Backlight module and display device

Abstract

A backlight module comprises a light guide plate, a light source, a first optical film and two second optical films. The first optical film is arranged corresponding to the light-emitting surface of the light guide plate and comprises a body, a plurality of prisms which are arranged on the body side by side and face the light-emitting surface, and a plurality of optical structures which are arranged on the body and back to the light-emitting surface of the light guide plate. Each second optical film is provided with a plurality of prism strips which are arranged in parallel and back to the first optical film, and the extending direction of the prism strips on one second optical film is different from the extending direction of the prism strips on the other second optical film. The invention further provides a display device comprising the backlight module.

Description

Backlight module and display device

[0001] This application claims priority to Chinese patent application number 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, and these scattering particles 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 cover blemishes, and have a 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 thus the blemish coverage 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 light collection and directivity of the light output angle while maintaining the blemish coverage 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 that improves light collection and directivity at a light output viewing angle.

[0006] The backlight module of the present invention includes a light guide plate, a light source, a first optical film and two second optical films. 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 first 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 second optical films are superimposed on the first optical film. Each second optical film has a plurality of prism strips arranged in parallel and facing away from the first optical film, and the extension direction of the prism strips on one second optical film is different from the extension direction of the prism strips on the other second optical film.

[0007] Another technical means of the present invention is that the two second optical films are an integrated structure.

[0008] Another technical solution of the present invention is that the first optical film and the second optical film adjacent to the first optical film are an integrated structure.

[0009] Another technical means of the present invention is that the first optical film and the two second optical films are an integrated structure.

[0010] Another technical means of the present invention is that each optical structure has a center line and a vertex, the center line is perpendicular to the body of the first optical film, and the vertex is located on the center line.

[0011] Another technical means of the present invention is that each optical structure also has multiple side surfaces surrounding the central line, and each side surface is a composite surface formed by two or more layers of surface units joined along the extension direction of the central line. Each surface unit has a normal line, and the angles between the normal lines of the surface units in the same layer surrounding the central line and the central line are the same, while the angles between the normal lines of the surface units in different layers along the central line and the central line are different.

[0012] Another technical means of the present invention is that the angle between the normal line and the center line of the surface unit closer to the vertex is smaller than the angle between the normal line and the center line of the surface unit farther from the vertex.

[0013] Another technical means of the present invention is that the backlight module further includes a reflective reflector located below the light guide plate, wherein the ratio of the prism angle of the prism of the first optical film to the roughness of the reflective reflector is between 700 and 900, including the endpoint value.

[0014] Another technical means of the present invention is that the prism angle of the prisms of the first optical film is between 70° and 90°, inclusive, and the roughness of the reflective reflective sheet is 0.1.

[0015] Another technical means of the present invention is that the backlight module further includes a diffuse reflective sheet located below the light guide plate, wherein the ratio of the prism angle of the prism of the first optical film to the roughness of the diffuse reflective sheet is greater than 200 and less than or equal to 250.

[0016] Another technical means of the present invention is that the prism angle of the prisms of the first optical film is greater than 80° and less than or equal to 100°, and the roughness of the diffusion reflective sheet is 0.4.

[0017] Another technical means of the present invention is that the ratio of the refractive index of the second optical film to the refractive index of the first optical film is greater than or equal to 1.08.

[0018] Another technical means of the present invention is that the refractive index of the second optical film is 1.62, and the refractive index of the first optical film is 1.55.

[0019] Another technical means of the present invention is that the prisms of the first optical film and the prism strips on one of the second optical films have a non-zero angle θ, each adjacent prism has a prism spacing T1, each adjacent prism strip has a prism strip spacing T2, and these prisms and prism strips are combined to form a plurality of moiré fringes, each adjacent moiré fringes has a moiré fringe spacing P, and the moiré fringe spacing P must satisfy the following relationship: The moiré fringe pitch P is less than 250 μm.

[0020] Another technical means of the present invention is that the light guide plate also has a bottom surface opposite to the light emitting surface and multiple light guide structures formed on the bottom surface. Each light guide structure has a light-facing surface and a non-light-facing surface connected to each other. The light-facing surface faces the direction of light travel from the light source. A light collection angle is formed between the light-facing surface and the bottom surface, and the light collection angle is less than or equal to 20°.

[0021] Another technical means of the present invention is that the main body of the first 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 multiple upwardly protruding arc surface areas, and multiple optical structures are arranged in each arc surface area.

[0022] Another technical means of the present invention is that the central lines of the optical structures in each arc surface area are not parallel to each other.

[0023] Another technical means of the present invention is that at least one of the height of the prisms of the first optical film, the height of the optical structure, and the height of the prism strips of the second optical film is randomly distributed.

[0024] Another technical means of the present invention is that each second optical film has a first edge and a second edge that are perpendicular to each other. Among the two second optical films, the extension direction E1 of the prism strips of one second optical film forms a first angle α1 with the first edge, and the extension direction E2 of the prism strips of the other second optical film forms a second angle α2 with the second edge.

[0025] Another technical means of the present invention is that 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.

[0026] Another technical means of the present invention is that the first optical film has a first side and a second side that are perpendicular to each other, and the optical structures of the first optical film are arranged in an array so that the line L1 connecting the vertices of at least some of the optical structures is substantially parallel to the first side of the first optical film and has an angle of an upper adjustment angle UA, or the line L1 is inclined at an angle of approximately 45 degrees and has an angle of the upper adjustment angle UA, and the upper adjustment angle UA is not zero, and its absolute value is between 3° and 5°, including the endpoint value.

[0027] Another technical means of the present invention is that the extension direction D1 of the prisms of the first optical film is substantially parallel to the extension direction E1 of the prism strips on a second optical film farther from the first optical film. A lower adjustment angle DA is defined between the extension direction D1 of the prisms of the first optical film and an edge of the first optical film parallel to the extension direction E1. The lower adjustment angle DA is not zero, and its absolute value is between 3° and 5°, inclusive.

[0028] 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.

[0029] The invention's effectiveness lies in allowing light from a light source to first pass through the prisms of the first optical film, enhancing directivity. The optical structure of the first optical film then concentrates the energy at the location where the prisms split the light, while also maintaining coverage. This allows the first optical film to focus the light while maintaining coverage. Finally, the two second optical films further concentrate the split light energy, enhancing the backlight module's light collection and brightness. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG1 is an exploded perspective view of a preferred embodiment of a backlight module of the present invention;

[0031] FIG2 is a schematic side view from a side view angle to assist in explaining FIG1 ;

[0032] FIG3 is a schematic diagram of an enlarged view of the frame shown in FIG2 ;

[0033] FIG4 is a graph illustrating the relationship between the refractive index ratio of the second optical film and the first optical film and the brightness;

[0034] 5 is a graph illustrating the relationship between the ratio of the prism angle of the first optical film to the roughness of the reflective reflector and the brightness;

[0035] FIG6 is a side view schematic diagram illustrating the backlight module using different types of reflective sheets;

[0036] 7 is a graph illustrating the relationship between the ratio of the prism angle of the first optical film to the roughness of the diffusion-type reflective sheet and the brightness;

[0037] 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;

[0038] 9 is a graph illustrating the relationship between the viewing angle and the luminance of the light guide structure of the light guide plate;

[0039] 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;

[0040] FIG11 is a schematic side view of a preferred embodiment of a display device of the present invention;

[0041] FIG12 is a schematic diagram illustrating how moiré fringes are formed;

[0042] FIG13 is a graph illustrating the relationship between the moiré fringe spacing and the luminance;

[0043] FIG14 is a side view schematically illustrating that the depths of the microstructures on the first optical film and the second optical film are randomly distributed;

[0044] FIG15 is a schematic top view illustrating the phenomenon in which the prism strips on the two second optical films are deflected to reduce moiré fringes;

[0045] FIG16 is a schematic top view illustrating the phenomenon that the optical structure on the first optical film is deflected to reduce moiré fringes;

[0046] FIG17 is a schematic top view illustrating a phenomenon in which the optical structures on the first optical film are deflected to reduce moiré fringes, wherein the arrangement of the optical structures is different from that in FIG16 ;

[0047] FIG18 is a schematic top view illustrating the phenomenon that prisms on the first optical film are deflected to reduce moire fringes; and

[0048] FIG19 is a side view schematically illustrating that the first surface of the first optical film has a plurality of upwardly convex curved surface areas, and a plurality of optical structures are disposed in each curved surface area. DETAILED DESCRIPTION

[0049] 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.

[0050] 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" is implied.

[0051] 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 first optical film 4, two second optical films 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 first optical film 4 is located between the second optical film 5 and the light emitting surface 22. The second optical film 5 is a prism sheet, and is located between the diffuser 6 and the first optical film 4 and is superimposed on the first optical film 4. Among the first optical film 4 and the two second optical films 5, at least two adjacent optical films are an integrated structure. In the embodiment shown in Figures 1 and 2, the first optical film 4 and the second optical film 5 adjacent to the first optical film 4 are both an integrated structure.

[0052] The first 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 second optical film 5 includes a plurality of prism strips 51 arranged in parallel and facing away from the first optical film 4. The extension direction E1 of the prism strips 51 on one second optical film 5 is different from the extension direction E2 of the prism strips 51 on another second optical film 5. In the embodiment shown in FIG1 , the prism strips 51 of the upper second optical film 5 extend along the extension direction E1, while the prism strips 51 of the lower second optical film 5 extend along the extension direction E2, with the extension direction E1 being perpendicular to the extension direction E2.

[0053] 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 first optical film 4, resulting in an effect of improved directivity. However, this has the problem of difficulty concentrating the atomized energy. In this case, the optical structure 43 of the first optical film 4 is then used to maintain the shielding effect. In this way, the first optical film 4 can still promote the concentrated emission of light while maintaining its shielding ability. Finally, the two second optical films 51 are used to concentrate the split light energy, thereby improving the light collection and brightness of the backlight module. Furthermore, at least two adjacent optical films are integrated into a structure, which not only improves assembly convenience but also avoids the problem of uneven light output caused by adsorption between the stacked optical films.

[0054] In this embodiment, the first optical film 4 and the adjacent second optical film 51 are integrally formed. This prevents relative displacement between the optical films, which could adversely affect the prisms 42 and optical structure 43. In some embodiments, the two second optical films 5 can be integrally formed. In other embodiments, the first optical film 4 and the two second optical films 5 can be integrally formed, further ensuring that there is no relative positional displacement between the three, facilitating easier assembly. After fabrication, the optical films are bonded together using adhesive. The bonding method is readily understood by those skilled in the art and will not be further described here.

[0055] Referring to Figures 2 and 3, the following describes how to use the optical structure 43 of the first optical film 4 to produce a concealing effect. Each optical structure 43 of the first 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 first 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 a plurality of 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 3, in this embodiment, the central line L of each optical structure 43 is perpendicular to the main body 41 of the first 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 a central line L. Each surface element has a normal. The normals of surface elements in the same layer surrounding the central line L have the same angle with the central line L, while the normals of surface elements in different layers along the central line L have different angles with the central 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 central line L, while the normal N2 of each second surface element 431c forms an angle θ2 with the central 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. Thus, the inclined surfaces with different inclinations refract and reflect light, thereby 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. This allows light to travel in different directions upon exit, thereby achieving uniform light and improving brightness. Furthermore, in this embodiment, the angle θ1 of the first surface unit 431b of each optical structure 43 closer to the vertex 430 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 second optical film 5 increases.Therefore, the manufacturing process is easier and the yield is higher, reducing the risk of process yield caused by the vertex 430 being too sharp. If the optical structure 43 is designed as a concave structure, the thickness of the first optical film 4 can be further reduced.

[0056] 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 second optical film 5 to the refractive index of the first 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 second optical film 5 is 1.62 and the refractive index of the first 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 without producing the adverse effect of reduced brightness.

[0057] 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 first 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 a smaller prism 42 with a 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 will result in a better 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%.

[0058] 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 first 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 matched with a larger prism 42 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 a better 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 matched with an appropriate reflector to maintain optimal brightness.

[0059] Referring to Figure 8, 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 Figure 9, first, when the light-collecting angle 243 is set to 5°, the brightness 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 the viewing angle of 70° and 80°, and the brightness 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 insufficient to maintain good brightness. Even when the viewing angle is between 70° and 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.

[0060] 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 .

[0061] Furthermore, because the prisms 42 of the first optical film 4 and the prism strips 51 on one of the second optical films 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.

[0062] Referring to FIG. 12 in conjunction with FIG. 2 , in certain embodiments, the prisms 42 of the first optical film 4 and the prism strips 51 on one of the second optical films 5 have a non-zero angle θ. Each adjacent prism 42 has a prism pitch T1, and each adjacent prism strip 51 has a prism strip pitch T2. These prisms 42 and prism strips 51 combine to form a plurality of moiré fringes. Each 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%.

[0063] In addition, the present invention also proposes the following solutions to avoid the generation of moiré fringes. Among them, the first solution is to make the height of the prism structure of the first optical film 4 and the second optical film 5 randomly distributed. Referring to Figure 14, as mentioned above, the first optical film 4 has prisms 42 and optical structures 43, and the second optical film 5 has prism strips 51. In this embodiment, at least one of the height of the prisms 42 of the first optical film 4, the height (or depth) of the optical structure 43, and the height of the prism strips 51 of the second optical film 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 second optical film 5 adjacent to the first optical film 4 all show irregular random number changes. In this way, the original rule of mutual interference between the prisms 42 and the optical structure 43 of the first optical film 4 can be destroyed, and the moiré fringes phenomenon can be alleviated. Alternatively, the prisms 42 and optical structures 43 of the first optical film 4 and the prism strips 51 of the second optical film 5 can all change height or depth randomly, which can also reduce the risk of moire fringes.

[0064] The second solution is to allow each film or the microstructure on the film to produce a small deflection. In the first method, as shown in Figure 15, each second optical film 5 has a first edge 501 and a second edge 502 that are perpendicular to each other. In the two second optical films 5, the extension direction E1 of the prism strip 51 (solid line in Figure 15) of one second optical film 5 has a first angle α1 with the first edge 501, and the extension direction E2 of the prism strip 51' (dashed line in Figure 15) of the other second optical film 5 has a second angle α2 with the second edge 502. In this embodiment, the extension direction E1 and the extension direction E2 are substantially close to vertical. 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. Since the prism strips 51 or 51 ′ of the second optical film 5 are slightly deflected, they are less likely to generate moiré fringes that interfere with the prisms 42 and optical structures 43 ′ of the approximately parallel first optical film 4 .

[0065] In the second embodiment, as shown in FIG16 , the first 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 first 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 first 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 first 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 second optical film 5.

[0066] In the third embodiment, referring to FIG. 18 , the extension direction D1 of the prisms 42 of the first optical film 4 is substantially parallel to the extension direction E1 of the prism strips 51 on one of the second optical films 5 located farther from the first optical film 4. A lower adjustment angle DA is defined between the extension direction D1 of the prisms 42 of the first optical film 4 and the edge of the first 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 first optical film 4 are slightly deflected, they are less likely to produce moiré fringes that interfere with the prism strips 51 or 51' of the approximately parallel second optical film 5.

[0067] In summary, whether the first solution involves randomly distributing the heights of the prism structures of the first optical film 4 and the second optical film 5, or the second solution involves slightly deflecting each film or the microstructures thereon, both are intended to increase the variation in the angle of travel of light as it passes through the first optical film 4 and the second optical film 5, thereby reducing interference and the generation of moiré fringes.

[0068] Furthermore, in order to avoid adsorption between stacked optical films, the present invention also proposes another solution. Referring to Figure 19, the main body 41 of the first 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 a UV adhesive layer coated 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 is formed. With this design, the first surface 411 of the first optical film 4 has a convex shape rather than a completely flat surface, which can reduce the phenomenon of contact and adsorption between the first optical film 4 and the second optical film 5 located above, thereby avoiding the uneven lighting caused by the mutual adsorption between the first optical film 4 and the second optical film 5 located above.

[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 first optical film 4 to produce an effect of improving directivity, and then pass through the optical structure 43 of the first optical film 4 to maintain shading. In this way, the first optical film 4 can still promote the concentrated emission of light while maintaining the shading ability, and finally use the two second optical films 51 to concentrate the split light energy to improve the light collection and directivity of the light output angle of the backlight module. Furthermore, at least two adjacent optical films are an integrated structure. In addition to improving the convenience of assembly, it can also avoid the problem of uneven light output caused by adsorption between the stacked optical films, and can also avoid 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 first 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 prism 42 and optical structure 43 of the first optical film 4 and the prism strips 51 of the second optical film 5 can all change the height or depth by random numbers, or deflect slightly to reduce the risk of moiré fringes. On the other hand, the first surface 411 of the first optical film 4 can also have a convexity instead of a completely flat surface, which can reduce the phenomenon of contact and easy adsorption with the second optical film 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] Reference Signs List

[0072] 2 Light guide plate

[0073] 21 Light incident surface

[0074] 22 Light-emitting surface

[0075] 23 Bottom

[0076] 24 Light guide structure

[0077] 241 Sun-facing side

[0078] 242 Non-light-facing side

[0079] 243 light receiving angle

[0080] 3 Light Source

[0081] 31 Luminous parts

[0082] 4. First optical film

[0083] 401 First Side

[0084] 402 Second side

[0085] 41 body

[0086] 411 First Surface

[0087] 412 curved area

[0088] 42 Prism

[0089] 43 Optical Structure

[0090] 430 vertices

[0091] 431a Side

[0092] 431b First level unit

[0093] 431c Second Level Unit

[0094] 5 Second optical film

[0095] 501 First Edge

[0096] 502 Second Edge

[0097] 51 Prism Bar

[0098] 6 Diffuser

[0099] 7a Reflective reflective sheet

[0100] 7b Diffusion reflector

[0101] 8 Display Panel

[0102] E1, E2 extension direction

[0103] L Central Line

[0104] L1 connection

[0105] N1, N2 normals

[0106] Angles θ, θ1, θ2

[0107] α1 first angle

[0108] α2 Second angle

[0109] Adjust the angle on UA

[0110] DA down to adjust the 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; The first 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 second optical films are stacked on the first optical film, wherein each of the second optical films has a plurality of prism strips arranged in parallel and facing away from the first optical film, and an extending direction E1 of the prism strips on one second optical film is different from an extending direction E2 of the prism strips on the other second optical film.

2. The backlight module according to claim 1, wherein: The two second optical films are an integrated structure.

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

4. The backlight module according to claim 1, wherein: The first optical film and the two second optical films 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, the center line is perpendicular to the body of the first 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 first optical film to the roughness of the reflective reflector is between 700 and 900, including end points.

9. The backlight module according to claim 8, wherein: The prism angle of the prism of the first 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: A ratio of a prism angle of the prisms of the first optical film to a roughness of the diffusion-type 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 first optical film is greater than 80° and less than or equal to 100°, and the roughness of the diffusion type reflection 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 second optical film to the refractive index of the first 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 second optical film is 1.62, and the refractive index of the first optical film is 1.

55.

14. The backlight module according to any one of claims 1 to 4, wherein: There is a non-zero angle θ between the prisms of the first optical film and the prism strips on one of the second optical films, there is a prism spacing T1 between each adjacent prism, there is a prism strip spacing T2 between each adjacent prism strip, these prisms and these prism strips are combined to form a plurality of moiré fringes, there is a moiré fringes spacing P between each adjacent moiré fringes, and 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 first 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 optical structures in each of the arc surface areas 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 first optical film, the height of the optical structure, and the height of the prism strips of the second optical film is randomly distributed.

19. The backlight module according to claim 1, wherein: Each of the second optical films has a first edge and a second edge that are perpendicular to each other. Among the two second optical films, an extension direction E1 of the prism strip of one of the second optical films has a first angle α1 with the first edge, and an extension direction E2 of the prism strip of the other second optical film 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 first optical film has a first side and a second side that are perpendicular to each other. The optical structures of the first optical film are arranged in an array so that a line L1 connecting the vertices of at least some of the optical structures is substantially parallel to the first side of the first optical film and there is an angle of an upper adjustment angle UA, or the line L1 is inclined at an angle of approximately 45 degrees and there is 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°, and includes the endpoint value.

22. The backlight module according to claim 1, wherein: An extension direction D1 of the prisms of the first optical film is substantially parallel to an extension direction E1 of the prism strips on one of the second optical films farther away from the first optical film. A lower adjustment angle DA is provided between the extension direction D1 of the prisms on the first optical film and an edge of the first 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.

23. A display device, comprising the backlight module according to any one of claims 1 to 22 and a display panel arranged on the backlight module.

Images