Flexible display device

Abstract

The present invention relates to a flexible display device. A flexible display device according to one embodiment of the present invention comprises a display panel, a support member disposed below the display panel, and a multilayer adhesive layer disposed between the display panel and the support member. The adhesive layer comprises a first layer comprising a first phase change particle and an adhesive resin, a second layer disposed on the first layer comprising an adhesive resin, and a third layer disposed on the second layer comprising a second phase change particle and an adhesive resin. Accordingly, folding reliability can be satisfied over a wide range of temperatures from low to high temperatures, and damage to the display panel caused by external heat can be reduced, thereby improving the lifespan of the flexible display device.

Description

Technology Field

[0001] The present invention relates to a flexible display device, and more specifically, to a flexible display device that satisfies folding reliability over a wide range of temperatures and reduces damage to the display panel caused by external heat, thereby improving the lifespan. Background Technology

[0002] With the recent entry into the information age, the field of displays, which visually represent electrical information signals, has developed rapidly. In response to this, various display devices with excellent performance characteristics such as thinness, lightness, and low power consumption are being developed. Specific examples of such display devices include Liquid Crystal Displays (LCDs), Plasma Display Panel Devices (PDPs), Field Emission Display Devices (FEDs), and Organic Light Emitting Display Devices (OLEDs).

[0003] Meanwhile, efforts to diversify the shape and size of display devices are continuing. For example, curved display devices with curved surfaces and flexible display devices of various shapes that can maintain display performance even when bent or folded are continuously being developed. Flexible display devices must be capable of bending and unfolding to have a specific curvature, and accordingly, each component constituting the display device, such as the display panel, adhesive layer, and support member, must satisfy folding reliability. The problem to be solved

[0004] Adhesives used in conventional flexible display devices maintain a low modulus within the temperature range from room temperature to high temperature (60°C), but the modulus increases rapidly as the temperature drops below 0°C. When the modulus rises rapidly at low temperatures in this manner, the stiffness of the adhesive layer increases, leading to a decrease in folding characteristics. Consequently, there was a problem in that folding reliability could not be satisfied at low temperatures.

[0005] To resolve the aforementioned problem, when using an adhesive with a low modulus to satisfy folding reliability within a temperature range of -40℃ to 60℃, folding reliability can be satisfied, but there is a problem that the rigidity of the adhesive is insufficient because the modulus is too low at room temperature to high temperature. When the rigidity of the adhesive is insufficient, it is difficult to control the process during the bonding process of the components, resulting in reduced workability and an increase in residual defects.

[0006] Accordingly, the problem that the present invention aims to solve is to provide a flexible display device including an adhesive layer capable of controlling rapid temperature changes in order to minimize the change in the modulus of the adhesive layer according to ambient temperature.

[0007] In addition, the problem that the present invention aims to solve is to provide a flexible display device having an adhesive layer that controls rapid temperature changes to satisfy folding reliability within a wide temperature range without reducing process efficiency.

[0008] In addition, the present invention aims to provide a flexible display device with an improved lifespan by reducing damage to the display panel caused by external heat.

[0009] The problems of the present invention are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0010] A flexible display device according to one embodiment of the present invention comprises a display panel, a support member disposed below the display panel, and a multilayer adhesive layer disposed between the display panel and the support member. The adhesive layer comprises a first layer comprising a first phase change particle and an adhesive resin, a second layer disposed on the first layer comprising an adhesive resin, and a third layer disposed on the second layer comprising a second phase change particle and an adhesive resin.

[0011] Specific details of other embodiments are included in the detailed description and drawings. Effects of the invention

[0012] The present invention allows for the control of external heat in a flexible display device by forming a multilayer structure by adding a phase change material to a portion of the upper layer and a portion of the lower layer of the adhesive layer, respectively. As a result, in a low-temperature environment, the modulus of the adhesive layer is controlled so that it does not rise due to heat dissipation by the phase change material, and thus, folding reliability can be satisfied within a wide temperature range from low to high temperatures.

[0013] In addition, the present invention allows phase change particles within the adhesive layer to absorb external heat in high-temperature environments, thereby reducing thermal damage to components such as display panels, and as a result, the lifespan of the flexible display device can be improved.

[0014] The effects according to the present invention are not limited to those exemplified above, and a wider variety of effects are included within the present invention. Brief explanation of the drawing

[0015] FIG. 1 is a schematic cross-sectional view of a flexible display device according to one embodiment of the present invention. Figure 2 is a schematic enlarged cross-sectional view according to the X region of Figure 1. FIG. 3 is a schematic cross-sectional view of a flexible display device according to another embodiment of the present invention. Figure 4 is a schematic enlarged cross-sectional view according to the X region of Figure 3. FIG. 5 is a schematic cross-sectional view of a flexible display device according to another embodiment of the present invention. Figure 6 is a schematic enlarged cross-sectional view according to the X region of Figure 5. FIG. 7a is a thermal image of a flexible display device according to Example 1 measured under high temperature conditions. FIG. 7b is a thermal image of a flexible display device according to Example 1 measured under low temperature conditions. FIG. 8a is a thermal image of a flexible display device according to Comparative Example 1 measured under high temperature conditions. FIG. 8b is a thermal image of a flexible display device according to Comparative Example 1 measured under low temperature conditions. FIG. 9a is a thermal image of a flexible display device according to Comparative Example 2 measured under high temperature conditions. FIG. 9b is a thermal image of a flexible display device according to Comparative Example 2 measured under low temperature conditions. Specific details for implementing the invention

[0016] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims.

[0017] Shapes, areas, ratios, angles, numbers, etc. disclosed in the drawings for explaining embodiments of the present invention are exemplary, and therefore the present invention is not limited to the depicted details. Throughout the specification, the same reference numerals refer to the same components. Furthermore, in describing the present invention, if it is determined that a detailed description of related prior art may unnecessarily obscure the essence of the present invention, such detailed description is omitted. Where terms such as "includes," "has," or "is made up" are used in the present invention, other parts may be added unless "only" is used. When a component is expressed in the singular, it includes cases where it is included in the plural unless specifically stated otherwise.

[0018] In interpreting the components, they are interpreted to include a margin of error even in the absence of a separate explicit statement.

[0019] In the case of describing a positional relationship, for example, when the positional relationship between two parts is described using expressions such as 'on,' 'upper,' 'lower,' or 'next to,' one or more other parts may be located between the two parts unless 'immediately' or 'directly' is used.

[0020] When an element or layer is referred to as "on" another element or layer, it includes cases where another layer or element is placed directly on top of or in between.

[0021] Additionally, terms such as first, second, etc. are used to describe various components, but these components are not limited by these terms. These terms are used merely to distinguish one component from another. Accordingly, the first component mentioned below may be the second component within the technical scope of the present invention.

[0022] Throughout the specification, the same reference numerals refer to the same components.

[0023] The area and thickness of each component shown in the drawings are illustrated for convenience of explanation, and the present invention is not necessarily limited to the area and thickness of the illustrated components.

[0024] The features of each of the various embodiments of the present invention may be combined or combined with one another, either partially or wholly, and may technically enable various interlocking and operation. Each embodiment may be implemented independently of one another or may be implemented together in an associated relationship.

[0025] The present invention will be described below with reference to the drawings.

[0026] FIG. 1 is a schematic cross-sectional view of a flexible display device according to one embodiment of the present invention. FIG. 2 is a schematic enlarged cross-sectional view according to the X area of ​​FIG. 1. Referring to FIG. 1 and FIG. 2, a flexible display device (100) according to one embodiment of the present invention includes a support member (120), an adhesive layer (Adh), a display panel (110), and a cover member (140), and the adhesive layer (Adh) includes a first layer (Adh1), a second layer (Adh2), and a third layer (Adh3).

[0027] First, the display panel (110) includes a display area and a non-display area. The display area is an area where a plurality of pixels are arranged to display an image. In the display area, pixels including a light-emitting area for displaying an image and a driving circuit for driving the pixels may be arranged. A pixel may include a plurality of sub-pixels. A sub-pixel is a minimum unit constituting the display area, and each sub-pixel may be configured to emit light of a specific wavelength band. For example, each sub-pixel may be configured to emit red, green, blue, or white light. The non-display area is arranged to surround the display area. The non-display area is an area where an image is not displayed, and is an area where various wiring, driving ICs, printed circuit boards, etc., for driving the pixels and driving circuits arranged in the display area are arranged. Various ICs, such as gate driver ICs and data driver ICs, may be arranged in the non-display area.

[0028] For example, the display panel (110) may be a liquid crystal display panel that includes a liquid crystal layer and displays an image by controlling the light transmittance of the liquid crystal. As another example, the display panel (110) may be an organic light-emitting display panel that includes an organic light-emitting layer and displays an image using light emitted therefrom. Unlike liquid crystal display panels, organic light-emitting display panels are self-emissive elements that do not require a separate light source and are thin and highly flexible. In the following, a flexible display device according to one embodiment of the present invention is described assuming that the display panel (110) is an organic light-emitting display panel, but is not limited thereto.

[0029] For example, the display panel (110) includes a flexible substrate, a thin-film transistor, and an organic light-emitting element.

[0030] The flexible substrate supports various elements constituting the display panel (110). The flexible substrate may be a plastic substrate having flexibility. For example, the plastic substrate may be selected from polyimide, polyamide imide, polyethersulfone, polyethylene terephthalate, and polycarbonate, but is not limited thereto. In the case of a plastic substrate, since the barrier properties against moisture or oxygen are relatively weak, it may have a structure in which a plastic film and an inorganic film are laminated to compensate for this. For example, the flexible substrate may have a multilayer structure in which a first plastic film, an inorganic film, and a second plastic film are sequentially laminated, but is not limited thereto.

[0031] A thin-film transistor for driving an organic light-emitting diode is disposed on a flexible substrate. The thin-film transistor may be disposed in each of a plurality of pixel regions. For example, the driving thin-film transistor includes a gate electrode, an active layer, a source electrode, and a drain electrode. Additionally, the thin-film transistor may further include a gate insulating layer for insulating the gate electrode and the active layer, and an interlayer insulating layer for insulating the gate electrode from the source and drain electrodes.

[0032] A planarization layer can be disposed on the thin-film transistor to flatten the upper surface.

[0033] An organic light-emitting diode is disposed on a planarization layer. The organic light-emitting diode may include an anode, a cathode, and an organic light-emitting layer disposed between them. In the organic light-emitting diode, holes injected from the anode and electrons injected from the cathode combine in the organic light-emitting layer to emit light. An image is displayed using the light emitted in this way.

[0034] An optical control layer may be disposed on the organic light-emitting element. The optical control layer uniformly transmits light to the outside of the display panel (110) without reducing the brightness of the light emitted from the organic light-emitting element, and improves display quality by reducing external light reflectivity. For example, the optical control layer may be a polarizing film.

[0035] A cover member (140) is placed on a display panel (110). For example, the cover member (140) may be placed on an organic light-emitting element or an optical control layer. The cover member (140) protects the flexible display device (100) from external impacts and scratches. The cover member (140) may be formed from a material that is transparent and has excellent impact resistance and scratch resistance. For example, the cover member (140) may be a polymer film such as polyimide, polyamide imide, polyethylene terephthalate, polymethyl methacrylate, polypropylene glycol, or polycarbonate. As another example, the cover member may be a photoisotropic polymer film such as a cycloolefin (co)polymer, photoisotropic polycarbonate, or photoisotropic polymethyl methacrylate.

[0036] A support member (120) is placed at the bottom of the display panel (110). The plastic substrate used as a flexible substrate has a thin thickness and lower rigidity compared to a glass substrate or a metal substrate. Accordingly, it may be difficult for the plastic substrate to maintain its shape consistently when folded, and sagging may occur. To compensate for this, a support member (120) is placed at the bottom of the display panel (110).

[0037] The support member (120) includes a back plate. For example, the back plate may be made of a metal material such as stainless steel (SUS) or Invar, or may be made of a plastic material such as polymethyl methacrylate (PMMA), polycarbonate (PC), polyvinyl alcohol (PVA), acrylonitrile-butadiene-styrene (ABS), polyethylene terephthalate (PET), silicone, or polyurethane (PU).

[0038] The support member (120) may further include a plate assembly. The plate assembly is positioned below the back plate. The plate assembly is positioned below the back plate to support the display panel (110) more firmly.

[0039] The plate assembly includes a plate top and a plate bottom. The plate top and the plate bottom may be formed integrally, and, if necessary, the plate top or the plate bottom may be omitted.

[0040] The plate bottom may include an opening pattern in a portion corresponding to the folding area of ​​the flexible display device (100). Accordingly, the rigidity of the display panel (110) can be strengthened, and stress can be effectively relieved during folding. For example, the plate bottom may be made of a metal material such as stainless steel (SUS) or Invar, or may be made of a plastic material such as polymethyl methacrylate (PMMA), polycarbonate (PC), polyvinyl alcohol (PVA), acrylonitrile-butadiene-styrene (ABS), polyethylene terephthalate (PET), silicone, or polyurethane (PU).

[0041] A plate top can be placed between a back plate and a plate bottom. The plate top can be made of a material with high rigidity to reinforce the rigidity of the display panel (110). Additionally, the plate top can prevent the opening pattern of the plate bottom from being visible through the display panel (110). For example, the plate top can be formed from a metallic material such as stainless steel (SUS), Invar, aluminum series, or magnesium. As another example, the plate top may be made of a plastic material such as polymethyl methacrylate (PMMA) or polycarbonate (PC).

[0042] An adhesive layer (Adh) is placed between the display panel (110) and the support member (120). The adhesive layer (Adh) bonds the display panel (110) and the support member (120).

[0043] The adhesive layer (Adh) may be a multilayer structure comprising a first layer (Adh1), a second layer (Adh2), and a third layer (Adh3). The first layer (Adh1) is positioned to be in contact with the support member (120), the second layer (Adh2) is positioned between the first layer (Adh1) and the third layer (Adh3), and the third layer (Adh3) is positioned to be in contact with the display panel (110).

[0044] Each of the first layer (Adh1), the second layer (Adh2), and the third layer (Adh3) comprises an adhesive resin (131), and the first layer (Adh1) and the third layer (Adh3) further comprise phase change particles. In order to distinguish the phase change particles included in each of the first layer (Adh1) and the third layer (Adh3) from one another, the phase change particle of the first layer (Adh1) is described as the first phase change particle (PCP1) and the phase change particle of the third layer (Adh3) is described as the second phase change particle (PCP2), but the first phase change particle (PCP1) and the second phase change particle (PCP2) may be substantially the same.

[0045] The adhesive resin (131) included in each of the first layer (Adh1), second layer (Adh2), and third layer (Adh3) may be an adhesive resin that can relieve stress during folding and satisfies folding reliability. Each of the first layer (Adh1), second layer (Adh2), and third layer (Adh3) may include the same adhesive resin or may include different adhesive resins.

[0046] For example, the adhesive resin (131) may be an acrylic resin having adhesive properties. For example, the acrylic resin may be a copolymer comprising a first acrylic resin and a second acrylic resin. The second acrylic resin has a lower glass transition temperature than the first acrylic resin. When copolymerizing an acrylic resin with such a lower glass transition temperature, the increase in modulus at low temperatures can be suppressed. Accordingly, the folding characteristics of the adhesive layer (Adh) can be improved at low temperatures.

[0047] For example, the glass transition temperature of the second acrylic resin may be -10°C or lower, -60°C to -10°C, or -50°C to -20°C. Within this range, the adhesive strength of the adhesive layer (Adh) can be maintained at a high level, and low-temperature folding characteristics can be improved without significantly reducing workability during the lamination process.

[0048] For example, the second acrylic resin may be a polymer comprising one or more monomers selected from ethyl acrylate, n-butyl acrylate, iso-butyl acrylate, 2-ethylhexyl acrylate, iso-propyl acrylate, n-propyl acrylate, hexyl methacrylate, n-octyl acrylate, iso-octyl acrylate, n-decyl methacrylate, n-tetradecyl methacrylate, etc. Such a polymer has a low glass transition temperature, which can improve the low-temperature folding characteristics of the adhesive layer (Adh).

[0049] The first acrylic resin is not particularly limited as long as it is an acrylic resin that has adhesive properties without reducing folding reliability and has a glass transition temperature higher than that of the second acrylic resin. For example, the first acrylic resin may have a glass transition temperature of 0°C or higher, 0°C to 40°C, or 0°C to 25°C.

[0050] For example, the first acrylic resin may be a polymer comprising one or more monomers selected from urethane (meth)acrylate, epoxy (meth)acrylate, methyl methacrylate, ethyl methacrylate, t-butyl methacrylate, iso-butyl methacrylate, iso-propyl methacrylate, n-propyl methacrylate, octadecyl methacrylate, etc., but is not limited thereto.

[0051] Each of the first layer (Adh1) and the third layer (Adh3) further comprises phase change particles. The first layer (Adh1) comprises an adhesive resin (131) and a first phase change particle (PCP1), wherein the first phase change particle (PCP1) exists in a dispersed state within the adhesive resin (131). The third layer (Adh3) comprises an adhesive resin (131) and a second phase change particle (PCP2), wherein the second phase change particle (PCP2) exists in a dispersed state within the adhesive resin (131).

[0052] Each of the first phase change particle (PCP1) and the second phase change particle (PCP2) consists of a core (C) and a shell (S). The core (C) contains a phase change material, and the shell (S) is formed to surround the core (C).

[0053] Phase change materials are thermal energy storage materials capable of absorbing, storing, or releasing heat depending on changes in the surrounding temperature. The heat exchanged without a change in temperature during a phase change is called latent heat; because phase change materials have a large latent heat, they can store a large amount of heat when the surrounding temperature rises and release a large amount of heat when the surrounding temperature drops. Accordingly, phase change materials can maintain a constant surrounding temperature until the phase change is completely finished by absorbing or releasing heat from the surroundings during the phase change.

[0054] For example, a phase change material may be a material that changes from a solid to a liquid by absorbing surrounding heat in an environment above the phase change temperature, and changes from a liquid to a solid by releasing heat into the surroundings in an environment below the phase change temperature.

[0055] For example, the phase change material may have a phase change temperature within the range of 0°C to 40°C. If the phase change temperature is within this range, it is possible to effectively prevent the modulus of the adhesive layer (Adh) from rising rapidly as the temperature decreases to 0°C or lower. Accordingly, folding reliability can be satisfied within a wide temperature range of -40°C to 60°C.

[0056] For example, a phase change material may have a latent heat of 100 J / g or more. Latent heat is the amount of heat per unit weight that a phase change material can absorb or release without a rise or fall in temperature. Accordingly, if the latent heat is less than 100 J / g, the amount of heat that the phase change material can absorb or release is small, so the temperature control effect may be insufficient. In addition, since the greater the latent heat, the more effective it is for controlling the ambient temperature, there is no specific upper limit.

[0057] For example, the phase change material may include one or more selected from aliphatic hydrocarbons having 10 to 40 carbon atoms and polyethylene glycol. For example, an aliphatic hydrocarbon having 10 to 40 carbon atoms is one selected from paraffinic hydrocarbons, n-octacosane, n-heptacosane, n-hexacosane, n-pentacosane, n-tetracosane, n-tricosane, n-docosane, n-heneicosane, n-eicosane, n-nonadecane, n-octadecane, n-heptadecane, n-hexadecane, n-pentadecane, n-tetradecane, n-tridecane, etc. It may be more than, but is not limited to.

[0058] As described above, the phase change material changes from a solid to a liquid at temperatures above the phase change temperature. Consequently, when the phase changes from solid to liquid, the phase change material may leach out to the outside of the adhesive layer, which can lead to a decrease in the adhesive strength of the adhesive layer and a reduction in the temperature control effect.

[0059] Accordingly, the core (C) containing the phase change material can be encapsulated by being surrounded by a shell (S). That is, each of the first phase change particle (PCP1) and the second phase change particle (PCP2) may be a particle having a core (C)-shell (S) structure in which the phase change material is encapsulated by the shell (S).

[0060] The shell (S) protects the liquid phase change material from leaching out of the adhesive layer (Adh) when the phase change material undergoes a phase change according to ambient temperature, particularly when it changes from a solid to a liquid state.

[0061] The shell (S) is not particularly limited as long as it is a material capable of encapsulating a phase change material without affecting mechanical properties such as adhesion and folding characteristics of the adhesive layer (Adh). For example, the shell (S) may include one or more resins selected from melamine-based resins, acrylic-based resins, urethane-based resins, and styrene-based resins.

[0062] For example, the average diameter of the core (C) containing the phase change material can be controlled within a range of 0.1 μm to 10 μm, and the average thickness of the shell (S) can be controlled within a range of 0.1 μm to 10 μm. Within this range, the temperature control effect by the first phase change particle (PCP1) and the second phase change particle (PCP2) is excellent, so the folding characteristics are excellent over a wide temperature range from low to high temperatures, and folding reliability can be satisfied. If the average diameter of the core (C) is too small, the amount of the phase change material is too small, so the effect of controlling the ambient temperature may be insufficient. On the other hand, if the average thickness of the shell (S) is too thick, the heat dissipation and heat absorption efficiency of the first phase change particle (PCP1) and the second phase change particle (PCP2) may decrease. Considering these points, it may be desirable for the average thickness of the shell (S) to be smaller than the average diameter of the core (C).

[0063] For example, the average diameter of each of the first phase change particle (PCP1) and the second phase change particle (PCP2) may be 5 μm to 20 μm or 10 μm to 15 μm. If the average diameter of each of the first phase change particle (PCP1) and the second phase change particle (PCP2) is smaller than 5 μm, the viscosity may increase during the adhesive manufacturing process, which may reduce processability and make uniform dispersion difficult. Additionally, if the average diameter of each of the first phase change particle (PCP1) and the second phase change particle (PCP2) is larger than 20 μm, efficient heat absorption and release may be difficult due to a decrease in the specific surface area, and if the average diameter of the phase change particle is excessively large relative to the thickness of the first layer (Adh1) and the third layer (Adh3), the phase change particle may protrude to the surface of the first layer (Adh1) and the third layer (Adh3), resulting in a problem where the surface is not smooth.

[0064] For example, the first layer (Adh1) may contain the first phase change particle (PCP1) in an amount of 30% to 70% or 40% to 60% by weight based on 100% by weight of the adhesive resin (131) of the first layer (Adh1). Additionally, the third layer (Adh3) may contain the second phase change particle (PCP2) in an amount of 30% to 70% or 40% to 60% by weight based on 100% by weight of the adhesive resin (131) of the third layer (Adh3). If the content of the phase change particle included in each layer is less than 30% by weight, the heat absorption and heat dissipation effects by the phase change particle are insufficient, and folding reliability at low temperatures may not be satisfied. If the content of phase change particles included in each layer exceeds 70% by weight, the viscosity of the adhesive becomes too high, causing processing difficulties, and the proportion of adhesive resin decreases relatively, which degrades adhesive properties and may also degrade folding properties.

[0065] For example, the thickness of each of the first layer (Adh1) and the third layer (Adh3) may be 10 μm to 25 μm, and the thickness of the second layer (Adh2) may be 10 μm to 50 μm. When the thickness of each of the first layer (Adh1), the second layer (Adh2), and the third layer (Adh3) is within the above range, the folding characteristics of the adhesive layer (Adh) are not degraded, and folding reliability can be satisfied within a wide temperature range from low temperature to high temperature.

[0066] Meanwhile, although not shown in the drawing, the support member (120) includes a back plate and a plate assembly, and an adhesive member may be disposed between them. At this time, as the adhesive member for bonding the back plate and the plate assembly, an adhesive layer having a multilayer structure including the first layer, second layer, and third layer described above may be used.

[0067] As described above, the adhesive resin constituting the adhesive layer has a problem in that, due to the inherent characteristics of the material, the modulus increases as the temperature decreases, which leads to a decrease in folding rigidity and fails to meet folding reliability requirements at low temperatures.

[0068] In a flexible display device (100) according to one embodiment of the present invention, the adhesive layer (Adh) comprises a first layer (Adh1), a second layer (Adh2), and a third layer (Adh3), wherein the first layer (Adh1) and the third layer (Adh3) comprise phase change particles. The phase change particles included in each of the first layer (Adh1) and the third layer (Adh3) of the adhesive layer (Adh) release heat in a low-temperature environment, thereby suppressing the lowering of the temperature of the adhesive layer (Adh) due to the influence of the ambient temperature. The decrease in the temperature of the adhesive layer (Adh) in a low-temperature environment can be delayed, and thereby the increase in modulus at low temperatures can be minimized. Accordingly, the problem of conventional adhesives in which folding characteristics deteriorate at low temperatures can be resolved, and folding reliability can be satisfied over a wide temperature range from low to high temperatures.

[0069] For example, the second layer (Adh2) itself, which does not contain phase change particles, has a modulus of 5.0 x 10⁻⁶ at a low temperature of -40°C to 0°C. 4 Pa to 1.0 X 10 7 It may be Pa. However, the adhesive layer (Adh) having a multilayer structure comprising a first layer (Adh1), a second layer (Adh2), and a third layer (Adh3) may have a lower modulus than this at low temperatures of -40°C to 0°C. For example, the adhesive layer (Adh) having a multilayer structure in which a first layer (Adh1) containing a first phase change particle (PCP1) is disposed below the second layer (Adh2), and a third layer (Adh3) containing a second phase change particle (PCP2) is disposed above the second layer (Adh2), has a modulus of 1.0 x 10⁻⁶ at -40°C to 60°C. 3 Pa to 1.0 x 10 5 It can be Pa. The first phase change particle (PCP1) included in the first layer (Adh1) and the second phase change particle (PCP2) included in the third layer (Adh3) can suppress the rise in modulus by releasing heat at low temperatures, so the modulus can be maintained low even at low temperatures. Accordingly, there is an advantage of excellent folding characteristics over a wide temperature range, ranging from low temperatures to high temperatures.

[0070] In addition, the phase change particles included in each of the first layer (Adh1) and the third layer (Adh3) absorb heat in a high-temperature environment. Accordingly, the adhesive layer (Adh) of the present invention absorbs heat in a high-temperature environment, thereby reducing thermal damage to the elements constituting the flexible display device (100), such as the display panel (110). Thus, it provides the effect of improving the lifespan of the flexible display device (100).

[0071] FIG. 3 is a schematic cross-sectional view of a flexible display device according to another embodiment of the present invention. FIG. 4 is a schematic enlarged cross-sectional view according to the X region of FIG. 3.

[0072] Referring to FIGS. 3 and 4, a flexible display device (200) according to another embodiment of the present invention comprises a support member (120), an adhesive layer (Adh'), a display panel (110), and a cover member (140), and the adhesive layer (Adh') comprises a first layer (Adh1), a second layer (Adh2'), a third layer (Adh3), and a side adhesive layer (Adh4). Since the flexible display device (200) illustrated in FIGS. 3 and 4 is substantially identical to the flexible display device (100) illustrated in FIGS. 1 and 2 except that the width of the second layer (Adh2') is different and it further includes a side adhesive layer (Adh4), a redundant description is omitted.

[0073] Referring to FIGS. 3 and 4, in a flexible display device (200) according to another embodiment of the present invention, the width of the second layer (Adh2') is different from the width of the first layer (Adh1) and the third layer (Adh3), respectively. The width of the second layer (Adh2') is smaller than the widths of the first layer (Adh1) and the third layer (Adh3).

[0074] A side adhesive layer (Adh4) may be placed between the first layer (Adh1) and the third layer (Adh3) to surround the side of the second layer (Adh2'). The side adhesive layer (Adh4) is placed between the first layer (Adh1) and the third layer (Adh3) to bond the first layer (Adh1) and the third layer (Adh3).

[0075] The side adhesive layer (Adh4) comprises a third phase change particle (PCP3) and an adhesive resin (231). The adhesive resin (231) is substantially the same as the adhesive resin (131) included in each of the first layer (Adh1), the second layer (Adh2'), and the third layer (Adh3). Therefore, a redundant description is omitted.

[0076] The third phase change particle (PCP3) is dispersed within the adhesive resin (231) of the side adhesive layer (Adh4). The third phase change particle (PCP3) consists of a core (C) and a shell (S). The core (C) contains a phase change material, and the shell (S) is formed to surround the core (C). That is, the third phase change particle (PCP3) may be a particle having a core (C)-shell (S) structure in which the phase change material is encapsulated by the shell (S). The third phase change particle (PCP3) is substantially identical to the first phase change particle (PCP1) contained in the first layer (Adh1) and the second phase change particle (PCP2) contained in the third layer (Adh3). Therefore, a redundant description is omitted.

[0077] That is, the composition of the side adhesive layer (Adh4) is substantially the same as that of the first layer (Adh1) and the third layer (Adh3), respectively. Meanwhile, although the side adhesive layer (Adh4) is depicted as a separate component separated from the first layer (Adh1) and the third layer (Adh3) in FIGS. 3 and 4, the side adhesive layer (Adh4) may be formed integrally with the first layer (Adh1) and the third layer (Adh3).

[0078] For example, the side adhesive layer (Adh4) may contain the third phase change particles (PCP3) in an amount of 30% to 70% or 40% to 60% by weight based on 100% by weight of the adhesive resin (231) of the side adhesive layer (Adh4) and the third phase change particles (PCP3). If the content of the third phase change particles (PCP3) is less than 30% by weight, the amount of phase change particles is small, so the heat absorption and heat dissipation effects according to temperature may be insufficient, and if the content exceeds 70% by weight, the viscosity of the adhesive becomes too high, causing difficulties in the process, and the relative proportion of the adhesive resin decreases, resulting in reduced adhesive properties and potential delamination during folding.

[0079] In a display device (200) according to another embodiment of the present invention, the adhesive layer (Adh') is composed of a first layer (Adh1), a second layer (Adh2'), a third layer (Adh3), and a side adhesive layer (Adh4). The first layer (Adh1) contains a first phase change particle (PCP1), the third layer (Adh3) contains a second phase change particle (PCP2), and the side adhesive layer (Adh4) contains a third phase change particle (PCP3). That is, phase change particles are included along the upper layer, lower layer, and outer periphery of the adhesive layer (Adh'). Accordingly, the adhesive layer (Adh') can more effectively control rapid thermal changes. Therefore, when the ambient temperature is lowered, the phase change particles (PCP1, PCP2, PCP3) can release heat to suppress the rapid increase in the modulus of the adhesive layer (Adh'), and when the ambient temperature is higher, they can absorb heat to minimize thermal damage to the device, such as the display panel (110), thereby contributing to the improvement of the lifespan of the flexible display device (200).

[0080] FIG. 5 is a schematic cross-sectional view of a flexible display device according to another embodiment of the present invention. FIG. 6 is an enlarged cross-sectional view according to the X area of ​​FIG. 5. Referring to FIG. 5 and FIG. 6, a flexible display device (300) according to another embodiment of the present invention includes a support member (120), an adhesive layer (Adh), a display panel (110), a cover member (140), and a side sealing portion (350), and the adhesive layer (Adh) includes a first layer (Adh1), a second layer (Adh2), and a third layer (Adh3). Since the flexible display device (300) shown in FIG. 5 is substantially identical to the flexible display device (100) shown in FIG. 1 and FIG. 2 except that it further includes a side sealing portion (350), a redundant description is omitted.

[0081] The side sealing portion (350) is positioned on the side of the support member (120), the adhesive layer (Adh), and the display panel (110). That is, the side sealing portion (350) surrounds the side of the support member (120), the adhesive layer (Adh), and the display panel (110). The side sealing portion (350) is positioned on the side of the flexible display device (300) to protect the side of the flexible display device (300) and prevent the penetration of moisture or foreign matter through the side.

[0082] Additionally, the side sealing portion (350) relieves interfacial stress between components caused by folding. Accordingly, stress caused by slip between components during folding is relieved, thereby reducing separation or delamination between components.

[0083] The side sealing portion (350) can be formed with a sealant (351) that has moisture resistance and satisfies folding reliability. For example, the sealant (351) may be one or more selected from acrylic resin, rubber, and silicone resin.

[0084] The side sealing portion (350) includes a fourth phase change particle (PCP4). The fourth phase change particle (PCP4) is dispersed in the sealant (351). The fourth phase change particle (PCP4) consists of a core (C) and a shell (S). The core (C) contains a phase change material, and the shell (S) is formed to surround the core (C). The fourth phase change particle (PCP4) may be a particle with a structure in which the phase change material is encapsulated by the shell (S). The fourth phase change particle (PCP4) is substantially identical to the first phase change particle (PCP1) contained in the first layer (Adh1) and the second phase change particle (PCP2) contained in the third layer (Adh3). Therefore, redundant description is omitted.

[0085] As the fourth phase change particle (PCP4) is included in the side sealing portion (350), the side of the flexible display device (300) is protected and the penetration of moisture or foreign matter is prevented, while the rapid thermal change of the adhesive layer (Adh) due to ambient temperature can be further delayed. Accordingly, folding characteristics can be further improved at low temperatures, and thermal damage to the device can be more effectively reduced at high temperatures.

[0086] Additionally, the side sealing portion (350) wraps around the side of the support member (120) and the display panel (110) as well as the adhesive layer (Adh), and can minimize rapid thermal changes of the support member (120) and the display panel (110) according to the ambient temperature. Accordingly, the folding characteristics of the flexible display device (300) at low temperatures can be further improved, and thermal damage of the flexible display device (300) at high temperatures can be further reduced, thereby further improving the lifespan of the device.

[0087] The effects of the present invention described above will be explained in more detail below through examples and comparative examples. However, the following examples are for illustrative purposes only and do not limit the scope of the present invention.

[0088] [Example 1]

[0089] 1. Preparation of core-shell structured phase change particles

[0090] A surfactant, a dispersant, and an antifoaming agent are added to water and stirred to dissolve them. Next, dodecane, a phase change material, is added and emulsified to prepare an emulsion solution. Next, melamine monomer and formaldehyde are added to the emulsion solution and stirred. Next, an aqueous hydrochloric acid solution is added to polymerize the melamine monomer and formaldehyde. After the polymerization is completed, phase change particles comprising a core containing dodecane and a shell formed of melamine-formaldehyde resin are prepared. It was confirmed that the average diameter of the phase change particles obtained in this way is 10 to 15 μm and the latent heat is 207 J / g.

[0091] 2. Preparation of the adhesive layer

[0092] An adhesive was prepared such that the content of phase change particles was 50% by weight relative to 100% by weight of the acrylic adhesive resin and the phase change particles prepared above. The adhesive was applied and cured to form a first layer. Next, an acrylic adhesive resin was applied and cured on the first layer to form a second layer. Next, an adhesive containing the phase change particles was applied and cured on the second layer to form a third layer.

[0093] 3. Manufacture of flexible display devices

[0094] After preparing a back plate and an organic light-emitting display panel, a flexible display device was manufactured by bonding the back plate and the organic light-emitting display panel using the adhesive layer prepared above.

[0095] [Comparative Example 1]

[0096] 1. Preparation of the adhesive layer

[0097] An acrylic adhesive resin identical to that of Example 1 was applied and cured on a substrate to form a first layer, and the same process was repeated to laminate a second layer and a third layer.

[0098] 2. Manufacture of flexible display devices

[0099] A flexible display device was manufactured in the same manner as in Example 1, except that an adhesive layer prepared according to Comparative Example 1 was used instead of the adhesive layer used in Example 1.

[0100] [Comparative Example 2]

[0101] 1. Preparation of the adhesive layer

[0102] An acrylic adhesive resin identical to that of Example 1 was applied and cured on a substrate to form a first layer, and an adhesive containing the phase change particles of Example 1 at a concentration of 50% by weight was applied and cured on the first layer to form a second layer. Next, an acrylic adhesive resin was applied and cured on the third layer to form a third layer.

[0103] 2. Manufacture of flexible display devices

[0104] A flexible display device was manufactured in the same manner as in Example 1, except that an adhesive layer prepared according to Comparative Example 2 was used instead of the adhesive layer used in Example 1.

[0105] [Experimental Example]

[0106] To investigate the thermal control effect of the flexible display devices manufactured according to Example 1, Comparative Example 1, and Comparative Example 2, respectively, specimens were prepared as follows and thermal images were measured. Two flexible display devices according to Example 1, Comparative Example 1, and Comparative Example 2 were prepared, and a heat source (e.g., a driving board such as an FPCB) was attached to the back of each display device to prepare the specimens. One specimen was left at a high temperature (60°C) for 24 hours, and the other specimen was left at a low temperature (-30°C) for 10 minutes, after which thermal images were measured at room temperature using a thermal imaging camera. The results are shown in Table 1 and Figures 7a to 9b below.

[0107] FIG. 7a is a thermal image of a flexible display device according to Example 1 measured under high temperature conditions, and FIG. 7b is a thermal image of a flexible display device according to Example 1 measured under low temperature conditions. FIG. 8a is a thermal image of a flexible display device according to Comparative Example 1 measured under high temperature conditions, and FIG. 8b is a thermal image of a flexible display device according to Comparative Example 1 measured under low temperature conditions. FIG. 9a is a thermal image of a flexible display device according to Comparative Example 2 measured under high temperature conditions, and FIG. 9b is a thermal image of a flexible display device according to Comparative Example 2 measured under low temperature conditions.

[0108] Example 1 Comparative Example 1 Comparative Example 2 High temperature conditions Highest temperature 43.5℃ 49.8℃ 48.2℃ average 37.8℃ 44.6℃ 43.8℃ Low temperature conditions lowest temperature -22.3℃ -26.2℃ -26.3℃ average -15.3℃ -19.0℃ -19.0℃

[0109] Referring to Table 1 and Figures 7a to 9b together, it can be seen that the flexible display device according to Example 1 has lower maximum temperature and average values ​​compared to Comparative Example 1 and Comparative Example 2 under high temperature conditions, and is about 4 to 5°C lower than Comparative Example 1 and Comparative Example 2. In addition, under low temperature conditions, the minimum temperature and average value of the flexible display device according to Example 1 are -22.3°C and -15.3°C, respectively, which are higher than both Comparative Example 1 and Comparative Example 2, and are about 4°C higher.

[0110] It can be seen that the flexible display device according to Example 1 includes phase change particles in each of the first and third layers of the adhesive layer, so that under high temperature conditions the phase change particles absorb heat and under low temperature conditions the phase change particles release the heat stored, thereby delaying temperature changes according to the surrounding environment.

[0111] Meanwhile, in the case of Comparative Example 2, it can be confirmed that despite containing the same phase change particles as Example 1, it has thermal characteristics equivalent to Comparative Example 1, which does not contain phase change particles. From this, it can be seen that when phase change particles are included in the second layer rather than the first and third layers, the thermal control effect is insufficient.

[0112] According to one embodiment of the present invention, it can be seen that low-temperature folding characteristics can be improved by suppressing a rapid rise in modulus at low temperatures, and thermal damage to the flexible display device caused by high temperatures can be minimized.

[0113] A flexible display device according to various embodiments of the present invention can be described as follows.

[0114] A flexible display device according to one embodiment of the present invention comprises a display panel, a support member disposed below the display panel, and a multilayer adhesive layer disposed between the display panel and the support member. The adhesive layer comprises a first layer comprising a first phase change particle and an adhesive resin, a second layer disposed on the first layer comprising an adhesive resin, and a third layer disposed on the second layer comprising a second phase change particle and an adhesive resin.

[0115] According to another feature of the present invention, each of the first phase change particle and the second phase change particle comprises a core containing a phase change material and a shell surrounding the core.

[0116] According to another feature of the present invention, the first layer comprises a first phase change particle and 30% to 70% by weight of the first phase change particle based on 100% by weight of the adhesive resin of the first layer, and the third layer comprises a second phase change particle and 30% to 70% by weight of the second phase change particle based on 100% by weight of the adhesive resin of the third layer.

[0117] According to another feature of the present invention, each of the first phase change particle and the second phase change particle may have an average diameter of 5 μm to 20 μm.

[0118] According to another feature of the present invention, the average diameter of the core may be 0.1 μm to 10 μm, and the average thickness of the shell may be 0.1 μm to 10 μm.

[0119] According to another feature of the present invention, the phase change material may include one or more selected from aliphatic hydrocarbons having 10 to 40 carbon atoms and polyethylene glycol.

[0120] According to another feature of the present invention, the shell may include one or more resins selected from melamine-based resins, acrylic-based resins, urethane-based resins, and styrene-based resins.

[0121] According to another feature of the present invention, the phase change material may have a phase change temperature within the range of 0°C to 40°C.

[0122] According to another feature of the present invention, the phase change material may have a latent heat of 100 J / g or more.

[0123] According to another feature of the present invention, the adhesive resin may be an acrylic resin.

[0124] According to another feature of the present invention, the acrylic resin may comprise a copolymer of a first acrylic resin and a second acrylic resin having a glass transition temperature lower than that of the first acrylic resin.

[0125] According to another feature of the present invention, the glass transition temperature of the second acrylic resin may be -10℃ or lower.

[0126] According to another feature of the present invention, the thickness of each of the first layer and the third layer may be 10 μm to 25 μm, and the thickness of the second layer may be 10 μm to 50 μm.

[0127] According to another feature of the present invention, the width of the second layer is smaller than the width of each of the first layer and the third layer, and the adhesive layer is arranged to surround the side of the second layer between the first layer and the third layer, and may further include a side adhesive layer comprising a third phase change particle and an adhesive resin.

[0128] According to another feature of the present invention, the third phase change particle comprises a core containing a phase change material and a shell surrounding the core, and the side adhesive layer may comprise the third phase change particle in an amount of 30% to 70% by weight based on 100% by weight of the adhesive resin of the third phase change particle and the side adhesive layer.

[0129] According to another feature of the present invention, the side adhesive layer may be formed integrally with the first layer and the third layer.

[0130] According to another feature of the present invention, a side sealing portion may be further included that is disposed on the side of a support member, an adhesive layer, and a display panel and includes a fourth phase change particle.

[0131] According to another feature of the present invention, the second layer has a modulus of 5.0 x 10 at -40°C to 0°C. 4 Pa to 1.0 X 10 7 It could be Pa.

[0132] According to another feature of the present invention, the adhesive layer has a modulus of 1.0 x 10 at -40°C to 60°C. 3 Pa to 1.0 x 10 5 It could be Pa.

[0133] Although embodiments of the present invention have been described in more detail with reference to the attached drawings, the present invention is not necessarily limited to these embodiments and may be modified in various ways within the scope of the technical spirit of the present invention. Accordingly, the embodiments disclosed in the present invention are intended to explain, not to limit, the technical spirit of the present invention, and the scope of the technical spirit of the present invention is not limited by these embodiments. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. The scope of protection of the present invention shall be interpreted by the claims below, and all technical spirits within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention. Explanation of the symbols

[0134] 100, 200, 300: Flexible display device 110: Display panel 120: Lack of support Adh, Adh': Adhesive layer Adh1: 1st floor Adh2, Adh2': 2nd floor Adh3: 3rd floor Adh4: Side adhesive layer 140: Cover missing PCP1: First phase change particle PCP2: Second phase change particle PCP3: Third phase change particle PCP4: Fourth phase change particle C: Core S: Shell 131, 231: Adhesive resin 350: Side sealing part 351: Sealant

Claims

Claim 1 A flexible display device comprising: a display panel; a support member disposed below the display panel; and a multilayer adhesive layer disposed between the display panel and the support member, wherein the adhesive layer comprises a first layer comprising a plurality of first phase change particles and an adhesive resin, a second layer disposed on the first layer comprising the adhesive resin, and a third layer disposed on the second layer comprising a plurality of second phase change particles and the adhesive resin, wherein the first layer is in contact with the support member, the third layer is in contact with the display panel, and the plurality of first phase change particles and the plurality of second phase change particles have the same phase change characteristics. Claim 2 A flexible display device according to claim 1, wherein each of the plurality of first phase change particles and the plurality of second phase change particles comprises a core containing a phase change material and a shell surrounding the core. Claim 3 A flexible display device according to claim 2, wherein the first layer comprises the plurality of first phase change particles and the plurality of first phase change particles in an amount of 30% to 70% by weight based on 100% by weight of the adhesive resin of the first layer, and the third layer comprises the plurality of second phase change particles and the plurality of second phase change particles in an amount of 30% to 70% by weight based on 100% by weight of the adhesive resin of the third layer. Claim 4 A flexible display device according to claim 1, wherein each of the plurality of first phase change particles and the plurality of second phase change particles has an average diameter of 5 μm to 20 μm. Claim 5 A flexible display device according to claim 2, wherein the average diameter of the core is 0.1 μm to 10 μm and the average thickness of the shell is 0.1 μm to 10 μm. Claim 6 A flexible display device according to claim 2, wherein the phase change material comprises one or more selected from aliphatic hydrocarbons having 10 to 40 carbon atoms and polyethylene glycol. Claim 7 A flexible display device according to claim 2, wherein the shell comprises one or more resins selected from melamine-based resin, acrylic-based resin, urethane-based resin, and styrene-based resin. Claim 8 In claim 2, the flexible display device wherein the phase change material has a phase change temperature within the range of 0°C to 40°C. Claim 9 In claim 2, the phase change material is a flexible display device having a latent heat of 100 J / g or more. Claim 10 A flexible display device according to claim 1, wherein the adhesive resin is an acrylic resin. Claim 11 A flexible display device according to claim 10, wherein the acrylic resin comprises a copolymer of a first acrylic resin and a second acrylic resin having a glass transition temperature lower than that of the first acrylic resin. Claim 12 A flexible display device according to claim 11, wherein the glass transition temperature of the second acrylic resin is -10℃ or lower. Claim 13 A flexible display device according to claim 1, wherein the thickness of each of the first layer and the third layer is 10㎛ to 25㎛, and the thickness of the second layer is 10㎛ to 50㎛. Claim 14 A flexible display device according to claim 1, wherein the width of the second layer is smaller than the width of each of the first layer and the third layer, the adhesive layer is disposed to surround the side of the second layer between the first layer and the third layer, and further comprises a side adhesive layer including a plurality of third phase change particles and the adhesive resin, wherein the plurality of third phase change particles have the same phase change characteristics as the plurality of first phase change particles and the plurality of second phase change particles. Claim 15 A flexible display device according to claim 14, wherein the plurality of third phase change particles comprises a core containing a phase change material and a shell surrounding the core, and the side adhesive layer comprises the plurality of third phase change particles in an amount of 30% to 70% by weight based on 100% by weight of the adhesive resin of the side adhesive layer and the plurality of third phase change particles. Claim 16 In claim 14, the flexible display device wherein the side adhesive layer is integrally formed with the first layer and the third layer. Claim 17 A flexible display device according to claim 1, further comprising a side sealing portion disposed on the side of the support member, the adhesive layer, and the display panel, and comprising a plurality of fourth phase change particles, wherein the plurality of fourth phase change particles comprises a core comprising a phase change material and a shell surrounding the core, and wherein the plurality of fourth phase change particles have the same phase change characteristics as the plurality of first phase change particles and the plurality of second phase change particles. Claim 18 In claim 1, the second layer has a modulus of 5.0 x 10 at -40℃ to 0℃. 4 Pa to 1.0 X 10 7 Pain, flexible display device. Claim 19 In claim 1, the adhesive layer has a modulus of 1.0 x 10 at -40℃ to 60℃. 3 Pa to 1.0 x 10 5 Pain, flexible display device.

Images