Backlight module and display device

Abstract

A backlight module, comprising a light guide plate (2), a light source (3), a structured optical diaphragm (4) and two prism sheets (5). The structured optical diaphragm (4) is arranged corresponding to a light-emergent surface (22) of the light guide plate (2); and comprises a body (41), a plurality of prisms (42) which are arranged in parallel on the body (41) and face the light-emergent surface (22), and a plurality of optical structures (43) which are arranged on the body (41) and face away from the light-emergent surface (22) of the light guide plate (2). Each prism sheet (5) is provided with a plurality of prism strips (51), which are arranged in parallel and face away from the structured optical diaphragm (4), wherein the extension direction of the prism strips (51) on one prism sheet (5) is different from that of the prism strips (51) on the other prism sheet (5).

Description

Backlight module and display device

[0001] This application claims priority to Chinese patent application No. 202311284181.0, filed on October 7, 2023, entitled “Backlight Module and Display Device,” and all of its contents are incorporated herein by reference. Technical Field

[0002] The present invention relates to an optical device, and in particular to a backlight module and a display device. Background Art

[0003] Existing backlight modules usually use diffusers to homogenize light. Currently, common diffusers have multiple scattering particles that can scatter light so that the light is dispersed and emitted, thereby homogenizing the light. However, the diffusers with scattering particles are usually used to conceal blemishes and have relatively low optical directivity, which destroys the high directivity of the light guide plate. If the directivity is to be improved, the haze of the diffuser must be reduced, and the concealing effect will be worse. As for the brightening sheet, although it is beneficial for improving the brightness, the haze of the upper and lower diffusers used in the backlight module will affect the brightness and optical appearance, making it difficult to further improve the brightness of the existing backlight module. Therefore, how to increase the optical rotation and directivity of the light output angle while maintaining the concealing ability has become the design focus of the backlight module.

[0004] Summary of the Invention

[0005] Therefore, an object of the present invention is to provide a backlight module with improved light radiating viewing angle and directivity.

[0006] The backlight module of the present invention includes: a light guide plate, a light source, a structured optical film and two prism sheets. The light guide plate has a light incident surface and a light exit surface connected to the light incident surface, and the light source is arranged corresponding to the light incident surface of the light guide plate. The structured optical film is arranged corresponding to the light exit surface of the light guide plate, and includes a main body, a plurality of prisms arranged in parallel on the main body and facing the light exit surface, and a plurality of optical structures arranged on the main body and facing away from the light exit surface of the light guide plate. The prisms are located between the light exit surface and the optical structure. The two prism sheets are superimposed on the structured optical film. Each prism sheet has a plurality of prism strips arranged in parallel and facing away from the structured optical film, and the extension direction of the prism strips on one prism sheet is different from the extension direction of the prism strips on the other prism sheet.

[0007] Another object of the present invention is to provide a display device comprising the backlight module as described above, and a display panel disposed on the backlight module.

[0008] The invention's effectiveness lies in allowing light from a light source to first pass through the prisms of the structured optical film, enhancing its directivity. The optical structure of the structured optical film then concentrates the energy at the location where the prisms split the light, while also maintaining a concealing effect. In this way, the structured optical film maintains its concealing properties while still concentrating the light. Finally, the two prisms concentrate the split light energy, enhancing the backlight unit's optical concentration and brightness. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG1 is an exploded perspective view of a preferred embodiment of a backlight module of the present invention;

[0010] FIG2 is a schematic side view from a side view angle to assist in explaining FIG1 ;

[0011] FIG3A is a schematic diagram of an enlarged view of the block diagram in FIG2 ;

[0012] FIG3B is a schematic diagram illustrating another embodiment different from FIG3A;

[0013] FIG3C is a schematic diagram illustrating yet another embodiment different from FIG3A ;

[0014] FIG3D is a schematic diagram illustrating another embodiment different from FIG3A ;

[0015] FIG4 is a graph illustrating the relationship between the refractive index ratio of the prism sheet and the structured optical film and the brightness;

[0016] FIG5 is a graph illustrating the relationship between the ratio of the prism angle of the structured optical film to the roughness of the reflective reflector and the brightness;

[0017] FIG6 is a side view schematic diagram illustrating the backlight module using different types of reflective sheets;

[0018] 7 is a graph illustrating the relationship between the ratio of the prism angle of the structured optical film to the roughness of the diffuse reflective sheet and the brightness;

[0019] FIG8 is a side view schematically illustrating that a plurality of light guide structures are formed on the bottom surface of the light guide plate of the backlight module;

[0020] 9 is a graph illustrating the relationship between the viewing angle and the luminance of the light guide structure of the light guide plate;

[0021] 10 is a schematic diagram illustrating the simulation effect of the spatial luminance distribution of the backlight module of the present invention corresponding to different light collection angles;

[0022] FIG11 is a side view schematic diagram of a preferred embodiment of the display device of the present invention;

[0023] FIG12 is a schematic diagram illustrating how moiré fringes are formed;

[0024] FIG13 is a graph illustrating the relationship between the moiré fringe spacing and the luminance;

[0025] FIG14 is a side view schematic diagram illustrating that the depths of the microstructures on the structured optical film and the prism sheet are randomly distributed;

[0026] FIG15 is a schematic top view illustrating the phenomenon in which the prism strips on the two prism sheets are deflected to reduce moiré fringes;

[0027] FIG16 is a schematic top view illustrating the phenomenon that the optical structure on the structured optical film forms a deflection to reduce moiré fringes;

[0028] FIG17 is a schematic top view illustrating a phenomenon in which optical structures on a structured optical film are deflected to reduce moiré fringes, wherein the arrangement of the optical structures is different from that in FIG16 ;

[0029] FIG18 is a schematic top view illustrating the phenomenon of prisms on a structured optical film being deflected to reduce moiré fringes; and

[0030] FIG19 is a side view schematically illustrating that the first surface of the structured optical film has a plurality of upwardly convex curved surface areas and a plurality of optical structures are disposed in each curved surface area.

[0031] FIG20 is a schematic diagram illustrating the simulation effect of the luminance distribution of the incident light source; and

[0032] FIG21 is a schematic diagram illustrating the simulation effect of the luminance distribution of the outgoing light source. DETAILED DESCRIPTION

[0033] The features and technical content of the related patent applications of this invention will be clearly presented in the detailed description of the preferred embodiments below with reference to the accompanying drawings. Before proceeding with the detailed description, it should be noted that similar elements are represented by the same reference numerals. The directional terms mentioned in the following embodiments, such as "up," "down," "left," "right," "front," "back," "bottom," and "top," are only used with reference to the directions in the accompanying drawings. Therefore, the directional terms used are for illustrative purposes only and are not intended to limit the present invention.

[0034] In the following description, the terms "about," "substantially," "approximately," or "the same" generally indicate a range within 10%, within 5%, within 3%, within 2%, within 1%, or within 0.5% of a given value. The quantities given herein are approximate, meaning that even without the specific wording "about," "substantially," "approximately," or "the same," the meaning of "about," "substantially," "approximately," or "the same" may be implied.

[0035] Referring to Figures 1 and 2, a preferred embodiment of the backlight module of the present invention comprises a light guide plate 2, a light source 3, a structured optical film 4, two prism sheets 5 and a diffuser 6. The light guide plate 2 has a light incident surface 21 and a light emitting surface 22 connected to the light incident surface 21. The light source 3 is arranged corresponding to the light incident surface 21 of the light guide plate 2, and has a plurality of light-emitting components 31 arranged along the light incident surface 21. The structured optical film 4 is located between the prism sheet 5 and the light emitting surface 22. The two prism sheets 5 are located between the diffuser 6 and the structured optical film 4 and are superimposed on the structured optical film 4. Among the structured optical film 4 and the two prism sheets 5, at least two adjacent optical films are an integrated structure. In the embodiments shown in Figures 1 and 2, the structured optical film 4 and the prism sheet 5 adjacent to the structured optical film 4 are both an integrated structure.

[0036] The structured optical film 4 is disposed corresponding to the light exit surface 22 of the light guide plate 2 and includes a body 41, a plurality of prisms 42 arranged in parallel on the body 41 and facing the light exit surface 22, and a plurality of optical structures 43 disposed on the body 41 and facing away from the light exit surface 22 of the light guide plate 2. The prisms 42 are located between the light exit surface 22 and the optical structures 43, and an extension direction E1 of the prisms 42 is parallel to the optical axis of the light-emitting element 31 of the light source 3. Each prism sheet 5 has a plurality of prism strips 51 arranged in parallel and facing away from the structured optical film 4. The extension direction E1 of the prism strips 51 on one prism sheet 5 is different from the extension direction E2 of the prism strips 51 on the other prism sheet 5. In the embodiment shown in FIG1 , the prism strips 51 of the upper prism sheet 5 extend along the extension direction E1, while the prism strips 51 of the lower prism sheet 5 extend along the extension direction E2, with the extension direction E1 being perpendicular to the extension direction E2.

[0037] The backlight module disclosed in this embodiment primarily allows the light emitted by the light source 3 to first pass through the prisms 42 of the structured optical film 4, resulting in an effect of improved directivity. However, this results in a problem in which the atomized energy is difficult to concentrate. In this case, the optical structure 43 of the structured optical film 4 is then used to maintain the concealing effect. In this way, the structured optical film 4 can still promote concentrated emission of light while maintaining its concealing ability. Finally, the two prism sheets 51 are used to concentrate the split light energy, thereby enhancing the optical concentration and brightness of the backlight module. Furthermore, at least two adjacent optical films are integrated into a single structure, which not only improves assembly convenience but also prevents the problem of uneven light output caused by adsorption between stacked optical films.

[0038] In this embodiment, the structured optical film 4 and the prism sheet 51 adjacent to the structured optical film 4 are both integrally formed. This prevents the optical films from being offset relative to each other, thereby preventing the adverse effects of structural damage to the prisms 42 and optical structure 43. In some embodiments, the two prism sheets 5 can also be integrally formed. In other embodiments, the structured optical film 4 and the two prism sheets 5 can be integrally formed, further ensuring that there is no relative positional offset between the three, making assembly more convenient. The optical films are bonded together using a fixing adhesive after fabrication. The bonding method is readily understood by those skilled in the art and will not be described in detail.

[0039] Referring to Figures 2 and 3A, the following describes how to use the optical structure 43 of the structured optical film 4 to produce a concealing effect. Each optical structure 43 of the structured optical film 4 has a central line L, a vertex 430 located on the central line L, and a plurality of side surfaces 431a surrounding the central line L. Light from the light source 3 enters the main body 41 through the prism 42, and then leaves the structured optical film 4 through the optical structure 43 to maintain concealment. The concealing effect is mainly produced because each optical structure 43 has a plurality of side surfaces 431a, which can bend the light through the side surfaces 431a and guide it to multiple light-emitting directions, thereby preventing the light energy from being too concentrated directly above the optical structure 43, thereby producing a concealing effect. Referring to Figure 3A, in this embodiment, the central line L of each optical structure 43 is perpendicular to the main body 41 of the structured optical film 4. Each optical structure 43 is a quadrangular pyramidal structure having four side surfaces 431a. Each side surface 431a is a composite surface formed by joining first and second surface elements 431b and 431c along the extension direction of a center line L. Each surface element has a normal. The normals of surface elements in the same layer surrounding the center line L have the same angle with the center line L, while the normals of surface elements in different layers along the center line L have different angles with the center line L. It should be noted that the "normal" referred to herein refers to a line perpendicular to the first and second surface elements 431b and 431c, respectively. More specifically, each first surface element 431b has a normal N1, and each second surface element 431c has a normal N2. The normal N1 of each first surface element 431b forms an angle θ1 with the center line L, while the normal N2 of each second surface element 431c forms an angle θ2 with the center line L. The angle θ1 between the normal line N1 and the center line L of each first surface unit 431b is the same, while the angle θ2 between the normal line N2 and the center line L of each second surface unit 431c is the same, but the angle θ1 and the angle θ2 are different. In other words, the first surface units 431b and the second surface units 431c form inclined surfaces with different inclinations. In some embodiments, the angle θ1 between the normal line N1 and the center line L of the surface units closer to the vertex 430 is smaller than the angle θ2 between the normal line N2 and the center line L of the surface units farther from the vertex 430, thereby forming inclined surfaces with different inclinations. In this way, light is refracted and reflected by the inclined surfaces at different inclinations, dispersing the light as much as possible. This reduces the tendency of light to be concentrated at a specific angle or directly above the surface, allowing the light to travel in different directions upon exiting, thereby achieving uniform light and improving the brightness of the emitted light. Furthermore, in this embodiment, the angle θ1 of the first surface unit 431b closer to the vertex 430 of each optical structure 43 is smaller than the angle θ2 of the second surface unit 431c farther from the vertex 430. In other words, the angle between the normal of the surface unit and the center line L decreases as the distance from the prism sheet 5 increases.In this way, the manufacturing process is easier and the yield is higher, reducing the risk of process defects caused by the apex 430 being too sharp. If the optical structure 43 adopts a concave structure design, the thickness of the structured optical film 4 can be further reduced.

[0040] Referring again to FIG. 3B , it illustrates another embodiment different from FIG. 3A . The primary difference is that the angle between the normal and the centerline of the facet elements closer to the vertex is greater than the angle between the normal and the centerline of the facet elements farther from the vertex. In other words, the angle between the normal and the centerline L of the facet elements increases with increasing distance from the prism sheet 5. This design effectively reduces scratches on the stacked films above.

[0041] Please refer to Figure 3C again, which discloses an alternative embodiment to Figure 3A . Each optical structure has a centerline, a platform, and multiple side surfaces surrounding the centerline. The centerline is perpendicular to the main body of the structured optical film, and the side surfaces connect the platform to the main body of the structured optical film. This design primarily uses a trapezoidal tool to create the microstructures within the mold, resulting in a platform shape corresponding to the platform of each optical structure. This reduces tool wear at the platform, extending the tool life, and maintaining the stability of the microstructure's molding.

[0042] Please refer to Figure 3D again, which discloses another embodiment different from Figure 3A. The main difference is that each optical structure has a center line and multiple side surfaces surrounding the center line. The center line is perpendicular to the main body of the structured optical film. Each side surface is a composite surface formed by two or more layers of surface units joined along the extension direction of the center line. The surface units closer to the vertex are curved surfaces, and the surface units farther from the vertex are sloped surfaces. This design is similar to the design in Figure 3C, but mainly uses R-shaped tools to form the microstructures in the mold. The position of the microstructures in the mold produces an arc shape to correspond to the curvature surface of each optical structure closer to the vertex. Therefore, it can reduce tool wear on the curved surface, maintain the tool life, and also maintain the molding stability of the microstructure.

[0043] Next, it will be further explained that the present invention can improve the brightness in the following ways. First, the brightness generated by the backlight module disclosed in Figures 1 and 2 is set to 100%. In this embodiment, the ratio of the refractive index of the prism sheet 5 to the refractive index of the structured optical film 4 is greater than or equal to 1.08. As shown in Figure 4, when the ratio of the refractive index is greater than or equal to 1.08, the brightness can be maintained at more than 100% and steadily improved as the refractive index increases. When the ratio of the refractive index is less than 1.08, an optical film with a specific refractive index can be selected. For example, in some embodiments, the refractive index of the prism sheet 5 is 1.62 and the refractive index of the structured optical film 4 is 1.55, which can maintain the brightness at around 100%. At this point, the brightness can at least maintain the original value, and the adverse effect of reduced brightness will not occur.

[0044] Referring to Figures 1 and 2, the backlight module also includes a reflective reflector 7a located below the light guide plate 2. The ratio of the prism angle of the prisms 42 of the structured optical film 4 to the roughness of the reflective reflector 7a is between 700 and 900, inclusive. In this embodiment, the reflective reflector 7a is selected from a silver reflector with a roughness of 0.1. This type of reflector needs to be paired with prisms 42 having a smaller prism angle. For example, the prism angle of each prism 42 is between 70° and 90°, inclusive. Preferably, the prism angle of each prism 42 is 80°, which results in the best brightness enhancement effect. It should be noted that the aforementioned roughness refers to the centerline average surface roughness (Ra), which is defined as the average value of the absolute value of the distance from each point on the actual contour of the measured surface to the contour centerline within the sampling length. Since the centerline average surface roughness value (commonly referred to as roughness, Ra) is well known to those skilled in the art, it will not be further described here. As shown in FIG5 , first, the luminance generated by the backlight module disclosed in FIG1 and FIG2 is set to 100%. By maintaining the ratio of the prism angle of prisms 42 to the roughness of reflective reflector sheet 7a between 700 and 900, the luminance can be maintained above 100%.

[0045] In addition to the reflective reflector 7a, another diffuse reflector can also be used. Referring to Figure 6, in some embodiments, the backlight module further includes a diffuse reflector 7b located below the light guide plate 2. The ratio of the prism angle of the prism 42 of the structured optical film 4 to the roughness of the diffuse reflector 7b is greater than 200 and less than or equal to 250. In this embodiment, the reflective reflector 7a is selected from a matte white reflector with a roughness of 0.4. This type of reflector needs to be paired with a prism 42 with a larger prism angle, for example, the prism angle of each prism 42 is greater than 80° and less than or equal to 100°. Preferably, the prism angle of each prism 42 is 90°, which will have the best brightness enhancement effect. As shown in Figure 7, first, set the brightness generated by the backlight module disclosed in Figures 1 and 2 to 100%. By maintaining the ratio of the prism angle of the prism 42 to the roughness of the reflective reflector 7a between 200 and 250, the brightness can be maintained above 100%. With this design, the prism angle of the prism 42 can be adjusted to match the appropriate reflector to maintain optimal brightness.

[0046] Referring to FIG8 , in some embodiments, the light guide plate 2 further has a bottom surface 23 opposite to the light emitting surface 22, and a plurality of light guide structures 24 formed on the bottom surface 23. Each light guide structure 24 has a light-facing surface 241 and a non-light-facing surface 242 that are connected to each other. The light-facing surface 241 faces the direction of light travel from the light source 3. A light-collecting angle 243 is formed between the light-facing surface 241 and the bottom surface 23. The light-collecting angle 243 is less than or equal to 20°. As shown in FIG9 , first, when the light-collecting angle 243 is set to 5°, the luminance generated by the backlight module is approximately 100%. When the light-collecting angle 243 is less than or equal to 20°, the light can be concentrated between a viewing angle of 70° and 80°, and the luminance in this range can be maintained above 60% for the most part. When the receiving angle 243 is greater than 35°, no matter the viewing angle is large or small, the light concentration effect is not produced, and the brightness is below 60%, which is not enough to maintain good brightness. Even at a viewing angle of 70° to 80°, the brightness still does not exceed 60%. Refer to Figure 10, which is a spatial brightness distribution diagram corresponding to the backlight module shown in Figure 8. It should be noted that the spatial brightness distribution diagram is a computer simulation diagram, and originally a color diagram, but in this case it is presented as a grayscale diagram. In addition, the vertical axis and the horizontal axis of Figure 10 both represent angles, and the center of the intersection of the vertical axis and the horizontal axis can represent the central axis of the light emitting surface 22 of the light guide plate 2. Generally speaking, the larger the receiving angle 243, the more dispersed the energy is and the more detrimental it is to the brightness. Therefore, the backlight module of the present invention further limits the receiving angle 243 to be less than or equal to 20°. In FIG10 , when the light collection angle 243 is 20°, energy concentration can be observed on both sides of the central axis. As the light collection angle 243 gradually decreases, the energy concentration on both sides of the central axis becomes more obvious, and the brightness is further improved. It can be seen from this that the light guide structure 24 is formed on the bottom surface 23 of the light guide plate 2, and the light collection angle 243 of the light guide structure 24 can produce an effective effect of improving the brightness at a specific angle. On the contrary, if the light collection angle gradually increases, for example, to 35°, there will be an adverse effect of a 10% decrease in brightness. It should be noted that in FIG10 , the light guide structure 24 is a concave design. In some embodiments, the light guide structure 24 can also be a convex design, which can also achieve the effect of improving the brightness.

[0047] As shown in FIG11 , a display panel 8 is provided on a backlight module, which is the display device of the present invention. It should be noted that the display panel 8 can also be provided on the backlight module shown in FIG2 or FIG6 .

[0048] Furthermore, because the prisms 42 of the structured optical film 4 and the prism strips 51 on one of the prism sheets 5 are both strip-shaped, they are susceptible to interference at a constant angle and frequency, producing a moiré pattern. Moiré is a visual effect of magnification or reduction created by overlapping or rotating two or more sets of different stripes. The principle is that when two sets of patterns with similar spatial frequencies interfere with each other, the lower-frequency (wider-pitch) pattern appears.

[0049] Referring to FIG. 12 in conjunction with FIG. 2 , in certain embodiments, the prisms 42 of the structured optical film 4 and the prism strips 51 on one of the prism sheets 5 have a non-zero angle θ. Each pair of adjacent prisms 42 has a prism pitch T1, and each pair of adjacent prism strips 51 has a prism strip pitch T2. These prisms 42 and prism strips 51 combine to form a plurality of moiré fringes. Each pair of adjacent moiré fringes has a moiré pitch P, and the moiré pitch P must satisfy the following relationship: As shown in FIG13 , first, the brightness of the backlight module shown in FIG1 and FIG2 is set to 100%. When the moiré fringe pitch P is less than 250 μm, the brightness can be effectively improved, maintaining the brightness above 100%.

[0050] In addition, in order to avoid the generation of moiré fringes, the present invention also proposes the following solutions. Among them, the first solution is to make the height of the prism structure of the structured optical film 4 and the prism sheet 5 randomly distributed. Referring to Figure 14, as mentioned above, the structured optical film 4 has prisms 42 and optical structures 43, and the prism sheet 5 has prism strips 51. In this embodiment, at least one of the height of the prisms 42 of the structured optical film 4, the height (or depth) of the optical structure 43, and the height of the prism strips 51 of the prism sheet 5 is randomly distributed. Due to the viewing angle, it can be seen in Figure 14 that the depth of the optical structure 43 or the height of the prism strips 51 of the prism sheet 5 adjacent to the structured optical film 4 are irregular and randomly varied. In this way, the original rule of mutual interference between the prisms 42 and the optical structure 43 of the structured optical film 4 can be destroyed, and the moiré fringes phenomenon can be alleviated. Alternatively, the prisms 42 and optical structures 43 of the structured optical film 4 and the prism strips 51 of the prism sheet 5 can all randomly change height or depth, which can also reduce the risk of generating moire fringes.

[0051] The second solution involves slightly deflecting each film sheet or microstructure on it. In the first approach, as shown in Figure 15 , each prism sheet 5 has a first edge 501 and a second edge 502 that are perpendicular to each other. In one of the two prism sheets 5, the extension direction E1 of the prism strips 51 (solid line in Figure 15) of one prism sheet 5 forms a first angle α1 with the first edge 501, while the extension direction E2 of the prism strips 51' (dashed line in Figure 15) of the other prism sheet 5 forms a second angle α2 with the second edge 502. In this embodiment, the extension directions E1 and E2 are substantially perpendicular. At least one of the first angle α1 and the second angle α2 is non-zero, and its absolute value is between 3° and 5°, inclusive. Because the prism strips 51 or 51' of the prism sheet 5 undergo a slight deflection, they are less likely to produce moiré fringes that interfere with the prisms 42 and optical structures 43' of the nearly parallel structured optical film 4.

[0052] In the second embodiment, as shown in FIG16 , the structured optical film 4 has a first side 401 and a second side 402 that are perpendicular to each other. The optical structures 43 of the structured optical film 4 are arranged in an array so that the line L1 connecting the vertices of at least some of the optical structures 43 is substantially parallel to the first side 401 of the structured optical film 4 and has an angle of the upper adjustment angle UA. Alternatively, as shown in FIG17 , the line L1 is tilted at an angle of approximately 45 degrees and has an angle of the upper adjustment angle UA. The upper adjustment angle UA is not zero, but has an absolute value between 3° and 5°, inclusive. Because the optical structures 43 of the structured optical film 4 are slightly deflected, they are less likely to produce moiré fringes that interfere with the prism strips 51 or prism strips 51' of the approximately parallel prism sheet 5.

[0053] In the third embodiment, referring to FIG. 18 , the extension direction D1 of the prisms 42 of the structured optical film 4 is substantially parallel to the extension direction E1 of the prism strips 51 of one of the prism sheets 5 located farther from the structured optical film 4. A lower adjustment angle DA is defined between the extension direction D1 of the prisms 42 of the structured optical film 4 and the edge of the structured optical film 4 parallel to the extension direction E1. The lower adjustment angle DA is not zero, but has an absolute value between 3° and 5°, inclusive. Because the prisms 42 of the structured optical film 4 are slightly deflected, they are less likely to produce moiré fringes due to angular interference with the prism strips 51 or 51' of the prism sheet 5, which are substantially parallel to the structured optical film 4.

[0054] In addition, in certain embodiments, when a reflective reflector is used in conjunction with the present invention, the refractive index of the structured optical film 4 is between 1.4 and 1.6, including the end values. When the refractive index is less than 1.4, the light output angle of the structured optical film 4 will be away from the forward direction and become more skewed. Conversely, when the refractive index is greater than 1.6, the light output angle of the structured optical film 4 will be biased toward the forward direction and become more collimated. Both will result in unsuitable light output angles, which are not easily utilized by the prism sheet 5 above, resulting in poor light output efficiency.

[0055] Each prism 42 of the structured optical film 4 has a prism angle, and each optical structure 43 of the structured optical film 4 has a vertex angle. The ratio of the prism angle to the vertex angle is between 0.636 and 1.5. Since the size of the prism angle determines the light splitting effect of the structured optical film 4 when emitting light, and the size of the vertex angle of each optical structure 43 determines the positive viewing angle of the structured optical film 4 when emitting light, therefore, when the present invention is used in conjunction with a reflective reflector, it is necessary to select a ratio of the prism angle to the vertex angle between 0.636 and 1.5 to produce a suitable light splitting effect and positive viewing angle, so as to provide the prism sheet 5 above for use and produce better light extraction efficiency.

[0056] In actual application, within the above-mentioned ratio range, the prism angle of each prism 42 is between 70° and 120°, including the end value. The size of the prism angle determines whether the light splitting effect of the structured optical film 4 is obvious when emitting light. When the prism angle is smaller, the light splitting effect will be more obvious and the light emitting areas will be separated farther and wider. When the prism angle is larger, the light splitting effect will be less obvious and the light emitting areas will be separated closer and more concentrated. In detail, when the prism angle is less than 70°, the light emitting areas of the structured optical film 4 will be separated too far. Conversely, when the prism angle is greater than 120°, the light emitting areas of the structured optical film will be separated too close. Both will produce an inappropriate light splitting effect, which is not easy to be used by the prism sheet 5 above, resulting in poor light extraction efficiency.

[0057] The vertex angle of each optical structure 43 is between 80° and 110°, inclusive. The vertex angle of each optical structure 43 determines the light output angle of the structured optical film 4. Specifically, when the vertex angle is less than 80°, the light output angle will be more positive. Conversely, when the prism angle is greater than 110°, the light output angle will be further away from the positive direction. Both results in an unsuitable light output angle, making it difficult for the prism sheet 5 above to be used, resulting in poor light output efficiency.

[0058] By means of the above-mentioned design, when a reflective reflector is applied, the incident light pattern shown in FIG20 can be converted into the outgoing light pattern shown in FIG21. In actual design, the peak position of the luminance of the incident light toward each prism 42 of the structured optical film 4 is between 3° and 15°, including the endpoint values, and the half-maximum width angle of the luminance is between 34° and 54° in the first direction (X-axis), including the endpoint values, and between 13° and 33° in the second direction (Y-axis), including the endpoint values. The first direction and the second direction are orthogonal to each other. Therefore, the incident light pattern when a reflective reflector is applied will be more concentrated and more biased towards the positive direction. When the incident light does not meet the aforementioned range, the efficiency of the outgoing light of the structured optical film 4 will be relatively poor, resulting in reduced luminance and the adverse effect of a skewed positive viewing angle.

[0059] In other words, only when the appropriate incident light pattern enters the structured optical film 4 within the aforementioned range will a suitable output light pattern be generated. The detailed numerical ranges are as follows: the peak brightness position of the light emitted from each optical structure 43 of the structured optical film 4 is between 20° and 40°, inclusive, and the half-maximum width angle of the brightness is between 15° and 25° (symmetrical in both the first direction, i.e., the X-axis, and the second direction, i.e., the Y-axis), inclusive. Similarly, when the output light does not meet the aforementioned range, it is not easily utilized by the prism sheet 5 above, resulting in a relatively poor efficiency of the light emitted from the prism sheet 5, resulting in reduced brightness and the unfavorable effect of a skewed viewing angle.

[0060] The above describes the present invention's use of reflective sheeting. Reflective sheeting typically refers to silver-plated reflectors, which exhibit a distinct mirror effect, reflecting incident light at the same angle of incidence as it strikes the mirrored surface. Polished metal objects are highly effective at reflecting light, and the reflective material used for the mirrored surface is typically aluminum or silver.

[0061] When the present invention is used in conjunction with a diffuse reflector, a different situation arises. A diffuse reflector generally refers to a reflector with a white surface. It exhibits a pronounced diffuse reflection effect, reflecting incident light at a certain angle of incidence onto the white surface over a range of angles. The white surface can be achieved by applying a matte coating. Matte coatings exhibit essentially perfect diffuse reflection, and surfaces made from non-absorbent powders (such as gypsum) can create a nearly perfect diffuse reflector.

[0062] Due to the characteristics of diffuse reflection, a certain range of angles of reflection will be generated, resulting in a more divergent viewing angle and a less obvious light splitting effect. In this case, a structured optical film 4 is required to produce a more concentrated light effect. The method is to design a smaller top angle of each optical structure 43, a smaller prism angle of each prism 42, and a larger refractive index of the structured optical film 4 when used in combination with a diffuse reflector, compared to a reflective reflector. The details are as follows.

[0063] In certain embodiments, when a diffuse reflector is used in conjunction with the present invention, the refractive index of the structured optical film 4 is between 1.45 and 1.7, inclusive. When the refractive index is less than 1.45, the light output angle of the structured optical film 4 will be further away from the forward direction and more skewed. Conversely, when the refractive index is greater than 1.7, the light output angle of the structured optical film 4 will be more collimated toward the forward direction. Both of these will result in an unsuitable light output angle, making it difficult for the prism sheet 5 above to be used, resulting in poor light output efficiency. Compared to when a reflective reflector is used in conjunction with the present invention, the refractive index of the structured optical film 4 is between 1.4 and 1.6. In this embodiment, a higher refractive index is used to make the structured optical film 4 produce a more concentrated light effect.

[0064] When the present invention is used in conjunction with a diffuse reflector, the ratio of the prism angle to the vertex angle must be selected to be between 0.6 and 1.57 to produce a suitable light-splitting effect and a positive viewing angle, so as to provide the prism sheet 5 above with better light extraction efficiency. In actual use, the prism angle of each prism 42 is between 60° and 110°, inclusive. When the prism angle is less than 60°, the light-exiting areas of the structured optical film 4 will be separated too far apart. Conversely, when the prism angle is greater than 110°, the light-exiting areas of the structured optical film will be separated too close. Both will produce an unsuitable light-splitting effect, making it difficult for the prism sheet 5 above to be used, resulting in poor light extraction efficiency. The vertex angle of each optical structure 43 is between 70° and 100°, inclusive. When the vertex angle is less than 70°, the light output angle will be more biased toward the positive direction. Conversely, when the prism angle is greater than 100°, the light output angle will be further away from the positive direction. Both of these will result in an unsuitable light output angle, making it difficult for the prism sheet 5 above to be used, resulting in poor light extraction efficiency. Compared to the use of a reflective reflector, the prism angle of each prism 42 is between 70° and 120°, inclusive, and the vertex angle of each optical structure 43 is between 80° and 110°, inclusive. This embodiment utilizes smaller prism angles and vertex angles to produce a more concentrated light effect on the structured optical film 4.

[0065] With the above design, when a diffuse reflector is used, the peak luminance position of the incident light toward each prism 42 of the structured optical film 4 is between 7° and 15°, inclusive. The full width at half maximum of the luminance is between 36° and 56°, inclusive, in the first direction (X-axis), and between 16° and 26°, inclusive, in the second direction (Y-axis). The first and second directions are orthogonal to each other. Therefore, when a diffuse reflector is used, the incident light pattern is wider and further away from the positive direction. When the incident light does not fall within the aforementioned range, the efficiency of the light emitted by the structured optical film 4 is relatively poor, resulting in the adverse effects of reduced luminance and a deviation from the positive viewing angle.

[0066] In other words, only when a suitable incident light type that meets the aforementioned range enters the structured optical film 4 will a suitable output light type be generated. The detailed numerical range is as follows. The peak position of the brightness of the light emitted from each optical structure 43 of the structured optical film 4 is between 20° and 40°, and includes the endpoint value, and the half-height angle of the brightness is between 20° and 30° (the first direction, i.e., the X-axis, and the second direction, i.e., the Y-axis, are symmetrical), and includes the endpoint value. Similarly, when the output light does not meet the aforementioned range, it is not easy to be used by the prism sheet 5 above, which will result in the efficiency of the output light of the prism sheet 5 being relatively poor, resulting in the adverse effects of reduced brightness and deviation of the positive viewing angle.

[0067] In summary, whether the first solution is to randomly distribute the heights of the prism structures of the structured optical film 4 and the prism sheet 5, or the second solution is to allow each film or the microstructure on the film to produce a small deflection, both are to allow the propagation angle of light when passing through the structured optical film 4 and the prism sheet 5 to have more variations, thereby reducing interference and reducing the generation of moiré fringes.

[0068] Furthermore, in order to avoid adsorption between optical films stacked on each other, the present invention also proposes another solution. Referring to Figure 19, the main body 41 of the structured optical film 4 has a first surface 411 facing away from the light-emitting surface 22 of the light guide plate 2, and the optical structure 43 is arranged on the first surface 411. The first surface 411 has a plurality of upwardly protruding arc surface areas 412, and a plurality of optical structures 43 are arranged in each arc surface area 412, and the central lines L of the optical structures 43 are not parallel to each other. The main body 41 can be coated with a UV adhesive layer on the base material layer, and after forming an upwardly protruding arc surface on the UV adhesive layer, the shape of the optical structure 43 is embossed. After the UV adhesive layer is cured and formed, a shape in which a plurality of optical structures 43 are arranged in each arc surface area 412 can be formed. With this design, the first surface 411 of the structured optical film 4 has a convex surface rather than a completely flat surface, which can reduce the phenomenon of the structured optical film 4 and the prism film 5 located above contacting and adsorbing each other, thereby avoiding the uneven lighting caused by the structured optical film 4 and the prism film 5 located above adsorbing each other.

[0069] The backlight module of the present invention mainly allows the light emitted by the light source 3 to first pass through the prism 42 of the structured optical film 4 to produce an effect of improving directivity, and then pass through the optical structure 43 of the structured optical film 4 to maintain the concealing effect. In this way, the structured optical film 4 can still promote the concentrated emission of light while maintaining the concealing ability, and finally use the two prism sheets 51 to concentrate the split light energy to improve the light output viewing angle, optical rotation and directivity of the backlight module. Furthermore, at least two adjacent optical films are an integrated structure, which not only improves the convenience of assembly, but also avoids the problem of uneven light output caused by adsorption between the stacked optical films, and also avoids the adverse effect of relative offset between the optical films causing structural damage to the optical structure. In addition, by combining the refractive index of different optical films, the prism angle of the prism 42 of the structured optical film 4 with different types of reflective films, the setting of the light guide structure 24 of the light guide plate 2, and the formation of a specific spacing of the moiré fringes, the brightness can be further improved while producing a concealing effect, thereby improving the brightness and light uniformity of the backlight module. On the other hand, the prisms 42 and optical structures 43 of the structured optical film 4 and the prism strips 51 of the prism sheet 5 can all randomly change height or depth, or deflect slightly to reduce the risk of moiré fringes. On the other hand, the first surface 411 of the structured optical film 4 can also have a convex rather than a completely flat surface to reduce the phenomenon of easy adsorption due to contact with the prism sheet 5 located above.

[0070] The above description is only a preferred embodiment of the present invention and should not be used to limit the scope of implementation of the present invention. That is, any simple equivalent changes and modifications made according to the scope of the claims and description of the present invention are still within the scope of the patent of the present invention.

[0071] [List of reference numerals] 2 Light guide plate 21 Light incident surface 22 Light emitting surface 23 Bottom surface 24 Light guide structure 241 Light-facing surface 242 Non-light-facing surface 243 Light collection angle 3 Light source 31 Light-emitting component 4 Structured optical film 401 First side edge 402 Second side edge 41 Main body 411 First surface 412 Arc area 42 Prism 43 Optical structure 430 Vertex 431a Side 431b First layer unit 431c Second layer unit 432 Platform 433 Side 5 Prism sheet 501 First edge 502 Second edge 51 Prism strip 6 Diffuser 7a Reflective reflector 7b Diffuser reflector 8 Display panels E1, E2 Extension direction L Central line L1 Connecting line N1, N2 Normals θ, θ1, θ2 Angle α1 First angle α2 Second angle UA Upper adjustment angle DA Lower adjustment angle

Claims

1. A backlight module, comprising: A light guide plate having a light incident surface and a light emitting surface connected to the light incident surface; A light source, which is arranged corresponding to the light incident surface of the light guide plate; A structured optical film is arranged corresponding to the light emitting surface of the light guide plate, and comprises a body, a plurality of prisms arranged in parallel on the body and facing the light emitting surface, and a plurality of optical structures arranged on the body and facing away from the light emitting surface of the light guide plate, wherein: The prism is located between the light emitting surface and the optical structure; and Two prism sheets are stacked on the structured optical film, wherein each of the prism sheets has a plurality of prism strips arranged in parallel and facing away from the structured optical film, and an extension direction E1 of the prism strips on one prism sheet is different from an extension direction E2 of the prism strips on the other prism sheet.

2. The backlight module according to claim 1, wherein: The two prism sheets are an integrated structure.

3. The backlight module according to claim 1, wherein: The structured optical film and the prism sheet adjacent to the structured optical film are an integrated structure.

4. The backlight module according to claim 1, wherein: The structured optical film and the two prism sheets are an integrated structure.

5. The backlight module according to any one of claims 1 to 4, wherein: Each of the optical structures has a center line and a vertex, wherein the center line is perpendicular to the body of the structured optical film, and the vertex is located on the center line.

6. The backlight module according to claim 5, wherein: Each of the optical structures also has a plurality of side surfaces surrounding the center line, each of the side surfaces being a composite surface formed by joining two or more layers of surface units along the extension direction of the center line, each of the surface units having a normal line, the angles between the normal lines of the surface units of the same layer surrounding the center line and the center line being the same, and the angles between the normal lines of the surface units of different layers along the center line and the center line being different.

7. The backlight module according to claim 6, wherein: The angle between the normal line of the surface unit closer to the vertex and the central line is smaller than the angle between the normal line of the surface unit farther from the vertex and the central line.

8. The backlight module according to any one of claims 1 to 4, further comprising a reflective reflector sheet located below the light guide plate, wherein: The ratio of the prism angle of the prism of the structured optical film to the roughness of the reflective reflector is between 700 and 900, including endpoint values.

9. The backlight module according to claim 8, wherein: The prism angle of the prism of the structured optical film is between 70° and 90°, including end values, and the roughness of the reflective reflector is 0.

1.

10. The backlight module according to any one of claims 1 to 4, further comprising a diffusion type reflective sheet located below the light guide plate, wherein: The ratio of the prism angle of the prisms of the structured optical film to the roughness of the diffuse reflective sheet is greater than 200 and less than or equal to 250.

11. The backlight module according to claim 10, wherein: The prism angle of the prism of the structured optical film is greater than 80° and less than or equal to 100°, and the roughness of the diffuse reflective sheet is 0.

4.

12. The backlight module according to any one of claims 1 to 4, wherein: The ratio of the refractive index of the prism sheet to the refractive index of the structured optical film is greater than or equal to 1.

08.

13. The backlight module according to any one of claims 1 to 4, wherein: The refractive index of the prism sheet is 1.62, and the refractive index of the structured optical film is 1.

55.

14. The backlight module according to any one of claims 1 to 4, wherein: The prisms of the structured optical film have a non-zero angle θ with the prism strips on one of the prism sheets, a prism spacing T1 is between every two adjacent prisms, and a prism strip spacing T2 is between every two adjacent prism strips. The prisms and the prism strips are combined to form a plurality of moiré fringes, and a moiré fringes spacing P is between every two adjacent moiré fringes. The moiré fringes spacing P needs to satisfy the following relationship: Wherein, the moiré fringe spacing P is less than 250 μm.

15. The backlight module according to any one of claims 1 to 4, wherein: The light guide plate also has a bottom surface opposite to the light emitting surface, and a plurality of light guide structures formed on the bottom surface, each of the light guide structures having a light-facing surface and a non-light-facing surface connected to each other, the light-facing surface facing the direction of light travel of the light source, a light collection angle being formed between the light-facing surface and the bottom surface, and the light collection angle being less than or equal to 20°.

16. The backlight module according to claim 5, wherein: The body of the structured optical film has a first surface facing away from the light emitting surface of the light guide plate, the optical structure is arranged on the first surface, the first surface has a plurality of upwardly protruding arc surface areas, and a plurality of the optical structures are arranged in each of the arc surface areas.

17. The backlight module according to claim 16, wherein: Central lines of the plurality of optical structures in each of the arc surface regions are not parallel to each other.

18. The backlight module according to claim 1, wherein: At least one of the height of the prisms of the structured optical film, the height of the optical structures, and the height of the prism strips of the prism sheet is randomly distributed.

19. The backlight module according to claim 1, wherein: Each of the prism sheets has a first edge and a second edge perpendicular to each other. In the two prism sheets, an extension direction E1 of a prism strip of one prism sheet has a first angle α1 with the first edge, and an extension direction E2 of a prism strip of the other prism sheet has a second angle α2 with the second edge.

20. The backlight module according to claim 18, wherein: At least one of the first angle α1 and the second angle α2 is not 0, and its absolute value is between 3° and 5°, including the endpoint value.

21. The backlight module according to claim 5, wherein: The structured optical film has a first side and a second side perpendicular to each other. The optical structures of the structured optical film are arranged in an array so that a line L1 connecting vertices of at least some of the optical structures is substantially parallel to the first side of the structured optical film.

22. The backlight module according to claim 5, wherein: The structured optical film has a first side and a second side that are perpendicular to each other. The optical structures of the structured optical film are arranged in an array so that a line L1 connecting the vertices of at least some of the optical structures forms an angle of an upper adjustment angle UA with the first side of the structured optical film, or the line L1 is inclined at an angle of approximately 45° and forms an angle of the upper adjustment angle UA, and the upper adjustment angle UA is not 0, and its absolute value is between 3° and 5°, including the endpoint value.

23. The backlight module according to claim 1, wherein: An extending direction D1 of the prisms of the structured optical film is substantially parallel to an extending direction E1 of the prism strips on one of the prism sheets that is farther from the structured optical film.

24. The backlight module according to claim 1, wherein: There is a lower adjustment angle DA between the extension direction D1 of the prism of the structured optical film and the edge of the structured optical film parallel to the extension direction E1. The lower adjustment angle DA is not 0, and its absolute value is between 3° and 5°, including the endpoint value.

25. The backlight module according to any one of claims 1 to 4 further comprises a reflective reflector located below the light guide plate, the refractive index of the structured optical film is between 1.4 and 1.6 and includes endpoint values, each of the prisms of the structured optical film has a prism angle, each of the optical structures of the structured optical film has a vertex angle, and the ratio of the prism angle to the vertex angle is between 0.636 and 1.

5.

26. The backlight module according to claim 25, wherein: The prism angle of each of the prisms is between 70° and 120°, including endpoint values, and the vertex angle of each of the optical structures is between 80° and 110°, including endpoint values.

27. The backlight module according to any one of claims 1 to 4, further comprising a reflective reflector sheet located below the light guide plate, wherein: The peak position of the brightness of the incident light toward each of the prisms of the structured optical film is between 3° and 15°, and includes the endpoint value. The half-width angle of the brightness is between 34° and 54° in the first direction, and includes the endpoint value. The half-width angle of the brightness is between 13° and 33° in the second direction, and the first direction is orthogonal to each other. The peak position of the brightness of the outgoing light from each of the optical structures of the structured optical film is between 20° and 40°, and includes the endpoint value. The half-width angle of the brightness is between 15° and 25°, and includes the endpoint value.

28. The backlight module according to any one of claims 1 to 4 further comprises a diffuse reflective sheet located below the light guide plate, the refractive index of the structured optical film is between 1.45 and 1.7 and includes endpoint values, each of the prisms of the structured optical film has a prism angle, each of the optical structures of the structured optical film has a vertex angle, and the ratio of the prism angle to the vertex angle is between 0.6 and 1.

57.

29. The backlight module according to claim 28, wherein: The prism angle of each of the prisms is between 60° and 110°, including endpoint values, and the vertex angle of each of the optical structures is between 70° and 100°, including endpoint values.

30. The backlight module according to any one of claims 1 to 4, further comprising a diffusion reflector located below the light guide plate, wherein: The peak position of the brightness of the incident light toward each of the prisms of the structured optical film is between 7° and 15°, and includes the endpoint value. The half-width angle of the brightness is between 36° and 56° in the first direction, and includes the endpoint value, and is between 16° and 26° in the second direction, and includes the endpoint value. The first direction and the second direction are orthogonal to each other. The peak position of the brightness of the outgoing light from each of the optical structures of the structured optical film is between 20° and 40°, and includes the endpoint value. The half-width angle of the brightness is between 20° and 30°, and includes the endpoint value.

31. The backlight module according to claim 6, wherein: The angle between the normal line of the surface unit closer to the vertex and the central line is greater than the angle between the normal line of the surface unit farther from the vertex and the central line.

32. The backlight module according to any one of claims 1 to 4, wherein: Each of the optical structures has a central line, a platform, and a plurality of side surfaces surrounding the central line. The central line is perpendicular to the body of the structured optical film. The side surfaces connect the platform and the body of the structured optical film.

33. The backlight module according to any one of claims 1 to 4, wherein: Each of the optical structures has a center line and a plurality of side surfaces surrounding the center line, wherein the center line is perpendicular to the body of the structured optical film, and each of the side surfaces is a composite surface formed by joining two or more layers of surface units along the extension direction of the center line, wherein the surface unit closer to the vertex is a curvature surface, and the surface unit farther from the vertex is a slope surface.

34. A display device comprising: The backlight module according to any one of claims 1 to 33; and A display panel is arranged on the backlight module.

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