Window substrate and display device having the same

Abstract

A window substrate for protecting an electronic display device is disclosed, the window substrate comprising a first glass substrate, a second glass substrate and an intermediate layer, wherein the first glass substrate has a first thickness, the second glass substrate has a second thickness, and the intermediate layer is arranged between the first glass substrate and the second glass substrate, and the intermediate layer has a third thickness, wherein the sum of the first thickness, the second thickness and the third thickness is equal to or less than about 190 μm. A display device is also disclosed, the display device comprising a display panel for displaying an image and the window substrate.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2016-0147526, filed on November 7, 2016, which is hereby incorporated by reference for all purposes as if fully set forth herein. Technical Field

[0003] The present invention generally relates to a window substrate, and more particularly, to a flexible window substrate and a display device having the same. Background Art

[0004] Recently, flexible display devices having flat panel displays have been developed. Flat panel displays generally include liquid crystal displays (LCDs), organic light emitting diode (OLED) displays, electrophoretic displays (EPDs), and the like.

[0005] Since the flexible display device has bending and folding characteristics, the flexible display device can be folded or rolled. Therefore, the flexible display device with a large screen can be conveniently carried. The flexible display device can be applied to various fields, including not only mobile devices such as mobile phones, portable multimedia players (PMPs), navigation, ultra mobile PCs (UMPCs), e-books, and e-newspapers, but also TVs, monitors, etc.

[0006] When external impact force is applied, defects may occur in the flexible display device, including defects that affect display quality or resolution. In this case, in order to avoid degradation of display quality, the flexible display device should be resistant to external impact. With the advent of flexible display devices, materials used to protect them from external impact are becoming thinner and thinner.

[0007] The above information disclosed in this Background section is only for enhancement of understanding of the background of the inventive concept and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. Summary of the invention

[0008] The window substrate constructed according to the principles of the present invention can protect the display device from external impact and / or prevent the display device from being damaged even when the display device is folded multiple times, while maintaining its flexible characteristics. For example, the applicant has found that a window substrate having at least two glass substrates and an intermediate layer arranged between the glass substrates can provide excellent resistance to external impact while also preventing damage caused by the display device being folded multiple times, wherein each glass substrate has a predetermined thickness to provide a compressive stress distribution.

[0009] Example embodiments also provide a display device having a window substrate constructed according to the principles of the present invention.

[0010] Additional aspects will be set forth in the detailed description which follows, and in part will be apparent from the disclosure, or may be learned by practice of the inventive concepts.

[0011] According to one aspect of the present invention, a window substrate for protecting an electronic display device includes a first glass substrate, a second glass substrate and an intermediate layer, wherein the first glass substrate has a first thickness, the second glass substrate has a second thickness, and the intermediate layer is arranged between the first glass substrate and the second glass substrate, and the intermediate layer has a third thickness, wherein the sum of the first thickness, the second thickness and the third thickness is approximately 190 μm or less.

[0012] Each of the first thickness and the second thickness may be about 50 μm or less.

[0013] The electronic display device may be a flexible display device, and when the window substrate is bent so that the first glass substrate is arranged toward the outside of the flexible display device and the second glass substrate is arranged toward the inside of the flexible display device, the first thickness may be smaller than the second thickness. The first thickness may be about 40 μm or less, and the second thickness may be about 50 μm or less.

[0014] The third thickness may be about 100 μm or less. Alternatively, the third thickness may be about 10 μm to about 30 μm.

[0015] The intermediate layer may include an optically clear adhesive.

[0016] The window substrate may have impact resistance such that the window substrate is not damaged when a 5.8 g pen is dropped vertically from a first height onto one surface of the window substrate, and wherein the first height may be about 4 cm or more.

[0017] At least one of the first glass substrate and the second glass substrate may include a first region extending from one surface of at least one of the first glass substrate and the second glass substrate to a first depth, where an ion exchange process occurs and has a first compressive stress. The first depth may be about 1 μm or more, and the first compressive stress may be about 600 MPa to about 1200 MPa.

[0018] The window substrate may have a light transmittance of about 90% or more.

[0019] When the window substrate is exposed to UVB light having a wavelength of 280 nm to 360 nm for up to 72 hours, the yellowness index change of the window substrate may be about 2.0 or less.

[0020] An absorbed load when a 5.5 g iron ball freely falls on one surface of the window substrate may be 5% or more of the impact load of the iron ball.

[0021] The window substrate may further include a cover layer disposed on the first glass substrate or the second glass substrate.

[0022] The cover layer may include at least one of an anti-reflection layer, an anti-fouling layer, and an anti-fingerprint layer.

[0023] At least a portion of the window substrate may be flexible.

[0024] The window substrate can be used in a display device together with a display panel. More specifically, and according to another aspect of the present invention, the display device includes a display panel and a window substrate, wherein the display panel is configured to display an image on its front surface, and the window substrate is arranged on the front surface of the display panel. The window substrate may include a first glass substrate, a second glass substrate, and an intermediate layer, wherein the first glass substrate has a first thickness, the second glass substrate has a second thickness, and the intermediate layer is arranged between the first glass substrate and the second glass substrate, and the intermediate layer has a third thickness, wherein the sum of the first thickness, the second thickness, and the third thickness is about 190 μm or less.

[0025] When the window substrate is bent to a position where the first glass substrate is arranged toward the outside of the display device and the second glass substrate is arranged toward the inside of the display device, the first thickness may be smaller than the second thickness. One surface of the display panel may contact one surface of the second glass substrate.

[0026] The foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings, which are included to provide a further understanding of the inventive concept and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the inventive concept and together with the description serve to explain the principles of the inventive concept.

[0028] In the accompanying drawings, for clarity of illustration, the dimensions may be exaggerated. It should be understood that when an element is referred to as being "between" two elements, the element may be the only element between the two elements, or one or more intermediate elements may also be present. Throughout the specification, the same reference numerals indicate the same elements.

[0029] Figure 1A is a perspective view showing a first embodiment of a window substrate constructed according to the principles of the present invention.

[0030] Figure 1B is along Figure 1A The line I-I' is obtained in the expanded position Figure 1A A cross-sectional view of a window substrate.

[0031] Figure 1C is along Figure 1A The line I-I' obtained in the folded position Figure 1A A cross-sectional view of a window substrate.

[0032] Figure 2A is a schematic cross-sectional view of a first glass substrate or a second glass substrate in a window substrate according to one or more exemplary embodiments.

[0033] Figure 2B is a graph showing stress with respect to distance Figure 2A A graph of the distance from the surface of the glass substrate.

[0034] Figure 3 is a cross-sectional view of a second embodiment of a window substrate constructed in accordance with the principles of the present invention.

[0035] Figure 4 is a cross-sectional view of a third embodiment of a window substrate constructed in accordance with the principles of the present invention.

[0036] Figure 5 It is constructed according to the principle of the present invention and has Figure 1A A stereoscopic view of a first embodiment of a display device having a window substrate.

[0037] Fig. 6A is along Figure 5 The line II-II' is obtained in the expanded position Figure 5 A cross-sectional view of a display device.

[0038] Figure 6B is along Figure 5 The line II-II' is obtained in the folded position Figure 5 A cross-sectional view of a display device.

[0039] Figure 7 is a block diagram of the major electronic components of a display panel constructed according to the principles of the present invention.

[0040] Figure 8 yes Figure 7 Circuit diagram of one of the pixels in FIG.

[0041] Fig. 9 The invention is shown to have a structure that can be folded about a single fold line. Figure 1A A perspective view of a second embodiment of a display device constructed according to the principles of the present invention having a window substrate.

[0042] Fig.10 is a plan view showing a display device according to one or more exemplary embodiments, in which only a flexible region, a folding line, and two rigid regions are shown.

[0043] Fig.11A It is shown that the invention has a structure that can be folded around two folding lines. Figure 1A A perspective view of a third embodiment of a display device constructed according to the principles of the present invention having a window substrate.

[0044] Fig. 11B is shown in the folded position Fig.11A A three-dimensional diagram of a display device.

[0045] Fig. 12A is a base having a foldable structure about a single offset fold line Figure 1A A perspective view of a fourth embodiment of a display device constructed according to the principles of the present invention having a window substrate.

[0046] Fig. 12B is shown in a curled position Fig. 12A A three-dimensional diagram of a display device.

[0047] Fig.13 is a graph showing the impact resistance of existing window substrates and window substrates constructed according to the principles of the present invention.

[0048] Fig.14 is a graph illustrating impact loading in a window substrate constructed according to the principles of the present invention when the thickness of the first and second glass substrates are constant but the thickness of the interlayer varies. DETAILED DESCRIPTION

[0049] In the following description, for the purpose of explanation, numerous specific details are set forth to provide a thorough understanding of the various exemplary embodiments. However, it is apparent that the various exemplary embodiments may be practiced without these specific details or with one or more equivalent arrangements. In other instances, well-known structures and devices are shown in block diagram form to avoid unnecessary confusion of the various exemplary embodiments.

[0050] In the drawings, the size and relative sizes of layers, films, panels, regions, etc., may be exaggerated for clarity and descriptive purposes. In addition, like reference numerals denote like elements.

[0051] When an element or layer is referred to as being "on", "connected to" or "coupled to" another element or layer, the element or layer may be directly on, directly connected to or directly coupled to another element or layer, or there may be an intermediate element or layer. However, when an element or layer is referred to as being "directly" "on", "directly connected to" or "directly coupled to" another element or layer, there is no intermediate element or layer. For the purposes of this disclosure, "at least one of X, Y and Z" and "at least one selected from the group consisting of X, Y and Z" may be interpreted as any combination of only X, only Y, only Z or two or more of X, Y and Z, such as, for example, XYZ, XYY, YZ and ZZ. Throughout the specification, similar reference numerals indicate similar elements. As used herein, the term "and / or" includes any and all combinations of one or more of the relevant listed items.

[0052] Although the words first, second, etc. can be used to describe various elements, components, regions, layers and / or parts in this article, these elements, components, regions, layers and / or parts should not be limited by these words. These words are used to distinguish an element, component, region, layer and / or part from another element, component, region, layer and / or part. Therefore, without departing from the teachings of the present disclosure, the first element, first component, first region, first layer and / or first part discussed below can be referred to as the second element, second component, second region, second layer and / or second part.

[0053] Spatially relative terms such as "beneath," "below," "lower," "above," "upper," and the like may be used herein for descriptive purposes and thereby describe the relationship of one element or feature to another element (or elements) or feature (or features) as shown in the accompanying drawings. Spatially relative terms are intended to also encompass different orientations of the device in use, operation, and / or manufacture in addition to the orientations depicted in the accompanying drawings. For example, if the device in the accompanying drawings is turned over, an element described as being "below" or "below" other elements or features will subsequently be oriented to be "above" the other elements or features. Thus, the exemplary term "below" may include both above and below orientations. Furthermore, the device may be oriented in other ways (e.g., rotated 90 degrees or in other orientations), and thus, the spatially relative descriptors used herein are interpreted accordingly.

[0054] The terms used herein are for the purpose of describing specific embodiments and are not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" as used herein are intended to include the plural forms as well. In addition, when the words "comprise", "comprises", "includes", "includes", and / or "comprising" are used in this specification, they indicate the presence of the stated features, wholes, steps, operations, elements, parts, and / or combinations thereof, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, parts, and / or combinations thereof.

[0055] Various exemplary embodiments are described herein with reference to schematically illustrated cross-sectional views as idealized exemplary embodiments and / or intermediate structures. Thus, variations in the illustrated shapes caused by, for example, manufacturing techniques and / or tolerances are to be expected. Therefore, the exemplary embodiments disclosed herein should not be interpreted as being limited to the specific illustrated regional shapes, but rather include deviations in shape caused by, for example, manufacturing. For example, an implanted region shown as a rectangle will typically have rounded or curved features and / or an implant concentration gradient at its edges, rather than a binary change from an implanted region to a non-implanted region. Similarly, a buried region formed by implantation may produce some implantation in the region between the buried region and the surface for implantation. Therefore, the regions shown in the drawings are schematic in nature, and their shapes are not intended to illustrate the actual shape of the region of the device, and are not intended to be limiting.

[0056] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present disclosure belongs. Unless explicitly defined as such herein, terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology and will not be interpreted in an idealized or overly formal sense.

[0057] One or more exemplary embodiments relate to a window substrate including a glass substrate. The window substrate can be used in a display device. Specifically, the window substrate can be used as a window panel located on the front surface of the display panel. Therefore, in one or more exemplary embodiments, the window panel is referred to as a window substrate. However, the use of the window substrate constructed according to the principles of the present invention is not limited thereto, and the window substrate can be used in any other application requiring a transparent insulating substrate. For example, the window substrate can be used as a base substrate or an opposing substrate, wherein, in a display device, an element is mounted on a base substrate and the opposing substrate is opposite to the base substrate. In addition, the window substrate can be used as a substrate for a touch screen panel arranged on a display substrate.

[0058] Figure 1Ais a perspective view showing a first embodiment of a window substrate constructed according to the principles of the present invention. Figure 1B is along Figure 1A The line I-I' is obtained in the expanded position Figure 1A A cross-sectional view of a window substrate. Figure 1C is along Figure 1A The line I-I' obtained in the folded position Figure 1A A cross-sectional view of a window substrate.

[0059] Reference Figures 1A to 1C , the window substrate WD according to the illustrated embodiment is shown to have a rectangular plate shape, but any other shapes known in the art may also be used.

[0060] Specifically, for ease of explanation, it has been assumed that the planar shape of the window substrate WD is a rectangular shape having a pair of long sides and a pair of short sides when viewed in a plan view. In addition, it has been shown that the long sides extend longitudinally in the first direction D1, and the short sides extend in the second direction D2 orthogonal to the first direction D1, and the third direction D3 is perpendicular to both the first direction D1 and the second direction D2. However, the shape of the window substrate WD is not limited thereto, but the window substrate WD may have various shapes. For example, the window substrate WD may be set to various shapes, such as a closed shape polygon including linear edges, a circle including curved edges, an ellipse, etc., and a semicircle including linear edges and curved edges, a semi-ellipse, etc. In one embodiment, when the window substrate WD has linear edges, at least a portion of each of the corners in the shape may be formed as a curve. For example, when the window substrate WD has a rectangular shape, the portion where adjacent linear edges meet each other may be replaced by a curve having a predetermined curvature. That is, the vertex portion of the rectangular shape may be formed with a curved edge, wherein the curved edge has two adjacent ends respectively connected to two adjacent linear edges, and the curved edge has a predetermined curvature. The curvature may be defined differently depending on the location. For example, the curvature may vary depending on the location where the curve starts, the length of the curve, etc.

[0061] The window substrate WD includes a first glass substrate GL1 , a second glass substrate GL2 , and an intermediate layer ML located between the first glass substrate GL1 and the second glass substrate GL2 .

[0062] Each of the first glass substrate GL1 and the second glass substrate GL2 is configured in a plate shape having opposite surfaces. Each of the first glass substrate GL1 and the second glass substrate GL2 may be made of a glass material including silicate. In one or more exemplary embodiments, various materials may be further added to the glass material to provide excellent durability, surface smoothness and transparency. For example, the glass substrate may be made of a material including aluminosilicate, borosilicate, borosilicate, etc. In one or more exemplary embodiments, the glass substrate may also include an alkali metal or an alkaline earth metal and an oxide thereof.

[0063] In one or more exemplary embodiments, materials of the first and second glass substrates GL1 and GL2 are not limited to the above components, and the first and second glass substrates GL1 and GL2 may be changed using various other materials known in the art and various ratios thereof.

[0064] The intermediate layer ML allows the first glass substrate GL1 and the second glass substrate GL2 to be attached to each other. In addition, the intermediate layer ML disperses stress generated in the first glass substrate GL1 and the second glass substrate GL2. In other words, when an impact is applied to a portion of the first glass substrate GL1 and / or the second glass substrate GL2, the intermediate layer ML offsets the tensile stress generated in the glass substrate due to the impact to prevent the glass substrate from breaking, and absorbs the impact energy generated when the glass substrate breaks to prevent the dispersion of tiny glass fragments. To this end, the intermediate layer ML may have an elastic material to absorb the impact energy, and a flexible material that is bendable or foldable.

[0065] The middle layer ML may be made of an optically transparent glue or adhesive. The material constituting the middle layer ML may include acrylic polymers, ethylene vinyl acetate polymers, nitrile polymers, silicone rubber, butyl rubber, styrene block copolymers, vinyl ether polymers, polyurethane polymers, epoxy polymers, etc. For example, the middle layer ML may be made of polyurethane polymers, or may be made of polyurethane polymers to which rubber or acrylic polymers are added. However, the material constituting the middle layer ML is not limited thereto, and may include various adhesive materials known in the art.

[0066] In one or more exemplary embodiments, the window substrate WD may be flexible and thus may be bent, folded, or curled. In one or more exemplary embodiments, the window substrate WD may be folded or curled in the third direction D3 or in a direction opposite to the third direction D3. That is, the window substrate WD may be folded in a direction so that a portion of the outer surface of the second glass substrate GL2 faces the remaining portion of the outer surface of the second glass substrate GL2. The terms "folded" or "bent" do not refer to a fixed shape, but to a deformable shape from an initial shape to another shape, and include a folded shape, a bent shape, a curved shape, or a curled shape, such as a roll along one or more specific lines.

[0067] In one or more exemplary embodiments, the first glass substrate GL1, the second glass substrate GL2, and the intermediate layer ML may have a total thickness of about 190 μm or less. That is, if the distance between the opposite surfaces of the first glass substrate GL1 is the first thickness t1, the distance between the opposite surfaces of the second glass substrate GL2 is the second thickness t2, and the thickness of the intermediate layer ML located between the first glass substrate GL1 and the second glass substrate GL2 is the third thickness t3, then the sum of the first thickness t1 to the third thickness t3 may be about 190 μm or less. The applicant has found that a total maximum thickness of about 190 μm is particularly advantageous. When the window substrate WD has a thickness greater than 190 μm, the repulsive force against deformation of the window substrate WD is excessively increased, and thus bending of the window substrate WD is difficult.

[0068] In one or more exemplary embodiments, the first glass substrate GL1, the second glass substrate GL2, and the intermediate layer ML may have a total thickness of about 50 μm or more. That is, the sum of the first thickness t1 to the third thickness t3 may be about 50 μm or more. When the thickness of the window substrate WD is less than 50 μm, the rigidity of the window substrate WD is low, and thus the window substrate WD may be damaged during processing. However, it is preferred to make the thickness of the window substrate WD as thin as possible, and thus the window substrate WD can be manufactured to have a thickness of less than about 50 μm within the constraints of satisfying rigidity and processing capabilities. The window substrate WD being damaged refers to a state in which the window substrate WD cannot be used for its intended purpose, such as a state in which the window substrate WD is broken, a state in which a defect or crack is generated in the window substrate WD, a state in which a defect or crack is extended, or a state in which the window substrate WD is broken.

[0069] In detail, the first thickness t1 of the first glass substrate GL1 may be about 10 μm to about 50 μm, and the second thickness t2 of the second glass substrate GL2 may be about 10 μm to about 50 μm. In addition, the third thickness t3 of the middle layer ML may be about 10 μm to about 100 μm. In another embodiment of the present invention, the first thickness t1 may be about 30 μm to about 50 μm, and the second thickness t2 may be about 30 μm to about 50 μm. In addition, the third thickness t3 may be about 10 μm to about 30 μm.

[0070] Therefore, the window substrate WD constructed according to the principles of the present invention may be bent with a relatively small radius of curvature R. Therefore, the window substrate WD may have a radius of curvature R of about 1 mm to about 10 mm or about 1 mm to about 5 mm.

[0071] In one or more exemplary embodiments, the thicknesses of the first glass substrate GL1 and the second glass substrate GL2 may be equal to each other, or may be different from each other. Specifically, when the window substrate WD is folded based on any one surface of the window substrate WD so that a portion of the surface and the remaining portion of the surface face each other, the thicknesses of the first glass substrate GL1 and the second glass substrate GL2 may be different to minimize stress applied to the first glass substrate GL1 and the second glass substrate GL2.

[0072] For example, when a reference line about which the window substrate WD is folded is represented as a folding line FL, the folding line FL may be located at the surface of the second glass substrate GL2 of the window substrate WD. The window substrate WD may be folded about the folding line FL so that a portion of the surface of the second glass substrate GL2 and the remaining portion of the surface of the second glass substrate GL2 face each other. In this case, the inner side of the second glass substrate GL2 is arranged at the outer side of the first glass substrate GL1, one surface of the first glass substrate GL1 becomes the outer peripheral surface, and one surface of the second glass substrate GL2 becomes the inner peripheral surface. When the window substrate WD is bent, the first thickness t1 of the first glass substrate GL1 at the outer side of the window substrate WD may have a smaller value than the second thickness t2 of the second glass substrate GL2 arranged at the inner side. In an embodiment, the first thickness t1 may be about 20 μm to about 40 μm, and the second thickness t2 may be 30 μm to about 50 μm.

[0073] As described above, the window substrate WD includes two glass substrates having a small thickness of 50 μm or less. Therefore, when an object having a narrow cross-sectional area (such as a pen) collides with the window substrate, bending breakage may occur due to the glass substrate being broken due to the stress applied to the glass substrate. In order to reduce bending breakage, the impact resistance of the glass substrate must be improved. To this end, the glass substrate constructed according to the principles of the present invention may be a glass chemically strengthened by an ion exchange process to improve its impact resistance. In one or more exemplary embodiments, the term "ion exchange process" refers to the glass exchanging positive ions of the same atomic value with positive ions located on or near the surface of the glass. For example, the ion exchange process may refer to the exchange of positive ions inside the glass (for example, positive ions of alkali metals such as Na + or Li + ) is exchanged with another positive ion from the outside. The ion exchange process can be used to increase the compressive stress distribution of the glass to a specific depth extending from the two surfaces of the glass. When such a compressive stress distribution is provided in the glass substrate, as long as the defect exists in the area defined by the reference line where the compressive stress is greater than 0 in the compressive stress diagram, high strength is provided to resist the bending of the glass substrate. Here, the defined area can be the area between the surface of the glass and a specific depth from the surface. Therefore, chemical enhancement of the two surfaces of the glass can be achieved by the ion exchange process.

[0074] Figure 2A is a schematic cross-sectional view of a first glass substrate GL1 or a second glass substrate GL2 in a window substrate according to one or more exemplary embodiments. Figure 2B is a graph showing stress with respect to distance Figure 2A The first glass substrate GL1 and the second glass substrate GL2 have substantially the same shape except for their thickness. Therefore, hereinafter, the first glass substrate GL1 and the second glass substrate GL2 are collectively referred to as glass substrates GL.

[0075] Reference Figure 2A and Figure 2B The glass substrate GL includes a first region RG1, a second region RG2 and a third region RG3, wherein the first region RG1 extends from one surface of the glass substrate GL (hereinafter, referred to as the first surface S1) to a first depth DOL1, the second region RG2 extends from the other surface of the glass substrate GL (hereinafter, referred to as the second surface S2) to a second depth DOL2, and the third region RG3 is located between the first region RG1 and the second region RG2.

[0076] In the first region RG1, the first depth DOL1 is a depth at which positive ions inside the glass substrate GL are exchanged with positive ions from the outside. Therefore, the first region RG1 has a first thickness T1. The first compressive stress CS1 is applied to the first region RG1 by ion exchange. The first compressive stress CS1 decreases from the first surface S1 to the first depth DOL1 according to a predetermined function, and becomes 0 at the first depth DOL1. Here, the total compressive stress stored in the first region RG1 can be represented by an area under a specific function in the depth direction of the layer from the first surface S1.

[0077] The first region RG1 may offset tensile stress generated in the glass substrate GL while the glass substrate GL is folded, particularly tensile stress reaching a maximum value near the first surface S1 .

[0078] In the second region RG2, the second depth DOL2 is a depth at which positive ions inside the glass substrate GL are exchanged with positive ions from the outside. Therefore, the second region RG2 has a second thickness T2. The second compressive stress CS2 is applied to the second region RG2 by ion exchange. The second compressive stress CS2 decreases from the second surface S2 to the second depth DOL2 according to a predetermined function, and becomes 0 at the second depth DOL2. The total compressive stress stored in the second region RG2 can also be represented by an area under a specific function in the depth direction of the layer from the second surface S2.

[0079] The second region RG2 may offset the tensile stress generated in the glass substrate GL while the glass substrate GL is folded, particularly the tensile stress reaching a maximum value near the second surface S2 .

[0080] The function related to the above-mentioned compressive stress may vary according to the type of glass substrate GL, the type of ions exchanged by ion exchange, the condition (or conditions) in ion exchange, etc., but may decrease in the direction from the first surface S1 to the third region RG3 and in the direction from the second surface S2 to the third region RG3. In the present embodiment shown, for ease of explanation, the two functions have been shown in the form of straight lines. However, the increase or decrease of the function is not limited to this, and the function value to the first depth DOL1 or to the second depth DOL2 may be changed differently. For example, the function value may be constant, may decrease and then increase, or may increase and then decrease.

[0081] In one or more exemplary embodiments, the first depth DOL1 and / or the second depth DOL2 may be different according to the thickness of the glass substrate GL. For example, the first depth DOL1 and / or the second depth DOL2 may be set equal to or less than 1 / 3 or 1 / 4 of the thickness of the glass substrate GL.

[0082] If it is assumed that the positive ions from the outside are first ions and the positive ions located inside the glass substrate GL are second ions, the first ions may be K + , and the second ion may be Na + or Li + .

[0083] The first compressive stress CS1 and the second compressive stress CS2 are balanced by the central tension CT stored in the third region RG3. The central tension CT is a tensile stress.

[0084] In one or more exemplary embodiments, the first depth DOL1 is substantially the same as the second depth DOL2. In addition, the first compressive stress CS1 at the first surface S1 of the glass substrate GL is substantially the same as the second compressive stress CS2 at the second surface S2 of the glass substrate GL. Therefore, the compressive stresses at the two surfaces of the glass substrate GL are symmetrical to each other.

[0085] When the glass substrate GL is folded or rolled, compressive stress is applied to the surface corresponding to the inner peripheral surface, and tensile stress is applied to the surface corresponding to the outer peripheral surface.

[0086] In one or more exemplary embodiments, in the glass substrate GL, each of the first depth DOL1 and the second depth DOL2 may be about 1 μm to about 15 μm. In another embodiment of the glass substrate GL, each of the first depth DOL1 and the second depth DOL2 may be about 6 μm to about 10 μm.

[0087] In addition, each of the first compressive stress CS1 and the second compressive stress CS2 applied by chemical strengthening in the glass substrate GL may be about 600 MPa to about 1200 MPa. Chemical strengthening may be achieved by an ion exchange process. In another embodiment, each of the first compressive stress CS1 and the second compressive stress CS2 applied by chemical strengthening may be about 730 MPa to about 850 MPa. Here, the first compressive stress CS1 may be the entire compressive stress stored in the first region RG1, and the second compressive stress CS2 may be the entire compressive stress stored in the second region RG2.

[0088] When a defect is generated in at least one of the opposite surfaces of the glass substrate GL, if the defect exists in a region defined by a reference line where the compressive stress is 0 and a positive compressive stress value, the tensile strength is compensated by the compressive strength. In this case, the glass substrate GL is not broken, and damage caused by the defect is prevented. When the first depth DOL1 and the second depth DOL2 are out of the above range, that is, when the defect does not exist in the above region and / or when the first compressive stress CS1 and the second compressive stress CS2 are out of the above range, it is difficult to fully compensate for the tensile stress applied to the glass substrate GL.

[0089] In one or more exemplary embodiments, chemical strengthening may be performed symmetrically on two opposite surfaces of the glass substrate GL. However, the inventive concept is not limited thereto, and chemical strengthening may be performed asymmetrically. Specifically, when the glass substrate GL is mainly folded in a specific direction, chemical strengthening for compensating stress may also be performed asymmetrically.

[0090] In another embodiment, chemical strengthening may be performed on each of the two glass substrates constituting the window substrate WD to the same degree or to different degrees. For example, the first glass substrate GL1 and the second glass substrate GL2 may be chemically strengthened to have compressive stresses equal to each other. However, the inventive concept is not limited thereto, and the first glass substrate GL1 and the second glass substrate GL2 may be chemically strengthened to have compressive stresses different from each other. In one or more exemplary embodiments, the second glass substrate GL2 may be chemically strengthened to have a compressive stress greater than that of the first glass substrate GL1. Therefore, the second glass substrate GL2 may have a depth greater than that of the first glass substrate GL1.

[0091] As described above, even in the case where a defect is generated in a surface to which tensile stress is applied when the glass substrate (i.e., the first glass substrate GL1 and the second glass substrate GL2) is folded or curled, damage to the glass substrate is minimized. Specifically, although the first glass substrate GL1 and the second glass substrate GL2 are ultra-thin substrates having a thickness of 50 μm or less, the generation or growth of defects caused by tensile stress when the first glass substrate GL1 and the second glass substrate GL2 are folded or curled can be reduced. Therefore, the possibility of damage to the entire window substrate WD can be surprisingly reduced.

[0092] The light transmittance of the window substrate WD having the above structure may be about 90% or more. Light emitted from a pixel of a display panel to be described below may be viewed by a user via the window substrate WD. In addition, light emitted from a pixel may pass through the window substrate WD. The window substrate WD has sufficient light transmittance so that the brightness of light emitted from the display panel can be prevented from being reduced.

[0093] In one or more exemplary embodiments, even when the window substrate WD is exposed to medium-wave ultraviolet (UVB) light having a wavelength of 280nm to 360nm for up to 72 hours, the window substrate WD may have a yellow index change (ΔY1) of 2.0 or less. When the window substrate WD is applied to another device such as a display device, the window substrate WD may be exposed to direct light including UV. However, under such conditions, no color change occurs in the window substrate WD. The window substrate WD constructed according to the principles of the present invention satisfies such a condition.

[0094] In one or more exemplary embodiments, the window substrate WD may have a haze value of 1.5% or less. In one or more exemplary embodiments, the window substrate WD may have a pen hardness of 8H to 9H.

[0095] In one or more exemplary embodiments, since the window substrate WD includes the first glass substrate GL1, the second glass substrate GL2, and the intermediate layer ML disposed between the first glass substrate GL1 and the second glass substrate GL2, the window substrate WD may have impact resistance, specifically, bending deformation due to point impact and compressive deformation and / or tensile deformation due to surface impact are reduced.

[0096] The bending deformation due to the point impact can be checked by a pen drop impact resistance test. In one or more exemplary embodiments, the impact resistance against the point impact is evaluated in the following manner, that is, in this manner, by allowing a specific pen (Fine BIC pen produced by Societe BIC) with a weight of about 5.8 g covered with a cap to fall freely according to gravity in a state where the specific pen is perpendicular to the surface of the window substrate, it is checked whether the window substrate is damaged. In one or more exemplary embodiments, the window substrate may have an impact resistance of at least about 4 cm. That is, when a pen with a weight of about 5.8 g falls toward the window substrate at a height of about 4 cm or less, the window substrate may not break.

[0097] One surface of the window substrate is often in contact with a sharp tool such as a stylus. The impact of the front surface caused by the tool has a relatively narrow area in contact with the window substrate, and thus corresponds to a point impact in which a high pressure is applied to a narrow area of ​​the window substrate when the tool falls from the top. Therefore, bending deformation occurs as the window substrate bends at the position where the impact is applied. Therefore, the bending deformation causes damage to the window substrate or causes a bright spot failure of the display panel. However, the window substrate constructed according to the principle of the present invention has sufficient impact resistance to resist the point impact, and thus the above-mentioned damage or failure can be prevented.

[0098] The compression deformation and / or tensile deformation due to surface impact can be checked by impact resistance testing.

[0099] Generally, the stress applied to the glass substrate can be expressed as: applied load (N) / unit area (m 2 ). When a tool such as a ball applies an impact to a glass substrate, resistance to the impact is improved as the area to which the ball is applied to the glass substrate increases when the ball contacts the glass substrate. In an embodiment, a first glass substrate and a second glass substrate are provided, and an intermediate layer is provided between the first glass substrate and the second glass substrate, whereby, although a tool such as a ball applies an impact to one of the two substrates, the volume at the point where accumulated stress forms and defects such as cracks grow increases, thereby improving impact resistance (Fracture criterion for glass under impact loading, S. Bouzid et al., International Journal of Impact Engineering 25 (2001) 831-845).

[0100] In one or more exemplary embodiments, the impact resistance against surface impact is evaluated in a manner in which how much impact load the window substrate absorbs is measured by allowing an iron ball having a diameter of 25.4 mm and a mass of 5.5 g to fall freely according to gravity at a height of 5 cm from the surface of the window substrate. The window substrate according to the embodiment may absorb at least about 5% of the impact load.

[0101] In addition to sharp tools such as styluses, the window substrate is often in contact with tools having a relatively wide contact area. Since the window substrate is compressed at the impact location and stretched near the impact location by the surface impact applied by the tool, compression deformation and tensile deformation occur. Compression deformation and tensile deformation may also cause damage to the window substrate and bright spot failure of the display panel. However, the window substrate constructed according to the principles of the present invention has sufficient impact resistance to resist surface impact, and thus the above-mentioned damage or failure can be prevented.

[0102] In one or more exemplary embodiments, the window substrate may have a folding reliability of 200,000 times. Folding reliability means that the window substrate will not be damaged even if the window substrate is folded many times. The folding reliability can be performed in multiple cycles using a flip folding reliability test. The flip folding reliability test can be performed in a form in which the steps of allowing the two ends of the window substrate to face each other and then stretching the window substrate into a flat state are used as a cycle, thereby repeating the cycle. In an embodiment, when the window substrate is applied to another device (e.g., a display device), the window substrate may be folded many times. Therefore, a folding reliability test is performed as a test for ensuring reliability when the window substrate is folded many times. In the folding reliability test, the window substrate is attached to an optically transparent adhesive and then placed on a test board. The test board includes a fixed plate and a rotatable plate that can rotate between the fixed plate and a single-axis or multi-axis folding device. In the folding reliability test, the glass substrate is kept flat for a predetermined time (for example, about 1 second) by arranging the window substrate on a fixed plate and a rotatable plate placed on the same plane, and then the rotatable plate is moved to be parallel to the fixed plate in a state where the rotatable plate is separated from the fixed plate. Therefore, the window substrate is in a state where it is folded between the two plates and has a predetermined curvature at the same time. In this state, the glass substrate is kept flat again for a predetermined time (for example, about 1 second). Then, as the rotatable plate returns to the initial state, the glass substrate is kept flat in the initial state by arranging the window substrate on a fixed plate and a rotatable plate placed on the same plane, thereby completing one cycle. The folding speed is 2.4 seconds / time, and the total time required is 124 hours. The number of folding times (cycles) is 200,000 times. When no abnormality occurs in the window substrate after the window substrate is folded 200,000 times, the folding reliability of the window substrate is evaluated as OK. When abnormality such as damage occurred in the window substrate after the window substrate was folded 200,000 times, the folding reliability of the window substrate was evaluated as NG.

[0103] Conditions in the folding reliability test may vary. When the rotatable plate is parallel to the fixed plate in a state where the rotatable plate is spaced apart from the fixed plate, the distance between the rotatable plate and the fixed plate is D, and D / 2 substantially corresponds to the radius of curvature. The distance D may be controlled to be about 1 mm to about 10 mm using the folding device.

[0104] For example, the conditions in the folding reliability test may be changed according to the thickness of the window substrate WD, the target radius of curvature, and the compressive stress after chemical enhancement by the ion exchange process. In addition, the folding reliability test may be performed in one direction. However, the folding reliability test may be performed in one direction and in a direction opposite to the one direction.

[0105] In one or more exemplary embodiments, when the window substrate WD is deformed, the window substrate WD may have a repulsive force of 20 N or less. When the window substrate WD is applied to a display device, etc., the window substrate WD may be folded multiple times, and the repulsive force when the user folds the window substrate WD is preferably such that the user does not feel inconvenienced.

[0106] The repulsive force resisting the deformation of the window substrate may be defined by Equation 1 and Equation 2 below.

[0107]

[0108]

[0109] In Equation 1 and Equation 2, E is Young's modulus, t is glass thickness, w is the width of the window substrate, and D is the distance between the two ends of the window substrate facing each other in folding. Folding is performed by folding the window substrate having a width w into a form in which the two ends of the window substrate face each other. Since D corresponds to twice the radius of curvature of the window substrate, the window substrate may have a radius of curvature of about 1 mm to about 10 mm or a radius of curvature of about 1 mm to about 5 mm that satisfies the D value corresponding thereto.

[0110] In one or more exemplary embodiments, the window substrate has high bending strength. The bending strength can be checked by a 2-point bending test. The 2-point bending test is performed in a manner in which a lower clamp and an upper clamp parallel to each other are prepared, a sample having a predetermined size (for example, 7.2 inches) is placed between the lower clamp and the upper clamp in a state in which the sample is bent, and then a load is applied to the upper clamp in a downward direction. At this time, the sample is bent so that the two ends of the sample face each other. One of the two ends is in contact with the upper clamp, and the other of the two ends is in contact with the lower clamp. In the 2-point bending test, the maximum load that does not damage the sample is measured. In an embodiment, the window substrate may exhibit a bending strength of 1.3 GPa or greater.

[0111] In one or more exemplary embodiments, the window substrate may have a radius of curvature of about 1 mm to about 10 mm or a radius of curvature of about 1 mm to about 5 mm. In this case, the window substrate is not damaged. In one or more exemplary embodiments, although the window substrate is damaged, breakage in the damage is prevented.

[0112] In one or more exemplary embodiments, it has been shown that the window substrate WD includes a first glass substrate GL1, a second glass substrate GL2, and an intermediate layer ML located between the first glass substrate GL1 and the second glass substrate GL2. However, this is provided for ease of description, and the present inventive concept is not limited thereto. For example, the window substrate may also include three or more glass substrates, and the intermediate layer may be provided between the corresponding glass substrates.

[0113] Figure 3 is a cross-sectional view of a second embodiment of a window substrate constructed in accordance with the principles of the present invention.

[0114] Reference Figure 3 The window substrate WD may include a first glass substrate GL1, a second glass substrate GL2, and a third glass substrate GL3 stacked in sequence. A first intermediate layer ML1 may be disposed between the first glass substrate GL1 and the second glass substrate GL2, and a second intermediate layer ML2 may be disposed between the second glass substrate GL2 and the third glass substrate GL3.

[0115] In the present embodiment, the thickness of each of the first to third glass substrates GL1, GL2, and GL3 may be equal to each other, but in another embodiment, they may be different from each other. As described above, when the window substrate WD is folded so that a portion of any one of the surfaces of the window substrate WD faces the remaining portion of the surface, the thickness of the first to third glass substrates GL1, GL2, and GL3 may be determined to minimize the stress applied to the first to third glass substrates GL1, GL2, and GL3.

[0116] For example, the window substrate WD may be bent around a fold line at the surface of the third glass substrate GL3 so that a portion of the surface of the third glass substrate GL3 and the remaining portion of the surface of the third glass substrate GL3 face each other. In this case, one surface of the first glass substrate GL1 becomes an outer peripheral surface, and one surface of the third glass substrate GL3 becomes an inner peripheral surface. In this case, the thickness of the first glass substrate GL1 may have a value smaller than the thickness of the second glass substrate GL2 and the third glass substrate GL3. In the same manner, the thickness of the second glass substrate GL2 may have a value smaller than the thickness of the third glass substrate GL3. In an embodiment, when the window substrate WD is bent, the thicknesses of the first intermediate layer ML1 and the second intermediate layer ML2 may also have different values ​​so as to enhance the damping effect of the first intermediate layer ML1 and the second intermediate layer ML2.

[0117] Figure 4 is a cross-sectional view of a third embodiment of a window substrate constructed in accordance with the principles of the present invention.

[0118] Reference Figure 4The window substrate WD may include various functional layers. For example, the window substrate WD may further include a cover layer CVL provided as a functional layer on one surface of the window substrate WD.

[0119] In one or more exemplary embodiments, the cover layer CVL may be disposed on a surface of the window substrate WD at a side facing the user. That is, the cover layer CVL is a surface directly exposed to the user and may be disposed on a surface in contact with a user's finger, a stylus pen, or another external object.

[0120] The cover layer CVL may be an anti-reflection layer that minimizes reflection on the surface of the glass substrate. The cover layer CVL may be an anti-fouling layer that prevents stains or smudges such as handprints (eg, fingerprints) of a user, but the inventive concept is not limited thereto. Figure 4 The middle cover layer CVL is illustrated as a single layer, but the inventive concept is not limited thereto, and layers having various functions may be provided as a plurality of layers.

[0121] In the present embodiment, the covering layer CVL arranged only on the user-facing surface of the window substrate WD is shown as a functional layer, but the inventive concept is not limited thereto. The functional layer may be arranged on the back surface that does not face the user. In this case, the functional layer may be an additional layer for improving the impact resistance of the window substrate WD and preventing scattered damage to the window substrate WD. The additional layer may include at least one selected from polyurethane resins, epoxy resins, polyester resins, polyether resins, acrylic resins, acrylonitrile-butadiene-styrene (ABS) resins and rubber. The additional layer may be directly connected to the window substrate WD. The additional layer may be formed on the window substrate WD using a coating technique. For example, the additional layer may be formed on the window substrate WD using slide coating, rod coating, spin coating, etc.

[0122] Although not shown in the present drawing, the window substrate WD may have a first glass substrate GL1 and / or a second glass substrate GL2 formed in various shapes, for example, formed with a protrusion or a recess. According to this type of embodiment, the first glass substrate GL1 and / or the second glass substrate GL2 may have a recessed portion that is recessed inward from the surface at the back surface. The shape of the recessed portion may be set differently. When viewed in a plan view, the recessed portion may be formed with various sizes at various positions on the glass substrate. For example, considering the direction in which the glass substrate is to be folded or curled, the recessed portion may be provided in a region corresponding to the direction. For example, when the glass substrate is folded or curled so that one surface of the glass substrate becomes an inner peripheral surface, the recessed portion may be provided on the one surface. Alternatively, the recessed portion may be formed in a region corresponding to almost the entire surface of the glass substrate.

[0123] When the recessed portion is provided in the entire region or a partial region on the glass substrate, the thickness of the glass substrate in the region provided with the recessed portion is reduced, and thus the tensile stress generated in the glass substrate is reduced. Therefore, the glass substrate is more easily bent or curled.

[0124] The above-mentioned window substrate WD can be combined with various devices recognized by those skilled in the art. Specifically, the window substrate WD can be used as a protective substrate for protecting a display panel of a display device.

[0125] Figure 5 It is constructed according to the principle of the present invention and has Figure 1A A stereoscopic view of a first embodiment of a display device having a window substrate. Fig. 6A is along Figure 5 The line II-II' is obtained in the expanded position Figure 5 A cross-sectional view of a display device. Figure 6B is along Figure 5 The line II-II' is obtained in the folded position Figure 5 A cross-sectional view of a display device.

[0126] Reference Figure 5 , Fig. 6A and Figure 6B , the display device according to this embodiment can be folded or bent.

[0127] The display device includes a display panel DP displaying an image and a window substrate WD disposed on one surface of the display panel DP.

[0128] The display panel DP displays arbitrary visual information on its front surface, for example, text, video, picture, two-dimensional or three-dimensional image, etc. The type of the display panel DP is not limited as long as the display panel DP can display an image.

[0129] The entire or at least a portion of the display panel DP may have flexibility. For example, the display panel DP may have flexibility in its entire region. Alternatively, the display panel DP may have flexibility in a region corresponding to the flexible region FA.

[0130] In the illustrated embodiment, the display panel DP is provided in a plate shape having a front surface and a back surface, wherein an image is displayed on the front surface and the back surface is opposite to the front surface. The display panel DP displays an image on the front surface. In one or more exemplary embodiments, the display panel DP may display an image on both the front surface and the back surface. However, in the present embodiment, a case where an image is displayed on the front surface is described as an example. Figure 5 , the direction of the front surface on which the image is displayed has been indicated by an arrow.

[0131] The display panel DP includes a display area DA in which an image is displayed and a non-display area NDA located at at least one side of the display area DA. For example, the non-display area NDA may be provided in a shape surrounding the display area DA.

[0132] As is known in the art, the display area DA is a region in which a plurality of pixels PXL are disposed to display an image.

[0133] The display area DA may be set to a shape corresponding to the shape of the display device. For example, similar to the shape of the display device, the display area DA may be set to various shapes, such as a closed-shape polygon including linear edges, a circle including curved edges, an ellipse, etc., and a semicircle including linear edges and curved edges, a semiellipse, etc. In the illustrated embodiment, the display area DA is set to a rectangular shape.

[0134] The pixels PXL are disposed on the display area DA. Each of the pixels PXL is a minimum unit for displaying an image, and a plurality of pixels PXL may be provided. The pixels PXL may emit white light and / or colored light. Each pixel PXL may emit light of one color of red, green, and blue, but the inventive concept is not limited thereto. For example, each pixel PXL may emit light of a color such as cyan, magenta, or yellow.

[0135] The pixel PXL may be a light emitting device including an organic light emitting layer, but the inventive concept is not limited thereto. For example, the pixel PXL may be implemented in various forms, such as a liquid crystal device, an electrophoretic device, and an electrowetting device.

[0136] The pixel PXL will be described later.

[0137] The window substrate WD is disposed on the front surface of the display panel DP, and includes a first glass substrate GL1, a second glass substrate GL2, and an intermediate layer ML between the first glass substrate GL1 and the second glass substrate GL2. The window substrate described above may be used as the window substrate WD, and therefore only the differences from the above disclosure are mainly described to avoid redundancy.

[0138] The display panel DP may be disposed on the first glass substrate GL1 or the second glass substrate GL2 of the window substrate WD. In the illustrated embodiment, the display panel DP is disposed on the second glass substrate GL2 so that the window substrate WD and the display panel DP are arranged in a form in which the outer surface of the second glass substrate GL2 and the front surface of the display panel DP are in contact with each other. However, the arrangement of the window substrate WD and the display panel DP is not limited thereto, and the display panel DP may be disposed on the first glass substrate GL1 so that the window substrate WD and the display panel DP are arranged in a form in which the outer surface of the first glass substrate GL1 and the front surface of the display panel DP are in contact with each other.

[0139] Although not shown in these drawings, an optically transparent adhesive layer may be provided between the display panel DP and the window substrate WD. The optically transparent adhesive layer between the display panel DP and the window substrate WD may be selected from materials constituting the middle layer ML. However, the material of the optically transparent adhesive layer is not limited thereto.

[0140] In the present embodiment, the window substrate WD allows an image from the display panel DP to be transmitted therethrough while reducing an impact from the outside, thereby making it possible to prevent the display panel DP from being damaged or erroneously operated due to an impact from the outside. An impact from the outside refers to a force from the outside, such as stress, that causes a defect of the display panel DP.

[0141] As described above, the window substrate WD may have elasticity to absorb the impact from the outside and distribute the impact from the outside to its surroundings at the same time. For example, the window substrate WD is deformed due to the impact from the outside, and may have elasticity that enables the window substrate WD to return to its original state when the impact from the outside is eliminated. In addition, the window substrate WD has excellent impact resistance, which makes the window substrate WD less deformed or damaged due to the impact from the outside.

[0142] The window substrate WD reduces bending deformation of the display panel DP due to point impact and surface impact and compressive deformation and / or tensile deformation of the display panel DP due to surface impact, thereby preventing malfunction of the display panel DP.

[0143] The entirety or at least a portion of the window substrate WD may have flexibility. For example, the display panel DP may have flexibility in the entirety or a portion of the area thereof.

[0144] The display device including the display panel DP and the window substrate WD may be set in various shapes. For example, the window substrate WD may be set in a plate shape corresponding to the shape of the display panel DP, and may cover at least a portion of the front surface of the display panel DP. For example, when the display panel DP is set in a rectangular shape, the window substrate WD may also be set in a rectangular shape corresponding to the shape of the display panel DP. Alternatively, when the display panel DP is set in a circular shape, the window substrate WD may also be set in a circular shape corresponding to the shape of the display panel DP.

[0145] In one or more exemplary embodiments, although the display panel DP and the window substrate WD have slight differences in shape, the display panel DP and the window substrate WD may be configured to have substantially the same shape. Therefore, the display device including the display panel DP and the window substrate WD may be configured to have a rectangular plate shape. For ease of explanation, the illustrated embodiment shows a case where the display device is configured to have a rectangular shape having a pair of long sides and a pair of short sides. In addition, Figure 5A long side extending in a first direction D1 and a short side extending in a second direction D2 are shown, and a direction perpendicular to the extending direction of the long side and the short side is a third direction D3. However, the shape of the display device is not limited thereto, and the display device may have various shapes. For example, the display device may be arranged in various shapes such as a closed shape polygon including a linear side, a circle including a curved side, an ellipse, etc., and a semicircle including a linear side and a curved side, a semi-ellipse, etc. In an embodiment, when the display device has a linear side, at least a portion of the angle of each of the shapes may be formed as a curve. For example, when the display device has a rectangular shape, the portion where adjacent linear sides are connected to each other may be replaced by a curve having a predetermined curvature. That is, the vertex portion of the rectangular shape may be formed with a curved side, wherein the curved side has two adjacent ends connected to two adjacent linear sides, respectively, and the curved side has a predetermined curvature. The curvature may be determined differently depending on the position. For example, the curvature may vary according to the position where the curve starts, the length of the curve, etc.

[0146] At least a portion of the display device may be flexible, and the display device may be folded around a folding line or axis provided in the portion having flexibility. That is, the display device may include a flexible area FA having flexibility and being an area in which the display device is foldable, and a rigid area provided at least on one side of the flexible area FA and being an area (areas) in which the display device is not folded.

[0147] In the present embodiment, the area where the display panel DP is not folded is referred to as a rigid area, but this is provided for ease of explanation. The term "rigid" includes not only the case where the rigid area is hard without any flexibility, but also the case where the rigid area has a smaller amount of flexibility than the flexible area FA and the case where the rigid area is flexible but not foldable.

[0148] In one or more exemplary embodiments, the entire display device may correspond to the flexible area FA. For example, in the case where the display device is bent into a rolled shape, the entire display device may correspond to the flexible area FA.

[0149] Figure 5 An exemplary embodiment is shown in which the first rigid area RA1 , the flexible area FA, and the second rigid area RA2 are sequentially arranged along the first direction D1 . The flexible area FA longitudinally extends across the display area DA along the second direction D2 .

[0150] When it is assumed that the center line around which the display device is folded is the folding line FL, the folding line FL is disposed in the flexible area FA. The present embodiment shows that the folding line FL passes through the center of the flexible area FA, and the flexible area FA is arranged symmetrically with respect to the folding line FL, but the inventive concept is not limited thereto. That is, the folding line FL may be asymmetrically disposed in the flexible area FA. The flexible area FA and the folding line FL located on the flexible area FA may overlap with the area where the image of the display panel DP is displayed. When the display device is folded, the area where the image is displayed may be bent.

[0151] This embodiment shows a state in which one surface of each of the two rigid regions is positioned parallel to each other and folded to face each other. However, the inventive concept is not limited thereto. For example, the surfaces of the two rigid regions may be folded to form a predetermined angle (e.g., an acute angle, a right angle, or an obtuse angle), with the flexible region FA interposed between the two rigid regions.

[0152] In the display device, the folding line FL is disposed in the flexible area FA along the second direction D2 which is the extending direction of the flexible area FA. Therefore, the display device can be folded in the flexible area FA.

[0153] In one or more exemplary embodiments, when the display device is folded along the folding line FL, the display device may be folded so that two portions of the surface opposite to the surface on which the image is displayed face each other. In a state where the display device is folded, the window substrate WD may be exposed at the outermost side. In this case, even in a state where the display device is folded, an image may be provided to the outside, and a user may observe the image regardless of whether the display device is folded. However, the folding direction of the display device is not limited thereto. When the display device is folded along the folding line FL, the window substrate WD may be exposed at the outermost side. Figure 6B Unlike what is shown in , the display device can be folded so that two parts of the surface on which the image is displayed face each other.

[0154] For ease of explanation, the present embodiment shows that the first rigid region RA1 and the second rigid region RA2 have similar areas to each other, and the flexible region FA is located between the two rigid regions RA1 and RA2, but the inventive concept is not limited thereto. For example, the first rigid region RA1 and the second rigid region RA2 may have different areas from each other. In addition, the number of rigid regions is not necessarily two, and may be one or three or more. In this case, a plurality of rigid regions may be arranged to be spaced apart from each other, and the flexible region FA is interposed between the plurality of rigid regions.

[0155] In one or more exemplary embodiments, the flexible area FA and the rigid area of ​​the window substrate WD may have different thicknesses, different repulsions, different impact resistances, etc. Even if the window substrate WD is completely flexible, when repeated bending occurs in a specific area (e.g., the flexible area FA), the stress in the specific area may increase compared to other areas, and the window substrate WD may be deformed to prevent damage due to bending stress.

[0156] For example, each index of the window substrate WD in the flexible area FA may be differently determined by changing the thickness of the first glass substrate GL1 and / or the second glass substrate GL2 or by changing the depth at which chemical strengthening is performed on the first glass substrate GL1 and / or the second glass substrate GL2.

[0157] Next, each pixel PXL in the display panel DP will be described.

[0158] Figure 7 is a block diagram of the main electronic components of a display panel DP constructed according to the principles of the present invention. Figure 8 yes Figure 7 A circuit diagram of one of the pixels PXL in FIG.

[0159] Reference Figure 7 and Figure 8 , a display panel DP constructed according to the principle of the present invention includes a pixel PXL, a gate driver GDV, a data driver DDV and a timing controller TCN, wherein the pixel PXL is set on the display area DA, the gate driver GDV and the data driver DDV are used to drive the pixel PXL, and the timing controller TCN is used to control the driving of the gate driver GDV and the data driver DDV.

[0160] Each pixel PXL is disposed on the display area DA and includes a line unit including a gate line GL, a data line DL and a driving voltage line DVL, a thin film transistor connected to the line unit, and an organic light emitting device EL connected to the thin film transistor.

[0161] The gate line GL extends in one direction. The data line DL extends in another direction intersecting the gate line GL. The driving voltage line DVL extends in substantially the same direction as the data line DL. The gate line GL transmits a gate signal to the thin film transistor. The data line DL transmits a data signal to the thin film transistor. The driving voltage line DVL provides a driving voltage to the thin film transistor.

[0162] The thin film transistor may include a driving thin film transistor TR2 for controlling the organic light emitting device EL and a switching thin film transistor TR1 for switching the driving thin film transistor TR2. In the illustrated embodiment, one pixel PXL includes two thin film transistors TR1 and TR2. However, the inventive concept is not limited thereto, and one pixel PXL may include one thin film transistor and one capacitor, or may include three or more thin film transistors and two or more capacitors.

[0163] The gate electrode of the switching thin film transistor TR1 is connected to the gate line GL, and the source electrode of the switching thin film transistor TR1 is connected to the data line DL. The drain electrode of the switching thin film transistor TR1 is connected to the gate electrode of the driving thin film transistor TR2. In response to the gate signal applied to the gate line GL, the switching thin film transistor TR1 transmits the data signal applied to the data line DL to the driving thin film transistor TR2.

[0164] The gate electrode of the driving thin film transistor TR2 is connected to the drain electrode of the switching thin film transistor TR1, and the source electrode of the driving thin film transistor TR2 is connected to the driving voltage line DVL. The drain electrode of the driving thin film transistor TR2 is connected to the organic light emitting device EL.

[0165] The organic light emitting device EL includes a light emitting layer (not shown) and a first electrode (not shown) and a second electrode (not shown) opposite to each other, wherein the light emitting layer is interposed between the first electrode and the second electrode. The first electrode is connected to the drain electrode of the driving thin film transistor TR2. A common voltage is applied to the second electrode, and the light emitting layer emits light according to an output signal of the driving thin film transistor TR2, so that light is emitted or not emitted, thereby displaying an image. The light emitted from the light emitting layer may be white light or colored light.

[0166] The capacitor Cst may be connected between the gate electrode and the source electrode of the driving thin film transistor TR2 . The capacitor Cst charges and maintains the data signal input to the gate electrode of the driving thin film transistor TR2 .

[0167] The timing controller TCN receives a plurality of image signals RGB and a plurality of control signals CS from the outside of the display device. The timing controller TCN converts the data format of the image signal RGB into an interface specification suitable for the data driver DDV, and provides the converted image signal R'G'B' to the data driver DDV. In addition, based on the plurality of control signals CS, the timing controller TCN generates a data control signal D-CS (e.g., an output start signal, a horizontal start signal, etc.) and a gate control signal G-CS (e.g., a vertical start signal, a vertical clock signal, a vertical clock bar signal, etc.). The data control signal D-CS is provided to the data driver DDV, and the gate control signal G-CS is provided to the gate driver GDV.

[0168] The gate driver GDV sequentially outputs gate signals in response to the gate control signal G-CS provided from the timing controller TCN. Therefore, the plurality of pixels PXL may be sequentially scanned in units of rows by the gate signal.

[0169] In response to the data control signal D-CS provided from the timing controller TCN, the data driver DDV converts the image signal R'G'B' into a data signal and outputs the converted data signal. The output data signal is applied to the pixel PXL.

[0170] Therefore, each pixel PXL is turned on by the gate signal, and the turned-on pixel PXL receives a corresponding data voltage from the data driver DDV, thereby displaying an image having a desired gray scale.

[0171] Fig. 9 is a perspective view showing a display device according to an embodiment in which two display areas are provided.

[0172] Reference Fig. 9 , the display device may include a plurality of display areas. For example, the display device may include a first display area DA1 and a second display area DA2. A non-display area NDA may be provided at the periphery of the first display area DA1 and the second display area DA2, and the first display area DA1 and the second display area DA2 may be spaced apart from each other, wherein the non-display area NDA is interposed between the first display area DA1 and the second display area DA2. When viewed in a plan view, the display panel DP may include a first rigid area RA1, a second rigid area RA2, and a flexible area FA arranged between the first rigid area RA1 and the second rigid area RA2. The flexible area FA may overlap with the non-display area NDA located between the first display area DA1 and the second display area DA2.

[0173] Similar to the above-described embodiments, the folding line FL may be disposed substantially parallel to any side of the display device. However, the inventive concept is not limited thereto, and the folding line FL may be arranged in various directions regardless of the shape of the display device. For example, in one or more exemplary embodiments, the folding line FL may be disposed obliquely to any side of the display device.

[0174] Fig.10 is a plan view showing a display device according to one or more embodiments, in which only a flexible area, a folding line, and two rigid areas are schematically shown.

[0175] Reference Fig.10In this embodiment, the display device is arranged in a rectangular shape, and the folding line FL is arranged along the diagonal line of the rectangular shape. In the display device, the flexible area FA is also arranged in the diagonal direction along the folding line FL, and the first rigid area RA1 and the second rigid area RA2 may be arranged at both sides of the flexible area FA, respectively.

[0176] In one or more exemplary embodiments, a single folding line FL may be provided. However, the present inventive concept is not limited thereto, and a plurality of folding lines FL may be provided.

[0177] Fig.11A It is shown that the invention has a structure that can be folded around two folding lines. Figure 1A A perspective view of a third embodiment of a display device constructed according to the principles of the present invention having a window substrate. Fig. 11B is shown in the folded position Fig.11A A three-dimensional diagram of a display device.

[0178] Reference Fig.11A and Fig. 11B , a plurality of folding lines are provided, and therefore, the display device may have a plurality of flexible areas and a plurality of rigid areas. As an example, the present embodiment describes two folding lines, i.e., a first folding line FL1 and a second folding line FL2, and accordingly, describes a first rigid area RA1, a first flexible area FA1, a second rigid area RA2, a second flexible area FA2, and a third rigid area RA3 sequentially arranged in a first direction D1. The first flexible area FA1 and the second flexible area FA2 may extend in a second direction D2 corresponding to the first folding line FL1 and the second folding line FL2, respectively.

[0179] like Fig. 11B As shown in the figure, the display device can be folded in the first flexible area FA1 and the second flexible area FA2. This figure shows that the display device is folded so that the third rigid area RA3 is located between the first rigid area RA1 and the second rigid area RA2, but the inventive concept is not limited thereto. In another embodiment, the display device can be folded so that the second rigid area RA2 is located between the first rigid area RA1 and the third rigid area RA3.

[0180] The present embodiment shows both the first folding line FL1 and the second folding line FL2 extending in the second direction D2. However, the first folding line FL1 and the second folding line FL2 may extend in directions different from each other. For example, the first folding line FL1 may extend in the first direction D1, and the second folding line FL2 may extend in the second direction D2. Alternatively, both the first folding line FL1 and the second folding line FL2 extend in the first direction D1. Alternatively, the first folding line FL1 may extend in the first direction D1, and the second folding line FL2 may extend in a direction inclined to the first folding line FL1. In another embodiment, three or more folding lines may extend in any of the above directions or arrangements.

[0181] In one or more exemplary embodiments, the flexible region may be disposed at the outermost side of the display device in one direction so that a portion of the display device is rolled into a roll shape.

[0182] Fig. 12A is a diagram showing a device having a foldable structure about a single offset fold line. Figure 1A A perspective view of a fourth embodiment of a display device constructed according to the principles of the present invention having a window substrate. Fig. 12B is shown in a curled position Fig. 12A A three-dimensional diagram of a display device.

[0183] Reference Fig. 12A and Fig. 12B The display device has a rigid area RA and a flexible area FA. The flexible area FA may be disposed at one side of the rigid area RA. The flexible area FA may be disposed at the outermost side of the display device in the first direction D1. The display device may be rolled in the flexible area FA.

[0184] The display device having the structure described above includes the window substrate described above, whereby the impact resistance of the display device is improved. Therefore, specific evaluations of certain characteristics and tests will be described in the following examples.

[0185] Examples

[0186] 1. Used for testing optical and mechanical properties

[0187] Table 1 below shows results obtained by testing the optical and mechanical properties of existing window substrates (Comparative Examples 1 and 2) and a window substrate constructed according to the principles of the present invention (embodiment).

[0188] Each of Comparative Example 1, Comparative Example 2, and the embodiment was manufactured into a substrate having an aspect ratio of 16:9, the diagonal line of the substrate having a length of 7.2 inches (180 mm×105.2 mm).

[0189] Since Comparative Example 1 is manufactured into a polyimide substrate, the substrate is formed into two layers, each of which has a thickness of 50 μm, and the total thickness of the substrate is 100 μm. Comparative Example 2 is manufactured into a glass substrate with a thickness of 50 μm. The embodiment is manufactured to include a first glass substrate with a thickness of 30 μm, an intermediate layer with a thickness of 10 μm, and a second glass substrate with a thickness of 50 μm.

[0190] Table 1

[0191]

[0192] In Table 1, compressive stress refers to the compressive stress of each glass substrate in Comparative Example 2 and the embodiment. Chemical strengthening depth refers to the ion exchange depth (depth of length) of each glass substrate in Comparative Example 2 and the embodiment. Bending strength refers to the maximum load checked by a 2-point bending test. Impact absorption load refers to the load absorbed by each of the window substrates of Comparative Example 1, Comparative Example 2 and the embodiment when a load of 91.2 gf is applied to the window substrate by allowing an iron ball with a diameter of 25.4 mm and a mass of 5.5 g to fall freely at a height of 5 cm above the surface of the window substrate. Folding reliability indicates whether the example has passed 200,000 cycles of flip-folding reliability. Thickness uniformity indicates the average value of the thickness difference at 9 points specified at equal distances relative to each window substrate in the transverse and longitudinal directions.

[0193] Referring to Table 1, the embodiment exhibits optical and mechanical properties corresponding to those of Comparative Examples 1 and 2. Specifically, the impact resistance (pen drop) of the embodiment is 4 cm, which is an improved value compared to 3 cm of Comparative Example 1 and 2 cm of Comparative Example 2. The impact absorption load of the embodiment also exhibits a surprisingly larger value than that of Comparative Examples 1 and 2.

[0194] 2. Impact resistance evaluation (pencil down)

[0195] Table 2 below shows the results obtained by testing the impact resistance (pen drop) of an existing window substrate (Comparative Example) and a window substrate constructed according to the principle of the present invention (Embodiments 1 to 5).

[0196] Table 2

[0197]

[0198] Referring to Table 2, in the comparative example configured with only a glass substrate having a thickness of 50 μm, damage to the window substrate occurred at a height of 2 cm in the pen drop impact resistance test. On the other hand, in Embodiments 1 to 5, damage to all window substrates occurred at a height of 4 cm or more in the pen drop impact resistance test. Therefore, it can be seen that the impact resistance against point impact is improved in Embodiments 1 to 5.

[0199] Furthermore, even when the sum of the thicknesses of the first glass substrate and the second glass substrate was 100 μm or less, damage occurred to all the window substrates at a height of 4 cm or more in the pen drop impact resistance test.

[0200] 3. Impact resistance evaluation (falling ball)

[0201] Table 3 below shows the results obtained by testing the impact resistance of existing window substrates (Comparative Examples 2 to 5) and a window substrate constructed according to the principles of the present invention (embodiment). Fig.13 is a graph showing the impact resistance of a conventional window substrate obtained from Table 3 and a window substrate constructed according to the principles of the present invention.

[0202] The impact resistance against a falling ball was evaluated by measuring how much impact load the window substrate absorbed when an iron ball having a diameter of 25.4 mm and a mass of 5.5 g was freely dropped at a height of 5 cm above the surface of each window substrate.

[0203] Comparative Example 1 represents the impact load when an iron ball falls without any window substrate, and its impact load corresponds to 91.2gf. Comparative Examples 2 to 5 and the embodiment are tested using a substrate having an aspect ratio of 16:9, wherein the diagonal of the substrate has a length of 7.2 inches (180mm×105.2mm). Comparative Example 2 is manufactured as a window substrate as follows, in which a hard coating layer having a thickness of 50μm is formed on a polyimide film having a thickness of 50μm, and the total thickness of the window substrate is provided as 100μm. Comparative Example 3 is provided as a third-generation Gorilla Glass (Gorilla Glass 3) having a thickness of 50μm, which is a commercially available product available from Corning. Comparative Example 4 is provided as a third-generation Gorilla Glass having a thickness of 80μm. Comparative Example 5 is manufactured to include a polyimide film having a thickness of 40μm and a third-generation Gorilla Glass having a thickness of 50μm. The embodiment is manufactured to include a first glass substrate (Gorilla Glass 3) having a thickness of 30 μm, an intermediate layer (optically clear adhesive) having a thickness of 10 μm, and a second glass substrate (Gorilla Glass 3) having a thickness of 50 μm.

[0204] Table 3

[0205]

[0206]

[0207] Referring to Table 3, Comparative Example 2 can be bent at a curvature radius of 5 mm, but has a low absorption load. Comparative Examples 3 and 4 cannot be bent at a curvature radius of 5 mm. However, Comparative Example 5 and the embodiment can be bent at a curvature radius of 5 mm. In addition, the impact absorption rate of Comparative Example 5 and the embodiment is 5% or more.

[0208] 4. Repulsion Assessment

[0209] Table 4 below shows results obtained by evaluating repulsive force when the thicknesses of the first glass substrate and the second glass substrate are different from each other in the window substrate constructed according to the principles of the present invention.

[0210] Table 4

[0211]

[0212] Referring to Table 4, when the thickness of the first glass substrate was within a range of 30 μm to 50 μm and the thickness of the second glass substrate was within a range of 30 μm to 50 μm, all embodiments exhibited a repulsive force of 20 N or less.

[0213] In addition, the repulsive forces of Embodiment 2 and Embodiment 4 are 5.2 N and 6.5 N, respectively, and the repulsive force when the first glass substrate is thinner than the second glass substrate has a smaller value than the repulsive force when the first glass substrate is thicker than the second glass substrate. Therefore, it can be seen that the thickness of the glass substrate located at the outside is reduced according to the direction in which the window substrate is bent, thereby reducing the repulsive force.

[0214] 4. Impact resistance evaluation (surface impact)

[0215] Table 5 below shows results obtained by evaluating impact loads when the thicknesses of the first and second glass substrates are constant but the thicknesses of the intermediate layers are different in the window substrate constructed according to the principles of the present invention. Fig.14 is a graph showing Table 5. That is, Fig.14 is a graph illustrating the impact load of a window substrate constructed according to the principles of the present invention when the thickness of the first and second glass substrates are constant but the thickness of the interlayer varies.

[0216] The impact load was evaluated using a drop tower impact system as an evaluation device, and the evaluation was performed according to the ASTM D3763 evaluation standard. The evaluation was performed in a manner in which the load at the failure point where each window substrate was damaged when a component of 1.954 kg fell freely at a height of 10 cm was measured. In this case, the impact velocity in the evaluation corresponded to 0.77 m / s, and the impact energy in the evaluation corresponded to 0.579 J.

[0217] Table 5

[0218]

[0219] Referring to Table 5, the impact load decreases as the thickness of the intermediate layer increases. Therefore, whenever the thickness of the intermediate layer increases by about 10 μm, the impact load decreases by about 5%.

[0220] 5. Maximum stress assessment

[0221] Table 6 below shows the results obtained by measuring the maximum stress values ​​in display devices using existing window substrates (Comparative Examples 1 to Comparative Examples 3) and window substrates constructed according to the principles of the present invention (Implementation Examples 1 to 3). Table 6 shows the results obtained by measuring the maximum stress applied to the display panel when the existing window substrate and the window substrate constructed according to the principles of the present invention are arranged on the corresponding display panel and an iron ball with a diameter of 25.4 mm and a mass of 5.5 g falls freely at a height of 5 cm above each of the window substrates.

[0222] Table 6

[0223]

[0224]

[0225] Comparative Example 3 indicated by * was manufactured using a polyimide film instead of glass.

[0226] Referring to Table 6, Comparative Examples 1 to 3 all exhibited a maximum stress of 18 MPa or more, but Embodiments 1 to 3 all exhibited a maximum stress of 17.3 MPa or less. Specifically, it can be seen that the damping effect is improved by about 4% whenever the thickness of the intermediate layer increases by about 10 μm.

[0227] 5. Folding reliability assessment

[0228] Table 7 below shows the results obtained by measuring the folding reliability in a display device using a window substrate constructed according to the principle of the present invention (embodiment 1 to embodiment 7 and comparative example 1). In Table 7, as the thickness of each intermediate layer, 10 μm to 100 μm means that the test is performed by changing the thickness in units of 10 μm. That is, the folding reliability is tested by changing the thickness of the intermediate layer to 10 μm, 20 μm, 30 μm, ..., 100 μm.

[0229] Table 7

[0230]

[0231]

[0232] Referring to Table 7, it can be seen that when the thickness of the intermediate layer is about 100 μm or less, the folding reliability is high. However, it can be seen that when the total thickness of the window substrate exceeds 190 μm, the folding reliability is evaluated as NG. The display device according to the embodiment of the present invention is not limited to the above-mentioned shape, but may have various shapes.

[0233] The window substrate constructed according to the principle of the present invention and the display device having the window substrate can be used in various electronic devices. For example, the display device can be applied to televisions, notebook computers, cellular phones, smart phones, smart boards, PMPs, PDAs, navigation, and various wearable devices such as smart watches.

[0234] According to the inventive concept, it is possible to provide a window substrate capable of ensuring durability and user safety, and a display device having the same.

[0235] Although certain exemplary embodiments and implementations have been described herein, other embodiments and variations will be apparent from this description. Accordingly, the inventive concept is not limited to these embodiments, but to the broader scope of the appended claims and various obvious variations and equivalent arrangements.

Claims

1. A window substrate for protecting an electronic display device, the window substrate comprising: a first glass substrate; a second glass substrate; as well as an intermediate layer having opposite sides, the intermediate layer being arranged between the first glass substrate and the second glass substrate, one side of the intermediate layer being in contact with the first glass substrate, and the other side of the intermediate layer being in contact with the second glass substrate, wherein the first glass substrate has a first thickness, the second glass substrate has a second thickness, and the intermediate layer has a third thickness, and wherein the sum of the first thickness, the second thickness and the third thickness is less than 190 μm, wherein the electronic display device is a flexible display device, and when the window substrate is bent so that the first glass substrate is arranged toward the outside of the flexible display device and the second glass substrate is arranged toward the inside of the flexible display device, and the first thickness is smaller than the second thickness, and The first thickness is 20 μm to 40 μm, and the second thickness is 30 μm to 50 μm.

2. The window substrate according to claim 1, wherein The third thickness is 100 μm or less.

3. The window substrate according to claim 1, wherein The intermediate layer includes an optically clear adhesive.

4. The window substrate according to claim 1, wherein The window substrate has impact resistance such that the window substrate is not damaged when a 5.8 g pen is dropped vertically from a first height onto one surface of the window substrate, and wherein the first height is 4 cm or more.

5. The window substrate according to claim 1, wherein At least one of the first glass substrate and the second glass substrate includes a first region extending from one surface of at least one of the first glass substrate and the second glass substrate to a first depth, where an ion exchange process occurs and having a first compressive stress.

6. The window substrate according to claim 5, wherein The first depth is 1 μm or more, and the first compressive stress is 600 MPa to 1200 MPa.

7. The window substrate according to claim 1, wherein The window substrate has a light transmittance of 90% or more.

8. The window substrate according to claim 1, wherein When the window substrate is exposed to UVB light having a wavelength of 280 nm to 360 nm for 72 hours, the yellowness index of the window substrate changes to 2.0 or less.

9. The window substrate of claim 1, wherein: An absorbed load when a 5.5 g iron ball freely falls on one surface of the window substrate is 5% or more of an impact load of the iron ball.

10. The window substrate of claim 1, further comprising: A cover layer is arranged on the first glass substrate or the second glass substrate.

11. The window substrate of claim 10, wherein: The cover layer includes at least one of an anti-reflection layer, an anti-fouling layer and an anti-fingerprint layer.

12. The window substrate of claim 1, wherein: At least a portion of the window substrate is flexible.

13. The window substrate of claim 1, wherein: The window substrate can be bent with a radius of curvature of 1 mm to 10 mm.

14. The window substrate of claim 1, wherein: Each of the first thickness and the second thickness is greater than the third thickness.

15. A display device comprising: a display panel configured to display an image on a front surface thereof; as well as a window substrate arranged on the front surface of the display panel, Wherein, the window substrate comprises: a first glass substrate; a second glass substrate; and an intermediate layer having opposite sides, the intermediate layer being arranged between the first glass substrate and the second glass substrate, one side of the intermediate layer being in contact with the first glass substrate, and the other side of the intermediate layer being in contact with the second glass substrate, wherein the first glass substrate has a first thickness, the second glass substrate has a second thickness, and the intermediate layer has a third thickness, and wherein the sum of the first thickness, the second thickness and the third thickness is less than 190 μm, wherein the display device is a flexible display device, and when the window substrate is bent so that the first glass substrate is arranged toward the outside of the flexible display device and the second glass substrate is arranged toward the inside of the flexible display device, and the first thickness is smaller than the second thickness, and The first thickness is 20 μm to 40 μm, and the second thickness is 30 μm to 50 μm.

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