Flexible organic el display device and front panel for display device

Abstract

This invention provides a flexible organic light-emitting display device, which is a flexible organic light-emitting display device having a front panel disposed on the observer side of the aforementioned organic light-emitting display panel. The front panel has a glass substrate with a thickness of 100 μm or less on the organic light-emitting display panel and a resin layer on the glass substrate. When the composite elastic modulus in a first direction is set as E1 and the composite elastic modulus in a second direction orthogonal to the first direction is set as E2, the ratio of E1 / E2 is 1.2 or more. The angle between the bending direction of the flexible organic light-emitting display device and the first direction is 45° or more and 90° or less.

Description

Technical Field

[0001] This invention relates to flexible organic EL display devices and front panels for display devices. Background Technology

[0002] Traditionally, display devices have used front panels with glass or resin substrates to protect them. These front panels protect the display device from impacts and damage, requiring strength, impact resistance, and damage resistance. Glass substrates are characterized by high surface hardness, scratch resistance, and high transparency, while resin substrates are lightweight and not easily broken. Furthermore, generally, the thicker the front panel, the better its impact protection. The material and thickness of the front panel are selected appropriately based on factors such as weight, cost, and the size of the display device.

[0003] In recent years, the development of flexible displays, such as foldable displays, rollable displays, and bendable displays, has been actively underway.

[0004] In flexible displays, the front panel also needs to bend in accordance with the movement of the display device, thus a bendable front panel is used. In the case of glass substrates, research is being conducted on glass substrates such as ultra-thin glass (UTG) that are made bendable by thinning the glass (see, for example, Patent Document 1). Among glass, especially glass with high bending resistance is called chemically strengthened glass, which internalizes the stress of surface expansion, so that the tiny damage to the glass surface does not increase when bent, thus making the glass less prone to breakage.

[0005] Because glass has a higher modulus of elasticity than resin, it offers greater protection for display devices of the same thickness. Furthermore, glass's high optical transparency allows for the creation of displays with superior visibility. However, thinning glass makes it more prone to breakage, drastically reducing its impact resistance. If the glass substrate of the front panel cracks due to external impact, not only is its protective function for the display device diminished, but the resulting shards or sharp edges can also injure the user's fingertips.

[0006] Therefore, it has been proposed to laminate a resin layer onto a glass substrate. For example, Patent Document 2 discloses a laminate in which a thin glass plate and a resin film are laminated by an adhesive layer. In addition, Patent Document 3 discloses a glass cover sheet having a glass layer, a viscoelastic layer, and an acoustic impedance matching layer disposed between the glass layer and the viscoelastic layer.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2018-188335

[0010] Patent Document 2: Japanese Patent Application Publication No. 2019-25901

[0011] Patent Document 3: International Publication No. 2018 / 055998 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] In display devices with a front panel comprising a glass substrate and a resin layer, by positioning the resin layer closer to the viewer than the glass substrate, it is possible to suppress glass breakage due to impact, thereby improving impact resistance. However, as detailed below, the impact resistance and bending resistance of the resin layer are considered to be opposing properties. Therefore, a resin layer capable of balancing both impact resistance and bending resistance is needed.

[0014] The present invention was made in view of the above-mentioned actual situation, and its main objective is to provide a flexible organic EL display device with excellent impact resistance and bending resistance, and a front panel for the display device of the flexible organic EL display device.

[0015] Methods for solving problems

[0016] To address the aforementioned issues, the inventors of this invention conducted in-depth research and discovered that in a front panel comprising a glass substrate and a resin layer, by making the resin layer possess a predetermined anisotropy of elastic modulus, the directions of relatively high and relatively low elastic modulus within the surface of the resin layer are in a predetermined relationship with the bending direction of the display device. This allows for improved impact resistance while simultaneously enhancing bending resistance. This invention is based on this technical concept.

[0017] One embodiment of the present invention provides a flexible organic light-emitting display device, which is a flexible organic light-emitting display device having an organic light-emitting display panel and a front panel disposed on the observer side of the organic light-emitting display panel. The front panel has a glass substrate with a thickness of 100 μm or less on the organic light-emitting display panel and a resin layer on the glass substrate. When the composite elastic modulus in a first direction is set as E1 and the composite elastic modulus in a second direction orthogonal to the first direction is set as E2, the ratio of E1 / E2 is 1.2 or more. The angle between the bending direction of the flexible organic light-emitting display device and the first direction is 45° or more and 90° or less.

[0018] Another embodiment of the present invention provides a front panel for a display device, comprising: a glass substrate with a thickness of 100 μm or less; and a resin layer located on the glass substrate, wherein when the composite elastic modulus in a first direction is set as E1 and the composite elastic modulus in a second direction orthogonal to the first direction is set as E2, the ratio of E1 / E2 is 1.2 or more.

[0019] In this invention, the average value of the composite elastic modulus E1 in the first direction and the composite elastic modulus E2 in the second direction is preferably 4.0 GPa or higher. It should be noted that "GPa" refers to the unit of pressure, namely gigapascal.

[0020] Furthermore, the front panel of the display device in this invention can have an adhesive layer between the glass substrate and the resin layer.

[0021] Furthermore, the front panel of the display device in this invention can sequentially have the glass substrate, the resin layer, and the functional layer on the resin layer.

[0022] The effects of the invention

[0023] The present invention provides a flexible organic EL display device and a front panel for the display device that have excellent impact resistance and bending resistance. Attached Figure Description

[0024] Figure 1 This is a schematic cross-sectional view illustrating the flexible organic EL display device of the present invention.

[0025] Figure 2 This is a schematic top view illustrating the resin layer in this invention.

[0026] Figure 3 This is a schematic perspective view illustrating the flexible organic EL display device of the present invention.

[0027] Figure 4 This is a schematic cross-sectional view illustrating the flexible organic EL display device of the present invention.

[0028] Figure 5 This is a schematic cross-sectional view illustrating the front panel of the display device in this invention.

[0029] Figure 6 This is a schematic diagram used to illustrate a dynamic bending test.

[0030] Figure 7 This is a schematic diagram used to illustrate a static bending test.

[0031] Figure 8 This is a schematic diagram used to illustrate the measurement location for indentation hardness. Detailed Implementation

[0032] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the present invention can be implemented in many different ways and is not intended to be limited to the embodiments illustrated below. Furthermore, to make the description clearer, the drawings sometimes schematically represent the width, thickness, shape, etc., of various parts compared to the actual situation; however, these are always examples and are not intended to limit the interpretation of the present invention. Additionally, in this specification and the accompanying drawings, the same reference numerals are used for elements that are the same as those described in the previously mentioned drawings, and detailed descriptions are sometimes appropriately omitted.

[0033] In this specification, when describing the arrangement of other components above a component, the use of only "above" or "below" includes, unless otherwise specified, both the case where the other component is arranged directly above or below the component in contact with it, and the case where the other component is arranged above or below the component, further separated by another component. Similarly, in this specification, when describing the arrangement of another component on the surface of a component, the use of only "surface side" or "surface" includes, unless otherwise specified, both the case where the other component is arranged directly above or below the component in contact with it, and the case where the other component is arranged above or below the component, further separated by another component.

[0034] The flexible organic EL display device and the front panel for the display device of the present invention will be described in detail below.

[0035] A. Flexible Organic Electron Display Device

[0036] The flexible organic EL display device of the present invention is a flexible organic electroluminescent display device having an organic electroluminescent display panel and a front panel disposed on the observer side of the organic electroluminescent display panel. The front panel has a glass substrate with a thickness of 100 μm or less on the organic electroluminescent display panel and a resin layer on the glass substrate. When the composite elastic modulus in the first direction is set as E1 and the composite elastic modulus in the second direction orthogonal to the first direction is set as E2, the ratio of E1 / E2 is 1.2 or more. The angle between the bending direction of the flexible organic electroluminescent display device and the first direction is 45° or more and 90° or less.

[0037] Figure 1 This is a schematic cross-sectional view illustrating an example of the flexible organic EL display device of the present invention. Figure 1As shown, the flexible organic EL display device 10 includes an organic EL display panel 11 and a front panel 1 disposed on the observer side of the organic EL display panel 11. The front panel 1 has a glass substrate 2 and a resin layer 3 sequentially arranged from the organic EL display panel 11 side. The glass substrate 2 has a predetermined thickness, and the resin layer 3 has anisotropy with a predetermined composite elastic modulus. An adhesive layer 4 may be provided between the glass substrate 2 and the resin layer 3. Furthermore, in the flexible organic EL display device 10, an adhesive layer or bonding layer 12 may be disposed between the front panel 1 and the organic EL display panel 11.

[0038] In the front panel of this invention, the glass substrate is thin (below a specified value), raising concerns about its susceptibility to breakage and low impact resistance. However, by providing a resin layer on the side of the glass substrate opposite to the organic EL display panel, the resin layer absorbs the impact when the front panel of the flexible organic EL display device is subjected to an impact, thus suppressing the breakage of the glass substrate and improving impact resistance. Furthermore, even in the event of glass substrate breakage, the resin layer can prevent glass scattering.

[0039] In the front panel of this invention, such as Figure 2 As illustrated, when the composite elastic modulus in the first direction 21 is set as E1 and the composite elastic modulus in the second direction 22, which is orthogonal to the first direction 21, is set as E2, the ratio of E1 / E2 is 1.2 or higher. That is, the composite elastic modulus E1 in the first direction 21 is relatively high, and the composite elastic modulus E2 in the second direction 22 is relatively low. In other words, the resin layer 3 has a specified elastic modulus anisotropy.

[0040] Here, the composite elastic modulus is a physical property value that represents the degree to which elastic deformation is difficult to occur. In this invention, within the plane of the resin layer 3, the composite elastic modulus E1 in the first direction 21 is relatively high, and the composite elastic modulus E2 in the second direction 22 is relatively low. In both the first and second directions 22, it can be said that the resin layer 3 is relatively less prone to elastic deformation in the first direction 21, where the composite elastic modulus is relatively high, and is relatively more prone to elastic deformation in the second direction 22, where the composite elastic modulus is relatively low.

[0041] In the flexible organic EL display device of the present invention, such as Figure 2 As illustrated, the angle θ between the first direction 21, in which the in-plane composite elastic modulus of the resin layer 3 is relatively high, and the bending direction 20 of the flexible organic EL display device is 45° or more and 90° or less. In this case, the angle between the second direction 22, in which the in-plane composite elastic modulus of the resin layer 3 is relatively low, and the bending direction 20 of the flexible organic EL display device is 0° or more and 45° or less.

[0042] Figure 3(a) and (b) are schematic perspective views illustrating the flexible organic EL display device of the present invention. Figure 3 (a) indicates that the flexible organic EL display device 10 is turned on. Figure 3 (b) indicates the state in which the flexible organic EL display device 10 is bent. For example... Figure 3 As shown in (a) and (b), the bending direction 20 of the flexible organic EL display device 10 refers to the direction in which the flexible organic EL display device 10 is bent. It should be noted that the bending direction of the flexible organic EL display device can be either the length direction or the width direction of the flexible organic EL display device, and there is no particular limitation.

[0043] In this invention, by aligning the first direction 21 (with a relatively high composite elastic modulus) and the second direction 22 (with a relatively low composite elastic modulus) in the plane of the resin layer 3 with the bending direction 20 of the flexible organic EL display device as described above, the bending resistance can be improved. The reason for this is speculated as follows.

[0044] Here, for example, if Figure 3 When the flexible organic EL display device 10 is bent as shown in (b), stress is applied to the bent portion 25 of the flexible organic EL display device 10, resulting in strain. At this time, in the front panel of the flexible organic EL display device 10, since the elastic modulus of glass is higher than that of resin and the middle surface is a glass substrate, the stress and strain applied to the bent portion of the resin layer away from the middle surface during bending become larger.

[0045] For example, when the second direction, where the in-plane composite elastic modulus of the resin layer is relatively low, is approximately parallel to the bending direction of the flexible organic EL display device—that is, when the angle between the second direction and the bending direction is approximately 0°—the stress applied to the bent portion of the resin layer is smaller due to the relatively low composite elastic modulus in the second direction. Therefore, even after repeatedly bending the flexible organic EL display device and then opening it, the bent portion of the resin layer can withstand stress and remain resistant to plastic deformation. Consequently, it is speculated that the flexible organic EL display device easily returns to a flat state, exhibiting good resilience after repeated bending and being less prone to leaving creases or marks.

[0046] On the other hand, for example, when the first direction with a relatively high in-plane composite elastic modulus of the resin layer is approximately parallel to the bending direction of the flexible organic EL display device, i.e., when the angle between the first direction with a relatively high in-plane composite elastic modulus of the resin layer and the bending direction of the flexible organic EL display device is approximately 0°, the stress applied to the bent portion of the resin layer increases due to the relatively high in-plane composite elastic modulus of the resin layer in the first direction. Therefore, when the flexible organic EL display device is opened after repeated bending, the bent portion of the resin layer cannot withstand the stress and is prone to plastic deformation. As a result, it is speculated that the flexible organic EL display device is difficult to return to a flat state, i.e., it has low resilience after repeated bending and is prone to leaving creases or marks.

[0047] Furthermore, when the angle between the second direction, where the in-plane composite elastic modulus of the resin layer is relatively low, and the bending direction of the flexible organic EL display device is 0° or more and 45° or less, that is, when the angle θ between the first direction, where the in-plane composite elastic modulus of the resin layer is relatively high, and the bending direction of the flexible organic EL display device is 45° or more and 90° or less, compared to the case where the angle θ between the first direction, where the in-plane composite elastic modulus of the resin layer is relatively high, and the bending direction of the flexible organic EL display device is approximately 0°, the stress applied to the bent portion of the resin layer during repeated bending of the flexible organic EL display device is smaller. Therefore, even when the angle between the second direction (where the in-plane composite elastic modulus of the resin layer is relatively low) and the bending direction of the flexible organic EL display device is 0° to 45°, i.e., when the angle θ between the first direction (where the in-plane composite elastic modulus of the resin layer is relatively high) and the bending direction of the flexible organic EL display device is 45° to 90°, as described above, even after repeatedly bending the flexible organic EL display device and then opening it, the stress applied to the bent portion of the resin layer is small, and the bent portion of the resin layer can withstand the stress and maintain a state that is not prone to plastic deformation. As a result, it is speculated that the flexible organic EL display device easily returns to a flat state, that is, it has good resilience after repeated bending and is not prone to leaving creases or marks.

[0048] Here, increasing the elastic modulus of the resin layer can increase its surface hardness, thus suppressing glass substrate breakage, improving impact resistance, and enhancing the glass's scattering resistance. However, increasing the elastic modulus of the resin layer also increases the stress and strain applied to the bent portion during bending, potentially reducing its resilience after bending and thus its flexural strength. Therefore, it can be argued that impact resistance and flexural strength are opposite properties within the resin layer.

[0049] In contrast, according to the present invention, as described above, since the resin layer has a predetermined elastic modulus anisotropy, by increasing the composite elastic modulus in the first direction in the plane of the resin layer, the overall composite elastic modulus of the resin layer can be increased, thereby improving impact resistance. In addition, by decreasing the composite elastic modulus in the second direction in the plane of the resin layer, and by making the first and second directions in the plane of the resin layer have a predetermined relationship with the bending direction of the flexible organic EL display device, bending resistance can be improved.

[0050] Therefore, this invention improves both impact resistance and bending resistance. Furthermore, even if the glass substrate in the front panel breaks, the risk of injury to the human body is reduced, enabling the fabrication of a highly safe flexible organic EL display device.

[0051] The following describes the various components of the flexible organic EL display device of the present invention.

[0052] 1. Front panel

[0053] The front panel in this invention is a component disposed on the observer side of an organic EL display panel, and sequentially includes a glass substrate with a specified thickness and an anisotropic resin layer with a specified composite elastic modulus from the organic EL display panel side.

[0054] The following describes the various components of the front panel in this invention.

[0055] (1) Resin layer

[0056] In this invention, the resin layer is a component disposed on one side of a glass substrate. When the composite elastic modulus in the first direction of the resin layer is set as E1 and the composite elastic modulus in the second direction orthogonal to the first direction is set as E2, the ratio of E1 / E2 is 1.2 or higher. Furthermore, the angle between the bending direction of the flexible organic EL display device of this invention and the first direction of the resin layer is 45° or higher and 90° or lower. The resin layer is an impact-absorbing component and also functions as a component to suppress glass scattering when the glass substrate breaks. The resin layer is transparent and, in the flexible organic EL display device of this invention, is disposed closer to the observer than the glass substrate.

[0057] When the composite elastic modulus in the first direction of the resin layer is set as E1 and the composite elastic modulus in the second direction orthogonal to the first direction is set as E2, the ratio of E1 / E2 can be 1.2 or more, preferably 1.3 or more, and more preferably 1.4 or more. By increasing the composite elastic modulus in the first direction and decreasing the composite elastic modulus in the second direction of the resin layer in accordance with the ratio of E1 / E2 within the above-mentioned range, impact resistance can be ensured while flexural resistance can be improved.

[0058] Furthermore, the E1 / E2 ratio is preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less. If the above-mentioned E1 / E2 ratio is too large, it is difficult to improve the overall composite elastic modulus of the resin layer, and sometimes sufficient impact resistance cannot be obtained.

[0059] The composite elastic modulus E1 in the first direction and the composite elastic modulus E2 in the second direction of the resin layer are such that the ratio E1 / E2 is satisfied. The average value of the composite elastic modulus E1 in the first direction and the composite elastic modulus E2 in the second direction is preferably 4.0 GPa or more, more preferably 4.3 GPa or more, and even more preferably 4.5 GPa or more. By making the average value of E1 and E2 within the above range, the overall composite elastic modulus of the resin layer can be improved, the breakage of the glass substrate caused by impact can be suppressed, the impact resistance can be improved, and the anti-scattering property of the glass can be improved.

[0060] Furthermore, according to the method for measuring the composite elastic modulus described later, since the composite elastic modulus of the glass substrate is approximately 40 GPa, the average value of the composite elastic modulus E1 in the first direction and the composite elastic modulus E2 in the second direction of the resin layer is preferably 20 GPa or less, and more preferably 10 GPa or less.

[0061] The composite elastic modulus E1 in the first direction of the resin layer only needs to satisfy the ratio of E1 / E2, and thus satisfy the average value of the composite elastic modulus E1 in the first direction and the composite elastic modulus E2 in the second direction. For example, it is preferably 4.0 GPa or more and 40 GPa or less, more preferably 4.5 GPa or more and 20 GPa or less, and even more preferably 5.0 GPa or more and 10 GPa or less. By increasing the composite elastic modulus in the first direction of the resin layer to be within the above-mentioned range, the overall composite elastic modulus of the resin layer can be increased, the cracking of the glass substrate caused by impact can be suppressed, the impact resistance can be improved, and the anti-scattering property of the glass can be improved.

[0062] The composite elastic modulus E2 in the second direction of the resin layer only needs to satisfy the ratio of E1 / E2, and thus satisfy the average value of the composite elastic modulus E1 in the first direction and the composite elastic modulus E2 in the second direction. For example, it is preferably 3.0 GPa or more and 40 GPa or less, more preferably 3.5 GPa or more and 20 GPa or less, and even more preferably 4.0 GPa or more and 10 GPa or less. By reducing the composite elastic modulus E2 in the second direction of the resin layer to be within the above-mentioned range, the bending resistance can be improved.

[0063] Here, the composite elastic modulus of the resin layer is determined using the indentation hardness (H) of the resin layer. ITThe contact projected area A is calculated during the measurement. p The "indentation hardness" is calculated from the load-displacement curve of the indenter obtained by hardness measurement using nanoindentation method, which measures the load from the indenter to its unloading. The composite elastic modulus of the resin layer is the elastic modulus that includes the elastic deformation of the resin layer and the elastic deformation of the indenter.

[0064] It should be noted that, in this invention, the composite elastic modulus, which is based on the compressive elasticity of the indenter, is used as a parameter for bending resistance for the following reasons.

[0065] When bending a flexible organic EL display device that can be bent, the resin layer side of the glass substrate is bent as the concave side. At this time, the glass substrate with a high elastic modulus usually becomes the neutral axis, so compressive stress is applied to the resin layer during bending. Therefore, in order to approximate this state, a composite elastic modulus based on compressive elasticity rather than tensile elasticity is used as a parameter.

[0066] In addition, the composite elastic modulus based on tensile elasticity is prone to deviation due to the end face condition of the test piece. However, the composite elastic modulus based on compressive elasticity using an indenter has the advantages of being less affected by the end face condition and being easier to obtain stable results. Therefore, the composite elastic modulus based on compressive elasticity rather than tensile elasticity is used as the parameter.

[0067] Indentation hardness (H) ITIn the measurement, the "TI950 TriboIndenter" manufactured by BRUKER Corporation was used to measure the sample. Specifically, firstly, a block was prepared by embedding a 1mm × 10mm front panel with embedding resin. Then, a uniform slice without pores and with a thickness of 50nm to 100nm was cut from this block using a standard slicing method. The slices could be prepared using an "Ultramicrotome EM UC7" (manufactured by Leica Microsystems). Next, the block remaining after cutting this uniform slice without pores was used as the measurement sample. Then, in the cross-section obtained from the slice cut from this measurement sample, under the following measurement conditions, a Berkovich indenter (a triangular pyramid, BRUKER Corporation TI-0039) was vertically pressed into the center of the resin layer cross-section at an indentation speed of 10 nm / s until the indentation depth reached 200nm. Here, to avoid the influence of the glass substrate and the side edges of the resin layer, the Burkevich indenter is pressed into a portion of the resin layer that is at least 500 nm from the interface between the glass substrate and the resin layer towards the center of the resin layer, and also at least 500 nm from each of the two ends of the resin layer towards the center of the resin layer. It should be noted that if any layer, such as a hard coating, exists on the side of the resin layer opposite to the glass substrate side, the indenter is pressed into a portion of the resin layer that is at least 500 nm from the interface between the aforementioned layer and the resin layer towards the center of the resin layer. Afterward, it is held in place to alleviate residual stress, then unloaded, and the maximum load after stress relief is measured. This maximum load P is then used. max and contact projected area A p Through P max / A p Calculate the indentation hardness (H) IT The contact projected area mentioned above is the contact projected area corrected for the indenter tip curvature using fused silica (BRUKER 5-0098) of a standard specimen corrected for the indenter tip curvature using the Oliver-Pharr method. Indentation hardness (H...) IT The value represents the arithmetic mean of the values ​​obtained from measuring 15 locations. It should be noted that if any measured value deviates from the arithmetic mean by more than ±20%, that value should be removed and the measurement repeated. To determine whether a value deviates from the arithmetic mean by more than ±20%, when the measured value is designated as A and the arithmetic mean as B, the result (%) calculated by (A-B) / B×100 is determined by whether it is greater than ±20%. Indentation hardness (H) IT It can be adjusted according to the type of resin contained in the resin layer, as described later.

[0068] (Measurement conditions)

[0069] • Penetration depth: 200nm

[0070] • Indentation speed: 10 nanometers / second

[0071] • Duration: 5 seconds

[0072] • Unloading speed: 10 nanometers / second

[0073] • Measurement temperature: 25℃

[0074] The composite elastic modulus E of the resin layer r The contact projected area A, calculated during indentation hardness testing, is based on the following mathematical formula (1). p The composite elastic modulus is calculated by measuring the indentation hardness at 15 locations and determining the composite elastic modulus for each location. The result is the arithmetic mean of the composite elastic moduli obtained at the 15 locations.

[0075] [Number 1]

[0076]

[0077] (In the above mathematical formula (1), A) p E is the contact projection area. r (where S is the composite elastic modulus of the resin layer, and S is the contact stiffness represented by the slope of the load-displacement curve shortly after unloading.)

[0078] It should be noted that, when measuring the composite elastic modulus of the resin layer in the first direction, the indentation hardness is measured on a section cut along a second direction orthogonal to the first direction. Similarly, when measuring the composite elastic modulus of the resin layer in the second direction, the indentation hardness is measured on a section cut along a first direction orthogonal to the second direction.

[0079] In addition, in the above method for determining the composite elastic modulus of the resin layer, a test sample was made for the front panel, but a test sample can also be made for only the resin layer.

[0080] The first direction within the plane of the resin layer is preferably the principal stretching direction. That is, the first direction within the plane of the resin layer is preferably the direction in which the refractive index is maximized within the plane of the resin layer. This is because, in the resin layer, molecules generally tend to align along the principal stretching direction, and the composite elastic modulus in the principal stretching direction tends to be higher.

[0081] It should be noted that the main stretching direction refers to the stretching direction in unidirectional stretching and the stretching direction with the higher stretching ratio in bidirectional stretching.

[0082] Furthermore, the principal tensile direction of the resin layer can be either the MD direction or the TD direction. That is, when the first direction in the plane of the resin layer is the principal tensile direction, the first direction in the plane of the resin layer can be either the MD direction or the TD direction.

[0083] It should be noted that the MD direction (Machine Direction) refers to the flow direction of the resin membrane, while the TD direction (Transverse Direction) refers to the direction orthogonal to the MD direction.

[0084] In this invention, such as Figure 2 As illustrated, the angle θ formed by the first direction 21, in which the in-plane composite elastic modulus of the resin layer 3 is relatively high, and the bending direction 20 of the flexible organic EL display device is 45° or more and 90° or less. Preferably, the angle θ is 60° or more and 90° or less, more preferably 75° or more and 90° or less, further preferably 85° or more and 90° or less, and particularly preferably 90°. It should be noted that the angle θ refers to the smaller of the angles formed by the first direction, in which the in-plane composite elastic modulus of the resin layer is relatively high, and the bending direction of the flexible organic EL display device. By setting the angle θ to the aforementioned range, when the flexible organic EL display device is opened after repeated bending, it can easily return to a flat state, thus improving its resilience after repeated bending and reducing the likelihood of creases or marks. Therefore, the bending resistance of the flexible organic EL display device during repeated bending can be improved.

[0085] In the above case, the angle formed between the second direction, where the in-plane composite elastic modulus of the resin layer is relatively low, and the bending direction of the flexible organic EL display device is 0° to 45°, preferably 0° to 30°, more preferably 0° to 15°, further preferably 0° to 5°, and particularly preferably 0°. It should be noted that the above angle refers to the smaller of the angles formed between the second direction, where the in-plane composite elastic modulus of the resin layer is relatively low, and the bending direction of the flexible organic EL display device.

[0086] The resin layer is transparent. Specifically, the total light transmittance of the resin layer is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more. By achieving such high total light transmittance, a front panel with good transparency can be manufactured.

[0087] Here, the total light transmittance of the resin layer can be measured according to JIS K7361-1:1997, for example, using a haze meter HM150 manufactured by the Murakami Color Technology Research Institute.

[0088] Furthermore, the haze of the resin layer is preferably 5% or less, more preferably 2% or less, and even more preferably 1% or less. By making the haze low in this way, a front panel with good transparency can be produced.

[0089] Here, the haze of the resin layer can be measured according to JIS K-7136:2000, for example, using the HM150 haze meter manufactured by Murakami Color Technology Research Institute.

[0090] The resin included in the resin layer is not particularly limited as long as it satisfies the anisotropy of the aforementioned composite elastic modulus and is transparent. Examples include polyester resins, polyimide resins, polyamide-imide resins, and polyamide resins. Examples of polyester resins include polyethylene terephthalate and polyethylene naphthalate.

[0091] The resin layer may contain further additives as needed. Examples of additives include fillers, UV absorbers, antioxidants, light stabilizers, surfactants, adhesion enhancers, antistatic agents, and slip agents.

[0092] The thickness of the resin layer is not particularly limited as long as it provides sufficient impact absorption and anti-scattering properties of the glass. For example, it is preferably 10 μm to 200 μm, more preferably 20 μm to 150 μm, and even more preferably 30 μm to 100 μm. If the resin layer is too thin, sufficient impact absorption and anti-scattering properties of the glass may not be achieved. In addition, if the resin layer is too thick, flexibility may be compromised, or the resin layer may crack when the flexible organic EL display device is bent.

[0093] Here, the thickness of the resin layer can be the average of the thicknesses of any 10 locations measured from a cross-section in the thickness direction of the front panel of the display device observed by a transmission electron microscope (TEM), scanning electron microscope (SEM), or scanning transmission electron microscope (STEM). It should be noted that the method for measuring the thickness of other layers on the front panel can also be set in the same way.

[0094] As the resin layer, a resin film can be used, for example. As for the resin film, there are no particular limitations as long as the anisotropy of the composite elastic modulus is satisfied; for example, a uniaxially stretched film or a biaxially stretched film can be used. Among these, a biaxially stretched film is preferred.

[0095] As a method for controlling the composite elastic modulus in the first and second directions in a resin film, one example is to appropriately set the stretch ratio or stretching temperature. Specifically, there is a tendency that the higher the stretch ratio or the lower the stretching temperature, the higher the composite elastic modulus in the stretching direction; on the other hand, the lower the stretch ratio or the higher the stretching temperature, the lower the composite elastic modulus in the stretching direction.

[0096] (2) Glass substrate

[0097] The glass substrate in this invention has a thickness of less than 100 μm and serves as a component supporting the aforementioned resin layer.

[0098] As for the glass that constitutes the glass substrate, there are no particular limitations as long as it is transparent; examples include silicate glass and silica glass. Among these, borosilicate glass, aluminosilicate glass, and aluminoborosilicate glass are preferred, and alkali-free glass is more preferred. Commercially available glass substrates include, for example, Nippon Electric Glass's G-Leaf ultra-thin sheet glass and Matsunami Glass Industry Co., Ltd.'s ultra-thin film glass.

[0099] Furthermore, the glass constituting the glass substrate is preferably chemically strengthened glass. Chemically strengthened glass has excellent mechanical strength and can be thinned accordingly, making it preferred from this perspective. Chemically strengthened glass is typically glass in which sodium is replaced with potassium or the like near the surface of the glass, resulting in a partial exchange of ions, thereby enhancing the mechanical properties through a chemical method, and creating a compressive stress layer on the surface.

[0100] Examples of glasses that form the substrate of chemically strengthened glass include aluminosilicate glass, soda-lime glass, borosilicate glass, lead glass, alkaline barium glass, and aluminoborosilicate glass.

[0101] Commercially available products that serve as chemically strengthened glass substrates include Corning's Gorilla Glass and AGC's Dragontrail.

[0102] The thickness of the glass substrate can be 100 μm or less, preferably 15 μm or more but less than 100 μm, more preferably 20 μm or more but less than 90 μm, and even more preferably 25 μm or more but less than 80 μm. By making the glass substrate thinner than the above range, good flexibility and sufficient hardness can be obtained. In addition, curling of the front panel can be suppressed. Furthermore, it is preferable to have a lightweight front panel.

[0103] (3) Functional layer

[0104] The front panel of the present invention may further have a functional layer on the side of the resin layer opposite to the glass substrate. Examples of functional layers include, for example, a hard coating, an anti-reflective layer, and an anti-glare layer.

[0105] Furthermore, a functional layer can be a single layer or multiple layers. Additionally, a functional layer can be a layer with a single function, or it can consist of multiple layers with different functions.

[0106] (a) Hard coating

[0107] For example, Figure 4 As shown, the front panel of the present invention may further have a hard coating 5 on the side of the resin layer 3 opposite to the glass substrate 2. The hard coating is a component used to increase surface hardness. By configuring the hard coating, damage resistance can be improved.

[0108] Materials that can be used as hard coatings include, for example, organic materials, inorganic materials, and organic-inorganic composite materials.

[0109] The material of the hard coating is preferably an organic material. Specifically, the hard coating preferably comprises a cured product of a resin composition containing a polymerizable compound. The cured product of the resin composition containing the polymerizable compound can be obtained by polymerizing the polymerizable compound using a polymerization initiator and a known method, as needed.

[0110] The polymerizable compound has at least one polymerizable functional group within its molecule. As a polymerizable compound, at least one of, for example, free radical polymerizable compounds and cationic polymerizable compounds can be used.

[0111] A free radical polymerizable compound is a compound that possesses free radical polymerizable groups. The free radical polymerizable groups in a free radical polymerizable compound can be any functional group capable of undergoing a free radical polymerization reaction; there are no particular limitations. Examples include groups containing carbon-carbon unsaturated double bonds, such as vinyl groups and (meth)acryloyl groups. It should be noted that when a free radical polymerizable compound has two or more free radical polymerizable groups, these groups can be the same or different.

[0112] From the perspective of improving the hardness of the hard coating, the number of free radical polymerizable groups in one molecule of the free radical polymerizable compound is preferably two or more, and more preferably three or more.

[0113] It should be noted that in this specification, (meth)acryloyl group refers to acryloyl group and methacryloyl group respectively, and (meth)acrylate refers to acrylate and methacrylate respectively.

[0114] Cationic polymerizable compounds are compounds that possess cationic polymerizable groups. The cationic polymerizable groups in a cationic polymerizable compound can be any functional group capable of undergoing a cationic polymerization reaction; there are no particular limitations. Examples include epoxy groups, oxetyl groups, and vinyl ether groups. It should be noted that when a cationic polymerizable compound has two or more cationic polymerizable groups, these cationic polymerizable groups can be the same or different.

[0115] From the perspective of improving the hardness of the hard coating, the number of cationic polymeric groups in one molecule of the cationic polymeric compound is preferably two or more, and more preferably three or more.

[0116] Resin compositions containing the aforementioned polymerizable compounds may also contain polymerization initiators as needed. As polymerization initiators, free radical polymerization initiators, cationic polymerization initiators, and a combination of free radical and cationic polymerization initiators can be appropriately selected. These polymerization initiators are decomposed by at least one of light irradiation and heating, generating free radicals or cations, thereby enabling free radical polymerization and cationic polymerization. It should be noted that in hard coatings, sometimes the polymerization initiator is completely decomposed without residue.

[0117] Hard coatings may contain further additives as needed. These additives are selected appropriately based on the function imparted to the hard coating and are not particularly limited. Examples include fillers, UV absorbers, infrared absorbers, anti-glare agents, antifouling agents, antistatic agents, leveling agents, surfactants, slip agents, various sensitizers, flame retardants, adhesives, polymerization inhibitors, antioxidants, light stabilizers, and surface modifiers.

[0118] The thickness of the hard coating can be appropriately selected according to the function of the hard coating. For example, it is preferably 2μm or more and 50μm or less, more preferably 3μm or more and 30μm or less, even more preferably 5μm or more and 20μm or less, and particularly preferably 6μm or more and 10μm or less. If the thickness of the hard coating is within the above range, sufficient hardness can be obtained as the hard coating, and a front panel with good bending resistance can be obtained.

[0119] As a method for forming a hard coating, depending on the appropriate selection of the material of the hard coating, examples include: a method of coating a curable resin composition for a hard coating containing the polymeric compound and the like onto the above-mentioned resin layer and then curing it; or vapor deposition, sputtering, etc.

[0120] (4) Other components

[0121] In addition to the layers described above, the front panel of this invention may also have other layers as needed. Examples of other layers include, for instance, adhesive layers.

[0122] For example, Figure 1 As shown, the front panel of the present invention can have an adhesive layer 4 between the glass substrate 2 and the resin layer 3. The resin layer can be disposed on one side of the glass substrate by means of the adhesive layer.

[0123] The adhesive layer is preferably a relatively soft layer. Specifically, the shear storage modulus of the adhesive layer at a frequency of 950 Hz and a temperature of 23°C is preferably 20 MPa or less, more preferably 18 MPa or less, and even more preferably 15 MPa or less. Furthermore, the shear storage modulus of the adhesive layer is preferably 0.05 MPa or more, more preferably 0.5 MPa or more, and even more preferably 3 MPa or more. By setting the shear storage modulus of the adhesive layer to the above range, a relatively soft layer can be formed. In this case, by providing a relatively soft adhesive layer between the resin layer and the glass substrate, impact resistance can be improved. In this respect, it can be considered that by making the adhesive layer relatively soft and easily deformable, when an impact is applied to the front panel, the deformation of the resin layer is not suppressed by the adhesive layer, and the resin layer becomes easily deformable, thus exhibiting a greater impact absorption effect.

[0124] Here, the shear storage modulus of the adhesive layer at a frequency of 950 Hz and a temperature of 23 ℃ is the arithmetic mean of the three measurements taken at 950 Hz and 23 ℃.

[0125] It should be noted that the frequency is set to 950Hz because when an object is dropped freely from a height of a few centimeters, this frequency is within the frequency range where the surface of the front panel undergoes deformation of a few μm to tens of μm, and this frequency is also within the frequency range that causes damage to components such as the display panel located on the inner side of the flexible organic EL display device than the front panel.

[0126] Here, the shear storage modulus G' of the adhesive layer can be measured using a dynamic viscoelasticity measuring device (DMA). When measuring the shear storage modulus G' of the adhesive layer using the DMA, the adhesive layer is first punched into a rectangular shape of 10mm × 5mm to obtain a test sample. Two of these test samples are then prepared and mounted onto the solid shear clamp of the DMA. Specifically, the solid shear clamp has three plates in the horizontal direction (a 1mm thick metal middle plate and two metal outer plates disposed on both sides of the middle plate). One test sample is clamped between the middle plate and one outer plate, and another test sample is clamped between the middle plate and the other outer plate. In the DMA, the solid shear clamp is set with a clamping distance of 20mm. At a temperature of 23°C, while the middle plate is fixed, longitudinal vibration with a strain of 1% and a frequency of 950Hz is applied to the two outer plates, and the shear storage modulus G' is measured. As a dynamic viscoelasticity measuring device, the Rheogel-E4000 manufactured by UBM can be used, for example. It should be noted that the specific measurement conditions in the above method are shown below.

[0127] (Conditions for determining shear storage modulus)

[0128] • Sample to be measured: 2 rectangular pieces, each measuring 10mm × 5mm.

[0129] • Measuring fixture: Solid shear

[0130] • Strain waveform: Sine wave

[0131] • Strain control: Automatic adjustment

[0132] • Frequency: 950Hz

[0133] Temperature: 23℃

[0134] Furthermore, when determining the shear storage modulus of the adhesive layer, the measurement is performed after peeling the glass substrate and resin layer from the adhesive layer. The peeling of the glass substrate and resin layer can be performed, for example, as follows: First, the front panel is heated using a dryer, and then the tip of a cutter is inserted into the area considered the interface between the adhesive layer and other layers, and the layers are slowly peeled off. By repeatedly performing this heating and peeling process, the glass substrate and resin layer can be peeled off from the adhesive layer. It should be noted that despite this peeling process, it does not significantly affect the measurement.

[0135] The adhesive used in the adhesive layer is not particularly limited as long as it meets the aforementioned shear storage modulus, is transparent, and can bond the glass substrate to the resin layer. Examples include acrylic adhesives, silicone adhesives, rubber adhesives, and urethane adhesives, which can be appropriately selected based on the material of the resin layer. Among these, acrylic adhesives are preferred because they have excellent transparency, weather resistance, durability, and heat resistance, and are also low in cost.

[0136] The thickness of the adhesive layer is preferably 10 μm to 100 μm, more preferably 25 μm to 80 μm, and even more preferably 40 μm to 60 μm. If the adhesive layer is too thin, it may not be able to fully bond the glass substrate and the resin layer, and when an impact is applied to the front panel, it may not be able to achieve the desired effect of easily deforming the resin layer. In addition, if the adhesive layer is too thick, flexibility may be compromised.

[0137] As an adhesive layer, an adhesive film can be used, for example. Alternatively, the adhesive layer can be applied to a support, a glass substrate, or a resin layer using a composition to form an adhesive layer.

[0138] (5) Features of the front panel

[0139] The total light transmittance of the front panel in this invention is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more. This high total light transmittance allows for the production of a front panel with excellent transparency.

[0140] Here, the total light transmittance of the front panel can be measured according to JIS K7361-1:1997, for example, using the HM150 haze meter manufactured by the Murakami Color Technology Laboratory.

[0141] The haze of the front panel in this invention is preferably 25% or less, more preferably 2% or less, and even more preferably 1% or less. By making the haze so low, a front panel with good transparency can be produced.

[0142] Here, the haze of the front panel can be measured according to JIS K-7136:2000, for example, using the HM150 haze meter manufactured by Murakami Color Technology Research Institute.

[0143] The thickness of the front panel as a whole in this invention is not particularly limited as long as it allows for flexibility. For example, it is preferably 35 μm to 400 μm, more preferably 65 μm to 330 μm, and even more preferably 95 μm to 240 μm. By making the thickness of the front panel as a whole within the above range, a front panel with good flexibility can be manufactured.

[0144] 2. Organic EL display panel

[0145] The organic EL display panel in this invention can have the same configuration as a general organic EL display device.

[0146] 3. Other components

[0147] The flexible organic EL display device of this invention can have a touch panel component between the display panel and the front panel. The touch panel component can have the same configuration as a typical touch panel component.

[0148] 4. Flexible Organic Electron Display Device

[0149] The flexible organic EL display device of the present invention is preferably foldable. That is, the flexible organic EL display device of the present invention is preferably a foldable display. The flexible organic EL display device of the present invention has excellent bending resistance and is suitable as a foldable display.

[0150] B. Front panel for display device

[0151] The front panel of the display device in this invention has a glass substrate with a thickness of 100 μm or less and a resin layer on the glass substrate. When the composite elastic modulus in the first direction is set as E1 and the composite elastic modulus in the second direction, which is orthogonal to the first direction, is set as E2, the ratio of E1 / E2 is 1.2 or more.

[0152] Figure 5 This is a schematic cross-sectional view showing an example of a front panel for a display device according to the present invention. Figure 5 As shown, the front panel 1A for the display device has a glass substrate 2 and a resin layer 3 disposed on one side of the glass substrate 2. The glass substrate 2 has a specified thickness, and the resin layer 3 has anisotropy with a specified composite elastic modulus. The front panel 1A for the display device can have an adhesive layer 4 between the glass substrate 2 and the resin layer 3.

[0153] When used in a display device, the front panel of the display device according to the present invention, as described in item "A. Flexible Organic EL Display Device" above, allows the first and second directions in the plane of the resin layer to be in a predetermined relationship with the bending direction of the display device. Therefore, in the front panel of the display device according to the present invention, as described above, since the resin layer has a predetermined anisotropic elastic modulus, by increasing the composite elastic modulus in the first direction in the plane of the resin layer, the overall composite elastic modulus of the resin layer can be increased, thus improving impact resistance. Furthermore, by decreasing the composite elastic modulus in the second direction in the plane of the resin layer and ensuring that the first and second directions in the plane of the resin layer are in a predetermined relationship with the bending direction of the display device, bending resistance can be improved.

[0154] Therefore, this invention improves both impact resistance and bending resistance. Furthermore, it enables the manufacture of a front panel for a display device with high safety.

[0155] Regarding the front panel for the display device in this invention, it can be the same as the front panel in the flexible organic EL display device described above, so the description here is omitted.

[0156] The front panel for the display device in this invention has bend resistance. Specifically, it is preferable that the front panel for the display device does not crack or break when subjected to 200,000 dynamic bending tests as described below, and even more preferably, it does not crack or break when subjected to 1 million dynamic bending tests.

[0157] In a dynamic bending test, the front panel of the display device is repeatedly bent such that the angle between the bending direction of the front panel and the first direction within the surface of the resin layer is 90°. In this case, it is preferable that the front panel of the display device does not crack or break. More preferably, the front panel of the display device does not crack or break when it is repeatedly bent such that the angle between the bending direction of the front panel and the first direction within the surface of the resin layer is 45° or more and 90° or less. In particular, it is even more preferable that the front panel of the display device does not crack or break when it is repeatedly bent such that the bending direction of the front panel is in any direction within the surface of the resin layer.

[0158] In the dynamic bending test, the front panel of the display device can be folded with the glass substrate facing outwards or with the glass substrate facing inwards. In either case, it is preferable that the front panel of the display device does not crack or break.

[0159] (Dynamic bending test)

[0160] The dynamic bending test is conducted as follows. First, a test piece for the front panel of a display device, measuring 20mm × 100mm, is prepared. The length direction of the test piece is then parallel to the bending direction. For example, when bending the front panel of the display device at a 90° angle between the bending direction and the first direction within the resin layer, the length direction of the test piece is parallel to the bending direction and orthogonal to the first direction within the resin layer. Furthermore, in the dynamic bending test, as... Figure 6 As shown in (a), the short side portion 1C and the short side portion 1D facing the short side portion 1C of the front panel 1A of the display device are respectively fixed by the parallel-arranged fixing portions 51. Furthermore, as... Figure 6As shown in (a), the fixing part 51 can slide in the horizontal direction. Next, as... Figure 6 As shown in (b), the movable fixing parts 51 are brought closer together, thereby deforming the front panel 1A of the display device in a folding manner, and thus, as shown in the figure. Figure 6 As shown in (c), after moving the fixing part 51 to a position where the distance between the two opposing short sides 1C and 1D of the front panel 1A of the display device, which are fixed by the fixing part 51, reaches 10mm, the fixing part 51 is moved in the opposite direction to eliminate the deformation of the front panel 1A of the display device. This is achieved through... Figure 6 The movable fixing part 51 shown in (a) to (c) allows the front panel 1A of the display device to be folded 180°. Furthermore, by performing a dynamic bending test in a manner that prevents the bent portion 1E of the front panel 1A from protruding from the lower end of the fixing part 51, and by controlling the interval at which the fixing parts 51 are closest, it is possible to achieve a 10mm interval between the two opposing short sides 1C and 1D of the front panel 1A. In this case, the outer diameter of the bent portion 1E is considered to be 10mm.

[0161] In the front panel of the display device, preferably, no cracking or breakage occurs when the opposing short sides of the front panel 1A of the display device are repeatedly subjected to 200,000 dynamic bending tests of folding 180° with an interval of 10mm. More preferably, no cracking or breakage occurs when the opposing short sides of the front panel of the display device are repeatedly subjected to 200,000 dynamic bending tests of folding 180° with an interval of 10mm, 8mm, 6mm, 5mm, 4mm, 3mm, 2.5mm, or 2mm.

[0162] Furthermore, when the front panel of the display device is repeatedly subjected to the above-mentioned dynamic bending test 200,000 times in such a way that the angle between the bending direction of the front panel of the display device and the first direction in the surface of the resin layer is 90°, the angle after the dynamic bending test in the front panel of the display device is preferably 90° or more, more preferably 100° or more, and even more preferably 110° or more.

[0163] Furthermore, when the front panel of the display device is repeatedly subjected to the above-mentioned dynamic bending test 200,000 times in such a way that the angle formed between the bending direction of the front panel of the display device and the first direction in the surface of the resin layer is 45° or more and 90° or less, the angle after the dynamic bending test in the front panel of the display device is more preferably within the above-mentioned range.

[0164] The inner angle of the front panel of the display device after the dynamic bending test can be measured as follows. After repeated 200,000 dynamic bending tests, the fixing part is removed from one short side of the front panel of the display device, and the panel is opened in a folded state. The angle at which the front panel 1A of the display device naturally opens after 30 minutes at room temperature is measured. It should be noted that the larger the angle, the better the recovery, with a maximum of 180°.

[0165] In the dynamic bending test, the front panel of the display device can be folded with the glass substrate facing inwards, or the front panel of the display device can be folded with the glass substrate facing outwards. In either case, the angle after the dynamic bending test is preferably within the range described above.

[0166] Furthermore, when performing the static bending test described below on the front panel of the display device, the angle after the static bending test in the front panel of the display device is preferably 90° or more, more preferably 100° or more, and even more preferably 110° or more.

[0167] In the static bending test, the front panel of the display device is bent such that the angle between the bending direction of the front panel and the first direction in the resin layer is 90°. In this case, the angle after the static bending test is preferably within the range described above. More preferably, when the front panel of the display device is bent such that the angle between the bending direction of the front panel and the first direction in the resin layer is 45° or more and 90° or less, the angle after the static bending test is within the range described above.

[0168] (Static bending test)

[0169] The static bending test is conducted as follows. First, as... Figure 7 As shown in (a), the short side portion 1C and the short side portion 1D facing the short side portion 1C of the display device front panel 1A are respectively fixed by parallelly arranged fixing portions 52 with a spacing of 10mm between the short side portions 1C and 1D. Furthermore, with the display device front panel 1A folded, a static bending test is performed at 23°C for 240 hours. Afterwards, as... Figure 7 As shown in (b), after the static bending test, the fixing part 52 was removed from the short side 1D, thereby opening the folded state. The angle α at which the display device naturally opened with the front panel 1A after 30 minutes at room temperature was measured. It should be noted that the larger the angle α, the better the recovery, with a maximum of 180°.

[0170] In the static bending test, the front panel of the display device can be folded with the glass substrate facing inwards, or the front panel of the display device can be folded with the glass substrate facing outwards. In either case, the angle α after the static bending test is preferably within the range described above.

[0171] The front panel for a display device according to the present invention can be used as a component disposed on the observer side of the display panel in a display device. The front panel for a display device according to the present invention can be used in display devices such as smartphones, tablet terminals, wearable terminals, personal computers, televisions, digital signage, public information displays (PIDs), and vehicle displays. Furthermore, the front panel for a display device according to the present invention can be used in display devices such as organic EL displays and liquid crystal displays. Preferably, the front panel for a display device according to the present invention can be used in flexible displays such as foldable displays, rollable displays, and bendable displays.

[0172] In the front panel for the display device of the present invention, the surface that becomes the outermost surface after the front panel for the display device is disposed on the surface of the display device is preferably the surface on the resin layer side.

[0173] The method for placing the front panel of the display device according to the present invention on the surface of the display device is not particularly limited, and methods using adhesive layers or bonding layers can be cited as examples. As adhesive layers and bonding layers, known adhesive layers and bonding layers used in the bonding of the front panel of the display device can be used.

[0174] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are illustrative examples; any embodiment that has a substantially similar structure to the technical concept described in the claims of the present invention and can achieve the same effect is included within the technical scope of the present invention.

[0175] Example

[0176] The following examples and comparative examples are shown to further illustrate the present invention.

[0177] [Example 1]

[0178] Molten polyethylene terephthalate (PET) material at 290°C is extruded from a mold to form a sheet, which is then cooled by sealing it with a cooling roller, thereby producing an unstretched resin film. Next, using a biaxial tensile testing apparatus (manufactured by Toyo Seiki Co., Ltd.), the unstretched resin film is subjected to a first stretch at 120°C with a stretch ratio of 4.4, followed by a second stretch at a stretch ratio of 1.4 in a direction at 90° to the first stretch direction, resulting in a resin layer with a thickness of 50 μm.

[0179] A 50μm thick chemically strengthened glass substrate is bonded to one side of the resin layer using an acrylic adhesive (product name "8146-2", manufactured by 3M) to create the front panel.

[0180] [Example 2]

[0181] In Example 1, the unstretched resin film was first stretched at 120°C with a stretch ratio of 3.9 times, and then stretched a second time at a stretch ratio of 1.4 times in a direction at 90° to the first stretching direction to obtain a resin layer with a thickness of 50 μm. Otherwise, the front panel was manufactured in the same manner as in Example 1.

[0182] [Example 3]

[0183] In Example 1, the unstretched resin film was first stretched at 120°C with a stretch ratio of 5.8 times, and then stretched a second time at a stretch ratio of 1.4 times in a direction at 90° to the first stretching direction to obtain a resin layer with a thickness of 50 μm. Otherwise, the front panel was manufactured in the same manner as in Example 1.

[0184] [Example 4]

[0185] In Example 1, the unstretched resin film was first stretched at 120°C with a stretch ratio of 6.5 times, and then stretched a second time at a stretch ratio of 1.4 times in a direction at 90° to the first stretching direction to obtain a resin layer with a thickness of 50 μm. Otherwise, the front panel was manufactured in the same manner as in Example 1.

[0186] [Comparative Example 1]

[0187] In Example 1, the unstretched resin film was first stretched at 120°C with a stretch ratio of 2.5 times, and then stretched a second time at a stretch ratio of 1.4 times in a direction at 90° to the first stretching direction to obtain a resin layer with a thickness of 50 μm. Otherwise, the front panel was manufactured in the same manner as in Example 1.

[0188] [Comparative Example 2]

[0189] In Example 1, the unstretched resin film was first stretched at 120°C with a stretch ratio of 2.0 times, and then stretched a second time at a stretch ratio of 1.4 times in a direction at 90° to the first stretching direction to obtain a resin layer with a thickness of 50 μm. Otherwise, the front panel was manufactured in the same manner as in Example 1.

[0190] [evaluate]

[0191] (1) Composite elastic modulus

[0192] Determine the composite elastic modulus of the resin layer in the examples and comparative examples.

[0193] First, the indentation hardness of the resin layer is measured. Indentation hardness (H... IT In the determination of ), the "TI950 TriboIndenter" manufactured by BRUKER Corporation was used to measure the sample. Specifically, firstly, a block was prepared by embedding a resin layer cut into 1mm × 10mm pieces with embedding resin. Uniform slices without pores and with a thickness of 50nm to 100nm were then cut from this block using a standard slicing method. The slices could be prepared using an "Ultramicrotome EMUC7" (manufactured by Leica Microsystems). Then, the block remaining after cutting out the uniform slice without pores was used as the measurement sample. Next, in the cross-section obtained from the cut slice of the measurement sample, under the following measurement conditions, a Berkovich indenter (triangular pyramid, BRUKER Corporation TI-0039) was vertically pressed into the center of the resin layer cross-section at an indentation speed of 10 nm / s until the indentation depth reached 200nm. Here, to avoid the influence of the side edges of the resin layer, as... Figure 8 As shown, the Burkevich indenter is pressed into the central portion of resin layer 3 in the thickness direction (the dotted line in the figure) and the portion of resin layer 3 2 μm inside the front and back sides (the double-dotted line in the figure). Afterwards, it is held in place to alleviate residual stress, then unloaded, and the maximum load after stress relief is measured. This maximum load P is then used. max and contact projected area A p Through P max / A p Calculate the indentation hardness (H) IT The contact projected area mentioned above is the contact projected area corrected for the indenter tip curvature using fused silica (BRUKER 5-0098) of a standard specimen corrected for the indenter tip curvature using the Oliver-Pharr method. Indentation hardness (H...) IT Five measurements were taken at five locations: the central portion of the resin layer along its thickness direction, the portion of the resin layer 2 μm inside one side, and the portion of the resin layer 2 μm inside the other side. The arithmetic mean of the measurements from a total of 15 locations was calculated. It should be noted that if any measured value deviated from the arithmetic mean by more than ±20%, that value was removed and the measurement was repeated.

[0194] (Measurement conditions)

[0195] • Penetration depth: 200nm

[0196] • Indentation speed: 10 nanometers / second

[0197] • Duration: 5 seconds

[0198] • Unloading speed: 10 nanometers / second

[0199] • Measurement temperature: 25℃

[0200] Next, the indentation hardness (H) of the obtained resin layer was measured. IT The contact projected area A obtained from the above calculation is... p The composite elastic modulus is obtained from the above mathematical formula (1). For the composite elastic modulus, the indentation hardness is measured at 15 locations as described above, and the composite elastic modulus is calculated each time. The result is the arithmetic mean of the composite elastic modulus of the 15 locations.

[0201] It should be noted that, when measuring the composite elastic modulus of the resin layer in the first tensile direction, the indentation hardness is measured on a section cut along the second tensile direction. Similarly, when measuring the composite elastic modulus of the resin layer in the second tensile direction, the indentation hardness is measured on a section cut along the first tensile direction.

[0202] (2) Impact resistance

[0203] Impact tests were conducted on the front panels of the embodiments and comparative examples to evaluate their impact resistance. Specifically, with the resin layer side facing up, the front panel was placed on a 0.7 mm thick soda glass surface using a 50 μm thick acrylic adhesive (product name "8146-2", manufactured by 3M). Three impact tests were performed on each panel, in which a 100 g, 30 mm diameter iron ball was dropped from a height of 10 cm onto the resin layer of the front panel. It should be noted that the drop position of the iron ball was changed each time during the impact tests. Furthermore, after the impact tests, the soda glass was visually evaluated to determine whether it had cracked. Impact resistance was evaluated according to the following criteria.

[0204] A: The soda glass did not break in any of the three tests.

[0205] B: Sodium glass broke in more than one out of three attempts.

[0206] (3) Bending resistance (dynamic bending test)

[0207] Dynamic bending tests were conducted on the front panels of the embodiments and comparative examples to evaluate their bending resistance. Specifically, firstly, for a display device component measuring 20mm × 100mm, the short side (20mm) of the display device component was fixed to a durability testing machine (product name "DLDMLH-FS", manufactured by YUASA SYSTEM Co., Ltd.) using a fixing part. Figure 6(c) As shown, the front panel was adjusted with a minimum interval d of 10 mm between the two opposing short sides, and a dynamic bending test of 200,000 cycles of folding the front panel 180° was performed. In this test, the resin layer side of the front panel was folded inwards, and the glass substrate side was folded outwards. Similarly, using another front panel, a dynamic bending test was performed with the resin layer side facing outwards and the glass substrate side facing inwards, in the same manner.

[0208] It should be noted that when evaluating the flexural strength of the resin layer in the first tensile direction, the bending direction of the front panel is parallel to the first tensile direction of the resin layer. Similarly, when evaluating the flexural strength of the resin layer in the second tensile direction, the bending direction of the front panel is parallel to the second tensile direction of the resin layer. Furthermore, when evaluating the flexural strength of the resin layer in the oblique direction, the angle between the bending direction of the front panel and the first tensile direction of the resin layer is 23°, 45°, and 68°.

[0209] Furthermore, after the dynamic bending test, it is investigated whether cracking or breakage occurs at the bent portion. The bending resistance based on the dynamic bending test is evaluated according to the following criteria.

[0210] A: No cracks or fractures occurred in the bent portion during any dynamic bending test.

[0211] B: In any dynamic bending test, the bent portion cracked or broke.

[0212] In addition, after the dynamic bending test, the fixing part was removed from one of the short sides, thereby opening the folded state, and the natural opening state of the front panel was observed. The creases caused by the dynamic bending test were evaluated according to the following criteria.

[0213] A: In any dynamic bending test, the angle after the dynamic bending test is 90° or more.

[0214] B: In any dynamic bending test, the angle after the dynamic bending test is less than 90°.

[0215] (4) Bending resistance (static bending test)

[0216] Static bending tests were performed on the front panels of the embodiments and comparative examples to evaluate their bending resistance. Specifically, firstly, for components for display devices with dimensions of 20mm × 100mm, such as... Figure 7 As shown in (a), the short side portion 1C and the short side portion 1D facing the short side portion 1C of the display device front panel 1A are respectively fixed by parallelly arranged fixing portions 52 with a spacing of 10mm between the short side portions 1C and 1D. Furthermore, with the display device front panel 1A folded, a static bending test is performed at 23°C for 240 hours. Afterwards, as... Figure 7(b) shows that after the static bending test, the fixing part 52 is removed from the short side 1D, thereby opening the folded state. The angle at which the front panel 1A of the display device naturally opens after 30 minutes at room temperature is measured, i.e., the opening angle. At this time, the front panel is folded with the resin layer side facing inward and the glass substrate side facing outward. In addition, using another front panel, a static bending test is performed in the same manner as above, with the resin layer side facing outward and the glass substrate side facing inward.

[0217] It should be noted that when evaluating the flexural strength of the resin layer in the first tensile direction, the bending direction of the front panel is parallel to the first tensile direction of the resin layer. Similarly, when evaluating the flexural strength of the resin layer in the second tensile direction, the bending direction of the front panel is parallel to the second tensile direction of the resin layer. Furthermore, when evaluating the flexural strength of the resin layer in the oblique direction, the angle between the bending direction of the front panel and the first tensile direction of the resin layer is 23°, 45°, and 68°.

[0218] The creases caused by static bending tests are evaluated according to the following criteria.

[0219] A: In any static bending test, the angle after the static bending test is 90° or more.

[0220] B: In any static bending test, the angle after the static bending test is less than 90°.

[0221] [Table 1]

[0222]

[0223] [Table 2]

[0224]

[0225] In the front panels of Examples 1-4, the ratio of the composite elastic modulus E1 in the first direction to the composite elastic modulus E2 in the second direction, E1 / E2, is 1.2 or higher. Therefore, when the angle between the bending direction and the first direction of the resin layer is 45° or higher and 90° or lower, the bending resistance and impact resistance are excellent. On the other hand, in the front panels of Comparative Examples 1-2, the ratio of the composite elastic modulus E1 in the first direction to the composite elastic modulus E2 in the second direction, E1 / E2, is not 1.2 or higher. Therefore, compared with Examples 1-4, both bending resistance and impact resistance cannot be achieved.

[0226] Symbol Explanation

[0227] 1…Front panel

[0228] 1A…Front panel for display device

[0229] 2…glass substrate

[0230] 3…Resin layer

[0231] 4…Adhesive layer

[0232] 10… Flexible Organic EL Display Device

[0233] 11… Organic EL Display Panel

[0234] 20… Bending direction of flexible organic EL display device

[0235] 21…First direction within the surface of the resin layer

[0236] 22…Second direction within the surface of the resin layer

Claims

1. A flexible organic light-emitting display device, comprising an organic light-emitting display panel and a front panel disposed on the observer side of the organic light-emitting display panel, wherein, The front panel has a glass substrate with a thickness of less than 100 μm located on the organic electroluminescent display panel and a resin layer located on the glass substrate. When the composite elastic modulus in the first direction is set as E1 and the composite elastic modulus in the second direction (orthogonal to the first direction) is set as E2, and the ratio of E1 / E2 is 1.2 or higher, within the plane of the resin layer. The angle between the bending direction of the flexible organic electroluminescent display device and the first direction is more than 45° and less than 90°.

2. The flexible organic electroluminescent display device as described in claim 1, wherein, The average value of the composite elastic modulus E1 and E2 is above 4.0 GPa.

3. The flexible organic electroluminescent display device as described in claim 1 or claim 2, wherein, The front panel has an adhesive layer between the glass substrate and the resin layer.

4. The flexible organic electroluminescent display device as claimed in claim 1 or claim 2, wherein the organic electroluminescent display panel, the front panel, and a functional layer on the resin layer of the front panel are sequentially provided.

5. The flexible organic electroluminescent display device as described in claim 1 or claim 2, wherein, The E1 / E2 ratio is below 3.

0.

6. A front panel for a display device, comprising: Glass substrates with a thickness of less than 100 μm; and The resin layer located on the glass substrate, When the composite elastic modulus in the first direction is set as E1 and the composite elastic modulus in the second direction, which is orthogonal to the first direction, is set as E2, the ratio of E1 / E2 is 1.2 or higher.

7. The front panel for a display device as claimed in claim 6, wherein, The average value of the composite elastic modulus E1 in the first direction and the composite elastic modulus E2 in the second direction is 4.0 GPa or higher.

8. The front panel for a display device as claimed in claim 6 or 7, wherein an adhesive layer is provided between the glass substrate and the resin layer.

9. The front panel for a display device as claimed in claim 6 or claim 7, wherein the glass substrate, the resin layer, and a functional layer on the resin layer are sequentially formed.

10. The front panel for a display device as claimed in claim 6 or claim 7, wherein, The E1 / E2 ratio is below 3.0.

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