Display device

Disclosed herein is a display device. The display device comprises: a mid cover; a display panel disposed on the mid cover and having a plurality of pixels defined therein; a plurality of back bars disposed under the mid cover; and a roller fixed to the mid cover. The mid cover, the display panel and the plurality of back bars are wound around or unwound from the roller.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Republic of Korea Patent Application No. 10-2019-0115300 filed in the Korean Intellectual Property Office on Sep. 19, 2019, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

Technical Field

The present disclosure relates to a display device, and more particularly to a rollable display device that can display images even when it is rolled.

Description of the Related Art

Display devices employed by the monitor of a computer, a TV, a mobile phone or the like include an organic light-emitting display (OLED) that emits light by itself, and a liquid-crystal display (LCD) that requires a separate light source.

Such display devices find more and more applications, including computer monitors and televisions, as well as personal portable devices. Accordingly, research is ongoing to develop display devices having a larger display area with reduced volume and weight.

In addition, a rollable display device is attracting attention as the next generation display device. Such a rollable display device is fabricated by forming a display part and lines on a flexible substrate made of a flexible material such as plastic so that it is able to display images even if it is rolled.

SUMMARY

In view of the above, an object of the present disclosure is to provide a display device that includes a mid cover as well as a plurality of back bars on the rear side of a display panel so that stress applied to the display panel in the course of winding the display device can be reduced.

Another object of the present disclosure is to provide a display device that reduces the thickness of the display part and improves the side strength of the display panel.

Still another object of the present disclosure is to provide a display device that suppresses wrinkles on the display panel which may occur when the display device is wound and unwound to thereby improve the reliability.

According to an aspect of the present disclosure, there is provided a display device including a mid cover; a display panel disposed on a surface of the mid cover and having a plurality of pixels defined therein; a plurality of back bars disposed on an opposite surface of the mid cover; and a roller fixed to the mid cover. The mid cover, the display panel and the plurality of back bars are wound around or unwound from the roller.

According to another aspect of the present disclosure, there is provided a display device including: a roller; a mid cover fixed to the roller; a first adhesive layer disposed on an upper surface of the mid cover; a display panel attached to the mid cover by the first adhesive layer; a second adhesive layer disposed on a lower surface of the mid cover; and a plurality of back bars attached to the mid cover by the second adhesive layer.

According to an exemplary embodiment of the present disclosure, a mid cover and a plurality of back bars are disposed so that they cover a display area of a display panel, thereby improving side strength of the display panel and flatness of a display part to improve the reliability of the display device.

According to an exemplary embodiment of the present disclosure, the mid cover as well as the plurality of back bars give strength to the display panel, and thus the thickness of the display panel can be reduced.

According to an exemplary embodiment of the present disclosure, it is possible to prevent the plurality of back bars from being seen from the outside.

DETAILED DESCRIPTION

A rollable display device may also be referred to as a display device which is capable of displaying images even though the display device is rolled. The rollable display device may have a high flexibility as compared with a general display device of the related art. Depending on whether to use a rollable display device, a shape of the rollable display device may be freely varied. Specifically, when the rollable display device is not used, the rollable display device is rolled to be stored with a reduced volume. In contrast, when the rollable display device is used, the rolled rollable display device is unrolled to be used.

FIGS.1A and1Bare perspective views of a display device according to an exemplary embodiment of the present disclosure.

Referring toFIGS.1A and1B, a display device100according to an exemplary embodiment of the present disclosure includes a display part DP and a housing part HP.

The display part DP is an element for displaying images to a user. For example, a display element, circuitry for driving the display element, lines and components may be disposed in the display part DP. As the display device100according to the exemplary embodiment of the present disclosure is a rollable display device, the display part DP can be wound and unwound. For example, the display part DP may include a display panel and a mid cover having flexibility to allow winding or unwinding. The display part DP will be described in detail later with reference toFIGS.3A to4B.

The housing part HP is a case in which the display part DP can be accommodated. The display part DP may be wound and accommodated inside the housing part HP, and the display part DP may be unwound and disposed outside the housing part HP.

The housing part HP has an opening HPO (shown inFIG.1B) of the housing part so that the display part DP can move inside and outside the housing part HP. The display part DP may move in the vertical direction through the opening HPO of the housing part.

The display part DP of the display device100may be switched between a fully unwounded state and a fully wound state.

FIG.1Ashows the fully unwound state of the display part DP of the display device100, in which the display part DP of the display device100is disposed outside the housing part HP. That is to say, in order for a user to watch images on the display device100, the display part DP is fully unwound until it can no longer be unwound and disposed outside the housing part HP.

FIG.1Bshows the fully wound state of the display part DP of the display device100, in which the display part DP of the display device100is disposed inside the housing part HP. That is to say, when the user does not watch images on the display device100, it is advantageous in terms of appearance that the display part DP is not disposed outside the housing part HP. Therefore, the display part DP is wound and is accommodated inside the housing part HP, which may be defined as the fully wound state. In addition, when the display part DP is in the fully wound state, the volume of the display device100can be reduced and thus it is easier to carry.

A driver is disposed for winding or unwinding the display part DP to switch between the fully unwound state and the fully wound state.

FIG.2is a perspective view of a display device according to an exemplary embodiment of the present disclosure.

First, referring toFIG.2, the driver MP includes a roller unit150and an elevation mechanism160.

The roller unit150rotates clockwise or counterclockwise while the display part DP fixed to the roller unit150is wound around or unwound from it. The roller unit150includes a roller151and roller supports152.

The roller151is a member around which the display part DP is wound. The roller151may be formed in a cylindrical shape, for example. The lower edge of the display part DP may be fixed to the roller151. When the roller151rotates, the display part DP having its lower edge fixed to the roller151may be wound around the roller151. When the roller151rotates in the opposite direction, the display part DP wound around the roller151may be unwound from the roller151.

Referring toFIG.2, the roller151may be formed in a cylindrical shape. At least a part of the outer circumferential surface of the cylindrical shape may be formed as a flat surface, and the rest part of the outer circumferential surface of the cylindrical shape may be formed as a curved surface. The roller151may be formed generally in a cylindrical shape, with a part of it formed as a flat surface. That is to say, a part of the outer circumferential surface of the roller151may be formed as a flat surface, and the rest part of the outer circumferential surface thereof may be formed as a curved surface. A plurality of flexible films and printed circuit boards of the display part DP may be seated on the flat surface of the roller151. It is, however, to be noted that the roller151may be formed in a complete cylindrical shape or in any shape as long as the display part DP can be wound around it.

Referring back toFIG.2, the roller supports152support the roller151on both sides of the roller151. Specifically, the roller support152is disposed on the floor HPF of the housing part. The upper ends of the roller supports152are coupled with both ends of the roller151, respectively. Thus, the roller supports152may support the roller151so that it is spaced from the floor HPF of the housing part. The roller151may be coupled to the roller supports152so that it can rotate.

The elevation mechanism160moves the display part DP in the vertical direction in accordance with the driving of the roller unit150. The elevation mechanism160includes link units161, a head bar162, slide rails163, sliders164, a motor165, and rotors166.

Each of the link units161of the elevation mechanism160includes a plurality of links161aand161band a hinge161cconnecting between the links161aand161b. Specifically, for example, the plurality of link161aand161bincludes a first link161aand a second link161b, and the first link161aand the second link161bcross each other in a scissor shape and are rotatably engaged via the hinge161c. Accordingly, when the link unit161moves in the vertical direction, the links161aand161bmay rotate in a direction that is moved away from or closer to each other.

The head bar162of the elevation mechanism160is fixed to the top end of the display part DP. The head bar162may be connected to the link unit161and may move the display part DP in the vertical direction according to the rotation of the plurality of links161aand161bof the link unit161. In other words, the display part DP may be moved in the vertical direction by the head bar162and the link unit161.

The head bar162covers only a part of the surface adjacent to the top edge of the display part DP so as not to hide the images displayed on front face of the display part DP. The display part DP and the head bar162may be fixed with, but is not limited to, screws.

The slide rails163of the elevation mechanism160provide movement paths of the plurality of links161aand161b. A part of the links161aand161bis rotatably fastened to the slide rails163, so that movement can be guided along the trajectory of the slide rails163. A part of the links161aand161bmay be fastened to the sliders164that is movable along the slide rails163, so that they can move along the trajectory of the slide rails163.

The motor165may be connected to a power generator such as a separate external power supply or a built-in battery to receive power. The motor165generates a rotational force to provide a driving force to the rotors166.

The rotors166are connected to the motor165and are configured to convert rotational motion from the motor165into linear reciprocating motion. That is to say, the rotational motion of the motor165can be converted into a linear reciprocating motion of the structure fixed to the rotors166. For example, the rotors166may be implemented as, but is not limited to, a shaft and a ball screw including a nut fastened to the shaft.

The motor165and the rotors166may be interlocked with the link units161to elevate the display part DP. The link units161are formed in a link structure and receive the driving force from the motor165and the rotors166to repeatedly perform folding or unfolding operations.

Specifically, as the motor165is driven, the structure of the rotors166may perform a linear motion. That is to say, a part of the rotors166to which one end of the second link161bis connected may perform linear motion. As a result, one end of the second link161bmay move toward the motor165, and the plurality of links161aand161bmay be folded, so that the height of the link units161may be reduced. In addition, in the course that the links161aand161bare folded, the head bar162connected to the first link161aalso descends, and one end of the display part DP connected to the head bar162also descends.

Accordingly, when the display part DP is fully wound around the roller151, the link units161of the elevation mechanism160remains folded. That is to say, when the display part DP is fully wound around the roller151, the elevation mechanism160may have the shortest height. When the display part DP is fully unwound, the link units161of the elevation mechanism160remains unfolded. That is to say, when the display part DP is fully unwound, the elevation mechanism160may have the tallest height.

When the display part DP is wound, the roller151may rotate and the display part DP may be wound around the roller151. For example, the lower edge of the display part DP is connected to the roller151. When the roller151rotates in a first direction, the rear surface of the display part DP is in tight contact with the surface of the roller151so that the display part DP can be wound around it.

When the display part DP is unwound, the roller151may rotate and the display part DP may be unwound from the roller151. For example, when the roller151rotates in a second direction opposite to the first direction, the display part DP wound around the roller151is unwound from the roller151and may be disposed outside the housing part HP.

It is, however, to be understood that the present disclosure is not limited thereto. The front surface of the display part DP may be in tight contact with the surface of the roller151and may be wound around it.

In some exemplary embodiments, the driver MP having other structure than that of the above-described driver MP may be employed by the display device100. The configurations of the roller unit150and the elevation mechanism160may be altered, some of the configurations may be omitted or other configurations may be added, as long as the display part DP can be wound and unwound.

FIG.3Ais a plan view of a display part of a display device according to an exemplary embodiment of the present disclosure.FIG.3Bis a rear view showing a display part of a display device according to an exemplary embodiment of the present disclosure.FIG.3Cis a plan view of a mid cover of a display device according to an exemplary embodiment of the present disclosure.FIG.4Ais a cross-sectional view taken along line IVa-IVa′ ofFIG.3A.FIG.4Bis an enlarged cross-sectional view taken along line IVb-IVb′ ofFIG.3A. Referring toFIGS.3A to4B, the display part DP of the display device100includes a mid cover110, a display panel120, flexible films130, printed circuit boards140, and a plurality of back bars170.

Referring toFIGS.3A to4B, the mid cover110is disposed on the rear surface of the display panel120to support the rear surfaces of the display panel120, the flexible films130and the printed circuit boards140. When the display part DP is disposed outside the housing part HP, the mid cover110may have a size larger than the sizes of other elements of the display part DP, especially the display panel120so that it can protect the display panel120from an external impact. For example, the width of the mid cover100in the horizontal direction is larger than the width of the display panel120in the horizontal direction, so that the mid cover110can protect the display part DP when it is disposed outside the housing part HP.

The mid cover110is made of a material having flexibility so that deformation does not occur in the mid cover110even if the display part DP repeatedly performs winding and unwinding. Specifically, the mid cover110is made of a material having a yield stress that is larger than the stress applied to the mid cover110when the display part DP is wound. For example, the mid cover110may be made of a material such as metal, rubber, plastic and fabric. It is to be noted that the material of the mid cover110may be changed as long as the material satisfies the physical property conditions such as the amount of thermal deformation, the radius of curvature and the strength depending on the design choice.

The mid cover110has a thin thickness so that deformation does not occur in the mid cover110even if the display part DP repeatedly performs winding and unwinding. The mid cover110may have, but is not limited to, a thickness of approximately 0.1 mm or less.

The mid cover110includes a first area A1, a second area A2, a third area A3, a fourth area A4, and a fifth area A5. Specifically, the fifth area A5, the first area A1, the second area A2, the fourth area A4and the third area A3are arranged in this order from the top of the mid cover110. In the first area A1, the display panel120is disposed. In the second area A2, the printed circuit boards140electrically connected to the display panel120is disposed. The third area A3is fixed to the roller151. The fourth area A4is disposed between the second area A2and the third area A3. The fifth area A5is disposed at the top of the mid cover110.

The fifth area A5of the mid cover110is the uppermost area of the mid cover110and is fastened to the head bar162. First fastening holes AH1are formed in the fifth area A5for fastening with the head bar162. As described above with reference toFIG.2, the screws penetrating the head bar162and the first fastening holes AH1are disposed, so that the head bar162can be fastened to the fifth area A5of the mid cover110. As the fifth area A5is fastened to the head bar162, when the link units161fastened to the head bar162are elevated or lowered, the mid cover110may also be elevated or lowered together. In addition, the display panel120attached to the mid cover110may also be elevated or lowered together. Although the five first fastening holes AH1are shown inFIGS.3A to3C, the number of the first fastening holes AH1is not limited to five. In addition, although the mid cover110is fastened to the head bar162using the first fastening holes AH1in the example shown inFIGS.3A to3C, the present disclosure is not limited thereto. The mid cover110and the head bar162may be fastened without a separate fastening hole.

The third area A3of the mid cover110is the lowermost area of the mid cover110and is fixed to the roller151. Second fastening holes AH2may be formed in the third area A3for fastening with the roller151. For example, the screws penetrating the roller151and the second fastening holes AH2are disposed, so that the roller151and the third area A3of the mid cover110can be fastened. In addition, as the third area A3is fastened to the roller151, the mid cover110may be wound around or unwound from the roller151by rotation of the roller151. Although the two second fastening holes AH2are shown inFIGS.3A to3C, the number of the second fastening holes AH2is not limited to two.

The second area A2of the mid cover110is disposed between the fifth area A5and the third area A3. The flexible films130and the printed circuit boards140connected to one end of the display panel120are disposed and fixed in the second area A2.

In order to protect the flexible films130and the printed circuit boards140, the second area A2may allow the flexible films130and the printed circuit board140to be wound around the roller151as a flat surface instead of a curved surface. In addition, a part of the roller151that falls in the second area A2may also be formed as a flat surface.

A plurality of fixing holes112is disposed in the second area A2. The plurality of fixing holes112may be located between every two of the flexible films130, so that a base plate and a top cover may be fastened on and under the flexible films130and the printed circuit board140, respectively, by plurality of fixing holes112. In this manner, the flexible films130and the printed circuit boards140can be more stably fixed. The number of the plurality of fixing holes112shown inFIGS.3A to3Cis merely illustrative. The number of the plurality of fixing holes112may be determined based on the number of the printed circuit boards140and the number of the flexible films130.

The fourth area A4of the mid cover110is extended so that the display area AA of the display panel120can be disposed outside the housing part HP. The fourth area A4is extended from the second area A2to the third area A3. For example, when the mid cover110and the display panel120are fully unwound, the third area A3of the mid cover110fixed to the roller151and the second area A2where the flexible film130and the printed circuit boards140are attached may be disposed inside the housing part HP, whereas the first area A1and the fifth area A5having the display panel120attached thereto may be disposed outside the housing part HP. If the length from the third area A3fixed to the roller151to the second area A2is smaller than the length from the third area A3to the opening HPO of the housing part, a part of the first area A1having the display panel120attached thereto may be disposed inside the housing part HP. Therefore, since a part of the lower end of the display area AA of the display panel120is disposed inside the housing part HP, it may be difficult to watch images. Therefore, the display device may be designed so that the length from the third area A3fixed to the roller151to the second area A2is equal to the length from the third area A3fixed to the roller151to the opening HPO of the housing part.

A plurality of openings111is disposed in the fourth area A4. When the display part DP is wound or unwound, stress may be applied to the display part DP. When this happens, in the display device100according to an exemplary embodiment of the present disclosure, even if stress is applied to the display part DP while the display part DP is wound or unwound, the plurality of openings111of the mid cover110can be deformed flexibly so that the stress applied to the mid cover110can be relieved. Specifically, when the display part DP is wound or unwound, the fourth area A4of the mid cover110may be deformed as the openings111contract or expand. Accordingly, stress applied to the mid cover110can be reduced.

The first area A1of the mid cover110is disposed between the fifth area A5and the second area A2. Specifically, the first area A1is wound around or unwound from the roller151together with the display panel120and the plurality of back bars170. The first area A1may overlap at least the display panel120among the other elements of the display part DP.

The display panel120is a panel for displaying images to a user. In the display panel120, a display element for displaying images, a driving element for driving the display element, lines for transmitting various signals to the display element and the driving element, etc. may be disposed.

The display element may be defined differently depending on the type of the display panel120. For example, when the display panel120is an organic light-emitting display panel, the display element may be an organic light-emitting element that includes an anode, an organic emissive layer, and a cathode. For example, when the display panel120is a liquid-crystal display panel, the display element may be a liquid-crystal display element. In addition, when the display panel120is a light-emitting display panel including LEDs, the display element may be an LED. In the following description, the display panel120is described as an organic light-emitting display panel. It is, however, to be understood that the display panel120is not limited to the organic light-emitting display panel. As the display device100according to the exemplary embodiment of the present disclosure is a rollable display device, the display panel120may be implemented as a flexible display panel in order to be wound around or unwound from the roller151.

Referring toFIG.3A, the display panel120includes a display area AA and a non-display area NA.

In the display area AA, images are displayed on the display panel120. A plurality of pixels may be defined in the display area AA, and a plurality of sub-pixels forming each of the pixels and driver circuits for driving the plurality of sub-pixels may be disposed in the display area AA. The plurality of sub-pixels is the minimum units forming the display area AA. A display element may be disposed in each of the plurality of sub-pixels. For example, an organic light-emitting element including an anode, an organic light-emitting layer, and a cathode may be disposed in each of the plurality of sub pixels. It is, however, to be understood that the present disclosure is not limited thereto. In addition, driving elements, lines etc. may be included in the circuitry for driving a plurality of sub-pixels. For example, the circuitry may be formed of, but is not limited to, thin-film transistors, storage capacitors, gate lines, data lines, etc.

In the non-display area NA, no image is displayed. The non-display area NA surrounds the display area AA. In the non-display area NA, a variety of lines and circuits for driving the organic light-emitting elements in the display area AA, etc. may be disposed. For example, in the non-display area NA, link lines for transmitting signals to a plurality of sub-pixels and circuits of the display area AA, or driver ICs such as a gate driver and a data driver may be disposed. It is, however, to be understood that the present disclosure is not limited thereto.

More specifically, driver circuits such as the gate driver for driving the display area AA and a variety of signal lines connected to the driver circuits may be disposed in at least one of the non-display areas NA on both sides of the display area AA. The gate driver may be embedded in the non-display area NA on at least one side of the both sides of the display area AA by using the gate-in-panel (GIP) technology. That is to say, the gate driver may be disposed on either side of the display area AA, or may be disposed on at least one of the both sides of the display area AA.

The flexible film130is formed by disposing various elements on a flexible base film. The flexible film130may supply signals to a plurality of sub-pixels and circuits in the display area AA and may be electrically connected to the display panel120. The flexible film130is disposed at one end of the non-display area NA of the display panel120to supply voltage, data voltage, etc. to the plurality of sub-pixels and circuits in the display area AA. The number of flexible films130shown inFIG.3Ais merely illustrative, and the number of flexible films130may be changed depending on the design choice.

Driver ICs such as a gate driver IC and a data driver IC may also be disposed on the flexible films130, for example. The driver ICs are elements for processing data for displaying images and processing signals for processing the data. The driver ICs may be disposed by using the chip-on-glass (COG) technique, the chip-on-film (COF) technique, tape carrier package (TCP) technique, etc. In the following description, the driver ICs are mounted on the flexible films130by using the chip-on-film (COF) technique for convenience of illustration. It is, however, to be understood that the present disclosure is not limited thereto.

Referring toFIG.3A, the printed circuit boards140are disposed at one end of the flexible films130to be connected to the flexible films130. The printed circuit boards140supply signals to the driver ICs. The printed circuit board140supplies various signals, such as driving signals and data signals, to the driver ICs. A variety of elements may be disposed on the printed circuit boards140. For example, a timing controller, a power source, etc. may be disposed on the printed circuit boards140. Although two printed circuit boards140are shown inFIG.3A, the number of the printed circuit boards140is not limited to two but may be variously changed depending on the design choice.

Although not shown inFIG.3A, an additional printed circuit board connected to the printed circuit boards140may be further disposed. For example, the printed circuit boards140may be referred to as source printed circuit boards (S-PCB) on which the data driver is mounted, and an additional printed circuit board connected to the printed circuit boards140may be referred to as a control printed circuit board (C-PCB) on which the timing controller and the like are mounted. The additional printed circuit board may be disposed inside the roller151or may be disposed in the housing part HP outside the roller151.

Referring toFIG.3B, a plurality of back bars170are disposed under the mid cover110to support the mid cover110and the display panel120. Specifically, the plurality of back bars170are disposed on the surface of the mid cover110that is opposite to the surface on which the display panel120is disposed. The plurality of back bars170are disposed in the first area A1. That is to say, the plurality of back bars170are disposed in the first area A1overlapping the display panel120.

The plurality of back bars170have a longer axis in the row direction and a shorter axis in the column direction. On the rear surface of the mid cover110, One back bar170extended in the row direction is disposed in every row, and a plurality of back bars170are arranged in the column direction. The width of the plurality of back bars170is equal to or greater than the width of the mid cover110in the horizontal direction. The edges of the plurality of back bars170are disposed more to the outside than the edges of the display panel120. Accordingly, when the display part DP is disposed outside the housing part HP, it is possible to protect the other elements of the display part DP, especially the display panel120from outside impact. The thickness of the plurality of back bars170may be larger than the thickness of the mid cover110. The thickness of the plurality of back bars170may be defined as the distance between the upper surface and the lower surface facing the upper surface of the mid cover110. The thickness of the plurality of back bars170may be equal to or less than 2 mm.

The plurality of back bars170is made of a material having strength. For example, the plurality of back bars170may be made of a metal material such as steel use stainless (SUS) and Invar, or a material such as plastic. It is to be noted that the material of the mid cover110may be changed as long as the material satisfies the physical property conditions such as the amount of thermal deformation, the radius of curvature and the strength depending on the design choice.

The plurality of back bars170may have a trapezoidal cross-sectional shape. Accordingly, adjacent ones of the back bars170are spaced apart from one another by a predetermined angle. Accordingly, when the display part DP is wound, the angle between the back bars170may be adjusted so that the display panel120is wound. Specifically, the back bars170are bent in the column direction by the angle formed between adjacent ones of the back bars170. It is to be noted that the cross-sectional shape of the plurality of back bars170is not limited thereto, and may be various shapes such as a triangular shape.

The plurality of back bars170are disposed on the rear surface of the display part to support the display part DP. For example, when the display part DP is wound, the plurality of back bars170may be bent along the outer surface of the roller151so that the display panel120may be wound around the roller151. In the fully unwound state where the display part DP of the display device100is disposed outside the housing part HP, the plurality of back bars170are unfolded in a flat shape outside the housing part HP so that the display part DP remains flat. Accordingly, it is possible to reduce the deformation and wrinkles which may occur in the display panel120as it is wound and unwound repeatedly, thereby improving the flatness of the display panel120.

Referring toFIGS.4A and4B, the display panel120includes a substrate121, a buffer layer122, a pixel portion123, an encapsulation layer124, and an encapsulation substrate125.

The substrate121is a base member for supporting various elements of the display panel120and may be made of an insulating material. The substrate121may be made of a material having flexibility so that the display panel120can be wound or unwound, and may be made of a plastic material such as polyimide (PI), for example.

The buffer layer122can reduce diffusion of moisture and/or oxygen that has permeated from the outside of the substrate121. The buffer layer122may be made up of, but is not limited to, a single layer or a plurality of layers of silicon oxide (SiOx) and silicon nitride (SiNx).

The pixel portion123is an element in which a plurality of pixels is disposed, and includes an organic light-emitting element and a circuit for driving the organic light-emitting element. The pixel portion123may correspond to the display area AA. The organic light-emitting element may include an anode, an organic light-emitting layer and a cathode.

The anode may supply holes to the organic light-emitting layer, and may be made of a conductive material having a high work function. For example, the anode may be made of, but is not limited to, tin oxide (TO), indium tin oxide (ITO), indium zinc oxide (IZO), indium tin zinc oxide (ITZO), etc.

The organic light-emitting layer may receive holes from the anode and receive electrons from the cathode to emit light. The organic light-emitting layer may be a red organic light-emitting layer, a green organic light-emitting layer, a blue organic light-emitting layer, and a white organic light-emitting layer depending on the color of light emitted from the organic light-emitting layer. When the organic light-emitting layer is a white organic light-emitting layer, color filters of various colors may be additionally disposed.

The cathode may supply electrons to the organic light-emitting layer, and may be made of a conductive material having a low work function. For example, the cathode may be made of, but is not limited to, at least one selected from metals such as magnesium (Mg), silver (Ag) and aluminum (Al), and alloys thereof.

The display panel120may be either a top-emission display panel or a bottom-emission display panel depending on the direction in which light emitted from the organic light-emitting element exits.

In the top-emission display panel, the light emitted from the organic light-emitting element exits toward the upper side of the substrate SUB21where the organic light-emitting element is formed. When the display panel120is the top-emission display panel, a reflective layer may be formed on under the anode to propagate the light emitted from the organic light-emitting element toward the upper side of the substrate121, i.e., the cathode side.

In the bottom-emission display panel, the light emitted from the organic light-emitting element exits toward the lower side of the substrate SUB21where the organic light-emitting element is formed. In the bottom-emission display panel, in order to propagate the light emitted from the organic light-emitting element toward the lower side of the substrate SUB121, the anode may be made only of a transparent conductive material, and the cathode may be made of a metal material having high reflectivity.

In the following description, for convenience of illustration, the display device100according to the exemplary embodiment of the present disclosure is a bottom-emission display device. It is, however, to be understood that the present disclosure is not limited thereto.

A circuit for driving the organic light-emitting element is disposed in the pixel portion123. The circuit may be formed of a thin-film transistor, a storage capacitor, a gate line, a data line, a power line, etc., but may be variously changed depending on the design of the display device100.

The encapsulation layer124is on the pixel portion123to cover it. The encapsulation layer124seals the organic light-emitting element of the pixel portion123. The encapsulation layer124can protect the organic light-emitting element of the pixel portion123from the outside moisture, oxygen, impact, etc. The encapsulation layer124may be formed by alternately stacking a plurality of inorganic layers and a plurality of organic layers. For example, the inorganic layers may be made of an inorganic material such as silicon nitride (SiNx), silicon oxide (SiOx) and aluminum oxide (AlOx). The organic layer may be made of an epoxy-based or acrylic-based polymer. It is, however, to be understood that the present disclosure is not limited thereto.

The encapsulation substrate125is disposed on the encapsulation layer124. The encapsulation substrate125protects the organic light-emitting element of the pixel portion123together with the encapsulation layer124. The encapsulation substrate125can protect the organic light-emitting element of the pixel portion123from the outside moisture, oxygen, impact, etc. The encapsulation substrate125may be made of a metal material such as aluminum (Al), nickel (Ni), chromium (Cr), an alloy material of iron (Fe) and nickel, etc., which is resistant to corrosion and is easy to process into a foil or thin film. As the encapsulation substrate125is made of such a metal material, the ultra-thin encapsulation substrate125can be implemented, which is resistant to the outside impact, scratches.

A third adhesive layer AD3may be disposed between the encapsulation layer124and the encapsulation substrate125. The third adhesive layer AD3may attach the encapsulation layer124and the encapsulation substrate125together. The third adhesive layer AD3may be made of a material having adhesive properties, and may be a thermally-curable or naturally-curable adhesive. For example, the third adhesive layer AD3may be made of, but is not limited to, an optical clear adhesive (OCA), a pressure sensitive adhesive (PSA), etc.

The third adhesive layer AD3may be disposed to surround the encapsulation layer124and the pixel portion123. Specifically, the pixel portion123may be sealed by the buffer layer122and the encapsulation layer124, and the encapsulation layer124and the pixel portion123may be sealed by the buffer layer122and the third adhesive layer AD3. The third adhesive layer AD3can protect the organic light-emitting element of the pixel portion123from moisture, oxygen, and impact from outside, along with the encapsulation layer124and the encapsulation substrate125. To this end, the third adhesive layer AD3may further include a hygroscopic agent. The hygroscopic agent may be hygroscopic particles and can absorb moisture and oxygen from the outside, thereby suppressing the permeation of moisture and oxygen into the pixel portion123.

The mid cover110is disposed on the encapsulation substrate125. The mid cover110may be in contact with the encapsulation substrate125of the display panel120to protect the display panel120.

A first adhesive layer AD1is disposed between the encapsulation substrate125and the mid cover110. The first adhesive layer AD1is disposed on the upper surface of the mid cover110to attach the display panel120on which the encapsulation substrate125is disposed to the mid cover110. The first adhesive layer AD1may be made of a material having adhesive properties, and may be a thermally-curable or naturally-curable adhesive. For example, the first adhesive layer AD1may be made of, but is not limited to, an optical clear adhesive (OCA), a pressure sensitive adhesive (PSA), etc.

The plurality of back bars170are disposed on the mid cover110. The plurality of back bars170may be disposed on the rear surface of the display panel120to support the display panel120.

A second adhesive layer AD2may be disposed between the mid cover110and the plurality of back bars170. The second adhesive layer AD2may be disposed on the lower surface of the mid cover110to attach the mid cover110to the plurality of back bars170. The second adhesive layer AD2is made of a material having adhesive properties and is made of a material having elasticity. For example, the second adhesive layer AD2may be formed of, but is not limited to, a foam pad and an elastic resin.

In an existing rollable display device, a mid cover is disposed on the rear side of a display panel, a flexible film and a printed circuit board to support the display panel, the flexible film, the printed circuit board. As the thickness of display devices is ever reduced, a thin mid cover is used. As a result, the strength of the mid cover is lowered, such that the reliability and flatness of the display part have been lowered.

In addition, in an existing rollable display device, a plurality of back bars is disposed on the rear side of a display panel, a flexible film and a printed circuit board to support the display panel, the flexible film, the printed circuit board. However, there was a problem in that the boundaries of the back bars are seen from the front side of the display panel. To solve such a problem, it was contemplated to employ a thick adhesive layer or a foam pad. However, there was a problem in that the thickness is increased too much so that the rolling characteristics were deteriorated.

In this regard, in the display device100according to an exemplary embodiment of the present disclosure, the plurality of back bars170is disposed on the rear surface of the mid cover100, so that the flatness of the display part DP can be improved while the back bars170disposed on the rear side of the display panel120are not seen. In addition, the side strength can be improved even with the reduced thickness, and thus the reliability of the display device100can be improved.

First, the plurality of back bars170can improve the flatness of the display panel120. Previously, a mid cover is implemented as a single piece in the display part to support the shape of the display panel. Such a mid cover has insufficient force to support the display panel and thus there is a problem that deformation and wrinkles occur in the display panel as the winding and unwinding are repeated. In this regard, in the display device100according to an exemplary embodiment of the present disclosure, the flatness of the display panel120can be improved by attaching the plurality of back bars170to the rear surface of the mid cover110. For example, the plurality of back bars170have the shorter axis in the column direction to allow the display part DP to be wound and unwound. When the display part DP is unwound, the plurality of back bars170pass through the opening HPO of the housing part and unfolded flat outside the housing part HP. The plurality of back bars170have the longer axis in the row direction to fix the shape of the display panel120in the row direction and to allow the display part DP to remain flat. In this manner, the plurality of back bars170fall in a part of the mid cover110can improve the issues of the deformation and wrinkles of the display panel120which may occur as winding and unwinding repeat.

In addition, in the display device100according to an exemplary embodiment of the present disclosure, the mid cover110can reduce the boundaries of the back bars170from being seen. Specifically, the mid cover110having a thickness smaller than the thickness of the plurality of back bars170is disposed on one surface of the display panel120to reduce the boundaries of the back bars170from being seen. Accordingly, the mid cover110disposed to impart strength of the display part DP can also prevent the boundaries of the back bars170from being seen. As a result, in the display device100according to the exemplary embodiment of the present disclosure, the thickness of the second adhesive layer AD2can be reduced. For example, in an existing back bar structure, a foam pad having the thickness of 0.64 mm is disposed to prevent the boundaries of the back bars from being seen. In contrast, in the display device100according to the exemplary embodiment of the present disclosure, the foam pad is used as the second adhesive layer AD2, which has the thickness of 0.15 mm Therefore, the mid cover110together with the second adhesive layer AD2can reduce the boundaries of the plurality of back bars170from being seen, and the thickness of the second adhesive layer AD2disposed to prevent the boundaries of the back bars170from being seen can reduce the thickness.

The plurality of back bars170may be disposed together with the mid cover110to form a thin display part DP. The plurality of back bars170are made of a material having strength, and protects the display part DP from a force applied from the outside. Accordingly, the strength of the display part DP is achieved by the plurality of back bars170. Therefore, it is possible to dispose the mid cover110with a reduced thickness compared to the existing display part including the single mid cover. Specifically, the thickness of the mid cover110can be reduced by about half compared to when the existing single mid cover is disposed. Previously, a mid cover having a thickness of 0.2 to 0.23 mm was disposed to support a display part, for example. In contrast, in the display device100according to the exemplary embodiment of the present disclosure, the mid cover110having a thickness of 0.1 mm or less can be disposed. Next, the mid cover can also contribute to increasing the side strength of the display part DP. The mid cover110is disposed up to the outside of the display panel DP to impart strength to the display panel120. As a result, it is possible to reduce the thickness of the back bars170. Previously, back bars having the thickness of 4 mm was disposed to support a display part, for example. In contrast, in the display device100according to the exemplary embodiment of the present disclosure, the back bars170having a thickness of 2.5 mm or less can be disposed to achieve the same strength as the existing display part DP.

<Example of Back Bars>

The positions of the back bars170change along the outer circumferential surface of the roller151when the display part DP is wound around it. Accordingly, when the display part DP is wound, the angle between adjacent ones of the back bars170is changed, and the winding characteristics of the display part DP may vary depending on the angle between the back bars170. The angle formed by the adjacent back bars170are related to the length and thickness of the back bars170and radius of the roller151.

FIGS.5A and5Bare schematic cross-sectional views showing an exemplary embodiment of the present disclosure.FIGS.5A and5Bschematically show cross-sectional views of some of the back bars170arranged in the column direction. InFIGS.5A and5B, R denotes the rolling radius from the center of the roller151to the back bars170, t denotes the thickness of the back bar170, i.e., the distance between the first surface S1and the second surface S2of the back bar170, and l denotes the length of the back bar in the column direction, i.e., the length in the shorter axis direction of the back bar170. The angle between adjacent back bars among the plurality of back bars170may be equal to l/(R+t) to 2 tan−1{l/(2(t)}. Hereinafter, an angle range between the plurality of back bars170will be described with reference toFIGS.5A and5B.

First, the minimum angle between the plurality of back bars170may be equal to l/(R+t). Referring toFIG.5A, the minimum angle between the plurality of back bars170will be described. The cross section of the back bar170is trapezoidal. Each of the back bars170includes a first surface S1and a second surface S2facing the first surface S1. The first surface S1is closer to the mid cover110, while the second surface S2is disposed at the bottom of the display part DP. The second surface S2is smaller than the first surface S1. The edge of the first surface S1of one back bar170may be in contact with the edge of the first surface S1of another back bar170adjacent thereto. Since the second surface S2is smaller than the first surface S1, the second surface S2of one back bar170may be spaced apart from the second surface S2of another back bar170adjacent thereto. When the display part DP is wound, the edge of a second surface S2may be in contact with the edge of another second surface S2, and a back bar170may move as much as the angle between the back bar170and another adjacent back bar170. The minimum Θ1 may be equal to l/(R+t), where Θ denotes the angle between adjacent back bars170. The value of Θ1 can be obtained by using the formula to find the length of the arc of a fan. The plurality of back bars170are in contact with the roller151when the display part is wound. Accordingly, they may be in contact with the roller151at the boundary surface with adjacent back bars. In order for the back bars170to be in contact with the outer circumferential surface of the roller151, the value of l may be small. Considering that Θ1 is the minimum angle, the value of l may be equal to the length of an arc having the radius of (r+t) and the center angle Θ. Accordingly, the size l of the circumference may be equal to θ1*(R+t), and θ1 may be equal to l/(R+t). Therefore, the minimum angle θ1 between the back bars170may form l/(R+t).

Next, the maximum angle between the back bars170may be equal to 2 tan−1{l/(2(t)}. Referring toFIG.5B, the maximum angle between the plurality of back bars170will be described. The cross section of the back bars170is triangular. In order to maximize the angle between one back bar170and the adjacent back bar170, the plurality of back bars170may have a triangular cross section. Each of the back bars170includes a first surface S1and a second surface S2facing the first surface S1. The first surface S1of each of the back bars170is identical to the first surface S1ofFIG.5A. However, the second surface S2inFIG.5Bhas a pointed shape formed by two lines. Accordingly, the edge of the first surface S1of one back bar170is in contact with the edge of the first surfaces S1of another back bar170adjacent thereto. The lines forming the pointed shape as the second surface S2are spaced apart from each other. On the other hand, when rolled, the back bars170may move so that all of the lines forming the pointed shape as the second surface S2may be in contact with one another. If the angle between the plurality of back bars170is referred to as θ and the maximum value of θ is referred to as θ2, θ2 may be an angle formed by the back bars170having the triangular cross section. If the angle between the adjacent back bars170having the triangular cross section is referred to as θ2, θ2 is equal to the inner angle of the triangle facing the first surface S1. Therefore, the inner angle of the triangle facing the first surface S1may be equal to 2 tan−1{l/(2(t)}, and the maximum angle between the back bars170may be equal to 2 tan−1{l/(2(t)}. Accordingly, the maximum angle θ2 between the back bars170may form 2 tan−1{l/(2(t)}.

Accordingly, the angle θ between the back bars170having the same thickness and length may form the angle of l/(R+t) to 2 tan−1{l/(2(t)}.

<Specific Configuration of Mid Cover>

FIG.6Ais a plan view of a display part of a display device according to another exemplary embodiment of the present disclosure.FIG.6Bis a plan view of a mid cover of a display device according to another exemplary embodiment of the present disclosure. A display device600shown inFIGS.6A and6Bis substantially identical to the display device100shown inFIGS.1A to4Bexcept for a mid cover610; and, therefore, the redundant description will be omitted.

Referring toFIGS.6A and6B, openings611identical to the opening611formed in the fourth area A4are formed in the first area A1of the mid cover610. In the first area A1, a plurality of openings611is arranged and the display panel120is attached. Specifically, the first area A1is wound around or unwounded from the roller151together with the display panel120and the plurality of back bars170. The first area A1may overlap at least the display panel120among the other elements of the display part DP.

When the display part DP is wound or unwound, the openings611may be deformed due to the stress applied to the display part DP. Specifically, when the display part DP is wound or unwound, the first area A1of the mid cover610may be deformed as the openings611contract or expand. As the openings611contract or expand, it is possible to suppress the display panel120disposed on the first area A1of the mid cover610from slipping, so that the stress applied to the display panel120can be reduced.

When the display panel120and the mid cover610are wound around the roller151, due to the difference in the radius of curvature between the display panel120and the mid cover610, there is a difference in the length between the display panel120and the mid cover. For example, the length of the mid cover610when it is wound around the roller151once may be different from the length of the display panel120when it is wound around the roller151once. Specifically, since the display panel120is disposed more to the outside of the roller151than the mid cover610, the length of the display panel120when it is wound around the roller151once may be larger than the length of the mid cover610when it is wound around the roller151once. As such, when the display unit DP wound, there is a difference in the length between the mid cover610and the display panel120wound around the roller151due to the difference in the radius of curvature. As a result, the display panel120attached to the mid cover610may slide and thus may deviate from the original position. As used herein, a phenomenon that the display panel120slips from the mid cover610due to a difference in the radius of curvature and stress caused by winding may be defined as a slip phenomenon. If the slip is excessively large, the display panel120may be detached from the mid cover610, or defects such as cracks may occur.

In this regard, in the display device600according to another exemplary embodiment of the present disclosure, even if stress is applied to the display part DP while the display part DP is wound or unwound, the plurality of openings610of the mid cover611can be deformed flexibly so that the stress applied to the mid cover610and the display panel120can be relieved. For example, when the mid cover610and the display panel120are wound around the roller151, stress may be applied which deforms the mid cover610and the display panel120in the vertical direction. At this time, the plurality of openings611arranged in the first area A1and the fourth area A4of the mid cover610may be expanded in the vertical direction of the mid cover610, and the length of the mid cover610can also be flexibly changed. As a result, the difference in the length between the mid cover610and the display panel120due to the difference in the radius of curvature in the course of winding the mid cover610and the display panel120can be compensated for by the plurality of openings611of the mid cover610. In addition, the openings611are deformed in the course of winding the mid cover610and the display panel120so that stress applied to the display panel120from the mid cover610can also be relieved.

Referring toFIGS.6A and6B, the openings611are staggered with the openings611in adjacent rows. For example, the openings611arranged in a row are staggered with the openings611arranged in an adjacent row. Specifically, the centers of the openings611arranged in the odd rows may be staggered with the centers of the openings611arranged in the even rows. For example, they may be staggered by half the width of the openings611in the row direction. It is to be understood that the arrangement of the plurality of openings611illustrated inFIG.6Bis exemplary and is not limited thereto.

Referring toFIG.6B, the openings611have the maximum width in the row direction larger than the maximum width in the column direction. That is to say, as shown inFIG.6B, the maximum width of the openings611in the horizontal direction may be greater than the maximum width of the openings611in the vertical direction.

In the display device600according to another exemplary embodiment of the present disclosure, the plurality of back bars170is disposed on the rear surface of the mid cover610, so that the flatness of the display part DP can be improved while the back bars170disposed on the rear side of the display panel120are not seen. In addition, the side strength can be improved even with the reduced thickness, and thus the reliability of the display device100can be improved.

In addition, in the display device600according to another exemplary embodiment of the present disclosure, even if stress is applied to the display part DP while the display part DP is wound or unwound, the plurality of openings610of the mid cover611can be deformed flexibly so that the stress applied to the mid cover610and the display panel120can be relieved.

<Structure of Mid Cover>

FIG.7Ais a plan view of a display part of a display device according to yet another exemplary embodiment of the present disclosure.FIG.7Bis a plan view of a mid cover of a display device according to yet another exemplary embodiment of the present disclosure. A display device700shown inFIGS.7A and7Bis substantially identical to the display device600shown inFIGS.6A to6Bexcept for a mid cover710; and, therefore, the redundant description will be omitted.

Referring toFIGS.7A and7B, the mid cover710includes a first mid cover710aand a second mid cover710b. The first mid cover710aand the second mid cover710bmay be formed separately from each other. The first mid-cover710aand the second mid-cover710bare separated at the boundary between a first sub-area A21and a second sub-area A22, and the first sub-area A21and the second sub-area A22form a second area A2.

The first mid cover710ais disposed to overlap the display panel120. The second mid cover710bis fixed to the roller151. The first mid cover710aand the second mid cover710bare spaced apart from each other. In other words, there is a space between the first mid cover710aand the second mid cover710b. The first mid cover710aand the second mid cover710bmay be connected by a base plate and a top cover.

The first mid cover710aincludes a first area A1overlapping the display panel120, a fifth area A5extended away from the second mid cover710bfrom the first area A1, and a first sub-area A21extended from the first area A1toward the second mid cover710b. In addition, the second mid cover710bincludes a third area A3fastened to the roller151, a fourth area A4extended from the third area A3toward the first mid cover710a, and a second sub-area A22extended from the fourth area A4toward the first mid-cover710a.

The second mid cover710bis fixed to the roller151. The second mid cover710bincludes the third area A3, the fourth area A4and a part of the second area A2extended from the fourth area A4. The third area A3, the fourth area A4and a part of the second area A2extended from the fourth area A4of the second mid cover710bhave the same width. In other words, the second mid cover710bmay be defined as areas having the same width in the row direction.

In the display device700according to this exemplary embodiment of the present disclosure, the mid cover710includes the first mid cover710aand the second mid cover710bspaced apart from each other, so that the mid cover710can be adopted for a variety of display panels having different sizes. As display devices are becoming larger and larger, so are display panels. Since the mid cover should be larger than the display panel, a single-piece mid cover must be produced in a large size. It is very difficult to produce a single-piece mid cover for a large display device. In contrast, in the display device700according to yet another exemplary embodiment of the present disclosure, the mid cover710includes the first mid cover710aand the second mid cover710b, which have smaller size than the existing mid cover. In addition, since the first mid cover710aand the second mid cover710bare fixed by the base plate, the top cover and the fixing member, the first mid cover710aand the second mid cover710bcan perform the functionality of the existing mid cover and can be produced in a smaller size to improve productivity.

In the display device700according to yet another exemplary embodiment of the present disclosure, the plurality of back bars170is disposed on the rear surface of the mid cover710, so that the flatness of the display part DP can be improved while the back bars170disposed on the rear side of the display panel120are not seen. In addition, the side strength can be improved even with the reduced thickness, and thus the reliability of the display device100can be improved.

In addition, in the display device700according to yet another exemplary embodiment of the present disclosure, even if stress is applied to the display part DP while the display part DP is wound or unwound, the plurality of openings710of the mid cover711can be deformed flexibly so that the stress applied to the mid cover710and the display panel120can be relieved.

<Shape of Back Bars>

FIG.8is an enlarged, cross-sectional view of a display part of a display device according to yet another exemplary embodiment of the present disclosure. A display device800shown inFIG.8is substantially identical to the display device100shown inFIGS.1to4Bexcept for a plurality of back bars870; and, therefore, the redundant description will be omitted.

Referring toFIG.8, each of the plurality of back bars870has curved upper and lower surfaces. Specifically, the upper and lower surfaces of the back bars870have a convex curved shape toward the mid cover110. Therefore, when the display part is wound, the plurality of back bars870may be wound around the roller151while forming a curved surface along the surface shape of the roller151.

In the display device800according to this exemplary embodiment, since the upper and lower surfaces of the back bars870have curved shapes, the stress generated on the display panel120when the display device800is wound can be reduced. Specifically, since the upper and lower surfaces of the back bars870have the curved shape convex toward the mid cover110, the shape of the back bars870can conform to the shape of the roller151. Accordingly, when the display device800is wound, the lower surfaces of the back bars870provide the curved shape conforming to the roller151, so that the display panel120also can be wound conforming to the curved shape provided by the back bars870and thus the stress applied to the display panel120can be relieved. As the stress applied to the display panel120is relieved, it is possible to reduce cracks in the display part DP and to improve the reliability of the display panel120.

FIG.9is an enlarged, cross-sectional view of a display part of a display device according to yet another exemplary embodiment of the present disclosure. A display device900shown inFIG.9is substantially identical to the display device800shown inFIG.8except for a plurality of back bars970; and, therefore, the redundant description will be omitted.

A hollow971is disposed at the center of each of the plurality of back bars970. The hollow971may be elongated along the row direction to be opened up to both ends of each of the back bars970. The shape of the hollow971may conform to the shape of the back bars970. It is, however, to be understood that the present disclosure is not limited thereto. The upper and lower surfaces of the hollow971may be curved surfaces having the same curvature as the upper and lower surfaces of the back bars970. It is, however, to be understood that the present disclosure is not limited thereto.

In the display device900according to this exemplary embodiment, the same curved surfaces are disposed on the upper and lower surfaces of the back bars970at the center of each of the back bars970, so that the stress generated on the display panel120when the display device900is wound can be reduced. Specifically, an empty space is formed at the center of each of the back bars970instead of a material having rigidity, so that stress applied to the mid cover110and the display panel120can be relieved. For example, when the mid cover110and the display panel120are wound around the roller151, stress may be applied which deforms the mid cover110and the display panel120in the vertical direction. The hollow971may be elongated in the vertical direction and be more flexibly deformed. Accordingly, the difference in the length between the mid cover110and the display panel120due to the difference in the radius of curvature in the course of winding the mid cover110and the display panel120can be compensated for by the hollow971formed in each of the back bars970. As the stress applied to the display panel120is relieved, it is possible to prevent cracks in the display part DP and to improve the reliability of the display panel120.

Hereinafter, the effects of the display device200according to the exemplary embodiment of the present disclosure and the display device800according to the exemplary embodiment of the present disclosure will be described in detail with reference to Table 1.

Table 1 shows the stress-strain simulation results for Comparative Example and Examples. A display device according to Comparative Example is a typical display device which is different from the display device600according to the exemplary embodiment of the present disclosure in that no mid cover is disposed. Results of Example 1 were obtained from the display device600according to the exemplary embodiment of the present disclosure. Results of Example 2 were obtained from the display device800according to another exemplary embodiment of the present disclosure. In Comparative Example and Examples 1 and 2, aluminum having the Young's modulus of 69.3 GPa and the Poisson's ratio of 0.33 was employed as the plurality of back bars670and870, a foam pad having the Young's modulus of 85 MPa and the Poisson's ratio of 0.3 was employed as the first adhesive layer AD1and the second adhesive layer AD2, and a PET having the Young's modulus of 2.4 GPa and the Poisson's ratio of 0.4 was employed as the display panel120. In Examples 1 and 2, the mid covers610and810had the thickness of 0.2 mm and were made of an anisotropic material having different Young's Moduli depending on the directions. The Young's Modulus of the mid cover110was set to 0.83 GPa in the winding direction, 56 GPa in the vertical direction of the winding direction, and 81 GPa in the thickness direction. The stress-strain simulations were carried out by apply force from above using a jig having the radius of 40R, i.e., by bending with the radius of 40R.

The stress-strain simulation results for Comparative Example, Examples 1 and 2 are shown in Table 1 below:

First, in terms of stress, Example 1 exhibited a decrease in stress by about 10.6% compared to the stress of Comparative Example. Example 2 exhibited a decrease in stress by about 11.02% compared to the stress of Comparative Example.

Second, in terms of strain, Example 1 exhibited a decrease in strain by about 17.86% compared to the strain of Comparative Example. Example 2 exhibited a decrease in strain by about 18.22% compared to the strain of Comparative Example.

According to an aspect of the present disclosure, a display device comprises a mid cover; a display panel disposed on a surface of the mid cover and having a plurality of pixels defined therein; a plurality of back bars disposed on an opposite surface of the mid cover; and a roller fixed to the mid cover, wherein the mid cover, the display panel and the plurality of back bars are wound around or unwound from the roller.

The mid cover may comprise a first area where the display panel is disposed; a second area where a printed circuit board electrically connected to the display panel is disposed; a third area fixed to the roller; and a fourth area between the second area and the third area, wherein the plurality of back bars is disposed in the first area.

The mid cover may comprise a plurality of openings arranged in the fourth area.

The plurality of openings may be further arranged in the first area.

The mid cover may comprise a first mid cover where the first area and a first sub-area of the second area extended from the first area are disposed; and a second mid cover spaced apart from the first mid cover, wherein the third area, the fourth area and a second sub-area of the second area extended from the fourth area are disposed.

A stress applied to the mid cover may be equal to or less than a yield stress of the mid cover when the mid cover is wound around the roller.

A cross-sectional shape of each of the plurality of back bars may be a trapezoidal shape or a triangular shape.

Upper and lower surfaces of the plurality of back bars may have a curved shape convex toward the surface of the mid cover.

The display device may further comprise an adhesive layer disposed between the mid cover and the plurality of back bars.

A width of the mid cover in a horizontal direction may be larger than a width of the display panel in the horizontal direction, and wherein a width of the back bars in the horizontal direction may be equal to or larger than the width of the mid cover in the horizontal direction.

According to another aspect of the present disclosure, a display device comprises a roller; a mid cover fixed to the roller; a first adhesive layer disposed on an upper surface of the mid cover; a display panel attached to the mid cover by the first adhesive layer; a second adhesive layer disposed on a lower surface of the mid cover; and a plurality of back bars attached to the mid cover by the second adhesive layer.

The plurality of back bars may fall in a part of the mid cover.

The plurality of back bars may overlap with the display panel.

The part of the mid cover where the back bars are disposed may comprise a plurality of openings.

Each of the plurality of back bars may comprise a first surface and a second surface facing the first surface and smaller than the first surface, and wherein the first surface may be disposed closer to the mid cover than the second surface is.

The first surface and the second surface may be curved surfaces.

Each of the plurality of back bars may comprise a hollow.

An angle between adjacent ones of the back bars may be l/(R+t) to 2 tan−1{l/(2(t)}, wherein l denotes a length of a first surface in a shorter axis direction, R denotes a radius from a center of the roller to the back bars, and t denotes a distance between the first surface and a second surface.

The plurality of back bars may be made of metal or plastic.

The mid cover may be made of metal, rubber, plastic, or fabric.

A thickness of the mid cover may be smaller than a thickness of the plurality of back bars.