Patent Publication Number: US-2022231254-A1

Title: Display device

Description:
This application claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2021-0007586 filed on Jan. 19, 2021 in the Korean Intellectual Property Office, the contents of which in its entirety are herein incorporated by reference. 
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates to a display device. 
     2. Description of the Related Art 
     As the information-oriented society evolves, various demands for display devices are ever increasing. For example, display devices are being employed by a variety of electronic devices such as smart phones, digital cameras, laptop computers, navigation devices, and smart televisions. 
     Recently, a foldable display device is getting a lot of attention. A foldable display device has the advantages of both a smart phone and a tablet PC because it is easy to carry and may have a wide screen. A protective film for such a foldable display device is desirable to have high durability in order to protect the elements in the display device, and to have high flexibility for smooth folding. 
     SUMMARY 
     Aspects of the present disclosure provide a display device including a protective film that has impact resistance as well as flexibility. 
     It should be noted that objects of the present disclosure are not limited to the above-mentioned object; and other objects of the present disclosure will be apparent to those skilled in the art from the following descriptions. 
     An embodiment of a display device including folding areas, the display device includes a display panel, a first protection member disposed on the display panel, a second protection member disposed on the first protection member, a first adhesive member disposed between the display panel and the first protection member, and a second adhesive member disposed between the first protection member and the second protection member and having an elastic modulus equal to or smaller than an elastic modulus of the first adhesive member. 
     An embodiment of a display device including a first folding area and a second folding area spaced apart from each other and extended in a first direction, the display device includes a display panel, a first protection member disposed on the display panel, a second protection member disposed on the first protection member and having a storage modulus increasing with a frequency of an external impact applied to the second protection member, a first adhesive member disposed between the display panel and the first protection member, and a second adhesive member disposed between the first protection member and the second protection member, wherein the display device is folded inward along the first folding area and folded outward along the second folding area. 
     An embodiment of a display device including a first folding area and a second folding area spaced apart from each other and extended in a first direction, the display device includes a display panel, a first protection member disposed on the display panel, a second protection member disposed on the first protection member, a first adhesive member disposed between the display panel and the first protection member, and a second adhesive member disposed between the first protection member and the second protection member, wherein a storage modulus of the first protection member lies in a range of from 1,000 MPa to 2,000 MPa at −20° C., and in a range of from 100 MPa to 2,000 MPa at 85° C. 
     According to an embodiment of the present disclosure, a protective film of a display device may have impact resistance as well as flexibility. 
     It should be noted that effects of the present disclosure are not limited to those described above and other effects of the present disclosure will be apparent to those skilled in the art from the following descriptions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects and features of the present disclosure will become more apparent by describing in detail embodiments thereof with reference to the attached drawings, in which: 
         FIG. 1  is a perspective view of a display device according to an embodiment of the present disclosure when it is unfolded. 
         FIG. 2  is a perspective view of the display device according to the embodiment of the present disclosure when it is folded. 
         FIG. 3  is a cross-sectional view of a display device according to an embodiment of the present disclosure when the display device is unfolded. 
         FIG. 4  is an enlarged view of area A of  FIG. 3 . 
         FIG. 5  is a cross-sectional view of a display device according to an embodiment when the display device is folded inward at the first folding area. 
         FIG. 6  is an enlarged view of area B of  FIG. 5 . 
         FIG. 7  is a cross-sectional view of the display device according to the embodiment when the display device is folded outward at the second folding area. 
         FIG. 8  is a graph showing a relationship between the modulus of the second protection member and external impact according to an embodiment. 
         FIG. 9  is a cross-sectional view of a display panel according to an embodiment of the present disclosure. 
         FIG. 10  is a cross-sectional view showing a part of a display device according to another embodiment of the present disclosure. 
         FIG. 11  is a cross-sectional view showing a part of a display device according to yet another embodiment of the present disclosure. 
         FIG. 12  is a perspective view of a display device according to yet another embodiment of the present disclosure when it is unfolded. 
         FIG. 13  is a perspective view showing the display device according to the embodiment of  FIG. 12  when it is folded inward. 
         FIG. 14  is a perspective view showing the display device according to the embodiment of  FIG. 12  when it is folded outward. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     It will also be understood that when a layer is referred to as being “on” another layer or substrate, it may be directly on the other layer or substrate, or intervening layers may also be present. The same reference numbers indicate the same components throughout the specification. In the attached figures, the thickness of layers and regions is exaggerated for clarity. 
     Although the terms “first”, “second”, etc. may be used herein to describe various elements, these elements, should not be limited by these terms. These terms may be used to distinguish one element from another element. Thus, a first element discussed below may be termed a second element without departing from teachings of one or more embodiments. The description of an element as a “first” element may not require or imply the presence of a second element or other elements. The terms “first”, “second”, etc. may also be used herein to differentiate different categories or sets of elements. For conciseness, the terms “first”, “second”, etc. may represent “first-category (or first-set)”, “second-category (or second-set)”, etc., respectively. 
     Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. 
       FIG. 1  is a perspective view of a display device according to an embodiment of the present disclosure when it is unfolded.  FIG. 2  is a perspective view of the display device according to the embodiment of the present disclosure when it is folded. According to the embodiment shown in  FIG. 2 , the display device  1  is folded inward along a first folding area FDA 1  and is folded outward along a second folding area FDA 2 . 
     Referring to  FIGS. 1 and 2 , a display device  1  according to the embodiment of the present disclosure displays images or videos in a display area DA to be described later, and may include a variety of devices including the display area DA. For example, the display device  1  according embodiments of the present disclosure may be applied to a mobile phone, a tablet PC, a personal digital assistant (PDA), a portable multimedia player (PMP), a television set, a game machine, a wristwatch-type electronic device, a head-mounted display, a personal computer monitor, a laptop computer, a car navigation system, a car instrument cluster, a digital camera, a camcorder, an outdoor billboard, an electronic billboard, various medical apparatuses, various home appliances such as a refrigerator and a laundry machine, Internet of things (IoT) devices, etc., in addition to a smart phone. 
     The display device  1  includes a display area DA and a non-display area NDA. The display area DA may be defined as an area for displaying images. The display area DA may include a plurality of pixels. The plurality of pixels may be arranged in a matrix. No image may be displayed in the non-display area NDA. When the display device  1  has touch features, the display device  1  may further include a touch area where a touch input is sensed, and the touch area may overlap with the display area DA. Although not limited thereto, the touch area may be substantially identical to the display area DA. 
     The shape of the display area DA may conform to the shape of the display device  1  employing the display area DA. The display area DA may have a rectangular shape having corners at the right angle or rounded corners when viewed from the top. It is to be understood that the shape of the display area DA when viewed from the top is not limited to the rectangle shown in the drawings, but may have other shapes such as a circle and an ellipse. 
     In the example shown in the drawings, the shorter sides of the rectangle of the display area DA are extended in the first direction DR 1 , and the longer sides thereof are extended in a second direction DR 2  perpendicular to the first direction DR 1 . A third direction DR 3  is perpendicular to the first direction DR 1  as well as the second direction DR 2 , and may refer to the thickness direction of the display device  1 . It should be understood that the directions referred to in the embodiments are relative directions, and the embodiments are not limited to the directions mentioned. 
     As used herein, the terms “top”, “upper surface” and “upper side” in the third direction DR 3  refer to the display side of a display panel  10 , whereas the terms “bottom”, “lower surface” and “lower” refer to the opposite side of the display panel  10 , unless stated otherwise. 
     The non-display area NDA may surround the display area DA. The non-display area NDA may surround all sides of the display area DA, but the present disclosure is not limited thereto. The non-display area NDA may not be disposed near at least some of the four sides of the display area DA. The bezel area of the display device  1  may be formed as the non-display area NDA. 
     The display device  1  may be a foldable display device. As used herein, a foldable display device refers to a display device that is folded and has both a folded state and an unfolded state. When folded, the device is typically folded at an angle of approximately 180°. It is, however, to be understood that the present disclosure is not limited thereto. For example, when a device is folded at an angle greater than or less than 180°, e.g., at an angle of 90° or more but less than 180° or an angle of 120° or more and less than 180°, the device is also referred to as being folded. In addition, even when not completely folded, the device may be referred to as being folded if the device is not unfolded but is bent somewhat. For example, even if bent at an angle of 90 degrees or less, the device may be referred to as being folded in order to distinguish it from being unfolded as long as the maximum folding angle is 90 degrees or more. 
     The display device  1  may include folding areas FDA: FDA 1  and FDA 2  (or folding lines). The folding areas FDA may include a first folding area FDA 1  and a second folding area FDA 2  separated and spaced apart from each other. The first folding area FDA 1  may be disposed on one side of the second folding area FDA 2  in the second direction DR 2 . 
     Each of the folding areas FDA may be extended in a direction parallel to one side of the display device  1 . For example, each of the folding areas FDA may be extended in a direction in which the shorter sides of the display device  1  are extended (first direction DR 1 ). In the display device  1  in a rectangular shape having the sides extended in the second direction DR 2  longer than the sides extended in the first direction DR 1 , when the folding areas FDA are extended in the first direction DR 1  as in the example shown in the drawings, the longer sides (the sides extended in the second direction DR 2 ) of the display device  1  may be reduced to half or less while the shorter sides (the sides extended in the first direction DR 1 ) may remain the same after the display device  1  has been folded. In an embodiment, the folding areas FDA may be extended in the same direction (the second direction DR 2 ) as the direction of the longer sides (the sides extended in the second direction DR 2 ). 
     Each of the folding areas FDA may have a predetermined width in the second direction DR 2 . The width of each of the folding areas FDA in the second direction DR 2  may be smaller than the width thereof in the first direction DR 1 . 
     The display device  1  may be folded over the folding areas FDA. The design of a foldable display device may be sorted into in-folding design in which the display surface of the display device  1  is folded inward, and out-folding design in which the display surface thereof is folded outward. The display device  1  may have either the in-folding design or the out-folding design, or may have in-and-out-folding design. For a display device having the in-and-out-folding design, the device may be folded inward and outward along the same folding area FDA or may be folded inward and outward along different folding areas, respectively. According to the embodiment shown in  FIG. 2 , the display device  1  is folded inward along the first folding area FDA 1  and is folded outward along the second folding area FDA 2 . 
     The display device  1  may include non-folding areas NFA disposed near the folding areas FDA. The non-folding areas NFA may include a first non-folding area NFA 1  located on one side of the first folding area FDA 1  in the second direction DR 2 , a second non-folding area NFA 2  located on the opposite side of the first folding area FDA 1  in the second direction DR 2 , and a third non-folding area NFA 3  located on the opposite side of the second folding area FDA 2  in the second direction DR 2 . The second non-folding area NFA 2  may be disposed between the first folding area FDA 1  and the second folding area FDA 2 . The first non-folding area NFA 1  may be disposed on one side of the second non-folding area NFA 2  in the second direction DR 2  with the first folding area FDA 1  therebetween. The third non-folding area NFA 3  may be disposed on the opposite side of the second non-folding area NFA 2  in the second direction DR 2  with the second folding area FDA 2  therebetween. 
     The first non-folding area NFA 1 , the second non-folding area NFA 2  and the third non-folding area NFA 3  may have the same width in the second direction DR 2 . Depending on the positions of the folding areas FDA, the width of the first non-folding area NFA 1  in the second direction DR 2 , the width of the second non-folding area NFA 2  in the second direction DR 2 , and the width of the third non-folding area NFA 3  in the second direction DR 2  may be different from one another. 
     The display area DA and the non-display area NDA of the display device  1  may overlap the folding areas FDA and the non-folding areas NFA at the same locations. For example, a part of the display area DA may be in the non-folding area NFA, and another part of the display area DA may be in the folding area FA. For example, a part of the non-display area NDA may be in the non-folding area NFA, and another part of the non-display area NDA may be in the folding area FA. For example, a certain location of the display area DA may be in the first non-folding area NFA 1 . Another location of the non-display area NDA may be in the first non-folding area NFA 1 . Another location of the display area DA may be in the folding areas FDA. 
     The display area DA may be disposed across all of the first non-folding area NFA 1 , the second non-folding area NFA 2 , and the third non-folding area NFA 3 . The display area DA may also be located at the first folding area FDA 1  which is disposed between the first non-folding area NFA 1  and the second non-folding area NFA 2 , and at the second folding area FDA 2  which is disposed between the second non-folding area NFA 2  and the third non-folding area NFA 3 . The display area DA of the display device  1  may be continuously disposed irrespective of the boundaries between the non-folding areas NFA and the folding lines FDA, etc. It is, however, to be understood that the present disclosure is not limited thereto. The display area DA may be located only at one of the first non-folding area NFA 1 , the second non-folding area NFA 2  and the third non-folding area NFA 3 , or the display area DA may be disposed in the first non-folding area NFA 1 , the second non-folding area NFA 2  and the third non-folding area NFA 3  but not in the folding areas FDA. 
       FIG. 3  is a cross-sectional view of a display device according to an embodiment of the present disclosure when the display device is unfolded.  FIG. 4  is an enlarged view of area A of  FIG. 3 .  FIG. 5  is a cross-sectional view of a display device according to an embodiment when the display device is folded inward at the first folding area.  FIG. 6  is an enlarged view of area B of  FIG. 5 .  FIG. 7  is a cross-sectional view of the display device according to the embodiment when the display device is folded outward at the second folding area. 
     Referring to  FIGS. 3 to 7 , the display device  1  may include a display panel  10 , an anti-reflection member  20 , a first adhesive member PSA 1 , a first protection member  30 , a second adhesive member PSA 2 , and a second protection member  40  sequentially stacked on one side of the display panel  10  in the thickness direction (the third direction DR 3 ). The display device  1  may further include a polymer film layer FL, a cushion layer CU, and a heat dissipation member HP sequentially stacked on the opposite side of the display panel  10  in the thickness direction (the third direction DR 3 ). It is, however, to be understood that the present disclosure is not limited thereto. Another layer may be further disposed between the layers, and some of the elements stacked on one another may be eliminated. Not only between the anti-reflection member  20  and the first protection member  30  and between the first protection member  30  and the second protection member  40 , but also between the elements stacked on one another, at least one coupling member such as an adhesive layer and a detachable layer may be disposed to couple the adjacent elements stacked on one another. 
     The display panel  10  displays images or videos. Examples of the display panel  10  may include a self-luminous display panel such as an organic light-emitting display panel, an inorganic light-emitting display panel, a quantum-dot light-emitting display panel, a micro LED display panel, a nano LED display panel, a plasma display panel, a field emission display panel and a cathode ray display panel, as well as a light-receiving display panel such as a liquid-crystal display panel and an electrophoretic display panel. In the following description, the organic light-emitting display panel will be described as an example of the display panel  10 , and the organic light-emitting display panel will be referred to as the display panel  300  unless specifically stated otherwise. It is, however, to be understood that the embodiments of the present disclosure are not limited to the organic light-emitting display panel, and any other display panel listed above or well known in the art may be employed without departing from the scope of the present disclosure. The structure of the display panel  10  will be described in more detail later. 
     The anti-reflection member  20  may be disposed on the display panel  10 . The anti-reflection member  20  may reduce reflection of external light. The anti-reflection member  20  may be implemented as a polarizing film. The anti-reflection member  20  polarizes the light passing therethrough. It is, however, to be understood that the present disclosure is not limited thereto. The anti-reflection member  20  may be implemented as a color filter layer in the display panel  10 . 
     The first protection member  30  may be disposed above the anti-reflection member  20 . The first protection member  30  serves to cover and protect the display panel  10 . The first protection member  30  may have flexibility and thus may be curved, bent, folded, or rolled. The first protection member  30  may include or may be formed of polyether block amide (PEBA). It is, however, to be understood that the present disclosure is not limited thereto. The first protection member  30  may include or may be formed of at least one selected from the group consisting of: polyurethane, silicone, pentaerythritol triacrylate (PETA), and copolyester elastomers (COPE). 
     The first protection member  30  may be made of a transparent material. The first protection member  30  may include or may be formed of, for example, glass or plastic. When the first protective member  30  includes or is formed of glass, the glass may be ultra thin glass (UTG) or thin glass. When the first protection member  30  includes or is formed of plastic, the plastic may be, but is not limited to, a transparent polyimide. 
     The storage modulus of the first protection member  30  may be greater than 0 MPa (megapascal) and equal to or less than 9,000 MPa at −20° C. In some embodiments, the storage modulus of the first protection member  30  may be in the range of from 25 MPa to 5,000 MPa at −20° C. In some embodiments, the storage modulus of the first protection member  30  may be in the range of from 25 MPa to 2,000 MPa at −20° C. In some embodiment, the storage modulus of the first protection member  30  may be in the range of from 1,000 MPa to 2,000 MPa at −20° C. The storage modulus of the first protection member  30  may be in the range of from 100 MPa to 9,000 MPa at 85° C. In some embodiments, the storage modulus of the first protection member  30  may be in the range of from 100 MPa to 5,000 MPa at 85° C. In some embodiments, the storage modulus of the first protection member  30  may be in the range of from 100 MPa to 2,000 MPa at 85° C. In some embodiments, the storage modulus of the first protection member  30  may be in the range of from 1,000 MPa to 2,000 MPa at 85° C. 
     When the storage modulus of the first protection member  30  satisfies the above ranges, the display device  1  may have sufficient flexibility even when the display device  1  is folded inward at the first folding area FDA 1  and is folded outward at the second folding area FDA 2 , facilitating in-folding of the display device  1  as well as out-folding thereof. 
     The storage modulus of the first protection member  30  may be measured by, but is not limited to, dynamic mechanical analysis (DMA). 
     The first protection member  30  may have a second thickness TH 2 . For example, the second thickness TH 2  may refer to the thickness in the thickness direction (the third direction DR 3 ) of the first protection member  30 , and the first protection member  30  has the second thickness TH 2 . The second thickness TH 2  may be, but is not limited to, in the range of from 0.01 μm to 400 μm. In some embodiment, the second thickness TH 2  may be in the range of from 0.1 μm to 100 μm. In some embodiment, the second thickness TH 2  may be in the range of from 1 μm to 40 μm. 
     The first adhesive member PSA 1  may be disposed between the first protection member  30  and the anti-reflection member  20 . The first protection member  30  and the anti-reflection member  20  may be attached together by the first adhesive member PSA 1 . The first adhesive member PSA may include, but is not limited to, a pressure sensitive adhesive or an adhesive. The first adhesive member PSA 1  may be optically transparent. 
     The first adhesive member PSA 1  may have a first thickness TH 1 . For example, the first thickness TH 1  may refer to the thickness of the first adhesive member PSA 1  in the thickness direction (the third direction DR 3 ), and the first adhesive member PSA 1  may have the first thickness TH 1 . The first thickness TH 1  may be, but is not limited to, in the range of from 0.01 μm to 100 μm. In some embodiments, the first thickness TH 1  may be in the range of from 0.1 μm to 50 μm. In some embodiments, the first thickness TH 1  may be in the range of from 1 μm to 25 μm. 
     The second protection member  40  may be disposed above the first protection member  30 . The second protection member  40  may serve to protect the display panel  10  together with the first protection member  30 . The second protection member  40  may have flexibility and thus may be curved, bent, folded, or rolled. 
     The second protection member  40  may include or may be formed of a polymer film. The second protection member  40  may include or may be formed of at least one selected from the group consisting of: polyethylene terephthalate (PET), tri-acetyl cellulous (TAC), transparent polyimide, and aramid. 
     When the display device  1  is folded inward at the first folding area FDA 1 , the display device  1  may be folded along the first folding axis RX 1 . When the display device  1  is folded inward at the first folding area FDA 1 , a first radius of curvature R 1  of the second protection member  40  at the first folding area FDA 1  may be, for example, in the range of from 0.01 mm to 5.0 mm, or in the range of from 0.1 mm to 1.0 mm. It is, however, to be understood that the present disclosure is not limited thereto. The first radius of curvature R 1  may refer to a radius of curvature formed by the inner surface of the second protection member  40  at the first folding area FDA 1  when the display device  1  is folded inward at the first folding area FDA 1 . The first radius of curvature R 1  may be refer to a radius of curvature formed by the upper surface of the second protection member  40  disposed on the inner side when the display device  1  is folded inward as shown in  FIGS. 4 and 5 . 
     When the display device  1  is folded outward at the second folding area FDA 2 , the display device  1  may be folded along the second folding axis RX 2 . When the display device  1  is folded outward at the second folding area FDA 2 , a second radius of curvature R 2  of the second protection member  40  at the second folding area FDA 2  may be, for example, in the range of from 0.01 mm to 10.0 mm, or in the range of from 0.1 mm to 4.0 mm. It is, however, to be understood that the present disclosure is not limited thereto. The second radius of curvature R 2  of the second protection member  40  may be greater than the first radius of curvature R 1 . The second radius of curvature R 2  may refer to a radius of curvature formed by the outer surface of the second protection member  40  at the second folding area FDA 2  when the display device  1  is folded outward at the second folding area FDA 2 . The second radius of curvature R 2  may be refer to a radius of curvature formed by the upper surface of the second protection member  40  disposed on the outer side when the display device  1  is folded outward as shown in  FIG. 6 . 
     The second protection member  40  may have a fourth thickness TH 4 . For example, the fourth thickness TH 4  may refer to the thickness in the thickness direction (the third direction DR 3 ) of the second protection member  40 , and the second protection member  40  has the fourth thickness TH 4 . The fourth thickness TH 4  of the second protection member  40  may be greater than the second thickness TH 2  of the first protection member  30 , but is not limited to such. The fourth thickness TH 4  may be, but is not limited to, in the range of from 0.01 μm to 500 μm, in the range of from 0.1 μm to 100 μm, or in the range of from 1 μm to 50 μm. 
     The second protection member  40  includes or is formed of a material having a storage modulus that varies according to an external impact, and thus the modulus of the second protection member  40  may vary according to an external impact. When the display device  1  is folded inward as well as outward, the modulus of the second protection member  40  may vary according to an external impact, and thus, both flexibility and impact resistance may be obtained. 
       FIG. 8  is a graph showing a relationship between the storage modulus of the second protection member  40  and external impact according to an embodiment. The horizontal axis (x-axis) of the graph shown in  FIG. 8  represents the frequency (Hz) of a sinusoidal load applied as the external impact to the second protection member  40 , and the vertical axis (y-axis) represents the storage modulus. 
     Referring to  FIG. 8 , the storage modulus of the second protection member  40  may vary according to the frequency. The storage modulus of the second protection member  40  may increase as the frequency increases. 
     In the graph of the storage modulus of the second protection member  40  according to the frequency of the second protection member  40 , the slope may be changed with respect to the frequency of 1 Hz. For example, the slope in the graph of the storage modulus of the second protection member  40  according to the frequency of the second protection member  40  is greater when the frequency is greater than 1 Hz than when the frequency is less than 1 Hz. The storage modulus of the second protection member  40  increases as the frequency of the external impact applied to the second protection member  40  increases, and the storage modulus may increase more according to the increase in frequency when the frequency is greater than 1 Hz than when the frequency is less than 1 Hz. 
     At a frequency which is equal to or greater than 1 Hz, it may be regarded that an external impact is applied to the second protection member  40 . When an external impact with a frequency of 1 Hz or more is applied to the second protection member  40 , the storage modulus may increase, and the larger the external impact is, the more the storage modulus of the second protection member  40  may increase. 
     For example, when the frequency of the external impact applied to the second protection member  40  is 1 Hz, the storage modulus of the second protection member  40  may be greater than 6 gigapascal (GPa). When the frequency of the external impact applied to the second protection member  40  is 30,000 Hz, the storage modulus of the second protection member  40  may be greater than 8 GPa. Specifically, when the frequency of the external impact applied to the second protection member  40  is 1 Hz, the storage modulus of the second protection member  40  may be in the range of from 6 GPa to 1,000 GPa, or may be in the range of from 6 GPa to 100 GPa. When the frequency of the external impact applied to the second protection member  40  is 30,000 Hz, the storage modulus of the second protection member  40  may be in the range of from 8 GPa to 1,000 GPa, or may be in the range of from 8 GPa to 100 GPa. It is, however, to be understood that the storage modulus of the second protection member  40  is not limited thereto. 
     Even if an external impact is applied to the second protection member  40  and the storage modulus has increased, after the impact is gone, the storage modulus of the second protection member  40  may be restored to the original value before the external impact was applied. It is, however, to be understood that the present disclosure is not limited thereto. 
     The storage modulus according to the frequency of the second protection member  40  may be measured by dynamic mechanical analysis (DMA), but the present disclosure is not limited thereto. 
     As the storage modulus of the second protection member  40  increases due to an external impact, the second protection member  40  may have both flexibility and impact resistance against external impact. For example, when the display device  1  is folded inward at the first folding area FDA 1 , the second protection member  40  may have flexibility at the first folding area FDA with a relatively low modulus. At the same time, when the display device  1  is folded outward at the second folding area FDA 2  and an external impact is applied to that area, the storage modulus may increase and impact resistance may be obtained in that area. Accordingly, even though the display device  1  is folded inward and outward, the second protection member  40  may have both flexibility and impact resistance. 
     Referring again to  FIGS. 3 to 7 , the second adhesive member PAS 2  may be disposed between the second protection member  40  and the first protection member  30 . The second protection member  40  and the first protection member  30  may be attached together by the second adhesive member PSA 2 . The second adhesive member PSA 2  may include or may be formed of, but is not limited to, a pressure sensitive adhesive or an adhesive. The second adhesive member PSA 2  may include or may be formed of, but is not limited to, the same material as the first adhesive member PSA 1 . The second adhesive member PSA 2  may be optically transparent. 
     The second adhesive member PSA 2  may have a third thickness TH 3 . For example, the third thickness TH 3  may refer to the thickness of the first adhesive member PSA 1  in the thickness direction (the third direction DR 3 ), and the second adhesive member PSA 2  may have the third thickness TH 3 . The third thickness TH 3  may be substantially equal to the first thickness TH 1  of the first adhesive member PSA 1 , but the present disclosure is not limited thereto. 
     The elastic modulus of the second adhesive member PSA 2  may be equal to or smaller than the elastic modulus of the first adhesive member PSA 1 . Although not limited thereto, for example, the elastic modulus of the first adhesive member PSA 1  may be greater than 0 kPa (kilopascal) and less than 1,500 kPa at −20° C. In some embodiment, the elastic modulus of the first adhesive member PSA 1  may be greater than 0 kPa and less than 750 kPa at −20° C. In some embodiment, the elastic modulus of the first adhesive member PSA 1  may be greater than 0 kPa and less than 150 kPa at −20° C. The elastic modulus of the second adhesive member PSA 2  may be greater than 0 kPa (kilopascal) and less than 1,000 kPa −20° C. In some embodiment, the elastic modulus of the second adhesive member PSA 2  may be greater than 0 kPa and less than 500 kPa −20° C. In some embodiment, the elastic modulus of the second adhesive member PSA 2  may be greater than 0 kPa and less than 100 kPa at −20° C. 
     When the elastic modulus of the first adhesive member PSA 1  and the elastic modulus of the second adhesive member PSA 2  are within the above ranges, and the elastic modulus of the second adhesive member PSA 2  is equal to or less than that of the first adhesive member PSA 1 , it is possible to have the impact resistance in the out-folding area while having flexibility in the in-folding area even when the display device  1  is folded inward and outward at the different areas. In other words, as the second adhesive member PSA 2  having a relatively small elastic modulus is disposed between the first protection member  30  and the second protection member  40 , the impact resistance against external impact may be improved. As the first adhesive member PSA 1  having a relatively large elastic modulus is disposed between the anti-reflection member  20  and the first protection member  30 , the flexibility may be improved. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Elastic 
                 Elastic 
                 Folding 
                 Folding 
               
               
                   
                 modulus 
                 modulus 
                 strain of 
                 strain of 
               
               
                   
                 of second 
                 of first 
                 second 
                 the first 
               
               
                   
                 adhesive 
                 adhesive 
                 protection 
                 protection 
               
               
                   
                 member (kPa) 
                 member (kPa) 
                 member (%) 
                 member (%) 
               
               
                   
               
             
            
               
                 Comparative 
                 140 
                  97 
                 1.6 
                 5.3 
               
               
                 Example 1 
                   
                   
                   
                   
               
               
                 Comparative 
                 140 
                 109 
                 1.7 
                 4.7 
               
               
                 Example 2 
                   
                   
                   
                   
               
               
                 Example 1 
                 140 
                 140 
                 1.5 
                 4.6 
               
               
                 Comparative 
                 109 
                  97 
                 1.6 
                 5.2 
               
               
                 Example 3 
                   
                   
                   
                   
               
               
                 Example 2 
                 109 
                 109 
                 1.5 
                 4.5 
               
               
                 Example 3 
                 109 
                 140 
                 1.5 
                 4.4 
               
               
                 Comparative 
                  97 
                  97 
                 1.8 
                 4.3 
               
               
                 Example 4 
                   
                   
                   
                   
               
               
                 Example 4 
                  97 
                 109 
                 1.7 
                 3.6 
               
               
                 Example 5 
                  97 
                 140 
                 1.7 
                 3.5 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Elastic 
                 Elastic 
                 Folding 
                 Folding 
               
               
                   
                 modulus 
                 modulus 
                 strain of 
                 strain of 
               
               
                   
                 of second 
                 of first 
                 second 
                 the first 
               
               
                   
                 adhesive 
                 adhesive 
                 protection 
                 protection 
               
               
                   
                 member (kPa) 
                 member (kPa) 
                 member (%) 
                 member (%) 
               
               
                   
               
             
            
               
                 Comparative 
                 140 
                  97 
                 2.3 
                 7.9 
               
               
                 Example 5 
                   
                   
                   
                   
               
               
                 Comparative 
                 140 
                 109 
                 2.2 
                 7.1 
               
               
                 Example 6 
                   
                   
                   
                   
               
               
                 Example 6 
                 140 
                 140 
                 2.2 
                 6.9 
               
               
                 Comparative 
                 109 
                  97 
                 2.3 
                 7.8 
               
               
                 Example 7 
                   
                   
                   
                   
               
               
                 Example 7 
                 109 
                 109 
                 2.2 
                 6.9 
               
               
                 Example 8 
                 109 
                 140 
                 2.2 
                 6.7 
               
               
                 Comparative 
                  97 
                  97 
                 2.4 
                 6.3 
               
               
                 Example 8 
                   
                   
                   
                   
               
               
                 Example 9 
                  97 
                 109 
                 2.3 
                 5.1 
               
               
                 Example 10 
                  97 
                 140 
                 2.3 
                 4.9 
               
               
                   
               
            
           
         
       
     
     Tables 1 and 2 show the folding strains of the first protection member  30  and the second protection member  40  measured at the time of in-folding according to the elastic modulus of the first adhesive member PSA 1  and the elastic modulus of the second adhesive member PSA 2  at −20° C. and 85° C., respectively. The thickness of the second protection member  40  is 50 μm, and the second protection member  40  includes or is formed of optically transparent polyimide. Further, the thickness of the first protection member  30  is 75 μm, and the first protection member  30  includes or is formed of pentaerythritol triacrylate (PETA). 
     In Table 1, each of the elastic modulus of the first adhesive member PSA 1  and the elastic modulus of the second adhesive member PSA 2  is measured by a universal testing machine (UTM) at −20° C. In Table 2, each of the elastic modulus of the first adhesive member PSA 1  and the elastic modulus of the second adhesive member PSA 2  is measured by a universal testing machine (UTM) at −85° C. 
     When the folding strain (%) of the second protection member  40  is less than or equal to 2.3%, and the folding strain (%) of the first protection member  30  is equal to or less than 7.0%, the folding characteristics may be maintained, and the mechanical stability of the display device  1  may be maintained no matter how many times the second protection member  40  is repeatedly folded. In other words, when the folding strain of the second protection member  40  and the folding strain of the first protection member  30  are within the above ranges, it is possible to suppress or prevent the deterioration of the folding performance of the first protection member  30  and the second protection member  40  no matter how many times the display device  1  is repeatedly folded. 
     When the folding strain of the second protection member  40  and the folding strain of the first protection member  30  are within the above ranges, it is possible to suppress or prevent defects such as buckling between adjacent layers stacked on one another. 
     In Examples 1 to 10, the elastic modulus of the second adhesive member PSA 2  is less than 150 kPa, the elastic modulus of the first adhesive member PSA 1  is less than 100 kPa, and the elastic modulus of the second adhesive member PSA 2  is equal to or smaller than the elastic modulus of the adhesive member PSA 1 . In Comparative Examples 1 to 8, the elastic modulus of the second adhesive member PSA 2  is less than 150 kPa, the elastic modulus of the first adhesive member PSA 1  is less than 100 kPa, and the elastic modulus of the second adhesive member PSA 2  is greater than the elastic modulus of the adhesive member PSA 1 . 
     Comparing Examples to Comparative Examples, when the elastic modulus of the second adhesive member PSA 2  is less than 150 kPa, the elastic modulus of the first adhesive member PSA 1  is less than 100 kPa, and the elastic modulus of the second adhesive member PSA 2  is equal to or smaller than the elastic modulus of the adhesive member PSA 1 , the folding strain of the second protection member  40  and the folding strain of the first protection member  30  are reduced more than when the elastic modulus of the second adhesive member PSA 2  is greater than that of the first adhesive member PSA 1 . Accordingly, the folding performance of the first protection member  30  and the second protection member  40  may be maintained more reliably. In addition, when the folding strain of the second protection member  40  and the folding strain of the first protection member  30  are reduced, it is possible to suppress or prevent defects such as buckling between adjacent layers stacked on one another more effectively. 
     In the Examples, when the elastic modulus of the second adhesive member PSA 2  is smaller than that of the first adhesive member PSA 1 , the folding strain of the second protection member  40  and the folding strain of the first protection member  30  are reduced more when the elastic modulus of the second adhesive member PSA 2  is equal to that of the first adhesive member PSA 1 . 
     Although not shown in the drawings, a hard coating layer may be further disposed on the second protection member  40 . The hard coating layer may protect the surface of the second protection member  40 . For example, the hard coating layer may perform at least one of functions of anti-scattering when the second protection member  40  is broken, shock absorption, anti-scratch, anti-fingerprint, and anti-glare. 
     The polymer film layer FL may be disposed under the display panel  10 . The polymer film layer FL may include or may be formed of, for example, polyimide (PI), polyethylene terephthalate (PET), polycarbonate (PC), polyethylene (PE), polypropylene (PP), polysulfone (PSF), polymethyl methacrylate (PMMA), triacetyl cellulose (TAC), or cycloolefin polymer (COP). The polymer film layer FL may include a functional layer on at least one surface. The functional layer may include or may be formed of, e.g., a light-absorbing layer. The light-absorbing layer may include or may be formed of a light-absorbing material such as a black pigment and dye. The light-absorbing layer may be formed on a polymer film by coating or printing a black ink. 
     The cushion layer CU may be disposed under the polymer film layer FL. The cushion layer CU may increase durability against impacts that may be exerted in the thickness direction (third direction DR 3 ) of the display device  1 , and may mitigate impact on the display device  1  when it is dropped. The cushion layer CU may include or may be formed of polyurethane or the like. 
     The heat dissipation member HP may be disposed under the polymer film layer FL. The heat dissipation member HP serves to diffuse heat generated from the display panel  10  or other elements of the display device  1 . The heat dissipation member HP may include a metal plate. The metal plate may include or may be formed of, for example, metal having excellent thermal conductivity such as copper and silver. The heat dissipation member HP may include a heat dissipation sheet including graphite, carbon nanotubes, etc. 
     In order to facilitate folding of the display device  1 , some layers of the display device  1  may be separated into individual ones at the folding area FDA. For example, the heat dissipation member HP forming the bottom layer of the display device  1  and having a small flexibility may be separated into two individual heat dissipation members disposed at the first folding area FDA 1  and the second folding area FDA 2 , respectively. 
     For example, each of the cushion layer CU and the polymer film layer FL may also be separated into two individual ones at the first folding area FDA 1  and the second folding area FDA 2 , respectively. However, if they have enough flexibility, they may be continuously extended on the folding areas FDA and the non-folding areas NFA. 
     When the display device  1  is folded inward along the first folding area FDA 1  as shown in  FIG. 5 , the second non-folding area NFA 2  may overlap the first non-folding area NFA 1  in the thickness direction. When the display device  1  is folded outward along the second folding area FDA 2  as shown in  FIG. 7 , the second non-folding area NFA 2  may overlap the third non-folding area NFA 3  in the thickness direction. 
     Unlike the separated heat dissipation member HP, the display panel  10 , the polymer film layer FL, cushion layer CU, the anti-reflection member  20 , the first protection member  30  and the second protection member  40 , which are continuous example regardless of the folding areas FDA, may be curved along the width direction of the first folding area FDA 1  and the second folding area FDA 2  to form a curve in the cross section. 
     Hereinafter, a stack structure of the display panel  10  according to an embodiment will be described in detail with reference to  FIG. 9 . 
       FIG. 9  is a cross-sectional view of a display panel according to an embodiment of the present disclosure. 
     Referring to  FIG. 9 , the display panel  10  according to an embodiment of the present disclosure may include a plurality of pixels. Each of the pixels may include at least one thin-film transistor TR. The display panel  10  may include a substrate SUB, a barrier layer  110 , a buffer layer  120 , a semiconductor layer  130 , a first insulating layer ILL a first gate conductive layer  140 , a second insulating layer IL 2 , a second gate conductive layer  150 , a third insulating layer IL 3 , a data conductive layer  160 , a via layer VIA, an anode electrode ANO, a pixel-defining layer PDL defining an opening OP exposing the anode electrode ANO, a spacer SC disposed on the pixel-defining layer PDL, an emissive layer EML at least partially disposed in the opening OP of the pixel-defining layer PDL, a cathode electrode CAT disposed on the emissive layer EML and the pixel-defining layer PDL, and an encapsulation layer ENL disposed on the cathode electrode CAT. Each of the layers described above may be made up of a single film, or a stack of multiple films. Other layers may be further disposed between the layers. 
     The substrate SUB supports the layers disposed thereon. The substrate SUB may be made of an insulating material such as a polymer resin. Examples of the polymer material may include polyethersulphone (PES), polyacrylate (PA), polyacrylate (PAR), polyetherimide (PEI), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polyallylate, polyimide (PI), polycarbonate (PC), cellulose triacetate (CAT), cellulose acetate propionate (CAP) or a combination thereof. It is, however, to be understood that the present disclosure is not limited thereto. The substrate SUB may be a transparent plate or a transparent film. 
     The substrate SUB may be a flexible substrate that may be bent, folded, or rolled. An example of the material of the flexible substrate may be, but is not limited to, polyimide (PI). 
     The barrier layer  110  is disposed on the substrate SUB. The barrier layer  110  may prevent impurity ions from diffusing, may prevent permeation of moisture or outside air, and may provide a flat surface. The barrier layer  110  may include or may be formed of at least one of silicon oxide (SiOx), silicon nitride (SiNx), and silicon oxynitride (SiOxNy). It is, however, to be understood that the present disclosure is not limited thereto. The barrier layer  110  may be eliminated depending on the type of the substrate SUB or process conditions. 
     The buffer layer  120  is disposed on the barrier layer  110 . The buffer layer  120  may prevent impurity ions from diffusing, may prevent permeation of moisture or outside air, and may provide a flat surface. The buffer layer  120  may include or may be formed of silicon nitride (SiNx), silicon oxide (SiOx), or silicon oxynitride (SiOxNy). The buffer layer  120  may be eliminated depending on the type of the substrate SUB, process conditions, etc. 
     The semiconductor layer  130  is disposed on the buffer layer  120 . The semiconductor layer  130  forms the channel of the thin-film transistor TR of the pixel. The semiconductor layer  130  may include or may be formed of polycrystalline silicon. It is, however, to be understood that the present disclosure is not limited thereto. The semiconductor layer  130  may include or may be formed of at least one of monocrystalline silicon, low-temperature polycrystalline silicon, amorphous silicon, and an oxide semiconductor. Alternatively, the semiconductor layer  130  may include or may be formed of an oxide semiconductor. For example, the oxide semiconductor may include or may be formed of at least one of indium-gallium-zinc oxide (IGZO), zinc-tin oxide (ZTO), indium-tin oxide (IZO), etc. 
     The first insulating layer IL 1  is disposed on the semiconductor layer  130 . The first insulating layer IL 1  may be a first gate insulating film that has a gate insulating features. The first insulating layer IL 1  may include or may be formed of at least one of a silicon compound and a metal oxide. 
     The first gate conductive layer  140  is disposed on the first insulating layer ILL The first gate conductive layer  140  may include a gate electrode GAT of the thin-film transistor TR of the pixel, a scan line connected thereto, and a first electrode CE 1  of a storage capacitor. 
     The first gate conductive layer  140  may include or may be formed of at least one metal selected from the group consisting of: molybdenum (Mo), aluminum (Al), platinum (Pt), palladium (Pd), silver (Ag), magnesium (Mg), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), calcium (Ca), titanium (Ti), tantalum (Ta), tungsten (W), and copper (Cu). 
     A second insulating layer IL 2  may be disposed on the first gate conductive layer  140 . The second insulating layer IL 2  may be an interlayer dielectric layer or a second gate insulating layer. The second insulating layer IL 2  may include or may be formed of an inorganic insulating material such as silicon oxide, silicon nitride, silicon oxynitride, hafnium oxide, aluminum oxide, titanium oxide, tantalum oxide, and zinc oxide. 
     The second gate conductive layer  150  is disposed on the second insulating layer IL 2 . The second gate conductive layer  150  may include a second electrode CE 2  of the storage capacitor. The second gate conductive layer  150  may include or may be formed of at least one metal selected from the group consisting of: molybdenum (Mo), aluminum (Al), platinum (Pt), palladium (Pd), silver (Ag), magnesium (Mg), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), calcium (Ca), titanium (Ti), tantalum (Ta), tungsten (W) and copper (Cu). The second gate conductive layer  150  may be made of, but is not limited to, the same material as the first gate conductive layer  140 . 
     The third insulating layer IL 3  is disposed on the second gate conductive layer  150 . The third insulating layer IL 3  may be an interlayer dielectric film. The third insulating layer IL 3  may include or may be formed of an inorganic insulating material such as silicon oxide, silicon nitride, silicon oxynitride, hafnium oxide, aluminum oxide, titanium oxide, tantalum oxide, and zinc oxide. 
     The data conductive layer  160  is disposed on the third insulating layer IL 3 . The data conductive layer  160  may include a first electrode SD 1  and a second electrode SD 2  of a thin-film transistor TR of a pixel, and a first voltage line ELVDDE of the display panel. The first electrode SD 1  and the second electrode SD 2  of the thin-film transistor TR may be electrically connected to the source region and the drain region of the semiconductor layer  130 , respectively, through contact holes passing through the third insulating layer IL 3 , the second insulating layer IL 2  and the first insulating layer ILL The first supply voltage line ELVDDE may be electrically connected to the second electrode CE 2  of the storage capacitor through a contact hole penetrating through the third insulating layer IL 3 . 
     The data conductive layer  160  may include or may be formed of at least one metal selected from the group consisting of: aluminum (Al), molybdenum (Mo), platinum (Pt), palladium (Pd), silver (Ag), magnesium (Mg), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), calcium (Ca), titanium (Ti), tantalum (Ta), tungsten (W), and copper (Cu). The data conductive layer  160  may be made up of a single layer or multiple layers. For example, the data conductive layer  160  may have a stack structure of Ti/Al/Ti, Mo/Al/Mo, Mo/AlGe/Mo, or Ti/Cu. 
     The via layer VIA (or a planarization layer) is disposed on the data conductive layer  160 . The via layer VIA covers the data conductive layer  160 . The via layer VIA may include or may be formed of an organic insulating material. When the via layer VIA includes an organic material, it may have a flat upper surface despite the level differences thereunder. 
     The anode electrode ANO is disposed on the via layer VIA. The anode electrode ANO may be disposed on a surface VIAa of the via layer VIA. The anode electrode ANO may be a pixel electrode disposed in each of the pixels. The anode electrode ANO may be connected to the second electrode SD 2  of the thin-film transistor TR through a contact hole CNT penetrating the via layer VIA. The anode electrode ANO may at least partially overlap the emission area EMA of the pixel. 
     The anode electrode ANO may have, but is not limited to, a stack structure of a material layer having a high work function such as indium-tin-oxide (ITO), indium-zinc-oxide (IZO), zinc oxide (ZnO) and indium oxide (In 2 O 3 ), and a reflective material layer such as silver (Ag), magnesium (Mg), aluminum (Al), platinum (Pt), lead (Pb), palladium (Pd), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), lithium (Li), calcium (Ca) or a mixture thereof. A layer having a higher work function may be disposed on a higher layer than a reflective material layer so that it may be closer to the emissive layer EML. The anode electrode ANO may have, but is not limited to, a multilayer structure of ITO/Mg, ITO/MgF, ITO/Ag, or ITO/Ag/ITO. 
     The pixel-defining layer PDL may be disposed on the anode electrode ANO. The pixel-defining layer PDL may be disposed over the anode electrode ANO and may include an opening OP exposing the anode electrode ANO. The opening OP may be defined by the pixel-defining layer PDL, and may penetrate the pixel-defining layer PDL in the thickness direction. The emission area EMA and the non-emission area NEM may be distinguished by the pixel-defining layer PDL and the opening OP thereof. The pixel-defining layer PDL may include or may be formed of an organic insulating material. It is, however, to be understood that the present disclosure is not limited thereto. The pixel-defining layer PDL may include or may be formed of an inorganic material. 
     The spacer SC may be disposed on the pixel-defining layer PDL. The spacer SC may protrude from at least a part of the pixel-defining layer PDL on one side (upper side) in the thickness direction. The spacer SC may serve to maintain a gap with elements disposed thereabove. Although not limited thereto, for example, the spacer SC may prevent defects such as dent on the display panel  10  by a fine metal mask (FMM). The spacer SC may include or may be formed of an organic insulating material like the pixel-defining layer PDL. Although not limited thereto, the spacer SC may be formed via the same process with the pixel-defining layer PDL. 
     The emissive layer EML may be disposed on the anode electrode ANO exposed by the pixel-defining layer PDL. The emissive layer EML may include or may be formed of an organic material layer. The organic material layer of the emission layer may include an organic emission layer. In some embodiment, the organic material layer of the emission layer may further include a hole injecting/transporting layer and/or an electron injecting/transporting layer. 
     The cathode electrode CAT may be disposed on the emissive layer EML. The cathode electrode CAT may be a common electrode disposed across the pixels. The anode electrode ANO, the emissive layer EML and the cathode electrode CAT may form an organic light-emitting element. 
     The cathode electrode CAT may include or may be formed of a material layer having a small work function such as Li, Ca, LiF/Ca, LiF/Al, Al, Mg, Ag, Pt, Pd, Ni, Au, Nd, Ir, Cr, BaF and Ba, or a compound or mixture thereof (e.g., a mixture of Ag and Mg). The cathode electrode CAT may further include a transparent metal oxide layer disposed on the material layer having a small work function. 
     The encapsulation layer ENL including a first encapsulation film EN 1 , a second encapsulation film EN 2  and a third encapsulation film EN 3  is disposed on the cathode electrode CAT. The first encapsulation film EN 1  and the third encapsulation film EN 3  may be in contact with each other at the end of the encapsulation layer ENL. The second encapsulation film EN 2  may be encapsulated by the first encapsulation film EN 1  and the third encapsulation film EN 3 . 
     Each of the first encapsulation film EN 1  and the third encapsulation film EN 3  may include or may be formed of an inorganic material. Although not limited thereto, the inorganic material may include or may be formed of, for example, silicon nitride, silicon oxide, or silicon oxynitride. The second encapsulation film EN 2  may include or may be formed of an organic material. Although not limited thereto, the organic material may include or may be formed of, for example, an organic insulating material. 
     Hereinafter, other embodiments of the present disclosure will be described. In the following description, the same or similar elements will be denoted by the same or similar reference numerals, and redundant descriptions thereof will be omitted or briefly described. Descriptions will be made focusing on differences from the above embodiment. 
       FIG. 10  is a cross-sectional view showing a part of a display device according to another embodiment of the present disclosure. 
     The embodiment of  FIG. 10  is different from the embodiment of  FIG. 4  in that a second thickness TH 2 _ 1  of a first protection member  30 _ 1  of a display device  1 _ 1  is greater than a fourth thickness TH 4  of a second protection member  40 . Although not limited thereto, the second thickness TH 2 _ 1  of the first protection member  30 _ 1  may be, for example, in the range of from 0.01 μm to 750 μm, in the range of from 0.1 μm to 200 μm, or in the range of from 1 μm to 75 μm. Alternatively, the second thickness TH 2 _ 1  of the first protection member  30 _ 1  may be, for example, in the range of from 0.01 μm to 1,000 μm, in the range of from 0.1 μm to 300 μm, or in the range of from 1 μm to 100 μm. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Comparative 
                   
                   
               
               
                   
                 Example 9 
                 Example 11 
                 Example 12 
               
               
                   
               
             
            
               
                 Thickness of 
                 50 
                 50 
                  50 
               
               
                 second protection 
                   
                   
                   
               
               
                 member (μm) 
                   
                   
                   
               
               
                 Thickness of 
                 25 
                 25 
                  25 
               
               
                 second adhesive 
                   
                   
                   
               
               
                 member (μm) 
                   
                   
                   
               
               
                 Thickness of 
                 40 
                 75 
                 100 
               
               
                 first protection 
                   
                   
                   
               
               
                 member (μm) 
                   
                   
                   
               
               
                 Thickness of 
                 25 
                 25 
                  25 
               
               
                 first adhesive 
                   
                   
                   
               
               
                 member (μm) 
                   
                   
                   
               
               
                 Bright spot height (cm) 
                  2 
                  5 
                  6 
               
               
                   
               
            
           
         
       
     
     Table 3 shows the results of measuring the height at which bright spots occur according to the thickness of the first adhesive member PSA 1 , the first protection member  30 _ 1 , the second adhesive member PSA 2 , and the second protection member  40 . Herein, the height at which a bright spot occurs may refer to a height at which bright spot defects occur in the display device when an object is dropped from above the display device onto the display device. Therefore, it may be understood that the higher the height at which a bright spot occurs is, the greater the impact resistance is. 
     Comparative Example 9 may be substantially identical to the display device  1  (see  FIG. 1 ) according to the embodiment of  FIG. 4 , and the thickness (the second thickness TH 2 ) of the first protection member  30  (see  FIG. 4 ) may be smaller than the thickness (the fourth thickness TH 4 ) of the second protection member  40 . In Examples 11 and 12, the thickness of the first protection member  30 _ 1  (the second thickness TH 2 _ 1 ) is greater than the thickness of the second protection member  40  (the fourth thickness TH 4 ). 
     Comparing Comparative Example 9 to Example 11 and Example 12, when the thickness of the first protection member  30 _ 1  (the second thickness TH 2 _ 1 ) is greater than the thickness of the second protection member  40  (the fourth thickness TH 4 ), the height at which a bright spot occurs is higher than when the thickness of the first protection member  30  (see  FIG. 4 ) (the second thickness TH 2  (see  FIG. 4 )) is smaller than the thickness of the second protection member  40  (the fourth thickness TH 4 ). For example, when the thickness of the first protection member  30 _ 1  (the second thickness TH 2 _ 1 ) is greater than the thickness of the second protection member  40  (the fourth thickness TH 4 ), the impact resistance may be more improved than when the thickness of the first protection member  30  (see  FIG. 4 ) (the second thickness TH 2  (see  FIG. 4 )) is smaller than the thickness of the second protection member  40  (the fourth thickness TH 4 ). 
     Comparing Example 11 to Example 12, when the thickness of the first protection member  30 _ 1  (the second thickness TH 2 _ 1 ) is greater than the thickness of the second protection member  40  (the fourth thickness TH 4 ), the height at which a bright spot occurs becomes higher as the thickness of the first protection member  30  (see  FIG. 4 ) (the second thickness TH 2  (see  FIG. 4 )) becomes larger. For example, when the thickness of the first protection member  30 _ 1  (the second thickness TH 2 _ 1 ) is greater than the thickness of the second protection member  40  (the fourth thickness TH 4 ), the impact resistance may be improved as the thickness of the first protection member  30  (see  FIG. 4 ) (the second thickness TH 2  (see  FIG. 4 )) becomes larger. 
     Even in this instance, the storage modulus of the second protection member  40  may increase according to an external impact, and thus the display device  1 _ 1  may have both flexibility and impact resistance. Since the elastic modulus of the second adhesive member PSA 2  is equal to or smaller than the elastic modulus of the first adhesive member PSA 1 , it is possible to suppress or prevent deterioration of the folding performance. As the thickness of the first protection member  30 _ 1  (the second thickness TH 2 _ 1 ) is greater than the thickness of the second protection member  40  (the fourth thickness TH 4 ), the impact resistance may be improved. 
       FIG. 11  is a cross-sectional view showing a part of a display device according to yet another embodiment of the present disclosure. 
     The embodiment of  FIG. 11  is different from the embodiment of  FIG. 10  in that a first thickness TH 1 _ 2  of a first adhesive member PAS 1 _ 2  of a display device  1 _ 2  is greater than a third thickness TH 3  of a second adhesive member PAS 2 . Although not limited thereto, the first thickness TH 1 _ 2  of the first adhesive member PSA_ 2  may be, for example, in the range of from 0.01 μm to 500 μm, in the range of from 0.1 μm to 150 μm, or in the range of from 1 μm to 50 μm. 
     
       
         
           
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                 Comparative 
                   
               
               
                   
                 Example 10 
                 Example 13 
               
               
                   
               
             
            
               
                 Thickness of 
                 50 
                 50 
               
               
                 second protection 
                   
                   
               
               
                 member (μm) 
                   
                   
               
               
                 Thickness of 
                 25 
                 25 
               
               
                 second adhesive 
                   
                   
               
               
                 member (μm) 
                   
                   
               
               
                 Thickness of 
                 40 
                 75 
               
               
                 first protection 
                   
                   
               
               
                 member (μm) 
                   
                   
               
               
                 Thickness of 
                 25 
                 25 
               
               
                 first adhesive 
                   
                   
               
               
                 member (μm) 
                   
                   
               
               
                 Bright spot height (cm) 
                  5 
                  8 
               
               
                   
               
            
           
         
       
     
     Table 4 shows the results of measuring the height at which bright spots occur according to the thickness of the first adhesive member PSA 1 _ 2 , the first protection member  30 , the second adhesive member PSA 2 , and the second protection member  40 . 
     Comparative Example 10 may be substantially identical to the display device  10 _ 1  (see  FIG. 10 ) according to the embodiment of  FIG. 10 , and the thickness (the first thickness TH 1 ) of the first adhesive member PSA 1  (see  FIG. 10 ) may be smaller than the thickness (the third thickness TH 3 ) of the second adhesive member PAS 2  (see  FIG. 10 ). In Example 13, the thickness of the first adhesive member PAS_ 2  (the first thickness TH 1 _ 2 ) is greater than the thickness of the second adhesive member PAS 2  (the third thickness TH 3 ). 
     Comparing Comparative Example 10 to Example 13, when the thickness of the first adhesive member PAS 1 _ 2  (the first thickness TH 1 _ 2 ) is greater than the thickness of the second adhesive member PSA 2  (the third thickness TH 3 ), the height at which a bright spot occurs is higher than when the thickness of the first adhesive member PSA 1 _ 2  (see  FIG. 10 ) (the second thickness TH 2  (see  FIG. 10 )) is equal to the thickness of the second adhesive member PSA 2  (the third thickness TH 3 ). For example, when the thickness of the first adhesive member PSA 1 _ 2  (the first thickness TH 1 _ 2 ) is greater than the thickness of the second adhesive member PAS 2  (the third thickness TH 3 ), the impact resistance may be more improved than when the thickness of the first adhesive member PSA 1 _ 2  (see  FIG. 10 ) (the first thickness TH 1  (see  FIG. 10 )) is smaller than the thickness of the second adhesive member PAS 2  (the third thickness TH 3 ). 
     Even in this instance, the storage modulus of the second protection member  40  may increase according to an external impact, and thus the display device  1 _ 2  may have both flexibility and impact resistance. Since the elastic modulus of the second adhesive member PSA 2  is equal to or smaller than the elastic modulus of the first adhesive member PSA 1 , it is possible to suppress or prevent deterioration of the folding performance. As the thickness of the first adhesive member PAS 1 _ 2  (the first thickness TH 1 _ 2 ) is greater than the thickness of the second adhesive member PAS 2  (the third thickness TH 3 ), the impact resistance may be improved. 
       FIG. 12  is a perspective view of a display device according to yet another embodiment of the present disclosure when it is unfolded.  FIG. 13  is a perspective view showing the display device according to the embodiment of  FIG. 12  when it is folded inward.  FIG. 14  is a perspective view showing the display device according to the embodiment of  FIG. 12  when it is folded outward. 
     The embodiment of  FIGS. 12 to 14  is different from the embodiment of  FIG. 1  in that a display device  1 _ 3  is folded inward and outward at the same folding area FDA. For example, the display device  1 _ 3  may include a folding area FDA and non-folding areas NFA, and the display device  1 _ 3  may include a first folding area FDA 1 , and a first non-folding area NFA 1  and a second non-folding area NFA 2  respectively disposed on one side and the opposite side of the first folding area FDA 1  in the second direction DR 2 . For example, the first folding area FDA 1  may be folded inward as shown in  FIG. 13  and may be folded outward as shown in  FIG. 14 . 
     Even in this instance, the storage modulus of the second protection member  40  may increase according to an external impact, and thus the display device  1 _ 3  may have both flexibility and impact resistance. Since the elastic modulus of the second adhesive member PSA 2  is equal to or smaller than the elastic modulus of the first adhesive member PSA 1 , it is possible to suppress or prevent deterioration of the folding performance. A display device employing a variety of folding designs may be implemented as required by users. 
     In concluding the detailed description, those skilled in the art will appreciate that many variations and modifications may be made to the embodiments without substantially departing from the principles of the present disclosure. Therefore, the disclosed preferred embodiments of the invention are used in a generic and descriptive sense only and not for purposes of limitation.