Patent Publication Number: US-2023164936-A1

Title: Display device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority of Korean Patent Application No. 10-2021-0164748 filed on Nov. 25, 2021, which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     Field of the Disclosure 
     The present disclosure relates to a display device, and more particularly, to a rollable display device capable of inhibiting a display panel from being bent by moisture. 
     Description of the Background 
     As display devices used for a monitor of a computer, a TV set, a mobile phone, and the like, there are an organic light-emitting display (OLED) configured to autonomously emit, and a liquid crystal display (LCD) that requires a separate light source. 
     The range of application of the display devices is diversified from the monitor of the computer and the TV set to personal mobile devices, and studies are being conducted on the display devices having wide display areas and having reduced volumes and weights. 
     In addition, recently, a rollable display device, which is made by forming display parts, lines, and the like on a substrate made of a flexible plastic material having flexibility and thus may display images even in a case in which the rollable display device is rolled up, has attracted attention as a next-generation display device. 
     SUMMARY 
     Accordingly, the present disclosure is to provide a display device capable of unwinding and winding a display panel by using a lightweight configuration that replaces a roller. 
     The present disclosure is also to provide a display device capable of minimizing a situation in which a central portion of a display panel and a central portion of a back cover sag when the display panel is wound. 
     The present disclosure is not limited to the above-mentioned and other features, which are not mentioned above, can be clearly understood by those skilled in the art from the following descriptions. 
     According to an aspect of the present disclosure, a display device includes a first rolling guide parts and a second rolling guide parts each including at least one of a protruding portion and a groove portion; a connection part having one end fixed to the first rolling guide part and the other end fixed to the second rolling guide part; a back cover seated on the first and second rolling guide parts; and a display panel disposed on the back cover. 
     According to another aspect of the present disclosure, a display device includes a display panel having a plurality of pixels; a back cover disposed on a rear surface of the display panel so as to be rollable together with the display panel; a first rolling guide parts and a second rolling guide parts around which the back cover and the display panel are wound or unwound, the first and second rolling guide parts each including at least one of a protruding portion and a groove portion and configured such that the back cover is seated on the first and second rolling guide parts; and a connection part having one end and the other end at which the first and second rolling guide parts are disposed. 
     Other detailed matters of the exemplary aspects are included in the detailed description and the drawings. 
     The present disclosure may provide a display device, in which the roller is eliminated, and the rolling guide part and the connection part are used, such that the display device is lightweight. 
     According to the present disclosure, the protruding portions or groove portions of the back cover engage with the groove portions or protruding portions of the rolling guide parts when the back cover is wound. Therefore, the back cover may be wound at the exact position. 
     According to the present disclosure, the protruding portions or groove portions of the back cover engage with the groove portions or protruding portions of the rolling guide parts when the back cover is wound. Therefore, it is possible to minimize a situation in which the central portion of the wound back cover sags. 
     The effects according to the present disclosure are not limited to the contents exemplified above, and more various effects are included in the present specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and other advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIGS.  1 A and  1 B  are perspective views of a display device according to an aspect of the present disclosure; 
         FIG.  2    is a perspective view of the display device according to the aspect of the present disclosure; 
         FIG.  3    is a cross-sectional view of the display device according to the aspect of the present disclosure; 
         FIG.  4 A  is an exploded perspective view for explaining a first back cover and a second back cover of the display device according to the aspect of the present disclosure; 
         FIG.  4 B  is a top plan view of a display part of the display device according to the aspect of the present disclosure; 
         FIG.  5    is a perspective view for explaining a state in which the second back cover of the display device according to the aspect of the present disclosure is unwound; 
         FIG.  6    is a cross-sectional view for explaining a state in which the second back cover of the display device according to the aspect of the present disclosure is wound; 
         FIG.  7    is an enlarged perspective view illustrating a rolling guide part and a second back cover of a display device according to another aspect of the present disclosure; 
         FIG.  8    is an enlarged perspective view illustrating a rolling guide part and a second back cover of a display device according to still another aspect of the present disclosure; 
         FIG.  9    is a cross-sectional view for explaining a state in which a second back cover of a display device according to yet another aspect of the present disclosure is wound; 
         FIG.  10    is a cross-sectional view for explaining a state in which a second back cover of a display device according to still yet another aspect of the present disclosure is wound; 
         FIG.  11    is a perspective view for explaining a state in which a second back cover of a display device according to another further aspect of the present disclosure is unwound; 
         FIG.  12 A  is a perspective view for explaining a state in which a second back cover of a display device according to still another further aspect of the present disclosure is unwound; and 
         FIG.  12 B  is a cross-sectional view of the display device according to still another further aspect of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Advantages and characteristics of the present disclosure and a method of achieving the advantages and characteristics will be clear by referring to exemplary aspects described below in detail together with the accompanying drawings. However, the present disclosure is not limited to the exemplary aspects disclosed herein but will be implemented in various forms. The exemplary aspects are provided by way of example only so that those skilled in the art can fully understand the disclosures of the present disclosure and the scope of the present disclosure. Therefore, the present disclosure will be defined only by the scope of the appended claims. 
     The shapes, sizes, ratios, angles, numbers, and the like illustrated in the accompanying drawings for describing the exemplary aspects of the present disclosure are merely examples, and the present disclosure is not limited thereto. Like reference numerals generally denote like elements throughout the specification. Further, in the following description of the present disclosure, a detailed explanation of known related technologies may be omitted to avoid unnecessarily obscuring the subject matter of the present disclosure. The terms such as “including,” “having,” and “consist of” used herein are generally intended to allow other components to be added unless the terms are used with the term “only”. Any references to singular may include plural unless expressly stated otherwise. 
     Components are interpreted to include an ordinary error range even if not expressly stated. 
     When the position relation between two parts is described using the terms such as “on”, “above”, “below”, and “next”, one or more parts may be positioned between the two parts unless the terms are used with the term “immediately” or “directly”. 
     When an element or layer is disposed “on” another element or layer, another layer or another element may be interposed directly on the other element or therebetween. 
     Although the terms “first”, “second”, and the like are used for describing various components, these components are not confined by these terms. These terms are merely used for distinguishing one component from the other components. Therefore, a first component to be mentioned below may be a second component in a technical concept of the present disclosure. 
     Like reference numerals generally denote like elements throughout the specification. 
     A size and a thickness of each component illustrated in the drawing are illustrated for convenience of description, and the present disclosure is not limited to the size and the thickness of the component illustrated. 
     The features of various aspects of the present disclosure can be partially or entirely adhered to or combined with each other and can be interlocked and operated in technically various ways, and the aspects can be carried out independently of or in association with each other. 
     Hereinafter, various exemplary aspects of the present disclosure will be described in detail with reference to the accompanying drawings. 
     &lt;Display Device-Rollable Display Device&gt; 
     A rollable display device refers to a display device capable of displaying images even in a case in which the rollable display device is rolled up. The rollable display device may have higher flexibility than a general display device in the related art. A shape of the rollable display device may be freely changed depending on whether the rollable display device is used. Specifically, when the rollable display device is not used, the rollable display device may be rolled up and stored with a reduced volume. On the contrary, when the rollable display device is used, the rolled-up rollable display device may be unrolled again and used. 
       FIGS.  1 A and  1 B  are perspective views of a display device according to an aspect of the present disclosure. 
     Referring to  FIGS.  1 A and  1 B , a display device  100  according to an aspect of the present disclosure includes a display part DP and a housing part HP. 
     The display part DP is configured to display images to a user. For example, display elements and circuits, lines, and components for operating the display elements may be disposed on the display part DP. In this case, because the display device  100  according to the aspect of the present disclosure is a rollable display device, the display part DP may be configured to be wound or unwound. For example, the display part DP may include a display panel having flexibility so as to be wound or unwound, and a back cover. The display part DP will be described below in more detail with reference to  FIGS.  4 A and  4 B . 
     The housing part HP is a casing capable of accommodating the display part DP. 
     The housing part HP has an opening portion HPO through which the display part DP may move to the outside or the inside of the housing part HP. 
     Meanwhile, the display part DP of the display device  100  may switch from a fully unwound state illustrated in  FIG.  1 A  to a fully wound state illustrated in  FIG.  1 B  or switch from the fully wound state to the fully unwound state. 
     A drive part is disposed to wind or unwind the display part DP to switch the display part DP to the fully unwound state or the fully wound state. 
     &lt;Drive Part&gt; 
       FIG.  2    is a perspective view of the display device according to the aspect of the present disclosure. 
       FIG.  3    is a cross-sectional view of the display device according to the aspect of the present disclosure. 
       FIG.  3    is a schematic cross-sectional view for explaining a rolling guide part  151  and the display part DP of the display device  100  according to the aspect of the present disclosure. For the convenience of description,  FIG.  3    illustrates only the housing part HP, the rolling guide part  151 , and the display part DP. 
     First, referring to  FIG.  2   , a drive part MP includes a rolling unit  150  and a lifting unit  160 . 
     The rolling unit  150  winds or unwinds the display part DP, which is fixed to the rolling unit  150 , while rotating clockwise or counterclockwise. The rolling unit  150  includes rolling guide parts  151 , support parts  152 , and a connection shaft  153 . 
     The rolling guide part  151  is a member around which the display part DP is wound. The rolling guide part  151  may be made of plastic or metal, but the present disclosure is not limited thereto. For example, the rolling guide parts  151  may include a first rolling guide part  151   a  and a second rolling guide part  151   b.  Two opposite sides of a lower edge of the display part DP may be fixed to the first and second rolling guide parts  151   a  and  151   b.    
     The first and second rolling guide parts  151   a  and  151   b  may be fixed to two opposite ends of the connection shaft  153 . That is, the first and second rolling guide parts  151   a  and  151   b  are respectively fastened to one end and the other end of the connection shaft  153 . The connection shaft  153  may be made of a material having rigidity. For example, the connection shaft  153  may be made of a metallic material such as SST (stainless steel), Invar, or the like. However, the present disclosure is not limited thereto. When the connection shaft  153  rotates, the rolling guide parts  151  rotate together with the connection shaft  153 . Therefore, when the connection shaft  153  rotates, the display part DP having the lower edge fixed to the rolling guide parts  151  may be wound around the rolling guide parts  151 . In contrast, when the connection shaft  153  rotates in a reverse direction, the display part DP wound around the rolling guide parts  151  may be unwound from the rolling guide parts  151 . 
     Referring to  FIG.  3   , at least a part of an outer peripheral surface of the rolling guide part  151  may be formed as a flat surface, and the remaining part of the outer peripheral surface of the rolling guide part  151  may be formed as a curved surface. That is, a part of the outer peripheral surface of the rolling guide part  151  is formed to be flat, and the remaining part of the outer peripheral surface of the rolling guide part  151  is formed to be curved. 
     Referring back to  FIG.  2   , the support parts  152  support the rolling guide parts  151 . Specifically, the support parts  152  respectively support the first and second rolling guide parts  151   a  and  151   b.  The support parts  152  are disposed on a bottom surface HPF of the housing part HP. Side surfaces of upper ends of the support parts  152  are coupled to two opposite ends of the rolling guide parts  151 . Therefore, the support parts  152  may support the rolling guide parts  151  so that the rolling guide parts  151  are spaced apart from the bottom surface HPF of the housing part HP. In this case, the rolling guide parts  151  may be rotatably coupled to the support parts  152 . 
     The lifting unit  160  moves the display part DP in an upward/downward direction in conjunction with an operation of the rolling unit  150 . The lifting unit  160  includes link units  161 , a head bar  162 , a motor  165 , and rotary units  166 . 
     The link unit  161  of the lifting unit  160  includes a plurality of links  161   a  and  161   b,  and a hinge  161   c  configured to connect the plurality of links  161   a  and  161   b.  Specifically, the plurality of links  161   a  and  161   b  include a first link  161   a  and a second link  161   b.  The first link  161   a  and the second link  161   b  are rotatably fastened by means of the hinge  161   c  while intersecting each other in a scissors shape. Therefore, when the link unit  161  moves in the upward/downward direction, the plurality of links  161   a  and  161   b  may rotate in a direction toward or away from one another. The link unit  161  may include the plurality of links  161   a  and  161   b  that intersect each other. However, the present disclosure is not limited thereto. The link unit  161  may include a single link that does not intersect. 
     The head bar  162  of the lifting unit  160  is fixed to an uppermost end of the display part DP. The head bar  162  may be connected to the link units  161  and move the display part DP in the upward/downward direction by means of the rotations of the plurality of links  161   a  and  161   b  of the link units  161 . That is, the display part DP may be moved in the upward/downward direction by the head bar  162  and the link units  161 . 
     The head bar  162  covers only a part of the display part DP adjacent to the edge of the uppermost end of the display part DP so as not to cover an image displayed on a front surface of the display part DP. The display part DP and the head bar  162  may be fixed by a screw, but the present disclosure is not limited thereto. 
     The motor  165  may be connected to a power generator such as a separate external power source or an embedded battery and supplied with power. The motor  165  generates a rotational force and provides driving power to the rotary unit  166 . 
     The rotary unit  166  is connected to the motor  165  and configured to convert a rotational motion provided from the motor  165  into a rectilinear reciprocating motion. That is, the rotational motion of the motor  165  may be converted into the rectilinear reciprocating motion of a structure fixed to the rotary unit  166 . For example, the rotary unit  166  may be implemented as a ball-screw mechanism including a shaft and a nut fastened to the shaft. However, the present disclosure is not limited thereto. 
     The motor  165  and the rotary unit  166  may operate in conjunction with the link unit  161 , thereby moving the display part DP upward or downward. The link unit  161  may have a link structure and be repeatedly folded or unfolded by receiving the driving power from the motor  165  and the rotary unit  166 . 
     Specifically, as the motor  165  may operate, the structure of the rotary unit  166  may rectilinearly move. That is, a part of the rotary unit  166  to which one end of the second link  161   b  is connected may rectilinearly move. Therefore, one end of the second link  161   b  may move toward the motor  165 , and the plurality of links  161   a  and  161   b  are folded, such that a height of the link unit  161  may decrease. In addition, during the process of folding the plurality of links  161   a  and  161   b,  the head bar  162  connected to the first link  161   a  also moves downward, and one end of the display part DP connected to the head bar  162  also moves downward. 
     Therefore, when the display part DP is fully wound around the rolling guide parts  151 , the link unit  161  of the lifting unit  160  is kept folded. That is, when the display part DP is fully wound around the rolling guide parts  151 , the lifting unit  160  may have the lowest height. When the display part DP is fully unwound, the link unit  161  of the lifting unit  160  is kept unfolded. That is, when the display part DP is fully unwound, the lifting unit  160  may have the highest height. 
     Meanwhile, to wind the display part DP, the rolling guide parts  151  may rotate, and the display part DP may be wound around the rolling guide parts  151 . Referring to  FIG.  3   , for example, a lower edge of the display part DP is connected to the rolling guide parts  151 . Further, when the rolling guide parts  151  rotates in a first direction DR 1 , i.e., clockwise, the display part DP may be wound so that only an edge of a rear surface of the display part DP comes into close contact with surfaces of the rolling guide parts  151 . 
     When the display part DP is unwound, the connection shaft  153  and the rolling guide parts  151  may rotate, and the display part DP may be unwound from the rolling guide parts  151 . Referring to  FIG.  3   , for example, when the rolling guide parts  151  rotate in a second direction DR 2 , i.e., counterclockwise, the display part DP wound around the rolling guide parts  151  may be unwound from the rolling guide parts  151  and disposed outside the housing part HP. 
     In some aspects, the drive part MP having other structures other than the above-mentioned drive part MP may be applied to the display device  100 . That is, the components of the rolling unit  150  and the lifting unit  160  may be changed, some of the components may be eliminated, or other components may be added as long as the components may wind and unwind the display part DP. 
     &lt;Display Part&gt; 
       FIG.  4 A  is an exploded perspective view for explaining a first back cover and a second back cover of the display device according to the aspect of the present disclosure. 
       FIG.  4 B  is a top plan view of the display part of the display device according to the aspect of the present disclosure. 
     Referring to  FIGS.  4 A and  4 B , the display part DP includes a first back cover  110   a,  a second back cover  110   b,  a display panel  120 , a plurality of flexible films  130 , and a first printed circuit board  140 . 
     Referring to  FIGS.  4 A and  4 B , the first back cover  110   a  is disposed on a rear surface of the display panel  120  and supports the display panel  120 . Because the first back cover  110   a  is disposed on the rear surface of the display panel  120 , the first back cover  110   a  may be referred to as a back cover. A size of the first back cover  110   a  may be larger than a size of the display panel  120 . The first back cover  110   a  may protect other components of the display part DP from the outside. 
     The flexible films  130  electrically connected to one end of the display panel  120  are disposed on one surface of the first back cover  110   a.  The first printed circuit board  140  electrically connected to the flexible films  130  is disposed on one surface of the first back cover  110   a.  That is, the first back cover  110   a  is disposed on rear surfaces of the display panel  120 , the flexible films  130 , and the first printed circuit board  140  and supports the display panel  120 , the flexible films  130 , and the first printed circuit board  140 . Therefore, the size of the first back cover  110   a  may be larger than the size of the display panel  120 . Meanwhile, the back cover  110  may be divided into the first back cover  110   a  and the second back cover  110   b  based on a second support area PA 2  of the first back cover  110   a.    
     The first back cover  110   a  may be made of a material having rigidity. At least a part of the first back cover  110   a  may have flexibility so as to be wound or unwound together with the display panel  120 . For example, the first back cover  110   a  may be made of a metallic material such as stainless steel (steel use stainless (SUS)) or Invar or a plastic material. However, the material of the first back cover  110   a  may be variously changed in accordance with design as long as the material of the first back cover  110   a  satisfies physical property conditions such as a thermal deformation amount, a radius of curvature, rigidity, and the like. However, the present disclosure is not limited thereto. 
     The first back cover  110   a  may be fastened to the head bar  162  and the second back cover  110   b.    
     The first back cover  110   a  includes a plurality of support areas PA and a ductile area MA. The plurality of support areas PA are areas in which a plurality of opening portions  111  are not disposed. The ductile area MA is an area in which the plurality of opening portions  111  are disposed. Specifically, the first back cover  110   a  includes a first support area PA 1 , the ductile area MA, and the second support area PA 2 . The first support area PA 1 , the ductile area MA, and the second support area PA 2  are sequentially disposed from the uppermost end of the first back cover  110   a.  In this case, because the first back cover  110   a  is wound or unwound in a Y direction, the plurality of support areas PA and the ductile area MA may be disposed in the Y direction. 
     The first support area PA 1  of the first back cover  110   a  is an uppermost end region of the first back cover  110   a  fastened to the head bar  162 . First fastening holes AH 1  may be formed in the first support area PA 1  so that the first support area PA 1  is fastened to the head bar  162 . For example, screws are disposed to penetrate the first fastening holes AH 1  and the head bar  162 , such that the head bar  162  and the first support area PA 1  may be fastened to each other. Further, because the first support area PA 1  is fastened to the head bar  162 , the first back cover  110   a  may also move upward or downward when the link unit  161  fastened to the head bar  162  moves upward or downward. Further, the display panel  120  attached to the first back cover  110   a  may also move upward or downward.  FIGS.  4 A and  4 B  illustrate five first fastening holes AH 1 . However, the number of first fastening holes AH 1  is not limited thereto. In addition, the configuration has been described in which the first back cover  110   a  is fastened to the head bar  162  by using the first fastening holes AH 1 . However, the present disclosure is not limited thereto, and the first back cover  110   a  and the head bar  162  may be fastened to each other without a separate fastening hole. 
     The ductile area MA of the first back cover  110   a  is an area extending downward from the first support area PA 1  to the lower side of the first back cover  110   a.  The ductile area MA is an area in which the plurality of opening portions  111  are disposed and to which the display panel  120  is attached. Specifically, the ductile area MA is an area that is wound around or unwound from the rolling guide parts  151 , together with the display panel  120 . The ductile area MA may overlap at least the display panel  120  among the other components of the display part DP. 
     The second support area PA 2  of the first back cover  110   a  is a lowermost area of the first back cover  110   a  that extends from the ductile area MA. One end of the display panel  120  is disposed in the second support area PA 2 . For example, a pad area, which is a non-display area disposed at one end of the display panel  120 , may be disposed in the second support area PA 2 . 
     Referring to  FIG.  4 A , second fastening holes AH 2  are disposed in the second support area PA 2 . The second fastening holes AH 2  may be holes for fixing a cover part to be described below, the second back cover  110   b,  and the first back cover  110   a.    FIG.  4 A  illustrates nine second fastening holes AH 2 . However, the number of second fastening holes AH 2  is an example, and the present disclosure is not limited thereto. 
     Meanwhile, the plurality of opening portions  111 , which are formed in the ductile area MA, are not formed in the first support area PA 1  and the second support area PA 2 . Specifically, the first fastening holes AH 1  are formed in the first support area PA 1 , and the second fastening holes AH 2  are formed in the second support area PA 2 . However, the plurality of opening portions  111  formed in the ductile area MA are not formed in the first support area PA 1  and the second support area PA 2 . In addition, the first and second fastening holes AH 1  and AH 2  are different in shape from the plurality of opening portions  111 . 
     The first support area PA 1  is an area fixed to the head bar  162 . The second support area PA 2  is an area that supports one end of the display panel  120 , the plurality of flexible films  130 , and the printed circuit board  140 . The first and second support areas may have higher rigidity than the ductile area MA. Further, because the first and second support areas PA 1  and PA 2  have rigidity, the first and second support areas PA 1  and PA 2  may be securely fixed to the head bar  162  and the second back cover  110   b.  The second support area PA 2  may maintain the first printed circuit board  140  and the pad area at one end of the display panel  120  in a flat shape, thereby protecting the first printed circuit board  140  and the pad area of the display panel  120 . Therefore, the display part DP may be fixed to the head bar  162  of the drive part MP and moved to the inside or outside of the housing part HP by the operation of the drive part MP. The second support area may protect the first printed circuit board  140  and the pad area at one end of the display panel  120 . 
     Meanwhile,  FIG.  4 A  illustrates that the plurality of support areas PA and the ductile area MA of the first back cover  110   a  are sequentially disposed in a column direction. However, in a case in which the first back cover  110   a  is wound in a row direction, the plurality of support areas PA and the ductile area MA may be disposed in the row direction. 
     The plurality of opening portions  111  disposed in the ductile area MA of the first back cover  110   a  may be deformed by stress applied to the display part DP while the display part DP is wound or unwound. Specifically, the ductile area MA of the first back cover  110   a  may be deformed as the plurality of opening portions  111  contract or expand while the display part DP is wound or unwound. Further, because the plurality of opening portions  111  contract or expand, a slip of the display panel  120  disposed in the ductile area MA of the first back cover  110   a  is minimized, such that stress to be applied to the display panel  120  may be minimized. 
     Referring to  FIG.  5   , one end of the second back cover  110   b  is fixed to the first and second rolling guide parts  151   a  and  151   b  to be described below, and the other end of the second back cover  110   b  overlaps the first back cover  110   a.  The second back cover  110   b  may be fastened to the first back cover  110   a  and the rolling guide parts  151  and connect the first back cover  110   a  and the rolling guide parts  151 . As described above, the second back cover  110   b  may connect the first back cover  110   a  and the rolling guide parts  151 , and finally connect the rolling guide parts  151  and the display panel  120  disposed on the first back cover  110   a.  However, the present disclosure is not limited thereto. The shape of the second back cover  110   b  or the connection method may be variously changed in accordance with design as long as the second back cover  110   b  may be connected to the first back cover  110   a  and the rolling guide parts  151 . However, the present disclosure is not limited thereto. 
     One end of the second back cover  110   b  is an uppermost end region of the second back cover  110   b  and may overlap one end of the first back cover  110   a.  For example, one end of the second back cover  110   b  may overlap the second support area PA 2 . One end of the second back cover  110   b  may be connected to and overlap a part of the first back cover  110   a  or connected to a part of the first back cover  110   a  by using a connection member or the like. However, the present disclosure is not limited thereto. 
     The second back cover  110   b  may include a plurality of fastening parts FP that overlap the first back cover  110   a.  The plurality of fastening parts FP are disposed at one end of the second back cover  110   b.  In addition, a plurality of third fastening holes AH 3  may be respectively disposed in the plurality of fastening parts FP so as to be fastened to the first back cover  110   a.  The plurality of fastening parts FP having the plurality of third fastening holes AH 3  are spaced apart from one another, such that a space in which the plurality of flexible films  130  may be bent may be ensured between the plurality of fastening parts FP. The third fastening holes AH 3  may be holes for fixing the second back cover  110   b  and the cover part to be described below.  FIG.  4 A  illustrates nine third fastening holes AH 3 . However, the number of third fastening holes AH 3  is an example, and the present disclosure is not limited thereto. 
       FIG.  4 A  illustrates that the second fastening holes AH 2  and the third fastening holes AH 3  for fastening the cover part, the first back cover  110   a,  and the second back cover  110   b  are respectively disposed in the second support area PA 2  of the first back cover  110   a  and one end of the second back cover  110   b.  However, the first back cover  110   a,  the second back cover  110   b,  and the cover part may be fixed to one another without a separate fastening hole. 
     Meanwhile, when the second support area PA 2  and the plurality of fastening parts FP are wound around the rolling guide parts  151 , the outer peripheral surfaces of the rolling guide parts  151  on which the second support area PA 2  and the plurality of fastening parts FP overlap one another may be flat portions. Therefore, the second support area PA 2  may be always kept flat regardless of a state in which the second support area PA 2  is wound around or unwound from the rolling guide parts  151 . The first printed circuit board  140  and the pad area at one end of the display panel  120  disposed on the second support area PA 2  may also be kept flat. 
     A region from one end to the other end of the second back cover  110   b  is a region extending so that a display area AA of the display panel  120  may be disposed outside the housing part HP. For example, when the first back cover  110   a  and the display panel  120  are in the fully unwound state, the region from the other end of the second back cover  110   b  fixed to the rolling guide parts  151  to one end of the second back cover  110   b  at which the plurality of flexible films  130  and the first printed circuit board  140  are disposed may be disposed inside the housing part HP. The ductile area MA on which the display area AA of the display panel  120  is disposed and the first support area PA 1  may be disposed outside the housing part HP. That is, the region from the other end of the second back cover  110   b  fixed to the rolling guide parts  151  to the second support area PA 2  and at least a part of one end of the second back cover  110   b  may be disposed inside the housing part HP. 
     The other end of the second back cover  110   b  is a lowermost end region of the second back cover  110   b  that is fastened to the rolling guide parts  151 . Fourth fastening holes AH 4  may be formed at the other end of the second back cover  110   b  so that the second back cover  110   b  is fastened to the rolling guide parts  151 . For example, fastening members are disposed to penetrate the rolling guide parts  151  and the fourth fastening holes AH 4 , such that the rolling guide parts  151  may be fastened to the other end of the second back cover  110   b.  Meanwhile, the other end of the second back cover  110   b  may be bonded to the rolling guide parts  151  by means of an adhesive tape instead of the fourth fastening holes AH 4 . Further, as the other end of the second back cover  110   b  is fastened or bonded to the rolling guide parts  151 , the display panel  120 , the first back cover  110   a,  and the second back cover  110   b  may be wound around or unwound from the rolling guide parts  151 .  FIG.  4 A  illustrates two fourth fastening holes AH 4 . However, the number of fourth fastening holes AH 4  is not limited thereto. 
     Meanwhile, the plurality of opening portions  111 , which are formed in the ductile area MA of the first back cover  110   a,  may not be formed in the second back cover  110   b.  Specifically, the third fastening holes AH 3  and the fourth fastening holes AH 4  are formed at one end and the other end of the second back cover  110   b.  However, the plurality of opening portions  111 , which are formed in the ductile area MA of the first back cover  110   a,  are not formed in the second back cover  110   b.  In addition, the third fastening hole AH 3  and the fourth fastening hole AH 4  are different in shape from the plurality of opening portions  111 . 
     The second back cover  110   b  may be made of a material having flexibility so that the second back cover  110   b  may be wound around or unwound from the rolling guide parts  151 . For example, the second back cover  110   b  may be made of a plastic material such as polyethylene terephthalate (PET). However, the material of the second back cover  110   b  may be variously changed in accordance with design as long as the material of the second back cover  110   b  satisfies physical property conditions such as a thermal deformation amount, a radius of curvature, rigidity, and the like. However, the present disclosure is not limited thereto. 
     In the present specification, the configuration has been described in which the first back cover  110   a  and the second back cover  110   b  are separately formed. However, the present disclosure is not limited thereto. The first back cover  110   a  and the second back cover  110   b  may be integrated. 
     Referring to  FIG.  4 B , the display panel  120  is disposed on one surface of the first back cover  110   a.  The display panel  120  is disposed in the ductile area MA on one surface of the first back cover  110   a.  The display panel  120  is a panel configured to display images to a user. The display panel  120  may include a display element configured to display images, a driving element configured to operate the display element, and lines configured to transmit various types of signals to the display element and the driving element. 
     The display elements may have different configurations depending on the type of display panel  120 . For example, in a case in which the display panel  120  is an organic light-emitting display panel  120 , the display element may be an organic light-emitting element including an anode, an organic light-emitting layer, and a cathode. For example, in a case in which the display panel  120  is a liquid crystal display panel, the display element may be a liquid crystal display element. Hereinafter, the assumption is made that the display panel  120  is the organic light-emitting display panel. However, the display panel  120  is not limited to the organic light-emitting display panel. In addition, because the display device  100  according to the aspect of the present disclosure is a rollable display device  100 , the display panel  120  may be implemented as a flexible display panel  120  so as to be wound around or unwound from the rolling guide parts  151 . 
     The display panel  120  include the display area AA and a non-display area NA. 
     The display area AA is an area of the display panel  120  in which images are displayed. The display area AA may include a plurality of subpixels constituting the plurality of pixels, and a drive circuit configured to operate the plurality of subpixels. The plurality of subpixels is minimum units constituting the display area AA. The display element may be disposed in each of the plurality of subpixels. For example, the plurality of subpixels may each include the light-emitting element including an anode, a light-emitting part, and a cathode. However, the present disclosure is not limited thereto. In addition, the drive circuit configured to operate the plurality of subpixels may include driving elements, lines, and the like. For example, the drive circuit may include, but not limited to, a thin-film transistor, a storage capacitor, a gate line, a data line, and the like. 
     The non-display area NA is an area in which no image is displayed. Various lines and circuits for operating the organic light-emitting element in the display area AA are disposed in the non-display area NA. For example, the non-display area NA may include, but not limited to, link lines for transmitting signals to the plurality of subpixels and the drive circuit in the display area AA. The non-display area NA may include a drive IC such as a gate driver IC and a data driver IC. 
     Meanwhile, the non-display area NA includes a pad area. 
     The pad area is an area in which a plurality of pads are disposed. The plurality of pads are electrodes for electrically connecting the plurality of flexible films  130  and the display panel  120 . The plurality of flexible films  130  and the display panel  120  may be electrically connected through the plurality of pads. In the non-display area NA, the pad area may be the non-display area NA that overlaps the second support area PA 2  of the first back cover  110   a.  However, the pad area may be formed in another portion of the non-display area NA in accordance with the arrangement of the plurality of flexible films  130 . However, the present disclosure is not limited thereto. 
     Referring to  FIG.  4 B , the plurality of flexible films  130  are disposed at one end of the display panel  120 . The plurality of flexible films  130  each are a film having various types of components disposed on a base film  131  having ductility in order to supply signals to the plurality of subpixels constituting the plurality of pixels and to the drive circuit in the display area AA. The plurality of flexible films  130  may be electrically connected to the display panel  120 . The plurality of flexible films  130  are disposed at one end of the non-display area NA of the display panel  120  and may supply power voltage, data voltage, and the like to the plurality of subpixels and the drive circuit in the display area AA. Meanwhile,  FIG.  4 B  illustrates eight flexible films  130 . However, the number of flexible films  130  may be variously changed in accordance with design. However, the present disclosure is not limited thereto. 
     The drive ICs  132  such as gate driver ICs and data driver ICs may be disposed on base films  131  of the plurality of flexible films  130 . The drive IC  132  is a component configured to process data for displaying the image and process a driving signal for processing the data. The drive IC  132  may be disposed in ways such as a chip-on-glass (COG) method, a chip-on-film (COF) method, and a tape carrier package (TCP) method depending on how the drive IC is mounted. However, in  FIG.  4 B , for the convenience of description, the configuration has been described in which the drive ICs  132  are mounted on the plurality of flexible films  130  by the chip-on-film method. However, the present disclosure is not limited thereto. 
     Meanwhile, the plurality of flexible films  130  are components including the base films, the data drivers configured to display images on the base films, and the various types of drive ICs configured to control the data drivers. The plurality of flexible films  130  are components for displaying the images. The plurality of flexible films  130  are electrically connected to the pad area at one end of the display panel  120  and bent toward the rear surface of the first back cover  110   a . One end of each of the plurality of flexible films  130  may be connected to one end of the display panel  120  on one surface of the first back cover  110   a,  and the other end of each of the plurality of flexible films  130  may be disposed on a surface of the first back cover  110   a  opposite to one surface of the first back cover  110   a.    
     Referring to  FIG.  4 B , the first printed circuit board  140  is disposed on the rear surface of the first back cover  110   a  and connected to the plurality of flexible films  130 . That is, the first printed circuit board  140  disposed adjacent to the rear surface of the first back cover  110   a  and electrically connected to the plurality of flexible films  130 . The first printed circuit board  140  is a component configured to supply a signal to the drive IC of each of the plurality of flexible films  130 . Various types of components for supplying the drive IC with various signals such as driving signals, data signals, and the like may be disposed on the first printed circuit board  140 . Meanwhile,  FIG.  4 B  illustrates two first printed circuit boards  140 . However, the number of first printed circuit boards  140  may be variously changed in accordance with design. The present disclosure is not limited thereto. 
     &lt;Shapes of Rolling Unit and Back Cover&gt; 
       FIG.  5    is a perspective view for explaining a state in which the second back cover of the display device according to the aspect of the present disclosure is unwound.  FIG.  6    is a cross-sectional view for explaining a state in which the second back cover of the display device according to the aspect of the present disclosure is wound. For the convenience of illustration,  FIGS.  5  and  6    illustrate only the second back cover  110   b  among the components of the display part DP.  FIG.  5    is a view illustrating a state in which the display part DP is fully unwound around the rolling unit  150 , and  FIG.  6    is a view illustrating a state in which the display part DP is wound around the rolling unit  150  once. 
     Referring to  FIG.  5   , the connection shaft  153  has one end and the other end fastened to middle regions of the first and second rolling guide parts  151   a  and  151   b.  The connection shaft  153  is connected to the first and second rolling guide parts  151   a  and  151   b  and transmits rotational power.  FIG.  5    illustrates that the connection shaft  153  has a cylindrical shape. However, the connection shaft  153  may have any shape capable of transmitting rotational power in addition to the cylindrical shape. In the case in which the connection shaft  153  has a cylindrical shape, the connection shaft  153  has a smaller diameter than each of the rolling guide parts  151 . 
     A torsion spring TS is fastened to the connection shaft  153  and the first rolling guide parts  151   a.  The torsion spring TS may transmit power to a rotation of the connection shaft  153  by providing tension. The first and second rolling guide parts  151   a  and  151   b  may rotate as the tension is provided. 
     A second printed circuit board  170  is disposed on a central portion of the connection shaft  153  and electrically connected to the first printed circuit board  140 . For example, the first printed circuit board  140  may be referred to as a source printed circuit board (source PCB; S-PCB) on which a data drive part is mounted. The second printed circuit board  170  connected to the first printed circuit board  140  may be referred to as a control printed circuit board (control PCB; C-PCB) on which a timing controller or the like is mounted. The second printed circuit board  170  may be fixed to the connection shaft  153  by means of a screw or fixed to the connection shaft  153  by means of an adhesive tape. Although not illustrated in the drawings, a flexible cable may electrically connect the first printed circuit board  140  and the second printed circuit board  170  and transmit an electrical signal to the display panel  110 . For example, the flexible cable may be a flexible flat cable (FFC). However, the present disclosure is not limited thereto. 
     A part of the outer peripheral surface of the rolling guide part  151  is formed to be flat, and the remaining part of the outer peripheral surface of the rolling guide part  151  is formed to be curved. The second support area PA 2  in which the first printed circuit board  140  and the flexible film  130  are disposed is wound while adjoining the flat portion of the rolling guide part  151 , such that the second support area PA 2  and the first printed circuit board  140  and the flexible film  130  in the second support area PA 2  may be kept flat without being curved. Therefore, the flexible film  130  and the first printed circuit board  140  may be always kept flat regardless of the state in which the display part DP is wound or unwound. Therefore, it is possible to inhibit the flexible film  130  and the first printed circuit board  140  from being bent and damaged. 
     The first and second rolling guide parts  151   a  and  151   b  each include a groove portion  154  provided in a middle region thereof. As illustrated in  FIG.  5   , a cross-section of the groove portion  154  may have a ⊏ shape, a V shape, or a U shape. However, the present disclosure is not limited thereto. 
     Referring to  FIG.  6   , the back cover  110  is seated on the first and second rolling guide parts  151   a  and  151   b.  In other words, in the case in which the first and second rolling guide parts  151   a  and  151   b  each include the groove portion  154 , the second back cover  110   b  includes a plurality of protruding portions  113 . The plurality of protruding portions  113  of the second back cover  110   b  may be disposed to engage with the groove portions  154  of the first and second rolling guide parts  151   a  and  151   b  when the second back cover  110   b  is in the fully wound state. In the case in which the rolling guide parts  151  include the groove portions  154 , the second back cover  110   b  include the plurality of protruding portions  113  corresponding to the groove portions  154 . The protruding portions  113  may be disposed at two opposite ends of the second back cover  110   b.  The protruding portions  113  may be disposed in a row in a direction perpendicular to the connection shaft  153 . The plurality of protruding portions  113  may be formed separately from the second back cover  110   b  and then attached or fastened to the second back cover  110   b.  However, the present disclosure is not limited thereto. As illustrated in  FIGS.  5  and  6   , the plurality of protruding portions  113  may each have a rectangular parallelepiped shape. However, the plurality of protruding portions  113  may each have a shape corresponding to the shape of the cross-section of the groove portion  154  of the rolling guide part  151 . For the convenience of description,  FIG.  6    illustrates that the groove portion  154  of each of the first and second rolling guide parts  151   a  and  151   b  is spaced apart from the protruding portion  113  of the second back cover  110   b.  However, the groove portion  154  and the protruding portion  113  may actually be disposed to adjoin each other. 
     The plurality of protruding portions  113  may have the same circumferential length as the groove portion  154  of each of the first and second rolling guide parts  151   a  and  151   b.  That is, the plurality of protruding portions  113  may have a length that may be wound around the groove portion  154  of the rolling guide part  151  once. 
     When the second back cover  110   b  is wound, the two opposite ends of the second back cover  110   b  adjoin the first and second rolling guide parts  151   a  and  151   b,  respectively. That is, the protruding portions  113  of the second back cover come into contact and engage with the groove portion  154  of the rolling guide part  151  when the second back cover  110   b  is wound. Therefore, the second back cover  110   b  may be wound at an exact position without slipping on an upper portion of the rolling guide part  151 . The two opposite ends of the second back cover  110   b  are supported by the rolling guide parts  151  in the state in which the second back cover  110   b  is wound around the rolling guide parts  151  once. The cylindrical shape of the second back cover  110   b  may be maintained even though the middle portion of the second back cover  110   b  is not supported. Therefore, when the second back cover  110   b  is fully wound, the connection shaft  153  and the second printed circuit board  170  may be disposed in the cylindrical second back cover  110   b.  On the contrary, when the second back cover  110   b  is fully unwound, the second printed circuit board  170  and the torsion spring TS disposed above the connection shaft  153  are exposed. In other words, the second printed circuit board  170  and the torsion spring TS are present in the housing part HP and disposed above the connection shaft  153 . However, the second printed circuit board  170  and the torsion spring TS are not disposed in a separate roller. 
     In a rollable display device in the related art, a back cover is wound so that a front surface of the other end of the back cover adjoins a roller. Therefore, the roller provides rigidity capable of supporting the back cover. However, a weight of the roller accounts for approximately ⅓ of an overall weight of the display device, for example. For this reason, the roller is excessively heavy in weight, which limits the implementation of a portable display device configured as a lightweight rollable display device. 
     The display device  100  according to the aspect of the present disclosure may be implemented as a rollable display device that is lightweight and replaces the heavy roller. That is, the rollable display device, in which the back cover  110  is wound while being supported on the rolling guide parts  151 , may be implemented only by using the rolling guide parts  151  and the connection shaft  153  without using the roller that was used in general. Therefore, the display device  100  according to the aspect of the present disclosure may be implemented to be lightweight and portable. 
     In addition, in the display device  100  according to the aspect of the present disclosure, the two opposite ends of the back cover  110  are supported by the rolling guide parts  151 . The central portion of the back cover  110 , which does not adjoin the rolling guide parts  151 , may be wound without sagging. In other words, the plurality of protruding portions  113  of the back cover  110  may be disposed to correspond to the groove portions  154  of the rolling guide parts  151 , such that the plurality of protruding portions  113  may engage with the groove portions  154  when the back cover  110  is wound. Therefore, in the display device  100  according to the aspect of the present disclosure, the cylindrical shape of the wound back cover  110  may be maintained, and the plurality of protruding portions  113  and the groove portions  154  may inhibit the central portion of the back cover  110  from sagging. 
     Meanwhile, in the several aspects, the plurality of protruding portions  113  of the second back cover  110   b  may be configured as magnetic elements, and the first and second rolling guide parts  151   a  and  151   b  may be made of metal, such that a magnetic force may be formed between the plurality of protruding portions  113  of the second back cover  110   b  and the groove portions  154  of the first and second rolling guide parts  151   a  and  151   b.  Alternatively, magnetic elements may be attached to the protruding portions  113 , and the first and second rolling guide parts  151   a  and  151   b  may be made of metal, such that a magnetic force is formed between the plurality of protruding portions  113  of the second back cover  110   b  and the groove portions  154  of the first and second rolling guide parts  151   a  and  151   b.  That is, the first and second rolling guide parts  151   a  and  151   b  may be made of metal, and the plurality of protruding portions  113  may be configured as magnetic elements, or magnetic elements may be attached to the plurality of protruding portions  113 , such that a magnetic force may be formed between the plurality of protruding portions  113  and the groove portions  154  of the first and second rolling guide parts  151   a  and  151   b.  Therefore, an attachment force between the plurality of protruding portions  113  and the groove portions  154  of the first and second rolling guide parts  151   a  and  151   b  increases, such that the central portion of the back cover  110  is further inhibited from sagging. In this case, the available magnetic element may be a magnet or a rubber magnet, for example. In particular, when the rubber magnet is used as the magnetic element, a frictional force generated by the rubber material may also be added, it is possible to further inhibit the central portion of the back cover  110  from sagging. 
       FIG.  7    is an enlarged perspective view illustrating a rolling guide part and a second back cover of a display device according to another aspect of the present disclosure. The display device  700  illustrated in  FIG.  7    is substantially identical in configuration to the display device  100  illustrated in  FIGS.  1  to  6   , except for a plurality of protruding portions  713  of a second back cover  710   b.  Therefore, repeated descriptions of the identical components will be omitted. For the convenience of illustration,  FIG.  7    illustrates a part of the second back cover  710   b  among the components of the display part DP and illustrates only a second rolling guide part  751   b  and the connection shaft  153  among the components of the rolling unit.  FIG.  7    illustrates only the second rolling guide part  751   b  between the first rolling guide part and the second rolling guide part  751   b.  However, the first rolling guide part may be identical to the second rolling guide part  751   b.    
     Referring to  FIG.  7   , the first rolling guide part and the second rolling guide part  751   b  each include at least two groove portions  754 . The plurality of protruding portions  713  of the second back cover  710   b  are disposed at two opposite sides of the second back cover  710   b.  The plurality of protruding portions  713  are disposed to extend in at least two rows in the direction perpendicular to the connection shaft  153 . In this case, when the back cover is in the fully wound, one of the plurality of protruding portions  713  of the second back cover  710   b  is disposed to correspond to one of the groove portions  754 . In the case in which the second rolling guide part  751   b  includes the plurality of groove portions  754 , the plurality of protruding portions  713  are provided at one end of the second back cover  710   b  and correspond to the plurality of groove portions  754 . The same configuration is also applied to the first rolling guide part and the other end of the second back cover  710   b.  For example, as illustrated in  FIG.  7   , the two groove portions  754  of each of the first rolling guide part and the second rolling guide part  751   b  may be continuously disposed. The two protruding portions  713  may be respectively disposed at one end and the other end of the second back cover  710   b  so that one protruding portion  713  corresponds to one groove portion  754 .  FIG.  7    illustrates that the plurality of protruding portions  713  are disposed in two rows and provided at the two opposite ends of the second back cover  710   b . However, the number of protruding portions  713  respectively disposed at one end and the other end of the second back cover  710   b  is not limited thereto. In addition, the number of groove portions  754  of each of the first rolling guide part and the second rolling guide part  751   b  may be changed to be equal to the number of protruding portions  713 . The plurality of protruding portions  713  are formed separately from the second back cover  710   b  and then attached or fastened to the second back cover  710   b.  The plurality of protruding portions  713  may be disposed in a rectangular parallelepiped shape. However, the plurality of protruding portions may each have a shape corresponding to the shape of the cross-section of the groove portion  754  of the rolling guide part. 
     In the display device  700  according to another aspect of the present disclosure, the heavy roller is eliminated, and the first rolling guide part, the second rolling guide part  751   b,  and the connection shaft  153  are disposed. Therefore, the display device  700  with lightweight and portable characteristics can be achieved. 
     In addition, in the display device  700  according to another aspect of the present disclosure, the two opposite ends of the back cover are supported by the first rolling guide part and the second rolling guide part  751   b.  Therefore, even the central portion of the back cover, which does not adjoin the rolling guide parts, may be wound without sagging. In other words, the plurality of protruding portions  713  of the second back cover  710   b  may engage with the plurality of groove portions  754  of the rolling guide parts when the second back cover  710   b  is wound. Therefore, in the display device  700  according to another aspect of the present disclosure, the cylindrical shape of the wound back cover may be maintained, and the plurality of protruding portions  713  and the plurality of groove portions  754  may more efficiently inhibit the central portion of the back cover from sagging. 
       FIG.  8    is an enlarged perspective view illustrating a rolling guide part and a second back cover of a display device according to still another aspect of the present disclosure. The display device  800  illustrated in  FIG.  8    is substantially identical in configuration to the display device  100  illustrated in  FIGS.  1  to  6   , except for a plurality of protruding portions  813  of a second back cover  810   b.  Therefore, repeated descriptions of the identical components will be omitted. For the convenience of illustration,  FIG.  8    illustrates a part of the second back cover  810   b  among the components of the display part DP and illustrates only the second rolling guide part  151   b  and the connection shaft  153  among the components of the rolling unit. 
     Referring to  FIG.  8   , in the case in which the rolling guide parts  151  include the groove portions  154 , the second back cover  810   b  include the plurality of protruding portions  813  corresponding to the groove portions  154 . The plurality of protruding portions  813  may each include a plurality of patterns. The plurality of patterns of the plurality of protruding portions  813  may be provided at two opposite ends of the second back cover  810   b  and disposed in a row in the direction perpendicular to the connection shaft  153 . The plurality of protruding portions  813  are formed separately from the second back cover  810   b  and then attached or fastened to the second back cover  810   b.  As illustrated in  FIG.  8   , the plurality of patterns of the plurality of protruding portions  813  may each have a rectangular parallelepiped shape. However, the plurality of patterns of the plurality of protruding portions may each have a shape corresponding to the shape of the cross-section of the groove portion  154  of the rolling guide part. The protruding portions  813 , which is disposed at one end of the second back cover  810   b  and having the plurality of patterns disposed in a row, correspond to the groove portion  154  of the first rolling guide part. The protruding portions  813 , which is disposed at the other end of the second back cover  810   b  and having the plurality of patterns disposed in a row, correspond to the groove portion  154  of the second rolling guide part. 
     In the display device  800  according to still another aspect of the present disclosure, the heavy roller in the related art is eliminated, and the first rolling guide part, the second rolling guide part  151   b,  and the connection shaft  153  are disposed. Therefore, it is possible to provide the display device  800  that is lightweight and portable. 
     In addition, in the display device  800  according to still another aspect of the present disclosure, the two opposite ends of the back cover are supported by the first rolling guide part and the second rolling guide part  151   b.  Therefore, even the central portion of the back cover, which does not adjoin the rolling guide parts, may be wound without sagging. In other words, the plurality of protruding portions  813  of the second back cover  810   b,  which include the plurality of patterns, may engage with the groove portions  154  of the first and second rolling guide parts when the second back cover  810   b  is wound. Therefore, in the display device  800  according to still another aspect of the present disclosure, the cylindrical shape of the wound back cover may be maintained, and the plurality of protruding portions  813  having the plurality of patterns and the groove portions  153  may more efficiently inhibit the central portion of the back cover from sagging. 
     In addition, in the display device  800  according to still another aspect of the present disclosure, the plurality of protruding portions  813  have the plurality of patterns. Therefore, it is possible to minimize a problem that the plurality of protruding portions  813  are separated from the second back cover  810   b  because of a level difference and curvature of the protruding portions  813  when the second back cover  810   b  is wound. In a case in which the plurality of protruding portions each have a single pattern, a slip may occur between the second back cover and the plurality of protruding portions while the second back cover is wound. Further, the second back cover and the plurality of protruding portions may be separated from one another because of a difference in extension length between the plurality of protruding portions disposed at the inside and the second back cover disposed at the outside. However, in the display device  800  according to still another aspect of the present disclosure, the plurality of protruding portions  813  each have the plurality of patterns. Therefore, a difference between an extension length of one pattern of the protruding portion  813  and an extension length of a region of the second back cover  810   b  corresponding to one pattern of the protruding portion  813  is smaller than a difference between an extension length of the protruding portion having the single pattern and an extension length of a region of the second back cover corresponding to the protruding portion having the single pattern. Therefore, in the display device  800  according to still another aspect of the present disclosure, a degree to which the slip occurs between the second back cover  810   b  and the plurality of patterns of the plurality of protruding portions  813  is significantly small even though the slip occurs between the second back cover  810   b  and the plurality of patterns of the plurality of protruding portions  813  while the second back cover  810   b  is wound. Therefore, it is possible to minimize the problem that the plurality of protruding portions  813  are separated from the second back cover  810   b,  thereby improving reliability. 
       FIG.  9    is a cross-sectional view for explaining a state in which a second back cover of a display device according to yet another aspect of the present disclosure is wound. The display device  900  illustrated in  FIG.  9    is substantially identical in configuration to the display device  100  illustrated in  FIGS.  1  to  6   , except for a second back cover  910   b  and a rolling unit  950 . Therefore, repeated descriptions of the identical components will be omitted. For the convenience of illustration,  FIG.  9    illustrates only the second back cover  910   b  among the components of the display part DP.  FIG.  9    is a view illustrating a state in which the display part DP is wound around the rolling unit  950  once. 
     Referring to  FIG.  9   , the first and second rolling guide parts  951   a  and  951   b  each include a protruding portion  955  provided in a middle region thereof. A height of the protruding portion  955  does not exceed a thickness of the second back cover  910   b.  This is to inhibit the first back cover wound on the second back cover  910   b,  which is wound previously, from being lifted up by the protruding portion  955  while the back cover is wound. As illustrated in  FIG.  9   , a cross-section of the protruding portion  955  may have a ⊏ shape, a V shape, or a U shape. However, the present disclosure is not limited thereto. The protruding portion  955  of the rolling guide part may be made of the same material as the rolling guide part  951  and integrated with the rolling guide part  951 . However, the present disclosure is not limited thereto. 
     In the case in which the rolling guide part  951  includes the protruding portion  955 , the second back cover  910   b  includes a plurality of groove portions  914  corresponding to the protruding portion  955 . The plurality of groove portions  914  of the second back cover  910   b  are disposed to engage with the protruding portions  955  of the first and second rolling guide parts  951   a  and  951   b  when the second back cover  910   b  is in the fully wound state. The groove portions  914  may be provided at two opposite ends of the second back cover  910   b  and disposed in a row in the direction perpendicular to the connection shaft  153 . As illustrated in  FIG.  9   , the plurality of groove portions  914  may each have any shape as long as the plurality of groove portions  914  engage with the protruding portions  955  of the rolling guide parts  951 . For example, the plurality of groove portions  914  may each have a rectangular parallelepiped shape. However, the present disclosure is not limited thereto. 
     The plurality of groove portions  914  may have the same circumferential length as the rolling guide part  951 . That is, the plurality of groove portions  914  may have a length that may be wound around the rolling guide part  951  once. 
     When the second back cover  910   b  is wound, the two opposite ends of the second back cover  910   b  adjoin the first and second rolling guide parts  951   a  and  951   b,  respectively. That is, the groove portion  914  of the second back cover and the protruding portion  955  of the rolling guide part are coupled while engaging with each other when the second back cover  910   b  is wound. Therefore, the second back cover  910   b  may be wound at an exact position without slipping on an upper portion of the rolling guide part  951 . The two opposite ends of the second back cover  910   b  are supported by the rolling guide parts  951  in the state in which the second back cover  910   b  is wound around the rolling guide parts  951  once. The cylindrical shape of the second back cover  910   b  may be maintained even though the middle portion of the second back cover  910   b  is not supported. Therefore, when the second back cover  910   b  is wound, the connection shaft  153  and the second printed circuit board  170  may be disposed in the cylindrical second back cover  910   b . On the contrary, when the second back cover  910   b  is fully unwound, the second printed circuit board  170  and the torsion spring TS disposed above the connection shaft  153  are exposed. In other words, the second printed circuit board  170  and the torsion spring TS are present in the housing part HP and disposed above the connection shaft  153 . However, the second printed circuit board  170  and the torsion spring TS are not disposed in a separate roller. 
     In the display device  900  according to yet another aspect of the present disclosure, the heavy roller in the related art is eliminated, and the first rolling guide part  951   a,  the second rolling guide part  951   b,  and the connection shaft  153  are disposed. Therefore, it is possible to provide the display device  900  that is lightweight and portable. 
     In addition, in the display device  900  according to yet another aspect of the present disclosure, the two opposite ends of the back cover are supported by the first rolling guide part  951   a  and the second rolling guide part  951   b.  Therefore, even the central portion of the back cover, which does not adjoin the rolling guide parts  951 , may be wound without sagging. In other words, the plurality of groove portions  914  of the second back cover  910   b  may engage with the protruding portions  955  of the rolling guide parts  951  when the second back cover  910   b  is wound. Therefore, in the display device  900  according to yet another aspect of the present disclosure, the cylindrical shape of the wound back cover may be maintained, and the plurality of protruding portions  955  and the plurality of groove portions  914  may more efficiently inhibit the central portion of the back cover from sagging. 
       FIG.  10    is a cross-sectional view for explaining a state in which a second back cover of a display device according to still yet another aspect of the present disclosure is wound. The display device  1000  illustrated in  FIG.  10    is substantially identical in configuration to the display device  900  illustrated in  FIG.  9   , except for a second back cover  1010   b  and a rolling unit  1050 . Therefore, repeated descriptions of the identical components will be omitted. For the convenience of illustration,  FIG.  10    illustrates only the second back cover  1010   b  among the components of the display part DP.  FIG.  10    is a view illustrating a state in which the display part DP is wound around the rolling unit  1050  twice. 
     Referring to  FIG.  10   , the first and second rolling guide parts  1051   a  and  1051   b  each include a protruding portion  1055  provided in a middle region thereof. A height of the protruding portion  1055  does not exceed a thickness of a structure in which the second back cover  1010   b  is doubly superimposed. This is to inhibit the first back cover wound on the second back cover  1010   b,  which is wound previously, from being lifted up by the protruding portion  1055  while the back cover is wound. 
     In the case in which the rolling guide part  1051  includes the protruding portion  1055 , the second back cover  1010   b  includes a plurality of groove portions  1014  corresponding to the protruding portion  1055 . The plurality of groove portions  1014  of the second back cover  1010   b  are disposed to engage with the protruding portions  1055  of the first and second rolling guide parts  1051   a  and  1051   b  when the second back cover  1010   b  is in the fully wound state. The groove portions  1014  may be provided at two opposite ends of the second back cover  1010   b  and disposed in a row in the direction perpendicular to the connection shaft  153 . 
     The plurality of groove portions  1014  may have a circumferential length twice the circumferential length of the rolling guide part  1051 . The plurality of groove portions  1014  may have a length that may be wound around the rolling guide part  1051  twice. 
     When the second back cover  1010   b  is wound, the two opposite ends of the second back cover  1010   b  adjoin the first and second rolling guide parts  1051   a  and  1051   b,  respectively. That is, the groove portion  1014  of the second back cover and the protruding portion  1055  of the rolling guide part are coupled while engaging with each other when the second back cover  1010   b  is wound. The second back cover  1010   b  may flatten the protruding portion  1055  of the rolling guide part when the second back cover  1010   b  is wound around the rolling guide part  1051  twice. Therefore, the second back cover  1010   b  may be wound at an exact position without slipping on an upper portion of the rolling guide part  1051 . The two opposite ends of the second back cover  1010   b  are supported by the rolling guide parts  1051  in the state in which the second back cover  1010   b  is wound around the rolling guide parts  1051  twice. The cylindrical shape of the second back cover  1010   b  may be maintained even though the middle portion of the second back cover  1010   b  is not supported. Therefore, when the second back cover  1010   b  is wound, the connection shaft  153  and the second printed circuit board  170  may be disposed in the cylindrical second back cover  1010   b.  On the contrary, when the second back cover  1010   b  is fully unwound, the second printed circuit board  170  and the torsion spring TS disposed above the connection shaft  153  are exposed. In other words, the second printed circuit board  170  and the torsion spring TS are present in the housing part HP and disposed above the connection shaft  153 . However, the second printed circuit board  170  and the torsion spring TS are not disposed in a separate roller. 
     In the display device  1000  according to still yet another aspect of the present disclosure, the heavy roller in the related art is eliminated, and the first rolling guide part  1051   a,  the second rolling guide part  1051   b,  and the connection shaft  153  are disposed. Therefore, it is possible to provide the display device  1000  that is lightweight and portable. 
     In addition, in the display device  1000  according to still yet another aspect of the present disclosure, the two opposite ends of the back cover are supported by the first rolling guide part  1051   a  and the second rolling guide part  105  lb. Therefore, even the central portion of the back cover, which does not adjoin the rolling guide parts  1051 , may be wound without sagging. In other words, the plurality of groove portions  1014  of the second back cover  1010   b  may engage with the protruding portions  1055  of the rolling guide parts  1051  when the second back cover  1010   b  is wound twice. Therefore, in the display device  1000  according to still yet another aspect of the present disclosure, a length of a portion where the second back cover  1010   b  and the rolling guide part  1051  engage with each other is increased, which makes it possible to more efficiently inhibit the central portion of the back cover from sagging. 
       FIG.  11    is a perspective view for explaining a state in which a second back cover of a display device according to another further aspect of the present disclosure is unwound. The display device  1100  illustrated in  FIG.  11    is substantially identical in configuration to the display device  100  illustrated in  FIGS.  1  to  6   , except for a second back cover  1110   b.  Therefore, repeated descriptions of the identical components will be omitted. For the convenience of illustration,  FIG.  11    illustrates only the second back cover  1110   b  among the components of the display part DP. 
     Although not illustrated in  FIG.  11   , the first and second rolling guide part  151   a  and  151   b  each include the groove portion  154  provided in the middle region thereof, as illustrated in  FIGS.  5  and  6   . A cross-section of the groove portion  154  may have a ⊏ shape, a V shape, or a U shape. However, the present disclosure is not limited thereto. 
     In the case in which the rolling guide parts  151  include the groove portions  154 , the second back cover  1110   b  include the plurality of protruding portions  113  corresponding to the groove portions  154 . The protruding portions  113  may be disposed at two opposite ends of the second back cover  1110   b.  The protruding portions  113  may be disposed in a row in a direction perpendicular to the connection shaft  153 . The plurality of protruding portions  113  are formed separately from the second back cover  1110   b  and then attached or fastened to the second back cover  1110   b.  The plurality of protruding portions  113  may be disposed in a rectangular parallelepiped shape. However, the plurality of protruding portions may each have a shape corresponding to the shape of the cross-section of the groove portion  154  of the rolling guide part. 
     The plurality of protruding portions  113  and the groove portions  154  of the rolling guide parts  151  may be attached to one another. The plurality of protruding portions  113  may be bonded to the groove portions  154  of the rolling guide parts  151  by means of a bondable material applied onto surfaces of the plurality of protruding portions  113 . Alternatively, the plurality of protruding portions  113  may be fastened to the groove portions  154  of the rolling guide parts  151  by means of screws. 
     The plurality of protruding portions  113  may have a length equal to the circumferential length of the groove portion  154  of the rolling guide part  151 . That is, the plurality of protruding portions  113  have a length that is wound around the groove portion  154  of the rolling guide part  151  once. 
     Referring to  FIG.  11   , when the back cover is fully unwound, a part of the second back cover  1110   b  is wound around the first and second rolling guide parts  1051   a  and  1051   b  once, thereby maintaining a cylindrical shape. That is, the plurality of protruding portions  113  of the second back cover  1110   b  and the groove portions  154  of the rolling guide parts  151  are kept attached to and engaging with one another. Therefore, the connection shaft  153 , the second printed circuit board  170 , and the torsion spring TS are disposed in the second back cover  1110   b  without being exposed even when the back cover is fully unwound. 
     The remaining part of the second back cover  1110   b  is supported by the cylindrical second back cover  1110   b  when the second back cover  1110   b  is wound. That is, the remaining part of the second back cover  1110   b  may be wound while adjoining a part of the cylindrical second back cover  1110   b.    
     In the display device  1100  according to another further aspect of the present disclosure, the heavy roller in the related art is eliminated, and the first rolling guide part  151   a,  the second rolling guide part  151   b,  and the connection shaft  153  are disposed. Therefore, it is possible to provide the display device  1100  that is lightweight and portable. In particular, in the display device  1100  according to another further aspect of the present disclosure, the lightweight second back cover  1110   b  may provide the same function as the roller instead of the heavy roller. 
     In addition, in the display device  1100  according to still yet another aspect of the present disclosure, the two opposite ends of the back cover are supported by the first rolling guide part  151   a  and the second rolling guide part  151   b . Therefore, even the central portion of the back cover, which does not adjoin the rolling guide parts  151 , may be wound without sagging. 
     In addition, in the display device  1100  according to another further aspect of the present disclosure, the cylindrical shape, which is made by winding the second back cover  1110   b  around the rolling guide parts  151  once, may be always maintained. Therefore, the remaining part of the second back cover  1110   b  is supported by the second back cover  1110   b  that maintains the cylindrical shape when the second back cover  1110   b  is wound. Therefore, it is possible to additionally inhibit the central portion of the back cover from sagging. 
     &lt;Modification of Connection Part&gt; 
       FIG.  12 A  is a perspective view for explaining a state in which a second back cover of a display device according to still another further aspect of the present disclosure is unwound.  FIG.  12 B  is a cross-sectional view of the display device according to still another further aspect of the present disclosure. The display device  1200  illustrated in  FIGS.  12 A and  12 B  is substantially identical in configuration to the display device  100  illustrated in  FIGS.  1  to  6   , except for a rolling unit  1250 . Therefore, repeated descriptions of the identical components will be omitted. For the convenience of illustration,  FIGS.  12 A and  12 B  illustrate only the second back cover  110   b  among the components of the display part DP. 
     Referring to  FIGS.  12 A and  12 B , the rolling unit  1250  includes: a first rolling guide part  1251   a  and a second rolling guide part  1251   b;  and a fastening bar  1253  disposed on outer peripheral surfaces of the first and second rolling guide parts  1251   a  and  1251   b  and having one end and the other end fastened to the first and second rolling guide parts  1251   a  and  1251   b.    
     A part of an outer peripheral surface of the fastening bar  1253  has a curved surface corresponding to a cylindrical shape formed when the back cover  110  is in the fully wound state. The remaining part of the outer peripheral surface of the fastening bar  1253  has a flat surface. The flat surface of the fastening bar  1253  corresponds to a first flat portion F 1  of flat surfaces of the outer peripheral surface of each of the first and second rolling guide parts  1251   a  and  1251   b.  The curved surface of the fastening bar  1253  corresponds to the cylindrical shape of the back cover when the back cover is in the fully wound state. 
     Fastening holes may be formed at one end and the other end of the fastening bar  1253  so as to be fastened to the rolling guide parts  1251  and the second back cover  110   b.  For example, fastening members may be disposed to penetrate the fastening holes of the fastening bar  1253 , the fourth fastening holes AH 4  of the second back cover  110   b,  and the rolling guide parts  1251 , such that the rolling guide parts  1251 , the second back cover  110   b,  and the fastening bar  1253  may be simultaneously fastened. Meanwhile, the fastening bar  1253  may be bonded to the second back cover  110   b  by means of an adhesive tape instead of the fastening holes of the fastening bar  1253 . 
     The fastening bar  1253  is connected to the first and second rolling guide parts  1251   a  and  1251   b  and transmits rotational power. A spring tape may be fastened to the flat surface of the fastening bar  1253  and the first rolling guide part  1251   a.  The spring tape may transmit power to a rotation of the fastening bar  1253  by providing tension. The first and second rolling guide parts  1251   a  and  1251   b  may rotate as the tension is provided. 
     A part of the outer peripheral surface of the rolling guide part  1251  is formed to be flat, the first flat portion F 1  of the flat surfaces corresponds to the fastening bar  1253 . The remaining second flat portion F 2 , except for the first flat portion F 1 , corresponds to the second support area PA of the first back cover  110   a  when the display part DP is wound. The second support area PA 2  in which the first printed circuit board  140  and the flexible film  130  are disposed is wound while adjoining the flat portion of the rolling guide part  1251 , such that the second support area PA 2  and the first printed circuit board  140  and the flexible film  130  in the second support area PA 2  may be kept flat without being curved. Therefore, the flexible film  130  and the first printed circuit board  140  may be always kept flat regardless of the state in which the display part DP is wound or unwound. Therefore, it is possible to inhibit the flexible film  130  and the first printed circuit board  140  from being bent and damaged. 
     The second printed circuit board  170  is disposed on a central portion of the fastening bar  1253  and electrically connected to the first printed circuit board  140 . For example, although not illustrated in the drawings, a support may be disposed between the second printed circuit board  170  and the central portion of the fastening bar  1253  so that the second printed circuit board  170  is disposed on the central portion of the rolling guide part  1251 . The second printed circuit board  170  may be fixed to the support by means of an adhesive tape or screw. 
     The first and second rolling guide parts  1251   a  and  1251   b  each include a groove portion  1254  provided in a middle region thereof. In the case in which the rolling guide parts  1251  include the groove portions  1254 , the second back cover  110   b  include the plurality of protruding portions  113  corresponding to the groove portions  1254 . The protruding portions  113  may be disposed at two opposite ends of the second back cover  110   b.  The protruding portions  113  may be disposed in a row in a direction perpendicular to the connection shaft  153 . The plurality of protruding portions  113  are formed separately from the second back cover  110   b  and then attached or fastened to the second back cover  110   b.    
     When the second back cover  110   b  is wound, the two opposite ends of the second back cover  110   b  adjoin the first and second rolling guide parts  1251   a  and  1251   b,  respectively. That is, the protruding portions  113  of the second back cover come into contact and engage with the groove portion  1254  of the rolling guide part  1251  when the second back cover  110   b  is wound. In addition, a part of the wound second back cover  110   b  is supported by the fastening bar  1253 . Therefore, the second back cover  110   b  may be wound at an exact position without slipping on an upper portion of the rolling guide part  1251 . The two opposite ends of the second back cover  110   b  are supported by the rolling guide parts  1251  and the fastening bar  1253  in the state in which the second back cover  110   b  is wound around the rolling guide parts  1251  once. The cylindrical shape of the second back cover  110   b  may be maintained even though the middle portion of the second back cover  110   b  is not supported. Therefore, when the second back cover  110   b  is wound, the fastening bar  1253  and the second printed circuit board  170  may be disposed in the cylindrical second back cover  110   b.  On the contrary, when the second back cover  110   b  is fully unwound, the second printed circuit board  170  disposed above the fastening bar  1253  is exposed. In other words, the second printed circuit board  170  is present in the housing part HP and disposed above the fastening bar  1253 . However, the second printed circuit board  170  is not disposed in a separate roller. 
     The display device  1200  according to still another further aspect of the present disclosure may be implemented as a display device that is lightweight and portable and replaces the heavy roller in the related art. That is, the roller in the related art is eliminated, and the rolling guide parts  1251  and the fastening bar  1253  are disposed, such that the rollable display device in which the back cover  110  is wound while being supported by the rolling guide parts  1251  and the fastening bar  1253  may be implemented. 
     In addition, in the display device  1200  according to still another further aspect of the present disclosure, the two opposite ends of the back cover are supported by the rolling guide parts  1251  and the fastening bar  1253 . Therefore, even the central portion of the back cover  110 , which does not adjoin the rolling guide part  151 , may be wound without sagging. In other words, the plurality of protruding portions  113  may be disposed at the two opposite ends of the second back cover  110   b  and correspond to the groove portions  1254  of the rolling guide parts  1251 , such that the plurality of protruding portions  113  may engage with the groove portions  1254  when the back cover  110  is wound. Furthermore, a part of the second back cover  110   b  is supported by the fastening bar  1253 . Therefore, in the display device  1200  according to still another further aspect of the present disclosure, the cylindrical shape of the wound back cover  110  may be maintained, and the plurality of protruding portions  113  and the plurality of groove portions  1254  may more efficiently inhibit the central portion of the back cover  110  from sagging. 
     The exemplary aspects of the present disclosure can also be described as follows: 
     According to an aspect of the present disclosure, a display device may comprising: a first rolling guide parts and a second rolling guide parts each comprising at least one of a protruding portion and a groove portion; a connection part having one end fixed to the first rolling guide part and the other end fixed to the second rolling guide part; a back cover seated on the first and second rolling guide parts; and a display panel disposed on the back cover. 
     The back cover may comprise a first back cover disposed on a rear surface of the display panel and configured to support the display panel; and a second back cover having one end fixed to the first and second rolling guide parts and the other end configured to overlap the first back cover. 
     The connection part may be a connection shaft having one end and the other end fastened to middle regions of the first and second rolling guide parts. 
     The display device may further comprise a flexible film electrically connected to one end of the display panel and disposed on one surface of the first back cover; a first printed circuit board electrically connected to the flexible film and disposed on one surface of the first back cover; and a second printed circuit board electrically connected to the first printed circuit board and disposed on the connection shaft. 
     When the back cover is in a fully unwound state, the second back cover maintains a cylindrical shape formed by winding the second back cover around the first and second rolling guide parts once, and the connection shaft and the second printed circuit board may be disposed in the cylindrical second back cover. 
     The connection shaft and the second printed circuit board may be exposed when the back cover is in a fully unwound state. 
     The connection part may be a fastening bar disposed on outer peripheral surfaces of the first and second rolling guide parts. 
     The display device may further comprise a flexible film electrically connected to one end of the display panel and disposed on one surface of the first back cover; a first printed circuit board electrically connected to the flexible film and disposed on one surface of the first back cover; and a second printed circuit board electrically connected to the first printed circuit board and disposed on the fastening bar. 
     An outer peripheral surface of the fastening bar may have a curved surface corresponding to a cylindrical shape formed when the back cover is in a fully wound state. 
     The fastening bar and the second printed circuit board may be exposed when the back cover is in a fully unwound state. 
     The first and second rolling guide parts each comprise the protruding portion, and the second back cover comprises a plurality of groove portions, and the plurality of groove portions of the second back cover may be disposed to engage with the protruding portions of the first and second rolling guide parts when the second back cover is in a fully wound state. 
     The plurality of groove portions of the second back cover may have a length once or twice a circumferential length of each of the first and second rolling guide parts. 
     The first and second rolling guide parts each comprise the groove portion, and the second back cover comprises a plurality of protruding portions, and wherein the plurality of protruding portions of the second back cover may be disposed to engage with the groove portions of the first and second rolling guide parts when the second back cover is in a fully wound state. 
     The plurality of protruding portions of the second back cover are configured as magnetic elements, and the first and second rolling guide parts may be made of metal, such that a magnetic force is formed between the plurality of protruding portions of the second back cover and the groove portions of the first and second rolling guide parts. 
     The magnetic elements are attached to the plurality of protruding portions of the second back cover, and the first and second rolling guide parts may be made of metal, such that a magnetic force is formed between the plurality of protruding portions of the second back cover and the groove portions of the first and second rolling guide parts. 
     The plurality of protruding portions of the second back cover may have a length equal to a circumferential length of the groove portion of each of the first and second rolling guide parts. 
     The first and second rolling guide parts each comprise at least two groove portions, and the plurality of protruding portions of the second back cover provided at two opposite sides of the second back cover and disposed and extending in at least two rows in a direction perpendicular to the connection part, and wherein one of the plurality of protruding portions of the second back cover may correspond to one of the groove portions when the back cover is in a fully wound state. 
     The plurality of protruding portions of the second back cover may each comprise a plurality of patterns. 
     According to another aspect of the present disclosure, a display device may comprising: a display panel having a plurality of pixels; a back cover disposed on a rear surface of the display panel so as to be rollable together with the display panel; a first display device  100  and a second rolling guide parts around which the back cover and the display panel are wound or unwound, the first and second rolling guide parts each comprising at least one of a protruding portion and a groove portion and configured such that the back cover is seated on the first and second rolling guide parts; and a connection part having one end and the other end at which the first and second rolling guide parts are disposed. 
     The connection part is a connection shaft may have one end and the other end fastened to middle regions of the first and second rolling guide parts. 
     The connection part may be a fastening bar configured to adjoin a part of an outer peripheral surface of each of the first and second rolling guide parts. 
     The first and second rolling guide parts each comprise the protruding portion, and the back cover comprises a plurality of groove portions in a lower region of the display panel, and the plurality of groove portions of the back cover may be disposed to engage with the protruding portions of the first and second rolling guide parts when the back cover is in a fully wound state. 
     The first and second rolling guide parts each comprise the groove portion, the back cover comprises a plurality of protruding portions in a lower region of the display panel, and the plurality of protruding portions of the back cover may be disposed to engage with the groove portions of the first and second rolling guide parts when the back cover is in a fully wound state. 
     Although the exemplary aspects of the present disclosure have been described in detail with reference to the accompanying drawings, the present disclosure is not limited thereto and may be embodied in many different forms without departing from the technical concept of the present disclosure. Therefore, the exemplary aspects of the present disclosure are provided for illustrative purposes only but not intended to limit the technical concept of the present disclosure. The scope of the technical concept of the present disclosure is not limited thereto. Therefore, it should be understood that the above-described exemplary aspects are illustrative in all aspects and do not limit the present disclosure. The protective scope of the present disclosure should be construed based on the following claims, and all the technical concepts in the equivalent scope thereof should be construed as falling within the scope of the present disclosure.