Abstract:
A display device according to an exemplary embodiment of the present invention includes: a display panel configured to display an image; a first supporting plate positioned to support the display panel thereon, the first supporting plate being rotatable based on a first rotation axis extending in a first direction; a second supporting plate positioned to support the display panel thereon, the second supporting plate being rotatable based on a second rotation axis extending in the first direction so that the first and second supporting plates then face each other with the display panel folded therebetween; and a first tension application unit disposed at the first supporting plate and configured to apply tension to the display panel in a second direction crossing the first direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to, and the benefit of, Korean Patent Application No. 10-2016-0037730 filed in the Korean Intellectual Property Office on Mar. 29, 2016, the entire contents of which are incorporated herein by reference. 
       BACKGROUND 
     (a) Technical Field 
       [0002]    Embodiments of the present invention relate generally to display devices. More specifically, embodiments of the present invention relate to foldable display devices. 
       (b) Description of the Related Art 
       [0003]    Currently popular display devices include the liquid crystal display (LCD), the plasma display panel (PDP), the organic light emitting diode (OLED) display, the field effect display (FED), and the electrophoretic display (EPD). 
         [0004]    The OLED display includes two electrodes and an organic emission layer disposed therebetween. Here, electrons from one electrode and holes from the other electrode combine in the organic emission layer to thereby form excitons, which release energy to emit light. 
         [0005]    An organic light emitting diode display has a self-luminous characteristic, and because the organic light emitting diode display does not need a separate light source, unlike a liquid crystal display, it can have a relatively small thickness and weight. Further, the OLED display exhibits high-quality characteristics such as low power consumption, high luminance, and fast response speed, and thus receives attention as a next generation display device. 
         [0006]    Recently, flexible display devices that are bendable or foldable have been under development. 
         [0007]    However, unfolding a flexible display device currently can result in the display panel floating or partially detaching from a supporting plate supporting the display panel. 
         [0008]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
       SUMMARY 
       [0009]    Embodiments of the present invention provide a display device in which the display panel is prevented from floating from the supporting plate supporting the display panel when unfolding the display panel. 
         [0010]    A display device according to an exemplary embodiment of the present invention includes: a display panel configured to display an image; a first supporting plate positioned to support the display panel thereon, the first supporting plate being rotatable based on a first rotation axis extending in a first direction; a second supporting plate positioned to support the display panel thereon, the second supporting plate being rotatable based on a second rotation axis extending in the first direction so that the first and second supporting plates then face each other with the display panel folded therebetween; and a first tension application unit disposed at the first supporting plate and configured to apply tension to the display panel in a second direction crossing the first direction. 
         [0011]    The first tension application unit may be positioned at a side of the first supporting plate that is opposite to a side of the first supporting plate at which that the first rotation axis is positioned. 
         [0012]    The first tension application unit may include a first roller having a surface to which a side of the display panel is coupled, and a first winder coupled to the first roller and configured to rotate the first roller. 
         [0013]    The first roller may be disposed to be parallel to the first rotation axis. 
         [0014]    The first winder may include a spring. 
         [0015]    The first rotation axis and the second rotation axis may be separated by a predetermined interval. 
         [0016]    The first supporting plate and the second supporting plate may be formed such that they face each other. 
         [0017]    The first supporting plate and the second supporting plate may be substantially quadrangular. 
         [0018]    The first supporting plate may further include a first groove formed in a surface of the first supporting plate that faces the display panel. 
         [0019]    The first groove may be positioned proximate to the first rotation axis. 
         [0020]    A width of the first groove in the first direction may be equal to or larger than a width of the display panel in the first direction. 
         [0021]    A second tension application unit disposed at the second supporting plate and configured to apply tension to the display panel in the second direction may be further included. 
         [0022]    The second tension application unit may be positioned at a side of the second supporting plate that is opposite to a side of the second supporting plate at which the second rotation axis is positioned. 
         [0023]    The second tension application unit may include a second roller having a surface to which a side of the display panel is coupled, and a second winder coupled to the second roller and configured to rotate the second roller. 
         [0024]    The second roller may be disposed to be parallel to the second rotation axis. 
         [0025]    The second winder may include a spring. 
         [0026]    The second supporting plate may further include a second groove formed at a second surface of the second supporting plate that faces the display panel. 
         [0027]    The second groove may be positioned proximate to the second rotation axis. 
         [0028]    A width of the second groove in the first direction may be equal to or larger than a width of the display panel in the first direction. 
         [0029]    According to the above-described display device, when unfolding the display panel, the display panel is close to the supporting plate supporting the display panel, thereby preventing the display panel from being lifted from the supporting plate. 
         [0030]    Also, damage to the display panel may be prevented by reducing the stress applied to the bending region of the display panel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]      FIG. 1  is a schematic perspective view of a display device according to an exemplary embodiment of the present invention. 
           [0032]      FIG. 2  is a cross-sectional view taken along a line II-II of  FIG. 1 . 
           [0033]      FIG. 3  is a cross-sectional view showing a state in which the display device of  FIG. 2  is folded. 
           [0034]      FIG. 4  is an enlarged view of a region A of  FIG. 1 . 
           [0035]      FIG. 5  is a cross-sectional view of a display device according to another exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0036]    Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the attached drawings such that the present invention can be easily put into practice by those skilled in the art. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. The drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. 
         [0037]    In addition, the size and thickness of each component shown in the drawings are arbitrarily shown for better understanding and ease of description, but the present invention is not limited thereto. 
         [0038]    In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. In the drawings, for better understanding and ease of description, the thickness of some layers and areas is exaggerated. The drawings are thus not necessarily to scale. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. 
         [0039]    In addition, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. Furthermore, when a first part is described as being arranged “on” a second part, this indicates that the first part is arranged at an upper side or a lower side of the second part without the limitation to the upper side thereof on the basis of the gravity direction. 
         [0040]    All numerical values are approximate, and may vary. All examples of specific materials and compositions are to be taken as nonlimiting and exemplary only. Other suitable materials and compositions may be used instead. 
         [0041]    Next, a display device according to an exemplary embodiment of the present invention will be described with reference to  FIG. 1  to  FIG. 3 . 
         [0042]      FIG. 1  is a schematic perspective view of a display device according to an exemplary embodiment of the present invention,  FIG. 2  is a cross-sectional view taken along a line II-II of  FIG. 1 , and  FIG. 3  is a cross-sectional view showing a state in which the display device of  FIG. 2  is folded. However, in  FIG. 1 , an illustration of the display panel P is omitted for clarity. 
         [0043]    Referring to  FIG. 1  to  FIG. 3 , the display device according to the present exemplary embodiment includes a display panel P, a first supporting plate  110 , a second supporting plate  130 , a first tension application unit  300 , and a second tension application unit  500 . In the present exemplary embodiment, the display panel P may be folded or unfolded by rotation of the first supporting plate  110  relative to the second supporting plate  130 , and when the display panel P is unfolded, the display panel P may be maintained to be flat by the first tension application unit  300  and the second tension application unit  500 . 
         [0044]    The display panel P may emit light to display an image. In this case, the display panel P, in addition to being a display panel of an organic light emitting diode (OLED) display, may alternatively be employ a liquid crystal display (LCD), a plasma display panel (PDP), an electric field effect display (FED) device, an electrophoretic display (EPD), and the like. 
         [0045]    The display panel P is disposed on both the first supporting plate  110  and the second supporting plate  130 . A shape of the display panel P may be changed by rotation of the first supporting plate  110  and the second supporting plate  130  that support the display panel P. For example, when the first supporting plate  110  and the second supporting plate  130  are coplanar, the display panel P is unfolded. In contrast, if the first supporting plate  110  and the second supporting plate  130  face parallel to each other, the display panel P is folded. 
         [0046]    Referring to  FIG. 1  and  FIG. 2 , the first supporting plate  110  may have a plate shape. In this case, a first surface  111  of the first supporting plate  110  is in contact with the display panel P and may be flat. When the first surface  111  of the first supporting plate  110  is flat, the surface of the display panel P supported by the first supporting plate  110  may be flat. That is, unevenness or bending of the surface of the display panel P may be prevented. 
         [0047]    Also, as shown in  FIG. 1 , the first supporting plate  110  may form a quadrangular plane by corresponding to a half of the display panel P. In  FIG. 1 , for convenience of description, the display panel P positioned on the first supporting plate  110  and the second supporting plate  130  is omitted. 
         [0048]    In this case, an area of the first supporting plate  110  may be formed to be equal to or larger than half of the display panel P. Accordingly, the first supporting plate  110  may support half of the display panel P. Here, the area of the first supporting plate  110  represents an area parallel to the plane formed by an X-axis and a Y-axis in  FIG. 1 . 
         [0049]    On the other hand, referring to  FIG. 2 , the first supporting plate  110  may be rotated based on the first rotation axis RA 1 . The first rotation axis RA 1  may be positioned at a left side of the first supporting plate  110  and may be disposed to be parallel to the first direction. Here, the first direction represents the X-axis of the coordinates shown in  FIGS. 1 and 2 . Also, the first rotation axis RA 1  shown in  FIG. 1  to  FIG. 3  corresponds to an imaginary line that is a reference when the first supporting plate  110  is rotated. 
         [0050]    Like the first supporting plate  110 , the second supporting plate  130  may also have a plate shape. A second surface  131  of the second supporting plate  130  in contact with the display panel P may be flat. As the first surface  111  of the first supporting plate  110  and the second surface  131  of the second supporting plate  130  are both flat, as shown in  FIG. 2 , the entire surface of the display panel P may be maintained substantially flat. 
         [0051]    On the other hand, as shown in  FIG. 1 , the second supporting plate  130  corresponds to the shape of half of the display panel P, thereby forming a quadrangular plane. 
         [0052]    In this case, the area of the second supporting plate  130  may be formed to be equal to or larger than half of the display panel P. Like the first supporting plate  110 , the second supporting plate  130  may support the other half of the display panel P. Here, like the area of the first supporting plate  110 , the area of the second supporting plate  130  represents an area parallel to the plane formed by the X-axis and the Y-axis. 
         [0053]    When the first supporting plate  110  and the second supporting plate  130  are unfolded so as to be coplanar, the collective shape formed by the first supporting plate  110  and the second supporting plate  130  may be a quadrangle corresponding to the entire shape of the display panel P. 
         [0054]    In this case, the collective area of the first supporting plate  110  and the second supporting plate  130  may be formed to be equal to or larger than the entire area of the display panel P. Accordingly, the first supporting plate  110  and the second supporting plate  130  may support the entire display panel P. 
         [0055]    The second supporting plate  130  may be rotated based on the second rotation axis RA 2 . The second rotation axis RA 2  may be positioned at the right side of the second supporting plate  130  and may be disposed to be parallel to the first rotation axis RA 1 . That is, the first rotation axis RA 1  and the second rotation axis RA 2  may each be disposed to be parallel to the first direction. In this case, the second rotation axis RA 2  shown in  FIG. 1  to  FIG. 3  corresponds to an imaginary line that is a reference when the second supporting plate  130  is rotated, similar to the first rotation axis RA 1 . 
         [0056]    Referring to  FIG. 2  and  FIG. 3 , while the first supporting plate  110  and the second supporting plate  130  are respectively rotated based on the first rotation axis RA 1  and the second rotation axis RA 2 , the first supporting plate  110  and the second supporting plate  130  may be rotated so as to be coplanar, or the first surface  111  of the first supporting plate  110  and the second surface  131  of the second supporting plate  130  may be disposed to face each other. 
         [0057]    In detail, as shown in  FIG. 2 , if the first supporting plate  110  and the second supporting plate  130  are coplanar, an angle formed by the first surface  111  of the first supporting plate  110  and the second surface  131  of the second supporting plate  130  is about 180 degrees. Also, if the first supporting plate  110  is rotated in a counterclockwise direction based on the first rotation axis RA 1  and the second supporting plate  130  is rotated in a clockwise direction based on the second rotation axis RA 2 , as shown in  FIG. 3 , the angle formed by the first surface  111  and the second surface  131  is about 0 degrees. 
         [0058]    According to the present exemplary embodiment, the first supporting plate  110  is rotated in the counterclockwise direction based on the first rotation axis RA 1 , from an initial orientation parallel to the Y-axis. Also, when the second supporting plate  130  is initially oriented parallel to the Y-axis, the second supporting plate  130  is only rotated in the clockwise direction based on the second rotation axis RA 2 . That is, when the first supporting plate  110  and the second supporting plate  130  are disposed as shown in  FIG. 2 , the first supporting plate  110  may not be rotated in the clockwise direction based on the first rotation axis RA 1 , and the second supporting plate  130  may not be rotated in the counterclockwise direction based on the second rotation axis RA 2 . 
         [0059]    Accordingly, as shown in  FIG. 3 , two halves of the display panel P may be disposed to face each other. Thus, if the first supporting plate  110  and the second supporting plate  130  are rotated and disposed to face each other, the display panel P is positioned in the folded state between the first supporting plate  110  and the second supporting plate  130 . 
         [0060]    Again referring to  FIG. 1  and  FIG. 2 , the first tension application unit  300  applying a tension to the display panel P may be disposed in the first supporting plate  110 . The first tension application unit  300  applies tension to the display panel P at the edge of the display panel P along a second direction crossing the first direction. Here, the second direction represents the Y-axis of the coordinates in the drawing. 
         [0061]    In this case, the first tension application unit  300  may be positioned at the opposite side of the first supporting plate  110  as the first rotation axis RA 1 . As shown in  FIG. 2 , the first rotation axis RA 1  may be formed at the left side of the first supporting plate  110 , and the first tension application unit  300  may be formed at the right side of the first supporting plate  110 . 
         [0062]    Also, the first tension application unit  300  may be disposed in a first receiving part  113  formed at the right side of the first supporting plate  110 . The first receiving part  113  may be a groove shaped feature at the right side of the first supporting plate  110 . 
         [0063]    The second tension application unit  500  applies tension to the display panel P and may be disposed in the second supporting plate  130 . The second tension application unit  500  applies tension to the display panel P at the edge of the display panel P along the second direction. 
         [0064]    In this case, the second tension application unit  500  may be positioned at the opposite side of the second supporting plate  130  as the second rotation axis RA 2 . As shown in  FIG. 2 , the second rotation axis RA 2  is disposed at the right side of the second supporting plate  130 , and the second tension application unit  500  is disposed at the left side of the second supporting plate  130 . 
         [0065]    Also, the second tension application unit  500  may be disposed in a second receiving part  115  formed at the left side of the second supporting plate  130 . Like the first receiving part  113 , the second receiving part  115  may be formed as a groove shaped feature at the left side of the second supporting plate  130 . 
         [0066]    In the present exemplary embodiment, the first tension application unit  300  and the second tension application unit  500  apply tension to the display panel P in opposite directions to each other. For example, in  FIG. 2 , the first tension application unit  300  applies tension in the right direction and the second tension application unit  500  applies tension in the left direction. 
         [0067]    Referring to  FIG. 2 , when the first supporting plate  110  and the second supporting plate  130  are unfolded to be coplanar, the display panel P may be lifted in a neighborhood region M of the first rotation axis RA 1  and the second rotation axis RA 2 . For example, the display panel P may be separated from the first supporting plate  110  and the second supporting plate  130  in a third direction without being in contact therewith. If the display panel P is separated from the first supporting plate  110  and the second supporting plate  130 , bending is generated on the display panel P such that the image emitted from the display panel P may be distorted. Here, the third direction represents a Z-axis in the coordinates in the drawing. 
         [0068]    However, according to the present exemplary embodiment, since the first tension application unit  300  and the second tension application unit  500  apply tension to the display panel P, the display panel P may be close to the first supporting plate  110  and the second supporting plate  130 . That is, the first tension application unit  300  and the second tension application unit  500  improve flatness of the display panel P, thereby preventing distortion of the image emitted from the display panel P. 
         [0069]    Referring to  FIG. 2  and  FIG. 4 , the first tension application unit  300  may include a first roller  310  and a first winder  330 . 
         [0070]    One end part of the display panel P is bonded to an external circumferential surface of the first roller  310 . In  FIG. 4 , if the first roller  310  is rotated in the clockwise direction based on the third rotation axis RA 3 , tension may be applied to the display panel P. 
         [0071]    In this case, the first winder  330  is bonded to the first roller  310 , thereby rotating the first roller  310  in the clockwise direction. According to the present exemplary embodiment, the first winder  330  may employ a spring. The spring is a thin steel strip that is rolled and bonded to the first roller  310 , and the first roller  310  may be rotated in the clockwise direction by a force when the thin steel strip is unrolled. 
         [0072]    The second tension application unit  500  may be formed with the same configuration as the first tension application unit  300 . That is, the second tension application unit  500  may include a second roller and a second winder. The second tension application unit  500  has the same configuration as the first tension application unit  300  such that the detailed description thereof is omitted. 
         [0073]    Referring to  FIG. 1  and  FIG. 2 , a first groove  117  may be formed close to the first rotation axis RA 1  at the first surface  111  of the first supporting plate  110 . The first groove  117  is formed to extend along the first direction. A width of the first groove  117  in the first direction may be formed to be the same as the width of the display panel P in the first direction or to be larger than the width of the display panel P in the first direction. Accordingly, when the display panel P is folded, part of the display panel P may be bent or extend into the first groove  117 . Further description thereof exists below. 
         [0074]    On the other hand, a second groove  119  may be formed close to the second rotation axis RA 2  at the second surface  131  of the second supporting plate  130 . The second groove  119  is formed to extend along the first direction. The width of the second groove  119  in the first direction, like the first groove  117 , may be formed to be the same as the width of the display panel P in the first direction or to be larger than the width of the display panel P in the first direction. Accordingly, when folding the display panel P, part of the display panel P may be drop into the second groove  119 . 
         [0075]    Referring to  FIG. 3 , if the first supporting plate  110  and the second supporting plate  130  are disposed to face each other, the display panel P is bent in the region close to the first rotation axis RA 1  and the second rotation axis RA 2 . In this case, part of the display panel P is bent and enters into the first groove  117  and the second groove  119 . Accordingly, the stress generated in the bending of the display panel P may be reduced. 
         [0076]    In detail, in the present exemplary embodiment, the radius of curvature of the display panel P may be increased in the bending region by the first groove  117  and the second groove  119 . If the first groove  117  and the second groove  119  are not formed in the display panel P, the radius of curvature of the display panel P in the bending region is smaller than the curvature of the display panel P in the present exemplary embodiment. In the present exemplary embodiment, increasing the radius of curvature of the display panel P in the bending region can reduce the stress generated at the display panel P in the bending region. 
         [0077]    Meanwhile, referring to  FIG. 2  and  FIG. 3 , the first rotation axis RA 1  and the second rotation axis RA 2  may be disposed to be separated by a predetermined interval W. In this case, to control the curvature of the display panel P of the bending region, the interval W may be controlled. For example, if the interval W increases, the radius of curvature of the display panel P of the bending region may be increased, and in contrast, if the interval W decreases, the radius of curvature of the display panel P of the bending region may be reduced. 
         [0078]    Next, the display device according to another exemplary embodiment of the present invention will be described with reference to  FIG. 5 . When describing the current exemplary embodiment, detailed description of the same configurations as in the above-described exemplary embodiment is omitted. 
         [0079]      FIG. 5  is a cross-sectional view of a display device according to another exemplary embodiment of the present invention. 
         [0080]    Referring to  FIG. 5 , different from the above-described exemplary embodiment, the first tension application unit  300  is only formed in the first supporting plate  110 . That is, the tension application unit made of the roller and the winder is not formed in the second supporting plate  130 . 
         [0081]    In the present exemplary embodiment, the display panel P positioned at the second supporting plate  130  is fixed and bonded to the left side of the second supporting plate  130 . Also, the first tension application unit  300  is positioned at the right side of the first supporting plate  110 . 
         [0082]    When the first supporting plate  110  and the second supporting plate  130  are unfolded to be coplanar, the first tension application unit  300  applies tension to the display panel P at the edge of the display panel P along the second direction. Accordingly, the display panel P may be close to the first supporting plate  110  and the second supporting plate  130 . The first tension application unit  300  and the second tension application unit  500  improve the flatness of the display panel P, and distortion of the image emitted from the display panel P may thus be prevented. 
         [0083]    In the display device according to an exemplary embodiment of the present invention, the first tension application unit  300  and the second tension application unit  500  are disposed at the first supporting plate  110  and the second supporting plate  130 , respectively, thereby the display panel P may be prevented from being lifted from the first supporting plate  110  and the second supporting plate  130 . Also, when folded, part of the display panel P is bent into the first groove  117  of the first supporting plate  110  and the second groove  119  of the second supporting plate  130 , thereby reducing the stress applied to the display panel P in the bending region. 
         [0084]    While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Various features of the above described and other embodiments can be mixed and matched in any manner, to produce further embodiments consistent with the invention. 
       DESCRIPTION OF SYMBOLS 
       [0000]    
       
         
           
             RA 1  first rotation axis 
             RA 2  second rotation axis 
             RA 3  third rotation axis 
             P display panel 
               110  first supporting plate 
               111  first surface 
               113  first receiving part 
               115  second receiving part 
               130  second supporting plate 
               131  second surface 
               300  first tension application unit 
               310  first roller 
               330  first winder 
               500  second tension application unit