shown above in  FIG. 17 . Therefore, the description of the structure of the flexible frame  500  will be substituted by the earlier description. 
     Referring to  FIG. 22B , a mobile terminal  3000  includes a first body  3100 , a second body  3200  and a third body  3300  which are configured to be relatively movable. The first body  3100 , the second body  3200 , and the third body  3300  may have the same size. 
     In a first state in which the first body  3100 , the second body  3200  and the third body  3300  are unfolded flat, the flexible display unit  50  are disposed over the first body  3100 , the second body  3200 , and the third body  3300  to constitute a large screen. 
     In a second state in which the first body  3100 , the second body  3200  and the third body  3300  are sequentially folded as shown in  FIG. 22B , the flexible display unit  50  is also folded in a corresponding manner thereto. 
     The mobile terminal  3000  is configured to freely modify its form from a first state to a second state, or from a second state to a first state. 
     In order to achieve this, the first body  3100  and the second body  3200  may be respectively connected to a first hinge portion  3000 ′ to be rotatable with respect to the first hinge portion  3000 ′, and the second body  3200  and the third body  3300  may be respectively connected to a second hinge portion  3000 ″ to be rotatable with respect to the second hinge portion  3000 ″. 
     The description of each structure will be substituted by the earlier description of  FIGS. 16 and 21 . 
       FIG. 23  is a conceptual view showing still another example of the flexible frame  600  of the present disclosure. 
     Referring to  FIG. 23 , at least one or more flexible portions  611 ,  612 ,  613 ,  614 ,  615  may be provided in the flexible frame  600 . Here, the flexible portions  611 ,  612 ,  613 ,  614 ,  615  may have an asymmetric shape. 
     In other words, in  FIG. 1 , the second flexible portions  112  having the same maximum curvature are formed to have the same length on both sides of the first flexible portion  111  to have a shape symmetrical with respect to the center of the first flexible portion  111 , but a shape of the flexible frame  100  is not limited to such a symmetric shape. 
     A degree to which each of the plurality of flexible portions  611 ,  612 ,  613 ,  614 ,  615  is bendable to the maximum, namely, a maximum curvature, may be designed to have a different value. Furthermore, the lengths of the plurality of flexible portions  611 ,  612 ,  613 ,  614 ,  615  may be designed to be different. 
     In this drawing, it is shown that five flexible portions  611 ,  612 ,  613 ,  614 ,  615  are designed to have different maximum curvatures, and their lengths are also set to be different.