KR20170072973A - Optical cleared adhesive and foldable display device including the same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foldable display device, and more particularly to an optical adhesive layer for a display device having improved durability and a display device including the same.
A feature of the present invention is to define an optical adhesive layer interposed between a cover window and a touch panel and between an OLED panel and a back plate so that the cover window, the OLED panel and the back plate are integrally bonded and modularized into a folded area and a non- , The folded region has a low modulus value, and the unfolded region has a high modulus value.
As a result, the durability of the optical adhesive layer itself is improved, durability of the display device itself is improved, and plastic deformation of the display device can be prevented.
Therefore, it is possible to prevent the folding and unfolding of the foldable display device from being restricted, and also to prevent the occurrence of defective appearance, thereby preventing the problem of damage to the OLED panel or deterioration of display quality .

Description

TECHNICAL FIELD [0001] The present invention relates to an optical adhesive layer for a display device,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foldable display device, and more particularly to an optical adhesive layer for a display device having improved durability and a display device including the same.

2. Description of the Related Art [0002] In recent years, as the society has become a full-fledged information age, a display field for processing and displaying a large amount of information has rapidly developed, and a variety of flat display devices have been developed Be in the spotlight.

Specific examples of such a flat panel display device include a liquid crystal display device (LCD), a plasma display panel (PDP), a field emission display (FED) Devices such as an electroluminescence display device (ELD) and an organic light emitting diode (OLED). These flat panel display devices have excellent performance in reducing the thickness, weight, and power consumption of a conventional cathode ray tube : CRT).

On the other hand, such a flat panel display uses a glass substrate to withstand the high heat generated during the manufacturing process, and thus has a limitation in providing light weight, thinness, and flexibility.

Therefore, a flexible display device which is manufactured so as to be able to maintain the display performance even if it is bent like paper by using a flexible material such as plastic instead of the conventional glass substrate having no flexibility is rapidly emerging as a next generation flat panel display device.

The flexible display device utilizes a non-glass plastic thin film transistor substrate to provide a durable, unbreakable, bendable, bendable, rollable, Foldable, etc. Such a flexible display device has advantages of space utilization, interior and design, and can have various application fields.

In recent years, in order to realize large size, light weight, small size, and large size, a foldable display device capable of being folded in a folded state and displaying an image in an unfolded state has been actively studied.

The folder-type display device can be applied not only to mobile devices such as a mobile phone, an ultra mobile PC, an electronic book, and an electronic newspaper, but also to various fields such as a TV and a monitor.

Such a foldable display device includes a display panel for largely implementing an image, a back plate for supporting the display panel at a lower portion of the display panel, and a cover window disposed in front of the display panel for protecting the display panel. and a cover window.

Here, an optical adhesive layer is interposed between the display panel and the cover window, and between the display panel and the back plate, and the display panel, the cover window and the back plate are integrally bonded and modularized with each other.

At this time, the optical adhesive layer applied to the display device of the foldable type is formed of OCA (Optical Cleared Adhesive). When the optical adhesive layer has a low modulus, the optical adhesive layer is limited in the folding and spreading of the display device Although it is not known, the recovery characteristic of the display device of the present invention is insufficient, resulting in plastic deformation of the display device as shown in Fig. 1A.

Plastic deformation of the display device of the foldable display is restricted in the folding and spreading, and also causes appearance defects, resulting in deterioration of the display quality of the display panel.

In addition, when the optical adhesive layer has a high modulus, restrictions are imposed on the folding and unfolding of the display device of the foldable type. As a result, bending stress is generated, and as shown in FIG. 1B, .

This results in damage to the display panel.

SUMMARY OF THE INVENTION It is a first object of the present invention to provide a foldable display device having no limitations in folding and unfolding and having improved durability.

A second object of the present invention is to prevent deterioration of the display quality of the display panel and to prevent the display panel from being damaged.

In order to achieve the above object, the present invention provides a display device comprising a display panel, a cover window positioned in front of the display panel, a back plate positioned behind the display panel, And an optical adhesive layer interposed between the display panel and the back plate, wherein the optical adhesive layer has a first modulus value at a central folding region, and a non-folding region located at both sides of the folding region, And a second modulus value larger than the first modulus value.

As described above, according to the present invention, an optical adhesive layer which is interposed between the cover window and the touch panel, and between the OLED panel and the back plate to integrally adhere and modulate the cover window, the OLED panel and the back plate, The durability of the optical adhesive layer itself is improved by dividing it into a folded region and a non-folded region corresponding to the folded region and the non-folded region, forming the folded region to have a low modulus value and the unfolded region to have a high modulus value .

As a result, the durability of the display device itself can be improved, and plastic deformation of the display device can be prevented.

Therefore, it is possible to prevent the folding and unfolding of the foldable display device from being restricted, and also to prevent the occurrence of defective appearance, thereby preventing a problem that the OLED panel is damaged or the display quality is deteriorated There is an effect that can be.

Further, the modulus of the folded region can be maximized by the low modulus value of the folded region, and the modulus characteristic is gradually changed from the outside of the unfolded region toward the folded region, The boundary is blurred, so that the visibility according to the material characteristics of the folded region and the non-folded region is not generated even though the modulus characteristic differs depending on the folded region and the non-folded region.

1A is a photograph showing a plastic deformation problem of a back plate;
1B is a photograph showing the lifting phenomenon of the cover window.
2 is a schematic view schematically showing a folderable display device according to an embodiment of the present invention;
3 is a cross-sectional view schematically showing the display panel of Fig. 2;
4A to 4C are schematic views schematically showing a manufacturing process of an optical adhesive layer according to an embodiment of the present invention.
5A to 5B are simulation results of measuring the plastic deformation of the display device of the present invention.

The present invention relates to a display device comprising a display panel, a cover window disposed in front of the display panel, a back plate positioned behind the display panel, and a back plate disposed between the display panel and the cover window, Wherein the optical adhesive layer has a first modulus value at the central folding region and a non-folding region at both sides of the first folding region having a second modulus value greater than the first modulus of elasticity Thereby providing a foldable display device.

In this case, the first modulus value is 10 ³ to 10 ⁴ Pa, the second modulus value is 10 ⁷ to 10 ⁸ Pa, and the density (density) of the optical adhesive layer itself gradually increases from the non- ) Is improved.

The present invention also relates to an optical fiber comprising a folded region having a first modulus value at the center and a non-folded region positioned at both sides of the folded region and having a second modulus value greater than the first modulus value, And the non-folded area are made of the same material.

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

FIG. 2 is a schematic view schematically showing a foldable display device according to an embodiment of the present invention, and FIG. 3 is a cross-sectional view schematically showing the display panel of FIG.

As shown in the figure, the display device 100 includes a display panel 110 for realizing an image, a touch panel 120 for forming a touch sensor (not shown), and a back plate 120 for supporting the display panel 110. [ a back plate 130, and a cover window 140 for protecting the display panel 110.

For the sake of convenience of description, if the direction of the drawing is defined, the back plate 130 is positioned at the back of the display panel 110, assuming that the display surface of the display panel 110 faces forward, The cover window 140 is located in front of the cover window 140.

The touch panel 120 is positioned between the display panel 110 and the cover window 140.

Here, the display panel 110 may be a liquid crystal display device (LCD), a plasma display panel (PDP), a field emission display (FED) Electroluminescence Display Device (ELD), and Organic Light Emitting Diodes (OLED). It is possible to use OLED, which is a representative of a flexible display device capable of maintaining display performance even when bent like paper desirable.

The OLED is a self-luminous element and can be lightweight and thin because a backlight used in a liquid crystal display device which is a non-luminous element is not required.

In addition, it has a better viewing angle and contrast ratio than liquid crystal display devices, is advantageous in terms of power consumption, can be driven by DC low voltage, has a fast response speed, is resistant to external impacts due to its solid internal components, It has advantages.

Particularly, since the manufacturing process is simple, it is advantageous in that the production cost can be saved more than the conventional liquid crystal display device.

The display panel 110 including the OLED is encapsulated with a protective film 102 on a substrate 101 on which a driving thin film transistor DTr and a light emitting diode E are formed.

Hereinafter, a display panel 110 (hereinafter referred to as an OLED panel) comprising an OLED will be described in detail with reference to FIGS. 2 and 3. FIG.

A semiconductor layer 104 is formed on the pixel region P on the substrate 101. The semiconductor layer 104 is made of silicon and has a central portion formed on both sides of the active region 104a and the active region 104a, Doped source and drain regions 104b and 104c.

A gate insulating layer 105 is formed on the semiconductor layer 104.

On the gate insulating film 105, gate electrodes 107 corresponding to the active regions 104a of the semiconductor layer 104 and gate wirings extending in one direction, though not shown in the figure, are formed.

A first interlayer insulating film 106a and a gate insulating film 105 under the first interlayer insulating film 106a are formed on the entire upper surface of the gate electrode 107 and the gate wiring (not shown) And first and second semiconductor layer contact holes 109 exposing the source and drain regions 104b and 104c, respectively, located on both sides of the semiconductor layer 104a.

Next, on the first interlayer insulating film 106a including the first and second semiconductor layer contact holes 109, source and drain regions (the first and second semiconductor layer contact holes 109, Source and drain electrodes 108a and 108b which are in contact with the source and drain electrodes 104a and 104b and 104c are formed.

The second interlayer insulating film 106b having the drain contact hole 112 exposing the drain electrode 108b over the first interlayer insulating film 106a exposed between the source and drain electrodes 108a and 108b and the two electrodes 108a and 108b, An insulating film 106b is formed.

At this time, the semiconductor layer 104 including the source and drain electrodes 108a and 108b and the source and drain regions 104b and 104c contacting the electrodes 108a and 108b and the gate insulating film 104 formed on the semiconductor layer 104 The gate electrode 105 and the gate electrode 107 constitute a driving thin film transistor DTr.

On the other hand, although not shown in the figure, data lines (not shown) for defining the pixel regions P intersect the gate lines (not shown) are formed. The switching thin film transistor (not shown) has the same structure as the driving thin film transistor DTr and is connected to the driving thin film transistor DTr.

In the drawings, the switching thin film transistor (not shown) and the driving thin film transistor DTr are shown as an example of a co-planar type in which the semiconductor layer 104 is a polysilicon semiconductor layer. As a variation thereof, And a bottom gate type of impurity amorphous silicon.

In addition, a portion of the second interlayer insulating film 106b, which substantially displays an image, has a relatively high work function value, for example, as a constituent element of the anode (anode) One electrode 111 is formed.

The first electrode 111 is connected to the drain electrode 108b of the driving thin film transistor DTr

The first electrode 111 is formed for each pixel region P and a bank 119 is located between the first electrodes 111 formed for each pixel region P. [

That is, the first electrode 111 is formed in a structure in which the bank 119 is divided into the pixel regions P with the boundary portion for each pixel region P being separated.

An organic light emitting layer 113 is formed on the first electrode 111.

Here, the organic light emitting layer 113 may be a single layer made of a light emitting material. In order to increase the light emitting efficiency, a hole injection layer, a hole transport layer, an emitting material layer, An electron transport layer, and an electron injection layer.

In general, the organic light emitting layer 113 displays red (R), green (G), and blue (B) colors. And organic materials 113a, 113b, and 113c that emit light of a different color (B) are used in a pattern.

A second electrode 115, which forms a cathode, is formed on the entire surface of the organic light emitting layer 113.

At this time, the second electrode 115 has a bilayer structure and includes a semitransparent metal film in which a metal material having a low work function is thinly deposited. In this case, the second electrode 115 may be a two-layer structure in which a transparent conductive material is thickly deposited on the semitransparent metal film.

Therefore, the light emitted from the organic light emitting layer 113 is driven to the top emission type, which is emitted toward the second electrode 115.

Or the second electrode 115 may be an opaque metal film and the light emitted from the organic light emitting layer 113 may be driven to a bottom emission type that is emitted toward the first electrode 111. [

When a predetermined voltage is applied to the first electrode 111 and the second electrode 115 according to a selected color signal, the OLED panel 110 emits a positive voltage, which is injected from the first electrode 111, The excitons are transported to the organic light emitting layer 113 to form excitons. When the excitons are transited from the excited state to the ground state, light is emitted and emitted in the form of visible light.

At this time, the emitted light passes through the transparent second electrode 115 or the first electrode 111 and exits to the outside, so that the OLED panel 110 realizes an arbitrary image.

A protective film 102 in the form of a thin film is formed on the driving thin film transistor DTr and the light emitting diode E so that the OLED panel 101 is encapsulated through the protective film 102, At least two inorganic protective films 102a are laminated on the protective film 102 to prevent external oxygen and moisture from penetrating into the OLED panel 110. In this case, It is preferable that an organic protective film 102b for compensating the impact resistance of the inorganic protective film 102a is interposed.

On the other hand, the substrate 101 may be made of a thin polyimide in order to have a flexible property. The substrate 101 made of such a thin polyimide is not suitable for the process of forming a component such as the thin film transistor DTr Therefore, the process of forming the constituent elements such as the thin film transistor DTr proceeds in a state in which a substrate made of polyimide is attached to a carrier substrate such as a glass substrate. Thereafter, the OLED panel 110 can be obtained by separating the carrier substrate from the polyimide substrate.

The OLED panel 110 and the touch panel 120 are attached to each other through an adhesive layer (not shown) of the touch panel 110. [

Although not shown in detail, the touch panel 120 includes a first touch film (not shown) having a first touch electrode (not shown) and a second touch film (not shown) having a second touch electrode They are spaced apart from each other.

The first touch electrode (not shown) is deposited on the entire surface of the first touch film (not shown), and the first touch electrode (not shown) is formed of indium tin oxide (ITO) or indium- (IZO).

A second touch electrode (not shown) is formed on the second touch film (not shown) facing the first touch film (not shown) (AlNd), magnesium (Mg), gold (Au), silver (Ag) or the like.

The first and second touch electrodes (not shown) form a touch sensor (not shown).

Accordingly, when the upper portion of the first touch film (not shown) is brought into contact with a point by a predetermined input means such as a finger or a pen, a first touch electrode (not shown) formed on the first touch film A second touch electrode (not shown) formed on a two-touch film (not shown) is mutually energized, a voltage value changed by the resistance value at that position is read, and then the position coordinate can be found in accordance with the variation of the potential difference in the control device .

The OLED panel 110 attached to the touch panel 120 is integrally modulated through the cover window 140 and the back plate 130. The touch panel 120 is disposed in front of the OLED panel 110, And a cover window 140 for protecting the OLED panel 110 is attached through a first optical adhesive layer 150 and a back plate for supporting the OLED panel 110 is formed on the back surface of the OLED panel 110 130 are attached through the second optical adhesive layer 160.

Here, the first and second optical adhesive layers 150 and 160 are made of OCA (Optical Cleared Adhesive). The first and second optical adhesive layers 150 and 160 of the display device 100 according to the embodiment of the present invention, 160 are divided into a folded area and a non-folded area corresponding to the folded area and the unfolded area of the display device 100 so that the first and second optical adhesive layers 150 and 160 have a high modulus modulus value, and the folded region has a lower modulus value than the unfolded region.

That is, the first and second optical adhesive layers 150 and 160 are formed by folding the foldable display device 100 on both sides of the folded area corresponding to the folded area so that the foldable display device 100 has a curvature when folded, The folded region has a low modulus value of softness, and the unfolded region has a hard, high modulus value, and the first non-folded region has a high modulus value, And the second optical adhesive layers 150 and 160 have a greater stiffness than the unfolded area.

For example, the unfolded region of the first and second optical adhesive layers 150 and 160 may have a modulus value of 10 ⁷ to 10 ⁹ Pa, and the folded region may have a modulus value of 10 ³ to 10 ⁴ Pa.

As a result, the first and second optical adhesive layers 150 and 160 have the first and second optical adhesive layers 150 and 160 formed by mixing a high modulus value and a low modulus value, Accordingly, the durability of the display device 100 itself is improved.

Further, due to the low modulus value of the folded region, the optical adhesive layers 150 and 160 do not limit the folding and spreading of the display device 100, and in particular, the folded region is folded Can be maximized.

In addition, elastic modulus is increased by the high modulus value of the unfolded region, and the recovery characteristic is improved, so that plastic deformation of the display device 100 can be prevented.

Accordingly, it is possible to prevent a problem that the OLED panel 110 is damaged or the display quality is deteriorated.

The cover window 140 protects the OLED panel 110 and the touch panel 120 from external impact and transmits light emitted from the OLED panel 110 so that the image displayed on the OLED panel 110 is viewed from the outside. do.

The cover window 140 may be made of a polymeric material such as polymethylmethacrylate (PMMA), polycarbonate (PC), cycloolefin polymer (COP), polyethylene terephthalate terephthalate (PET), polyimide (PI), and polyaramid (PA).

The back plate 130 is attached to the back surface of the OLED panel 110 in order to support the OLED panel 110 because the substrate 101 of the OLED panel 110 is too thin and a metal material such as stainless steel But are not limited to, polymethyl methacrylate (PMMA), polycarbonate (PC), polyvinyl alcohol (PVA), acrylonitrile-butadiene-styrene (ABS) And may be made of a polymer such as polyethylene terephthalate (PET).

The foldable display 100 according to the exemplary embodiment of the present invention includes the cover window 140 and the touch panel 120 as well as the OLED panel 110 and the back plate 130. The folded area has a low modulus And the unfolded area is attached and integrated through the optical adhesive layers 150 and 160 having a high modulus value to improve the durability of the display device 100. In addition, It is possible to prevent the problem that the quality is lowered.

4A to 4C are schematic views schematically showing a manufacturing process of an optical adhesive layer according to an embodiment of the present invention.

First, as shown in FIG. 4A, the optical adhesive layers 150 and 160 are divided into a folded region and a non-folded region, and UV is irradiated from each of the non-folded regions located on both sides of the folded region.

At this time, the optical adhesive layers 150 and 160 may be formed of acrylate, epoxy, polyimide, vinyl, and the like, preferably OCA (Optical Cleared Adhesive).

These optical adhesive layers 150 and 160 are cured by UV.

In particular, as shown in FIG. 4B, when the UV is irradiated, the unbrawn region includes an optical adhesive layer 150, 160 (not shown) by UV curing, ) Is cured as its density increases.

The initiator may be Iracure # 184 or Ilukure # 819 from BASF.

4C, the density of the optical adhesive layers 150 and 160 itself increases toward the folded region from the outside of the unfolded region, as shown in FIG. 4C, when the UV is irradiated to the outside of the unfolded region of the optical adhesive layers 150 and 160 The unfolded region has a high modulus value, and the folded region has a lower modulus value than the unfolded region.

That is, the optical adhesive layers 150 and 160 according to the embodiment of the present invention are made of the same material in both the folded region and the non-folded region, but only the modulus characteristic is changed according to the folded region and the non-folded region.

Particularly, as the modulus characteristic gradually changes from the outside of the non-folded region toward the folded region, the boundary between the folded region and the non-folded region becomes ambiguous.

Thus, even if the modulus characteristic differs between the folded region and the non-folded region, the visibility according to the material characteristics of the folded region and the non-folded region is not generated.

In addition, since the optical adhesive layers 150 and 160 themselves have a high modulus characteristic and a low modulus, the durability of the optical adhesive layers 150 and 160 themselves is improved.

5A to 5B show simulation results of plastic deformation measurement of the display device.

Prior to the explanation, plastic deformation measurement of the display device of the foldable display (100 of Fig. 2) was performed after the foldable display device (100 of Fig. 2) was subjected to a folding and spreading test of 100 to 10,000.

FIG. 5A is a simulation result of measuring the plastic deformation of a typical display device of a foldable display, and it can be confirmed that a plastic deformation occurs in a general foldable display device corresponding to a folded area at the center.

Here, the waviness value of the general foldable display device of Fig. 5A is 0.28 mm for the plastic deformation, and the surface wave value is the amplitude of the convex portion having the lowest height from the convex portion projecting the highest from the measurement surface It is the average value of measured values.

It can be confirmed that the plastic deformation generated in the general folder display device is also visually displayed.

In contrast, the foldable display device 100 of FIG. 5B according to the embodiment of the present invention has less plastic deformation than the conventional foldable display device of FIG. 5A.

The surface waveform value for the plastic deformation of the foldable display device (100 in FIG. 2) according to the embodiment of the present invention is 0.05 mm, Respectively.

In addition, it can be confirmed that the plastic deformation generated in the folder-type display apparatus (100 in FIG. 2) according to the embodiment of the present invention is visibly displayed too small.

2) is defined by a folding region and a non-folding region, and the folding region is defined by a low modulus value as a non-folding region, By forming the folded region to have a high modulus value, it is possible to prevent plastic deformation of the display device (100 in Fig. 2) from occurring.

That is, since the optical adhesive layer (150, 160 in FIG. 4C) has both high and low modulus characteristics, the durability of the optical adhesive layer itself is improved.

Therefore, the durability of the display device of the foldable display (100 of FIG. 2) is improved, and plastic deformation of the display device of the foldable display (100 of FIG. 2) can be prevented from occurring.

2) of the cover window (140 in FIG. 2) and the touch panel (120 in FIG. 2) and the OLED panel (110 in FIG. 2) And an optical adhesive layer (not shown) interposed between the cover window (140 in FIG. 2) and the OLED panel (110 in FIG. 2) and the back plate (150, 160 in FIG. 4C) is defined as a folded area and a non-folded area corresponding to the folded area and the non-folded area of the display device (100 in FIG. 2), the folded area has a low modulus value, By forming the folded region to have a high modulus value, the durability of the optical adhesive layer (150, 160 in FIG. 4C) itself is improved.

Thus, the durability of the display device (100 of FIG. 2) itself is improved, and plastic deformation of the display device (100 of FIG. 2) can be prevented from occurring.

Therefore, it is possible to prevent the folding and unfolding of the foldable display device (100 in Fig. 2) from being restricted, and also to prevent occurrence of appearance defects, so that the OLED panel (110 in Fig. 2) It is possible to prevent a problem that the display quality is lowered.

Further, the folding in the folding region can be maximized by the low modulus value of the folding region of the optical adhesive layer (150, 160 in FIG. 4C), and the modulus characteristic is gradually changed from the outside of the non- The boundary between the folded region and the non-folded region is blurred, so that the visibility according to the material characteristics of the folded region and the non-folded region is not generated even though the modulus characteristic differs depending on the folded region and the non-folded region.

In the above description, the touch panel (120 in FIG. 2) is positioned above the OLED panel 110 (FIG. 2) in which the image is implemented in the display device (FIG. 2) , The touch panel (120 in Fig. 2) can be deleted.

The present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention.

110: display device
120: back plate
130: Touch panel
140: Cover window
150, 160: first and second optical adhesive layers

Claims (4)

A display panel;
A cover window positioned in front of the display panel;
A back plate positioned behind the display panel;
An optical adhesive layer interposed between the display panel and the cover window and between the display panel and the back plate,
Wherein the optical adhesive layer has a first modulus value at a center folding region and a non-folding region located at both sides of the folding region has a second modulus value greater than the first modulus.
The method according to claim 1,
Wherein the first modulus value is 10 ³ to 10 ⁴ Pa and the second modulus value is 10 ⁷ to 10 ⁸ Pa.
The method according to claim 1,
Wherein a density of the optical adhesive layer itself is gradually increased from the non-folded area toward the folded area.
A folded region having a first modulus value at the center;
A non-folded region having a second modulus value greater than the first modulus value, the non-folded region being located on both sides of the folded region,
Wherein the folded region and the non-folded region are made of the same material.

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