Display device

Abstract

To suppress reflection irregularity because of curling of a display panel, and secure a design property in a display device having both surfaces of the flexible display panel adhered to other member via an adhesive.SOLUTION: A display device 1 comprises: an optical adhesion layer 3; a display panel 4 that has flexibility; and a rear surface adhesion layer 5. The display panel 4 has the optical adhesion layer 3 arranged on a front surface 4a, and the rear surface adhesion layer 5 arranged on a rear surface 4b, respectively, and both surfaces are adhered to other member via these layers. A Young's modulus of the rear surface adhesion layer 5 is equal to or less than 100 times as large as that of the optical adhesion layer 3.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a display device. [Background technology]

[0002] Conventionally, an example of a display device using a flexible display panel such as an organic light-emitting diode (OLED) panel is that described in Patent Document 1. The display device described in Patent Document 1 comprises an upper module such as a cover film and a lower module such as a heat dissipation substrate, with a touch panel and an OLED panel superimposed in this order via an adhesive or the like. This display device is configured to be foldable or bendable by ensuring a predetermined relationship between the rigidity of the upper module and touch panel and the rigidity of the OLED panel and lower module. OLED is also referred to as organic EL (electroluminescence). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2019-528480 Summary of the Invention [Problem to be solved by the invention]

[0004] As a result of extensive research by the inventors, it was found that in display devices in which adhesive is applied to both sides of an OLED panel and the panel is sandwiched between other components, undulations can occur in the OLED panel due to the adhesive. When undulations occur in the OLED panel, external light is reflected unevenly on the surface of the OLED panel, causing a deterioration in the appearance.

[0005] In view of the above, an object of the present invention is to suppress undulation of a display panel and ensure design in a display device in which other components are attached to both sides of a flexible display panel via an adhesive. [Means for solving the problem]

[0006] In order to achieve the above object, the display device described in claim 1 comprises a transparent cover (2), a flexible display panel (4) having a front surface (4a) which is the surface of the transparent cover and a back surface (4b) which is the surface opposite the front surface, a housing (7) which is arranged on the back surface side and to which the transparent cover is attached, an optical adhesive layer (3) which is arranged between the transparent cover and the display panel and adhered to the front surface, and a back adhesive layer (5) which is arranged between the display panel and the housing and adhered to the back surface, and the Young's modulus of the back adhesive layer is 100 times or less than the Young's modulus of the optical adhesive layer.

[0007] This display device has a flexible display panel with an optical adhesive layer on the front surface and a back surface adhesive layer on the back surface, which is bonded to other components, and has a structure in which tensile forces are applied to both surfaces of the display panel by the adhesive layers. The back surface adhesive layer has a Young's modulus that is 100 times or less than that of the optical adhesive layer. This maintains a balance between the tensile forces acting on the front and back surfaces of the display panel, and suppresses the occurrence of undulations on the front surface of the display panel. As a result, this display device has a structure in which uneven reflection of external light on the surface of the flexible display panel is reduced, ensuring aesthetic design.

[0008] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a perspective view showing a display device according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing the cross-sectional configuration taken along line II-II in FIG. [Figure 3A] 10A and 10B are diagrams showing examples of the arrangement of rear adhesive layers. [Figure 3B] 10A and 10B are diagrams showing other examples of the arrangement of the back adhesive layer. [Figure 3C] 10A and 10B are diagrams showing other examples of the arrangement of the back adhesive layer. [Figure 3D]10A and 10B are diagrams showing other examples of the arrangement of the back adhesive layer. [Figure 4A] 10A and 10B are explanatory diagrams for explaining the occurrence of undulations in a display panel and the resulting uneven reflection of external light when the rear adhesive layer is composed of a plurality of divided portions. [Figure 4B] 10A and 10B are explanatory diagrams for explaining the occurrence of undulations in a display panel and the accompanying uneven reflection of external light when the back adhesive layer is configured with a solid pattern. [Figure 5] 1 is a graph showing the relationship between the ratio of Young's modulus of the optical adhesive layer to the back adhesive layer and the visibility of reflection unevenness in appearance evaluation. [Figure 6] FIG. 10 is a perspective view showing a display device according to a second embodiment. [Figure 7] FIG. 10 is an exploded perspective view showing a schematic configuration of a display device according to a second embodiment. [Figure 8] 8 is a cross-sectional view showing a cross-sectional configuration taken along line VIII-VIII in FIG. 6, and corresponds to FIG. 2. [Figure 9] 10 is a cross-sectional view corresponding to FIG. 2, showing an example of a modified example of the display device of the second embodiment. FIG. [Figure 10] 10A and 10B are diagrams showing other examples of the arrangement of the back adhesive layer. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following embodiments, parts that are identical or equivalent to each other will be denoted by the same reference numerals.

[0011] (First embodiment) A display device 1 according to a first embodiment will be described with reference to Fig. 1 to Fig. 5. The display device 1 according to this embodiment is suitable for use as an in-vehicle display device mounted on a moving body such as an automobile, but can of course also be used for other purposes.

[0012] In Fig. 1, to make it easier to understand the configuration of the display device 1, the outline of the display panel 4 covered with a transparent cover 2 (described later) is shown by a dashed line. In Figs. 3A to 3D, to make it easier to understand the arrangement of a back surface adhesive layer 5 (described later), the outline of the display panel 4 is shown by a dashed line, and the back surface adhesive layer 5 is hatched, although this does not show a cross section. In Fig. 4, the tensile forces caused by the optical adhesive layer 3 and the back surface adhesive layer 5 (described later) are shown by hollow arrows.

[0013] [Basic configuration] 1, the display device 1 of this embodiment includes a transparent cover 2, a display panel 4, and a housing 7 to which the transparent cover 2 is attached. As shown in FIG. 2, the display device 1 further includes an optical adhesive layer 3 for attaching the display panel 4 to the transparent cover 2, a back adhesive layer 5 for adhering the display panel 4 to the housing 7, and a peripheral adhesive 6 for adhering the transparent cover 2 to the housing 7. The display device 1 is configured such that the display panel 4 is covered by the transparent cover 2 and is positioned within a recess 72 of the housing 7.

[0014] The transparent cover 2 is a flexible, transparent, plate-like member having a thickness of 1 mm or less and a first surface 2a and a second surface 2b, which are opposite surfaces. The transparent cover 2 may be, for example, a plate made of glass or tempered glass having a thickness of 0.7 mm or less, or a rigid and light-transmitting resin material (e.g., polycarbonate). In this specification, a case where the transparent cover 2 is made of a glass plate having a thickness of 0.7 mm or less will be described as a representative example. For example, the display panel 4 is attached to the second surface 2b of the transparent cover 2 via an optical adhesive layer 3 in a region that is located inside the first recess 71 when the transparent cover 2 is attached to the housing 7. The transparent cover 2 is adhered to the housing 7 by a peripheral adhesive 6 that is located outside the second recess 72 of the housing 7. In this embodiment, the transparent cover 2 is held by the housing 7 in a flat plate shape. The first surface 2a of the transparent cover 2 is the surface opposite the housing 7, and the second surface 2b is the surface facing the housing 7.

[0015] The optical adhesive layer 3 is, for example, an optical adhesive such as OCA (abbreviation of Optical Clear Adhesive) or OCR (abbreviation of Optical Clear Resin). The optical adhesive layer 3 is disposed in the gap between the display surface of the display panel 4, which is the surface that displays various images, and the other surface 2b of the transparent cover 2, and bonds them together. The optical adhesive layer 3 has, for example, approximately the same planar size as the display panel 4, and is disposed in advance on the other surface 2b of the transparent cover 2 or the surface 4a, which is the display surface, of the display panel 4, before the transparent cover 2 is attached to the housing 7. The optical adhesive layer 3 has, for example, a thickness in the range of 0.1 mm to 0.4 mm.

[0016] The display panel 4 is, for example, an organic light-emitting diode (OLED) panel and has a flexible configuration. In the case of an OLED panel, the display panel 4 has a configuration in which a TFT circuit having a plurality of thin film transistors (TFTs) and a pixel group made up of OLED elements are stacked in this order on a substrate made of a flexible resin material. The display panel 4 is connected to a circuit board (not shown) via wiring (not shown) such as an FPC (abbreviation for flexible printed circuits), and various display controls are performed.

[0017] The circuit board (not shown) is, for example, an electronic control unit having a power supply circuit, a cooling fan, a CPU, a ROM, a RAM, and an I / O mounted on a wiring board, and is disposed on the rear surface 7b (opposite the front surface 7a) of the housing 7. In this case, as shown in FIG. 3A, for example, the housing 7 has an opening 73 on the bottom surface of a second recess 72 (described later), and wiring (not shown) connecting the display panel 4 and the circuit board (not shown) passes through the opening 73. The arrangement of the circuit board (not shown) and wiring in the display device 1 is not limited to the above example and can be changed as appropriate.

[0018] Furthermore, the display panel 4 is not limited to an OLED panel and may be other display panels as long as it has a flexible structure capable of displaying various images. The configurations and materials used for OLED panels and other display panels are well known, and therefore detailed descriptions thereof will be omitted in this specification. The display panel 4 has a surface 4a facing the transparent cover 2, and a back surface 4b on the opposite side, which is a back surface adhesive layer 5.

[0019] The back surface adhesive layer 5 is an adhesive that adheres the display panel 4 to the housing 7 while thermally connecting them. The back surface adhesive layer 5 may be, for example, a general adhesive such as an acrylic, urethane, or silicone adhesive, or a sheet made of such an adhesive resin material, but may also contain a filler with high thermal conductivity, such as alumina. The Young's modulus of the back surface adhesive layer 5 is at least 100 times or less than the Young's modulus of the optical adhesive layer 3. For example, when an adhesive sheet is used, the back surface adhesive layer 5 is attached to the back surface 4b of the display panel 4, and when an adhesive is used, the adhesive is applied to the back surface 4b of the display panel 4 of the housing 7 using a dispenser or the like.

[0020] The thickness of the back surface adhesive layer 5 is preferably within a range of 0.1 mm to 1.0 mm. If the back surface adhesive layer 5 is too thin, it may be subjected to strong shear stress in an environment with large temperature changes, such as in an in-vehicle application, and reliability may not be ensured. On the other hand, if the back surface adhesive layer 5 is too thick, it becomes difficult to satisfy the predetermined relational expression described below with respect to the Young's modulus of the optical adhesive layer 3, and this may reduce the heat dissipation performance of the display panel 4 and cause an increase in the weight and manufacturing costs of the display device 1.

[0021] The back adhesive layer 5 may be a solid pattern covering the entire display area of the back surface 4b of the display panel 4, as shown in FIG. 3A, or a strip-like pattern as shown in FIG. 3B. In the latter case, the back adhesive layer 5 has a pattern arrangement consisting of multiple separate portions. The arrangement and number of portions may be appropriately changed depending on the size and planar shape of the display panel 4. For example, if the planar shape of the display panel 4 is rectangular, the back adhesive layer 5 may be arranged parallel to the short side of the display panel 4 as shown in FIG. 3B, or may be arranged parallel to the long side of the display panel 4. Furthermore, the back adhesive layer 5 may have a pattern arrangement in which multiple vertical and horizontal patterns are arranged parallel to each other in the long and short sides of the display panel 4, as shown in FIG. 3C. Furthermore, the back adhesive layer 5 may have a dot pattern consisting of multiple island-like portions evenly spaced apart, as shown in FIG. 3D. In this way, the rear surface adhesive layer 5 can be formed in either a solid shape or a divided pattern shape, but in either case, it is configured to have a predetermined Young's modulus relative to the optical adhesive layer 3 from the viewpoint of suppressing undulation of the display panel 4. Details of adjusting the Young's modulus of the rear surface adhesive layer 5 will be described later.

[0022] The peripheral adhesive 6 is an adhesive used to directly adhere the transparent cover 2 to the housing 7, and may be a general adhesive such as an acrylic, urethane, or silicone adhesive. The peripheral adhesive 6 is applied to the transparent cover 2 or the housing 7 using, for example, a dispenser.

[0023] The housing 7 is a member to which the transparent cover 2 is adhered with a peripheral adhesive 6, and has recesses 71 and 72 that serve as a storage space for the display panel 4 attached to the transparent cover 2. The housing 7 is made of, for example, a metal material with high thermal conductivity such as Al (aluminum) or Mg (magnesium), an alloy material thereof, or a lightweight resin material, and serves as a heat dissipation member that dissipates heat from the display panel 4 to the outside.

[0024] The housing 7 has, for example, recesses 71 and 72 formed on its front surface 7a facing the transparent cover 2. The recesses 71 and 72 have a planar size larger than the planar size of the display panel 4 and are recessed toward the back surface 7b. The housing 7 has, for example, a configuration in which a second recess 72 is further formed in an area including the center of the bottom surface of the first recess 71. The housing 7 has a peripheral adhesive 6 arranged in a peripheral area of the bottom surface of the first recess 71 that is outside the second recess 72.

[0025] The above is the basic configuration of the display device 1 of this embodiment.

[0026] The display device 1 is manufactured, for example, by the following process. First, a transparent cover 2 is prepared, and a display panel 4 is attached to the other surface 2b of the transparent cover 2 with an optical adhesive layer 3. For example, wiring such as an FPC (not shown) is attached to the display panel 4 before the display panel 4 is attached to the transparent cover 2. Then, a sheet-like back adhesive layer 5 is attached to the display panel 4 attached to the transparent cover 2, or an adhesive is applied to the display panel 4 or the housing 7 using a dispenser or the like to form the back adhesive layer 5. Meanwhile, a peripheral adhesive 6 is applied in a pattern to the other surface 2b of the transparent cover 2 or the peripheral region of the first recess 71 of the housing 7 using a dispenser or the like. Next, the transparent cover 2 is attached to the housing 7 using a laminating device (not shown), and the transparent cover 2 and the housing 7 are bonded together with the peripheral adhesive 6, while the display panel 4 and the housing 7 are bonded together with the back adhesive layer 5. At this time, wiring (not shown) connected to the display panel 4 is passed through the opening 73 of the housing 7 and connected to a circuit board (not shown) located on the rear surface 7b side. This completes the manufacture of the display device 1 of this embodiment.

[0027] This display device 1 has an optical adhesive layer 3 disposed on the front surface 4a of the display panel 4 and a back surface adhesive layer 5 disposed on the back surface 4b, with other members adhered to both surfaces of the display panel 4, and a tensile force due to the adhesive acts on both surfaces of the display panel 4. Furthermore, by adjusting the Young's moduli of the optical adhesive layer 3 and the back surface adhesive layer 5 to have a predetermined relationship, the occurrence of undulations in the display panel 4 is reduced, resulting in a display device 1 with a structure in which uneven reflection of external light is suppressed.

[0028] [Suppression of undulations in display panels] Next, suppression of undulation of the display panel 4 by adjusting the Young's modulus of the optical adhesive layer 3 and the back adhesive layer 5 will be described.

[0029] First, the occurrence of undulations in the display panel 4 will be described with reference to FIGS. 4A and 4B.

[0030] For example, as shown in FIGS. 4A and 4B , in a structure in which adhesive layers are disposed on the front surface 4a and the back surface 4b of a display panel 4 and other components are bonded to both surfaces of the display panel 4, tensile forces act on both surfaces of the display panel 4, as indicated by the white arrows. If the tensile forces acting on both surfaces are unbalanced, the display panel 4 may deform in the direction of the stronger tensile force, resulting in undulations. Specifically, as shown in FIG. 4A , for example, if the back surface adhesive layer 5 of the display panel 4 has a pattern arrangement in which multiple sections are separated, the portion of the display panel 4 that is bonded only to the optical adhesive layer 3 may be pulled toward the transparent cover 2, causing a localized convexity on a portion of the front surface 4a. Furthermore, as shown in FIG. 4B , even if the back surface adhesive layer 5 of the display panel 4 has a solid pattern, if the tensile force of the back surface adhesive layer 5 is greater than the tensile force of the optical adhesive layer 3, a localized imbalance in the tensile force may cause a localized convexity on a portion of the back surface 4b. In either case, when the display panel 4 undulates, the surface 4a of the display panel 4 is locally deformed, and the external light L o is reflected by the surface 4a and scattered along the undulating shape of the surface 4a, and the external light L o The direction of reflection of the external light L is different. o If scattering occurs, the user will visually perceive uneven reflection along the undulations of the display panel 4, which will deteriorate the appearance when viewed from the transparent cover 2 side.

[0031] As a result of intensive studies by the present inventors, it was found that by adjusting the Young's moduli of the adhesive layers disposed on both sides of the display panel 4 so as to have a predetermined relationship, it is possible to suppress waviness of the display panel 4 and reduce uneven reflection of external light. In the case of this embodiment, by adjusting the Young's moduli of the optical adhesive layer 3 adhered to the front surface 4a of the display panel 4 and the back surface adhesive layer 5 adhered to the back surface 4b, it is possible to reduce waviness of the display panel 4.

[0032] The present inventors fabricated Examples 1 and 2 and Comparative Examples 1 to 3, each having a structure in which a housing 7, a back surface adhesive layer 5, a display panel 4, an optical adhesive layer 3, and a transparent cover 2 were laminated in this order, and the Young's modulus of the back surface adhesive layer 5 was varied relative to the Young's modulus of the optical adhesive layer 3. Appearance evaluations were then performed on these prototypes. Specifically, the Young's modulus of the optical adhesive layer 3 was defined as E1, and the Young's modulus of the back surface adhesive layer 5 was defined as E2. E1 was set to 0.1 MPa, and E2 was varied to 3 MPa, 10 MPa, 25 MPa, 40 MPa, and 60 MPa. In Examples 1 and 2 and Comparative Examples 1 to 3, the back surface adhesive layer 5 had the pattern arrangement shown in FIG. 3B, with the pattern width approximately 10 mm and the spacing between the patterns approximately 2 mm. In Examples 1 and 2 and Comparative Examples 1 to 3, the transparent cover 2 was made of glass with a thickness of 0.3 to 0.4 mm, the display panel 4 was set to a thickness of 0.4 to 0.6 mm, and the housing 7 was made of an Mg alloy.

[0033] The appearance evaluation was performed visually by many people, and the percentage of people who judged that the reflection unevenness was visible was calculated as the visibility rate of the reflection unevenness. In addition, in Figure 5, the ratio of the Young's modulus E2 of the back adhesive layer 5 to the Young's modulus E1 of the optical adhesive layer 3 is shown as E2 / E1.

[0034] In addition, the Young's modulus of the optical adhesive layer 3 and the back adhesive layer 5 in Figure 5 can be calculated, for example, by pouring the material to be used into a rectangular mold, solidifying it to a certain thickness, and then punching it into a shape in accordance with JIS (Japanese Industrial Standards), and performing a tensile test.

[0035] As shown in Figure 5, the percentage of people who could see the reflection unevenness decreased with a decrease in the Young's modulus E2 of the back adhesive layer 5, i.e., a decrease in E2 / E1, and it was found that when E2 / E1 was 100 or less, more than 90% of people could no longer see the reflection unevenness. Specifically, the percentage of people who could see the reflection unevenness, i.e., the visibility of the reflection unevenness, for samples with E2 / E1 of 30, 100, 250, 400, and 600 were 0, 0.1, 0.3, 0.6, and 1.0, respectively. In other words, in Examples 1 and 2 where E2 was 3 MPa and 10 MPa, i.e., E2 / E1 was 30 and 100, the percentage of people who could see the reflection unevenness was less than 10%, and the appearance was good. In contrast, in Comparative Examples 1 to 3 where E2 was 25 MPa, 40 MPa, and 60 MPa, i.e., E2 / E1 was 250, 400, and 600, the proportion of people who could see the reflection unevenness was 30% or more, and the reflection unevenness was noticeable. This result shows that when the Young's modulus of the back surface adhesive layer 5 is configured to be at least 100 times or less than the Young's modulus of the optical adhesive layer 3, the waviness of the display panel 4 and the accompanying reflection unevenness are suppressed, and deterioration of the appearance can be prevented.

[0036] Because the material used for the optical adhesive layer 3 is softer than general adhesives that do not require translucency, if the back adhesive layer 5 is made of a material that is harder than the optical adhesive layer 3, the display panel 4 will be pulled toward the back adhesive layer 5 after these adhesive layers harden. Furthermore, if the back adhesive layer 5 is arranged in a pattern and an area where only the optical adhesive layer 3 is adhered to the display panel 4 is created, this area will be pulled by the optical adhesive layer 3. To maintain a balance of the tensile forces acting on both sides of the display panel 4 and suppress waviness of the display panel 4, as obtained from the above results, the ratio of the Young's modulus of the back adhesive layer 5 to that of the optical adhesive layer 3 needs to be at least 100 times or less.

[0037] 4A, when the display panel 4 is undulated, the height H1 between the tip of the part of the surface 4a that is convex and the other part of the surface 4a is 30 μm or less in Examples 1 and 2. On the other hand, in Comparative Examples 1 to 3, H1 is about 50 μm, and the external light L oIn addition, when the display panel 4 undulates as shown in FIG. 4B, the height between the tip of the part of the rear surface 4b that is convex and the other part of the rear surface 4b is defined as H2. In this case, H2 is the difference between the external light L o It is considered necessary to set the thickness to 30 μm or less in order to prevent the uneven reflection from being visible.

[0038] According to intensive research by the present inventors, by configuring the back surface adhesive layer 5 to have a larger elongation amount than the optical adhesive layer 3, it is possible to reduce undulation of the display panel 4, resulting in a display device 1 that suppresses uneven reflection of external light as viewed from the transparent cover 2 side. The "elongation amount" here refers to the thickness after curing minus the original thickness, where the thickness immediately after disposing the optical adhesive layer 3 or back surface adhesive layer 5 is the original thickness.

[0039] Specifically, the elongation amount and the original thickness of the optical adhesive layer 3 are ΔL1 and t 01 (unit: mm), the strain is ε1, and the elongation amount and original thickness of the back adhesive layer 5 are ΔL2 and t 02 (Unit: mm) and strain is ε2. In this case, ΔL1 and ΔL2 are expressed by the following equations (1-1) and (2-1) according to Hooke's law.

[0040] ΔL1=t 01 ×ε1 (1-1) ΔL2=t 02 ×ε2 (2-1) Furthermore, since the strain ε is expressed as σ / E, formulas (1-1) and (2-1) are expressed as the following formulas (1-2) and (2-2), respectively. σ is stress. Since the housing 7 is a rigid body and the external forces acting on the optical adhesive layer 3 and the back surface adhesive layer 5 are mainly external forces and restoring forces acting on the transparent cover 2, the stresses in the optical adhesive layer 3 and the back surface adhesive layer 5 can be considered to be the same when the adhesive area with the display panel 4 is the same.

[0041] ΔL1=t 01 ×σ / E1 (1-2) ΔL2=t 02×σ / E2 (2-2) Formula (1-2) is based on the premise that the optical adhesive layer 3 is adhered to the entire surface 4a of the display panel 4, and the area of the surface 4a of the display panel 4 and the adhesive area between the optical adhesive layer 3 and the surface 4a are the same. As with formula (1-2), formula (2-2) is based on the premise that the back surface adhesive layer 5 is adhered to the entire back surface 4b of the display panel 4.

[0042] Here, since the rear surface adhesive layer 5 can be formed in a solid or divided pattern shape, the area of the rear surface 4b of the display panel 4 is defined as S1 (unit: cm 2 ), and the contact area between the rear surface adhesive layer 5 and the rear surface 4b is S2 (unit: cm 2 ), then equation (2-2) can be expressed as equation (2-3) below.

[0043] ΔL2=t 02 ×{σ / (S2 / S1)} / E2 (2-3) When ΔL1≦ΔL2 holds, the following equation (3) holds.

[0044] E2 / t 02 ≦{E1 / (S2 / S1)} / t 01 ···(3) When formula (3) is satisfied between the optical adhesive layer 3 and the back adhesive layer 5, the waviness of the display panel 4 is reduced, resulting in a display device 1 in which uneven reflection of external light is suppressed.

[0045] Let t1 and t2 be the thicknesses of the optical adhesive layer 3 and the backside adhesive layer 5 after curing, respectively. If t1 is 0.1 mm or more and 0.4 mm or less, and t2 is 0.1 mm or more and 1.0 mm or less, t1 is one order of magnitude larger than ΔL1, and t2 is one order of magnitude larger than ΔL2. In this case, equation (3) can be regarded as equation (4-1). Furthermore, equation (4-1) can be transformed into equation (4-2).

[0046] E2 / t2≦{E1 / (S2 / S1)} / t1 (4-1) E1 / t1≧(E2·S2) / (S1·t2)···(4-2) In other words, even if the formula (4-1) holds between the optical adhesive layer 3 and the back adhesive layer 5, the display device 1 has a structure in which deterioration of the appearance due to the reduction of the waviness of the display panel 4 is suppressed and design is ensured.

[0047] Furthermore, when formula (3) or formula (4-1) is satisfied, the tensile stress applied to the display panel 4 is 0.1 MPa or less, which suppresses layer peeling within the display panel 4 and makes it possible to prevent damage to the display panel 4.

[0048] The display device 1 of this embodiment has a flexible display panel 4, with an optical adhesive layer 3 on the front surface 4a and a back surface adhesive layer 5 on the back surface 4b. The display panel 4 is bonded to other components via these layers, and tensile forces are applied to both surfaces of the adhesive layer. The back surface adhesive layer 5 has a Young's modulus that is 100 times or less than that of the optical adhesive layer 3, and satisfies the above formula (3) or (4-1). This maintains a balance between the tensile forces acting on the front surface 4a and the back surface 4b of the display panel 4, suppressing undulation on the front surface 4a of the display panel 4 and, ultimately, uneven reflection of external light. Therefore, the display device 1 reduces deterioration of the appearance due to undulation of the flexible display panel 4, ensuring a designable structure.

[0049] (Second embodiment) The display device 1 of the second embodiment will be described with reference to FIG.

[0050] 6, as in Fig. 1, the outline of the display panel 4 covered by the transparent cover 2 is shown by a dashed line. In Fig. 7, the portions of the outlines of the components of the display device 1 that overlap with other components are shown by dashed lines.

[0051] The display device 1 of this embodiment differs from the first embodiment in that the transparent cover 2 has a curved shape with one surface 2a thereof being concave, and the display panel 4 has a curved surface shape that follows this, as shown in Fig. 6. This difference will be mainly described in this embodiment.

[0052] In this embodiment, the transparent cover 2 is held by the housing 7 in a bent state (hereinafter referred to as "concave bending") with one surface 2a concave, as shown in FIGS. 6 and 8. However, as shown in FIG. 7, the transparent cover 2 is flat before being bonded to the housing 7. That is, the transparent cover 2 is bent to a curved shape along the curved surface of the housing 7 by cold bending, and then bonded to the housing 7 with a peripheral adhesive 6, so to speak, by a post-bending method. As a result, the display device 1 of this embodiment has a structure in which the influence of dimensional tolerances with the housing 7 is reduced and manufacturing costs are reduced compared to a pre-bending method in which the transparent cover 2 is pre-formed to a curved shape along the curved portion of the housing 7 and then bonded to the housing 7. In this embodiment, the transparent cover 2 is, for example, a glass plate with a thickness of approximately 0.3 to 0.4 mm.

[0053] The transparent cover 2, for example, with the optical adhesive layer 3, the display panel 4, and the back adhesive layer 5 laminated on the other surface 2b, is attached to the housing 7 using a roll (not shown) or a jig having a curved shape that follows the curved shape of the front surface 7a of the housing 7. The transparent cover 2 is bent concavely by cold bending when it is attached to the housing 7, so that a restoring force is generated that tries to return it to a flat shape, but the back adhesive layer 5 and the peripheral adhesive 6 keep it in this curved shape.

[0054] In this embodiment, the display panel 4 has a curved shape that follows the concavely bent transparent cover 2, but before the transparent cover 2 is attached to the housing 7, it has a flat plate shape similar to the transparent cover 2. In this embodiment, the display panel 4 is in a state where the restoring force of the concavely bent transparent cover 2 acts on it via the optical adhesive layer 3.

[0055] In this embodiment, the optical adhesive layer 3 is configured so that its Young's modulus E1 satisfies a predetermined relationship, as in the first embodiment, i.e., the Young's modulus E2 of the back adhesive layer 5 is 100 times or less than E1, and equation (3) or (4-1) satisfies the relationship.

[0056] According to this embodiment, the display device 1 has a curved configuration in which the transparent cover 2 and the display panel 4 are held in a concavely curved shape, but still provides the same effects as those of the first embodiment. Furthermore, by using a curved display device in which the transparent cover 2 is curved by a post-bending method, the display device 1 is less susceptible to the effects of dimensional tolerances and has the effect of reducing manufacturing costs compared to a pre-bending method in which the transparent cover 2 is curved in advance to fit the housing 7.

[0057] (Modification of the second embodiment) In the above, an example has been described in which the transparent cover 2 has a concave curved surface 2a and the display panel 4 has a curved shape that follows this concave curve. However, the display device 1 is not limited to this curved surface shape. For example, as shown in FIG. 9, the display device 1 may be a curved display device in which the transparent cover 2 has a convex curved surface 2a and the display panel 4 follows this curved surface and is similarly convexly curved. In this case, the housing 7 has a curved shape in which the front surface 7a and the bottom surfaces of the recesses 71 and 72 are convex, and the transparent cover 2 is convexly bent along this curved shape. Furthermore, in this modification, for example, the transparent cover 2 is in a flat state before being attached to the housing 7, and is convexly bent by the post-bending method described above.

[0058] Furthermore, the display device 1 may be a curved display device in which the transparent cover 2 and the display panel 4 have a substantially S-shape including concavely curved portions and convexly curved portions, or other curved shapes.

[0059] This modification also provides the display device 1 that can achieve the same effects as the second embodiment.

[0060] (Other embodiments) Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and modifications within the scope of equivalents. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one, or less than one, are also within the scope and spirit of the present disclosure.

[0061] (1) In the above-described embodiments and their modified examples, examples have been described in which the display panel 4 is directly bonded to the transparent cover 2 via the optical adhesive layer 3, but the display device 1 is not limited to this configuration. For example, the display device 1 may be configured such that an optical member such as a polarizing plate or a retardation plate is disposed between the transparent cover 2 and the display panel 4, and the surface 4a of the display panel 4 is directly bonded to such an optical member and indirectly attached to the transparent cover 2.

[0062] (2) In each of the above-described embodiments and their variations, the rear surface adhesive layer 5 may cover only a portion of the rear surface 4b of the display panel 4 that is located in the display area, and may be configured in a continuous pattern shape, such as a spiral, as shown in FIG. 10.

[0063] (3) In the above-described embodiments and their modifications, a typical example has been described in which the housing 7 has the first recess 71 and the second recess 72, and the front surface 7a is located on the outermost surface. However, the present invention is not limited to this configuration. For example, the housing 7 may have only the second recess 72 as a recess, and a protruding rib may be provided in an area of the front surface 7a located outside the second recess 72, with the transparent cover 2 abutting against the tip surface of the rib. The configuration of the housing 7 may be modified as appropriate. [Explanation of symbols]

[0064] 2 transparent covers 3 Optical adhesive layer 4 Display panel 4a surface 4b Back 5 Back adhesive layer 6 Periphery adhesive

Claims

1. A display device, A transparent cover (2), a flexible display panel (4) having a front surface (4a) that is the surface on the transparent cover side and a back surface (4b) that is the opposite surface to the front surface; a housing (7) disposed on the rear surface side and to which the transparent cover is attached; an optical adhesive layer (3) disposed between the transparent cover and the display panel and adhered to the surface; a back surface adhesive layer (5) disposed between the display panel and the housing and adhered to the back surface; A display device, wherein the Young's modulus of the back adhesive layer is 100 times or less than the Young's modulus of the optical adhesive layer.

2. The display device according to claim 1 , wherein the back surface adhesive layer covers at least the entire area of the back surface located in the display area of the display panel.

3. The display device according to claim 1 , wherein the rear adhesive layer has a pattern arrangement consisting of a plurality of portions spaced apart from each other.

4. The display device according to claim 1 , wherein the rear surface adhesive layer has a single continuous pattern shape and covers only a portion of the rear surface that is located in a display area of the display panel.

5. The Young's modulus and thickness of the optical adhesive layer are E １ , t １ and the Young's modulus and thickness of the back adhesive layer are E ２ , t ２ and the area of the rear surface of the display panel is S １ and the contact area between the rear adhesive layer and the display panel is S ２ As, The optical adhesive layer and the back adhesive layer are １ / t １ ≧(E ２ ・S ２ ) / (S １ ・t ２ 5. The display device according to claim 1, wherein the following relationship holds:

6. The thickness of the optical adhesive layer is 0.1 mm or more and 0.4 mm or less, 6. The display device according to claim 1, wherein the rear adhesive layer has a thickness of 0.1 mm or more and 1.0 mm or less.

7. Further provided is a peripheral adhesive (6) that bonds the transparent cover and the housing, The housing has a curved surface on the front surface (7a) to which the transparent cover is attached, 7. The display device according to claim 1, wherein the transparent cover is glass having a thickness of 1.0 mm or less, has a flat shape before being adhered to the housing with the peripheral adhesive, and is held in a curved shape that follows the curved shape of the housing.

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