Display device

Abstract

A display device according to an embodiment of the present invention may include: a display panel; a first auxetic structure including a first pattern defining a plurality of first openings, overlapping the display panel, and having a negative Poisson's ratio; a second auxetic structure including a second pattern defining a plurality of second openings, overlapping the first auxetic structure, and having a negative Poisson's ratio; and a support layer disposed under the display panel and supporting the display panel.

Description

Technical Field

[0001] The present disclosure relates to a display device, and more particularly, to a flexible display device and a rollable display device. Background Art

[0002] The present disclosure relates to a display device, and more particularly, to a flexible display device and a rollable display device.

[0003] Electronic devices such as smart phones, tablet computers, laptop computers, car navigation systems, and smart TVs are being developed. These electronic devices are provided with a display device for providing information.

[0004] Various types of display devices are being developed to meet the user experience / user interface (UX / UI) of users. Among them, flexible display devices and rollable display devices are actively developed. Summary of the Invention

[0005] Technical Problem

[0006] The present disclosure provides a display device having improved impact resistance and improved surface quality after being rolled up and folded.

[0007] Technical Solution

[0008] Embodiments of the inventive concept provide a display device including: a display panel; a first auxetic structure including a first pattern defining a plurality of first openings, stacked with the display panel, and having a negative Poisson's ratio; a second auxetic structure including a second pattern defining a plurality of second openings, stacked with the first auxetic structure, and having a negative Poisson's ratio; and a support layer disposed under the display panel and supporting the display panel.

[0009] In an embodiment, the display device may further include an adhesive layer disposed between the first auxetic structure and the second auxetic structure to join the first auxetic structure and the second auxetic structure, wherein the adhesive layer may have a modulus smaller than those of the first auxetic structure and the second auxetic structure.

[0010] In an embodiment, the display panel may provide a display surface defined by a first direction and a second direction, and in a first mode of the display device, the display surface may provide a flat surface, and in a second mode of the display device, at least a part of the display surface may provide a curved surface with respect to a reference axis.

[0011] In an embodiment, the support layer may include a plurality of support bars parallel to the reference axis, and in the first mode, the plurality of support bars may be arranged in a direction intersecting the reference axis.

[0012] In an embodiment, the first auxetic structure and the second auxetic structure may both have a Poisson's ratio equal to or greater than about -0.9 and equal to or less than about -0.1.

[0013] In an embodiment, the first pattern may be superimposed on the second pattern, and the first pattern and the second pattern may be the same pattern as each other.

[0014] In an embodiment, when the first pattern and the second pattern are superimposed, the aperture ratio of the planar pattern defined by the first pattern and the second pattern may be equal to or greater than about 10% and equal to or less than about 60%.

[0015] In an embodiment, the first pattern may be superimposed on the second pattern, and the second pattern may be a pattern in which the first pattern is rotated in a plane by an angle equal to or greater than about 45 degrees and equal to or less than about 180 degrees.

[0016] In an embodiment, the first auxetic structure may have a thickness equal to or greater than about 10 micrometers (μm) and equal to or less than about 500 μm, and the second auxetic structure may have a thickness equal to or greater than about 10 μm and equal to or less than about 500 μm.

[0017] In an embodiment, the first auxetic structure and the second auxetic structure may both be disposed between the display panel and the support layer.

[0018] In an embodiment, the display device may further include a digital converter disposed below the display panel, wherein the first auxetic structure and the second auxetic structure may both be disposed below the display panel and may include a non-magnetic material that does not respond to a magnetic field.

[0019] In an embodiment, the first auxetic structure and the second auxetic structure may both be disposed on the upper surface of the display panel.

[0020] In an embodiment, the first auxetic structure and the second auxetic structure may both include a material having a light transmittance equal to or greater than about 90%.

[0021] In an embodiment, the display device may further include an optical adhesive layer, wherein the first auxetic structure and the second auxetic structure may be impregnated into the optical adhesive layer.

[0022] In an embodiment, the refractive index of the optical adhesive layer, the refractive index of the first auxetic structure, and the refractive index of the second auxetic structure may be substantially the same.

[0023] In an embodiment, the display device may further include a display panel protective layer disposed on the lower surface of the display panel and having a modulus equal to or greater than about 1 gigapascal (GPa) and equal to or less than about 10 GPa.

[0024] In an embodiment, the display device may further include an elastic layer disposed on the support layer or on the display panel and including an elastomer.

[0025] In an embodiment of the inventive concept, a display device includes: a display panel; a plurality of stress control layers stacked with the display panel; and a support layer disposed under the plurality of stress control layers and supporting the display panel, wherein the plurality of stress control layers include a first stress control layer disposed on an upper surface of the display panel and a second stress control layer disposed on a lower surface of the display panel, and both the first stress control layer and the second stress control layer include: a first auxetic structure including a first pattern defining a plurality of first openings and having a negative Poisson's ratio; and a second auxetic structure stacked with the first auxetic structure, including a second pattern defining a plurality of second openings and having a negative Poisson's ratio.

[0026] In an embodiment, both the first auxetic structure and the second auxetic structure may have a Poisson's ratio equal to or greater than about -0.9 and equal to or less than about -0.1.

[0027] In an embodiment, the first stress control layer may include a material having a transmittance equal to or greater than about 90%, and the second stress control layer may include a non-magnetic material that does not respond to a magnetic field.

[0028] The first pattern may be superimposed on the plurality of second openings in a plane, and the second pattern may be superimposed on the plurality of first openings in a plane, and when the first pattern and the second pattern are superimposed, the planar opening ratio of the entire first auxetic structure and the second auxetic structure may be equal to or greater than about 10% and equal to or less than about 60%.

[0029] Advantageous Effects

[0030] According to an embodiment of the inventive concept, the first auxetic structure and the second auxetic structure are stacked, and thus stress due to mechanical deformation (such as repeated curling or folding) can be reduced.

[0031] In addition, curlability and impact resistance can be ensured by arranging the planar pattern defined by the first pattern and the second pattern to have a small opening ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1a and Figure 1b is a perspective view of a display device according to an embodiment of the inventive concept;

[0033] Figure 2a and Figure 2b is a perspective view of a display device according to an embodiment of the inventive concept;

[0034] Figure 3 is a cross-sectional view of a display device according to an embodiment of the inventive concept;

[0035] Figure 4a is a cross-sectional view of a display panel according to an embodiment of the inventive concept;

[0036] Figure 4b is a perspective view of a support layer according to an embodiment of the inventive concept;

[0037] Figure 5a and Figure 5b is a graph showing the step characteristics and surface roughness according to Poisson's ratio;

[0038] Figure 6 is a perspective view of a stress control layer according to an embodiment of the inventive concept;

[0039] Figure 7a is a plan view showing a first auxetic structure according to an embodiment of the inventive concept;

[0040] Figure 7b is a plan view showing a second auxetic structure according to an embodiment of the inventive concept;

[0041] Figure 8 is a plan view showing a stacked first auxetic structure and second auxetic structure according to an embodiment of the inventive concept;

[0042] Figure 9 is a plan view showing a first unit cell and a second unit cell according to an embodiment of the inventive concept;

[0043] Figure 10a is a plan view showing a first auxetic structure according to an embodiment of the inventive concept;

[0044] Figure 10b is a plan view showing a second auxetic structure according to an embodiment of the inventive concept;

[0045] Figure 11 is a plan view showing a stacked first auxetic structure and second auxetic structure according to an embodiment of the inventive concept;

[0046] Figure 12 is a graph showing the stress-strain curves of a stress control layer according to a comparative example and an example of the inventive concept;

[0047] Figure 13a and Figure 13b is a plan view showing a first auxetic structure and a second auxetic structure according to an embodiment of the inventive concept;

[0048] Figure 13c is an enlarged plan view of a stacked first unit cell and second unit cell according to an embodiment of the inventive concept;

[0049] Figure 14a andFigure 14b is a plan view showing a first auxetic structure and a second auxetic structure according to an embodiment of the inventive concept;

[0050] Figure 14c is a plan view magnifying stacked first unit cells and second unit cells according to an embodiment of the inventive concept;

[0051] Figure 15a and Figure 15b is a plan view showing a first auxetic structure and a second auxetic structure according to an embodiment of the inventive concept;

[0052] Figure 15c is a plan view magnifying stacked first unit cells and second unit cells according to an embodiment of the inventive concept;

[0053] Figure 16 is a cross-sectional view of a display device according to an embodiment of the inventive concept;

[0054] Figure 17 is a cross-sectional view of a display device according to an embodiment of the inventive concept;

[0055] Figure 18 is a cross-sectional view of a display device according to an embodiment of the inventive concept; and

[0056] Figures 19a to 19d is a cross-sectional view of a display device according to a comparative example and an example of the inventive concept. DETAILED DESCRIPTION

[0057] In this specification, when an element (or region, layer, part, etc.) is referred to as being "on" another element, "connected to" or "coupled to" another element, this means that the element can be disposed directly on / connected directly to / coupled directly to the other element, or a third element can be disposed therebetween.

[0058] Like reference numerals refer to like elements. Also, in the drawings, for an effective description of technical content, the thickness, ratio, and size of elements are exaggerated. The term "and / or" includes all combinations of one or more of the associated configurations that can be defined.

[0059] It will be understood that although terms such as "first" and "second" may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of the exemplary embodiments of the inventive concept, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. Unless the context clearly indicates otherwise, singular terms may include plural forms.

[0060] Additionally, terms such as "below", "lower (bottom)", "on", and "upper (top)" are used to describe the relationship of the structures shown in the drawings. The terms are used as relative concepts and are described with reference to the directions indicated in the drawings.

[0061] It should be understood that the term "comprising" or "having" is intended to state that there are the stated features, integers, steps, operations, elements, components, or combinations thereof in the disclosure, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

[0062] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It will also be understood that terms defined in a general dictionary should be interpreted as having a meaning consistent with their meaning in the context of the prior art, and are not to be interpreted in an idealized or overly formal sense unless explicitly so defined herein. Additionally, terms (such as those defined in a general dictionary) should be interpreted as having a meaning consistent with their meaning in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless explicitly so defined herein.

[0063] Hereinafter, embodiments of the inventive concept will be described with reference to the drawings.

[0064] Figure 1a and Figure 1b are perspective views of a display device DD according to an embodiment of the inventive concept. Figure 2a and Figure 2b are perspective views of a display device DD according to an embodiment of the inventive concept.

[0065] Figure 1a and Figure 1b illustrate a foldable display device DD as an example of a flexible display device, Figure 2a and Figure 2b illustrate a rollable display device DD as an example of a flexible display device. However, embodiments of the inventive concept are not limited thereto, and may be applied to other display devices such as a slidable display device.

[0066] Figure 1aThe unfolded state (first mode) of the foldable display device DD is shown. The display surface DD-IS is parallel to the plane defined by the first direction DR1 and the second direction DR2. The normal direction of the display surface DD-IS (i.e., the thickness direction of the display device DD) is indicated by the third direction DR3. The front surface (or upper surface) and the rear surface (or lower surface) of the corresponding member are defined with respect to the third direction DR3. Hereinafter, the first to third directions respectively correspond to the directions indicated by the first to third direction axes DR1, DR2, and DR3, and are given the same reference numerals.

[0067] As Figure 1a shown, the display surface DD-IS includes a display area DD-DA where the display image IM is displayed and a non-display area DD-NDA positioned adjacent to the display area DD-DA. The non-display area DD-NDA is an area where no image is displayed. In Figure 1a it, an icon image is shown as an example of the image IM. For example, the display area DD-DA may have a quadrilateral shape. The non-display area DD-NDA may surround the display area DD-DA. However, embodiments of the inventive concept are not limited thereto, and the shapes of the display area DD-DA and the non-display area DD-NDA may be modified.

[0068] Figure 1b The folded state (second mode) of the foldable display device DD is shown. As Figure 1b shown, the display device DD may include a plurality of regions defined according to the operation mode. The display device DD may include a folding region FA folded with respect to the folding axis FX, a first planar region NFA1 and a second planar region NFA2 positioned adjacent to the folding region FA. In the present embodiment, the folding axis FX may be parallel to the first direction DR1. The folding region FA is a region that substantially forms a curvature. The folding region FA provides a curved display surface DD-IS in the second mode. The folding axis FX may be a reference axis of the folding region FA.

[0069] In the present embodiment, a display device DD in which a folding axis FX parallel to the long axis of the display device DD is defined is shown as an example. However, embodiments of the inventive concept are not limited thereto, and the folding axis FX may be parallel to the short axis of the display device DD.

[0070] As Figure 1a and Figure 1b shown, the display device DD may be folded or bent inward such that the display surface DD-IS of the first planar region NFA1 faces the display surface DD-IS of the second planar region NFA2. In embodiments of the inventive concept, the display device DD may be folded or bent outward such that the display surface DD-IS is exposed to the outside.

[0071] In an embodiment of the inventive concept, the display device DD may include a plurality of folding regions FA. Additionally, the folding regions FA may be defined corresponding to a mode in which a user operates the display device DD. For example, when viewed on a plane, the folding regions FA may be defined in an oblique direction intersecting a first direction DR1 and a second direction DR2. The area of the folding regions FA is not determined and may vary according to the radius of curvature.

[0072] In an embodiment of the inventive concept, the display device DD may be configured to repeatedly perform an inner folding operation or an outer folding operation from an unfolding operation, but embodiments of the inventive concept are not limited thereto. In an embodiment of the inventive concept, the display device DD may select any one of an unfolding operation, an inner folding operation, and an outer folding operation.

[0073] Referring to Figure 2a and Figure 2b , the rollable display device DD may enter and leave the housing HS through a storage opening HS-OP. One end of the rollable display device DD may be connected to a handle HND. The rollable display device DD may be guided by a support portion SUP. The support portion SUP may include components of a support frame that are gradually withdrawn during an unfolding operation. The roller ROL has a shape extending in the first direction DR1 and may rotate with respect to a rotation axis. The rotation axis may be a reference axis of the rollable display device DD.

[0074] Figure 2a An unfolded state (first mode) of the rollable display device DD is shown. Figure 2b A rolled-up state (second mode) of the foldable display device DD is shown. When the display device DD is unfolded in the first mode, at least a portion of the display device DD exposed from the housing HS may provide a flat display surface DD-IS. In the first mode or the second mode, at least a portion of the display device DD disposed in the housing HS substantially forms a curvature. A bent portion of the display device DD provides a bent display surface DD-IS. In an embodiment of the inventive concept, a stress control layer, which will be described later, may be disposed to overlap at least an area providing the bent display surface of the display device DD. In an embodiment of the inventive concept, for example, the stress control layer may be disposed at least in the folding regions FA of the foldable display device DD. In an embodiment of the inventive concept, for example, the stress control layer may be disposed in the entire area of the rollable display device DD. The stress control layer is disposed in the area providing the bent display surface, and thus, stress caused by mechanical deformation (such as repeated folding or rolling) of the display device may be reduced.

[0075] Figure 3 is a cross-sectional view of the display device DD according to an embodiment of the inventive concept. Figure 4aA cross-sectional view of a display panel DP according to an embodiment of the inventive concept. Figure 4b A perspective view of a support layer SPL according to an embodiment of the inventive concept. Hereinafter, Figure 2a and Figure 2b the rollable display device DD shown in

[0076] will be mainly described. Figure 3 Referring to Figure 3 , the display device DD according to an embodiment of the inventive concept may include a support layer SPL, a digitizer DIG, a first elastic layer ESL1, a stress control layer SRL, a display panel protection film PF, a display module DM, a window WM, and a second elastic layer ESL2. In addition, the display device DD may further include a zeroth adhesive layer PSA0 to a fifth adhesive layer PSA5 disposed between components of the display device DD to bond the components. However, those skilled in the art will understand that, in addition to

[0077] the components shown in

[0078] , the display device DD according to an embodiment of the inventive concept may further include other general components.

[0079] The support layer SPL may be disposed under the display panel DP to support the display panel DP. The digitizer DIG may be disposed under the display panel DP to convert the movement of a tool (such as a pen) into a digital signal. The digitizer DIG may be a substrate that generates or senses a magnetic field. However, the digitizer DIG may be omitted as needed.

[0080] The modulus of the first elastic layer ESL1 can be proportional to the stiffness of the material. In the case of the first elastic layer ESL1 having a relatively small modulus, when the same stress is applied, the strain rate can be higher, and the elastic range capable of exhibiting elastic force and restoring force can be larger than the case of a large modulus. Therefore, the introduction of the first elastic layer ESL1 can be beneficial in terms of curling and restoring the display device DD. However, the first elastic layer ESL1 can be omitted as needed.

[0081] The stress control layer SRL can include a first auxetic structure AX1, a second adhesive layer PSA2, and a second auxetic structure AX2. The stress control layer SRL can be disposed between the display panel DP and the support layer SPL to overlay the display panel DP. The stress control layer SRL can be adhered to the first elastic layer ESL1 through the first adhesive layer PSA1.

[0082] The stress control layer SRL can be a bi-auxetic structure including a first auxetic structure AX1 and a second auxetic structure AX2. Since the stress control layer SRL is a bi-auxetic structure, the thickness of a single auxetic structure can be reduced. In the case of using a bi-auxetic structure, the rollability of the display device DD is greater than the case of using a single auxetic structure having a thickness corresponding to the sum of the thicknesses of the first auxetic structure AX1 and the second auxetic structure AX2. In this case, a greater rollability indicates that less force is required to curl and unfold the display device DD and less force is required to return the curled display device DD to a flat state.

[0083] The first auxetic structure AX1 and the second auxetic structure AX2 can be disposed between the display panel DP and the support layer SPL. The first auxetic structure AX1 and the second auxetic structure AX2 can include a non-magnetic material that does not respond to a magnetic field. When the first auxetic structure AX1 and the second auxetic structure AX2 include or are formed of a non-magnetic material, the operation of the digitizer DIG that uses a magnetic field to identify user input can be not disturbed.

[0084] The first auxetic structure AX1 can have a thickness T1 of about 10 micrometers (μm) to about 500 μm along the third direction DR3. The second auxetic structure AX2 can have a thickness T2 of about 10 μm to about 500 μm along the third direction DR3.

[0085] The first auxetic structure AX1 and the second auxetic structure AX2 can have a negative Poisson's ratio that is stretchable in the biaxial direction. The Poisson's ratio of the first auxetic structure AX1 can be about -0.9 to about -0.1. The Poisson's ratio of the second auxetic structure AX2 can be about -0.9 to about -0.1.

[0086] The first bulking structure AX1 and the second bulking structure AX2 may be joined by a second adhesive layer PSA2. A resin, a pressure-sensitive adhesive (PSA), etc. may be used as the second adhesive layer PSA2. However, the type of the second adhesive layer PSA2 is not limited thereto, and various types of adhesives may be used.

[0087] The display module DM may include a display panel DP, an input sensing unit ISP, and an antireflection layer RPL. The display module DM may generate an image. The display module DM may sense a user input through the input sensing unit ISP. In this case, the input sensing unit ISP may be omitted as needed.

[0088] The display panel DP may be a flexible display panel. The display panel DP of an embodiment of the inventive concept may be a light-emitting display panel and is not particularly limited. In an embodiment of the inventive concept, for example, the display panel DP may be an organic light-emitting display panel or an inorganic light-emitting display panel. The emission layer of the organic light-emitting display panel may include an organic light-emitting material. The emission layer of the inorganic light-emitting display panel may include quantum dots, quantum rods, etc.

[0089] The input sensing unit ISP may be disposed on the display panel DP. The input sensing unit ISP may include a plurality of sensors (not shown) for sensing an external input in a capacitive mode. The input sensing unit ISP may be directly fabricated on the display panel DP. However, the embodiment of the inventive concept is not limited thereto, and the input sensing unit ISP is fabricated as a panel separate from the display panel DP and may be joined to the display panel DP through an adhesive layer.

[0090] The antireflection layer RPL may be disposed on the input sensing unit ISP. However, the embodiment of the inventive concept is not limited thereto, and the antireflection layer RPL may be joined to the input sensing unit ISP through an adhesive layer. The antireflection layer RPL may be defined as an external light antireflection film. The antireflection layer RPL may reduce the reflectance of external light incident on the display panel DP from the upper portion of the display device DD.

[0091] When the external light incident on the display panel DP is reflected from the display panel DP and provided back to the external user, like a mirror, the user may view the external light. To prevent the above phenomenon, as an embodiment, the antireflection layer RPL may include a plurality of color filters that display the same color as the pixels of the display panel DP. The color filters may filter the external light to the same color as the pixels. In this case, the external light may not be viewed by the user.

[0092] As another embodiment, the antireflection layer RPL may include a polarizing film for reducing the reflectance of external light. The polarizing film may include a retarder and / or a polarizer. The color filters may be directly formed on the input sensing unit ISP. The polarizing film may be joined to the input sensing unit ISP through an adhesive layer.

[0093] The display panel protective layer PF can be disposed on the lower surface of the display panel DP to protect the display panel DP from impacts. The display panel protective layer PF can be joined to the stress control layer SRL through a third adhesive layer PSA3. The display panel protective layer PF is positioned close to the display panel DP adjacent to the neutral plane, and when the display device DD is curled, the deformation may not be significant. Therefore, even when the display panel protective layer PF is relatively thick or has a large modulus, cracks are less likely to occur.

[0094] The display panel protective layer PF can have a modulus of about 1 gigapascal (GPa) to about 10 GPa. When the modulus of the display panel protective layer PF is less than about 1 GPa, the display panel DP may not be protected. When the modulus of the display panel protective layer PF is greater than about 10 GPa, cracks may occur due to the deformation caused by the curling of the display device DD.

[0095] The display panel protective layer PF can have a thickness of about 10 μm to about 100 μm. When the thickness of the display panel protective layer PF is less than about 10 μm, the display panel DP may not be protected. When the thickness of the display panel protective layer PF is greater than about 100 μm, cracks may occur due to the deformation caused by the curling of the display device DD.

[0096] The window WM can be disposed on the antireflection layer RPL. The window WM can be joined to the antireflection layer RPL through a fourth adhesive layer PSA4. The window WM can protect the display panel DP, the input sensing unit ISP, and the antireflection layer RPL from external scratches and impacts.

[0097] The second elastic layer ESL2 can be joined to the window WM through a fifth adhesive layer PSA5. The second elastic layer ESL2 can be disposed on the window WM and can include an elastomer. In an embodiment of the inventive concept, for example, the second elastic layer ESL2 can include at least one of thermoplastic polyurethane, silicone resin, thermoplastic rubber, elastic olefin, thermoplastic olefin, polyamide, polyether block amide, synthetic polyisoprene, polybutadiene, chloroprene rubber, butyl rubber, styrene-butadiene, epichlorohydrin rubber, polyacrylic rubber, silicone rubber, fluorosilicone rubber, fluorine-containing elastomer, ethylene-vinyl acetate, and polydimethylsiloxane (PDMS). However, the material of the second elastic layer ESL2 is not limited thereto.

[0098] When the display device DD is curled, a neutral plane where no deformation occurs can be disposed around the display panel DP. When the display device DD is curled, the second elastic layer ESL2 is spaced far from the display panel DP, and thus can have a greater deformation than components closer to the display panel DP. Therefore, when the second elastic layer ESL2 has a relatively large modulus, cracks may be caused. The second elastic layer ESL2 can have a modulus of about 5 MPa to about 100 MPa.

[0099] The modulus of the second elastic layer ESL2 can be proportional to the stiffness of the material. In the case of the second elastic layer ESL2 having a relatively small modulus, when the same stress is applied, the strain rate can be higher, and the elastic range capable of exhibiting elastic force and restoring force can be greater than that in the case of a large modulus. Therefore, the introduction of the second elastic layer ESL2 can be beneficial in curling and restoring the display device DD. The second elastic layer ESL2 can protect the window WM from external impacts and contamination.

[0100] Referring to Figure 4a , the display panel DP can include a substrate layer SUB, a pixel layer PXL, and a thin film encapsulation layer TFE. The display panel DP can generate an image. However, in addition to the components shown in Figure 4a , the display panel DP can also include other general components.

[0101] The substrate layer SUB can include a display area DD-DA and a non-display area DD-NDA around the display area DD-DA. The substrate layer SUB can include a flexible plastic substrate. In an embodiment of the inventive concept, for example, the substrate layer SUB can include a flexible plastic material such as polyimide (PI).

[0102] The pixel layer PXL can be stacked with the display area DD-DA. The pixel layer PXL can include a plurality of pixels, and each of the pixels can include a pixel driving circuit and a light emitting element. The thin film encapsulation layer TFE can include at least two inorganic layers and an organic layer disposed between the inorganic layers. The inorganic layer can include an inorganic material and can protect the pixel layer PXL from the influence of moisture / oxygen. The organic layer can include an organic material and can protect the pixel layer PXL from foreign substances such as dust particles.

[0103] Referring to Figure 4b , the support layer SPL can include support bars ST and an outer layer LM. The support bars ST can extend in the same direction as the direction in which the roller ROL (see Figure 2a ) extends. A plurality of support bars ST can be parallel. A plurality of support bars ST can be arranged along a first direction DR1 intersecting the roller ROL. A plurality of support bars ST can be spaced apart at equal intervals, but the spacing of the support bars ST is not limited thereto.

[0104] Multiple support rods ST may have rigid properties. In an embodiment of the inventive concept, for example, the multiple support rods ST may include a metal. The support rods ST may include aluminum, stainless steel, or invar. Additionally, the support rods ST may include a metal joined to a magnet.

[0105] The multiple support rods ST may support Figure 3 the display module DM shown in, such that the display device DD of the first mode described with reference to Figure 2a can provide a flat display surface DD-IS.

[0106] In Figure 4b , multiple support rods ST having a rectangular cross-section are shown as an example, but are not limited thereto. The multiple support rods ST may be stacked in two layers along the third direction DR3.

[0107] The outer layer LM may fix the multiple support rods ST spaced apart from each other. The outer layer LM may absorb the stress generated by the multiple support rods ST during repeated curling.

[0108] The outer layer LM may include an elastic polymer having elasticity. In an embodiment of the inventive concept, for example, the outer layer LM may include at least one of thermoplastic polyurethane, silicone resin, thermoplastic rubber, elastic olefin, thermoplastic olefin, polyamide, polyether block amide, synthetic polyisoprene, polybutadiene, chloroprene rubber, butyl rubber, styrene-butadiene, epichlorohydrin rubber, polyacrylic rubber, silicone rubber, fluorosilicone rubber, fluorine-containing elastomer, ethylene-vinyl acetate, and polydimethylsiloxane (PDMS). However, the material of the outer layer LM is not limited thereto.

[0109] When the outer layer LM is not used and the support rods ST are joined to the lower surface of the display module DM to support the display module DM, the display module DM may be deformed. In an embodiment of the inventive concept, for example, when the display module DM is repeatedly curled and unfolded, the portion of the display module DM that overlaps with the space between the multiple support rods ST may be stretched and sag downward. Such deformation may be regarded as a wrinkled shape externally. That is, the display module DM may have deteriorated surface quality.

[0110] The support rods ST may have a modulus greater than that of the outer layer LM. The outer layer LM may have a modulus of about 20 kPa to about 20 MPa. The support rods ST may have a modulus of about 1 GPa to about 200 GPa.

[0111] The support bar ST with greater rigidity can support the display module DM, and the outer layer LM with a predetermined elasticity can provide a flat surface to the display module DM. The display module DM is joined to the outer layer LM with a flat surface, and thus, the portion of the display module DM that overlaps with the space between the support bars ST is not deformed and can remain flat. That is, the display module DM can have an improved surface quality.

[0112] Figure 5a and Figure 5b is a graph showing the step characteristics and surface roughness according to the Poisson's ratio.

[0113] In Figure 5a and Figure 5b , the results of the curling test of the display device for testing are shown as a graph. The display device for testing may include two PDMS (polydimethylsiloxane) layers formed by spin coating on a plurality of support bars ST (see Figure 4b ), a auxetic structure disposed between the two PDMS layers, and a polyimide layer disposed on the upper portion of the PDMS layer.

[0114] Figure 5a and Figure 5b In the comparative example (reference) of Figure 5a and Figure 5b the display device for testing is a case where the auxetic structure is not provided, Figure 2a and in Figure 2b the display device for testing with Poisson's ratios of -0.1, -0.3, and -0.8 is a case where the Poisson's ratios of the organic structures are -0.1, -0.3, and -0.8, respectively. The curling test shows the results of 20,000 curling operations. One curling operation indicates starting in the first mode of

[0115] Figure 5a The vertical axis of the graph of Figure 5a indicates the height difference caused by the deformation of the polyimide layer before and after the curling test. Referring to

[0116] Figure 5b in the case where the auxetic structure is not provided (reference), the height difference of the polyimide layer is about 1.15 μm, indicating that the deformation of the polyimide layer is greater than in other cases (0.65 μm, 0.33 μm, and 0.25 μm) where the auxetic structure is provided. In addition, when the Poisson's ratio of the auxetic structure is about -0.1, it is seen that the height difference of the polyimide layer is 0.25 μm, which is the smallest. It is seen that as the Poisson's ratio of the auxetic structure approaches 0, the deformation of the polyimide layer becomes smaller.

[0116] Figure 5b The vertical axis of the graph in Figure 5b, it can be seen that the surface roughness (2.2 nm, 2.17 nm, 1.9 nm) in the case where the auxetic structure is provided is less than the surface roughness (4.64 nm) in the case where the auxetic structure is not provided (reference). In addition, it can be seen that as the Poisson's ratio of the auxetic structure approaches 0, the surface roughness of the polyimide layer becomes smaller. Refer to Figure 5a and Figure 5b , when the Poisson's ratio of the auxetic structure approaches 0, the stress generated during curling decreases, resulting in less deformation of the polyimide layer and a decrease in surface roughness, leading to improved surface quality.

[0117] Figure 6 is a perspective view of the stress control layer SRL according to an embodiment of the inventive concept. Figure 7a is a plan view showing a first auxetic structure AX1 according to an embodiment of the inventive concept. Figure 7b is a plan view showing a second auxetic structure AX2 according to an embodiment of the inventive concept.

[0118] Refer to Figure 6 , the stress control layer SRL may include a first auxetic structure AX1, a second adhesive layer PSA2, and a second auxetic structure AX2. The first auxetic structure AX1, the second adhesive layer PSA2, and the second auxetic structure AX2 may be sequentially stacked.

[0119] Refer to Figure 7a , the first auxetic structure AX1 may include a first pattern LP1 that defines a first opening OP1. The first pattern LP1 may form a plurality of closed curves. The first pattern LP1 may have a shape in which the closed curves of the same shape are repeated. The repeated unit closed curve may be a first unit cell AXP1.

[0120] The first unit cell AXP1 may include a plurality of first protrusions PP1 and a plurality of first recesses CP1. The plurality of first protrusions PP1 may be curved portions having a convex shape from the center of the first unit cell AXP1 to the outside of the first unit cell AXP1. The plurality of first recesses CP1 may be curved portions having a convex shape from the outside of the first unit cell AXP1 toward the center of the first unit cell AXP1.

[0121] The plurality of first recesses CP1 may be provided between the plurality of first protrusions PP1. The first protrusions PP1 and the first recesses CP1 may have the same radius of curvature.

[0122] The plurality of first protrusions PP1 of the first unit cell AXP1 may have the same maximum distance from the center of the first unit cell AXP1. The plurality of first recesses CP1 of the first unit cell AXP1 may have the same minimum distance from the center of the first unit cell AXP1. The first recess CP1 of the first unit cell AXP1 may overlap with the first protrusions PP1 of other adjacent unit cells.

[0123] The plurality of first protrusions PP1 may maintain a constant angle with respect to the center of the first unit cell AXP1 as the rotation axis. That is, one protrusion among the first protrusions PP1 may overlap with another protrusion among the first protrusions PP1 when rotated by a predetermined angle with respect to the first unit cell AXP1. In an embodiment of the inventive concept, for example, Figure 7a One protrusion among the plurality of first protrusions PP1 shown in may overlap with another protrusion among the plurality of first protrusions PP1 when rotated 120° with respect to the center of the first unit cell AXP1 as the rotation axis.

[0124] The plurality of first recesses CP1 may maintain a constant angle with respect to the center of the first unit cell AXP1 as the rotation axis. That is, one recess among the first recesses CP1 may overlap with another recess among the first recesses CP1 when rotated by a predetermined angle with respect to the first unit cell AXP1. In an embodiment of the inventive concept, for example, Figure 7a One recess among the plurality of first recesses CP1 shown in may overlap with another recess among the plurality of first recesses CP1 when rotated 120° with respect to the center of the first unit cell AXP1 as the rotation axis.

[0125] Figure 7a It is shown that the number of the first protrusions PP1 and the first recesses CP1 is three, but is not limited thereto, and the number of the first protrusions PP1 and the first recesses CP1 may be increased or decreased.

[0126] The first opening OP1 may be defined inside the first unit cell AXP1. Figure 7a The first auxetic structure AX1 shown in may be an auxetic structure having a Poisson's ratio of about -0.1. However, the shape of the first auxetic structure AX1 is not limited thereto and may vary.

[0127] Referring to Figure 7b , the second auxetic structure AX2 may include a second pattern LP2 that defines a second opening OP2. The second pattern LP2 may form a plurality of closed curves. The second pattern LP2 may have a shape in which the closed curves having the same shape are repeated. The repeated unit closed curve may be the second unit cell AXP2. The second opening OP2 may be defined inside the second unit cell AXP2.

[0128] The second unit cell AXP2 may include a plurality of second protrusions PP2 and a plurality of second recesses CP2. The plurality of second protrusions PP2 may be curved portions having a convex shape from the center of the second unit cell AXP2 to the outside of the second unit cell AXP2. The plurality of second recesses CP2 may be curved portions having a convex shape from the outside of the second unit cell AXP2 toward the center of the second unit cell AXP2.

[0129] The plurality of second recesses CP2 may be disposed between the plurality of second protrusions PP2. The second protrusions PP2 and the second recesses CP2 may have the same radius of curvature as each other.

[0130] The plurality of second protrusions PP2 of the second unit cell AXP2 may have the same maximum distance from the center of the second unit cell AXP2. The plurality of second recesses CP2 of the second unit cell AXP2 may have the same minimum distance from the center of the second unit cell AXP2. The second recesses CP2 of the second unit cell AXP2 may be superimposed on the second protrusions PP2 of other adjacent unit cells.

[0131] The plurality of second protrusions PP2 may maintain a constant angle with respect to the center of the second unit cell AXP2 as a rotation axis. That is, one of the second protrusions PP2 may be superimposed on another one of the second protrusions PP2 when rotating at a predetermined angle with respect to the center of the second unit cell AXP2. In an embodiment of the inventive concept, for example, Figure 7b one of the plurality of second protrusions PP2 shown in may be superimposed on another one of the plurality of second protrusions PP2 when rotating 120° with respect to the center of the second unit cell AXP2 as a rotation axis.

[0132] The plurality of second recesses CP2 may maintain a constant angle with respect to the center of the second unit cell AXP2 as a rotation axis. That is, one of the second recesses CP2 may be superimposed on another one of the second recesses CP2 when rotating at a predetermined angle with respect to the center of the second unit cell AXP2. In an embodiment of the inventive concept, for example, Figure 7b one of the plurality of second recesses CP2 shown in may be superimposed on another one of the plurality of second recesses CP2 when rotating 120° with respect to the center of the second unit cell AXP2 as a rotation axis.

[0133] Figure 7b The number of the second protrusions PP2 and the second recesses CP2 is shown as three, but is not limited thereto, and the number of the second protrusions PP2 and the second recesses CP2 may be increased or decreased.

[0134] Refer to Figure 7a and Figure 7b, the second pattern LP2 may be a pattern in which the first pattern LP1 is rotated 180 degrees on a plane. However, the rotation angle on the plane here is not limited to 180 degrees and can be changed as needed.

[0135] The first protrusion PP1 disposed on the upper part of the first unit cell AXP1 may face left with reference to a reference line passing through the center of the first unit cell AXP1 and parallel to the second direction DR2. The second protrusion PP2 disposed on the upper part of the second unit cell AXP2 may face right with reference to a reference line passing through the center of the second unit cell AXP2 and parallel to the second direction DR2. Therefore, the first protrusion PP1 of the first unit cell AXP1 and the second protrusion PP2 of the second unit cell AXP2 may not overlap on the plane.

[0136] Figure 8 is a plan view showing the superimposed first auxetic structure AX1 and second auxetic structure AX2 according to an embodiment of the inventive concept. Figure 9 is a plan view showing the first unit cell AXP1 and the second unit cell AXP2 according to an embodiment of the inventive concept.

[0137] Referring to Figure 8 , the first pattern LP1 of the first auxetic structure AX1 may overlap with the second opening OP2 of the second auxetic structure AX2 on the plane. The second pattern LP2 of the second auxetic structure AX2 may overlap with the first opening OP1 of the first auxetic structure AX1 on the plane. That is, on the plane, the first pattern LP1 may cover the second opening OP2, and the second pattern LP2 may cover the first opening OP1. Therefore, when the first auxetic structure AX1 and the second auxetic structure AX2 are superimposed, the entire first auxetic structure AX1 and second auxetic structure AX2 may have a planar opening ratio of about 10% to about 60%.

[0138] When the opening ratio of the entire first auxetic structure AX1 and second auxetic structure AX2 is less than about 10%, the impact resistance may be improved, but the rollability may be reduced. When the opening ratio of the entire first auxetic structure AX1 and second auxetic structure AX2 is greater than 60%, the rollability may be improved, but the impact resistance may be reduced. Therefore, when considering both the impact resistance and the rollability, the opening ratio of the entire first auxetic structure AX1 and second auxetic structure AX2 may preferably be about 10% to about 60%.

[0139] Referring to Figure 9, when the first unit cell AXP1 and the second unit cell AXP2 are stacked on a plane, the first pattern LP1 and the second pattern LP2 can cross each other. On the plane, the first pattern LP1 can pass through the region occupied by the second opening OP2. On the plane, the second pattern LP2 can pass through the region occupied by the first opening OP1. A plurality of first protrusions PP1 of the first unit cell AXP1 can protrude in different directions from a plurality of second protrusions PP2 of the second unit cell AXP2.

[0140] Figure 10a is a plan view showing a first auxetic structure AX1 according to an embodiment of the inventive concept. Figure 10b is a plan view showing a second auxetic structure AX2 according to an embodiment of the inventive concept.

[0141] Referring to Figure 10a , the first auxetic structure AX1 may include a first pattern LP1 that defines a first opening OP1. The first pattern LP1 may define a first unit cell AXP1, and the first unit cell AXP1 includes a plurality of first protrusions PP1 and a plurality of first recesses CP1 disposed between the plurality of first protrusions PP1. Figure 10a The first auxetic structure AX1 shown in Figure 7a may be the same as the first auxetic structure AX1 shown in

[0142] Referring to Figure 10b , the second auxetic structure AX2 may include a second pattern LP2 that defines a second opening OP2. The second pattern LP2 may define a second unit cell AXP2, and the second unit cell AXP2 includes a plurality of second protrusions PP2 and a plurality of second recesses CP2 disposed between the plurality of second protrusions PP2. The second opening OP2 may be defined inside the second unit cell AXP2. Figure 10b The second auxetic structure AX2 shown in Figure 10a may be the same as the first auxetic structure AX1 shown in

[0143] Figure 11 is a plan view showing the stacked first auxetic structure AX1 and second auxetic structure AX2 according to an embodiment of the inventive concept.

[0144] Referring to Figure 11, the first pattern LP1 of the first auxetic structure AX1 can be superimposed on the second pattern LP2 of the second auxetic structure AX2 in a plane. As described above, the first pattern LP1 and the second pattern LP2 are the same pattern, and thus, when the first pattern LP1 and the second pattern LP2 are superimposed at corresponding positions, the first pattern LP1 may not be superimposed on the second opening OP2 in the plane, and the second pattern LP2 may not be superimposed on the first opening OP1 in the plane. However, when the line widths of the first pattern LP1 and the second pattern LP2 are different or the first pattern LP1 and the second pattern LP2 are not completely superimposed at corresponding positions, a part of the first pattern LP1 may be superimposed on the second opening OP2 in the plane, and a part of the second pattern LP2 may be superimposed on the first opening OP1 in the plane.

[0145] Thus, when the first pattern LP1 and the second pattern LP2 are the same pattern, in the plane, the first pattern LP1 and the second pattern LP2 may not cover the first opening OP1 and the second opening OP2. Therefore, when the first auxetic structure AX1 and the second auxetic structure AX2 are superimposed, the entire first auxetic structure AX1 and the second auxetic structure AX2 may have a planar opening ratio of about 70% or more. This is in contrast to Figure 8 the case where the planar opening ratio of the entire first auxetic structure AX1 and the second auxetic structure AX2 is about 10% to about 60%.

[0146] When the planar opening ratio of the entire first auxetic structure AX1 and the second auxetic structure AX2 is greater than about 70%, the impact resistance may be reduced, but the rollability may be improved. Therefore, when the display panel DP does not require much protection or the display device DD requires relatively high rollability, the first auxetic structure AX1 and the second auxetic structure AX2 shown in Figure 11 may be used.

[0147] Figure 12 is a graph showing the stress-strain curves of the stress control layer SRL according to the comparative example and the embodiments of the inventive concept.

[0148] Referring to Figure 12, tensile tests were performed on the stress control layers SRL of Comparative Examples 1 to 3 and Examples 1 and 2 of the inventive concept. In Comparative Example 1, black polyimide (BPI) with a thickness of 50 μm was used as the stress control layer SRL. In Comparative Example 2, a single auxetic structure with a thickness of 50 μm was used as the stress control layer SRL. In Comparative Example 3, thermoplastic polyurethane (TPU) with a thickness of 100 μm was used as the stress control layer SRL. In Example 1, two auxetic structures with a thickness of 50 μm and a pressure-sensitive adhesive (PSA) with a thickness of 16 μm for joining the two auxetic structures were used as the stress control layer SRL. In Example 2, two auxetic structures with a thickness of 50 μm and a pressure-sensitive adhesive with a thickness of 25 μm for joining the two auxetic structures were used as the stress control layer SRL. In this case, the auxetic structure may include stainless steel (SUS) or be formed of stainless steel (SUS).

[0149] The experimental results of Comparative Example 1 are shown in Graph 1, the experimental results of Comparative Example 2 are shown in Graph 2, the experimental results of Example 1 of the inventive concept are shown in the curve Figure 3 , the experimental results of Example 2 of the inventive concept are shown in Graph 4, and the experimental results of Comparative Example 3 are shown in Graph 5. The specific experimental data are shown in the following table.

[0150] [Table 1]

[0151] Comparative Example 1 Comparative Example 2 Example 1 Example 2 Comparative Example 3 Elongation (%) 46 138 157 162 302 Modulus 2 GPa 161 MPa 86 MPa 64 MPa 14 MPa

[0152] Referring to Table 1 and Figure 12 , it can be seen that the stress control layers SRL of Examples 1 and 2 of the inventive concept exhibit behavior similar to that of an elastomer. That is, it can be seen that when two auxetic structures and a pressure-sensitive adhesive for joining the two auxetic structures are used as the stress control layer SRL, the behavior is similar to that of the thermoplastic polyurethane of Comparative Example 3, which is an elastomer. Based on this elasticity, even when the display device DD (see Figure 2a ) is repeatedly folded or curled, the stress control layers SRL of Examples 1 and 2 can reduce the deformation of the display device DD, thereby improving the surface quality.

[0153] The stress control layer SRL of Example 1 has a modulus of about 86 MPa, which is lower than that of Comparative Example 1 having a modulus of about 2 GPa and Comparative Example 2 having a modulus of about 161 MPa. This is because the modulus of the pressure-sensitive adhesive provided between the two auxetic structures in Example 1 is relatively low, being about 1 MPa or less. The stress control layer SRL of Example 2 has a modulus of about 64 MPa, which is lower than the moduli of Comparative Examples 1 and 2. Additionally, Example 2 has a modulus of about 64 MPa, which is lower than that of Example 1 having a modulus of about 86 MPa. This is because the pressure-sensitive adhesive of Example 2 having a lower modulus has a thickness of about 25 μm, which is greater than the thickness of the pressure-sensitive adhesive of Example 1 having a thickness of about 16 μm.

[0154] When the modulus is low, when the strain rate is the same, the stress generated is small, and thus the external force required for deformation can be reduced. Additionally, compared with Comparative Examples 1 and 2, the elastic range of Examples 1 and 2 is increased, and thus the restoring force can be maintained even when a relatively high strain is applied. Therefore, the display device DD (see Figure 2a ) to which the stress control layer SRL of the embodiment of the inventive concept is applied requires a smaller force for curling and has excellent restoring properties to return to the initial state after curling, resulting in improved rollability. However, the thermoplastic polyurethane of Comparative Example 3 is hardly regarded as a sturdy structure resistant to deformation, and thus the impact resistance may be reduced. Therefore, considering both the impact resistance and the rollability, the stress control layer SRL of Examples 1 and 2 of the inventive concept may be the most suitable.

[0155] Figure 13a and Figure 13b are a plan view showing a first auxetic structure AX1 and a second auxetic structure AX2 according to an embodiment of the inventive concept. Figure 13c is a plan view magnifying the stacked first unit cell AXP1 and second unit cell AXP2 according to an embodiment of the inventive concept.

[0156] Referring to Figure 13a , the first auxetic structure AX1 may include a first pattern LP1, the first pattern LP1 having a negative Poisson's ratio and defining a first opening OP1. Figure 13a The first auxetic structure AX1 of may have a Poisson's ratio of about -0.8. The first pattern LP1 may include a 1-1 component LP1-1 and a 1-2 component LP1-2 extending in a different direction from the 1-1 component LP1-1.

[0157] The first component LP1-1 can extend in the second direction DR2. The first component LP1-2 can extend in the first direction DR1. Each of the first components LP1-1 can be disposed between two adjacent first components LP1-2 in the second direction DR2. Each of the first components LP1-2 can be concave and extend in the first direction DR1.

[0158] Two adjacent first components LP1-1 in the first direction DR1 and two adjacent first components LP1-2 in the second direction DR2 can form a first unit cell AXP1.

[0159] Referring to Figure 13b , the second auxetic structure AX2 can include a second pattern LP2, which has a negative Poisson's ratio and defines a second opening OP2. The second pattern LP2 can include a second component LP2-1 and a second component LP2-2 that extends in a different direction from the second component LP2-1.

[0160] The second pattern LP2 can be a pattern in which the first pattern LP1 (see Figure 13a ) is rotated 90 degrees in the plane. However, the rotation angle in the plane here is not limited to 90 degrees and can be changed as needed.

[0161] The second component LP2-1 and the second component LP2-2 are Figure 13a the cases where the first component LP1-1 and the first component LP1-2 are rotated 90 degrees in the plane, and their detailed descriptions will be omitted.

[0162] Two adjacent second components LP2-1 in the second direction DR2 and the second component LP2-2 adjacent in the first direction DR1 can form a second unit cell AXP2.

[0163] Referring to Figure 13c , it shows the shapes of the first unit cell AXP1 and the second unit cell AXP2 in the plane when Figure 13a the first auxetic structure AX1 and Figure 13b the second auxetic structure AX2 are stacked.

[0164] The first pattern LP1 of the first auxetic structure AX1 may be superimposed on the second opening OP2 of the second auxetic structure AX2 in a plane. The second pattern LP2 of the second auxetic structure AX2 may be superimposed on the first opening OP1 of the first auxetic structure AX1 in a plane. That is to say, in the plane, the first pattern LP1 may cover the second opening OP2, and the second pattern LP2 may cover the first opening OP1. Therefore, when the first auxetic structure AX1 and the second auxetic structure AX2 are superimposed, the entire first auxetic structure AX1 and the second auxetic structure AX2 may have a planar opening ratio of about 10% to about 60%.

[0165] Figure 14a and Figure 14b is a plan view showing the first auxetic structure AX1 and the second auxetic structure AX2 according to an embodiment of the inventive concept. Figure 14c is an enlarged plan view of the superimposed first unit cell AXP1 and second unit cell AXP2 according to an embodiment of the inventive concept.

[0166] Referring to Figure 14a , the first auxetic structure AX1 may include a first pattern LP1, the first pattern LP1 having a negative Poisson's ratio and defining a first opening OP1. The first auxetic structure AX1 may have a Poisson's ratio of about -0.5. The first pattern LP1 may include a 1-1 component LP1-1 and a 1-2 component LP1-2 extending in a different direction from the 1-1 component LP1-1.

[0167] The 1-1 component LP1-1 may be bent multiple times and may extend along a second direction DR2. The 1-2 component LP1-2 may be bent multiple times and may extend along a first direction DR1. Two adjacent 1-1 components LP1-1 in the first direction DR1 and two adjacent 1-2 components LP1-2 in the second direction DR2 may form a first unit cell AXP1.

[0168] Referring to Figure 14b , the second auxetic structure AX2 may include a second pattern LP2, the second pattern LP2 having a negative Poisson's ratio and defining a second opening OP2. The second pattern LP2 may include a 2-1 component LP2-1 and a 2-2 component LP2-2 extending in a different direction from the 2-1 component LP2-1. Except that the center of the second unit cell AXP2 and Figure 14a the center of the first unit cell AXP1 of Figure 14a are offset from each other, the second pattern LP2 may be the same pattern as

[0169] Referring to Figure 14c , shows when Figure 14aThe shapes of the first unit cell AXP1 and the second unit cell AXP2 in a plane when the first auxetic structure AX1 and the second auxetic structure AX2 are stacked.

[0170] The first pattern LP1 of the first auxetic structure AX1 can be stacked in a plane with the second opening OP2 of the second auxetic structure AX2. The second pattern LP2 of the second auxetic structure AX2 can be stacked in a plane with the first opening OP1 of the first auxetic structure AX1. That is, in a plane, the first pattern LP1 can cover the second opening OP2, and the second pattern LP2 can cover the first opening OP1. Therefore, when the first auxetic structure AX1 and the second auxetic structure AX2 are stacked, the entire first auxetic structure AX1 and the second auxetic structure AX2 can have a planar opening ratio of about 10% to about 60%.

[0171] Figure 15a and Figure 15b are plan views showing the first auxetic structure AX1 and the second auxetic structure AX2 according to an embodiment of the inventive concept. Figure 15c is an enlarged plan view of the stacked first unit cell AXP1 and second unit cell AXP2 according to an embodiment of the inventive concept.

[0172] Referring to Figure 15a , the first auxetic structure AX1 can include a first pattern LP1, the first pattern LP1 having a negative Poisson's ratio and defining a first opening OP1. The first pattern LP1 can define a first unit cell AXP1 that bends multiple times and includes four protrusions.

[0173] Referring to Figure 15b , the second auxetic structure AX2 can include a second pattern LP2, the second pattern LP2 having a negative Poisson's ratio and defining a second opening OP2. The second pattern LP2 can be a pattern in which Figure 15a the first pattern LP1 is rotated 45 degrees in a plane. However, the rotation angle in the plane here is not limited to 45 degrees and can be changed as needed.

[0174] Referring to Figure 15c , shows the shapes of the first unit cell AXP1 and the second unit cell AXP2 in a plane when Figure 15a the first auxetic structure AX1 and Figure 15b the second auxetic structure AX2 are stacked.

[0175] The first pattern LP1 of the first auxetic structure AX1 may be superimposed on the second opening OP2 of the second auxetic structure AX2 in a plane. The second pattern LP2 of the second auxetic structure AX2 may be superimposed on the first opening OP1 of the first auxetic structure AX1 in a plane. That is, in the plane, the first pattern LP1 may cover the second opening OP2, and the second pattern LP2 may cover the first opening OP1. Therefore, when the first auxetic structure AX1 and the second auxetic structure AX2 are superimposed, the entire first auxetic structure AX1 and the second auxetic structure AX2 may have a planar opening ratio of about 10% to about 60%.

[0176] Figure 16 is a cross-sectional view of a display device DD according to an embodiment of the inventive concept.

[0177] Except for the position of the stress control layer SRL, Figure 16 the display device DD shown in Figure 3 is the same as the display device DD shown in, and thus descriptions of the same components are omitted.

[0178] The stress control layer SRL may be disposed on the upper surface of the display panel DP. In this case, the stress control layer SRL is disposed in a channel through which light emitted from the display panel DP passes out. Therefore, the stress control layer SRL may include a material having a light transmittance of about 90% or more to prevent the stress control layer SRL from reflecting the light of the display panel DP or distorting the light of the display panel DP. That is, the first auxetic structure AX1, the second adhesive layer PSA2, and the second auxetic structure AX2 may all be formed of a material having a light transmittance of about 90% or more or include a material having a light transmittance of about 90% or more.

[0179] Metals such as stainless steel (SUS) are mainly used as the first auxetic structure AX1 and the second auxetic structure AX2, but materials such as plastics may be used to increase the light transmittance of the first auxetic structure AX1 and the second auxetic structure AX2. In an embodiment of the inventive concept, for example, polyethylene terephthalate (PET), polycarbonate (PC), polyimide (PI), etc. having a light transmittance of about 90% or more may be used as the first auxetic structure AX1 and the second auxetic structure AX2. An optically clear resin (OCR) or an optically clear adhesive (OCA) having a light transmittance of about 90% or more may be used as the second adhesive layer PSA2. However, the materials of the first auxetic structure AX1, the second auxetic structure AX2, and the second adhesive layer PSA2 are not limited thereto, and various materials having a light transmittance of about 90% or more may be used.

[0180] Figure 17 is a cross-sectional view of a display device DD according to an embodiment of the inventive concept.

[0181] Reference Figure 17 , except having a plurality of stress control layers SRL1 and SRL2, Figure 17 the display device DD is the same as Figure 16 the display device DD shown in, and thus the description of the same components is omitted.

[0182] The first stress control layer SRL1 may be disposed on the lower surface of the display panel DP. That is to say, the first auxetic structure AX1, the second adhesive layer PSA2, and the second auxetic structure AX2 may be disposed between the display panel DP and the support layer SPL.

[0183] The first auxetic structure AX1, the second adhesive layer PSA2, and the second auxetic structure AX2 may include non-magnetic materials that do not respond to a magnetic field. The first auxetic structure AX1, the second adhesive layer PSA2, and the second auxetic structure AX2 include non-magnetic materials or are formed of non-magnetic materials, and thus may not interfere with the operation of the digitizer DIG that uses a magnetic field to identify user input.

[0184] The second stress control layer SRL2 may include a third auxetic structure AX3, a seventh adhesive layer PSA7, and a fourth auxetic structure AX4. The second stress control layer SRL2 may be disposed on the upper surface of the display panel DP. The third auxetic structure AX3, the seventh adhesive layer PSA7, and the fourth auxetic structure AX4 may be disposed on the upper side of the window WM to serve as a protective layer for the window WM.

[0185] The second stress control layer SRL2 may be disposed on the upper surface of the display panel DP. In this case, the second stress control layer SRL2 is arranged in the channel through which the light emitted from the display panel DP passes out. Therefore, the second stress control layer SRL2 may include a material having a light transmittance of about 90% or more to prevent the second stress control layer SRL2 from reflecting the light of the display panel DP or distorting the light of the display panel DP. That is to say, for example, the third auxetic structure AX3, the seventh adhesive layer PSA7, and the fourth auxetic structure AX4 may include a material having a light transmittance of about 90% or more or may all be formed of a material having a light transmittance of about 90% or more.

[0186] Metals such as stainless steel (SUS) are mainly used as auxetic structures AX3 and AX4, but materials such as plastics can be used to increase the light transmittance of the auxetic structures AX3 and AX4. For example, polyethylene terephthalate (PET), polycarbonate (PC), polyimide (PI), etc. having a light transmittance of about 90% or more can be used as the third auxetic structure AX3 and the fourth auxetic structure AX4. An optically clear resin (OCR) or an optically clear adhesive (OCA) having a light transmittance of about 90% or more can be used as the seventh adhesive layer PSA7. However, the materials of the third auxetic structure AX3, the fourth auxetic structure AX4, and the seventh adhesive layer PSA7 are not limited thereto, and various materials having a light transmittance of about 90% or more can be used.

[0187] Figure 18 is a cross-sectional view of a display device DD according to an embodiment of the inventive concept.

[0188] In addition to the first stress control layer SRL1, the second stress control layer SRL2, the first protective layer HMF, and the second protective layer LMF, Figure 18 the display device DD of Figure 17 is the same as the display device DD of

[0189] The first stress control layer SRL1 may include a first auxetic structure AX1, a second auxetic structure AX2, and a first optically clear adhesive layer OCR1. The first stress control layer SRL1 may be disposed under the display panel DP. The first auxetic structure AX1 and the second auxetic structure AX2 may be impregnated into the first optically clear adhesive layer OCR1. The first auxetic structure AX1 and the second auxetic structure AX2 may be spaced apart at regular intervals and disposed inside the first optically clear adhesive layer OCR1. The first optically clear adhesive layer OCR1 may surround all surfaces of the first auxetic structure AX1 and the second auxetic structure AX2.

[0190] The first stress control layer SRL1 may include a non-magnetic material that does not respond to a magnetic field. The first auxetic structure AX1, the second auxetic structure AX2, and the first optically clear adhesive layer OCR1 include a non-magnetic material or are entirely formed of a non-magnetic material, and thus may not interfere with the operation of the digital converter DIG that senses a user input using a magnetic field.

[0191] The first optically clear adhesive layer OCR1 may be an optically clear adhesive material having improved impact resistance. The first optically clear adhesive layer OCR1 may be formed using an optically clear resin (OCR) in an atypical liquid form. For the first optically clear adhesive layer OCR1, an adhesive material such as an acrylic-based, silicone-based, or urethane-based adhesive material may be used. However, the first optically clear adhesive layer OCR1 is not limited thereto, and an adhesive material having various shapes and components may be used.

[0192] The refractive index of the first optical adhesive layer OCR1 can be substantially the same as the refractive indices of the first auxetic structure AX1 and the second auxetic structure AX2.

[0193] The first auxetic structure AX1 and the second auxetic structure AX2 are impregnated into the first optical adhesive layer OCR1, and thus, when the display device DD is repeatedly curled and unfolded, deformation or peeling of the first auxetic structure AX1 and the second auxetic structure AX2 can be prevented. Accordingly, deterioration of the surface quality of the display device DD can be prevented.

[0194] The second stress control layer SRL2 can include a third auxetic structure AX3, a fourth auxetic structure AX4, and a second optical adhesive layer OCR2. The second stress control layer SRL2 is the same as the first stress control layer SRL1 except that the second stress control layer SRL2 is disposed above the display panel DP. However, since the second stress control layer SRL2 is a passage through which light emitted from the display panel DP passes, the third auxetic structure AX3, the fourth auxetic structure AX4, and the second optical adhesive layer OCR2 can have a light transmittance of about 90% or more.

[0195] The first protective layer HMF can be disposed on the upper surface of the display panel DP. The first protective layer HMF is arranged close to the display panel DP adjacent to the neutral plane and is less likely to cause cracks even when the modulus is large. The first protective layer HMF can have a modulus of about 1 GPa to about 10 GPa. The first protective layer HMF can have a thickness of about 10 μm to about 100 μm. When the display device DD is curled, the first protective layer HMF can protect the display panel DP from external impact.

[0196] The second protective layer LMF can be disposed on the upper surface of the first protective layer HMF. The second protective layer LMF is arranged away from the display panel DP adjacent to the neutral plane and is more likely to cause cracks when the modulus is large. The second protective layer LMF can have a modulus of about 1 MPa to about 1 GPa. When an external impact is applied to the display device DD, the second protective layer LMF can act as an energy damper. That is, the second protective layer LMF can reduce the impact energy applied to the display device DD.

[0197] Figures 19a to 19d is a cross-sectional view of a display device according to a comparative example and an embodiment of the inventive concept.

[0198] Figure 19a is a cross-sectional view of the display device DD of Comparative Example 1. Figure 19b is a cross-sectional view of the display device DD of Comparative Example 2. Figure 19c is a cross-sectional view of the display device DD according to Example 3 of the inventive concept. Each of the first auxetic structure AX1 and the second auxetic structure AX2 in Example 3 is the same asFigure 11 The first stretchable structure AX1 and the second stretchable structure AX2 are the same. Figure 19d is a cross-sectional view of the display device DD according to Example 4 of the inventive concept. Each of the first stretchable structure AX1 and the second stretchable structure AX2 in Example 4 is the same as Figure 8 the first stretchable structure AX1 and the second stretchable structure AX2.

[0199] Pen-drop tests and rollability tests are performed on the display devices DD of Comparative Examples 1 and 2 and Examples 3 and 4. In the pen-drop test, the minimum height that does not cause bright spots is determined by dropping a pen on the display surface of the display device DD placed on a pedestal in the dark mode. In the rollability test, when the display device DD is unrolled after being stored in a rolled state at 60 °C and 93% relative humidity for 240 hours, the radius of curvature of the display device DD is determined. The test results are shown in Table 2 below.

[0200] [Table 2]

[0201] Comparative Example 1 Comparative Example 2 Example 3 Example 4 Pen down 6 cm 4 cm 6 cm 8 cm Rollability 1.5 cm 2 cm 2.5 cm 2.5 cm

[0202] As shown in Table 2, it is seen that the display devices DD of Examples 3 and 4 show pen-drop results that are the same as or better than those of Comparative Examples 1 and 2, and thus have excellent impact resistance. In addition, it is seen that the display devices DD of Examples 3 and 4 show a maximum radius of curvature of about 2.5 centimeters (cm), and thus, the recovery after curling of the display device DD is optimal. Therefore, it is seen that as in Example 4, when the stress control layer SRL has a dual structure of the first stretchable structure AX1 and the second stretchable structure AX2 and the first stretchable structure AX1 and the second stretchable structure AX2 are stacked, both impact resistance and rollability can be ensured when the aperture ratio is reduced (see Figure 8 ).

[0203] Although the present disclosure has been described with reference to the preferred embodiments of the inventive concept, it will be understood that the inventive concept should not be limited to these preferred embodiments, and various changes and modifications can be made by those skilled in the art without departing from the spirit and scope of the present disclosure. Therefore, the technical scope of the present disclosure is not limited to the detailed description in the specification, but should be determined only with reference to the claims.

[0204] Industrial Applicability

[0205] By applying the present invention to a newly developed rollable display device or a foldable display device to improve the surface quality characteristics of the display device, the present invention is considered to have industrial applicability.

Claims

1. A display device, the display device comprising: A display panel; A first auxetic structure, including a first pattern defining a plurality of first openings, stacked with the display panel, and having a negative Poisson's ratio; A second auxetic structure, including a second pattern defining a plurality of second openings, stacked with the first auxetic structure, and having a negative Poisson's ratio; And A support layer, disposed below the display panel and supporting the display panel.

2. The display device according to claim 1, the display device further comprising an adhesive layer, the adhesive layer being disposed between the first auxetic structure and the second auxetic structure to bond the first auxetic structure and the second auxetic structure, Among them, The adhesive layer has a modulus smaller than that of the first auxetic structure and the second auxetic structure.

3. The display device according to claim 1, wherein, The display panel provides a display surface defined by a first direction and a second direction, and In a first mode of the display device, the display surface provides a flat surface, and in a second mode of the display device, at least a portion of the display surface provides a curved surface relative to a reference axis.

4. The display device according to claim 3, wherein, The support layer includes a plurality of support bars parallel to the reference axis, and In the first mode, the plurality of support bars are arranged along a direction intersecting the reference axis.

5. The display device according to claim 1, wherein, Both the first auxetic structure and the second auxetic structure have a Poisson's ratio equal to or greater than about -0.9 and equal to or less than about -0.

1.

6. The display device according to claim 1, wherein, The first pattern is stacked with the second pattern, and the first pattern and the second pattern are identical to each other.

7. The display device according to claim 1, wherein, When the first pattern and the second pattern are stacked, the aperture ratio of the planar pattern defined by the first pattern and the second pattern is equal to or greater than about 10% and equal to or less than about 60%.

8. The display device according to claim 1, wherein, The first pattern is stacked with the second pattern, and the second pattern is a pattern obtained by rotating the first pattern in a plane by an angle equal to or greater than about 45 degrees and equal to or less than about 180 degrees.

9. The display device according to claim 1, wherein, The first auxetic structure has a thickness equal to or greater than about 10 microns and equal to or less than about 500 microns, and The second auxetic structure has a thickness equal to or greater than about 10 microns and equal to or less than about 500 microns.

10. The display device according to claim 1, wherein, Both the first auxetic structure and the second auxetic structure are disposed between the display panel and the support layer.

11. The display device according to claim 1, the display device further comprising a digital converter disposed below the display panel, Among them, Both the first auxetic structure and the second auxetic structure are disposed below the display panel and include non-magnetic materials that do not respond to a magnetic field.

12. The display device according to claim 1, wherein, Both the first auxetic structure and the second auxetic structure are disposed on the upper surface of the display panel.

13. The display device according to claim 12, wherein, Both the first auxetic structure and the second auxetic structure include materials having a light transmittance equal to or greater than about 90%.

14. The display device according to claim 1, the display device further comprising an optical adhesive layer, Among them, Both the first auxetic structure and the second auxetic structure are impregnated into the optical adhesive layer.

15. The display device according to claim 14, wherein, The refractive index of the optical adhesive layer, the refractive index of the first auxetic structure, and the refractive index of the second auxetic structure are substantially the same.

16. The display device according to claim 1, further comprising a display panel protective layer disposed on a lower surface of the display panel and having a modulus equal to or greater than about 1 GPa and equal to or less than about 10 GPa.

17. The display device according to claim 1, further comprising an elastic layer disposed on the support layer or on the display panel and comprising an elastomer.

18. A display device, comprising: a display panel; a plurality of stress control layers stacked with the display panel; and a support layer disposed below the plurality of stress control layers and supporting the display panel, wherein the plurality of stress control layers includes a first stress control layer disposed on an upper surface of the display panel and a second stress control layer disposed on a lower surface of the display panel, the first stress control layer and the second stress control layer each include: a first auxetic structure including a first pattern defining a plurality of first openings and having a negative Poisson's ratio; and a second auxetic structure stacked with the first auxetic structure, including a second pattern defining a plurality of second openings and having a negative Poisson's ratio.

19. The display device according to claim 18, wherein, The first auxetic structure and the second auxetic structure each have a Poisson's ratio equal to or greater than about -0.9 and equal to or less than about -0.

1.

20. The display device according to claim 18, wherein, The first stress control layer includes a material having a light transmittance equal to or greater than about 90%, and the second stress control layer includes a non-magnetic material that does not respond to a magnetic field.

21. The display device according to claim 18, wherein, The first pattern is superimposed on the plurality of second openings in a plane, and the second pattern is superimposed on the plurality of first openings in a plane, and when the first pattern and the second pattern are superimposed, the planar opening ratio of the entire first auxetic structure and the second auxetic structure is equal to or greater than about 10% and equal to or less than about 60%.

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