Display device

Abstract

An embodiment of the present invention relates to a display device that may include a display panel and a window portion disposed on the display panel. The window portion may include: a window film having flexibility; and at least one coating disposed on the window film. The window film may have elastic deformation in a first interval when the tensile stress applied to the window film increases, and plastic deformation in a second interval after the first interval. The first interval and the second interval may be defined according to the relationship between the tensile stress applied to the window film and the deformation rate of the window film based on the tensile stress. The window film may have a yield strain rate of 1.9% to 2.25%, and the yield strain rate may be defined as the deformation rate of the window film when the yield stress of the first interval is applied to the window film.

Description

Technical Field

[0001] The present invention relates to a window portion and a display device including the window portion, and more particularly, to a window portion capable of reducing deformation of a folding portion and a display device including the window portion. Background Art

[0002] Generally, electronic devices such as smartphones, digital cameras, laptop computers, navigators, and smart TVs that provide images to users include a display device for displaying images. The display device generates an image and provides the image to the user through a display screen.

[0003] In recent years, with the technological development of display devices, various forms of display devices have been developed. For example, various flexible display devices that can be deformed in a curved shape, folded, or curled are being developed. The flexible display device is easy to carry and can improve user convenience.

[0004] The flexible display device includes a window portion on the upper part for protecting the display surface. The window portion can protect the display surface from external scratches and impacts. Summary of the Invention

[0005] An object of the present invention is to provide a window portion that reduces the amount of deformation of a folding portion so that the deformation of the folding portion is not externally recognizable, and a display device including the window portion.

[0006] A display device according to an embodiment of the present invention may include a display panel and a window portion disposed on the display panel. The window portion may include: a window portion film having flexibility; and at least one coating disposed on the window portion film. The window portion film may have elastic deformation in a first section when the tensile stress acting on the window portion film increases, and plastic deformation in a second section after the first section. The first section and the second section may be defined according to the relationship between the tensile stress applied to the window portion film and the deformation rate of the window portion film based on the tensile stress. The window portion film may have a yield strain rate of 1.9% to 2.25%, and the yield strain rate may be defined as the deformation rate of the window portion film when the yield stress of the first section is applied to the window portion film.

[0007] (Advantages of the Invention)

[0008] According to an embodiment of the present invention, there is provided a window portion that reduces the amount of deformation of a folding portion so that the deformation of the folding portion is not externally recognizable, and a display device including the window portion. Brief Description of the Drawings

[0009] Figure 1 It is a perspective view of a window portion according to an embodiment of the present invention.

[0010] Figure 2Yes Figure 1 A cross-sectional view taken along the line I-I' shown in the figure.

[0011] Figures 3 to 5 Indicates the results of the first to third physical property inspections of the window film of the window part related to an embodiment of the present invention.

[0012] Figure 6 Is a perspective view of a display device related to an embodiment of the present invention.

[0013] Figure 7 Indicates Figure 6 A perspective view of the folded state of the display device shown in the figure.

[0014] Figure 8 Is a perspective view of a display device related to an embodiment of the present invention.

[0015] Figure 9 Indicates Figure 8 A perspective view of the folded state of the display device shown in the figure.

[0016] Figure 10 Is an exploded perspective view of a display device related to an embodiment of the present invention.

[0017] Figure 11 Is Figure 10 A cross-sectional view taken along the line II-II' shown in the figure.

[0018] Figure 12 Is Figure 11 An exemplary cross-sectional view of a pixel of the pixel layer shown in the figure.

[0019] Figure 13 Is a side view of the display device as viewed from the first direction Figure 9 of the display device shown in the figure.

[0020] (Symbol Explanation)

[0021] DD: Display device; DP: Display panel; WIN: Window part; CL: Coating; FI: Window film; AP: Adhesive part; SUB: Substrate; PXL: Pixel layer; TFE: Thin film encapsulation layer. Detailed Description of the Embodiment

[0022] In this specification, when it is mentioned that a certain component (or region, layer, part, etc.) is located on, connected to, or combined with another component, it means that it is directly disposed / connected / combined on the other component, or a third component may be disposed therebetween.

[0023] The same reference numerals refer to the same components. Additionally, in each drawing, the thickness, ratio, and size of each component are exaggerated for the effective illustration of the technical content.

[0024] "And / or" includes more than one combination that can define relevant components.

[0025] Terms such as first, second, etc. can be used to describe various components, but the components should not be limited to such terms. The terms are only used for the purpose of differentiating one component from another. For example, without exceeding the scope of the rights of the present invention, the first component can be named the second component, and similarly, the second component can also be named the first component. Singular expressions include plural expressions when there is no clear contrary meaning in the text.

[0026] In addition, terms such as "below", "lower side", "above", "upper side", etc. are used to illustrate the connection relationships of the various components shown in the drawings. The terms are relative concepts and are described based on the directions shown in the drawings.

[0027] Unless otherwise defined, all terms (including technical terms and scientific terms) used in this specification have the same meaning as commonly understood by those skilled in the art. In addition, terms such as those defined in commonly used dictionaries should be interpreted as having a consistent meaning in the relevant technical context, and are clearly defined herein as long as they are not interpreted as ideal or overly formal meanings.

[0028] Terms such as "include" or "have" should be understood as referring to the presence of the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and do not preclude the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts, or combinations thereof in advance.

[0029] Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0030] Figure 1 It is a perspective view of a window portion related to an embodiment of the present invention. Figure 2 Is Figure 1 A cross-sectional view taken along the line I-I' shown.

[0031] Referring to Figure 1 And Figure 2 , the window portion WIN related to the embodiment of the present invention may include a coating CL and a window film FI. The coating CL may be disposed on the window film FI. The coating CL may have a plane defined by a first direction DR1 and a second direction DR2 that intersects the first direction DR1.

[0032] Hereinafter, a direction that substantially perpendicularly intersects the plane defined by the first direction DR1 and the second direction DR2 is defined as the third direction DR3. In addition, "when observed on the plane" in this specification may mean the state of observation from the third direction DR3.

[0033] When the coating CL is observed on the plane, the coating CL may have a rectangular shape. However, the shape of the coating CL is not limited to this.

[0034] The coating CL may be a flexible coating. For example, the coating CL can be bent or folded under the action of an external force. If the external force acting on the coating CL is removed, the coating CL can return to its original shape. In this embodiment, the coating CL is implemented by a single layer, but it is not limited to this. The coating CL may include multiple coatings.

[0035] The window film FI may be disposed below the coating CL. The window film FI may have a plane defined by the first direction DR1 and the second direction DR2. When observed on the plane, the window film FI may have a rectangular shape. However, the shape of the window film FI is not limited to this.

[0036] The window film FI may be a flexible film. For example, the window film FI can be bent or folded under the action of an external force. If the external force acting on the window film FI is removed, the window film FI can return to its original shape.

[0037] The window film FI may have a high transmittance and a low haze. For example, the window film FI may have a transmittance of more than 85% and a haze of 3% or less.

[0038] The window film FI may be a polymer having at least one monomer of ODPA (Oxy diphthalic anhydride), PMDA (Pyromellitic dianhydride), BAPB (Bis-aminophenoxybiphenyl), and BAPS (Bis-amino phenoxy phenylsulfone). For example, the window film FI may be a polymer such as polyimide (PI), polyethylene terephthalate (PET), polycarbonate (PC), and polymethyl methacrylate (PMMA). However, the material of the window film FI is not limited to this.

[0039] The window film FI can be manufactured by an extrusion molding method, a solution stirring method, etc.

[0040] According to an embodiment of the present invention, the window film FI may have physical properties suitable for a flexible display device. The physical properties of the window film FI can be utilized with Figure 1The same product with the same composition as the window film FI shown is used for inspection. Hereinafter, such physical properties will be described in detail.

[0041] Figure 3 Shows the results of the first physical property inspection of the window film of the window part related to one embodiment of the present invention.

[0042] Figure 3 In it, the X-axis and Y-axis respectively represent the strain rate s of the window film FI and the stress f acting on the window film FI. The units of the strain rate s and the stress f are % and MPa respectively. The stress f can be tensile stress. The strain rate s can be measured based on the shape of the window film FI before applying the stress f.

[0043] The first physical property inspection can be an inspection of applying stress f to the window film FI. In the first physical property inspection, the stress can be gradually increased.

[0044] Refer to Figure 3 , the window film FI can elastically deform in the first interval P1 as the stress f acting on the window film FI increases, and plastically deform in the second interval P2.

[0045] The first interval P1 can be defined as the elastic deformation interval. In the first interval P1, the strain rate s of the window film FI can have a linear relationship with the stress f. The second interval P2 can be defined as the plastic deformation interval. In the second interval P2, the strain rate s and the stress f of the window film FI can have a non-linear relationship.

[0046] Yield stress f y is the maximum value of the first interval P1 and can be defined as the maximum tensile stress of the first interval P1. In the first interval P1, the stress acting on the window film FI can be at the yield stress f y Hereinafter, in the second interval P2, the stress acting on the window film FI can be greater than the yield stress f y .

[0047] Yield Strain s y can be defined as the strain rate of the window film FI when the yield stress f is applied to the window film FI y . According to this embodiment, the yield strain rate s of the window film FI y can be greater than or equal to 1.9%, and preferably can be 1.9% to 2.25%.

[0048] The inclination within the first interval P1 can be defined as the elastic coefficient. The inclination within the second interval P2 can be defined as the plastic coefficient.

[0049] As described above, in the first interval P1, the strain rate s and the stress f may have a linear relationship. Therefore, the elastic coefficient tan(α) may have a constant value. In the second interval P2, the strain rate s and the stress f may have a non-linear relationship. Therefore, the plastic coefficient tan(β) may vary.

[0050] In this embodiment, in order to determine the plastic coefficient tan(β), a specified strain rate s is defined d . The specified strain rate s d can be defined as the strain rate at a certain position in the second interval P2. Specifically, the specified strain rate s d can be set to a specific strain rate within the strain rate range of the window film FI from the yield strain rate s y to 2.75%. Preferably, the specified strain rate s d can be set to a specific strain rate within the strain rate range of 2.25% to 2.75%.

[0051] The plastic index of the window film FI can be defined as the value obtained by dividing the plastic coefficient tan(β) by the elastic coefficient tan(α). The plastic index related to this embodiment can be greater than or equal to 0.5.

[0052] As a result, the window film FI related to this embodiment can have a yield strain rate of greater than or equal to 1.9% (preferably 1.9% to 2.25%) in the first physical property inspection. In addition, in the first physical property inspection, the plastic index of the window film FI can be greater than or equal to 0.5.

[0053] Figure 4 Shows the results of the second physical property inspection of the window film of the window related to an embodiment of the present invention.

[0054] In Figure 4 , the X-axis and the Y-axis respectively represent the strain rate s of the window film FI and the stress f acting on the window film FI. The units of the strain rate s and the stress f are % and MPa respectively. The stress f can be a tensile stress. The strain rate s can be measured based on the shape of the window film FI before the physical property inspection.

[0055] The second physical property inspection may include multiple tensile inspections. In each tensile inspection, stress may be applied until the strain rate s of the window film FI reaches the first set strain rate s s . Specifically, the first tensile inspection TT1 can be carried out as follows.

[0056] (ⅰ) Apply stress f to the window film FI. Before applying the stress f, the strain rate s of the window film FI can be 0.

[0057] (ii) Increase the stress f until the deformation rate s of the window film FI reaches the first set deformation rate s s At this point. If the stress f is increased to the first stress f1, the deformation rate s of the window film FI can reach the first set deformation rate s s .

[0058] (iii) Release the stress f. When the stress f reaches 0, the deformation rate s of the window film FI is defined as the first deformation rate s1. The first deformation rate s1 can be greater than 0.

[0059] Next, perform the second tensile inspection TT2.

[0060] (iv) Apply the stress f to the window film FI again. Before applying the stress f, the deformation rate s of the window film FI is the first deformation rate s1.

[0061] (v) Increase the stress f until the deformation rate s of the window film FI reaches the first set deformation rate s from the first deformation rate s1 s At this point. If the stress f is increased to the second stress f2, the deformation rate s of the window film FI can reach the first set deformation rate s s . The second stress f2 can be less than the first stress f1.

[0062] (vi) Release the stress f. When the stress f becomes 0, the deformation rate s of the window film FI is defined as the second deformation rate s2. The second deformation rate s2 can be greater than the first deformation rate s1.

[0063] When the nth tensile inspection TTn ends, the deformation rate s of the window film FI is defined as the nth deformation rate sn n . In this embodiment, n can be 1000, but is not limited thereto.

[0064] When multiple tensile inspections are completed, the recovery deformation rate of the window film FI can be defined as the value obtained by subtracting the nth deformation rate sn s from the first set deformation rate s n [[ID=3--5]]5]].

[0065] According to this embodiment, the recovery rate can be defined as the value obtained by converting the value obtained by dividing the recovery deformation rate by the first set deformation rate s n into a percentage value. When expressed by a mathematical formula, the recovery rate can be defined as (s s – s n ) / s s × 100%. According to this embodiment, the recovery rate of the window film FI can be 85% to 100%. For example, when the first set deformation rate s s is 2%, the nth deformation rate sn n can be 0% to 0.3%.

[0066] As a result, in the second physical property inspection, the recovery rate of the window film FI can be 85% to 100%.

[0067] Figure 5 Shows the results of the third physical property inspection of the window film of the window part related to an embodiment of the present invention.

[0068] In Figure 5 , the X-axis and Y-axis can be defined as time t and the deformation rate s of the window film FI, respectively. The units of time t and deformation rate s are hr (hours) and %, respectively. The deformation rate s can be measured based on the shape of the window film FI before the third physical property inspection.

[0069] Refer to Figure 5 , in the third physical property inspection, stress f is continuously applied to the window film FI until the first time point t1, and the stress f acting on the window film FI can be released after the first time point t1. In the third physical property inspection, a stress f of a constant magnitude acts on the window film FI.

[0070] The deformation rate s of the window film FI can reach the second set deformation rate s s -1 through the stress f. The second set deformation rate s s -1 can be a value equal to the first set deformation rate s s .

[0071] As the stress f continues until the first time point t1, the deformation rate s of the window film FI can increase from the second set deformation rate s s -1 to the maximum deformation rate s c . The deformation rate s of the window film FI can further increase by an amount obtained by subtracting the second set deformation rate s c from the maximum deformation rate s s -1. The further increased deformation rate of the window film FI can be defined as the additional deformation rate. In this embodiment, the first time point t1 is set to 1 hour from the time point when the stress f is applied, but the first time point is not limited to this.

[0072] The creep deformation rate can be defined as the value obtained by dividing the additional deformation rate by the second set deformation rate s s -1 and converting it to a percentage value. When expressed by a mathematical formula, the creep deformation rate can be defined as (s c –(s s -1)) / (s s -1)×100%. According to this embodiment, the creep deformation rate of the window film FI can be 0% to 20%. For example, if the second set deformation rate s s -1 is 2%, then the maximum deformation rate s c can be less than or equal to 2.4%.

[0073] As the stress f is released starting from the first time point t1, the window film FI can recover. The deformation rate s of the window film FI can be reduced to the residual deformation rate s at the second time point t2. cr In this embodiment, the second time point t2 is set to 1 hour from the time point when the stress is released (i.e., the first time point t1), but the second time point is not limited thereto.

[0074] The creep residual deformation rate can be defined as dividing the residual deformation rate s cr by the second set deformation rate s s -1 and converting the obtained value into a percentage value. When expressed by a mathematical formula, the creep residual deformation rate can be defined as s cr / (s s -1)×100%. According to this embodiment, the creep residual deformation rate of the window film FI can be 0% to 20%. For example, if the second set deformation rate s s -1 is 2%, then the residual deformation rate s cr can be less than or equal to 0.4.

[0075] As a result, according to this embodiment, the creep deformation rate of the window film FI can be 0% to 20%. In addition, the creep residual deformation rate of the window film FI can be 0% to 20%.

[0076] According to an embodiment of the present invention, the window film FI satisfies the following physical property conditions.

[0077] - Yield strain rate: 1.9% to 2.25%

[0078] - Plasticity index: 0.5 or more

[0079] - Recovery rate: 85% to 100%

[0080] - Creep deformation rate: 0% to 20%

[0081] - Creep residual deformation rate: 0% to 20%

[0082] The window film that satisfies the above physical property conditions can be a film suitable for a flexible display device. In this regard, it will be described in detail together with experimental data. The window film that satisfies the above physical property conditions can be provided under the coating to manufacture a window.

[0083] Figure 6 It is a diagram showing a display device according to an embodiment of the present invention. Figure 7 It shows Figure 6 a diagram of the folded state of the display device shown.

[0084] Refer to Figure 6, the display device DD according to an embodiment of the present invention may have a rectangular shape including a short side in a first direction DR1 and a long side in a second direction DR2 intersecting the first direction DR1. However, it is not limited thereto, and the display device DD may also have various shapes such as a circular shape and a polygonal shape. The display device DD may be a flexible display device.

[0085] The display device DD may include a folding region FA and a plurality of non-folding regions (NFA1, NFA2). The non-folding regions (NFA1, NFA2) may include a first non-folding region NFA1 and a second non-folding region NFA2. The folding region FA may be disposed between the first non-folding region NFA1 and the second non-folding region NFA2. The folding region FA, the first non-folding region NFA1, and the second non-folding region NFA2 may be arranged in the first direction DR1.

[0086] As an illustration, one folding region FA and two non-folding regions (NFA1, NFA2) are shown, but the number of the folding region FA and the non-folding regions (NFA1, NFA2) is not limited thereto. For example, the display device DD may include more than two non-folding regions and a plurality of folding regions disposed between the more than two non-folding regions.

[0087] Refer to Figure 7 , the display device DD may be a foldable display device DD that can be folded or unfolded. For example, the folding region FA is bent based on a folding axis FX parallel to the second direction DR2, so that the display device DD can be folded. The folding axis FX may be defined as a long axis parallel to the long side of the display device DD.

[0088] When the display device DD is folded, the first non-folding region NFA1 and the second non-folding region NFA2 face each other, and the display device DD may be in-folded so that the display surface is not exposed to the outside.

[0089] [[ID=***]] Figure 8 FIG. is a view showing a display device according to an embodiment of the present invention. Figure 9 is a view showing Figure 8 the folded state of the display device shown in

[0090] Refer to Figure 8 and Figure 9, the display device DD may include a folding region FA' and a plurality of non-folding regions (NFA1', NFA2'). The non-folding regions (NFA1', NFA2') may include a first non-folding region NFA1' and a second non-folding region NFA2'. The folding region FA' may be disposed between the first non-folding region NFA1' and the second non-folding region NFA2'. The folding region FA', the first non-folding region NFA1', and the second non-folding region NFA2' may be arranged in a second direction DR2.

[0091] The folding region FA' may be bent with respect to a folding axis FX' parallel to a first direction DR1, so that the display device DD may be folded. The folding axis FX' may be defined as a short axis parallel to the short side of the display device DD.

[0092] Figure 6 The illustrated display device DD may be folded with respect to the long axis, while Figure 8 The illustrated display device DD may be folded with respect to the short axis. The display device DD may be in-folded so that the display surface is not exposed to the outside.

[0093] Figure 10 is a perspective view of a display device according to an embodiment of the present invention. Figure 11 is Figure 10 a cross-sectional view taken along line II-II' shown. For ease of explanation, in Figure 10 and Figure 11 the window portion WIN and the display panel DP are separately illustrated. Figure 10 and Figure 11 The window portion WIN shown may be Figure 1 the window portion shown. Hereinafter, the description of the window portion is omitted, and the structure of the display panel is mainly described.

[0094] Referring to Figure 10 and Figure 11 , the display device DD may include a window portion WIN and a display panel DP. The window portion WIN may protect the display panel DP from scratches and impacts from the outside. The window portion WIN may be attached to the display panel DP through an adhesion portion AP. For example, the adhesion portion AP may include a PSA (Pressure Sensitive Adhesive) adhesive.

[0095] The display panel DP may have a rectangular shape including a short side in a first direction DR1 and a long side in a second direction DR2 intersecting the first direction DR1.

[0096] An embodiment of the present invention relates to a display panel DP, which may be a light-emitting display panel, but there is no particular limitation. For example, the display panel DP may be an organic light-emitting display panel or a quantum dot light-emitting display panel. The light-emitting layer of the organic light-emitting display panel may include an organic light-emitting substance. The light-emitting layer of the quantum dot light-emitting display panel may include quantum dots and quantum rods, etc. Hereinafter, the display panel DP will be described by taking an organic light-emitting display panel as an example.

[0097] The display panel DP may include a substrate SUB, a pixel layer PXL disposed on the substrate SUB, and a thin film encapsulation layer TFE disposed on the substrate SUB to cover the pixel layer PXL. The substrate SUB may be a transparent substrate and may include a flexible plastic substrate. For example, the substrate SUB may include polyimide (PI).

[0098] The pixel layer PXL may be disposed on the substrate SUB. The pixel layer PXL may include a plurality of pixels, and each pixel may include a light-emitting element respectively.

[0099] The thin film encapsulation layer TFE may include at least two inorganic layers and an organic layer disposed between the inorganic layers. Each inorganic layer may include an inorganic substance to protect the pixel layer PXL from moisture / oxygen. The organic layer may include an organic substance to protect the pixel layer PXL from foreign substances such as dust particles.

[0100] Figure 12 is Figure 11 An exemplary cross-sectional view of the pixel of the pixel layer shown.

[0101] Referring to Figure 12 , the pixel PX may include a light-emitting element OLED and a transistor TR connected to the light-emitting element OLED. The light-emitting element OLED may include a first electrode E1, a second electrode E2, and an organic light-emitting layer OEL disposed between the first electrode E1 and the second electrode E2. The light-emitting element OLED may be defined as an organic light-emitting element.

[0102] The first electrode E1 may be an anode, and the second electrode E2 may be a cathode. The first electrode E1 may be defined as a pixel electrode, and the second electrode E2 may be defined as a common electrode.

[0103] The pixel PX may be divided into a pixel region PA and a non-pixel region NPA surrounding the pixel region PA. The light-emitting element OLED may be disposed in the pixel region PA, and the transistor TR may be disposed in the non-pixel region NPA.

[0104] The transistor TR and the light-emitting element OLED may be disposed on the substrate SUB. A buffer layer BFL may be disposed on the substrate SUB, and the buffer layer BFL may include an inorganic substance.

[0105] The semiconductor layer SM of the transistor TR can be disposed on the buffer layer BFL. The semiconductor layer SM can include a semiconductor of an inorganic material such as amorphous silicon or polycrystalline silicon, or an organic semiconductor. In addition, the semiconductor layer SM can include an oxide semiconductor. Although not shown, the semiconductor layer SM can include a source region, a drain region, and a channel region between the source region and the drain region.

[0106] A first insulating layer INS1 can be disposed on the buffer layer BFL to cover the semiconductor layer SM. The first insulating layer INS1 can include an inorganic substance. A gate electrode GE of the transistor TR overlapping with the semiconductor layer SM can be disposed on the first insulating layer INS1. The gate electrode GE can be configured to overlap with the channel region of the semiconductor layer SM.

[0107] A second insulating layer INS2 can be disposed on the first insulating layer INS1 to cover the gate electrode GE. The second insulating layer INS2 can include an organic substance and / or an inorganic substance.

[0108] A source electrode SE and a drain electrode DE of the transistor TR can be disposed separately from each other on the second insulating layer INS2. The source electrode SE can be connected to the source region of the semiconductor layer SM through a first contact hole CH1 defined in the first insulating layer INS1 and the second insulating layer INS2. The drain electrode DE can be connected to the drain region of the semiconductor layer SM through a second contact hole CH2 defined in the first insulating layer INS1 and the second insulating layer INS2.

[0109] A third insulating layer INS3 can be disposed on the second insulating layer INS2 to cover the source electrode SE and the drain electrode DE of the transistor TR. The third insulating layer INS3 can be defined as a planarization film providing a flat upper surface and can include an organic substance.

[0110] A first electrode E1 can be disposed on the third insulating layer INS3. The first electrode E1 can be connected to the drain electrode DE of the transistor TR through a third contact hole CH3 defined in the third insulating layer INS3.

[0111] A pixel defining layer PDL exposing a predetermined portion of the first electrode E1 can be disposed on the first electrode E1 and the third insulating layer INS3. An opening PX_OP exposing a predetermined portion of the first electrode E1 can be defined in the pixel defining layer PDL.

[0112] In the opening PX_OP, an organic light-emitting layer OEL can be disposed on the first electrode E1. The organic light-emitting layer OEL can generate light of any one of red, green, and blue. However, it is not limited thereto, and the organic light-emitting layer OEL can also generate white light by combining organic substances that generate red, green, and blue.

[0113] A second electrode E2 can be disposed on the pixel defining film PDL and the organic light-emitting layer OEL. The thin film encapsulation layer TFE can be disposed on the light-emitting element OLED to cover the pixel PX. The layer between the substrate SUB and the thin film encapsulation layer TFE can be defined as the pixel layer PXL.

[0114] A voltage can be applied to the first electrode E1 and the second electrode E2. Holes and electrons injected into the organic light-emitting layer OEL combine to form excitons. While the excitons transition to an excited state, the light-emitting element OLED can emit light. The light-emitting element OLED can emit red, green, and blue light as current flows, thereby displaying an image.

[0115] Figure 13 is a side view of the display device as viewed in the first direction Figure 9 shown in the display device.

[0116] For ease of explanation, the bonding portion AP is not shown in Figure 13 the figure.

[0117] Referring to Figure 13 , the display device DD can be folded along the short axis. As the display device DD is folded, tensile stress can be generated on one surface of the window film FI of the window WIN. One surface of the window WIN can be defined as the surface facing and in contact with the display panel DP.

[0118] When the folding and unfolding of the display device DD are repeatedly performed, deformation can occur on one surface of the window film FI. The deformation of the window film FI may reduce the durability of the flexible display device.

[0119] In an embodiment of the present invention, the window film FI having the physical property conditions described above is used for the flexible display device, thereby improving the durability of the flexible display device. The reason therefor will be described with reference to Tables 1 and 2 below.

[0120] Table 1 shows the results of examining the physical properties of a plurality of window films (A to E). The physical properties of the window films related to Table 1 are the results of inspections performed before actually applying the window films to the flexible display device.

[0121] Table 2 shows the results of actually applying the plurality of window films (A to E) described in Table 1 to the flexible display device. The initial deformation amount and the permanent deformation amount in Table 2 mean Figure 13The amount of deformation at the position P shown. When the display device DD is folded, the position P can be defined as the part where the tensile stress acts most on the window film FI in the folding part. The initial amount of deformation can be measured immediately after the folded display device is unfolded. The permanent amount of deformation can be measured after a predetermined time has elapsed from the time point when the initial amount of deformation is measured. The amount of deformation of the window film does not further decrease after a predetermined time has elapsed.

[0122] [Table 1]

[0123]

[0124] Referring to Table 1, the window films of A, B, and C all satisfy the above physical property conditions. Specifically, the A window film can have a yield strain rate of 2.14%, a recovery rate of 88%, a plasticity index of 0.66, a creep deformation rate of 20%, and a creep residual deformation rate of 19%. The B window film can have a yield strain rate of 2.02%, a recovery rate of 92%, a plasticity index of 0.6, a creep deformation rate of 17.5%, and a creep residual deformation rate of 8%. Finally, the C window film can have a yield strain rate of 1.97%, a recovery rate of 94%, a plasticity index of 0.51, a creep deformation rate of 10%, and a creep residual deformation rate of 15%.

[0125] As a result, the window films of A, B, and C all satisfy the physical property conditions of (i) yield strain rate: 1.9% to 2.25%, (ii) recovery rate: 85% to 100, (iii) plasticity index: 0.5 or more, (iv) creep deformation rate: 0% to 20%, and (v) creep residual deformation rate: 0% to 20%.

[0126] On the contrary, the D window film can have a yield strain rate of 1.53%, a recovery rate of 78%, a plasticity index of 0.39, a creep deformation rate of 47%, and a creep residual deformation rate of 28.5%. The E window film can have a yield strain rate of 1.83%, a recovery rate of 88%, a plasticity index of 0.48, a creep deformation rate of 40%, and a creep residual deformation rate of 10%.

[0127] As a result, the window films of D and E do not satisfy the above physical property conditions.

[0128] The window films (A to E) having the physical properties as described above were actually applied to a flexible display device and the amount of deformation was observed.

[0129] The suitability of the window film can be judged by whether the deformed part is recognized from the outside. If the user can observe the deformation of the window film from the outside, this window film may not be suitable for a flexible display device.

[0130] Specifically, when the initial deformation amount of the window film is less than or equal to 20 μm and the permanent deformation amount of the window film is less than or equal to 4 μm, the window film can be a film suitable for a flexible display device. When the initial deformation amount of the window film is greater than 20 μm and the permanent deformation amount is greater than 4 μm, it is determined that the deformation of the window film will be externally recognized.

[0131] [Table 2]

[0132] Experimental Example Initial Deformation (μm) Permanent Deformation (μm) Suitability A 18.2 2.5 O B 19.8 4 O C 18.4 3.6 O D 22.7 9 X E 20.2 4.6 X

[0133] Referring to Table 2, the window films of A, B, and C can be suitably used for a flexible display device. Specifically, the initial deformation amount and the permanent deformation amount of the window film of A are 18.2 μm and 2.5 μm, respectively. The initial deformation amount and the permanent deformation amount of the window film of B are 19.8 μm and 4 μm, respectively. The initial deformation amount and the permanent deformation amount of the window film of C are 18.4 μm and 3.6 μm, respectively. The initial deformation amounts of the window films of A, B, and C are all less than 20 μm. The permanent deformation amounts of the window films of A, B, and C are all less than or equal to 4 μm.

[0134] On the contrary, the window films of D and E may not be suitable for use in a flexible display device. Specifically, the initial deformation amount and the permanent deformation amount of the window film of D are 22.7 μm and 9 μm, respectively. The initial deformation amount and the permanent deformation amount of the window film of E are 20.2 μm and 4.6 μm, respectively. The initial deformation amounts of the window films of D and E are both greater than 20 μm, and the permanent deformation amounts of the window films of D and E are both greater than 4 μm.

[0135] As a result, the window films of A, B, and C can be suitable films because the deformed parts are not externally recognized. The window films of D and E may be unsuitable films because the deformed parts are externally recognized.

[0136] As described above, the description has been made with reference to the embodiments. However, those skilled in the art should be able to understand that various modifications and changes can be made to the present invention without departing from the spirit and scope of the present invention described in the claims. In addition, the embodiments disclosed in the present invention do not limit the technical idea of the present invention, and it should be interpreted that all technical ideas within the scope of the claims and their equivalents are included in the scope of the present invention.

Claims

1. A display device, comprising: A display panel; And A window portion disposed on the display panel, The window portion includes: A window film having flexibility; And At least one coating disposed on the window film, When the tensile stress applied to the window film increases, the window film has elastic deformation in a first interval and plastic deformation in a second interval after the first interval. The first interval and the second interval are defined according to the relationship between the tensile stress applied to the window film and the deformation rate of the window film based on the tensile stress. The window film has a yield strain rate of 1.9% to 2.25%, a plasticity index of 0.5 or more, a recovery rate of 85% to 100%, a creep deformation rate of 0% to 20%, and a creep residual deformation rate of 0% to 20%. The yield strain rate is defined as the deformation rate of the window film when the yield stress in the first interval is applied to the window film. The plasticity index is defined as the value obtained by dividing the plasticity coefficient defined as the inclination of the second interval by the elastic coefficient defined as the inclination of the first interval. The window film includes at least one monomer of diaminophenoxy biphenyl and diaminophenoxy phenyl sulfone.

2. The display device according to claim 1, wherein The plasticity coefficient is defined by the inclination of a specified deformation rate which is the deformation rate of the window film at a certain position in the second interval. The specified deformation rate is set using a value within the deformation rate of the window film from the yield strain rate to 2.75%.

3. The display device according to claim 2, wherein The specified deformation rate is set to a value within the deformation rate range of 2.25% to 2.75% of the window film.

4. The display device according to claim 1, wherein When multiple tensile forces are applied to the window film, the window film has a recovery rate. The recovery rate is defined as the value obtained by converting the value obtained by dividing the recovery deformation rate by the first set deformation rate into a percentage value. The recovery deformation rate is defined as the value obtained by subtracting the deformation rate of the window film measured after applying the multiple tensile forces from the first set deformation rate.

5. The display device according to claim 1, wherein When stress is applied to the window film until a certain time point and the stress is released after passing the certain time point, the window film has a creep deformation rate. The creep deformation rate is defined as the value obtained by converting the value obtained by dividing the additional deformation rate by the second set deformation rate into a percentage value. The additional deformation rate is defined as the deformation rate of the window film that further increases when the stress is continuously applied.

6. The display device according to claim 5, wherein The creep residual deformation rate is defined as the value obtained by converting the value obtained by dividing the residual deformation rate by the second set deformation rate into a percentage value. The residual deformation rate is defined as the deformation rate of the window film after a predetermined time from the time point when the stress is released.

7. The display device according to claim 1, wherein The window film includes at least one polymer among polyimide, polyethylene terephthalate, polycarbonate, and polymethyl methacrylate.

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