Ultra-slim Backlight Unit

Abstract

One embodiment of the present invention provides a backlight unit comprising a substrate, a plurality of light-emitting elements mounted on the substrate, and an optical sheet disposed on top of the light-emitting elements, wherein the optical sheet contacts the light-emitting surface of at least one of the light-emitting elements through one surface, and emits light from the light-emitting elements incident on the one surface to another surface opposite to the one surface, and emits the light by refracting or dispersing it in a direction different from the direction of incidence by means of an optical pattern formed therein.

Description

Technology Field

[0001] An embodiment of the present invention relates to an ultra-slim backlight unit. Background Technology

[0002] A light-emitting diode (LED) is a type of semiconductor device capable of producing light of various colors by forming a light source through the formation of a PN diode of a compound semiconductor. Such light-emitting devices have the advantages of a long lifespan, miniaturization and lightweight design, and low-voltage operation. Additionally, these LEDs are resistant to shock and vibration, require no warm-up time or complex operation, and can be mounted on a substrate or lead frame in various forms and packaged, allowing them to be modularized for various uses and applied to backlight units or various lighting devices.

[0003] Meanwhile, backlight units can be classified into edge-type or direct-type depending on the arrangement of the light source and the form of light transmission. Among them, the direct-type backlight unit has the advantage of high light efficiency because the light source, such as an LED, is placed on the back of the display device and the light emitted from the light source is directly supplied to the display panel.

[0004] The light source device used in a direct-type backlight unit may include a light-emitting diode and a substrate that mounts the light-emitting diode and includes circuit elements for driving it. Additionally, since light uniformity is reduced when using a point light source LED as the light source, various types of diffusion members may be included to improve light uniformity. For example, an optical lens and a diffusion plate may be included to diffuse the light emitted from the light-emitting element into light of uniform brightness, and a sufficient optical distance for light diffusion must be considered.

[0005] Conventional direct-type backlight units are equipped with optical lenses and diffusers for light diffusion, and since a sufficient optical distance must be secured between the light source and the diffuser, there was a problem in that it was difficult to reduce the thickness below a certain level. In addition, because they include such optical lenses and multiple optical sheets, there was a limiting problem in realizing a flexible display. The problem to be solved

[0006] The embodiments of the present invention are intended to solve the aforementioned problems and provide a backlight unit capable of realizing a surface light source that satisfies high brightness and color uniformity even when the diffuser plate and optical lens are removed from a direct-type backlight unit. means of solving the problem

[0007] One embodiment of the present invention provides a backlight unit comprising a substrate, a plurality of light-emitting elements mounted on the substrate, and an optical sheet disposed on top of the light-emitting elements, wherein the optical sheet contacts the light-emitting surface of at least one of the light-emitting elements through one surface, and emits light from the light-emitting elements incident on the one surface to another surface opposite to the one surface, and emits the light by refracting or dispersing it in a direction different from the direction of incidence by means of an optical pattern formed therein.

[0008] In one embodiment of the present invention, the optical sheet may form the optical pattern between the one surface and the other surface such that the angle of emission of light emitted from the other surface is greater than the angle of incidence of light incident on the one surface.

[0009] In one embodiment of the present invention, the distance from the surface of the optical sheet that is not in contact with the light-emitting surface of the light-emitting element to the upper surface of the substrate may be 1.5 times or less the height of the light-emitting element.

[0010] In one embodiment of the present invention, a color conversion sheet in contact with the other side of the optical sheet and a light conversion sheet in contact with the color conversion sheet may be further included.

[0011] In one embodiment of the present invention, the optical sheet may further include a fixing means for fixing the optical sheet to the upper surface of the substrate.

[0012] In one embodiment of the present invention, the optical pattern formed inside the optical sheet has a repeating pattern structure and can refract and disperse light incident on one surface of the optical sheet.

[0013] In one embodiment of the present invention, the pattern structure may be one of a hexagon, a cone, a pyramid, a trapezoid, or an embossing.

[0014] In one embodiment of the present invention, the pattern structure may be a nano-lens pattern.

[0015] In one embodiment of the present invention, the optical sheet comprises a first optical sheet and a second optical sheet disposed on top of the first optical sheet, and the first optical sheet and the second optical sheet may each have an optical pattern formed therein.

[0016] In one embodiment of the present invention, the optical pattern of the first optical sheet and the optical pattern of the second optical sheet may be arranged so as not to overlap.

[0017] Another embodiment of the present invention provides a backlight unit comprising a substrate, a plurality of light-emitting elements mounted on the substrate, and an optical sheet disposed on top of the light-emitting elements, wherein the light-emitting elements are spaced apart and arranged on the substrate, and the optical sheet contacts at least a portion of the light-emitting surface of the light-emitting element disposed at the outermost of the plurality of light-emitting elements through one surface, and emits light from the light-emitting element incident on the one surface to another surface opposite to the one surface, and emits the light by refracting or dispersing it in a direction different from the direction of incidence by means of an optical pattern formed inside.

[0018] In another embodiment of the present invention, the optical sheet may form the optical pattern between the one surface and the other surface such that the angle of exit of light exiting the other surface is greater than the angle of incidence of light incident on the one surface.

[0019] In one embodiment of the present invention, the distance from the surface of the optical sheet that is not in contact with the light-emitting surface of the light-emitting element to the upper surface of the substrate may be 1.5 times or less the height of the light-emitting element.

[0020] In one embodiment of the present invention, a color conversion sheet in contact with the other side of the optical sheet and a light conversion sheet in contact with the color conversion sheet may be further included.

[0021] In one embodiment of the present invention, the optical sheet may further include a fixing means for fixing the optical sheet to the upper surface of the substrate.

[0022] In one embodiment of the present invention, the optical pattern formed inside the optical sheet has a repeating pattern structure and can refract and disperse light incident on one surface of the optical sheet.

[0023] In one embodiment of the present invention, the pattern structure may be one of a hexagon, a cone, a pyramid, a trapezoid, or an embossing.

[0024] In one embodiment of the present invention, the pattern structure may be a nano-lens pattern.

[0025] In one embodiment of the present invention, the optical sheet comprises a first optical sheet and a second optical sheet disposed on top of the first optical sheet, and the first optical sheet and the second optical sheet may each have an optical pattern formed therein.

[0026] In one embodiment of the present invention, the optical pattern of the first optical sheet and the optical pattern of the second optical sheet may be arranged so as not to overlap.

[0027] Other aspects, features, and advantages other than those described above will become clear from the following drawings, claims, and detailed description of the invention. Effects of the invention

[0028] A backlight unit according to embodiments of the present invention can improve luminance characteristics and color uniformity without using a diffuser plate and an optical lens, and can realize an ultra-slim backlight unit by reducing the overall thickness of the backlight unit by reducing the optical distance.

[0029] In addition, the backlight unit according to the embodiments of the present invention can provide a backlight unit that is more effective for implementing a flexible display by not applying a diffuser plate and an optical lens, and can reduce the cost of optical lenses, thereby achieving a reduction in manufacturing costs.

[0030] In addition, the backlight unit according to the embodiments of the present invention can implement a surface light source by uniformly diffusing light while minimizing the loss of brightness of light emitted from a light source, and can reduce light source costs by widening the spacing between light sources to implement a surface light source using fewer light sources. Brief explanation of the drawing

[0031] FIG. 1 is a cross-sectional view schematically illustrating a backlight unit according to one embodiment of the present invention. Figure 2 is a cross-sectional view showing an enlarged view of part A of Figure 1. FIG. 3a is a perspective view of an optical sheet according to one embodiment of the present invention. FIG. 3b is a perspective view of an optical sheet according to one embodiment of the present invention. FIG. 3c is a perspective view of an optical sheet according to one embodiment of the present invention. FIG. 4 is a cross-sectional view of a backlight unit according to one embodiment of the present invention, and is a drawing for explaining the first optical sheet and the second optical sheet. FIG. 5 is a cross-sectional view of a backlight unit according to one embodiment of the present invention. FIG. 6 is a drawing showing one embodiment of a backlight unit. FIG. 7 shows the results of a performance test of a backlight unit according to one embodiment of the present invention and a conventional backlight unit. Specific details for implementing the invention

[0032] Hereinafter, the following embodiments will be described in detail with reference to the attached drawings. When describing with reference to the drawings, identical or corresponding components are given the same reference numerals, and redundant descriptions thereof will be omitted.

[0033] Since the embodiments are capable of various modifications, specific embodiments are illustrated in the drawings and described in detail in the detailed description. The effects and features of the embodiments and the methods for achieving them will become clear by referring to the details described below in conjunction with the drawings. However, the embodiments are not limited to those disclosed below and can be implemented in various forms.

[0034] In the following embodiments, terms such as first, second, etc. are used not in a limiting sense, but for the purpose of distinguishing one component from another.

[0035] In the following embodiments, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0036] In the following examples, terms such as "include" or "have" mean that the features or components described in the specification are present, and do not preclude the possibility that one or more other features or components may be added.

[0037] In the following embodiments, when a part such as a unit, area, or component is described as being on or above another part, it includes not only cases where it is directly on top of another part, but also cases where another unit, area, or component is interposed in between.

[0038] In the following embodiments, terms such as "connect" or "combine" do not necessarily imply a direct and / or fixed connection or combination of two members unless the context clearly indicates otherwise, nor do they exclude the interposition of another member between the two members.

[0039] This means that the features or components described in the specification exist, and does not preclude the possibility that one or more other features or components may be added.

[0040] In the drawings, the size of components may be exaggerated or reduced for convenience of explanation. For example, the size and thickness of each component shown in the drawings are depicted arbitrarily for convenience of explanation, so the following embodiments are not necessarily limited to those illustrated.

[0041] FIG. 1 is a cross-sectional view schematically illustrating a backlight unit according to one embodiment of the present invention, FIG. 2 is a cross-sectional view showing an enlarged view of portion A of FIG. 1, and FIG. 3a, FIG. 3b and FIG. 3c are perspective views of an optical sheet (300) according to one embodiment of the present invention.

[0042] Referring to FIGS. 1 to 3c, a backlight unit according to one embodiment of the present invention may include a substrate (100), a plurality of light-emitting elements (200) mounted on the substrate, and an optical sheet (300) disposed on top of the light-emitting elements. Additionally, a backlight unit according to one embodiment of the present invention may further include a color conversion sheet (400) and a light conversion sheet (500) disposed on top of the optical sheet (300).

[0043] The substrate (100) of the backlight unit is electrically connected to the light-emitting element (200) and can perform the role of mediating electrical signal transmission between the light-emitting element (200) and the circuit board. A circuit element and an electrode may be provided on one side of the substrate (100). The substrate (100) may be a printed circuit board (PCB) on which a wiring layer is formed, or a flexible printed circuit board (FPCB) made of a flexible material.

[0044] Additionally, the substrate (100) may be made of a material having suitable mechanical strength and insulation or a conductive material so as to mount and support a plurality of light-emitting elements (200). For example, the substrate may be a synthetic resin substrate such as resin or glass epoxy, or a ceramic substrate considering thermal conductivity, and may also be an insulating metal substrate such as aluminum, copper, zinc, tin, lead, gold, or silver, and may be a plate-shaped or lead frame-shaped substrate. In addition, the substrate (100) may be formed in a square or rectangular thin film shape, but is not limited thereto and may be formed in various shapes.

[0045] The substrate (100) supports the light-emitting element (200) and can perform the function of reflecting light emitted from the light-emitting element (200). Accordingly, light emitted from the light-emitting element (200) can be reflected through the upper surface of the substrate (100) and emitted in the upward direction of the backlight unit.

[0046] A light-emitting element (200) is disposed on a substrate (100) and can emit light in an upward direction. The light-emitting element (200) emits light through one surface, and the surface through which the light is emitted can be defined as a light-emitting surface. The light-emitting element (200) may emit light by receiving an electrical signal from a circuit board.

[0047] The light-emitting element (200) mounted on the substrate (100) may be a flip-chip type light-emitting element, but is not necessarily limited thereto, and the light-emitting element (200) may be various horizontal or vertical LEDs, or various types of light-emitting elements in which signal transmission media such as various bumps, wires, or solders are installed may all be applied.

[0048] The light-emitting element (200) can emit light of different wavelengths depending on the composition ratio of the compound semiconductor. For example, the light-emitting element (200) may be a blue LED that emits light of a blue wavelength, but is not limited thereto, and may be either a red LED or a green LED, and may also be an LED that emits light of various wavelengths or an ultraviolet LED.

[0049] LEDs can be classified according to the size of the LED chip into large LEDs (chip size: 1000 µm or more), medium LEDs (chip size: 300-500 µm), small LEDs (chip size: 200-300 µm), mini LEDs (chip size: 100-200 µm), and micro LEDs (chip size: 100 µm or less). As the size of the LED chip in the backlight unit decreases, the number of LEDs can be easily adjusted, and the brightness characteristics and color uniformity of the backlight unit can be improved. In addition, as the size of the LED chip decreases, the thickness of the backlight unit is reduced, allowing for a slimmer backlight unit, reduced power consumption, extended battery life, and improved performance in portable devices. For example, when using mini LEDs or micro LEDs, local dimming is possible because the LED size is smaller, and through local dimming, the image quality of the display device can be improved and power efficiency can be improved.

[0050] A plurality of light-emitting elements (200) may be arranged in a grid pattern on the substrate (100) to form a direct type. The light-emitting elements (200) mounted on the substrate (100) may be composed of various numbers. Additionally, the plurality of light-emitting elements (200) may be arranged spaced apart at regular intervals, but are not limited thereto, and may be mounted in various forms on the flat surface of the substrate (100) according to the designer's intention.

[0051] Light emitted from a plurality of light-emitting elements (200) can be diffused through an optical sheet (300) to be described later and output to the outside in a uniform size.

[0052] Meanwhile, the optical sheet (300) contacts the light-emitting surface of at least one light-emitting element (200) through one surface, and emits light from the light-emitting element (200) incident on one surface to the other surface opposite to said one surface, and can emit light by refracting or dispersing it in a direction different from the direction of incidence by means of an optical pattern formed inside.

[0053] An optical sheet (300) may be placed on top of a light-emitting element (200), and an optical pattern may be formed inside it to refract or disperse light incident on one side of the optical sheet (300) and emit it to the other side. One side of the optical sheet (300) is a surface positioned close to the light-emitting surface of the light-emitting element (200), through which light emitted from the light-emitting element (200) may be incident. The other side of the optical sheet (300) is a surface opposite to the one side, through which light incident into the interior of the optical sheet (300) may pass through the optical sheet (300) and be emitted to the other side.

[0054] The optical sheet (300) may be implemented in the form of a film made of a transparent material, but is not limited thereto. The optical sheet (300) is thin and generally transparent, and since most of the light incident on one side of the optical sheet (300) passes through and is emitted from the other side, the effect of high light transmittance and improved light efficiency can be obtained.

[0055] The optical sheet (300) may be made of a resin material capable of diffusing light. For example, the optical sheet (300) may be made of flexible polyimide (PI), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or polycarbonate (PC), but is not limited thereto.

[0056] The optical sheet (300) performs the role of diffusing light, and can refract or disperse light incident on one side of the optical sheet (300) by means of an optical pattern formed inside.

[0057] The optical sheet (300) illustrated in FIG. 2 is a cross-sectional view in which a cone-shaped optical pattern is formed inside. Light emitted from the light-emitting element (200) is incident on one side of the optical sheet (300) which is positioned above the light-emitting surface of the light-emitting element (200). The incident light is reflected, refracted, or dispersed by the optical pattern formed inside the optical sheet (300), and the reflected, refracted, or dispersed light is emitted to the other side opposite to the one side.

[0058] When the angle of incidence of light incident on one side of the optical sheet (300) is denoted as θ1 and the angle of emission of light emitted from the other side of the optical sheet (300) is denoted as θ2, a backlight unit according to one embodiment of the present invention may arrange the optical sheet (300) to satisfy the relationship θ1 < θ2. The angle of emission of light emitted from the other side is determined according to the angle of incidence of light incident on one side of the optical sheet (300). As light incident on one side of the optical sheet (300) is refracted or dispersed again by an optical pattern formed inside the optical sheet (300) and emitted from the other side of the optical sheet (300), it is refracted or dispersed once more, so that the angle of emission of light passing through the optical sheet (300) can be greater than the angle of incidence. Accordingly, by placing an optical sheet (300) having an optical pattern formed inside on top of a light-emitting element (200), a diffusion effect of light emitted from the light-emitting element (200) can be obtained, and the light of the light-emitting element (200), which is a point light source, can be easily realized as a surface light source.

[0059] One side of the optical sheet (300) disposed on top of the light-emitting element (200) may partially contact the light-emitting surface of the light-emitting element (200). The light-emitting surface of at least one of the plurality of light-emitting elements (200) may contact one side of the optical sheet (300). The optical sheet (300) is formed as a flexible sheet that can be bent or curved to some extent, so that only a part of one side of the optical sheet (300) may contact the light-emitting surface of the light-emitting element (200). The optical sheet (300) may be disposed on top of the light-emitting element (200) without gaps so that the entire light-emitting surface of the plurality of light-emitting elements (200) and one side of the optical sheet (300) may come into contact.

[0060] A portion of the optical sheet (300) that is not in contact with the light-emitting surface of the light-emitting element (200) may be positioned at a distance d from the upper surface of the substrate (100), wherein the distance (h2) between one side of the optical sheet (300) and the light-emitting surface of the light-emitting element (200) may be less than or equal to half the height (h1) of the light-emitting element (200). Accordingly, the distance (d) between one side of the optical sheet (300) that is not in contact with the light-emitting surface of the light-emitting element (200) and the upper surface of the substrate (100) may be 1.5 times or less the height (h1) of the light-emitting element (200).

[0061] The optical pattern formed inside the optical sheet (300) may consist of shapes such as hexagonal pyramids, cones, and pyramids spaced apart at regular intervals. However, this is a preferred embodiment of the optical pattern and the present invention is not limited thereto; the shape, spacing, and size of the optical pattern may be configured differently according to the designer's intent. For example, the optical pattern formed inside the optical sheet (300) may consist of cone shapes of uniform size arranged in a grid pattern, arranged with different spacing, cone shapes of different sizes arranged, or other shapes mixed together.

[0062] An optical sheet (300) according to one embodiment of the present invention may have an optical pattern formed therein, and the optical pattern may have a repeating pattern structure to refract and disperse light incident on one surface of the optical sheet (300). In addition, the repeating pattern structure may be one of a hexagon, a cone, a pyramid, a trapezoid, or an embossing, and may also be a nano-lens pattern.

[0063] The repeating pattern structure of the optical pattern may be a shape in which a geometric figure such as a hexagon, cone, pyramid, or trapezoid protrudes in the downward direction of the optical sheet (300) (in the direction of the surface where light is incident), may be an embossing in which a concave lens shape is repeated, or may be a nano-lens pattern in which nano-sized convex lenses are arranged. However, the present invention is not limited thereto, and any optical pattern capable of refracting or dispersing incident light may be applied. The optical pattern may be formed on one surface of a base substrate by a photolithography process, a master mold process, a printing process, and other physical processing methods, and any pattern forming method may be freely used.

[0064] By the diffusion of light from an optical sheet (300) formed internally with a repeating pattern structure of an optical pattern, the backlight unit according to the embodiments of the present invention can emit light from a light-emitting element, which is a point light source, as a surface light source, and can provide a backlight unit having uniform brightness.

[0065] An air gap may be formed between the substrate (100) and the optical sheet (300), and light emitted from the light-emitting surface of the light-emitting element (200) may be refracted or dispersed in the air gap due to a difference in refractive index. Among the diffused light, the light that returns in the direction of the substrate (100) may be re-reflected on the substrate (100) and incident on the optical sheet (300). The air gap may be formed between the substrate (100) and the optical sheet (300), or it may be formed between the upper surface of the light-emitting element (200) and the optical sheet (300) that is not in contact with the light-emitting element (200).

[0066] Conventional backlight units had to sufficiently secure an optical distance, defined as the distance between a light-emitting element (200) and optical members (such as a diffuser plate), in order to enhance the light diffusion effect and output light of uniform brightness, and to this end, they had to be equipped with a support member, etc. A backlight unit according to one embodiment of the present invention can reduce the optical distance to less than 1 / 2 of the thickness of the light source, can not use a support member, and can eliminate the optical distance by having the optical sheet (300) in direct contact with the light-emitting element (200). The thickness of the entire backlight unit can be reduced to the sum of the thicknesses of the light-emitting element (200) and the optical sheets, for example, 0.7 mm to 2 mm. Accordingly, a backlight unit according to one embodiment of the present invention can provide an ultra-slim backlight unit with a greatly reduced thickness, and can achieve slimness of a display device including such a backlight unit.

[0067] A backlight unit according to one embodiment of the present invention may further include a color conversion sheet (400) and a light conversion sheet (500) on top of an optical sheet (300). The color conversion sheet (400) may be in contact with the other side of the optical sheet (300), and the light conversion sheet (500) may be arranged to be in contact with the color conversion sheet (400).

[0068] The color conversion sheet (400) can convert the color of incident light by including a color conversion material that absorbs light of a specific wavelength range and emits light of a different wavelength range from the absorbed light. Generally, the light-emitting element (200) uses a blue LED, and the color conversion sheet (400) can convert blue light into white light by including a color conversion material such as a phosphor.

[0069] The light conversion sheet (500) can change the path of incident light. The light conversion sheet (500) may contain a light conversion material or have a pattern formed on one surface to change the path of incident light, and may play a role in adjusting the brightness and uniformity of the emitted light according to the designer's intention. For example, the light conversion sheet (500) may contain a light conversion material to reduce the brightness difference between areas with high and low light levels. The light conversion sheet (500) may be a diffusion sheet or a prism sheet, but is not limited thereto, and any light path conversion sheet that changes the path of incident light can be applied.

[0070] By arranging the color conversion sheet (400) and the light conversion sheet (500) to be in contact on the upper surface of the optical sheet (300), the backlight unit according to one embodiment of the present invention can provide a surface light source with improved brightness and color uniformity, and can significantly reduce the overall thickness of the backlight unit.

[0071] FIG. 4 is a cross-sectional view of a backlight unit according to one embodiment of the present invention, and is a drawing for explaining a second optical sheet (320) placed on a first optical sheet (310).

[0072] Referring to FIG. 4, the optical sheet (300) of a backlight unit according to one embodiment of the present invention may include multiple optical sheets (300). For example, the optical sheet (300) may include a first optical sheet (310) and a second optical sheet (320). When the backlight unit includes two optical sheets (300), the first optical sheet (310) may be placed on top of a light-emitting element (200), and the second optical sheet (320) may be placed on top of the first optical sheet (310). The first optical sheet (310) may come into contact with the light-emitting surface of the light-emitting element (200), and the second optical sheet (320) may be placed adjacent to the first optical sheet (310) or placed without a gap from the first optical sheet (310) to come into contact with the first optical sheet (310). The first optical sheet (310) and the second optical sheet (320) may be made of the same material and may have an optical pattern formed inside. The optical patterns of the first optical sheet (310) and the second optical sheet (320) may be the same, but are not limited thereto and may be formed differently.

[0073] The second optical sheet (320) is positioned on top of the first optical sheet (310) and can serve to refract and disperse light emitted from the first optical sheet (310). By positioning the second optical sheet (320) on top of the first optical sheet (310), the light emitted from the light-emitting element (200) can be dispersed more uniformly.

[0074] According to one embodiment of the present invention, the optical pattern of the second optical sheet (320) may be arranged so as not to overlap with the optical pattern of the first optical sheet (310). For example, as shown in FIG. 4, when both the first optical sheet (310) and the second optical sheet (320) are optical sheets having a cone-shaped optical pattern formed thereon, the second optical sheet (320) may be arranged such that the vertex of the cone shape of the second optical sheet (320) is positioned between the vertices of the cone shape of the first optical sheet (310). By arranging the optical patterns of the first optical sheet (310) and the second optical sheet (320) placed on the upper part of the light-emitting element (200) so as not to overlap, the light emitted from the light-emitting element (200) can be dispersed and emitted more effectively, and a surface light source can be easily implemented.

[0075] FIG. 5 is a cross-sectional view of a backlight unit according to one embodiment of the present invention, illustrating a schematic cross-section of a backlight unit further comprising a fixing means (600) for fixing an optical sheet (300) to the upper part of a substrate (100).

[0076] Referring to FIG. 5, the optical sheet (300) can be fixed together with the substrate (100) by a fixing means (600). For example, the fixing means (600) may be a bracket type that combines the substrate (100), the optical sheet (300), the color conversion sheet (400), and the light conversion sheet (500) together, or a cover type that encloses the bottom surface, the side surface, and the optical member of the substrate. However, the fixing means (600) is not limited to this, and any fixing means that fixes the optical sheet (300) to the top of the substrate (100) may be used.

[0077] For example, the optical sheet (300) may be attached and fixed to the light-emitting surface of at least one light-emitting element (200). In one embodiment, the optical sheet (300) may be directly attached to the light-emitting surface of the light-emitting element (200) by means of an adhesive means. In another embodiment, the backlight unit may use the fixing means (600) of FIG. 5 to induce one side of the optical sheet (300) to come into contact with the light-emitting surface of the light-emitting element (200).

[0078] FIG. 6 is a drawing showing an embodiment of a backlight unit, and is a drawing for explaining a light-emitting element (210) placed at the outermost edge.

[0079] Referring to FIG. 6, the light-emitting elements (200) may be spaced apart on the substrate (100), and the light-emitting element (210) placed at the outermost among the plurality of light-emitting elements (200) mounted on the substrate (100) may be positioned so as to make at least partial contact with one surface of the optical sheet (300).

[0080] The light-emitting element (200) can be arranged in various ways, such as a checkerboard arrangement or a concentric circle arrangement. By ensuring that the light-emitting surface of the light-emitting element (210) placed at the outermost edge contacts at least a portion of one surface of the optical sheet (300), the entire surface of the optical sheet (300) can be arranged adjacent to the light-emitting surface of the light-emitting element (200). Accordingly, light incident on one surface of the optical sheet (300) is stably incident, refracted or dispersed by the optical pattern formed inside the optical sheet (300), and can be emitted to the other surface of the optical sheet (300).

[0081] Here, one side of the optical sheet (300) may be attached and fixed to the light-emitting surface of the light-emitting element (210) placed at the outermost edge using an adhesive means. Alternatively, as shown in FIG. 5, one side of the optical sheet (300) may come into contact with the light-emitting surface of the light-emitting element (210) placed at the outermost edge by means of a fixing means (600, see FIG. 5).

[0082] FIG. 7 shows the results of a performance test of a backlight unit according to one embodiment of the present invention and a conventional backlight unit.

[0083] Referring to FIG. 7, the upper photograph is the result of an experiment with a backlight unit according to a comparative example, showing the appearance when a diffuser plate is applied to the upper part of the light source without an optical distance and a color conversion sheet (400) and a light conversion sheet (500) are added and applied to the upper part of the diffuser plate, and the lower photograph is the appearance when an optical sheet (300) according to an embodiment of the present invention is applied.

[0084] It can be seen that, according to the comparative embodiment, the backlight unit uses a diffuser plate and applies a color conversion sheet (400), resulting in a hot spot with a large amount of light occurring above the light source, and exhibiting uneven brightness compared to the part without the light source.

[0085] In contrast, when an optical sheet (300) according to one embodiment of the present invention is applied, it can be seen that the light from the light source is uniformly diffused and a uniform brightness output can be obtained even though the optical sheet (300) is positioned so that the optical distance is close to 0.

[0086] Accordingly, a backlight unit according to one embodiment of the present invention can reduce the optical distance and reduce the thickness of the entire backlight unit by effectively diffusing light emitted from a light-emitting element (200) through an optical sheet (300) or a first optical sheet (310) and a second optical sheet (320). It can also be made easier to implement a flexible display by eliminating unnecessary optical components such as optical lenses and support members. Furthermore, as light can be effectively diffused, the spacing between light-emitting elements (200) on a substrate (100) can be widened, and a manufacturing cost reduction effect can be obtained accordingly.

[0087] As such, the present invention has been described with reference to an embodiment illustrated in the drawings, but this is merely illustrative, and those skilled in the art will understand that various modifications and variations of the embodiments are possible therefrom. Accordingly, the true technical scope of protection of the present invention should be determined by the technical spirit of the appended claims. Explanation of the symbols

[0088] 100 : Substrate 200 : Light-emitting element 210 : Light-emitting element placed at the outermost edge 300 : Optical sheet 310: First optical sheet 320: Second optical sheet 400 : Color Conversion Sheet 500 : Light conversion sheet 600 : Fixing means

Claims

Claim 1 A backlight unit comprising: a substrate; a plurality of light-emitting elements mounted on the substrate; a first optical sheet disposed on the upper portion of the light-emitting elements and having a first optical pattern formed therein; and a second optical sheet disposed on the first optical sheet and having a second optical pattern formed therein; wherein the first optical sheet is in direct contact with the light-emitting surface of at least one of the light-emitting elements through one surface, and emits light from the light-emitting elements incident on the one surface to the other surface opposite to the one surface, wherein the light is refracted or dispersed in a direction different from the direction of incidence by the first optical pattern formed therein of the first optical sheet and emits the light, and the first optical pattern of the first optical sheet and the second optical pattern of the second optical sheet are non-overlapping with each other. Claim 2 A backlight unit according to claim 1, wherein the first optical sheet forms the first optical pattern between the first surface and the other surface such that the angle of emission of light emitted to the other surface is greater than the angle of incidence of light incident on the first surface. Claim 3 A backlight unit according to claim 1, characterized in that the distance from the surface of the first optical sheet that does not contact the light-emitting surface of the light-emitting element to the upper surface of the substrate is 1.5 times or less the height of the light-emitting element. Claim 4 A backlight unit according to claim 1, further comprising a color conversion sheet disposed on the first optical sheet and a light conversion sheet disposed on the color conversion sheet. Claim 5 A backlight unit according to claim 1, further comprising a fixing means for fixing the first optical sheet to the upper surface of the substrate. Claim 6 A backlight unit according to claim 1, wherein the first optical pattern formed inside the first optical sheet has a repeating pattern structure that refracts and disperses light incident on one side of the first optical sheet. Claim 7 A backlight unit according to claim 6, wherein the pattern structure is one of a hexagon, a cone, a pyramid, a trapezoid, or an embossed shape. Claim 8 A backlight unit characterized in that, in claim 6, the pattern structure is a nano-lens pattern. Claim 9 delete Claim 10 delete Claim 11 A backlight unit comprising: a substrate; a plurality of light-emitting elements mounted on the substrate; a first optical sheet disposed on the upper portion of the light-emitting elements and having a first optical pattern formed therein; and a second optical sheet disposed on the first optical sheet and having a second optical pattern formed therein; wherein the light-emitting elements are spaced apart and arranged on the substrate, and the first optical sheet makes at least partial direct contact with the light-emitting surface of the light-emitting element disposed at the outermost portion among the plurality of light-emitting elements through one surface, and emits light from the light-emitting element incident on the one surface to the other surface opposite to the one surface, wherein the light is refracted or dispersed in a direction different from the incident direction by the first optical pattern formed inside the first optical sheet and emits the light, and the first optical pattern of the first optical sheet and the second optical pattern of the second optical sheet are non-overlapping with each other. Claim 12 A backlight unit according to claim 11, wherein the first optical sheet forms the first optical pattern between the first surface and the other surface such that the angle of emission of light emitted to the other surface is greater than the angle of incidence of light incident on the first surface. Claim 13 A backlight unit according to claim 11, characterized in that the distance from the surface of the first optical sheet that does not contact the light-emitting surface of the light-emitting element to the upper surface of the substrate is 1.5 times or less the height of the light-emitting element. Claim 14 A backlight unit according to claim 11, further comprising a color conversion sheet disposed on the first optical sheet and a light conversion sheet disposed on the color conversion sheet. Claim 15 A backlight unit according to claim 11, further comprising a fixing means for fixing the first optical sheet to the upper surface of the substrate. Claim 16 A backlight unit according to claim 11, wherein the first optical pattern formed inside the first optical sheet has a repeating pattern structure that refracts and disperses light incident on one side of the first optical sheet. Claim 17 A backlight unit according to claim 16, wherein the pattern structure is one of a hexagon, a cone, a pyramid, a trapezoid, or an embossed shape. Claim 18 A backlight unit characterized in that, in claim 16, the pattern structure is a nano-lens pattern. Claim 19 delete Claim 20 delete

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