WO2018154888A1

WO2018154888A1 - Display device

Info

Publication number: WO2018154888A1
Application number: PCT/JP2017/041831
Authority: WO
Inventors: 太介鎌田; 安弘神保; 浩平横山; 越智　貴志; 通園田
Original assignee: 株式会社半導体エネルギー研究所; シャープ株式会社
Priority date: 2017-02-22
Filing date: 2017-11-21
Publication date: 2018-08-30
Also published as: JP2020064704A

Abstract

[Problem] To provide a display device having flexural resistance which can withstand repeated flexing in a small radius of curvature. [Solution] One mode of this invention is a display device comprising a first resin layer 11, a first inorganic layer 13a positioned above the first resin layer, an EL layer 13c positioned above the first inorganic layer, a second inorganic layer 23a positioned above the EL layer, and a second resin layer 21a positioned above the second inorganic layer. The first resin layer, the first inorganic layer, the EL layer, the second resin layer and the second inorganic layer are constituted so as to be able to bend, and when bending, the first inorganic layer and the second inorganic layer have respective distortion rates not exceeding 0.4%.

Description

Display device

The present invention relates to a display device.

In recent years, there has been a demand for high image quality for smartphone displays, and in particular, high definition, wide color gamut, and high brightness have been demanded. The trend of high definition is accelerating, and smartphones equipped with a liquid crystal display with a resolution of 4K (3840） x 2160) in 5.5 inches have been released, and the pixel density has reached 806ppi. It is expected that the flow of high definition will further accelerate in the future. As for the wide color gamut, B.T.2020 is attracting attention as a standard for 4k and 8k displays. By expanding the color gamut, it is possible to reproduce images that are directly viewed by the human eye. In addition, High Dynamic Range (HDR) has attracted attention for high brightness. By widening the brightness range, it is possible to reproduce daily light such as the glare of sunlight, which has the advantage of displaying images that give a more realistic feel. One of the displays that can meet such market demand is an OLED display. In addition to the above characteristics, the OLED display has a higher response speed than a liquid crystal display, can be driven at high frequency, and has good moving image characteristics. Furthermore, since it is a self-luminous device, the black level is low and a high contrast can be achieved, so that an image with a clear outline can be displayed. As described above, since the OLED display has many features, it is rapidly developed as a next-generation display. In fact, many set makers are considering installing OLED displays on smartphones, and capital investment is progressing.

In addition, the OLED display has a feature that it can be easily made flexible. In recent years, flexible OLED panels using flexible substrates have been adopted in smartphones and smart watches and shipped as products. Since a flexible film is used for the support substrate, it can be made lighter and thinner than conventional displays using glass substrates. In addition, since a flexible substrate is used, it is possible to bend it, which was impossible with a panel made of a conventional glass substrate. Therefore, new designs and functions can be considered and new values can be proposed. For example, OLED panels whose entire screen is gently curved and panels whose edges on both sides of the panel are curved are on the market.

In addition, a method of using the flexible panel that can be bent one step further is being studied, and it can be applied to various uses such as a display that can be folded compactly and a display that is rolled up and rolled up. We are promoting. In fact, many reports have been reported at academic societies regarding displays that can be folded and rolled up, and are expected as market needs. However, no manufacturer has commercialized a display that can be folded, and each company is developing to increase bending resistance.

Many manufacturers are developing products that can be folded, and it is important to improve bending resistance such as repeated bending tests. In order to increase bending resistance, structural design and neutral surface control that relieve stress applied to each layer of the flexible panel are important. For example, the following papers have been published to examine the structure of the display.
(1) Information display January / February 2015 VOL. 31, NO. 1 P.M. 12-P16
(2) Information display March / April 2015 VOL. 32, NO. 2P. 18-P23

In these papers, a structure for relieving the stress applied when the display is bent is proposed using structural calculation software. However, the above structural calculation is a calculation that assumes one-time bending, and only proposes a structure for relieving the stress applied to the constituent members and films. In addition, only the bending resistance improvement assuming internal bending in which the display surface is bent inward is discussed.

Therefore, a method of controlling the neutral plane has been proposed as a method for manufacturing a display that simultaneously satisfies both the inner bending and the outer bending resistance (see, for example, Patent Document 1). In this method, a structural design capable of withstanding both the internal bending and the external bending required for a display to be folded is important.

Here, considering the actual use of the display that can be folded, it is important to design a structure that can withstand multiple bends rather than one bend. When assuming that the product life is 3 years and the product is bent 50 times or more or 100 times or more per day, it is required to withstand a repeated bending test of 50,000 times or more or 100,000 times or more. In particular, the inorganic layer is a brittle material in addition to having a high Young's modulus, and as a result, high stress continues to be applied by repeated bending tests of 50,000 times or more or 100,000 times or more, resulting in film breakage due to accumulation of bending fatigue. I think that. It is very important to design a structure so as not to cause film breakage in order to commercialize a foldable display.

JP2015-228367A

Since the inorganic layer tends to be weak against tensile stress, the inorganic layer in the flexible panel is easily broken when the flexible panel is bent.

An object of one embodiment of the present invention is to provide a display device having bending resistance that can withstand repeated bending with a small radius of curvature.

One embodiment of the present invention includes a first resin layer, a first inorganic layer located on the first resin layer, an EL layer located on the first inorganic layer, and the EL layer. A second inorganic layer positioned and a second resin layer positioned on the second inorganic layer, wherein the first resin layer, the first inorganic layer, the EL layer, the first layer The second resin layer and the second inorganic layer are configured to be foldable, and a strain rate applied to each of the first inorganic layer and the second inorganic layer at the time of the bending is greater than 0 and 0. It is a display device characterized by being 4% or less.

According to one embodiment of the present invention, when the display device is bent, the strain rate applied to each of the first inorganic layer and the second inorganic layer, which is weak against tensile stress, is set to 0.4% or less. The breakage of the first and second inorganic layers can be suppressed. As a result, a display device having bending resistance that can withstand repeated bending with a small radius of curvature can be realized.

In one embodiment of the present invention, each of the first inorganic layer and the second inorganic layer may include a metal oxide, a metal nitride, a compound of Si and O, or a compound of Si and N.

In one embodiment of the present invention, a first hard coat layer may be located on the second resin layer.

In one embodiment of the present invention, the third resin layer positioned between the second inorganic layer and the second resin layer, the third resin layer, and the second resin layer It is good to have the 2nd hard-coat layer located in between.

In one embodiment of the present invention, a third hard coat layer may be located under the first resin layer.

In one embodiment of the present invention, the fourth resin layer positioned between the first inorganic layer and the first resin layer, the fourth resin layer, and the first resin layer And a fourth hard coat layer positioned therebetween.

Further, in one embodiment of the present invention, a fifth resin layer may be located between the EL layer and the second inorganic layer.

In one embodiment of the present invention, a color filter may be positioned between the EL layer and the second inorganic layer.

In one embodiment of the present invention, the average thickness of the fifth resin layer is preferably 9 μm or less.

In one embodiment of the present invention, the first resin layer, the first inorganic layer, and the first inorganic layer so that a strain rate of 0.4% is applied to each of the first inorganic layer and the second inorganic layer. In the case where a test of repeatedly bending the EL layer, the second resin layer, and the second inorganic layer 50,000 times is performed, it is preferable that display defects do not occur.

By applying one embodiment of the present invention, a display device having bending resistance that can withstand repeated bending with a small radius of curvature can be provided.

FIG. 4A is a cross-sectional view schematically illustrating a display device according to one embodiment of the present invention, and FIG. 4B is a cross-sectional view schematically illustrating the display device according to one embodiment of the present invention. FIG. 4A is a cross-sectional view schematically illustrating a display device according to one embodiment of the present invention, and FIG. 4B is a cross-sectional view schematically illustrating the display device according to one embodiment of the present invention. 1 is a cross-sectional view schematically illustrating a display device (flexible panel) according to one embodiment of the present invention. Sectional drawing which shows a book type repeated bending tester typically. (A-1) is a photograph of a flexible panel before the test, (B-1) is a photograph immediately after the internal bending test of R = 5 mm, (C-1) is a photograph immediately after the storage test, and (A-2) is a test. A photograph of the previous flexible panel, (B-2) is a photograph immediately after the outer bending test of R = 5 mm, and (C-2) is a photograph immediately after the storage test. (A-1) is a photograph of a flexible panel before the test, (B-1) is a photograph immediately after the internal bending test of R = 3 mm, (C-1) is a photograph immediately after the storage test, and (A-2) is a test. A photograph of the previous flexible panel, (B-2) is a photograph immediately after the outer bending test of R = 3 mm, and (C-2) is a photograph immediately after the storage test. (A-1) is a photograph of a flexible panel before the test, (B-1) is a photograph immediately after the internal bending test of R = 2 mm, (C-1) is a photograph immediately after the storage test, and (A-2) is a test. A photograph of the previous flexible panel, (B-2) is a photograph immediately after the outer bending test with R = 2 mm. (A) is sectional drawing which shows typically the state before bending the flexible panel 1, (B) is sectional drawing which shows the state which bent the flexible panel 1 of (A). (A) is sectional drawing which shows the example in which the neutral surface NP approaches inside, and sectional drawing which shows the example in which an inorganic layer moves away from the neutral surface NP. Sectional drawing which shows the model used for the outside bending simulation. Sectional drawing which shows the laminated structure model of the flexible panel used for the outside bending simulation. (A) thru | or (C) is a figure which shows the stress distribution by simulation when the curvature radius of an external bending is R = 2mm, and the film thickness of the laminated film 32 is 13 micrometers. The figure which shows the result of having calculated the position of the neutral plane when it bends with the calculation model of FIG. Sectional drawing which is a laminated structure of the flexible panel used for the outside bending simulation, and shows the model which changes the film thickness of the laminated film 32. FIG. The figure which shows the result of having calculated the relationship between the film thickness 32a of the laminated film shown in FIG. 14, and the bending stress which arises in the CF side inorganic layer. STEM image of a cross section of a flexible panel subjected to repeated bending tests. The figure which shows nine points (P1 thru | or P9) which measure the thickness of the resin layer of the display area of a flexible panel. (A-1) is a photograph of the flexible panel before the test, (A-2) is a photograph immediately after the external bending test of R = 2 mm and 75,000 times, (A-3) is a photograph immediately after the storage test, B-1) is a photograph of the flexible panel before the test, (B-2) is a photograph immediately after the internal bending test of R = 2 mm and 100,000 times, and (B-3) is a photograph immediately after the storage test. The graph which reflected the repeated bending test result of Table 2 in FIG. (A) is a perspective view which shows the state which bent the flexible panel 1, (B) is sectional drawing which shows the state before bending the flexible panel 1. FIG. The figure for demonstrating how to obtain | require a curvature radius. The figure which compared the distortion rate (calculation) by the simulation of bending with the fracture rate (measurement).

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that modes and details can be variously changed without departing from the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited to the description of the embodiments below.

[Embodiment 1]
FIG. 1A is a cross-sectional view schematically illustrating a display device according to one embodiment of the present invention.
This display device (also referred to as a flexible panel) includes at least a resin layer 11 (also referred to as a first resin layer) that is a film, and a moisture-proof layer 13a (also referred to as a first inorganic layer) formed on the resin layer 11. The EL layer 13c formed on the moisture-proof layer 13a, the moisture-proof layer 23a (also referred to as second inorganic layer) formed on the EL layer 13c, and the resin layer 21a (second layer) formed on the moisture-proof layer 23a It is also called a resin layer. This will be described in detail below.

The display device illustrated in FIG. 1A includes a resin layer 11, and an adhesive resin layer 12 b (also referred to as a fourth resin layer) is formed over the resin layer 11. A moisture-proof layer 13a is formed on the adhesive resin layer 12b, and a layer 13b such as an FET (Field effector transistor) is formed on the moisture-proof layer 13a. An EL layer 13c is formed on the layer 13b such as an FET. A moisture-proof layer 23a is formed on the upper surface of the EL layer 13c, the side surfaces of the EL layer 13c and the layer 13b such as an FET, and the moisture-proof layer 13a. That is, the EL layer 13c and the FET layer 13b are covered with the moisture-

proof layers

13a and 23a, so that moisture can be prevented from entering the EL layer 13c and the FET layer 13b.

Further, an adhesive resin layer 22b (also referred to as a third resin layer) is formed on the moisture-proof layer 23a. That is, the resin layer 11 is bonded to the moisture-proof layer 13a by the adhesive resin layer 12b, and the moisture-proof layer 23a is bonded to the resin layer 21a by the adhesive resin layer 22b.

A hard coat layer 21b (also referred to as a first hard coat layer) is formed on the resin layer 21a. The resin layer 21a and the hard coat layer 21b are referred to as a film 21. Each of the moisture-proof layer 13a (first inorganic layer) and the moisture-proof layer 23a (second inorganic layer) preferably contains a metal oxide, a metal nitride, a compound of Si and O, or a compound of Si and N.

The display device is configured so that it can be bent. When the display device in FIG. 1A is bent, the strain rate applied to each of the moisture-proof layer 13a and the moisture-proof layer 23a is greater than 0 and 0.4% or less (preferably 0.27% or less).

In other words, the curvature radius when the display device is bent so that the strain rate applied to each of the moisture-proof layer 13a and the moisture-proof layer 23a is greater than 0 and 0.4% or less (preferably 0.27% or less). The material and thickness of each of the resin layer 11, adhesive resin layer 12b, moisture-proof layer 13a, FET layer 13b, EL layer 13c, moisture-proof layer 23a, adhesive resin layer 22b, resin layer 21a, and hard coat layer 21b of this display device Sato should be decided.

According to the present embodiment, when the display device is bent, the strain rate applied to each of the moisture-proof layer 13a as the first inorganic layer and the moisture-proof layer 23a as the second inorganic layer is greater than 0 and equal to or less than 0.4% ( Preferably it is 0.27% or less. In other words, by setting the strain applied to the inorganic layer that is weak against the tensile stress to 0.4% or less (preferably 0.27% or less), breakage of the inorganic layer in the flexible panel can be suppressed. As a result, it is possible to realize a display device having bending resistance that can withstand repeated bending with a small radius of curvature.

[Embodiment 2]
FIG. 1B is a cross-sectional view schematically illustrating a display device according to one embodiment of the present invention, in which the same portions as those in FIG.

1B includes a solid sealing resin 31 (also referred to as a fifth resin layer) and a hard coat layer 21c (also referred to as a second hard coat layer) in the display device illustrated in FIG. It has been added. This will be described in detail below.

1B has a resin layer 11 (first resin layer), and an adhesive resin layer 12 b (fourth resin layer) is formed on the resin layer 11. A moisture-proof layer 13a (first inorganic layer) is formed on the adhesive resin layer 12b. That is, the resin layer 11 is bonded to the moisture-proof layer 13a by the adhesive resin layer 12b.

Further, a layer 13b such as an FET is formed on the moisture-proof layer 13a. An EL layer 13c is formed on the layer 13b such as an FET. A solid sealing resin layer 31 is formed on the EL layer 13c, the FET layer 13b, and the moisture-proof layer 13a. That is, the EL layer 13 c and the layer 13 b such as an FET are sealed with the solid sealing resin layer 31. A moisture-proof layer 23a (second inorganic layer) is formed on the solid sealing resin layer 31. That is, the EL layer 13c and the FET layer 13b are covered with the moisture-

proof layers

The adhesive resin layer 22b is formed on the moisture-proof layer 23a, and the hard coat layer 21c is formed on the adhesive resin layer 22b. A resin layer 21a (second resin layer) is formed on the hard coat layer 21c, and a hard coat layer 21b (first hard coat layer) is formed on the resin layer 21a. The hard coat layer 21c, the resin layer 21a, and the hard coat layer 21b are referred to as a film 21. That is, the moisture-proof layer 23a is bonded to the hard coat layer 21c by the adhesive resin layer 22b.

As in the first embodiment, the display device is configured to be bent. When the display device in FIG. 1B is bent, the strain rate applied to each of the moisture-proof layer 13a and the moisture-proof layer 23a is greater than 0 and 0.4% or less (preferably 0.27% or less).

Also in this embodiment, the same effect as in the first embodiment can be obtained.

Further, the average thickness of the solid sealing resin 31 (fifth resin layer) is preferably 9 μm or less. Thereby, the thickness of the display device can be further reduced. As a result, when the display device is bent, the strain rate applied to each of the moisture-proof layer 13a and the moisture-proof layer 23a can be further reduced, and the breakage of the inorganic layer in the display device can be further suppressed.

[Embodiment 3]
FIG. 2A is a cross-sectional view schematically illustrating a display device according to one embodiment of the present invention. The same portions as those in FIG. 1B are denoted by the same reference numerals, and only different portions will be described.

2A is a display device in which a color filter 23b is added to the display device shown in FIG. Specifically, the color filter 23b is located between the EL layer 13c and the moisture-proof layer 23a, and the solid sealing resin 31 is disposed between the color filter 23b and the EL layer 13c.

Also in this embodiment, the same effect as in the second embodiment can be obtained.

[Embodiment 4]
FIG. 2B is a cross-sectional view schematically illustrating a display device according to one embodiment of the present invention. The same portions as those in FIG. 2A are denoted by the same reference numerals, and only different portions will be described.

2 (B) is obtained by removing the hard coat layer 21c from the display device shown in FIG. 2 (A). Specifically, the adhesive resin layer 22b is formed on the moisture-proof layer 23a, and the resin layer 21a is formed on the adhesive resin layer 22b. A hard coat layer 21b is formed on the resin layer 21a. The hard coat layer 21b and the resin layer 21a are referred to as a film 21. That is, the moisture-proof layer 23a is bonded to the resin layer 21a by the adhesive resin layer 22b.

Also in this embodiment, the same effect as in the third embodiment can be obtained.

[Embodiment 5]
FIG. 3 is a cross-sectional view schematically illustrating a display device according to one embodiment of the present invention. The same portions as those in FIG. 2A are denoted by the same reference numerals, and only different portions will be described.

The display device of FIG. 3 is obtained by adding hard coat layers 11b and 11c to the display device shown in FIG. Specifically, a resin layer 11a (first resin layer) is formed on the hard coat layer 11b (also referred to as a third hard coat layer), and the hard coat layer 11c (fourth resin layer) is formed on the resin layer 11a. (Also referred to as a hard coat layer). The hard coat layer 11c, the resin layer 11a, and the hard coat layer 11b are referred to as a film 11. The hard coat layer 11c is bonded to the moisture-proof layer 13a by the adhesive resin layer 12b.

Note that Embodiments 1 to 5 can be implemented in combination with each other as appropriate.

≪Repeated bending test≫
In order to test whether or not the flexible panel, which is a display device according to the example, has bending resistance capable of withstanding bending with a small radius of curvature, a repeated bending test was performed. The flexible panel of Example 5 shown in FIG. 3 was used for the flexible panel of the Example. The flexible panel has a laminated structure of a film 11 having a thickness of 23 μm, a resin 12b having a thickness of 10 μm, a moisture-proof layer (inorganic layer) 13a having a thickness of 2 μm, a solid sealing resin layer (resin layer) 31 having a thickness of 13 μm, and a thickness. This is a structure in which a moisture-proof layer (inorganic layer) 23 a having a thickness of 1 μm, an adhesive resin layer (resin layer) 22 b having a thickness of 10 μm, and a film 21 having a thickness of 23 μm are sequentially laminated. The test method is as follows.

(Repeated bending test method)
The repeated bending test was performed using a book-type repeated bending tester shown in FIG. This book-type repeated bending tester has a first stage 4, and the first stage 4 is connected to a second stage 5 by a rotating shaft 6. The rotation shaft 6 is connected to a rotation drive mechanism (not shown), and the rotation drive mechanism is configured to be capable of rotating 180 ° as indicated by an arrow. The flexible panel 1 is fixed on the first and

second stages

4 and 5, and the second stage 5 is rotated by 180 ° about the rotation shaft 6, whereby the flexible panel 1 is bent at the curvature radius R. Next, the second stage 5 is rotated 180 ° in the reverse direction about the rotation axis 6, whereby the bending of the flexible panel 1 is released and the flexible panel 1 is returned to a planar shape. By repeating this, a repeated bending test of the flexible panel 1 is performed. The speed of the repeated bending test is 2 seconds / time. The radius of curvature R can be adjusted from 1 mm to 5 mm at 1 mm intervals.

The repeated bending test includes an inner bending test and an outer bending test. The inner bend test is a test in which the display surface is bent inward when the flexible panel is bent, and the outer bend test is a test in which the display surface is bent outward when the flexible panel is bent.

In this test, the flexible panel of the example was subjected to an internal bending test and an external bending test with a radius of curvature R = 5 mm, 3 mm, and 2 mm, each with 100,000 repetitions.

(Repeated bending test results)
FIG. 5A-1 is a photograph of the display surface of the flexible panel before the test. FIG. 5 (B-1) is a photograph immediately after an internal bending test is performed on the flexible panel shown in FIG. 5 (A-1) with a radius of curvature R = 5 mm. It was done in the form of bending.

FIG. 5C-1 is a photograph immediately after a storage test in which the flexible panel subjected to the internal bending test shown in FIG. 5B-1 is exposed to an atmosphere of 65 ° C. and 95% humidity for 100 hours. It is.

As shown in FIGS. 5 (B-1) and 5 (C-1), no failure occurred in the flexible panel in the internal bending test of R = 5 mm.

Fig. 5 (A-2) is a photograph of the display surface of the flexible panel before the test. FIG. 5 (B-2) is a photograph immediately after an external bending test is performed on the flexible panel shown in FIG. 5 (A-2) with a radius of curvature R = 5 mm. It was done in the form of bending.

FIG. 5 (C-2) shows a photograph immediately after a storage test in which the flexible panel shown in FIG. 5 (B-2) was subjected to an external bending test in an atmosphere of 65 ° C. and 95% humidity for 100 hours. It is.

As shown in FIGS. 5 (B-2) and (C-2), no failure occurred in the flexible panel in the external bending test of R = 5 mm.

Fig. 6 (A-1) is a photograph of the display surface of the flexible panel before the test. FIG. 6 (B-1) is a photograph immediately after the internal bending test was performed on the flexible panel shown in FIG. 6 (A-1) with a radius of curvature R = 3 mm. It was done in the form of bending.

6C-1 is a photograph immediately after a storage test in which the flexible panel subjected to the internal bending test shown in FIG. 6B-1 is exposed to an atmosphere of 65 ° C. and 95% humidity for 100 hours. It is.

As shown in FIGS. 6 (B-1) and (C-1), in the internal bending test of R = 3 mm, no defect occurred in the flexible panel.

Fig. 6 (A-2) is a photograph of the display surface of the flexible panel before the test. FIG. 6 (B-2) is a photograph immediately after an external bending test is performed on the flexible panel shown in FIG. 6 (A-2) with a radius of curvature R = 3 mm. It was done in the form of bending.

FIG. 6C-2 is a photograph immediately after a storage test in which the flexible panel shown in FIG. 6B-2 is exposed to an atmosphere of 65 ° C. and 95% humidity for 100 hours. It is.

As shown in FIGS. 6 (B-2) and (C-2), no failure occurred in the flexible panel in the outer bending test of R = 3 mm.

Fig. 7 (A-1) is a photograph of the display surface of the flexible panel before the test. FIG. 7 (B-1) is a photograph immediately after the internal bending test is performed on the flexible panel shown in FIG. 7 (A-1) with a radius of curvature R = 2 mm. It was done in the form of bending.

FIG. 7C-1 is a photograph immediately after a storage test in which the flexible panel subjected to the internal bending test shown in FIG. 7B-1 is exposed to an atmosphere of 65 ° C. and 95% humidity for 100 hours. It is.

As shown in FIGS. 7 (B-1) and (C-1), no failure occurred in the flexible panel in the internal bending test of R = 2 mm.

Fig. 7 (A-2) is a photograph of the display surface of the flexible panel before the test. FIG. 7 (B-2) is a photograph immediately after an external bending test is performed on the flexible panel shown in FIG. 7 (A-2) with a radius of curvature R = 2 mm. It was done in the form of bending.

As shown in FIG. 7 (B-2), cracks occurred in the flexible panel in the outer bending test of R = 2 mm. Note that the flexible panel shown in FIG. 7B-2 was cracked, so a storage test was not performed by exposing it to an atmosphere of 65 ° C. and 95% humidity for 100 hours.

≪Bending to flexible panel due to bending≫
FIG. 8A is a cross-sectional view schematically showing a state before the flexible panel 1 is bent. The flexible panel 1 includes

films

11 and 21, and a layer 33 such as a resin layer, an inorganic layer, or an EL layer is disposed between the film 11 and the film 21.

FIG. 8B is a cross-sectional view showing a state where the flexible panel 1 of FIG. 8A is bent.
By bending, the outer side of the flexible panel 1 is stretched as indicated by

arrows

34a and 34b, so that tensile stress is generated, and the inner side of the flexible panel 1 is compressed as indicated by

arrows

35a and 35b, so that compressive stress is generated. Further, a neutral plane NP that does not expand or contract exists near the center of the flexible panel 1 in the thickness direction, specifically, at the position of the thickness T1 from the surface of the film 21. The stress applied to the neutral plane NP is zero. The tensile and compressive stress increases in proportion to the distance from the neutral plane NP. When the inorganic layer (moisture-proof layer) in the layer 33 is separated from the neutral plane NP, the stress applied to the inorganic layer increases. Since the inorganic layer is susceptible to tensile stress, the further away the inorganic layer from the neutral plane NP, the greater the tensile stress applied to the inorganic layer, and as a result, cracks occur in the inorganic layer. It is expected to lead to. Therefore, since the inorganic layer in the flexible panel is easily broken as the inorganic layer (moisture-proof layer) in the layer 33 is separated from the neutral plane NP, the flexible panel is considered to be weak in repeated bending tests.

There are two possible causes for the inorganic layer to move away from the neutral plane.
(1) If the laminated structure of the flexible panel is asymmetric, the stress balance due to bending is lost, and the neutral plane NP is shifted to either the outer side or the inner side. For example, as shown in FIG. 9A, the neutral surface NP is moved inward so that the neutral surface NP is positioned at a thickness T <b> 2 from the surface of the film 21.
(2) As shown in FIG. 9B, the thicker the resin layer (such as the sealing resin layer) near the neutral surface in the layer 33, the thicker the flexible panel 1 is. Therefore, the thickness of the flexible panel 1 on the outer side from the neutral surface NP is increased so that the neutral surface NP is positioned at the thickness T3 from the surface of the film 21, and the inorganic layer is easily moved away from the neutral surface NP.

≪Bending simulation≫
A flexible panel external bending simulation will be described.
10 is a cross-sectional view schematically illustrating a flexible panel according to one embodiment of the present invention, and is a diagram illustrating a flexible panel in which the display device in FIG. 3A is simplified for simulation.

(Simulation method and calculation results)
Simulation was performed using the heat transfer-structure coupled analysis software ANSYS Mechanical APDL. In order to simplify the calculation, a model shown in FIG. 10 was constructed in which an actual flexible panel was simplified using “two-dimensional”, “bending range of 0.5 mm only”, and “linear elastic region”.

10 has a film 11, and a resin 12 is formed on the film 11. An FET side inorganic layer 13 is formed on the resin layer 12, and a laminated film 32 in which an EL layer, a resin layer, and a CF (color filter) are sequentially laminated is formed on the FET side inorganic layer 13. A CF-side inorganic layer 23 is formed on the laminated film 32, and a resin layer 22 is formed on the CF-side inorganic layer 23. A film 21 is formed on the resin layer 22.

In order to reproduce the bending state by calculation, the model was set so that the top and bottom of the model were restrained as shown in FIG. External bending (panel display surface is outside) was expressed by applying downward force to both ends. Furthermore, in carrying out the simulation, the laminated structure shown in FIG. 11 was assumed for the laminated structure of the flexible panel. This laminated structure includes a film 11 having a thickness of 23 μm, a resin 12 having a thickness of 10 μm, an FET-side inorganic layer 13 having a thickness of 2 μm, a laminated film 32 having a thickness of 13 μm, a CF-side inorganic layer 23 having a thickness of 1 μm, and a thickness of 10 μm. The resin layer 22 and the film 21 having a thickness of 23 μm are sequentially laminated. The laminated film 32 has a structure in which an organic interlayer film, an EL layer, a resin layer, and CF are laminated in this order. In the calculation, the property values of each layer and the set values of the calculation conditions were used. Table 1 shows the setting values for the calculation conditions.

FIG. 12 shows the calculation result of the stress distribution when the structure model in FIG. 11 is bent outward with a radius of curvature R = 2 mm. FIG. 12A is a view showing a state where the flexible panel is bent by restraining the upper and lower sides of the flexible panel shown in FIG. 10 and applying a force to both ends of the surface of the film 21, and FIG. FIG. 13 is an enlarged view of a region surrounded by a broken line shown in FIG. As shown in FIG. 12C, in the gray scale, minus is compressive stress and plus is tensile stress. When the figure which expanded only the bending part of FIG. 12 (B) is seen, it turns out that the compressive stress has generate | occur | produced the bending inner side as a whole, and the tensile stress has generate | occur | produced on the bending outer side. It can also be seen that large bending stresses are generated particularly in the inorganic layers such as the FET-side inorganic layer 13 and the CF-side inorganic layer 23. This is because the inorganic layer has a larger Young's modulus than the organic layer.

The stress generated by bending is proportional to the Young's modulus and the distance from the neutral plane, and inversely proportional to the radius of curvature. The position of the neutral plane was calculated using the calculation model shown in FIG. The result is shown in FIG. Since the distance between the neutral surface 101 and the CF-side inorganic layer 23 is about 10 μm, and the distance between the neutral surface 101 and the FET-side inorganic layer 13 is about 6 μm, the distance between the neutral surface 101 and the inorganic layer is It is biased between the CF side and the FET side. The FET-side inorganic layer 13 is thicker than the CF-side inorganic layer 23 because it includes a gate insulating film and the like. Therefore, the neutral surface 101 is closer to the FET-side inorganic layer 13, and as a result, the CF-side inorganic layer 23 (moisture-proof layer) having a larger distance from the neutral surface 101 is considered to be easily cracked because of higher bending stress. . The calculation result of the neutral surface 101 tended to coincide with the experimental result (see FIG. 7) having low resistance to external bending.

Most of the defects observed in the repeated bending test of the flexible panel are due to the fracture of the CF-side inorganic layer (moisture-proof layer) 23 during external bending. Therefore, as shown in FIG. 14, the film thickness 32a of the laminated film 32 in which the organic interlayer film, the EL layer, the resin layer, and the CF are sequentially laminated is changed by changing the thickness of the resin layer in the laminated film 32, The stress generated in the CF side inorganic layer (moisture-proof layer) 23 at that time was calculated. This stress is a stress generated in the CF-side inorganic layer 23 depending on the thickness of the resin layer (sealing resin layer) in the laminated film 32. The film thickness 32 a of the laminated film 32 is a thickness obtained by adding a thickness of 2 μm corresponding to the total thickness of the organic interlayer film, the EL layer, and the CF to the thickness of the sealing resin layer. The structural model in FIG. 14 is merely an example used for calculation, and may be another structural model, for example, a structure in which CF is omitted (FIG. 1B). Further, a structure in which the resin layer and CF in the laminated film 32 are omitted, and the CF-side inorganic layer 23 is formed directly on the EL layer (FIG. 1A) may be used. In that case, it is necessary to discuss the distortion rate generated in the inorganic layer 23 formed directly on the EL layer.

The sum of the thicknesses of the organic interlayer film, the EL layer, and the CF in the laminated film 32 is set to 2 μm, and the thickness of the resin layer (sealing resin layer) is changed from 4 μm to 11 μm. FIG. 15 shows the result of calculating the relationship between the stresses generated in the CF-side inorganic layer 23 when the radius of curvature of the outer bend at 32a is R = 2, 3, 5 mm. In FIG. 15, the horizontal axis is the film thickness 32 a (μm) of the laminated film 32, and the vertical axis is the maximum stress (MPa) generated in the CF-side inorganic layer (moisture-proof layer) 23. For example, the thickness of the organic interlayer film is less than 1 μm, the thickness of CF is about 1 μm, and the thickness of the EL layer is sufficiently thinner than the organic interlayer film or CF, for example, about 0.3 μm. Therefore, the sum of these thicknesses was assumed to correspond to 2 μm.

15, it can be seen that the maximum bending stress generated in the CF-side inorganic layer 23 is linearly related to the film thickness (μm) of the laminated film. It can also be seen that the smaller the radius of curvature R, the more sensitive to changes in the thickness of the laminated film 32 and the greater the inclination.

≪Repeated bending test≫
(Measurement result of resin layer thickness of flexible panel of Example)
In order to confirm the consistency between the calculation results and the experimental results (pass / fail of the bending test), the thickness of the resin layer (sealing resin layer) of the flexible panel on which the repeated bending test is performed was investigated. The thickness of the resin layer was measured by cross-sectional STEM observation of the flexible panel. FIG. 16 shows an example of a cross-sectional STEM image. The film thickness measurement location 32b measured the distance between the moisture-proof layer 23 / CF (G) interface and the organic layer (resin layer) / inorganic layer 13 interface at three points, and the average value of the three points was the thickness of the resin layer. . With this method, the thickness of the resin layer at nine points (P1 to P9) in the display area of the flexible panel shown in FIG. 17 was measured. As a result, the average thickness of the nine resin layers in the panel display area was 9 μm ± 18%. ± 18% indicates that the thicknesses of the nine resin layers were all within the range of ± 18% of the average thickness.

(Repeated bending test method)
For the flexible panel manufactured under the same conditions as the flexible panel shown in FIG. 16, using the book-type repeated bending tester shown in FIG. 4, the curvature radius is R = 2 mm, the number of repetitions is 50,000 times, 75,000 times, 100,000 times. An outer bending test and an inner bending test were performed.

(Repeated bending test results)
FIG. 18A-1 is a photograph of the display surface of the flexible panel before the test. FIG. 18 (A-2) is a photograph immediately after an external bending test with a curvature radius of R = 2 mm and a repetition count of 75,000 times is performed on the flexible panel shown in FIG. 18 (A-1). This was done by bending the broken line in the center of the panel. As shown in FIG. 18A-2, a display defect occurred at the bent portion.

FIG. 18A-3 is a photograph immediately after a storage test in which the flexible panel subjected to the outer bending test shown in FIG. 18A-2 is exposed to an atmosphere at a temperature of 65 ° C. and a humidity of 95% for 100 hours. It is. As shown in FIG. 18A-3, display failure occurred at the bent portion. In the outer bending test with the radius of curvature R = 2 mm and the number of repetitions of 50,000 times, no display defect occurred immediately after the outer bending test and immediately after the storage test.

Fig. 18 (B-1) is a photograph of the display surface of the flexible panel before the test. FIG. 18 (B-2) is a photograph immediately after the internal bending test with the radius of curvature R = 2 mm and the number of repetitions of 100,000 times is performed on the flexible panel shown in FIG. 18 (B-1). It was done in the form of bending in the broken line frame of the part.

18B-3 shows a photograph immediately after a storage test in which the flexible panel subjected to the internal bending test shown in FIG. 18B-2 is exposed to an atmosphere of 65 ° C. and 95% humidity for 100 hours. It is.

As shown in FIGS. 18B-2 and B-3, display failure did not occur in the flexible panel in the internal bending test of R = 2 mm. In the internal bending test with the curvature radius R = 2 mm and the number of repetitions of 50,000 times and 75,000 times, no display defect occurred immediately after the internal bending test and immediately after the storage test.

Table 2 summarizes the results of repeated bending tests and resin layer thickness measurements for different thicknesses of the laminated film. When the thickness of the laminated film is 13 μm, the repeated bending test of 100,000 times can be cleared at the outer bending R = 3 mm and R = 5 mm (see FIGS. 5 and 6). On the other hand, when the thickness of the laminated film was in the range of about 8 μm to 9.5 μm (average 9 μm), the external bending test was cleared 50,000 times, but the external bending test was 75,000 times NG.

(Comparison between repeated bending test results and calculation results)
FIG. 19 shows a graph reflecting the repeated bending test results in Table 2 in FIG. That is, FIG. 19 is a diagram in which the repeated bending test results shown in Table 2 are reflected on the relationship (calculation results) between the film thickness 32a of the laminated film shown in FIG. 14 and the bending stress generated in the CF-side inorganic layer 23. In FIG. 19, the horizontal axis is the film thickness 32 a (μm) of the laminated film 32, and the vertical axis is the maximum stress (MPa) generated in the CF-side inorganic layer (moisture-proof layer) 23. In addition, the film thickness range 36 shown in FIG. 19 shows the dispersion after removing an abnormal value from the film thickness of the laminated film (the thickness of the sealing resin layer + 2 μm) measured in the display area of the flexible panel shown in FIG. It is the range shown.

Further, when the thickness of the laminated film shown in FIG. 19 is 13 μm and the outer bending is R = 3 mm and R = 5 mm, the repeated bending test of 100,000 times is cleared. In the outer bend R = 2 mm shown in FIG. 19, a greater stress is generated in the CF-side inorganic layer 23 at all film thicknesses than the outer bend R = 3 mm and R = 5 mm. For example, it is estimated that a stress of about 300 MPa is generated in a sample including a laminated film having a thickness of 13 μm that has cleared a repeated bending test of an outer bend R = 3 mm. Therefore, in order to clear the 100,000 times repeated bending test with the outer bending R = 2 mm, the film thickness 32a of the laminated film shown in FIG. 14 is 7 μm or less (preferably 6 μm or less so that the generated stress is about 300 MPa or less. ).

≪Calculation of distortion rate≫
The strain rate was calculated by inputting the physical property values of each layer of the flexible panel to the simulation of the finite element method and reproducing the panel bending. Here, the heat transfer-structure interaction analysis software “ANSYS Mechanical APDL” was used. In the simulation model, as shown in FIG. 20A, the cross section of the panel is cut along a plane orthogonal to the axis 102 for bending the flexible panel 1, and the laminated structure is expressed by the cross section of the panel shown in FIG. A two-dimensional model was used. FIG. 20A is a perspective view showing a state in which the flexible panel 1 is bent, and FIG. 20B is a panel sectional view before the flexible panel 1 is bent.

In the simulation model, not the entire panel, but only the area with a width of 0.5 mm. Only the linear elastic region was assumed and plastic deformation was not included in the calculation. The details of the simulation are described in the “Bending simulation” column.

In the simulation, the radius of curvature of the bending was controlled by the magnitude of the force applied to the left and right ends of the model. First, after carrying out a bending simulation by applying an arbitrary force, as shown in FIG. 21, the coordinates of the three points at both ends and the center of the model lower side after bending are calculated and obtained by the simulation software. The radius of the drawn arc was obtained. Specifically, the center point 103 existing at an equal distance from these three points was calculated using the solver function of the spreadsheet software Excel. The distance from the obtained center point 103 to each of the three points is the bending radius of curvature R.

In order to obtain the desired radius of curvature, the magnitude of the force applied to the left and right ends was adjusted, the simulation was performed to calculate the radius of curvature again, and this was repeated until the radius of curvature reached the target value.

When the load having the desired radius of curvature was found, the magnitude of the distortion generated in the model after calculation was displayed. The distortion rate ε is calculated by the following (Equation 1).
Distortion ε = λ (deformation amount) / L (original length) (Formula 1)

That is, since it is the inorganic layer that actually breaks when the panel is bent, the radius of curvature R of the inorganic layer is determined by the method shown in FIG. 21 while limiting the range from the inorganic layer to the inorganic layer in the model. The deformation amount λ of the inorganic layer was determined from the radius of curvature R. The original length L of the inorganic layer is a width of 0.5 mm, which is the object of the simulation model. The maximum distortion rate ε was calculated by substituting λ and L of the inorganic layer into the above (formula 1).

Specifically, as shown in Table 2, the CF-side inorganic layer (moisture-proof layer) 23 does not break even when a laminated panel 32 having a thickness of 9 μm is bent 50,000 times with a radius of curvature R = 2 mm. It was. Based on this result, the above-described method for calculating the distortion rate is used to simulate a new model with a thickness of the laminated film 32 of 9 μm, and the distortion rate of the CF-side inorganic layer (moisture-proof layer) 23 when R = 2 mm. Was calculated to be 0.40%. Therefore, if the laminated structure of the flexible panel or the radius of curvature is set so that the strain rate of the inorganic layer does not exceed 0.4%, it can withstand 50,000 bending tests.

Similarly, when calculating the distortion when the flexible panel is bent with a radius of curvature R = 3 mm and R = 5 mm in a model having a thickness of 9 μm, the distortion at the curvature radius R = 3 mm is 0.27. %, And the curvature at the radius of curvature R = 5 mm was 0.16%. In other words, if the flexural panel is bent with a radius of curvature R = 3 mm, the bending rate can withstand 100,000 bending tests if it does not exceed 0.27%.

Further, the measurement result of the fracture strain rate of the CF side inorganic layer was 0.95%. This result and the above result are shown in FIG. In FIG. 22, the distortion ratios of the curvature radii R = 2 mm, R = 3 mm, and R = 5 mm indicate the distortion ratio in the bending simulation. The ratio of tensile strength to fatigue limit in steel materials: 0.33 or more and 0.59 or less (edited by the Japan Society of Mechanical Engineers, from the practical handbook of machinery), the breaking strain rate of the inorganic layer is 0.33 or more and 0.59 or less The value multiplied by is considered the fatigue limit strain rate. Comparing the strain rate of the CF side inorganic layer (moisture-proof layer) at R = 2 mm and R = 3 mm obtained by bending simulation with the strain rate of the fatigue limit, the strain rate of R = 2 mm is the strain rate of the fatigue limit. Although included in the range, the distortion rate of R = 3 mm is a value below the lower limit, and the actual results of 50,000 repeated bending tests correspond to the results of R = 2 mm and 3 mm being OK. In view of the above, it is preferable to design the structure so that the strain rate of the inorganic layer is greater than 0 and 0.95% or less, preferably 0.4% or less, and more preferably 0.27% or less.

That is, even when a test is performed to repeatedly bend the flexible panel 50,000 times so that the CF-side inorganic layer (moisture-proof layer) 23 and the FET-side inorganic layer 13 each have a strain rate greater than 0 and 0.4%, display failure It can be said that does not occur.

DESCRIPTION OF SYMBOLS 1 Flexible panel 4 1st stage 5 2nd stage 6 Rotating shaft 11 Film, resin layer (1st resin layer)
11a Resin layer (first resin layer)
11b Hard coat layer (third hard coat layer)
11c Hard coat layer (fourth hard coat layer)
12 Resin 12b Adhesive resin layer (fourth resin layer)
13 FET-side inorganic layer 13a Moisture-proof layer (first inorganic layer)

13b FET layer

13c EL layer 21 Film 21a Resin layer (second resin layer)
21b Hard coat layer (first hard coat layer)
21c Hard coat layer (second hard coat layer)
22 resin layer 22b adhesive resin layer (third resin layer)
23 CF side inorganic layer (moisture-proof layer)
23a Moisture-proof layer (second inorganic layer)
23b Color filter 31 Solid encapsulating resin layer (fifth resin layer)
32 EL layer, resin layer, CF laminated layer 32a Laminated film thickness 32b Thickness measurement location 33 Resin layer, inorganic layer, EL layer, etc. 34a, 34b, 35a, 35b Arrow 36 Thickness range 101 Neutral surface 102 Folding axis 103 Center point

Claims

A first resin layer;
A first inorganic layer located on the first resin layer;
An EL layer located on the first inorganic layer;
A second inorganic layer located on the EL layer;
A second resin layer located on the second inorganic layer;
Comprising
The first resin layer, the first inorganic layer, the EL layer, the second resin layer, and the second inorganic layer are configured to be bendable,
A display device, wherein a strain rate applied to each of the first inorganic layer and the second inorganic layer during the bending is 0.4% or less.
In claim 1,
Each of the first inorganic layer and the second inorganic layer includes a metal oxide, a metal nitride, a compound of Si and O, or a compound of Si and N.
In claim 1 or 2,
A display device, wherein a first hard coat layer is located on the second resin layer.
In claim 3,
A third resin layer located between the second inorganic layer and the second resin layer;
A second hard coat layer located between the third resin layer and the second resin layer;
A display device comprising:
In any one of Claims 1 thru | or 4,
A display device, wherein a third hard coat layer is located under the first resin layer.
In claim 5,
A fourth resin layer located between the first inorganic layer and the first resin layer;
A fourth hard coat layer located between the fourth resin layer and the first resin layer;
A display device comprising:
In any one of Claims 1 thru | or 6,
A display device, wherein a fifth resin layer is located between the EL layer and the second inorganic layer.
In any one of Claims 1 thru | or 7,
A display device, wherein a color filter is located between the EL layer and the second inorganic layer.
In claim 7,
The upper limit of the average thickness of the fifth resin layer is 9 μm or less.
In any one of Claims 1 thru | or 9,
The first resin layer, the first inorganic layer, the EL layer, and the second resin layer so that a strain rate of 0.4% is applied to each of the first inorganic layer and the second inorganic layer. And when the test which repeats the said 2nd inorganic layer is repeated 50,000 times is performed, the display defect does not generate | occur | produce.