阅读说明：本技术 显示装置 (Display device ) 是由 申宪政 李贞燮 吴弦俊 于 2020-07-22 设计创作，主要内容包括：本发明的一实施例涉及的显示装置可以包括显示面板以及配置在所述显示面板上的窗部。所述窗部可以包括：窗部膜,具有挠性；以及至少一个涂层,配置在所述窗部膜上。所述窗部膜可以在作用于所述窗部膜的拉伸应力增加时,在第一区间具有弹性变形,且在所述第一区间之后的第二区间具有塑性变形。可以根据施加到所述窗部膜的所述拉伸应力与基于所述拉伸应力的所述窗部膜的变形率的关系,定义所述第一区间和所述第二区间。所述窗部膜可以具有1.9％至2.25％的屈服应变率,所述屈服应变率可以定义为在向所述窗部膜施加所述第一区间的屈服应力时所述窗部膜的变形率。(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 part 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 section and plastic deformation in a second section subsequent to the first section when tensile stress applied to the window film increases. The first and second intervals may be defined according to a relationship between the tensile stress applied to the window film and a 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%, which may be defined as a deformation rate of the window film when the yield stress of the first interval is applied to the window film.)

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,

the window film having elastic deformation in a first section and plastic deformation in a second section subsequent to the first section when a tensile stress acting on the window film increases, the first section and the second section being defined according to a relationship between the tensile stress applied to the window film and a 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%, the yield strain rate being defined as a deformation rate of the window film when the first interval of yield stress is applied to the window film.

2. The display device according to claim 1,

the window film has a plasticity index of 0.5 or more,

defining the plasticity index by using a value obtained by dividing a plasticity coefficient defined as the inclination of the second interval by an elasticity coefficient defined as the inclination of the first interval.

3. The display device according to claim 2,

defining the plasticity coefficient with an inclination of a specified deformation rate defined as a deformation rate of the window section film at a certain position of the second section,

setting the specified deformation rate using a value within a deformation rate of the window film of 2.75% of the yield strain rate.

4. The display device according to claim 3,

the specified deformation ratio is set to a value within a range of deformation ratios of the window film of 2.25% to 2.75%.

5. The display device according to claim 1,

the window film has a recovery rate of 85% to 100% when a stretching force is applied to the window film a plurality of times,

defining the recovery rate by a numerical value obtained by converting a value obtained by dividing the recovery deformation rate by the first set deformation rate into% and,

the return deformation ratio is defined by a value obtained by subtracting the deformation ratio of the window film measured after the application of the plurality of tensile forces from the first set deformation ratio.

6. The display device according to claim 1,

the window film has a creep deformation ratio of 0% to 20% when stress is applied to the window film until a certain time point and the stress is released after the certain time point elapses,

defining the creep deformation ratio by a value obtained by dividing the additional deformation ratio by the second set deformation ratio and converting the value into% value,

the additional deformation ratio is defined as a deformation ratio of the window film that further increases when the stress is continuously applied.

7. The display device according to claim 6,

the window film has a creep residual deformation ratio of 0% to 20%,

defining the creep residual deformation ratio by a numerical value obtained by converting a value obtained by dividing the residual deformation ratio by the second set deformation ratio into% and,

the residual deformation ratio is defined as a deformation ratio of the window film after a predetermined time has elapsed from a time point at which the stress is released.

8. The display device according to claim 1,

the window film includes at least one monomer of diphenyl ether tetracarboxylic dianhydride, pyromellitic dianhydride, bisaminophenoxybiphenyl, and bisaminophenoxyphenylsulfone.

9. The display device according to claim 8,

the window film includes at least one polymer of polyimide, polyethylene terephthalate, polycarbonate, and polymethyl methacrylate.

Technical Field

The present invention relates to a window and a display device including the window, and more particularly, to a window capable of reducing deformation of a folded portion and a display device including the window.

Background

Generally, electronic devices such as smart phones, digital cameras, notebook computers, navigators, and smart televisions, which provide images to users, include display devices for displaying images. The display device generates an image and provides the image to a user through a display screen.

In recent years, with the 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 form or folded or rolled are being developed. The flexible display device is easy to carry, and can improve the convenience of a user.

The flexible display device includes a window portion at an upper portion for protecting the display surface. The window portion can protect the display surface from external scratches and impacts.

Disclosure of Invention

An object of the present invention is to provide a window portion in which deformation of a folded portion is reduced so that the deformation of the folded portion is not recognized from the outside, and a display device including the window portion.

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 part 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 section and plastic deformation in a second section subsequent to the first section when tensile stress applied to the window film increases. The first and second intervals may be defined according to a relationship between the tensile stress applied to the window film and a 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%, which may be defined as a deformation rate of the window film when the yield stress of the first interval is applied to the window film.

(effect of the invention)

According to an embodiment of the present invention, there are provided a window portion and a display device including the window portion, in which deformation of a folded portion is reduced so that the deformation of the folded portion is not recognized from the outside.

Drawings

Fig. 1 is a perspective view of a window according to an embodiment of the present invention.

Fig. 2 is a sectional view taken along line I-I' shown in fig. 1.

Fig. 3 to 5 show results of the first to third physical property inspections of the window film of the window according to the embodiment of the present invention.

Fig. 6 is a perspective view of a display device according to an embodiment of the present invention.

Fig. 7 is a perspective view showing a folded state of the display device shown in fig. 6.

Fig. 8 is a perspective view of a display device according to an embodiment of the present invention.

Fig. 9 is a perspective view showing a folded state of the display device shown in fig. 8.

Fig. 10 is an exploded perspective view of a display device according to an embodiment of the present invention.

Fig. 11 is a sectional view taken along line ii-ii' of fig. 10.

Fig. 12 is an exemplary cross-sectional view of a pixel of the pixel layer shown in fig. 11.

Fig. 13 is a side view of the display device shown in fig. 9 as viewed from a first direction.

(symbol description)

DD: a display device; DP: a display panel; WIN: a window portion; CL: coating; FI: a window film; AP: an adhesive portion; SUB: a substrate; PXL: a pixel layer; TFE: and (7) a thin film packaging layer.

Detailed Description

In the present specification, when a certain component (or a region, a layer, a portion, or the like) is located on, connected to, or coupled to another component, it means that the component is directly disposed on, connected to, or coupled to the other component, or a third component may be disposed therebetween.

Like reference numerals refer to like elements. In the drawings, the thickness, ratio, and size of each component are exaggerated for effective explanation of technical contents.

"and/or" includes all combinations of more than one of the associated constituents that may be defined.

The terms first, second, etc. may be used to describe various components, but the components should not be limited to the terms. The above-described terms are used only for the purpose of distinguishing one constituent element from another. For example, a first component may be named a second component, and similarly, a second component may also be named a first component, without departing from the scope of the present invention. Singular references include plural references when not explicitly stated to the contrary in the context.

The terms "below", "above" and "above" are used to describe the connection relationship of the respective components shown in the drawings. The terms are relative concepts, and are described with reference to the directions shown in the drawings.

Unless otherwise defined, all terms (including technical and scientific terms) used in the present specification have the same meaning as commonly understood by one of ordinary skill in the art. In addition, terms such as those defined in commonly used dictionaries should be interpreted as having a consistent meaning in the context of the relevant art and will be defined only in a definite manner so long as they are not interpreted in an idealized or overly formal sense.

The terms "comprises," "comprising," "includes" and "including" are to be interpreted as referring to the presence of the stated features, integers, steps, operations, elements, components, or groups thereof, but not to preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or groups thereof.

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

Fig. 1 is a perspective view of a window according to an embodiment of the present invention. Fig. 2 is a sectional view taken along line I-I' shown in fig. 1.

Referring to fig. 1 and 2, a window WIN according to an 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 intersecting the first direction DR 1.

Hereinafter, a direction substantially perpendicularly intersecting a plane defined by the first direction DR1 and the second direction DR2 is defined as a third direction DR 3. Further, "when viewed on a plane" in the present specification may mean a state viewed from the third direction DR 3.

The coating layer CL may have a rectangular shape when viewed on a plane. However, the shape of the coating layer CL is not limited thereto.

The coating CL may be a flexible coating. For example, the coating CL may be bent or folded under an external force. When the external force acting on the coating layer CL is released, the coating layer CL can be restored to its original shape. In the present embodiment, the coating layer CL is implemented by a single layer, but is not limited thereto. The coating CL may comprise a plurality of coatings.

The window film FI may be disposed below the coating layer CL. The window film FI may have a plane defined by a first direction DR1 and a second direction DR 2. The window film FI may have a rectangular shape when viewed on a plane. However, the shape of the window film FI is not limited thereto.

The window film FI may be a flexible film. For example, the window film FI may be bent or folded by an external force. When the external force applied to the window film FI is released, the window film FI can be restored to its original shape.

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

The window film FI may be a polymer having at least one monomer of ODPA (Oxy-phthalic anhydride), PMDA (Pyromellitic dianhydride), BAPB (Bis-aminophenoxy biphenol), and BAPS (Bis-aminophenoxy phenylsulfone). For example, the window film FI may be a polymer such as Polyimide (PI), polyethylene terephthalate (PET), Polycarbonate (PC), polymethyl methacrylate (PMMA), or the like. However, the material of the window film FI is not limited to this.

The window film FI can be produced by extrusion molding, solution stirring, or the like.

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 inspected by the same product having the same configuration as the window film FI shown in fig. 1. Hereinafter, such physical properties will be described in detail.

Fig. 3 shows the result of a first physical property inspection of a window film of a window according to an embodiment of the present invention.

In fig. 3, the X axis and the Y axis respectively mean the deformation rate s of the window film FI and the stress f acting on the window film FI. The units of the deformation ratio s and the stress f are% and MPa, respectively. The stress f may be a tensile stress. The deformation rate s may be measured based on the shape of the window film FI before the stress f is applied.

The first physical property inspection may be an inspection in which a stress f is applied to the window film FI. The stress may be gradually increased in the first physical property inspection.

Referring to fig. 3, the window film FI may be elastically deformed in the first section P1 and plastically deformed in the second section P2 as the stress f applied to the window film FI increases.

The first interval P1 may be defined as an elastic deformation interval. In the first section P1, the deformation ratio s of the window film FI may have a linear relationship with the stress f. The second interval P2 may be defined as the plastic deformation interval. In the second section P2, the deformation ratio s and the stress f of the window film FI may have a nonlinear relationship.

Yield stress f_yIs 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 may be at the yield stress f_yHereinafter, in the second interval P2, the stress acting on the window film FI may be greater than the yield stress f_y。

Yield Strain rate (Yield Strain) s_yCan be defined as applying a yield stress f to the window film FI_yThe deformation rate of the window film FI. According to the present embodiment, the yield strain rate s of the window film FI_yMay be greater than or equal to 1.9%, and may preferably be from 1.9% to 2.25%.

The inclination within the first interval P1 may be defined as the elastic coefficient. The inclination within the second interval P2 may be defined as the plasticity number.

As described above, in the first section P1, the deformation ratio s and the stress f may have a linear relationship. Therefore, the elastic coefficient tan (α) may have a constant value. In the second section P2, the deformation ratio s and the stress f may have a non-linear relationship. Thus, the plasticity factor tan (β) may vary.

In the present embodiment, in order to determine the plasticity number tan (β), a specified deformation ratio s is defined_d. Specified deformation ratio s_dMay be defined as a deformation rate at a certain position of the second section P2. Specifically, the deformation ratio s is specified_dCan be set to yield strain rate s_yTo a specific deformation ratio within the range of 2.75% of the deformation ratio of the window film FI. Preferably, the deformation ratio s is specified_dA specific deformation ratio within a range of deformation ratios of 2.25% to 2.75% may be set.

The Plastic Index (Plastic Index) of the window film FI can be defined as a value obtained by dividing a Plastic coefficient tan (β) by an elastic coefficient tan (α). The plasticity index referred to in this example may be greater than or equal to 0.5.

As a result, the window film FI according to the present embodiment may have a yield strain rate of 1.9% or more (preferably 1.9% to 2.25%) in the first physical property inspection. In the first physical property inspection, the plasticity index of the window film FI may be 0.5 or more.

Fig. 4 shows the result of the second physical property inspection of the window film of the window according to the embodiment of the present invention.

In fig. 4, the X axis and the Y axis respectively indicate the deformation rate s of the window film FI and the stress f acting on the window film FI. The units of the deformation ratio s and the stress f are% and MPa, respectively. The stress f may be a tensile stress (tesile stress). The deformation rate s can be measured based on the shape of the window film FI before the physical property inspection.

The second physical examination may include a plurality of tensile examinations. Each tensile test may apply stress until the deformation rate s of the window film FI reaches the first set deformation rate s_sUntil now. Specifically, the first stretch check TT1 may be performed as follows.

The window film FI is subjected to a stress f. The deformation rate s of the window film FI may be 0 before the stress f is applied.

(ii) increasing the stress f until the deformation ratio s of the window film FI reaches the first set deformation ratio s_sUntil now. If the stress f increases to the first stress f₁The deformation rate s of the window film FI may reach the first set deformation rate s_s。

(iii) relieving the stress f. When the stress f reaches 0, the deformation ratio s of the window film FI is defined as a first deformation ratio s₁. First deformation ratio s₁And may be greater than 0.

Next, a second stretch check TT2 is performed.

(iv) again applies stress f to the window film FI. The deformation rate s of the window film FI before the stress f is applied is the first deformation rate s₁。

(v) increasing the stress f until the deformation ratio s of the window film FI is from the first deformation ratio s₁To achieve a first set deformation rate s_sUntil now. If the stress f increases to a second stress f₂The deformation rate s of the window film FI may reach the first set deformation rate s_s. Second stress f₂May be smaller than the first stress f₁。

(vi) stress f is relieved. When the stress f becomes 0, the deformation ratio s of the window film FI is defined as a second deformation ratio s₂. Second deformation ratio s₂May be greater than the first deformation ratio s₁。

When the nth stretch check TTn ends, the deformation ratio s of the window film FI is defined as the nth deformation ratio s_n. In the present embodiment, n may be 1000, but is not limited thereto.

When the multi-stretch inspection is finished, the restoration deformation rate of the window film FI may be defined as a deformation rate s from the first set deformation rate_sMinus the nth deformation rate s_nAnd the resulting value.

According to the present embodiment, the recovery rate may be defined as the recovery deformation rate divided by the first set deformation rate s_nAnd the obtained value is converted into a numerical value of%. When expressed by a mathematical expression, the recovery rate can be defined as(s)_s–s_n)/s_sX 100%. According to this embodiment, the restoration rate of the window film FI may be 85% to 100%. For example, at a first set deformation ratio s_sAt 2%, the n-th deformation rate s_nMay be 0% to 0.3%.

As a result, the restoration rate of the window film FI in the second physical property test may be 85% to 100%.

Fig. 5 shows the result of a third physical inspection of the window film of the window according to the embodiment of the present invention.

In fig. 5, the X-axis and the Y-axis may be defined as time t and a deformation rate s of the window film FI, respectively. The units of time t and deformation rate s are hr (hour) and%, respectively. The deformation rate s may be measured based on the shape of the window film FI before the third physical inspection.

Referring to fig. 5, in the third physical examination, until the first time point t₁Applying stress f to the window film FI until the first time point t₁The stress f applied to the window film FI can be released later. In the third physical inspection, a stress f of a constant magnitude is applied to the window film FI.

The deformation rate s of the window film FI can be set to a second set deformation rate s by the stress f_s-1. Second set deformation ratio s_s-1 may be at a first set deformation ratio s_sEqual values.

As the stress f continues to the first time t₁The deformation ratio s of the window film FI may be set from the second set deformation ratio s_s-1 increasing to a maximum deformation ratio s_c. The deformation rate s of the window film FI may be further increased from the maximum deformation rate s_cMinus a second set deformation rate s_sA degree of 1. The deformation ratio of the window film FI further increased may be defined as an additional deformation ratio. In the present embodiment, the first time point t₁Is set to 1 hour from the time point of applying the stress f, but the first time point is not limited thereto.

The creep deformation ratio may be defined by dividing the additional deformation ratio by the second set deformation ratio s_sThe values obtained for-1 are converted to% values. Expressed by a mathematical formula, the creep deformation ratio can be defined as(s)_c–(s_s-1))/(s_s-1) × 100%. According to the present embodiment, the window portionThe creep deformation rate of the film FI may be 0% to 20%. For example, if the second set deformation ratio s_s1 is 2%, the maximum deformation ratio s_cMay be less than or equal to 2.4%.

With stress f from a first point in time t₁And begins to be released, the window film FI can be restored. The deformation rate s of the window film FI may be at the second time point t₂Reduced to residual deformation rate s_cr. In the present embodiment, the second time point t₂Is set from the stress-relief time point (i.e., the first time point t)₁) First 1 hour, but the second time point is not limited thereto.

The creep residual deformation ratio may be defined as the residual deformation ratio s_crDivided by a second set deformation ratio s_sThe values obtained for-1 are converted to% values. Expressed by a mathematical expression, the creep residual deformation ratio can be defined as s_cr/(s_s-1) × 100%. According to the present embodiment, the creep residual deformation rate of the window film FI may be 0% to 20%. For example, if the second set deformation ratio s_s2% for-1, the residual deformation ratio s_crMay be less than or equal to 0.4.

As a result, according to the present embodiment, the creep deformation rate of the window film FI may be 0% to 20%. Further, the creep residual deformation rate of the window film FI may be 0% to 20%.

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

Yield strain rate: 1.9 to 2.25 percent

-plasticity index: 0.5 or more

-recovery rate: 85 to 100 percent

Creep deformation ratio: 0 to 20 percent

-creep residual deformation ratio: 0 to 20 percent

The window film satisfying the above physical property conditions may be a film suitable for a flexible display device. This will be explained in detail together with the experimental data. The window can be produced by providing a window film satisfying the above physical property conditions at the lower part of the coating layer.

Fig. 6 is a diagram showing a display device according to an embodiment of the present invention. Fig. 7 is a view showing a folded state of the display device shown in fig. 6.

Referring to fig. 6, the display device DD according to the 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 crossing the first direction DR 1. However, the display device DD is not limited to this, and may have various shapes such as a circle and a polygon. The display device DD may be a flexible display device.

The display device DD may include a folding area FA and a plurality of non-folding areas (NFA1, NFA 2). The non-folding regions (NFA1, NFA2) may include a first non-folding region NFA1 and a second non-folding region NFA 2. The folding area FA may be arranged between the first non-folding area NFA1 and the second non-folding area NFA 2. The folding region FA, the first non-folding region NFA1 and the second non-folding region NFA2 may be aligned in the first direction DR 1.

For example, although one folding region FA and two non-folding regions (NFA1, NFA2) are illustrated, the number of folding regions FA and non-folding regions (NFA1, NFA2) is not limited thereto. For example, the display device DD may include a plurality of non-folding areas more than two and a plurality of folding areas disposed between the more than two non-folding areas.

Referring to fig. 7, the display device DD may be a foldable (foldable) display device DD that is folded or unfolded. For example, the folding area FA is bent with reference to a folding axis FX parallel to the second direction DR2 so that the display device DD may be folded. The folding axis FX may be defined as a long axis parallel to the long side of the display device DD.

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 folded in (in-folding) so that the display surface is not exposed to the outside.

Fig. 8 is a diagram showing a display device according to an embodiment of the present invention. Fig. 9 is a view showing a folded state of the display device shown in fig. 8.

Referring to fig. 8 and 9, the display device DD may include a folding area FA ' and a plurality of non-folding areas (NFA1', NFA2 '). The non-folding region (NFA1', NFA2') may include a first non-folding region NFA1 'and a second non-folding region NFA 2'. The folding area FA ' may be arranged between the first non-folding area NFA1' and the second non-folding area NFA2 '. The folding region FA ', the first non-folding region NFA1', and the second non-folding region NFA2' may be aligned in the second direction DR 2.

The folding area FA 'may be bent with reference to a folding axis FX' parallel to the 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.

The display device DD shown in fig. 6 may be folded with reference to a long axis, and the display device DD shown in fig. 8 may be folded with reference to a short axis. The display device DD may be folded-in (in-folding) such that the display surface is not exposed to the outside.

Fig. 10 is a perspective view of a display device according to an embodiment of the present invention. Fig. 11 is a sectional view taken along line ii-ii' of fig. 10. For convenience of explanation, the window WIN and the display panel DP are illustrated separately in fig. 10 and 11. The window WIN shown in fig. 10 and 11 may be the window shown in fig. 1. Hereinafter, the description of the window portion will be omitted, and the structure of the display panel will be mainly described.

Referring to fig. 10 and 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 external scratches and impacts. The window portion WIN may be attached to the display panel DP by the adhesive portion AP. For example, the Adhesive portion AP may include PSA (Pressure Sensitive Adhesive) Adhesive.

The display panel DP may have a rectangular shape including a short side in the first direction DR1 and a long side in the second direction DR2 crossing the first direction DR 1.

The display panel DP according to an embodiment of the present invention may be a light emitting type display panel, but is not particularly limited. 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, quantum rods, and the like. Hereinafter, the display panel DP will be described as an organic light emitting display panel.

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 comprise a flexible plastic substrate. For example, the substrate SUB may include Polyimide (PI).

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.

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 so that the pixel layer PXL is protected from moisture/oxygen. The organic layer may include an organic substance so that the pixel layer PXL is protected from foreign substances such as dust particles.

Fig. 12 is an exemplary cross-sectional view of a pixel of the pixel layer shown in fig. 11.

Referring to fig. 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 emission 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.

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.

The pixels PX may be divided into a pixel area PA and a non-pixel area NPA around the pixel area 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.

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.

A semiconductor layer SM of the transistor TR may be disposed on the buffer layer BFL. The semiconductor layer SM may include a semiconductor of an inorganic material such as Amorphous (amophorus) silicon or polycrystalline (Poly) silicon or an organic semiconductor. In addition, the semiconductor layer SM may include an oxide semiconductor (oxide semiconductor). Although not shown, the semiconductor layer SM may include a source region, a drain region, and a channel region between the source region and the drain region.

The first insulating layer INS1 may be disposed on the buffer layer BFL so as to cover the semiconductor layer SM. The first insulating layer INS1 may include an inorganic substance. The gate electrode GE of the transistor TR, which overlaps with the semiconductor layer SM, may be disposed on the first insulating layer INS 1. The gate electrode GE may be configured to overlap a channel region of the semiconductor layer SM.

A second insulating layer INS2 may be disposed on the first insulating layer INS1 so as to cover the gate electrode GE. The second insulating layer INS2 may include an organic substance and/or an inorganic substance.

The source electrode SE and the drain electrode DE of the transistor TR may be disposed on the second insulating layer INS2 separately from each other. The source electrode SE may 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 INS 2. The drain electrode DE may 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 INS 2.

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

A first electrode E1 may be disposed on the third insulating layer INS 3. The first electrode E1 may be connected to the drain electrode DE of the transistor TR through a third contact hole CH3 defined in the third insulating layer INS 3.

A pixel defining film PDL exposing a predetermined portion of the first electrode E1 may be disposed on the first electrode E1 and the third insulating layer INS 3. An opening portion PX _ OP exposing a predetermined portion of the first electrode E1 may be defined in the pixel defining film PDL.

The organic light emitting layer OEL may be disposed on the first electrode E1 in the opening PX _ OP. The organic light emitting layer OEL can generate light of any one color of red, green, and blue. However, the organic light emitting layer OEL is not limited to this, and white light may be generated by a combination of organic materials that generate red, green, and blue colors.

The second electrode E2 may be disposed on the pixel defining film PDL and the organic light emitting layer OEL. The thin film encapsulation layer TFE may be disposed on the light emitting element OLED so as to cover the pixels PX. A layer between the substrate SUB and the thin film encapsulation layer TFE may be defined as a pixel layer PXL.

A voltage may be applied to the first electrode E1 and the second electrode E2. The holes and electrons injected into the organic light emitting layer OEL are combined to form excitons (exiton), and the light emitting element OLED can emit light while the excitons transition to an excited state. The light emitting element OLED may emit red, green, and blue light as a current flows, so that an image may be displayed.

Fig. 13 is a side view of the display device shown in fig. 9 as viewed in a first direction.

For convenience of explanation, the adhesive portion AP is not shown in fig. 13.

Referring to fig. 13, the display device DD may be folded along a short axis. As the display device DD is folded, a tensile stress may be generated at one side of the window film FI of the window WIN. One face of the window portion WIN may be defined as a face facing and in contact with the display panel DP.

In the case where the folding and unfolding of the display device DD are repeatedly performed, deformation may be generated at one side of the window film FI. The deformation of the window film FI may reduce the durability of the flexible display device.

In the embodiment of the present invention, the window film FI having the physical property conditions as described above is used for the flexible display device, so that the durability of the flexible display device can be improved. The reason is described with reference to tables 1 and 2 below.

Table 1 shows the results of examining the physical properties of the plurality of window films (a to E). The physical properties of the window film referred to in table 1 are the results of an inspection performed before the window film is actually applied to a flexible display device.

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 the deformation amount at the position P shown in fig. 13. The position P may be defined as a portion where tensile stress is most exerted on the window film FI in the folded portion when the display device DD is folded. The initial amount of deformation may be measured immediately after unfolding the folded display device. The permanent deformation amount may be measured after a predetermined time has elapsed from the time point at which the initial deformation amount is measured. The amount of deformation of the window film may not be further reduced after the predetermined time has elapsed.

[ Table 1]

The window films of A, B and C all satisfy the above-mentioned physical property conditions, as shown in Table 1. Specifically, the a-window film may 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 may 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 may 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%.

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

In contrast, the D-window film may 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 may 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%.

As a result, the window films of D and E failed to satisfy the above-mentioned physical property conditions.

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

The suitability of the window film can be judged by whether or not the deformed portion is recognized from the outside. If the user can observe the deformation of the window film from the outside, such a window film may not be suitable for the flexible display device.

Specifically, in the case where the initial deformation amount of the window film is 20 μm or less and the permanent deformation amount of the window film is 4 μm or less, the window film may 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 is recognized from the outside.

[ Table 2]

Examples of the experiments	Initial deflection (. mu.m)	Permanent deformation amount (μm)	Suitability for use in a plant
				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

The window film referring to tables 2, A, B and C may be suitably used for the flexible display device. Specifically, the initial deformation amount and the permanent deformation amount of the a window film were 18.2 μm and 2.5 μm, respectively. The initial and permanent deformation of the B window film were 19.8 μm and 4 μm, respectively. The initial and permanent set of the C window film was 18.4 μm and 3.6 μm, respectively. A. The initial deformation amounts of the window films of B and C are less than 20 μm. A. The permanent deformation of the window film of B and C is not more than 4 μm.

In contrast, 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 D window film were 22.7 μm and 9 μm, respectively. The initial and permanent set of the E-window film was 20.2 μm and 4.6 μm, respectively. The initial deformation of the window films of D and E are both greater than 20 μm, and the permanent deformation of the window films of D and E are both greater than 4 μm.

As a result, the window films of A, B and C are not likely to be deformed to the outside, and thus can be suitable films. The window films of D and E may be unsuitable films because the deformed portions are recognized at the outside.

Although the present invention has been described with reference to the embodiments, it should be understood by those skilled in the art that various modifications and changes may be made to the present invention without departing from the spirit and scope of the present invention as set forth in the claims. In addition, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, and it should be construed that all technical spirit within the scope of claims and their equivalents are included in the scope of the present invention.