Flexible organic el display device, and front surface plate for display device

Abstract

To provide a flexible organic EL display device having excellent impact resistance and flex resistance, and a front surface plate for a display device used in the same.SOLUTION: The present disclosure provides a flexible organic electroluminescence display device comprising an organic electroluminescence display panel and a front surface plate placed on an observer side of the organic electroluminescence display panel, wherein the front surface plate includes a glass substrate, with a thickness of 100 μm or less, on the organic electroluminescence display panel, and a resin layer formed of a single resin on the glass substrate; in a plane of the resin layer, when a composite elastic modulus of a first direction is regarded as E1, a composite elastic modulus of a second direction that is a direction orthogonally crossing the first direction is regarded as E2, E1 / E2 is 1.2 or more; and an angle formed by a folding direction of the flexible organic electroluminescence display device and the first direction is 45° or more and 90° or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a flexible organic electroluminescence display device and a front panel for the display device. [Background technology]

[0002] Conventionally, display devices have used front panels having glass substrates or resin substrates for the purpose of protecting the display device. These front panels protect the display device from impacts and scratches and are required to have strength, impact resistance, scratch resistance, and the like. Glass substrates are characterized by high surface hardness, scratch resistance, and high transparency, while resin substrates are characterized by light weight and crack resistance. In general, the thicker the front panel, the better its ability to protect the display device from impacts, and the material and thickness of the front panel are appropriately selected based on factors such as weight, cost, and the size of the display device.

[0003] In recent years, flexible displays such as foldable displays, rollable displays, and bendable displays have been actively developed.

[0004] In flexible displays, the front panel must also bend in accordance with the movement of the display device, and therefore a bendable front panel is used. In the case of glass substrates, studies are underway to develop glass substrates that can be bent by thinning the glass, such as ultra-thin glass (UTG) (see, for example, Patent Document 1). Among glass substrates, chemically strengthened glass has particularly high bending resistance. By incorporating expansion stress into the glass surface, minute scratches on the glass surface do not become larger when bent, making the glass less likely to break.

[0005] Glass has a higher elastic modulus than resin, so it has a better ability to protect a display device than resin at the same thickness. Glass also has high optical transparency, making it possible to manufacture display devices with better visibility. However, as glass becomes thinner, it becomes more fragile, dramatically reducing its impact resistance. If the glass substrate of the front panel is broken by an external impact, not only will its ability to protect the display device be reduced, but the resulting fragments and sharp edges may injure the user's fingertips, etc.

[0006] Therefore, it has been proposed to laminate a resin layer on a glass substrate. For example, Patent Document 2 discloses a laminate in which a thinned glass plate and a resin film are laminated via an adhesive layer. Furthermore, for example, Patent Document 3 discloses a cover glass including a glass layer, a viscoelastic layer, and an acoustic impedance adjustment layer disposed between the glass layer and the viscoelastic layer. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2018-188335 [Patent Document 2] Japanese Patent Application Publication No. 2019-25901 [Patent Document 3] International Publication No. 2018 / 055998 Summary of the Invention [Problem to be solved by the invention]

[0008] In a display device having a front panel including a glass substrate and a resin layer, by arranging the resin layer closer to the viewer than the glass substrate, the resin layer can suppress glass cracking due to impact and improve impact resistance. However, as will be described in detail later, the impact resistance and flex resistance of a resin layer are considered to be contradictory properties. Therefore, a resin layer that can achieve both impact resistance and flex resistance is desired.

[0009] The present disclosure has been made in view of the above-described circumstances, and has as its main object to provide a flexible organic EL display device having excellent impact resistance and bending resistance, and a front panel for the display device used therein. [Means for solving the problem]

[0010] In order to solve the above problems, the inventors of the present disclosure conducted extensive research and found that, in a front panel having a glass substrate and a resin layer, by making the resin layer have a predetermined anisotropy of elastic modulus and by establishing a predetermined relationship between the direction in the plane of the resin layer where the elastic modulus is relatively high and the direction where the elastic modulus is relatively low and the bending direction of the display device, it is possible to improve both impact resistance and flex resistance. The present disclosure is based on this finding.

[0011] One embodiment of the present disclosure provides a flexible organic electroluminescent display device comprising an organic electroluminescent display panel and a front panel arranged on the viewer side of the organic electroluminescent display panel, wherein the front panel has a glass substrate located on the organic electroluminescent display panel and having a thickness of 100 μm or less, and a resin layer located on the glass substrate, wherein, within the plane of the resin layer, when E1 is a composite elastic modulus in a first direction and E2 is a composite elastic modulus in a second direction perpendicular to the first direction, E1 / E2 is 1.2 or more, and 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.

[0012] Another embodiment of the present disclosure provides a front panel for a display device, comprising a glass substrate having a thickness of 100 μm or less and a resin layer on the glass substrate, wherein, in the plane of the resin layer, when a composite elastic modulus in a first direction is E1 and a composite elastic modulus in a second direction perpendicular to the first direction is E2, E1 / E2 is 1.2 or more.

[0013] In the present disclosure, it is preferable that 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 more, where "Gpa" represents gigapascals, a unit of pressure.

[0014] The front panel for a display device according to the present disclosure may also have an adhesive layer between the glass substrate and the resin layer.

[0015] Furthermore, the front panel for a display device according to the present disclosure can have, in this order, the glass substrate, the resin layer, and a functional layer on the resin layer. [Effects of the Invention]

[0016] The present disclosure has an effect of providing a flexible organic EL display device and a front panel for the display device that are excellent in impact resistance and bending resistance. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic cross-sectional view illustrating a flexible organic EL display device according to the present disclosure. [Figure 2] FIG. 2 is a schematic plan view illustrating a resin layer in the present disclosure. [Figure 3] 1 is a schematic perspective view illustrating a flexible organic EL display device according to the present disclosure. [Figure 4] 1 is a schematic cross-sectional view illustrating a flexible organic EL display device according to the present disclosure. [Figure 5] 1 is a schematic cross-sectional view illustrating a front panel for a display device according to the present disclosure. [Figure 6] FIG. 1 is a schematic diagram for explaining a dynamic bending test. [Figure 7] FIG. 1 is a schematic diagram for explaining a static bending test. [Figure 8] FIG. 2 is a schematic diagram for explaining the measurement position of indentation hardness. DETAILED DESCRIPTION OF THE INVENTION

[0018] Embodiments of the present disclosure will be described below with reference to the drawings and the like. However, the present disclosure can be implemented in many different forms, and should not be construed as being limited to the description of the embodiments exemplified below. Furthermore, to clarify the explanation, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual form, but these are merely examples and are not intended to limit the interpretation of the present disclosure. Furthermore, in this specification and each drawing, elements similar to those described above with reference to the previous drawings will be designated by the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0019] In this specification, when describing a mode in which another component is placed on a certain component, the terms "above" or "below" are used, unless otherwise specified, to include both a case in which another component is placed directly above or below a certain component so as to be in contact with the component, and a case in which another component is placed above or below a certain component with another component interposed therebetween. Also, in this specification, when describing a mode in which another component is placed on the surface of a certain component, the terms "on the surface side" or "on the surface" are used, unless otherwise specified, to include both a case in which another component is placed directly above or below a certain component so as to be in contact with the component, and a case in which another component is placed above or below a certain component with another component interposed therebetween.

[0020] The flexible organic EL display device and the front panel for the display device according to the present disclosure will be described in detail below.

[0021] A. Flexible OLED display The flexible organic EL display device of the present disclosure is a flexible organic electroluminescent display device comprising an organic electroluminescent display panel and a front panel arranged on the viewer side of the organic electroluminescent display panel, wherein the front panel has a glass substrate located on the organic electroluminescent display panel and having a thickness of 100 μm or less, and a resin layer located on the glass substrate, wherein, within the plane of the resin layer, when a composite elastic modulus in a first direction is E1 and a composite elastic modulus in a second direction perpendicular to the first direction is E2, E1 / E2 is 1.2 or more, and 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.

[0022] Fig. 1 is a schematic cross-sectional view showing an example of a flexible organic EL display device according to the present disclosure. As shown in Fig. 1, flexible organic EL display device 10 includes an organic EL display panel 11 and a front substrate 1 arranged on the viewer's side of organic EL display panel 11. Front substrate 1 includes, in this order from the organic EL display panel 11 side, a glass substrate 2 and a resin layer 3. Glass substrate 2 has a predetermined thickness, and resin layer 3 has a predetermined anisotropy of composite elastic modulus. Front substrate 1 may include an adhesive layer 4 between glass substrate 2 and resin layer 3. In flexible organic EL display device 10, an adhesive or bonding layer 12 may be disposed between front substrate 1 and organic EL display panel 11.

[0023] In the front panel of the present disclosure, the glass substrate has a thickness of less than a predetermined value, which is a concern because it is thin and therefore prone to breakage and has low impact resistance. However, by disposing a resin layer on the side of the glass substrate opposite the organic EL display panel, when an impact is applied to the front panel of the flexible organic EL display device, the resin layer absorbs the impact and can prevent the glass substrate from breaking, thereby improving impact resistance. Furthermore, even if the glass substrate breaks, the resin layer can prevent the glass from shattering.

[0024] 2, in the front panel of the present disclosure, when the composite elastic modulus in a first direction 21 is E1 and the composite elastic modulus in a second direction 22 perpendicular to the first direction 21 is E2, the ratio E1 / E2 is 1.2 or more within the plane of the resin layer 3, i.e., 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 predetermined elastic modulus anisotropy.

[0025] Here, the composite elastic modulus is a physical property value that represents the resistance to elastic deformation. In the present disclosure, 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, and it can be said that the resin layer 3 is relatively less susceptible to elastic deformation in the first direction 21 where the composite elastic modulus is relatively high and relatively more susceptible to elastic deformation in the second direction 21 where the composite elastic modulus is relatively low.

[0026] 2, in the flexible organic EL display device of the present disclosure, the angle θ formed between a first direction 21 in which the composite elastic modulus is relatively high in the plane of the resin layer 3 and a bending direction 20 of the flexible organic EL display device is 45° or more and 90° or less. In this case, the angle formed between a second direction 22 in which the composite elastic modulus is relatively low in the plane of the resin layer 3 and the bending direction 20 of the flexible organic EL display device is 0° or more and 45° or less.

[0027] 3(a) and 3(b) are schematic perspective views illustrating a flexible organic EL display device according to the present disclosure, where FIG. 3(a) shows the flexible organic EL display device 10 in an unfolded state, and FIG. 3(b) shows the flexible organic EL display device 10 in a folded state. The folding direction 20 of the flexible organic EL display device 10 refers to the direction in which the flexible organic EL display device 10 is folded, as shown in FIGS. 3(a) and 3(b). The folding direction of the flexible organic EL display device may be, for example, either the longitudinal direction or the width direction of the flexible organic EL display device, and is not particularly limited.

[0028] In the present disclosure, the bending resistance can be improved by establishing the above-mentioned relationship between the first direction 21 in which the composite elastic modulus is relatively high and the second direction 22 in which the composite elastic modulus is relatively low within the plane of the resin layer 3, and the bending direction 20 of the flexible organic EL display device. The reason for this is presumed to be as follows.

[0029] 3(b), for example, stress is applied to the bent portion 25 of the flexible organic EL display device 10, causing distortion. At this time, in the front panel of the flexible organic EL display device 10, glass has a higher elastic modulus than resin, and the neutral plane is the glass substrate, so when the flexible organic EL display device 10 is bent, the stress and distortion applied to the bent portion of the resin layer that is away from the neutral plane becomes large.

[0030] For example, when the second direction in the plane of the resin layer, in which the composite elastic modulus is relatively low, and the bending direction of the flexible organic EL display device are substantially parallel, i.e., when the angle between the second direction in the plane of the resin layer, in which the composite elastic modulus is relatively low, 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 is small because the composite elastic modulus in the second direction in the plane of the resin layer is relatively low. Therefore, even when the flexible organic EL display device is repeatedly bent and then unfolded, the bent portion of the resin layer can withstand the stress and remain in a state where plastic deformation is unlikely to occur. As a result, it is presumed that the flexible organic EL display device easily returns to a flat state, i.e., has good recovery after repeated bending, and is less likely to develop creases or creases.

[0031] On the other hand, for example, when the first direction in the plane of the resin layer, in which the composite elastic modulus is relatively high, and the bending direction of the flexible organic EL display device are substantially parallel, i.e., when the angle between the first direction in the plane of the resin layer, in which the composite elastic modulus 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 is large because the composite elastic modulus in the first direction in the plane of the resin layer is relatively high. Therefore, when the flexible organic EL display device is repeatedly bent and then opened, the bent portion of the resin layer cannot withstand the stress and is likely to undergo plastic deformation. As a result, it is thought that the flexible organic EL display device has difficulty returning to a flat state, i.e., has poor recovery after repeated bending, and is prone to creases and creases.

[0032] Furthermore, when the angle between the second direction in the plane of the resin layer in which the composite elastic modulus is relatively low and the bending direction of the flexible organic EL display device is 0° or more and 45° or less, i.e., when the angle θ between the first direction in the plane of the resin layer in which the composite elastic modulus is relatively high and the bending direction of the flexible organic EL display device is 45° or more and 90° or less, the stress applied to the bent portion of the resin layer when the flexible organic EL display device is repeatedly bent is smaller than when the angle θ between the first direction in the plane of the resin layer in which the composite elastic modulus is relatively high and the bending direction of the flexible organic EL display device is approximately 0°. Therefore, even when the angle θ between the second direction in the plane of the resin layer, in which the composite elastic modulus is relatively low, and the bending direction of the flexible organic EL display device is between 0° and 45°, i.e., when the angle θ between the first direction in the plane of the resin layer, in which the composite elastic modulus is relatively high, and the bending direction of the flexible organic EL display device is between 45° and 90°, as described above, even when the flexible organic EL display device is repeatedly bent and then unfolded, the stress applied to the bent portions of the resin layer is small, and the bent portions of the resin layer can withstand the stress and remain in a state where plastic deformation is unlikely to occur. As a result, it is presumed that the flexible organic EL display device easily returns to a flat state, i.e., has good recovery after repeated bending, and is unlikely to develop creases or creases.

[0033] Here, increasing the elastic modulus of the resin layer can increase the surface hardness of the resin layer, thereby suppressing cracking of the glass substrate and improving impact resistance, and also improving the shatter resistance of the glass. However, increasing the elastic modulus of the resin layer increases the stress and strain applied to the bent portion of the resin layer when bent, which may reduce the recovery ability after bending and reduce the flex resistance. Thus, impact resistance and flex resistance are considered to be contradictory properties of the resin layer.

[0034] In contrast, according to the present disclosure, as described above, the resin layer has a predetermined elastic modulus anisotropy, and therefore by increasing the composite elastic modulus in a first direction within the plane of the resin layer, the composite elastic modulus of the entire resin layer can be increased, thereby improving impact resistance; further, by decreasing the composite elastic modulus in a second direction within the plane of the resin layer and establishing a predetermined relationship between the first and second directions within the plane of the resin layer and the bending direction of the flexible organic EL display device, bending resistance can be improved.

[0035] Therefore, in the present disclosure, it is possible to improve impact resistance and flex resistance, and even if the glass substrate of the front panel is broken, the risk of injury to the human body can be reduced, resulting in a highly safe flexible organic EL display device.

[0036] Hereinafter, each component of the flexible organic EL display device according to the present disclosure will be described.

[0037] 1.Front plate The front panel in the present disclosure is a component arranged on the viewer's side of the organic EL display panel, and includes, in order from the organic EL display panel side, a glass substrate having a predetermined thickness and a resin layer having a predetermined anisotropic composite elastic modulus.

[0038] Hereinafter, each configuration of the front panel in the present disclosure will be described.

[0039] (1) Resin layer The resin layer according to the present disclosure is a member disposed on one surface of the glass substrate, and when E1 is a composite modulus of elasticity in a first direction within the plane of the resin layer and E2 is a composite modulus of elasticity in a second direction perpendicular to the first direction, E1 / E2 is 1.2 or greater. The angle between the bending direction of the flexible organic EL display device according to the present disclosure and the first direction of the resin layer is 45° or greater and 90° or less. The resin layer is a member having impact absorption properties and also functions as a member for suppressing glass shattering when the glass substrate is broken. The resin layer is transparent, and in the flexible organic EL display device according to the present disclosure, is disposed closer to the viewer than the glass substrate.

[0040] When the composite modulus of elasticity in a first direction within the plane of the resin layer is E1 and the composite modulus of elasticity in a second direction perpendicular to the first direction is E2, E1 / E2 can be 1.2 or more, preferably 1.3 or more, and more preferably 1.4 or more. By increasing the composite modulus of elasticity in the first direction within the plane of the resin layer and decreasing the composite modulus of elasticity in the second direction so that the E1 / E2 ratio falls within the above range, it is possible to improve flex resistance while ensuring impact resistance.

[0041] Furthermore, E1 / E2 is, for example, preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less. If the E1 / E2 ratio is too large, it becomes difficult to increase the composite elastic modulus of the entire resin layer, and sufficient impact resistance may not be obtained.

[0042] The composite elastic modulus E1 in the first direction and the composite elastic modulus E2 in the second direction of the resin layer need only satisfy the E1 / E2 ratio, but 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 keeping the average values ​​of E1 and E2 within the above ranges, the composite elastic modulus of the entire resin layer can be increased, which can suppress cracking of the glass substrate due to impact, improve impact resistance, and improve shatter resistance of the glass.

[0043] Furthermore, according to the method for measuring the composite elastic modulus described below, the composite elastic modulus of the glass substrate is approximately 40 GPa, so 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, for example, 20 GPa or less, and more preferably 10 GPa or less.

[0044] The composite elastic modulus E1 in the first direction of the resin layer may be any value that satisfies the E1 / E2 ratio and further satisfies the average value of the composite elastic modulus E1 in the first direction and the composite elastic modulus E2 in the second direction, and is, for example, preferably 4.0 GPa to 40 GPa, more preferably 4.5 GPa to 20 GPa, and even more preferably 5.0 GPa to 10 GPa. By increasing the composite elastic modulus in the first direction so that the composite elastic modulus E1 of the resin layer in the first direction is within the above range, the composite elastic modulus of the entire resin layer can be increased, which can suppress cracking of the glass substrate due to impact, improve impact resistance, and improve shatter resistance of the glass.

[0045] The composite elastic modulus E2 in the second direction of the resin layer may be any value that satisfies the E1 / E2 ratio and also satisfies the average value of the composite elastic modulus E1 in the first direction and the composite elastic modulus E2 in the second direction, and is, for example, preferably 3.0 GPa to 40 GPa, more preferably 3.5 GPa to 20 GPa, and even more preferably 4.0 GPa to 10 GPa. By lowering the composite elastic modulus in the second direction so that the composite elastic modulus E2 of the resin layer in the second direction is within the above range, bending resistance can be improved.

[0046] Here, the composite elastic modulus of the resin layer is the indentation hardness (H IT ) when measuring the contact projection area A p"Indentation hardness" is a value determined from the load-displacement curve from loading to unloading of the indenter obtained by hardness measurement using the nanoindentation method. The composite elastic modulus of the resin layer is an elastic modulus that includes the elastic deformation of the resin layer and the elastic deformation of the indenter. In the present disclosure, the reason why the composite elastic modulus, which is based on compressive elasticity using an indenter, is used as a parameter for flex resistance is as follows. When a bendable flexible organic EL display device is bent, the glass substrate is bent with the resin layer side facing the concave side. Since the glass substrate, which usually has a high elastic modulus, serves as the neutral axis, compressive stress is applied to the resin layer when the display device is bent. Therefore, to approximate this state, a composite elastic modulus, which is based on compressive elasticity rather than tensile elasticity, was used as a parameter. Furthermore, the composite modulus of elasticity, which is based on tensile elasticity, tends to produce results that vary depending on the condition of the end surface of the test piece, whereas the composite modulus of elasticity, which is based on compressive elasticity using an indenter, has the advantage of being less susceptible to the condition of the end surface and more likely to produce stable results. Therefore, the composite modulus of elasticity, which is based on compressive elasticity, was used as the parameter rather than tensile elasticity.

[0047] Indentation hardness (H ITThe measurement of the surface roughness (S) is performed on the measurement sample using a BRUKER TI950 TriboIndenter. Specifically, a 1 mm x 10 mm cut-out front panel is embedded in embedding resin to create a block, and uniform, hole-free sections with a thickness of 50 nm to 100 nm are cut from this block using a standard sectioning method. An Ultramicrotome EM UC7 (Leica Microsystems) or similar instrument can be used to prepare the sections. The remaining block from which the hole-free, uniform sections are cut serves as the measurement sample. Next, a Berkovich indenter (triangular pyramid, BRUKER TI-0039) is pressed vertically into the center of the cross section of the resin layer to a depth of 200 nm at a pressing speed of 10 nm / sec under the following measurement conditions: Here, in order to avoid the influence of the glass substrate and the side edges of the resin layer, the Berkovich indenter is pressed into a portion of the resin layer that is 500 nm or more away from the interface between the glass substrate and the resin layer toward the center of the resin layer, and 500 nm or more away from each of the two ends of the resin layer toward the center of the resin layer. If an optional layer such as a hard coat layer is present on the surface of the resin layer opposite to the surface facing the glass substrate, the Berkovich indenter is pressed into a portion of the resin layer that is 500 nm or more away from the interface between the optional layer and the resin layer toward the center of the resin layer. Thereafter, the residual stress is relaxed by holding the pressure constant, and then the pressure is released, and the maximum load after relaxation is measured, and the maximum load P max and contact projection area A p Using and, P max / A p The indentation hardness (H IT The above contact projected area is the contact projected area corrected for the indenter tip curvature by the Oliver-Pharr method using a standard sample of fused quartz (5-0098 manufactured by BRUKER). Indentation hardness (H IT) is the arithmetic mean value of the values ​​obtained by measuring at 15 points. If the measured values ​​include values ​​that deviate from the arithmetic mean value by more than ±20%, those values ​​shall be excluded and remeasured. Whether or not there are any measured values ​​that deviate from the arithmetic mean value by more than ±20% shall be judged by whether the value (%) calculated by (AB) / B x 100 is more than ±20%, where A is the measured value and B is the arithmetic mean value. Indentation hardness (H IT ) can be adjusted by the type of resin contained in the resin layer, which will be described later.

[0048] (Measurement conditions) Indentation depth: 200nm Push speed: 10nm / sec ·Holding time: 5 seconds ·Loading and unloading speed: 10nm / sec ·Measurement temperature: 25℃

[0049] Composite elastic modulus of resin layer E r is the contact projected area A obtained during the indentation hardness measurement using the following formula (1). p The composite elastic modulus is determined by measuring the indentation hardness at 15 locations, calculating the composite elastic modulus each time, and taking the arithmetic mean value of the composite elastic moduli obtained at the 15 locations.

[0050]

number

[0051] (In the above formula (1), A p is the contact projected area, and E r is the composite elastic modulus of the resin layer, and S is the contact stiffness indicated by the slope of the load-displacement curve immediately after the start of unloading.

[0052] When measuring the composite elastic modulus of the resin layer in the first direction, the indentation hardness is measured on a cross section cut along a second direction perpendicular to the first direction. When measuring the composite elastic modulus of the resin layer in the second direction, the indentation hardness is measured on a cross section cut along the first direction perpendicular to the second direction.

[0053] In the above method for measuring the composite elastic modulus of the resin layer, a measurement sample is prepared for the front panel, but a measurement sample may also be prepared for only the resin layer.

[0054] The first direction in the plane of the resin layer is preferably the main stretching direction. That is, the first direction in the plane of the resin layer is preferably the direction showing the maximum refractive index in the plane of the resin layer. This is because, in a resin layer, molecules generally tend to be oriented along the main stretching direction, and the composite elastic modulus in the main stretching direction tends to be high.

[0055] The main stretching direction refers to the stretching direction in the case of uniaxial stretching, and refers to the stretching direction with a higher stretch ratio in the case of biaxial stretching.

[0056] The main stretching direction of the resin layer may be, for example, either the MD direction or the TD direction. That is, when the first direction in the plane of the resin layer is the main stretching direction, the first direction in the plane of the resin layer may be, for example, either the MD direction or the TD direction.

[0057] The MD direction (machine direction) refers to the direction in which the resin film flows, and the TD direction (transverse direction) refers to the direction perpendicular to the MD direction.

[0058] In the present disclosure, as illustrated in FIG. 2 , the angle θ between a first direction 21 in the plane of the resin layer 3, in which the composite elastic modulus is relatively high, and a bending direction 20 of the flexible organic EL display device is 45° or more and 90° or less. The angle θ is preferably 60° or more and 90° or less, more preferably 75° or more and 90° or less, even more preferably 85° or more and 90° or less, and particularly preferably 90°. Note that the angle θ refers to the smaller angle between the first direction in the plane of the resin layer, in which the composite elastic modulus is relatively high, and the bending direction of the flexible organic EL display device. By setting the angle θ within the above range, the flexible organic EL display device can easily return to a flat state when opened after repeated folding. This improves the recovery ability after repeated folding, making it less likely to develop creases or creases. Therefore, the flexible organic EL display device can have improved bending resistance when repeatedly folded.

[0059] In the above case, the angle formed between the second direction in the plane of the resin layer in which the composite elastic modulus is relatively low and the bending direction of the flexible organic EL display device is from 0° to 45°, preferably from 0° to 30°, more preferably from 0° to 15°, even more preferably from 0° to 5°, and particularly preferably 0°. Note that the above angle refers to the smaller angle between the second direction in the plane of the resin layer in which the composite elastic modulus is relatively low and the bending direction of the flexible organic EL display device.

[0060] The resin layer has transparency. 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. Such a high total light transmittance allows for a front panel with good transparency.

[0061] The total light transmittance of the resin layer can be measured in accordance with JIS K7361-1:1997, for example, using a haze meter HM150 manufactured by Murakami Color Research Laboratory.

[0062] The haze of the resin layer is preferably 5% or less, more preferably 2% or less, and even more preferably 1% or less. Such a low haze allows for a front panel with good transparency.

[0063] The haze of the resin layer can be measured in accordance with JIS K-7136:2000, for example, using a haze meter HM150 manufactured by Murakami Color Research Laboratory.

[0064] The resin contained in the resin layer is not particularly limited as long as it satisfies the anisotropy of the composite elastic modulus described above and has transparency, and examples thereof include polyester-based resins, polyimide-based resins, polyamide-imide-based resins, polyamide-based resins, etc. Examples of polyester-based resins include polyethylene terephthalate and polyethylene naphthalate.

[0065] The resin layer may further contain additives as needed, such as fillers, ultraviolet absorbers, antioxidants, light stabilizers, surfactants, adhesion improvers, antistatic agents, and lubricants.

[0066] The thickness of the resin layer is not particularly limited as long as it is thick enough to exhibit impact absorption and shatterproof properties for glass, and can be, for example, 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 shatterproof properties for glass may not be obtained. Furthermore, if the resin layer is too thick, flexibility may be impaired, or the resin layer may crack when the flexible organic EL display device is bent.

[0067] The thickness of the resin layer can be the average value of thicknesses measured at any 10 locations on a cross section of the front panel for a display device in the thickness direction as observed with a transmission electron microscope (TEM), a scanning electron microscope (SEM), or a scanning transmission electron microscope (STEM). The thicknesses of other layers in the front panel can be measured in the same manner.

[0068] The resin layer may be, for example, a resin film. The resin film is not particularly limited as long as it satisfies the anisotropy of the composite elastic modulus described above, and may be, for example, a uniaxially stretched film or a biaxially stretched film. Among these, a biaxially stretched film is preferred.

[0069] Examples of methods for controlling the composite elastic modulus in the first and second directions of a resin film include appropriately setting the stretching ratio, stretching temperature, etc. Specifically, the composite elastic modulus in the stretching direction tends to increase as the stretching ratio increases and the stretching temperature decreases, while the composite elastic modulus in the stretching direction tends to decrease as the stretching ratio decreases and the stretching temperature increases.

[0070] (2) Glass substrate The glass substrate in the present disclosure has a thickness of 100 μm or less and is a member that supports the resin layer.

[0071] The glass constituting the glass substrate is not particularly limited as long as it has transparency, and examples thereof include silicate glass, silica glass, etc. Among them, borosilicate glass, aluminosilicate glass, and aluminoborosilicate glass are preferred, and alkali-free glass is more preferred. Examples of commercially available glass substrates include ultra-thin glass G-Leaf from Nippon Electric Glass Co., Ltd. and ultra-thin glass from Matsunami Glass Industry Co., Ltd.

[0072] The glass constituting the glass substrate is also preferably chemically strengthened glass. Chemically strengthened glass is preferable because it has excellent mechanical strength and can be made thinner accordingly. Chemically strengthened glass is typically glass whose mechanical properties have been strengthened by a chemical method by partially exchanging ion species, such as replacing sodium with potassium, near the surface of the glass, and has a compressive stress layer on the surface.

[0073] Examples of glasses that can be used to form chemically strengthened glass substrates include aluminosilicate glass, soda-lime glass, borosilicate glass, lead glass, alkali barium glass, and aluminoborosilicate glass.

[0074] Examples of commercially available chemically strengthened glass substrates include Gorilla Glass from Corning and Dragontrail from AGC.

[0075] The thickness of the glass substrate is 100 μm or less, preferably 15 μm or more and 100 μm or less, more preferably 20 μm or more and 90 μm or less, and even more preferably 25 μm or more and 80 μm or less. A glass substrate having a thin thickness within the above range can provide good flexibility and sufficient hardness. It can also suppress curling of the front panel. Furthermore, this is preferable in terms of reducing the weight of the front panel.

[0076] (3) Functional layer The front panel of the present disclosure may further include a functional layer on the side of the resin layer opposite the glass substrate, such as a hard coat layer, an anti-reflection layer, or an anti-glare layer.

[0077] The functional layer may be a single layer or may have multiple layers, and may be a layer having a single function or may have multiple layers having different functions.

[0078] (a) Hard coat layer The front panel of the present disclosure may further include a hard coat layer 5 on the side of the resin layer 3 opposite the glass substrate 2, as shown in Fig. 4, for example. The hard coat layer is a member for increasing surface hardness. The presence of the hard coat layer can improve scratch resistance.

[0079] As the material for the hard coat layer, for example, an organic material, an inorganic material, an organic-inorganic composite material, or the like can be used.

[0080] In particular, the material of the hard coat layer is preferably an organic material. Specifically, the hard coat layer preferably contains a cured product of a resin composition containing a polymerizable compound. The cured product of the resin composition containing a polymerizable compound can be obtained by polymerizing the polymerizable compound using a polymerization initiator as needed by a known method.

[0081] The polymerizable compound has at least one polymerizable functional group in the molecule, and may be, for example, at least one of a radical polymerizable compound and a cation polymerizable compound.

[0082] The radical polymerizable compound is a compound having a radical polymerizable group. The radical polymerizable group of the radical polymerizable compound is not particularly limited as long as it is a functional group capable of causing a radical polymerization reaction, and examples thereof include groups containing a carbon-carbon unsaturated double bond, and specific examples thereof include a vinyl group and a (meth)acryloyl group. When the radical polymerizable compound has two or more radical polymerizable groups, these radical polymerizable groups may be the same or different.

[0083] The number of radically polymerizable groups that the radically polymerizable compound has in one molecule is preferably 2 or more, more preferably 3 or more, from the viewpoint of improving the hardness of the hard coat layer.

[0084] In this specification, (meth)acryloyl refers to both acryloyl and methacryloyl, and (meth)acrylate refers to both acrylate and methacrylate.

[0085] The cationically polymerizable compound is a compound having a cationically polymerizable group. The cationically polymerizable group of the cationically polymerizable compound is not particularly limited as long as it is a functional group capable of causing a cationic polymerization reaction, and examples thereof include an epoxy group, an oxetanyl group, and a vinyl ether group. When the cationically polymerizable compound has two or more cationically polymerizable groups, these cationically polymerizable groups may be the same or different.

[0086] The number of cationically polymerizable groups that the cationically polymerizable compound has in one molecule is preferably 2 or more, more preferably 3 or more, from the viewpoint of improving the hardness of the hard coat layer.

[0087] The resin composition containing the polymerizable compound may contain a polymerization initiator as needed. The polymerization initiator may be appropriately selected from radical polymerization initiators, cationic polymerization initiators, radical and cationic polymerization initiators, etc. These polymerization initiators are decomposed by at least one of light irradiation and heating to generate radicals or cations, thereby promoting radical polymerization and cationic polymerization. Note that in some cases, the polymerization initiator may be completely decomposed and not remain in the hard coat layer.

[0088] The hard coat layer may further contain additives as necessary. The additives are appropriately selected depending on the function to be imparted to the hard coat layer, and are not particularly limited, and examples thereof include fillers, ultraviolet absorbers, infrared absorbers, antiglare agents, antifouling agents, antistatic agents, leveling agents, surfactants, lubricants, various sensitizers, flame retardants, adhesion promoters, polymerization inhibitors, antioxidants, light stabilizers, and surface modifiers.

[0089] The thickness of the hard coat layer may be appropriately selected depending on the function of the hard coat layer, and is, for example, preferably from 2 μm to 50 μm, more preferably from 3 μm to 30 μm, even more preferably from 5 μm to 20 μm, and particularly preferably from 6 μm to 10 μm. If the thickness of the hard coat layer is within the above range, sufficient hardness as a hard coat layer can be obtained, and a front panel with good flex resistance can be obtained.

[0090] The method for forming the hard coat layer is appropriately selected depending on the material of the hard coat layer, etc., and examples thereof include a method of applying a curable resin composition for the hard coat layer containing the polymerizable compound or the like onto the resin layer and curing the composition, a vapor deposition method, a sputtering method, etc.

[0091] (4) Other configurations In addition to the layers described above, the front panel of the present disclosure may also include other layers, such as an adhesive layer, as needed.

[0092] 1, the front panel of the present disclosure can have an adhesive layer 4 between a glass substrate 2 and a resin layer 3. The resin layer can be disposed on one surface of the glass substrate via the adhesive layer.

[0093] 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, for example, preferably 0.05 MPa or more, more preferably 0.5 MPa or more, and even more preferably 3 MPa or more. Having the shear storage modulus of the adhesive layer within the above range allows the layer to be relatively soft. In this case, the placement of a relatively soft adhesive layer between the resin layer and the glass substrate can improve impact resistance. This is thought to be because the adhesive layer is relatively soft and easily deformed, and therefore, when an impact is applied to the front panel, the adhesive layer does not inhibit deformation of the resin layer, making the resin layer more susceptible to deformation, resulting in a greater impact absorption effect.

[0094] Here, the shear storage modulus of the adhesive layer at a frequency of 950 Hz and a temperature of 23°C is determined by measuring the shear storage modulus at a frequency of 950 Hz and a temperature of 23°C three times and calculating the arithmetic mean value of the three measurements.

[0095] The frequency of 950 Hz was chosen because this frequency is within the frequency range in which the surface of the front panel deforms by several μm to several tens of μm when an object is allowed to fall freely from a height of several cm, and is also within the frequency range in which components such as the display panel that are positioned inside the front panel in a flexible organic EL display device are damaged.

[0096] 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 a dynamic viscoelasticity measuring device (DMA), the adhesive layer is first punched out into a 10 mm x 5 mm rectangular shape to obtain a measurement sample. Two of these measurement samples are then prepared and attached to the solid shear jig of the dynamic viscoelasticity measuring device. Specifically, the solid shear jig has three horizontal plates (a 1 mm-thick metal middle plate and two metal outer plates located on either side of the middle plate). One measurement sample is sandwiched between the middle plate and one of the outer plates, and the other measurement sample is sandwiched between the middle plate and the other outer plate. The solid shear jig is then placed in the dynamic viscoelasticity measuring device with a chuck distance of 20 mm. The shear storage modulus G' is measured in an environment of 23°C by applying a 1% strain to the two outer plates and a longitudinal vibration of 950 Hz to the outer plates while the middle plate is fixed. As the dynamic viscoelasticity measuring device, for example, Rheogel-E4000 manufactured by UBM Co., Ltd. Specific measurement conditions for the above method are shown below.

[0097] (Shear storage modulus measurement conditions) Measurement sample: 10mm x 5mm rectangle (2 pieces) Measurement jig: solid shear Distortion waveform: Sine wave Distortion control: Automatic adjustment Frequency: 950Hz ·Temperature: 23℃

[0098] In addition, when measuring the shear storage modulus of the adhesive layer, the glass substrate and the resin layer are peeled off from the adhesive layer before measurement. The peeling of the glass substrate and the resin layer can be performed, for example, as follows. First, the front panel is heated with a dryer, and the tip of a cutter is inserted into the area that is thought to be the interface between the adhesive layer and other layers, and the layers are slowly peeled off. By repeating this heating and peeling process, the glass substrate and the resin layer can be peeled off from the adhesive layer. Note that even if such a peeling process is performed, it does not have a significant effect on the measurement.

[0099] The adhesive used in the adhesive layer is not particularly limited as long as it satisfies the above-mentioned shear storage modulus, has transparency, and is capable of adhering the above-mentioned glass substrate and resin layer, and examples thereof include acrylic adhesives, silicone adhesives, rubber adhesives, urethane adhesives, etc., and can be appropriately selected depending on the material of the above-mentioned resin layer, etc. Among them, acrylic adhesives are preferred because they have excellent transparency, weather resistance, durability, heat resistance, and low cost.

[0100] The thickness of the adhesive layer is preferably, for example, 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, the glass substrate and the resin layer may not be sufficiently bonded, and the effect of making the resin layer easily deformable when an impact is applied to the front panel may not be fully achieved. Furthermore, if the adhesive layer is too thick, flexibility may be impaired.

[0101] The adhesive layer may be, for example, an adhesive film. Alternatively, the adhesive layer may be formed by applying a composition for adhesive layer onto a support, a glass substrate, or a resin layer.

[0102] (5) Characteristics of the front panel The front panel in the present disclosure preferably has a total light transmittance of, for example, 85% or more, more preferably 88% or more, and even more preferably 90% or more. Such a high total light transmittance allows for a front panel with good transparency.

[0103] The total light transmittance of the front panel can be measured in accordance with JIS K7361-1:1997, for example, using a haze meter HM150 manufactured by Murakami Color Research Laboratory.

[0104] The haze of the front panel in the present disclosure is, for example, preferably 25% or less, more preferably 2% or less, and even more preferably 1% or less. Such a low haze allows for a front panel with good transparency.

[0105] The haze of the front panel can be measured in accordance with JIS K-7136:2000, for example, using a haze meter HM150 manufactured by Murakami Color Research Laboratory.

[0106] The total thickness of the front panel in the present disclosure is not particularly limited as long as it is a thickness that provides flexibility, and can be, for example, preferably 35 μm to 400 μm, more preferably 65 μm to 330 μm, and even more preferably 95 μm to 240 μm. By having the total thickness of the front panel within the above range, the front panel can have good flexibility.

[0107] 2. Organic EL display panel The organic EL display panel of the present disclosure can have the same configuration as a general organic EL display device.

[0108] 3. Other configurations The flexible organic EL display device according to the present disclosure may have a touch panel member between the display panel and the front panel, which may have the same configuration as a general touch panel member.

[0109] 4. Flexible OLED display The flexible organic EL display device according to the present disclosure is preferably foldable. That is, the flexible organic EL display device according to the present disclosure is preferably a foldable display. The flexible organic EL display device according to the present disclosure has excellent bending resistance and is suitable as a foldable display.

[0110] B. Front panel for display device The front panel for a display device according to the present disclosure comprises a glass substrate having a thickness of 100 μm or less and a resin layer on the glass substrate, and in the plane of the resin layer, when E1 is a composite elastic modulus in a first direction and E2 is a composite elastic modulus in a second direction perpendicular to the first direction, E1 / E2 is 1.2 or more.

[0111] Fig. 5 is a schematic cross-sectional view showing an example of a display device front panel according to the present disclosure. As shown in Fig. 5, display device front panel 1A includes glass substrate 2 and resin layer 3 disposed on one surface of glass substrate 2. Glass substrate 2 has a predetermined thickness, and resin layer 3 has a predetermined anisotropy of composite elastic modulus. Display device front panel 1A may include adhesive layer 4 between glass substrate 2 and resin layer 3.

[0112] When the front panel for a display device according to the present disclosure is used in a display device, the first and second directions in the plane of the resin layer can have a predetermined relationship with the bending direction of the display device, as described above in the section "A. Flexible organic EL display device." Therefore, in the front panel for a display device according to the present disclosure, as described above, the resin layer has a predetermined elastic modulus anisotropy, and therefore, by increasing the composite elastic modulus in the first direction in the plane of the resin layer, the composite elastic modulus of the entire resin layer can be increased and impact resistance can be improved. Furthermore, by decreasing the composite elastic modulus in the second direction in the plane of the resin layer and establishing a predetermined relationship between the first and second directions in the plane of the resin layer and the bending direction of the display device, bending resistance can be improved.

[0113] Therefore, in the present disclosure, it is possible to improve impact resistance and flex resistance, and furthermore, to provide a highly safe front panel for a display device.

[0114] The front panel for a display device in the present disclosure can be the same as the front panel in the flexible organic EL display device described above, and therefore a description thereof will be omitted here.

[0115] The front panel for a display device according to the present disclosure has flex resistance. Specifically, it is preferable that the front panel for a display device does not crack or break when subjected to a dynamic flex test described below 200,000 times, and it is even more preferable that the front panel for a display device does not crack or break when subjected to a dynamic flex test 1,000,000 times.

[0116] In the dynamic bending test, the front panel for a display device is repeatedly bent so that the angle between the bending direction of the front panel for a display device and the first direction in the plane of the resin layer is 90°. In this case, it is preferable that the front panel for a display device does not crack or break. In particular, it is more preferable that the front panel for a display device does not crack or break when repeatedly bent so that the angle between the bending direction of the front panel for a display device and the first direction in the plane of the resin layer is 45° or more and 90° or less. In particular, it is even more preferable that the front panel for a display device does not crack or break when repeatedly bent so that the bending direction of the front panel for a display device is in any direction in the plane of the resin layer.

[0117] In the dynamic bending test, the front panel for a display device may be folded so that the glass substrate is on the outside, or the front panel for a display device may be folded so that the glass substrate is on the inside, but in either case, it is preferable that the front panel for a display device does not crack or break.

[0118] (Dynamic bending test) The dynamic bending test is performed as follows. First, a test piece of a display front panel measuring 20 mm × 100 mm is prepared. The longitudinal direction of the test piece is parallel to the bending direction. For example, when bending the display front panel so that the angle between the bending direction of the display front panel and a first direction in the plane of the resin layer is 90°, the longitudinal direction of the test piece is parallel to the bending direction and perpendicular to the first direction in the plane of the resin layer. Then, in the dynamic bending test, as shown in FIG. 6(a), short side 1C of display front panel 1A and short side 1D opposite short side 1C are fixed by parallel-arranged fixing members 51. As shown in FIG. 6(a), fixing members 51 are slidable horizontally. Next, as shown in FIG. 6(b), the fixing portions 51 are moved closer to each other to deform the display device front panel 1A so that it folds. Then, as shown in FIG. 6(c), the fixing portions 51 are moved to a position where the distance between the two opposing short sides 1C and 1D of the display device front panel 1A fixed by the fixing portions 51 is 10 mm. The fixing portions 51 are then moved in the opposite direction to eliminate the deformation of the display device front panel 1A. By moving the fixing portions 51 as shown in FIGS. 6(a) to 6(c), the display device front panel 1A can be folded 180°. Furthermore, by performing a dynamic bending test to ensure that the bent portion 1E of the display device front panel 1A does not protrude beyond the bottom end of the fixing portions 51 and controlling the distance when the fixing portions 51 are closest to each other, the distance between the two opposing short sides 1C and 1D of the display device front panel 1A can be set to 10 mm. In this case, the outer diameter of the bent portion 1E is considered to be 10 mm.

[0119] It is preferable that the front panel for a display device does not crack or break when a dynamic bending test is repeated 200,000 times in which the front panel for a display device 1A is folded 180° so that the distance between the opposing short sides is 10 mm, but it is even more preferable that the front panel for a display device does not crack or break when a dynamic bending test is repeated 200,000 times in which the front panel for a display device is folded 180° so that the distance between the opposing short sides is 10 mm, 8 mm, 6 mm, 5 mm, 4 mm, 3 mm, 2.5 mm, or 2 mm.

[0120] Furthermore, when the dynamic bending test described above is repeated 200,000 times on a front panel for a display device so that the angle between the bending direction of the front panel for a display device and the first direction in the plane of the resin layer is 90°, the opening angle of the front panel for a display device after the dynamic bending test is, for example, preferably 90° or more, more preferably 100° or more, and even more preferably 110° or more.

[0121] Furthermore, when the above-mentioned dynamic bending test is repeated 200,000 times so that the angle between the bending direction of the front panel for a display device and the first direction in the plane of the resin layer is 45° or more and 90° or less, it is more preferable that the opening angle of the front panel for a display device after the dynamic bending test is within the above-mentioned range.

[0122] The interior angle of a display front panel after a dynamic bending test can be measured as follows. After repeating the dynamic bending test 200,000 times, the fixing portion is removed from one short side of the display front panel, the folded state is released, and the opening angle, which is the angle at which the display front panel 1A naturally opens after 30 minutes at room temperature, is measured. Note that a larger opening angle indicates better recovery, and the maximum opening angle is 180°.

[0123] In the dynamic bending test, the front panel for a display device may be folded so that the glass substrate is on the inside, or the front panel for a display device may be folded so that the glass substrate is on the outside, but in either case, it is preferable that the opening angle after the dynamic bending test is within the above range.

[0124] Furthermore, when the static bending test described below is performed on the front panel for a display device, the opening angle of the front panel for a display device after the static bending test is, for example, preferably 90° or more, more preferably 100° or more, and even more preferably 110° or more.

[0125] In the static bending test, the front panel for a display device is bent so that the angle between the bending direction of the front panel for a display device and the first direction in the plane of the resin layer is 90°. In this case, the opening angle after the static bending test is preferably within the above range. In particular, when the front panel for a display device is bent so that the angle between the bending direction of the front panel for a display device and the first direction in the plane of the resin layer is 45° or more and 90° or less, the opening angle after the static bending test is more preferably within the above range.

[0126] (Static bending test) The static bending test is performed as follows. First, as shown in FIG. 7(a), short side 1C of display device front panel 1A and short side 1D opposite short side 1C are fixed with fixing parts 52 arranged parallel to each other so that the distance between short side 1C and short side 1D is 10 mm. Then, a static bending test is performed in which display device front panel 1A is left in a folded state at 23°C for 240 hours. After the static bending test, fixing parts 52 are removed from short side 1D to unfold the panel, and the opening angle α, which is the angle at which display device front panel 1A naturally opens after 30 minutes at room temperature, is measured. The larger the opening angle α, the better the restoration property, and the maximum opening angle is 180°.

[0127] In the static bending test, the front panel for a display device may be folded so that the glass substrate is on the inside, or the front panel for a display device may be folded so that the glass substrate is on the outside, but in either case, it is preferable that the opening angle α after the static bending test is in the above range.

[0128] The display device front panel according to the present disclosure can be used as a component disposed closer to the viewer than the display panel in a display device. The display device front panel according to the present disclosure can be used in display devices such as smartphones, tablet devices, wearable devices, personal computers, televisions, digital signage, public information displays (PIDs), and in-vehicle displays. The display device front panel according to the present disclosure can also be used in display devices such as organic electroluminescence (EL) display devices and liquid crystal display devices. In particular, the display device front panel according to the present disclosure can be suitably used in flexible displays such as foldable displays, rollable displays, and bendable displays.

[0129] In the front panel for a display device according to the present disclosure, the surface that will become the outermost surface after the front panel for a display device is placed on the surface of the display device is preferably the surface on the resin layer side.

[0130] The method for disposing the display device front panel of the present disclosure on the surface of the display device is not particularly limited, and examples thereof include a method using an adhesive layer or a adhesive layer, etc. As the adhesive layer or adhesive layer, known adhesive layers and adhesive layers used for bonding display device front panels can be used.

[0131] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0132] The present disclosure will be further described below with reference to examples and comparative examples.

[0133] [Example 1] A polyethylene terephthalate material melted at 290°C was extruded through a mold to form a sheet, which was then cooled by contact with a cooling roll to produce an unstretched resin film. Next, using a biaxial stretching tester (manufactured by Toyo Seiki Co., Ltd.), the unstretched resin film was subjected to a first stretching at 120°C at a stretching ratio of 4.4 times, and then a second stretching at a stretching ratio of 1.4 times in a direction 90° from the first stretching direction, to obtain a resin layer with a thickness of 50 μm.

[0134] A front panel was produced by bonding a 50 μm thick chemically strengthened glass substrate to one side of the resin layer via a 50 μm thick acrylic adhesive (product name "8146-2", manufactured by 3M).

[0135] [Example 2] In Example 1, the unstretched resin film was subjected to a first stretching at a stretching ratio of 3.9 times at 120°C, and then a second stretching at a stretching ratio of 1.4 times in a direction 90° to the first stretching direction, thereby obtaining a resin layer with a thickness of 50 μm. Except for this, a front panel was produced in the same manner as in Example 1.

[0136] [Example 3] In Example 1, the unstretched resin film was subjected to a first stretching at a stretching ratio of 5.8 times at 120°C, and then a second stretching at a stretching ratio of 1.4 times in a direction 90° to the first stretching direction, thereby obtaining a resin layer with a thickness of 50 μm. Except for this, a front panel was produced in the same manner as in Example 1.

[0137] [Example 4] In Example 1, the unstretched resin film was subjected to a first stretching at a stretching ratio of 6.5 times at 120°C, and then a second stretching at a stretching ratio of 1.4 times in a direction 90° to the first stretching direction, thereby obtaining a resin layer with a thickness of 50 μm. A front panel was produced in the same manner as in Example 1, except that the unstretched resin film was subjected to a first stretching at a stretching ratio of 6.5 times at 120°C, and then a second stretching at a stretching ratio of 1.4 times in a direction 90° to the first stretching direction.

[0138] [Comparative Example 1] In Example 1, the unstretched resin film was subjected to a first stretching at a stretching ratio of 2.5 times at 120°C, and then a second stretching at a stretching ratio of 1.4 times in a direction 90° to the first stretching direction, thereby obtaining a resin layer with a thickness of 50 μm. A front panel was produced in the same manner as in Example 1, except that the unstretched resin film was subjected to a first stretching at a stretching ratio of 2.5 times at 120°C, and then a second stretching at a stretching ratio of 1.4 times in a direction 90° to the first stretching direction.

[0139] Comparative Example 2 In Example 1, the front panel was produced in the same manner as in Example 1, except that the unstretched resin film was subjected to a first stretching at a stretching ratio of 2.0 times at 120°C, and then a second stretching at a stretching ratio of 1.4 times in a direction 90° to the first stretching direction, thereby obtaining a resin layer with a thickness of 50 μm.

[0140] [evaluation] (1) Composite modulus The composite elastic modulus of the resin layer was determined in the examples and comparative examples.

[0141] First, the indentation hardness of the resin layer was measured. ITMeasurements of the σ were performed on the measurement sample using a BRUKER TI950 TriboIndenter. Specifically, a 1 mm × 10 mm piece of resin layer was first embedded in an embedding resin to prepare a block. From this block, uniform, hole-free sections with a thickness of 50 nm to 100 nm were cut using a standard sectioning method. An Ultramicrotome EM UC7 (Leica Microsystems) was used to prepare the sections. The remaining block from which the uniform, hole-free sections were cut served as the measurement sample. Next, a Berkovich indenter (triangular pyramid, BRUKER TI-0039) was pressed vertically into the center of the cross section of the resin layer to a depth of 200 nm at a pressing speed of 10 nm / sec under the following measurement conditions: Here, in order to avoid the influence of the side edges of the resin layer, the Berkovich indenter was pressed into the central part in the thickness direction of the resin layer 3 (the dashed line in the figure) and into the part 2 μm inward from the front and back surfaces of the resin layer 3 (the dashed line in the figure), as shown in Figure 8. After that, the residual stress was relaxed by holding it constant, and then the load was released and the maximum load after relaxation was measured, and this maximum load P max and contact projection area A p Using and, P max / A p The indentation hardness (H IT The above contact projected area was calculated by correcting the indenter tip curvature using the Oliver-Pharr method using a standard sample of fused quartz (5-0098 manufactured by BRUKER). IT ) was measured at five locations in the center of the resin layer in the thickness direction, at a location 2 μm inward from one side of the resin layer, and at a location 2 μm inward from the other side of the resin layer, for a total of 15 measurement locations, and the arithmetic mean value was calculated. If any of the measurement values ​​deviated from the arithmetic mean value by more than ±20%, those measurement values ​​were excluded and remeasured.

[0142] (Measurement conditions) Indentation depth: 200nm Push speed: 10nm / sec ·Holding time: 5 seconds ·Loading and unloading speed: 10nm / sec ·Measurement temperature: 25℃

[0143] Next, the indentation hardness (H IT ) the above contact projection area A p The composite elastic modulus was calculated from the above formula (1) using the above formula. As described above, the indentation hardness was measured at a total of 15 locations, and the composite elastic modulus was calculated each time, and the arithmetic mean value of the composite elastic moduli obtained at the 15 locations was used.

[0144] When measuring the composite elastic modulus of the resin layer in the first stretching direction, the indentation hardness was measured on a cross section cut along the second stretching direction.When measuring the composite elastic modulus of the resin layer in the second stretching direction, the indentation hardness was measured on a cross section cut along the first stretching direction.

[0145] (2) Impact resistance Impact tests were conducted on the front panels of the examples and comparative examples to evaluate their impact resistance. Specifically, the front panel was placed on the surface of a 0.7 mm thick soda glass sheet with a 50 μm thick acrylic adhesive (product name "8146-2" manufactured by 3M) interposed between them, with the resin layer side facing up. An iron ball weighing 100 g and measuring 30 mm in diameter was dropped onto the resin layer of the front panel from a height of 10 cm, and the impact test was conducted three times for each sheet. Note that the position from which the iron ball was dropped was changed each time the impact test was conducted. After the impact test, the soda glass sheet was visually evaluated for cracks. Impact resistance was evaluated according to the following criteria. A: The soda glass did not break all three times. B: The soda glass cracked at least once out of three times.

[0146] (3) Bending resistance (dynamic bending test) Dynamic bending tests were performed on the front panels of the examples and comparative examples to evaluate their bending resistance. Specifically, a display device component measuring 20 mm × 100 mm was first fixed to a durability testing machine (product name "DLDMLH-FS," manufactured by Yuasa System Co., Ltd.) with the short sides (20 mm) of the display device component secured by fasteners. The minimum distance between the two opposing short sides was adjusted to 10 mm, as shown in FIG. 6(c), and the front panel was then folded 180° in a dynamic bending test 200,000 times. The front panel was folded so that the resin layer side of the front panel faced inward and the glass substrate side faced outward. A dynamic bending test was also performed using another front panel, in the same manner as above, in which the resin layer side faced outward and the glass substrate side faced inward.

[0147] When evaluating the bending resistance in the first stretching direction of the resin layer, the bending direction of the front panel was parallel to the first stretching direction of the resin layer. When evaluating the bending resistance in the second stretching direction of the resin layer, the bending direction of the front panel was parallel to the second stretching direction of the resin layer. When evaluating the bending resistance in the diagonal direction of the resin layer, the angles between the bending direction of the front panel and the first stretching direction of the resin layer were 23°, 45°, and 68°.

[0148] After the dynamic bending test, the bending portion was inspected for cracks or breakage. The bending resistance in the dynamic bending test was evaluated according to the following criteria. A: No cracks or breaks occurred in the bent portion in any of the dynamic bending tests. B: In any dynamic bending test, cracks or fractures occurred at the bending portion.

[0149] After the dynamic bending test, the fixing portion was removed from one of the short sides to unfold the folded state, and the state in which the front panel naturally opened was observed. The creases in the dynamic bending test were evaluated according to the following criteria. A: In any dynamic bending test, the opening angle after the dynamic bending test was 90° or more. B: In all dynamic bending tests, the opening angle after the dynamic bending test was less than 90°.

[0150] (4) Bending resistance (static bending test) Static bending tests were performed on the front panels of the examples and comparative examples to evaluate their flex resistance. Specifically, as shown in FIG. 7(a), a display device component measuring 20 mm × 100 mm was first fixed by fastening parts 52 arranged parallel to each other so that the short side 1C of the display device front panel 1A and the short side 1D opposite to the short side 1C were spaced 10 mm apart. Then, a static bending test was performed in which the display device front panel 1A was left in a folded state at 23°C for 240 hours. After the static bending test, the fastening parts 52 were removed from the short side 1D, as shown in FIG. 7(b), and the display device front panel 1A was unfolded. The opening angle, which is the angle at which the display device front panel 1A naturally opened after 30 minutes at room temperature, was measured. The front panel was folded so that the resin layer side was facing inward and the glass substrate side was facing outward. In addition, a static bending test was carried out in the same manner as above using another front panel, in which the surface on the resin layer side was on the outside and the surface on the glass substrate side was on the inside.

[0151] When evaluating the bending resistance in the first stretching direction of the resin layer, the bending direction of the front panel was parallel to the first stretching direction of the resin layer. When evaluating the bending resistance in the second stretching direction of the resin layer, the bending direction of the front panel was parallel to the second stretching direction of the resin layer. When evaluating the bending resistance in the diagonal direction of the resin layer, the angles between the bending direction of the front panel and the first stretching direction of the resin layer were 23°, 45°, and 68°.

[0152] The creases in the static bending test were evaluated according to the following criteria. A: In any static bending test, the opening angle after the static bending test was 90° or more. B: In all static bending tests, the opening angle after the static bending test was less than 90°.

[0153] [Table 1]

[0154] [Table 2]

[0155] In the front panels of Examples 1 to 4, the ratio E1 / E2 of the composite elastic modulus E1 in the first direction to the composite elastic modulus E2 in the second direction was 1.2 or more, and therefore excellent flex resistance and impact resistance were achieved when the angle between the bending direction and the first direction of the resin layer was 45° or more and 90° or less. On the other hand, the front panels of Comparative Examples 1 and 2 did not have the ratio E1 / E2 of the composite elastic modulus E1 in the first direction to the composite elastic modulus E2 in the second direction of 1.2 or more, and therefore did not achieve both flex resistance and impact resistance compared to Examples 1 to 4. [Explanation of symbols]

[0156] 1 … Front plate 1A...Front panel for display device 2...Glass substrate 3...resin layer 4 … Adhesive layer 10... Flexible organic EL display device 11... OLED display panel 20 ... Bending direction of flexible organic EL display device 21 ... First direction in the plane of the resin layer 22 ... Second direction in the plane of the resin layer

Claims

1. an organic electroluminescent display panel; a front panel disposed on the viewer side of the organic electroluminescent display panel; A flexible organic electroluminescent display device comprising: the front panel is located on the organic electroluminescent display panel and includes a glass substrate having a thickness of 100 μm or less, and a resin layer made of a single resin and located on the glass substrate; In the plane of the resin layer, when a composite elastic modulus in a first direction is E1 and a composite elastic modulus in a second direction that is a direction perpendicular to the first direction is E2, E1 / E2 is 1.2 or more, The flexible organic electroluminescent display device, wherein an angle formed between a bending direction of the flexible organic electroluminescent display device and the first direction is 45° or more and 90° or less.

2. The flexible organic electroluminescent display device according to claim 1 , wherein the front panel has an adhesive layer between the glass substrate and the resin layer.

3. 3. The flexible organic electroluminescent display device according to claim 1, wherein the adhesive layer has a shear storage modulus of 0.05 MPa or more and 20 MPa or less at a frequency of 950 Hz and a temperature of 23°C.

4. 4. The flexible organic electroluminescent display device according to claim 1, wherein the resin layer is disposed flatly on the entire surface of at least one of the glass substrates.

5. A flexible organic electroluminescent display device according to any one of claims 1 to 4, comprising, in this order: the organic electroluminescent display panel; the front panel; and a functional layer on the resin layer of the front panel.

6. 6. The flexible organic electroluminescent display device according to claim 1, wherein the E1 / E2 ratio is 3.0 or less.

7. A glass substrate having a thickness of 100 μm or less; a resin layer made of a single resin and located on the glass substrate; and A front panel for a display device, wherein, within the plane of the resin layer, when the composite elastic modulus in a first direction is E1 and the composite elastic modulus in a second direction that is a direction perpendicular to the first direction is E2, E1 / E2 is 1.2 or more.

8. The front panel for a display device according to claim 7 , wherein the front panel has an adhesive layer between the glass substrate and the resin layer.

9. 9. The front panel for a display device according to claim 7, wherein the adhesive layer has a shear storage modulus of 0.05 MPa or more and 20 MPa or less at a frequency of 950 Hz and a temperature of 23°C.

10. 10. The front panel for a display device according to claim 7, wherein the resin layer is disposed flatly over the entire surface of at least one of the glass substrates.

11. 11. The front panel for a display device according to claim 7, comprising the glass substrate, the resin layer, and a functional layer on the resin layer in this order.

12. 12. The front panel for a display device according to claim 7, wherein the E1 / E2 ratio is 3.0 or less.

Images