Patent Publication Number: US-2023138250-A1

Title: Flexible display module and electronic device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a 35 U.S.C. 371 national phase application of PCT International Application No. PCT/CN2021/130650, filed on Nov. 15, 2021, which claims priority to a Chinese patent application with application number 202011563311.0, filed on Dec. 25, 2020 and entitled by “Flexible Display Module and Electronic Device”, the entire contents of both are incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to the field of display technology, and in particular, to a flexible display module and an electronic device. 
     BACKGROUND 
     With the development of Organic Light Emission Diode (OLED) display technology in recent years, products and researches on flexible display panels with for example curved surfaces and foldable features have received more and more attention. 
     At present, a flexible display module has multiple film layers, and the multiple film layers are adhered by glue. However, during the curling process, a dislocation phenomenon occurs between the respective film layers. That is, a strain accumulation phenomenon occurs. The thicker the curling module, the more the number of curling turns, and the more serious the strain accumulation of the film layers. The strain accumulation in the curling process is mainly absorbed by adhesive materials. If the strain accumulation reaches the limit value, the phenomenon of peeling will occur, and the key layers of the module (such as inorganic encapsulation layer, back plate, etc.) are prone to fracture and fail. 
     It should be noted that the information disclosed in the above Background section is only for enhancement of understanding of the background of the present disclosure, and therefore may contain information that does not constitute the prior art that is already known to a person of ordinary skill in the art. 
     SUMMARY 
     The purpose of the present disclosure is to provide a flexible display module and an electronic device, so as to overcome, at least to a certain extent, one or more problems caused by limitations and defects in the prior art. 
     A first aspect of the present disclosure provides a flexible display module, which is capable of curling. The flexible display module includes: a flexible display panel, having a display side and a rear side disposed opposite to each other in its thickness direction; a first functional film layer, formed on the display side of the flexible display panel; and a second functional film layer, formed on the rear side of the flexible display panel. 
     The ratio of the thickness of the second functional film layer to the thickness of the first functional film layer is from 0.5 to 1.5, and the ratio of the elasticity modulus of the second functional film layer to the elasticity modulus of the first functional film layer is from 0.5 to 1.5. 
     In an exemplary embodiment of the present disclosure, when the display side of the flexible display panel is closer to the outer curling side than the rear side thereof, the ratio of the thickness of the second functional film layer to the thickness of the first functional film layer is from 0.5 to 1, and the ratio of the elasticity modulus of the second functional film layer to the elasticity modulus of the first functional film layer is from 0.5 to 1. 
     Alternatively, when the display side of the flexible display panel is closer to the inner curling side than the rear side thereof, the ratio of the thickness of the second functional film layer to the thickness of the first functional film layer is from 1 to 1.5, and the ratio of the elasticity modulus of the second functional film layer to the elasticity modulus of the first functional film layer is from 1 to 1.5. 
     In an exemplary embodiment of the present disclosure, the thickness of the second functional film layer is equal to the thickness of the first functional film layer, and the elasticity modulus of the second functional film layer is the same as the elasticity modulus of the first functional film layer. 
     In an exemplary embodiment of the present disclosure, the elasticity modulus of the first functional film layer and the elasticity modulus of the second functional film layer are from 4 Gpa to 8 Gpa. 
     In an exemplary embodiment of the present disclosure, the first functional film layer includes a flexible cover plate and a first adhesive layer. The flexible cover plate is adhered to the display side of the flexible display panel through the first adhesive layer. 
     The second functional film layer includes a first support back film and a second adhesive layer. The first support back film is adhered to the rear side of the flexible display panel through the second adhesive layer. 
     In an exemplary embodiment of the present disclosure, the thickness of the flexible cover plate and the thickness of the first support back film are from 40 μm to 60 μm, and the elasticity modulus of the flexible cover plate and the elasticity modulus of the first support back film are from 4 Gpa to 8 Gpa. 
     The thickness of the first adhesive layer and the thickness of the second adhesive layer are from 10 μm to 50 μm, and the elasticity modulus of the first adhesive layer and the elasticity modulus of the second adhesive layer are from 20 Mpa to 100 Mpa. 
     In an exemplary embodiment of the present disclosure, the first functional film layer further includes a impact absorption layer and a third adhesive layer. The impact absorption layer is adhered to a side of the flexible cover plate away from the flexible display panel through the third adhesive layer. 
     The second functional film layer further includes a first buffer layer and a patterned metal layer. The first buffer layer is located on a side of the first support back film away from the flexible display panel. The patterned metal layer is located on the side of the first buffer layer away from the first support back film. 
     The elasticity modulus of the impact absorption layer is smaller than the elasticity modulus of the flexible cover plate. The elasticity modulus of the first buffer layer and the elasticity modulus of the patterned metal layer are smaller than the elasticity modulus of the first support back film. 
     In an exemplary embodiment of the present disclosure, the thickness of the impact absorption layer is from 100 μm to 200 μm, and the elasticity modulus of the impact absorption layer is from 10 Mpa to 200 Mpa. 
     The thickness of the third adhesive layer is from 10 μm to 50 μm, and the elasticity modulus of the third adhesive layer is from 20 Mpa to 100 Mpa. 
     The thickness of the first buffer layer is from 80 μm to 120 μm, the thickness of the patterned metal layer is from 100 μm to 200 μm, and the elasticity modulus of the first buffer layer and the elasticity modulus of the patterned metal layer are from 10 Mpa to 200 Mpa. 
     In an exemplary embodiment of the present disclosure, the materials of the flexible cover plate and the first support back film include polyimide organic materials. 
     The material of the impact absorption layer includes a polyurethane organic material. The materials of the first adhesive layer, the second adhesive layer, and the third adhesive layer include optical adhesives or pressure-sensitive adhesives. 
     The material of the first buffer layer includes a foam, and glue materials are provided on both sides of the foam to be respectively adhered to the first support back film and the patterned metal layer. The material of the patterned metal layer includes stainless steel. 
     In an exemplary embodiment of the present disclosure, the second functional film layer further includes a second buffer layer, and the second buffer layer is located on a side of the patterned metal layer away from the first buffer layer. 
     The elasticity modulus of the second buffer layer is smaller than the elasticity modulus of the first support back film. 
     In an exemplary embodiment of the present disclosure, the patterned metal layer includes a first metal layer, a sixth adhesive layer located on a side of the first metal layer away from the first buffer layer, and a second metal layer located on a side of the sixth adhesive layer away from the first metal layer. 
     The second metal layer includes a plurality of metal pattern portions arranged at intervals, and the metal pattern portions extend upward in the curling axis of the flexible display module. 
     In an exemplary embodiment of the present disclosure, the first functional film layer further includes a polarizer and a fourth adhesive layer. The polarizer is adhered to a side of the first adhesive layer close to the flexible display panel, and is further adhered to the display side of the flexible display panel through the fourth adhesive layer. 
     The second functional film layer further includes a second support back film and a fifth adhesive layer. The second support back film is adhered to the rear side of the first support back film through the fifth adhesive layer. 
     In an exemplary embodiment of the present disclosure, the polarizer and the second support back film have a thickness from 40 μm to 60 μm, and the elasticity modulus of the polarizer and the elasticity modulus of the second support back film are from 4 Gpa to 8 Gpa. 
     The thickness of the fourth adhesive layer and the thickness of the fifth adhesive layer are from 10 μm to 50 μm, and the elasticity modulus of the fourth adhesive layer and the elasticity modulus of the fifth adhesive layer are from 20 Mpa to 100 Mpa. 
     In an exemplary embodiment of the present disclosure, the material of the second support back film includes a polyimide organic material, and the materials of the fourth adhesive layer and the fifth adhesive layer include optical adhesives or pressure-sensitive adhesives. 
     In an exemplary embodiment of the present disclosure, the first functional film layer includes a polarizer and a fourth adhesive layer. The polarizer is adhered to the display side of the flexible display panel through the fourth adhesive layer. 
     The second functional film layer includes a second support back film and a fifth adhesive layer, and the second support back film is adhered to the rear side of the flexible display panel through the fifth adhesive layer. 
     A second aspect of the present disclosure provides an electronic device, including the flexible display module described in any one of the above embodiments. 
     Other features and advantages of the present disclosure will become apparent from the following detailed description, or be learned in part by practice of the present disclosure. 
     It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments consistent with the present disclosure and together with the description serve to explain the principle of the present disclosure. Obviously, the drawings in the following description are only some embodiments of the present disclosure, and for those of ordinary skill in the art, other drawings may also be obtained from these drawings without creative effort. 
         FIGS.  1  to  6    respectively show schematic structural diagrams of a flexible display module in Embodiments 1 to 6; 
         FIG.  7    shows a schematic diagram of the strain simulation results of each functional layer in the flexible display panel of the flexible display module in Embodiments 1 to 3 during the outward curling process; 
         FIG.  8    shows a schematic diagram of the strain simulation results of each functional layer in the flexible display panel of the flexible display module in Embodiments 3 and 4 during the outward curling process; 
         FIG.  9    shows a schematic diagram of the strain simulation results of each functional layer in the flexible display panel of the flexible display module in Embodiment 1, Embodiment 5, and Embodiment 6 during the outward curling process; 
         FIG.  10    shows a schematic diagram of the strain simulation results of the first adhesive layer whose material includes OCA under different numbers of turns of the flexible display module in Embodiments 1 and 5 during the outward curling process; 
         FIG.  11    shows a schematic diagram of the strain simulation results of the inorganic buffer film layer under different numbers of turns of the flexible display module in Embodiment 1, Embodiment 5, and Embodiment 6 during the outward curling process; 
         FIG.  12    shows a schematic diagram of the strain simulation results of the second inorganic encapsulation layer under different numbers of turns of the flexible display module in Embodiments 1, 5, and 6 during the outward curling process; 
         FIG.  13    is a schematic diagram showing the strain simulation results of the first inorganic encapsulation layer under different numbers of turns of the flexible display module in Embodiment 1, Embodiment 5, and Embodiment 6 during the outward curling process; 
         FIG.  14    shows a schematic diagram of the strain simulation results of the backplane under different numbers of turns of the flexible display module in Embodiment 1, Embodiment 5 and Embodiment 6 during the outward curling process; 
         FIG.  15    shows a schematic structural diagram of a flexible display module according to another embodiment; 
         FIG.  16    shows a bottom view of the flexible display module shown in  FIG.  15   ; and 
         FIG.  17    shows a schematic structural diagram of the flexible display module in Embodiment 7. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The technical solutions of the present disclosure will be further specifically described below through embodiments and in conjunction with the accompanying drawings. In the specification, the same or similar reference numerals refer to the same or similar parts. The following description of embodiments of the present disclosure with reference to the accompanying drawings is intended to explain the general inventive concept of the present disclosure, and should not be construed as a limitation of the present disclosure. 
     Furthermore, in the following detailed description, for convenience of explanation, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present disclosure. Obviously, however, one or more embodiments may be practiced without these specific details. 
     Unless otherwise defined, technical or scientific terms used in the present disclosure shall have the ordinary meaning as understood by one of ordinary skill in the art to which the present disclosure belongs. As used in the present disclosure, “first,” “second,” and similar terms do not denote any order, quantity, or importance, but are merely used to distinguish the various components. 
     Use of words like “comprising” or “having” in the present disclosure means that the elements or items appearing before such words encompass the elements or items listed after such words and their equivalents, but do not exclude other elements or items. 
     Embodiments of the present disclosure provide a flexible display module, which can perform morphological changes such as curling, bending, and folding. 
     The flexible display module according to an embodiment of the present disclosure may include a flexible display panel, a first functional film layer and a second functional film layer. The flexible display panel may have a display side and a rear side disposed opposite to each other in the thickness direction of the flexible display panel. For example, the flexible display panel may be an OLED display panel to ensure good properties such as curling and bending. The first functional film layer may be formed on the display side of the flexible display panel, and the second functional film layer may be formed on the rear side of the flexible display panel. 
     The structures of the flexible display modules according to different embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. 
     Embodiment 1 
     As shown in  FIG.  1   , the flexible display panel  10  may include an inorganic buffer film layer, a back plate, an encapsulation layer (not shown in the figures) and the like stacked in sequence. It should be understood that the back plate may include a driving circuit layer and an organic light-emitting device. The driving circuit layer may include inorganic insulation stacks, transistors, storage capacitors, signal lines, etc. The organic light-emitting devices may include anodes, organic light-emitting materials, cathodes, etc. In addition, the back plate may also include a planarization layer, a pixel definition layer, spacers, and the like made of organic materials. The encapsulation layer may be a single-layer structure made of inorganic materials, or a composite layer. That is, the encapsulation layer may include a first inorganic encapsulation layer, an organic encapsulation layer and a second inorganic encapsulation layer stacked in sequence. The first inorganic encapsulation layer is closer to the organic light-emitting device than the second inorganic encapsulation layer. 
     The first functional film layer may include a flexible cover plate  11 , a first adhesive layer  12 , a polarizer  13  and a fourth adhesive layer  14 . The flexible cover plate  11  may be adhered to the display side of the flexible display panel  10  through the first adhesive layer  12 . The polarizer  13  is adhered to the side of the first adhesive layer  12  close to the flexible display panel  10 , and is further adhered to the display side of the flexible display panel  10  through the fourth adhesive layer  14 . The second functional film layer may include a first support back film  15  and a second adhesive layer  16 . The first support back film  15  is adhered to the rear side of the flexible display panel  10  through the second adhesive layer  16 . 
     In an embodiment, the overall thickness and the elasticity modulus of the first functional film layer are much larger than the overall thickness and the elasticity modulus of the second functional film layer. That is, the overall thickness and the elasticity modulus of the first functional film layer are more than two times of the overall thickness and the elasticity modulus of the second functional film layer. It may be understood that the film layer structures on both sides of the flexible display panel  10  according to an embodiment of the present disclosure are overall asymmetrically designed. 
     For example, the first adhesive layer  12  in an embodiment may be an optical adhesive, but not limited thereto. The first adhesive layer  12  may also be a pressure-sensitive adhesive, etc. The second adhesive layer  16  and the fourth adhesive layer  14  may be pressure-sensitive adhesives, but not limited thereto, and they may also be optical adhesives, depending on the specific situations. 
     Embodiment 2 
     The main difference from Embodiment 1 is as below. 
     The overall design of the first functional film layer and the second functional film layer is different from the design in Embodiment 1, and the other designs (for example, the structure of the flexible display panel  10 ) may be the same as that in Embodiment 1, but not limited to this, and may also be different, depending on the specific situations. 
     In an embodiment of the present disclosure, the ratio of the thickness of the second functional film layer to the thickness of the first functional film layer is from 0.5 to 1.5, and the ratio of the elasticity modulus of the second functional film layer to the elasticity modulus of the first functional film layer is from 0.5 to 1.5. That is, the thickness of one of the first functional film layer and the second functional film layer cannot be less than half the thickness of the other, and the elasticity modulus of one of the first functional film layer and the second functional film layer cannot be less than half the elasticity modulus of the other. This design helps to ensure that the overall thickness and the elasticity modulus of the film layer structures on both sides of the flexible display panel  10  are similar. That is, it may be understood that the film layer structures on both sides of the flexible display panel  10  are symmetrical as a whole. 
     Since the film layer structures on both sides of the flexible display panel  10  in an embodiment of the present disclosure are generally symmetrically designed, compared with the asymmetrical design mentioned in Embodiment 1, this embodiment helps to ensure that similar strain absorption capabilities are provided on both sides of the flexible display panel  10  during the curling process. That is, the strain absorption capabilities on both sides of the flexible display panel  10  are balanced, so that the key layers of the flexible display panel  10  (i.e., inorganic buffer film layer, back plate, inorganic encapsulation layer, etc.) and the degree of strain accumulation of the functional film layers on both sides with the increasing number of curling turns is greatly reduced. This helps to alleviate or avoid the peeling of the flexible display panel  10  and the film layer structures on both sides thereof during the curling process. Besides, the case where the key layers of the flexible display panel  10  are broken and fail may also be alleviated or avoided during the curling process. That is, the entire flexible display module can meet the performance requirements of curling, and the product quality is improved. 
     It should be noted that the aforementioned symmetrical design includes, but is not limited to, the approximate thickness and the approximate elasticity modulus, and may also include the approximate material properties and the like. 
     For example, when the flexible display module is an outward curling product, that is, when the display side of the flexible display panel  10  is closer to the outer curling side than its rear side, or when the second functional film layer of the flexible display module is located on the inner curling layer and the first functional film layer is located on the outer curling layer, in order to meet the curling performance requirements of the flexible display module, the thickness of the second functional film layer may be made less than or equal to the thickness of the first functional film layer, and the thickness of the second functional film layer may be made greater than or equal to half of the thickness of the first functional film layer. That is, the ratio of the thickness of the second functional film layer to the thickness of the first functional film layer may be from 0.5 to 1, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc. At the same time, the elasticity modulus of the second functional film layer is made less than or equal to the elasticity modulus of the first functional film layer, and the elasticity modulus of the second functional film layer is further made greater than or equal to half of the elasticity modulus of the first functional film layer. That is, the ratio of the elasticity modulus of the second functional film layer to the elasticity modulus of the first functional film layer is from 0.5 to 1, such as 0.5, 0.6, 0.7, 0.8, 0.9, 1, etc. In this way, while ensuring the good curling performance of the second functional film layer, the degree of strain accumulation, with the increasing number of curling turns, of the key layers of the flexible display panel  10  and the functional film layers on both sides of the flexible display panel  10  may also be greatly reduced. This helps to alleviate or avoid the case where the flexible display panel and the film layer structures on both sides of the flexible display panel  10  are peeled off during the curling process. In addition, the key layers of the flexible display panel  10  may be relieved or prevented from being broken and thus failing during the curling process. 
     Similarly, when the flexible display module is an inward curling product, that is, when the display side of the flexible display panel  10  is closer to the outer curling side than its rear side, the thickness of the first functional film layer may be made less than or equal to the thickness of the second functional film layer, and the thickness of the first functional film layer is further made greater than or equal to half of the thickness of the second functional film layer. That is, the ratio of the thickness of the second functional film layer to the thickness of the first functional film layer may be from 1 to 1.5, such as 1, 1.1, 1.2, 1.3, 1.4, 1.5, etc. At the same time, the elasticity modulus of the first functional film layer is made less than or equal to the elasticity modulus of the second functional film layer, and the elasticity modulus of the first functional film layer is further made greater than or equal to half of the elasticity modulus of the second functional film layer. That is, the ratio of the elasticity modulus of the second functional film layer to the elasticity modulus of the first functional film layer may be from 1 to 1.5, for example, 1, 1.1, 1.2, 1.3, 1.4, 1.5, etc. 
     In an embodiment of the present disclosure, the overall elasticity modulus of the first functional film layer and the overall elasticity modulus of the second functional film layer may be from 4 Gpa to 8 Gpa, such as 4 Gpa, 5 Gpa, 6 Gpa, 7 Gpa, 8 Gpa, etc. The design not only meets the functional requirements of the first functional film layer and the second functional film layer, but also ensures the curling performance of the first functional film layer and the second functional film layer, so as to meet the curling requirements. 
     In order to make the flexible display module meet the requirements for inward curling and outward curling at the same time, that is, regardless of the flexible display module being curled inwardly or outwardly, the degree of strain accumulation of the key layers of the flexible display panel  10  and the functional film layers on both sides of the flexible display panel  10  with the increasing number of curling turns will be greatly reduced, in an embodiment of the present disclosure, the thickness of the second functional film layer may be equal to the thickness of the first functional film layer, and the elasticity modulus of the second functional film layer is equal to the elasticity modulus of the first functional film layer. 
     For example, as shown in  FIG.  2   , the first functional film layer in an embodiment of the present disclosure may include a flexible cover plate  11  and a first adhesive layer  12 . The flexible cover plate  11  may be adhered to the display side of the flexible display panel  10  through the first adhesive layer  12 . The second functional film layer may include a first support back film  15  and a second adhesive layer  16 . The first support back film  15  is adhered to the rear side of the flexible display panel  10  through the second adhesive layer  16 . 
     Optionally, the thickness of the flexible cover plate  11  and the first support back film  15  may be from 40 μm to 60 μm, such as 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, etc. The elasticity modulus of the flexible cover plate  11  and the elasticity modulus of the first support back film  15  may be from 4 Gpa to 8 Gpa, such as 4 Gpa, 5 Gpa, 6 Gpa, 7 Gpa, 8 Gpa, etc. This design not only meets the protection function requirements of the flexible cover  11  and the first support back film  15 , but also ensures the curling properties of the flexible cover plate  11  and the first support back film  15 , thereby meeting the curling requirements of the entire flexible display module. 
     The thickness of the first adhesive layer  12  and the thickness of the second adhesive layer  16  may be from 10 μm to 50 μm, such as 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, etc. The elasticity modulus of the first adhesive layer  12  and the elasticity modulus of the second adhesive layer  16  may be from 20 Mpa to 100 Mpa, such as 20 Mpa, 40 Mpa, 60 Mpa, 80 Mpa, 100 Mpa, etc. In addition to the adhesive stability between the first adhesive layer  12  and the second adhesive layer  16 , this design further ensures the curling performances of the first adhesive layer  12  and the second adhesive layer  16 , so as to meet the curling requirements of the entire flexible display module. 
     For example, the flexible cover plate  11  and the first support back film  15  may be a single-layer structure or a multi-layer composite structure. When the flexible cover plate  11  and the first support back film  15  are single-layer structures, the material of the flexible cover plate  11  and the material of the first support back film  15  may include polyimide (PI) organic materials, to ensure that the flexible cover plate  11  and the first support back film  15  have good flexibility, but not limited to this. The flexible cover plate  11  and the first support back film may also be made of other materials, such as polyethylene terephthalate (PET), polyimide (CPI) and other organic materials, depending on the specific situations. When the flexible cover plate  11  and the first support back film  15  are multi-layer composite structures, part of the film layers of the flexible cover plate  11  and the first support back film  15  may be organic film layers such as PI, and the other part may be a ultra-thin glass film layer. The ultra-thin glass film layer may be sandwiched between two PI organic film layers. 
     In addition, the flexible cover plate  11  may include a hard coating layer disposed away from the flexible display panel, so as to protect the flexible cover plate  11 . 
     The material of the first adhesive layer  12  and the material of the second adhesive layer  16  may be optical adhesives (OCA), so that the adhesive layer may also have good optical properties while ensuring the adhesive stability. 
     It should be noted that since the second adhesive layer  16  is located on the rear side of the flexible display panel  10 , the second adhesive layer  16  may not use OCA as the adhesive material, but other adhesive materials, such as pressure-sensitive adhesives (PSA)), which helps to reduce the cost while ensuring the adhesive stability. 
     In addition, when the second adhesive layer  16  is a pressure-sensitive adhesive and the first adhesive layer  12  is OCA, the thickness of the second adhesive layer  16  may be smaller than the thickness of the first adhesive layer  12 . For example, the thickness of the first adhesive layer  12  may be 50 μm, and the thickness of the second adhesive layer  16  may be 25 μm, etc. This helps to reduce the thickness of the flexible display module while ensuring the curling performance of the flexible display module. 
     Embodiment 3 
     The main difference from Embodiment 2 is as follows. 
     On the basis of Embodiment 2, as shown in  FIG.  3   , in addition to the flexible cover plate  11  and the first adhesive layer  12  mentioned in Embodiment 2, the first functional film layer may also include an impact absorption layer  17  and a third adhesive layer  18 . The impact absorption layer  17  is adhered to a side of the flexible cover plate  11  away from the flexible display panel  10  through the third adhesive layer  18 . The elasticity modulus of the impact absorption layer  17  may be smaller than that of the flexible cover plate  11 . While ensuring the curling performance, the design also helps to improve the impact resistance on the display side of the flexible display module, and ensure that the functionality of the flexible display module is not damaged. That is, performations such as the pen and ball drop performation of the flexible display module are improved. This helps to enhance the mechanical performance and the display effect of the flexible display module, broaden the scope of application and practical application of the curling module, and provide experience and theoretical guidance for the stacking design of the subsequent curling modules. 
     Meanwhile, as shown in  FIG.  3   , in addition to the first support back film  15  and the second adhesive layer  16  mentioned in Embodiment 2, the second functional film layer may also include a first buffer layer  19  and a patterned metal layer  20 . The first buffer layer  19  may be located on a side of the first support back film  15  away from the flexible display panel  10 . The patterned metal layer may be located on a side of the first buffer layer  19  away from the first support back film  15 . The elasticity modulus of the first buffer layer  19  and the elasticity modulus of the patterned metal layer  20  are smaller than the elasticity modulus of the first support back film  15 . This design helps to improve the impact resistance and support flatness performance on the rear side of the flexible display module while ensuring the curling performance, thereby enhancing the mechanical properties of the curling module. 
     In addition, in an embodiment, while the impact absorption layer  17  and the third adhesive layer  18  are added to the first functional film layer, the first buffer layer  19  and the patterned metal layer  20  are added to the second functional film layer. This helps to ensure the first functional film layer and the second functional film layer maintain a symmetrical design as a whole, so that the degree of strain accumulation of the key layers of the flexible display panel  10  and the functional film layers on both sides of the flexible display panel  10  with the increasing number of curling turns may be greatly reduced. This helps to alleviate or avoid peeling off of the flexible display panel  10  and the film layer structures on both sides thereof during the curling process. Besides, this further helps to alleviate or avoid the key layers of the flexible display panel  10  from being broken and thus failing during the curling process. 
     For example, the thickness of the impact absorption layer  17  in an embodiment may be from 100 μm to 200 μm, such as 100 μm, 120 μm, 140 μm, 160 μm, 180 μm, 200 μm, etc. The elasticity modulus of the impact absorption layer  17  may be from 10 Mpa to 200 Mpa, for example, 10 Mpa, 48 Mpa, 86 Mpa, 124 Mpa, 162 Mpa, 200 Mpa. This design not only ensures the buffer performance of the impact absorption layer  17 , but also ensures the curling performance of the impact absorption layer  17 , thereby meeting the curling requirements of the entire flexible display module. 
     The thickness of the first buffer layer  19  may be from 80 μm to 120 μm, such as 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, etc. The elasticity modulus of the first buffer layer  19  may be from 10 Mpa to 200 Mpa, such as 10 Mpa, 48 Mpa, 86 Mpa, 124 Mpa, 162 Mpa, 200 Mpa. This design helps to ensure the buffer performance of the first buffer layer  19 , and also ensure the curling performance of the first buffer layer  19 , so as to meet the curling requirements of the entire flexible display module. 
     The thickness of the patterned metal layer  20  may be from 100 μm to 200 μm, such as 100 μm, 120 μm, 140 μm, 160 μm, 180 μm, 200 μm, etc. The elasticity modulus of the patterned metal layer  20  may be from 10 Mpa to 200 Mpa, such as 10 Mpa, 48 Mpa, 86 Mpa, 124 Mpa, 162 Mpa, 200 Mpa. This design not only ensures the support performance of the patterned metal layer  20 , but also ensures the curling performance of the third adhesive layer  18 , so as to meet the curling requirements of the entire flexible display module. 
     The thickness of the third adhesive layer  18  may be from 10 μm to 50 μm, such as 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, etc. The elasticity modulus of the third adhesive layer  18  may be from 20 Mpa to 100 Mpa, such as 20 Mpa, 40 Mpa, 60 Mpa, 80 Mpa, 100 Mpa, etc. This design not only ensures the adhesive stability of the third adhesive layer  18 , but also ensures the curling performance of the third adhesive layer  18 , so as to meet the curling requirements of the entire flexibility display module. 
     The material of the impact absorption layer  17  may be a polyurethane organic material, but it is not limited thereto, and it may also be other organic materials. The material of the third adhesive layer  18  may be an optical adhesive, so as to ensure the good optical properties. But the present disclosure is not limited thereto, and the material of the third adhesive layer  18  may also be a pressure-sensitive adhesive. The material of the first buffer layer  19  may be foam, and glue materials are provided on both sides of the foam, to be adhered to the first support back film  15  and the patterned metal layer  20  respectively. That is to say, while the first buffer layer  19  plays a buffering role, it may also play a role of adhering the first support back film  15  and the patterned metal layer  20 . It is understood that the sum of the thickness of the foam and the thickness of the glue materials on both sides may be the thickness of the entire first buffer layer  19 . The material of the patterned metal layer  20  may include stainless steel, but it is not limited thereto, and it may also be other materials. It should be understood that in an embodiment of the present disclosure, the thickness of the patterned metal layer  20  and its opening pattern may be adjusted for adjusting the elasticity modulus thereof. 
     The patterned metal layer  20  may be a single-layer structure, but not limited thereto, and it may also be a multi-layer composite structure. For example, as shown in  FIG.  15   , the patterned metal layer  20  may include a first metal layer  201 , a sixth adhesive layer  202  located on a side of the first metal layer  201  away from the first buffer layer  19 , and a second metal layer located on a side of the sixth adhesive layer  202  away from the first metal layer  201 . It should be noted that the first metal layer  201  may be an unpatterned whole film layer; and the second metal layer may be a patterned film layer that has been patterned. In an embodiment of the present disclosure, the thickness of the first metal layer  201 , the thickness of the second metal layer or the pattern of the second metal layer may be adjusted for adjusting the elasticity modulus thereof. 
     Specifically, the second metal layer may include a plurality of metal pattern portions  203  arranged at intervals, and the metal pattern portions  203  extend upward in the curling axis of the flexible display module. This helps to ensure the support performance of the patterned metal layer, and also the good curling properties thereof are guaranteed. 
     It should be noted that the shape of the metal pattern portion  203  is not limited to the elongated shape shown in  FIG.  16   , but may also be a square, a circle, an ellipse, a hexagon, an octagon, etc. The arrangement of the metal pattern portions  203  is not limited to that shown in the figures, and may be determined according to actual needs. 
     The aforementioned first metal layer  201  and the metal pattern portion  203  may be made of stainless steel, but not limited thereto, and they may also be made of other metal materials. The sixth adhesive layer  202  may be a pressure-sensitive adhesive, but not limited thereto, and it may also be other adhesive materials, such as optical adhesives. 
     In view of above, in an embodiment of the present disclosure, the elasticity modulus of the impact absorption layer  17  and the elasticity modulus of the patterned metal layer  20  may be adjusted and matched, so that the first functional film layer and the second functional film layer are still symmetrical with respect to the flexible display panel  10  as a whole. This not only meets the performance requirements of curling, but also improve the impact resistance of the curling products, such as the pen and ball drop performance. 
     The flexible display module in Embodiment 3 is compared with the flexible display module in Embodiment 2, and its curling performance and the test results about the pen and ball drop performance are shown in Table 1 below. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 validation approach 
                 Embodiment 2 
                 Embodiment 3 
               
               
                   
                   
               
             
            
               
                   
                 curling performance 
                 pass 
                 pass 
               
               
                   
                 pen drop height/mm 
                 2 
                 10 
               
               
                   
                 ball drop height/mm 
                 1.6 
                 3.0 
               
               
                   
                   
               
            
           
         
       
     
     It can be seen from Table 1 that in the validation process of the curling performance, the curling performances of the flexible display modules of Embodiments 2 and 3 both meet the requirements, that is, passing the test. In the process of pen and ball drop test, the maximum pen drop height of the flexible display module in Embodiment 2 is 2 mm, and the maximum ball drop height is 1.6 mm; while the maximum pen drop height of the flexible display module in Embodiment 3 is 10 mm, and the maximum ball drop height is 3.0 mm. As compared with Embodiment 2, the maximum pen drop height is increased by 5 times, and the maximum ball drop height is increased by about 2 times. Therefore, it can be seen that Embodiment 3 has a better pen and ball drop performance compared with Embodiment 2. Thus, it can be seen that the design method in Embodiment 3 improves the impact resistance at the display side of the flexible display module in a better way. This ensures that the functionality of the flexible display module is not damaged, enhances the mechanical properties and display effects of the flexible display module, and widens the application range and the actual use of the curling module. In the meanwhile, this also provides experience and theoretical guidance for the stacking design of subsequent curling modules. 
     Embodiment 4 
     The main difference from Embodiment 3 is in that, the relative positional relationship among the impact absorption layer  17 , the flexible cover plate  11  and the flexible display panel  10  is different. Specifically, in Embodiment 3, the impact absorption layer  17  is located on a side of the flexible cover plate  11  away from the flexible display panel  10 . While in this Embodiment 4, as shown in  FIG.  4   , the impact absorption layer  17  is located on a side of the flexible cover plate  11  close to the flexible display panel  10 . 
     It should be noted that, except for the above-mentioned difference between Embodiment 4 and Embodiment 3, other features may be the same as those in Embodiment 3, which will not be repeated here. 
     It should be understood that in this Embodiment 4, the first functional film layer and the second functional film layer maintain a symmetrical design as a whole, so that the degree of strain accumulation of the key layers of the flexible display panel  10  and the functional film layers on both sides of the flexible display panel  10  with the increasing number of curling turns may be greatly reduced. This helps to alleviate or avoid the peeling of the flexible display panel and the film layer structures on both sides thereof during the curling process. Also, the key layers of the flexible display panel  10  may be alleviated or avoided from breaking and thus failing during the curling process. 
     Studies have shown that in Embodiment 4, the impact absorption layer  17  is placed on a side of the flexible cover plate  11  close to the flexible display panel  10 , which is compared with Embodiment 3, where the impact absorption layer  17  is placed on a side of the flexible cover plate  11  away from the flexible display panel  10 . In this case, the strain of the key layers in the flexible display panel  10  is likely to increase sharply during the curling process, as shown in  FIG.  8   , thereby affecting the display effect. 
     Embodiment 5 
     The main difference from Embodiment 2 is as follows. 
     On the basis of Embodiment 2, in addition to the flexible cover plate  11  and the first adhesive layer  12  mentioned in Embodiment 2, the first functional film layer may also include a polarizer  13  and a fourth adhesive layer  14 . The polarizer  13  is adhered to the side of the first adhesive layer  12  close to the flexible display panel  10 , and is further adhered to the display side of the flexible display panel  10  through the fourth adhesive layer  14 . By providing the polarizer  13 , the reflection may be reduced, thereby improving the display effect. 
     On the basis that the first functional film layer further includes the polarizer  13  and the fourth adhesive layer  14 , in order to make the second functional film layer and the first functional film layer in a symmetrical design as a whole with respect to the flexible display panel  10 , as shown in  FIG.  5   , in addition to the first support back film  15  and the second adhesive layer  16  mentioned in Embodiment 2, the second functional film layer in Embodiment 5 of the present disclosure may also include a second support back film  21  and a fifth adhesive layer  22 . The second support back film  21  is adhered to the rear side of the first support back film  15  through the fifth adhesive layer  22 . By ensuring that the first functional film layer and the second functional film layer maintain a symmetrical design as a whole, the degree of strain accumulation of the key layers of that flexible display panel  10  and the functional film layers on both sides with the increasing number of curling turns may be greatly reduced, so as to alleviate or avoid the peeling of the flexible display panel  10  and the film layer structures on both sides thereof during the curling process. It is also possible to alleviate or avoid the failure of the key layers of the flexible display panel  10  due to breakage during the curling process. 
     For example, the thickness of the polarizer  13  and the thickness of the second support back film  21  may be from 40 μm to 60 μm, such as 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, etc. The elasticity modulus of the polarizer  13  and the elasticity modulus of the second support back film  21  may be from 4 Gpa to 8 Gpa, such as 4 Gpa, 5 Gpa, 6 Gpa, 7 Gpa, 8 Gpa, etc. This design not only meets the functional requirements of the polarizer  13  and the second support back film  21 , but also ensures that the curling performances of the polarizer  13  and the second support back film  21 , so as to meet the curling requirements of the entire flexible display module. 
     The thickness of the fourth adhesive layer  14  and the thickness of the fifth adhesive layer  22  may be from 10 μm to 50 μm, such as 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, etc. The elasticity modulus of the fourth adhesive layer  14  and the elasticity modulus of the fifth adhesive layer  22  may be from 20 Mpa to 100 Mpa, such as 20 Mpa, 40 Mpa, 60 Mpa, 80 Mpa, 100 Mpa, etc. In addition to the adhesive stability of the fourth adhesive layer  14  and the fifth adhesive layer  22 , the curling performance of the fourth adhesive layer  14  and the fifth adhesive layer  22  may also be ensured, so as to meet the curling requirements of the entire flexible display module. 
     For example, the material of the second support back film  21  may be PI organic material, so as to ensure that the first support back film  15  has good flexibility, but the present disclosure is not limited to this. The second support back film  21  may also be made of other materials, depending on the specific applications. The polarizer  13  may be a composite structure, which is determined according to actual needs, and will not be described in detail here. The material of the fourth adhesive layer  14  and the material of the fifth adhesive layer  22  may be optical adhesives or pressure-sensitive adhesives to ensure adhesive stability. 
     It should be noted that the fourth adhesive layer  14  and the fifth adhesive layer  22  may preferably be pressure-sensitive adhesives, which helps to reduce the cost while ensuring the adhesive stability. In addition, this may also ensure the curling performance of the flexible display module, while reducing the thickness of the flexible display module. 
     It should be understood that in Embodiment 5, the first functional film layer and the second functional film layer may maintain a symmetrical design as a whole, so that the degree of strain accumulation of the key layers of the flexible display panel  10  and the functional film layers on both sides of the flexible display panel  10  with the increasing number of curling turns may be greatly reduced. This helps to alleviate or avoid the peeling of the flexible display panel and the film layer structures on both sides thereof during the curling process. This may also alleviate or avoid the key layers of the flexible display panel  10  from breaking and thus failing during the curling process. 
     Embodiment 6 
     The main difference from Embodiment 5 is as follows. 
     In Embodiment 6, the first functional film layer does not include the flexible cover plate  11  and the first adhesive layer  12 , and the second functional film layer does not include the first support back film  15  and the second adhesive layer  16 . That is, as shown in  FIG.  6   , the first functional film layer in Embodiment 6 may only include a polarizer  13  and a fourth adhesive layer  14 . The polarizer  13  is adhered to the display side of the flexible display panel  10  through the fourth adhesive layer  14 . The second functional film layer may only include the second support back film  21  and the fifth adhesive layer  22 . The second support back film  21  is adhered to the rear side of the flexible display panel  10  through the fifth adhesive layer  22 . 
     It should be noted that, with respect to the structures of the polarizer  13 , the fourth adhesive layer  14 , the second support back film  21 , and the fifth adhesive layer  22  in Embodiment 6 of the present disclosure, reference may be made to the contents in Embodiment 5, which will not be repeated here. 
     It should be understood that in Embodiment 6, the first functional film layer and the second functional film layer may maintain a symmetrical design as a whole, so that the degree of strain accumulation of the key layers of the flexible display panel  10  and the functional film layers on both sides of the flexible display panel  10  with the increasing number of curling turns may be greatly reduced. This helps to alleviate or avoid the peeling of the flexible display panel and the film layer structures on both sides thereof during the curling process. This may also alleviate or avoid the key layers of the flexible display panel  10  from breaking and thus failing during the curling process. 
     Embodiment 7 
     The main difference from Embodiment 3 is in that, in addition to the film layers mentioned in Embodiment 3, the second functional film layer, as shown in  FIG.  17   , may also include a second buffer layer  23 . The second buffer layer  23  is located on a side of the patterned metal layer  20  away from the first buffer layer  19 . It should be understood that the elasticity modulus of the second buffer layer  23  is smaller than the elasticity modulus of the first support back film  15 . 
     In Embodiment 7, the impact resistance and the support flatness of the flexible display module may be further improved by arranging the second buffer layer  23 . In addition, it is convenient to assemble the flexible display module and the whole machine. 
     It should be noted that, for the material and the thickness of the second buffer layer  23  in Embodiment 7 of the present disclosure, reference may be made to the material and the thickness of the first buffer layer  19  as mentioned above, which will not be repeated here. 
     In addition, it should be noted that the metal layer between the first buffer layer  19  and the second buffer layer  23  in Embodiment 7 of the present disclosure is not limited to a patterned film layer, and may also be an unpatterned film layer. When it is an unpatterned metal film layer, in order to ensure the overall curling performance, the unpatterned metal film layer may be designed to be thinner. 
     As can be seen from the contents of the foregoing embodiments, the first functional film layer and the second functional film layer in Embodiment 1 have an asymmetric design as a whole; while the first functional film layer and the second functional film layer in Embodiment 2 to Embodiment 7 is symmetrical in the overall design. The strain accumulation in each embodiment will be described in detail below in conjunction with the accompanying drawings. 
     It can be obtained from  FIG.  7    that in Embodiment 1, during the outward curling process of the flexible display module, the strain of the inorganic buffer film layer is about 0.43%, the strain of the encapsulation layer is about 0.49%, and the strain of the back plate is about 0.54%. In Embodiment 2, during the outward curling process of the flexible display module, the strain of the inorganic buffer film layer is about 0.39%, the strain of the encapsulation layer is about 0.39%, and the strain of the back plate is about 0.39%. In Embodiment 3, during the outward curling process of the flexible display module, the strain of the inorganic buffer film layer is about 0.28%, the strain of the encapsulation layer is about 0.28%, and the strain of the back plate is about 0.28%. 
     It can be seen that the first functional film layer and the second functional film layer in Embodiment 2 and Embodiment 3 are symmetrically designed, and the first functional film layer and the second functional film layer in Embodiment 1 are designed asymmetrically. The strain accumulation of each functional layer of the display panel  10  (i.e., the inorganic buffer film layer, the encapsulation layer and the back plate) is greatly reduced, so as to alleviate or avoid the failure of the functional layers of the flexible display panel  10  due to breakage during the curling process. 
     It can be obtained from  FIG.  8    that in Embodiment 3, during the outward curling process of the flexible display module, the strain of the inorganic buffer film layer is about 0.28%, the strain of the encapsulation layer is about 0.28%, and the strain of the back plate is about 0.28%. In Embodiment 4, during the outward curling process of the flexible display module, the strain of the inorganic buffer film layer is about 0.65%, the strain of the encapsulation layer is about 0.65%, and the strain of the back plate is about 0.65%. 
     It can be seen from above that, compared with the stacked design of the first functional film layer in Embodiment 3, according to the stacked design of the first functional film layer in Embodiment 4, the strain of each functional layer of the flexible display panel  10  (i.e., the inorganic buffer film layer, the encapsulation layer, and the back plate) increases sharply. Therefore, in Embodiment 3 and Embodiment 4, the laminated design of the first functional film layer in Embodiment 3 is preferred. Thus, the strain accumulation of each functional layer (i.e., the inorganic buffer film layer, the encapsulation layer, and the back plate) of the flexible display panel  10  is greatly reduced, so as to alleviate or avoid the failure of the functional layers of the flexible display panel due to breakage during the curling process, and further improve the impact resistance of the flexible display module. 
     It can be obtained from  FIG.  9    that in Embodiment 1, during the outward curling process of the flexible display module, the strain of the inorganic buffer film layer is about 0.43%, the strain of the first inorganic encapsulation layer is about 0.49%, the strain of the second inorganic encapsulation layer is about 0.43%, and the strain of the back plate is about 0.54%. In Embodiment 6, during the outward curling process of the flexible display module, the strain of the inorganic buffer film layer is approximately 0.39%, the strain of the first inorganic encapsulation layer is approximately 0.39%, the strain of the second inorganic encapsulation layer is approximately 0.39%, and the strain of the back plate is about 0.39%. In Embodiment 5, during the outward curling process of the flexible display module, the strain of the inorganic buffer film layer is about 0.28%, the strain of the first inorganic encapsulation layer is about 0.28%, the strain of the second inorganic encapsulation layer is about 0.28%, and the strain of the back plate is about 0.28%. 
     It can be seen that the first functional film layer and the second functional film layer in Embodiment 5 and Embodiment 6 are symmetrically designed, and the first functional film layer and the second functional film layer in Embodiment 1 are designed asymmetrically. The strain accumulation of each functional layer of the display panel  10  (i.e., the inorganic buffer film layer, the encapsulation layer and the back plate) is greatly reduced, so as to alleviate or avoid the failure of the functional layers of the flexible display panel  10  due to breakage during the curling process. 
     It can be obtained from  FIG.  10    that in Embodiment 1, during the outward curling process of the flexible display module, the strain value of the first adhesive layer  12  using OCA as its material with the increasing number of curling turns is 152.0. In Embodiment 5, during the outward curling process of the flexible display module, the strain value of the first adhesive layer  12  using OCA as its material tends to be 140.0 with the increasing number of curling turns. The strain of the first adhesive layer  12  changes with the number of turns. The strain value in Embodiment 5 is smaller than the strain value in Embodiment 1. 
     It can be seen that the first functional film layer and the second functional film layer in Embodiment 5 are in symmetrical design, and the first functional film layer and the second functional film layer in Embodiment 1 are in asymmetric design. This helps to alleviate or avoid that during the curling process, the first adhesive layer  12  is likely to be peeled off from the flexible display panel  10 , thereby improving the product stability. 
     It can be obtained from  FIG.  11    to  FIG.  14    that, the strain of the inorganic buffer film layer, the second inorganic encapsulation layer, the first inorganic encapsulation layer, and the back plate in the flexible display panel  10  changes with the number of turns. The strain values in Embodiment 5 are smaller than the strain values in Embodiments 1 and 6. 
     It can be seen from above that, compared with the design of the flexible display module in Embodiment 1, the design of the flexible display module in Embodiment 5 helps to greatly reduce the strain accumulation of the functional layers of the flexible display panel  10  (i.e., the inorganic buffer film layer, the encapsulation layer, and the back plate), thereby alleviating or avoiding the situation that the functional layer of the flexible display panel  10  breaks and fails during the curling process. 
     In view of the foregoing analysis, it can be seen that the structures in Embodiment 3, Embodiment 5 and Embodiment 7 of the present disclosure are best, the structures in Embodiment 2 and Embodiment 6 are better, and the structures in Embodiment 1 and Embodiment 4 are not that good. Therefore, the flexible display modules in Embodiment 3, Embodiment 5, Embodiment 2, and Embodiment 6 are preferred. Compared with the solutions in Embodiment 1 and Embodiment 4, the strain accumulation of each functional layer of the flexible display panel  10  (i.e., the inorganic buffer film layer, the encapsulation layer, and the back plate) is greatly reduced. This helps to alleviate or avoid the failure of the functional layer of the flexible display panel  10  during the curling process due to breakage, and also alleviate or avoid the case where the first adhesive layer  12  is easily peeled off from the flexible display panel  10  during the curling process, thereby improving the product stability. In addition, it can also improve the impact resistance at the display side of the flexible display module to ensure that the functionality of the flexible display module is not damaged. In turn, the mechanical properties and the display effects of the flexible display module can be enhanced, the applicable scope and practical applications of the curling module can be broadened, and experience and theoretical guidance can be provided for the subsequent stacking design of the curling modules. 
     An embodiment of the present disclosure further provides an electronic device, which includes the flexible display module as described in any of the foregoing embodiments. 
     It should be noted that, in addition to the aforementioned flexible display module, the electronic device may also include other components and elements, such as batteries, motherboards, casings, etc., which may be supplemented by those skilled in the art according to the specific use of the electronic device, which will not be repeated here. 
     In embodiments of the present disclosure, the specific type of the electronic device is not particularly limited, and any type of electronic devices commonly used in the art may be used, such as televisions, mobile phones, computers, medical equipment, etc., which may be selected accordingly by those skilled person in the art according to the specific use of the electronic device, and details are not repeated here. 
     Other embodiments of the present disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the contents disclosed herein. The present disclosure is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principle of the present disclosure and include common general knowledge or techniques in the technical field not disclosed by the present disclosure. The specification and examples are to be regarded as exemplary only, with the true scope and spirit of the present disclosure being indicated by the appended claims.