KR102506631B1 - Foldable display device - Google Patents

Abstract

In the foldable display device of the present invention, the elastic deformation period of the back plate is increased by forming the opening pattern in the folding region of the back plate. The opening pattern formed in the folding area acts as a spring to increase elastic restoring energy, thereby reducing a restoring time.
Accordingly, folding characteristics of the foldable display device are improved without increasing the thickness.

Description

Foldable display device {Foldable display device}

The present invention relates to a foldable display device, and more particularly, to a foldable display device capable of preventing damage occurring during folding and unfolding of the display device.

As society entered the information age in earnest, the display field, which processes and displays large amounts of information, has developed rapidly. Various flat panel display devices such as light emitting display device (OELD) have been developed and are in the spotlight.

A liquid crystal display device includes, as essential components, a liquid crystal panel including an upper substrate and a lower substrate bonded with a liquid crystal layer including liquid crystal molecules interposed therebetween, and the liquid crystal layer is moved by an electric field formed between a pixel electrode and a common electrode. It drives and displays the image.

An organic light emitting display device includes, as an essential component, a light emitting diode including an anode and a cathode facing each other with an organic light emitting layer interposed therebetween, and holes and electrons injected from the anode and the cathode are combined in the organic light emitting layer to emit light. will display

Meanwhile, recently, a demand for a foldable display device manufactured using a flexible substrate has increased. Since the foldable display can be carried in a folded state and displays an image in an unfolded state, it has the advantage of being easy to carry while being able to display a large screen.

1 is a schematic cross-sectional view of a conventional foldable display device.

As shown in FIG. 1 , the foldable display 10 includes a display panel 20 , a back plate 30 , and a cover window 40 .

The display panel 20 includes a flexible substrate 22 and a display element 24 formed on the flexible substrate 22 . For example, the flexible substrate 22 may be a polyimide substrate.

When the display panel 20 is a light emitting diode panel, the display element 24 may include a light emitting diode and a thin film transistor for driving the light emitting diode. In this case, the light emitting diode may include an anode connected to the thin film transistor, an organic light emitting layer formed on the anode, and a cathode formed on the organic light emitting layer. In addition, a barrier film may be formed to cover the light emitting diode and prevent penetration of external moisture.

Meanwhile, when the display panel 20 is a liquid crystal panel, the display element 24 includes a thin film transistor formed on the flexible substrate 22, a pixel electrode connected to the thin film transistor, and the flexible substrate 22. ), a common electrode formed on the flexible substrate 22 or the opposite substrate, and a liquid crystal layer interposed between the flexible substrate 22 and the opposite substrate.

A flexible display panel 20 may be obtained by forming components such as the thin film transistor and releasing the carrier substrate in a state where a carrier substrate (not shown) is attached to the lower portion of the flexible substrate 22 .

Since the flexible substrate 22 is too thin in the display panel 20 manufactured as described above, a back plate 30 capable of supporting the display panel 20 is attached to the lower portion of the flexible substrate 22 . For example, the back plate 20 may be made of polyethylene terephthalate (PET) and is attached to the flexible substrate 22 by an adhesive layer 32 .

The cover window 40 is attached to the upper portion of the display panel 20 to protect the display panel 20 from external impact. Although not shown, the cover window 40 may be attached to the display panel 20 by an adhesive layer.

Meanwhile, a PET film having a thickness of about 100 micrometers is used as the back plate 30 , and plastic deformation occurs in the back plate 30 when folding and unfolding operations of the foldable display device 10 are repeated. As a result, restoration of the foldable display device 10 becomes impossible.

That is, as shown in FIGS. 2A and 2B , since a problem of plastic deformation of the back plate, which is a PET film, occurs, folding/unfolding of the foldable display 10 is limited. In other words, a problem occurs in that the folding characteristics of the foldable display 10 are degraded.

By reducing the thickness of the back plate 30, the problem of plastic deformation of the back plate 30 can be reduced. However, when the thickness of the back plate 30 is reduced, elastic restoring energy is reduced, resulting in a long time required for restoration.

The present invention is intended to solve the problem of deterioration in folding characteristics of conventional foldable displays.

According to the present invention, the back play of the foldable display device has at least two opening patterns corresponding to the folding area.

In addition, the folding area may have a smaller thickness than the unfolding area, and the opening patterns formed in the folding area may have different sizes or different distances depending on positions.

In the foldable display device of the present invention, by forming two or more opening patterns spaced apart from each other in the folding area of the back plate, restoration is possible even if folding/unfolding operations of the foldable display device are repeated.

That is, the elastic deformation section is increased by the opening pattern formed in the folding area, and restoration is possible.

In addition, the opening pattern formed in the folding area acts as a spring to increase elastic restoration energy, thereby reducing restoration time.

Accordingly, folding characteristics of the foldable display device are improved without increasing the thickness.

In addition, by forming a step compensation layer on at least one surface of the back plate on which the opening pattern is formed, it is possible to prevent a problem of deterioration in image quality due to the opening pattern.

In addition, the thickness of the back plate is reduced in the folding region to relieve folding stress, and damage to the display panel due to folding can be prevented by adjusting the distance between the opening patterns or the size of the opening patterns.

1 is a schematic cross-sectional view of a conventional foldable display device.
2A and 2B are diagrams showing problems of plastic deformation of the back plate.
3 is a schematic cross-sectional view of a foldable display device according to a first embodiment of the present invention.
4A and 4B are schematic cross-sectional views showing examples of display panels.
5A to 5D are plan views illustrating a back plate.
6 is a schematic cross-sectional view of a foldable display device according to a second exemplary embodiment of the present invention.
7A to 7C are cross-sectional views showing the back plate.
8A to 8C are diagrams for explaining a back plate of a foldable display device according to a third embodiment of the present invention.
9A to 9C are diagrams for explaining a back plate of a foldable display device according to a fourth embodiment of the present invention.

In order to solve the above problems, the present invention is divided into a display panel and a folding area located on one surface of the display panel and an unfolding area on both sides of the folding area, and two or more opening patterns spaced apart from each other are provided in the folding area. A foldable display device including a back plate is provided.

In the foldable display device of the present invention, the opening pattern includes at least one first pattern positioned in a (2n-1)-th column and at least one second pattern positioned in a (2n)-th column, and the second A space between the patterns may be positioned to correspond to the first pattern.

In the foldable display device of the present invention, the opening pattern includes at least one first pattern positioned in a (2n-1)-th column and at least one second pattern positioned in a (2n)-th column, and the first Patterns may be positioned to correspond to the second patterns, respectively.

In the foldable display device of the present invention, the opening pattern includes a first pattern located in a (2n-1)-th column and two or more second patterns located in a (2n)-th column, and in the (2n)-th column , The distance between the second patterns may be equal to or smaller than the length of the second patterns.

In the foldable display device of the present invention, the opening pattern may have a rectangular shape, a diamond shape, or an elliptical shape with a constant minor axis length.

In the foldable display device of the present invention, one side of the back plate may be discontinuous in the folding area.

In the foldable display device of the present invention, the display panel includes a flexible substrate, and the modulus of the back plate may be greater than that of the flexible substrate.

In the foldable display device of the present invention, a step compensation layer covering the folding area may be positioned on at least one surface of the back plate.

In the foldable display device of the present invention, the step compensation layer may have a smaller modulus than that of the back plate.

In the foldable display device of the present invention, the back plate may have a concave portion corresponding to the folding area to have a first thickness in the folding area and a second thickness greater than the first thickness in the unfolding area. .

The foldable display device of the present invention may include a step compensation layer attached to one surface of the back plate on which the concave portion is formed.

In the foldable display device of the present invention, the display panel may include a plurality of pixel areas, and an edge of the concave portion may correspond to a boundary between the pixel areas.

In the foldable display of the present invention, the display panel is an organic light emitting diode panel, and an edge of the concave portion may correspond to a bank covering an edge of the first electrode of the organic light emitting diode.

In the foldable display device of the present invention, the step compensation layer may form a flat surface with the back plate.

In the foldable display device of the present invention, the concave portion may be located on an outer surface of the back plate, and the foldable display device may be folded toward the display panel.

In the foldable display device of the present invention, the concave portion may be located on an inner surface of the back plate, and the foldable display device may be folded toward the back plate.

In the foldable display device of the present invention, the folding area is divided into an edge portion and a central portion along a folding direction, and the opening pattern is spaced apart from the edge portion by a first distance along the folding direction and from the central portion in the folding direction. It may be spaced apart by a second distance smaller than the first distance along.

In the foldable display device of the present invention, the distance between the opening patterns may decrease from the edge to the center along the folding direction.

In the foldable display device of the present invention, the folding area is divided into an edge portion and a central portion along a folding direction, and the opening pattern has a first width along the folding direction at the edge portion and extends from the central portion in the folding direction. Accordingly, it may have a second width greater than the first width.

In the foldable display of the present invention, the size of the opening pattern may increase from the edge to the center along the folding direction.

Hereinafter, preferred embodiments according to the present invention will be described with reference to the drawings.

3 is a schematic cross-sectional view of a foldable display device according to a first embodiment of the present invention.

As shown, the foldable display device 100 according to the first embodiment of the present invention includes a display panel 110 and a display panel 110 positioned below the display panel 110 and placed in a folding region (FR). A back plate 180 having the above opening pattern 182 and a cover window 190 positioned above the display panel 110 are included.

The display panel 110 includes a flexible substrate 112 and a display element 114 formed on the flexible substrate 112 . For example, the flexible substrate 112 may be a polyimide substrate.

Since the flexible substrate 112 is not suitable for the formation process of the display element 114, the display element 114 is formed while the flexible substrate 112 is attached to a carrier substrate (not shown) such as a glass substrate. The formation process proceeds. After the display element 114 is formed on the flexible substrate 112 , the display panel 110 may be obtained by separating the carrier substrate and the flexible substrate 112 .

4A and 4B are schematic cross-sectional views showing examples of display panels. As shown in FIG. 4A , the display panel 110 may be a light emitting diode panel.

A buffer layer 120 is formed on the flexible substrate 112 , and a thin film transistor Tr is formed on the buffer layer 120 . The buffer layer 120 may be omitted.

A semiconductor layer 122 is formed on the buffer layer 120 . The semiconductor layer 122 may be made of an oxide semiconductor material or polycrystalline silicon.

When the semiconductor layer 122 is made of an oxide semiconductor material, a light blocking pattern (not shown) may be formed under the semiconductor layer 122, and the light blocking pattern prevents light from entering the semiconductor layer 122. Thus, the semiconductor layer 122 is prevented from being deteriorated by light. Alternatively, the semiconductor layer 122 may be made of polycrystalline silicon, and in this case, both edges of the semiconductor layer 122 may be doped with impurities.

A gate insulating layer 124 made of an insulating material is formed on the semiconductor layer 122 . The gate insulating layer 124 may be made of an inorganic insulating material such as silicon oxide or silicon nitride.

A gate electrode 130 made of a conductive material such as metal is formed on the gate insulating layer 124 corresponding to the center of the semiconductor layer 122 .

In FIG. 4A , the gate insulating film 124 is formed on the entire surface of the flexible substrate 112 , but the gate insulating film 124 may be patterned in the same shape as the gate electrode 130 .

An interlayer insulating film 132 made of an insulating material is formed on the gate electrode 130 . The interlayer insulating layer 132 may be formed of an inorganic insulating material such as silicon oxide or silicon nitride, or an organic insulating material such as benzocyclobutene or photo-acryl.

The interlayer insulating layer 132 has first and second contact holes 134 and 136 exposing both sides of the semiconductor layer 122 . The first and second contact holes 134 and 136 are spaced apart from the gate electrode 130 on both sides of the gate electrode 130 .

Here, the first and second contact holes 134 and 136 are also formed in the gate insulating layer 124 . Alternatively, when the gate insulating layer 124 is patterned in the same shape as the gate electrode 130 , the first and second contact holes 134 and 136 may be formed only in the interlayer insulating layer 132 .

A source electrode 140 and a drain electrode 142 made of a conductive material such as metal are formed on the interlayer insulating film 132 .

The source electrode 140 and the drain electrode 142 are spaced apart from each other with respect to the gate electrode 130, and both sides of the semiconductor layer 122 through the first and second contact holes 134 and 136, respectively. come into contact with

The semiconductor layer 122, the gate electrode 130, the source electrode 140, and the drain electrode 142 constitute the thin film transistor Tr, and the thin film transistor Tr is a driving element. ) function as

The thin film transistor Tr has a coplanar structure in which the gate electrode 130 , the source electrode 142 , and the drain electrode 144 are positioned on the semiconductor layer 120 .

Alternatively, the thin film transistor Tr may have an inverted staggered structure in which a gate electrode is positioned below the semiconductor layer and a source electrode and a drain electrode are positioned above the semiconductor layer. In this case, the semiconductor layer may be made of amorphous silicon.

Although not shown, a gate line and a data line cross each other to define a pixel area, and a switching element connected to the gate line and the data line is further formed. The switching element is connected to the thin film transistor Tr, which is a driving element.

In addition, a power line is formed to be spaced apart in parallel with the data line or the data line, and a storage capacitor for maintaining a constant voltage of the gate electrode of the thin film transistor (Tr), which is a driving element, for one frame is further provided. can be configured.

A protective layer 150 having a drain contact hole 152 exposing the drain electrode 142 of the thin film transistor Tr is formed to cover the thin film transistor Tr.

On the protective layer 150, a first electrode 160 connected to the drain electrode 142 of the thin film transistor Tr through the drain contact hole 152 is formed separately for each pixel area. The first electrode 160 may be an anode and may be made of a conductive material having a relatively high work function value. For example, the first electrode 160 may be made of a transparent conductive material such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO). .

Meanwhile, when the display panel 110 of the present invention is a top-emission type, a reflective electrode or a reflective layer may be further formed below the first electrode 160 . For example, the reflective electrode or the reflective layer may be made of an aluminum-palladium-copper (APC) alloy.

In addition, a bank layer 166 covering an edge of the first electrode 160 is formed on the passivation layer 150 . The bank layer 166 exposes the center of the first electrode 160 corresponding to the pixel area.

An organic emission layer 162 is formed on the first electrode 160 . The organic light emitting layer 162 may have a single layer structure of an emitting material layer made of a light emitting material. In addition, in order to increase the luminous efficiency, the organic light emitting layer 162 includes a hole injection layer, a hole transporting layer, a light emitting material layer, and an electron transporting layer sequentially stacked on the first electrode 160. It may have a multilayer structure of an electron transporting layer and an electron injection layer.

A second electrode 164 is formed on the flexible substrate 112 on which the organic emission layer 162 is formed. The second electrode 164 is located on the front surface of the display area and is made of a conductive material having a relatively low work function value and can be used as a cathode. For example, the second electrode 164 may be formed of any one of aluminum (Al), magnesium (Mg), and aluminum-magnesium alloy (AlMg).

The first electrode 160, the organic light emitting layer 162, and the second electrode 164 form an organic light emitting diode (D).

An encapsulation film 170 is formed on the second electrode 164 to prevent penetration of external moisture into the organic light emitting diode D. The encapsulation film 170 may have a stack structure of a first inorganic insulating layer 172 , an organic insulating layer 174 , and a second inorganic insulating layer 174 , but is not limited thereto.

In addition, a polarizer (not shown) may be attached to the encapsulation film 170 to reduce reflection of external light. For example, the polarizing plate may be a circular polarizing plate.

Meanwhile, as shown in FIG. 4B , the liquid crystal panel 210 may be used as the display panel 110 .

The liquid crystal panel 210 includes first and second flexible substrates 212 and 250 facing each other, and a liquid crystal interposed between the first and second flexible substrates 212 and 250 and including liquid crystal molecules 262. Layer 260 is included.

A first buffer layer 220 is formed on the first flexible substrate 212 , and a thin film transistor Tr is formed on the first buffer layer 220 . The first buffer layer 220 may be omitted.

A gate electrode 222 is formed on the first buffer layer 220 , and a gate insulating layer 224 is formed covering the gate electrode 222 . In addition, a gate wire (not shown) connected to the gate electrode 222 is formed on the buffer layer 220 .

A semiconductor layer 226 is formed on the gate insulating layer 224 to correspond to the gate electrode 222 . The semiconductor layer 226 may be made of an oxide semiconductor material. Meanwhile, the semiconductor layer 226 may include an active layer made of amorphous silicon and an ohmic contact layer made of impurity amorphous silicon.

A source electrode 230 and a drain electrode 232 spaced apart from each other are formed on the semiconductor layer 226 . In addition, a data line (not shown) connected to the source electrode 230 is formed crossing the gate line to define a pixel area.

The gate electrode 222, the semiconductor layer 226, the source electrode 230, and the drain electrode 232 constitute a thin film transistor Tr.

A protective layer 234 having a drain contact hole 236 exposing the drain electrode 232 is formed on the thin film transistor Tr.

On the protective layer 234, a pixel electrode 240 connected to the drain electrode 232 through the drain contact hole 236 and a common electrode 242 alternately arranged with the pixel electrode 240 are formed. is formed

A second buffer layer 252 is formed on the second flexible substrate 250, and on the second buffer layer 252, a black matrix covering non-display areas such as the thin film transistor Tr, the gate wiring, and the data wiring 254) is formed. In addition, a color filter layer 256 is formed corresponding to the pixel area. The second buffer layer 252 and the black matrix 254 may be omitted.

The first and second flexible substrates 212 and 250 are bonded with a liquid crystal layer 260 interposed therebetween, and the liquid crystal layer ( The liquid crystal molecules of 260) are driven.

Although not shown, an alignment layer may be formed on each of the first and second flexible substrates 212 and 250 in contact with the liquid crystal layer 260, and the first and second flexible substrates 212 and 250 respectively Polarizers having transmission axes perpendicular to each other may be attached to the outside of the .

Referring back to FIG. 3 , the back plate 180 is positioned below the display panel 110 and supports the display panel 110 . For example, the back plate 180 may be attached to the flexible substrate 112 using an adhesive layer (not shown).

The back plate 180 has greater stiffness than the flexible substrate 112 . That is, the back plate 180 has a greater modulus than the flexible substrate 112 (Youngs modulus).

For example, the back plate 180 may be made of a metal material such as stainless steel (SUS), polymethyl metacrylate (PMMA), polycarbonate (PC), or polyacrylate (PA). ), polyvinylalcohol (PVA), acrylonitrile-butadiene-styrene (ABS), and polyethylene terephthalate (PET).

When the back plate 180 is made of a highly rigid material such as SUS, it has a high restoring force. Accordingly, the thickness of the back plate 180 may be reduced.

When the back plate 180 is made of a high-rigidity material such as SUS, the back plate 180 can maintain desired rigidity even when its thickness decreases, and thus can serve as a support for the display panel 110 . In addition, the problem of plastic deformation of the back plate 180 can be reduced by reducing the thickness.

However, since the back plate 180 made of a highly rigid material and having a small thickness has a narrow elastic deformation region, it is very difficult to restore it after deformation. That is, after folding, it is not unfolded, and the time to maintain the shape at the time of folding increases.

In the foldable display device 100 of the present invention, at least one opening pattern 182 is formed in the folding region FR of the back plate 180 to expand the elastic deformation period of the back plate 180 . The opening pattern 182 formed in the folding region FR acts like a spring, and the restoring characteristics of the back plate 180 are improved. Accordingly, it is possible to solve the problem of increasing restoration time due to the decrease in the thickness of the back plate 180 .

In other words, the back plate 180 of the present invention is made of a high rigidity material and has a high restoring force, and the elastic deformation section is enlarged by the opening pattern 182 . Accordingly, foldable characteristics of the display device 100 are improved while the back plate 180 has a small thickness (eg, 2 mm).

Meanwhile, display defects may occur due to the opening pattern 182 formed on the back plate 180 .

To prevent this problem and protect the opening pattern 182 , first and second step compensation layers 186 and 188 may be formed on the lower and upper surfaces of the back plate 180 .

The first and second step compensation layers 186 and 188 are made of a material having less rigidity than that of the back plate 180 . For example, each of the first and second step compensation layers 186 and 188 is made of polyurethane (PU), thermoplastic polyurethane (TPU), polyacrylate, rubber, or silicon (Si). It can be done.

The first and second step compensation layers 186 and 188 cover and protect the opening pattern 182 and eliminate the step difference caused by the opening pattern 182 . Display defects in which the level difference caused by the opening pattern 182 is recognized on the display surface may occur. However, the first and second level difference compensation layers 186 and 188 can prevent such display defects from occurring. .

Only one of the first and second step compensation layers 186 and 188 may be formed, and both of the first and second step compensation layers 186 and 188 may be omitted. Also, the first and second step compensation layers 186 and 188 are illustrated as covering the entire surface of the back plate 180, but may be formed only in the folding region FR.

Also, the first and second step compensation layers 186 and 188 may be formed to fill the opening pattern 182 .

The cover window 190 protects the display panel 110 from external impact and prevents damage such as scratches, and may be omitted.

Meanwhile, although not shown, a touch panel may be positioned between the display panel 110 and the cover window 190 .

As described above, the foldable display device 100 of the present invention can reduce the thickness by including the back plate 180 having high rigidity, and the folding area FR of the back plate 180 serves as a spring. By forming the opening pattern 182 , the restoring force of the back plate 180 may be increased. That is, the back plate 180 having a small thickness and high restoring force can be provided.

Accordingly, it is possible to provide a thin foldable display device 100 having excellent folding/unfolding characteristics.

5A to 5D are plan views illustrating a back plate.

As shown in FIG. 5A , a first pattern 182a formed in a (2n-1)th column and a second pattern 182b formed in a (2n)th column are formed in the folding region FR of the back plate 180. An opening pattern 182 including is formed. (Here, n is a positive integer.)

Although the folding area FR is illustrated as being located in the center of the back plate 180 in FIG. 5A , the location of the folding area FR is not limited. Also, two or more folding regions FR may be defined.

Each of the first and second patterns 182a and 182b may have a rectangular shape. Also, a space between the second patterns 182b formed in the (2n)-th column may correspond to the first pattern 182a formed in the (2n−1)-th column.

Both ends of the first pattern 182a may be positioned within the folding area FR, and one end of the second pattern 182b may be positioned on one side of the back plate 180 in the folding area FR. .

That is, one side of the back plate 180 is discontinuous in the (2n)th column. In other words, in the folding region FR, one side surface of the back plate 180 is connected through a portion between the first and second patterns 182a and 182b and a portion between the two second patterns 182b. Thus, the folding region FR functions like a spring.

In FIG. 5A , one first pattern 182a is formed in odd-numbered columns and two second patterns 182b are formed in even-numbered columns. However, two or more first patterns 182a may be formed, and three or more second patterns 182b may be formed.

Each of the first and second patterns 182a and 182b extends in a column direction. That is, the long axis of each of the first and second patterns 182a and 182b may be parallel to the column direction.

In addition, the first distance D1 between the two second patterns 182b may be equal to or smaller than the first length L1 of each of the second patterns 182b, and preferably the first distance (D1) may be smaller than the first length (L1).

Accordingly, when the foldable display device ( 100 in FIG. 3 ) is unfolded, the folding region FR in which the opening pattern 182 is formed serves as a spring and increases elastic restoring energy of the back plate 180 . . Accordingly, the unfolding time of the foldable display 100 may be reduced.

Referring to FIG. 5B , the folding region FR of the back plate 280 includes a first pattern 282a formed in a (2n-1)th column and a second pattern 282b formed in a (2n)th column. An aperture pattern 282 is formed. (Here, n is a positive integer.)

Although the folding area FR is illustrated as being located in the center of the back plate 280 in FIG. 5B , the location of the folding area FR is not limited. Also, two or more folding regions FR may be defined.

Each of the first and second patterns 282a and 282b may have a diamond shape. In addition, the first pattern 282a formed in the (2n-1)th column may correspond to the second pattern 282b formed in the (2n)th column, and the first and second patterns 282a and 282b of each column are spaced apart from each other.

For example, the first patterns 282a of the (2n-1)th column are spaced apart from each other, and the second patterns 282b of the (2n)th column are spaced apart from each other. In addition, the first pattern 282a of the (2n−1)th column and the second pattern 282b of the (2n)th column are also spaced apart from each other.

For example, the first and second patterns 282a and 282b are spaced apart from each other by a second distance D2, and the second distance D2 is the distance between the first and second patterns 282a and 282b, respectively. It may be equal to or smaller than the second length L2, and preferably, the second distance D2 may be smaller than the second length L2.

Accordingly, when the foldable display device ( 100 in FIG. 3 ) is unfolded, the folding region FR in which the opening pattern 282 is formed serves as a spring and increases elastic restoring energy of the back plate 280 . . Accordingly, the unfolding time of the foldable display 200 may be reduced.

Referring to FIG. 5C , the folding region FR of the back plate 380 includes a first pattern 382a formed in a (2n-1)th column and a second pattern 382b formed in a (2n)th column. An aperture pattern 382 is formed. (Here, n is a positive integer.)

In FIG. 5C , the folding area FR is shown to be located in the center of the back plate 380, but the location of the folding area FR is not limited. Also, two or more folding regions FR may be defined.

Each of the first and second patterns 382a and 382b may have a diamond shape. Also, the first pattern 382a formed in the (2n−1)th column may correspond to the second pattern 382b formed in the (2n−1)th column. For example, the center of the first pattern 382a may correspond to the space between the second patterns 382b, and the center of the second pattern 382b may correspond to the space between the first patterns 382a.

For example, each of the first and second patterns 382a and 382b are spaced apart from each other by a third distance D3, and the third distance D3 is the distance between the first and second patterns 382a and 382b, respectively. It may be equal to or smaller than the third length L3, and preferably, the third distance D3 may be smaller than the third length L3.

Accordingly, when the foldable display device ( 100 in FIG. 3 ) is unfolded, the folding region FR in which the opening pattern 382 is formed serves as a spring and increases elastic restoring energy of the back plate 380 . . Accordingly, the unfolding time of the foldable display 100 may be reduced.

Referring to FIG. 5D , the folding region FR of the back plate 480 includes a first pattern 482a formed in a (2n-1)th column and a second pattern 482b formed in a (2n)th column. An aperture pattern 482 is formed. (Here, n is a positive integer.)

In FIG. 5D , the folding area FR is shown to be located in the center of the back plate 480, but the location of the folding area FR is not limited. Also, two or more folding regions FR may be defined.

Each of the first and second patterns 482a and 482b may have an elliptical shape with a constant minor axis length. That is, each of the first and second patterns 482a and 482b has a shape in which semicircles are coupled to both ends of the rectangle.

Also, the first pattern 482a formed in the (2n−1)th column may correspond to the second pattern 482b formed in the (2n)th column. For example, the center of the first pattern 482a may correspond to the space between the second patterns 482b, and the center of the second pattern 482b may correspond to the space between the first patterns 482a.

Each of the first and second patterns 482a and 482b extends in a column direction. That is, the long axis of each of the first and second patterns 482a and 482b may be parallel to the column direction. The fourth distance D4 between each of the first and second patterns 482a and 482b may be equal to or smaller than the fourth length L4 of each of the first and second patterns 482a and 482b, Preferably, the fourth distance D4 may be smaller than the fourth length L4. In addition, each end portion of the first and second patterns 482a and 482b has a predetermined radius of curvature RC.

Accordingly, when the foldable display device ( 100 in FIG. 3 ) is unfolded, the folding region FR in which the opening pattern 482 is formed serves as a spring and increases elastic restoring energy of the back plate 480 . . Accordingly, the unfolding time of the foldable display 100 may be reduced.

In FIGS. 5A to 5D , the opening patterns 180 , 280 , 380 , and 480 are shown to have a rectangular shape, a diamond shape, or an elliptical shape having a constant minor axis length, but the shape is not limited. For example, the opening patterns 180, 280, and 380 may have various shapes such as circular, elliptical, square, and trapezoidal shapes.

6 is a schematic cross-sectional view of a foldable display device according to a second exemplary embodiment of the present invention.

As shown in FIG. 6 , the foldable display device 500 according to the second embodiment of the present invention has a display panel 510 and a folding region (FR) located under the display panel 510. ), a back plate 580 having two or more opening patterns 582, and a cover window 590 positioned above the display panel 510.

Although not shown, the display panel 510 includes a flexible substrate and display elements formed on the flexible substrate. For example, the flexible substrate may be a polyimide substrate, and the display device may be an organic light emitting diode.

The back plate 580 is positioned under the display panel 510 and supports the display panel 510 . For example, the back plate 580 may be attached to the display panel 510 using an adhesive layer (not shown).

The back plate 580 has greater stiffness than the flexible substrate (not shown) of the display panel 510 . That is, the back plate 580 has a greater modulus than the flexible substrate (Youngs modulus).

In the foldable display device 500 of the present invention, the back plate 580 has a first thickness t1 in the folding region FR and in an unfolding region (UFR) on both sides of the folding region FR. It has a second thickness (t2) greater than the first thickness (t1). That is, a concave portion 584 is formed in the back plate 580 to correspond to the folding region FR.

For example, if the back plate 580 has a first thickness t1 in both the folding area FR and the unfolding area UFR, folding characteristics in the folding area FR may be satisfied, but the back plate 580 may be satisfied. A problem arises in supporting the display panel 510 in the unfolding region FR because the rigidity of the plate 580 is reduced.

Meanwhile, if the back plate 580 has the second thickness t2 in both the folding area FR and the unfolding area UFR, a problem occurs in the folding characteristic in the folding area FR.

However, in the present invention, since the back plate 580 has a relatively large second thickness t2 in the unfolding area UFR and a relatively small first thickness t1 in the folding area FR, the back plate 580 ), both stiffness and folding characteristics are satisfied.

In addition, by forming at least one opening pattern 582 on the back plate 580, the elastic deformation section of the back plate 580 is enlarged. That is, the opening pattern 582 is located in the concave portion 584 of the back plate 580 . The opening pattern 582 formed in the folding region FR acts like a spring, and the restoring characteristics of the back plate 580 are improved.

The opening pattern 582 may be variously changed as shown in FIGS. 5A to 5D .

For example, as shown in FIG. 5D, when each of the first and second patterns 482a and 482b has an elliptical shape with a constant minor axis length, the diameter of the end circle is the back plate in the folding region FR ( 580) or less than 1.5 times the first thickness t1 to improve folding characteristics without compromising the rigidity of the back plate 580 in the folding region FR. (t1≤2RC≤1.5*t1)

An etching process is performed on the base film constituting the back plate 580 to reduce the thickness of the folding region FR and form an opening pattern 582 . That is, after the concave portion 584 is formed by performing an etching process on the entire folding region FR, an additional etching process is performed on a portion of the folding region FR to form the opening pattern 582 .

In FIG. 6 , the foldable display 500 is folded toward the cover window 590 . That is, the back plate 580 is folded to be located on the outside, and the concave portion 584 is formed on the outer surface of the back plate 580 .

Alternatively, the foldable display 500 may be folded toward the back plate 580, and in this case, the concave portion 584 is formed on the inner surface of the back plate 580. That is, the concave portion 584 is formed on a surface facing the display panel 510 .

7A to 7C are cross-sectional views showing the back plate.

As shown in FIG. 7A , a first step compensation layer 586 may be formed on one side of the back plate 580 . That is, the first step compensation layer 586 is formed on the surface of the back plate 580 on which the concave portion 584 is formed.

Accordingly, the first step compensation layer 586 has a third thickness t3 in the folding region FR and a fourth thickness t4 smaller than the third thickness t3 in the unfolding region UFR. .

Meanwhile, referring to FIG. 7B , the first step compensation layer 586 may be formed only in the concave portion 584 . That is, the first step compensation layer 586 forms a flat surface with the back plate 580 .

Referring to FIG. 7C , a second step compensation layer 588 may be further formed on the other side of the back plate 580 . At this time, the second step compensation layer 588 has a substantially uniform fifth thickness t5, the fifth thickness t5 being smaller than the third thickness t3 and larger than the fourth thickness t4. can

The second step compensation layer 588 has a fifth thickness t5 smaller than the third thickness t3 of the first step compensation layer 586 in the concave portion 584, so that when folded, the back plate 580 has a compressive state. Accordingly, folding/unfolding characteristics of the foldable display 500 including the back plate 580 are further improved.

Each of the first and second step compensation layers 586 and 588 is made of a material having less rigidity than the back plate 580 and relieves stress applied to the back plate 580 by a folding operation. ) plays a role. That is, each of the first and second step compensation layers 586 and 588 has a modulus smaller than that of the back plate 580 .

For example, each of the first and second step compensation layers 586 and 588 is made of polyurethane (PU), thermoplastic polyurethane (TPU), polyacrylate, rubber, or silicon (Si). It can be done.

The first and second step compensation layers 586 and 588 cover and protect the opening pattern 582 and eliminate the step difference caused by the opening pattern 582 . Display defects in which the level difference caused by the opening pattern 582 is recognized on the display surface may occur. However, the first and second level difference compensation layers 586 and 588 can prevent such display defects from occurring. .

Meanwhile, since the first step compensation layer 586 is made of a material different from that of the back plate 580, the first step compensation layer 586 and the back plate 580 are formed at the end of the concave portion 584. boundaries can be recognized. That is, display quality may deteriorate due to a difference in refractive index between the first step compensation layer 586 and the back plate 580 .

To prevent this problem, the boundary between the first step compensation layer 586 and the concave portion 584, that is, the end (edge) of the concave portion 584 is arranged on the display panel (510 in FIG. 6). It may correspond to a boundary between adjacent pixel areas. For example, an end of the concave portion 584 may correspond to a bank ( 166 in FIG. 4A ) or a black matrix ( 254 in FIG. 4B ).

8A to 8C are diagrams for explaining a back plate of a foldable display device according to a third embodiment of the present invention.

As shown in FIG. 8A , a folding area FR and an unfolding area UFR are defined in the back plate 680, and the folding area FR is divided into a central portion CN and an edge portion ED. .

At this time, the opening patterns 682 formed in the folding region FR have the same size and have different distances therebetween. (pitch variable)

That is, in the folding direction, the opening patterns 682 have a first distance d1 from the edge portion ED and a second distance d2 smaller than the first distance d1 from the central portion CN. .

Referring to FIG. 8B showing the back plate 680 in a folded state, the back plate 680 configured to have different distances between the opening patterns 682 has a first edge ED of the folding area (FR in FIG. 8A). It has a radius of curvature and has a second radius of curvature smaller than the first radius of curvature at the central portion CN.

Meanwhile, as shown in FIG. 8C, the folding area (FR in FIG. 8A) is formed between the central portion CN and the first edge portion ED1 and the second edge portion ED2 between the central portion CN and the first edge portion ED1. ), and the opening pattern 682 has a first distance from the first edge portion ED1 in the folding direction, a second distance from the center portion CN, and a second distance greater than the second distance from the second edge portion ED2. It has a third distance smaller than the first distance.

That is, the distance of the opening pattern 682 may gradually decrease from the edge to the center of the folding region FR.

Stress is concentrated at the point where the curvature of the foldable display starts (ie, the edge portion ED or the first edge portion ED1), and thus damage to the display panel may occur. In the present invention, by adjusting the distance between the opening patterns 682 formed in the folding region FR of the back plate 680, the radius of curvature at the folding start point is increased and stress concentration is alleviated. Thus, damage to the display panel is minimized or prevented.

9A to 9C are diagrams for explaining a back plate of a foldable display device according to a fourth embodiment of the present invention.

As shown in FIG. 9A , a folding area FR and an unfolding area UFR are defined in the back plate 780, and the folding area FR is divided into a central portion CN and an edge portion ED. .

At this time, the opening patterns 782 formed in the folding region FR are arranged at the same distance and have different sizes. (size variable)

That is, in the folding direction, the opening pattern 782 has a first width w1 at the edge portion ED and a second width w2 greater than the first width w1 at the central portion CN. .

Referring to FIG. 9B showing the back plate 780 in a folded state, the back plate 780 having different opening patterns 782 has a first curvature at the edge ED of the folding region (FR in FIG. 9A ). It has a radius and has a second radius of curvature smaller than the first radius of curvature at the central portion CN.

Meanwhile, as shown in FIG. 9C, the folding area (FR in FIG. 9A) is formed between the central portion CN and the first edge portion ED1 and the second edge portion ED2 between the central portion CN and the first edge portion ED1. ), and the opening pattern 782 has a first width at the first edge portion ED1 in the folding direction, a second width at the central portion CN, and a width larger than the first width at the second edge portion ED2. It has a third width smaller than the second width.

That is, the size (width) of the opening pattern 782 may gradually increase from the edge to the center of the folding region FR.

In the present invention, by adjusting the size of the opening pattern 782 formed in the folding region FR of the back plate 780, the radius of curvature at the folding start point is increased and stress concentration is alleviated. Thus, damage to the display panel is minimized or prevented.

8A to 8C and 9A to 9C show that the distance between the opening patterns or the size of the opening patterns in the back plate including the concave portion is adjusted. Alternatively, the back plate may have a constant thickness without including a concave portion.

As described above, in the foldable display of the present invention, by forming two or more opening patterns spaced apart from each other in the folding area of the back plate, restoration is possible even if folding/unfolding operations of the foldable display are repeated. That is, the elastic deformation section is increased by the opening pattern formed in the folding area, and restoration is possible.

Accordingly, folding characteristics of the foldable display device are improved without increasing the thickness.

Although the above has been described with reference to preferred embodiments of the present invention, those skilled in the art can variously modify and change the present invention within the scope not departing from the technical spirit and scope of the present invention described in the claims below. You will understand that it can be done.

100, 500: foldable display device 110, 510: display panel
180, 280, 380, 480, 580, 680, 780: back plate
186, 188, 586, 588: step compensation layer
182, 282, 382, 482, 582, 682, 782: aperture pattern
584 concave portion FR folding area
UFR: Unfolding area

Claims (22)

a display panel;
a back plate located on one surface of the display panel and divided into a folding area and an unfolding area on both sides of the folding area, and having two or more opening patterns spaced apart from each other in the folding area;
The opening pattern includes at least one first pattern located in a (2n-1)-th column and at least one second pattern located in a (2n)-th column, and a space between the second patterns corresponds to the first pattern. A foldable display device positioned in such a way.

delete delete According to claim 1,
In the (2n) column, a distance between the second patterns is equal to or less than a length of the second patterns. (n is a positive integer)
According to claim 1,
The foldable display device of claim 1 , wherein the opening pattern has a rectangular shape, a diamond shape, or an elliptical shape having a constant minor axis length.
According to claim 1,
One side of the back plate is discontinuous in the folding area.
According to claim 1,
The display panel includes a flexible substrate, and the modulus of the back plate is greater than that of the flexible substrate.
According to claim 1,
The foldable display device of claim 1 , wherein a step compensation layer covering the folding area is positioned on at least one surface of the back plate.
According to claim 8,
The step compensation layer has a smaller modulus than the back plate.
According to claim 1,
The back plate has a concave portion corresponding to the folding area, has a first thickness in the folding area, and has a second thickness greater than the first thickness in the unfolding area.
According to claim 10,
A foldable display comprising a step compensation layer attached to one surface of the back plate on which the concave portion is formed.
According to claim 10,
The display panel includes a plurality of pixel areas, and an edge of the concave portion corresponds to a boundary between the pixel areas.
According to claim 10,
The display panel is an organic light emitting diode panel, and an edge of the concave portion corresponds to a bank covering an edge of the first electrode of the organic light emitting diode.
According to claim 11,
The step compensation layer forms a flat surface with the back plate.
According to claim 10,
The foldable display device of claim 1 , wherein the concave portion is positioned on an outer surface of the back plate, and the foldable display device is folded toward the display panel.
According to claim 10,
The foldable display device of claim 1 , wherein the concave portion is positioned on an inner surface of the back plate, and the foldable display device is folded toward the back plate.
According to claim 1,
The folding area is divided into an edge portion and a central portion along a folding direction, and the opening pattern is spaced apart from the edge portion by a first distance along the folding direction and is smaller than the first distance from the central portion along the folding direction. A foldable display that is separated by the distance.
According to claim 1,
A foldable display device in which a distance between the opening patterns decreases from an edge to a center in a folding direction.
According to claim 1,
The folding area is divided into an edge portion and a center portion along a folding direction, and the opening pattern has a first width along the folding direction at the edge portion and a second width greater than the first width along the folding direction at the center portion. A foldable display having a
According to claim 1,
The foldable display device of claim 1 , wherein a size of the opening pattern increases from an edge to a center in a folding direction. a display panel;
a back plate located on one surface of the display panel and divided into a folding area and an unfolding area on both sides of the folding area, and having two or more opening patterns spaced apart from each other in the folding area;
A step compensation layer provided on at least one surface of the back plate to cover the folding area.
A foldable display device including a.
a display panel;
a back plate located on one surface of the display panel and divided into a folding area and an unfolding area on both sides of the folding area, and having two or more opening patterns spaced apart from each other in the folding area;
The foldable display device of claim 1 , wherein the back plate is attached to the display panel through an adhesive layer.

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