Backlight module and display device

Abstract

A backlight module includes a light guide plate, a light source, a structured optical film, and two prisms. The structured optical film is disposed opposite a light-emitting surface of the light guide plate and includes a body, a plurality of prisms arranged side-by-side on the body and facing the light-emitting surface, and a plurality of optical structures disposed on the body and facing away from the light-emitting surface of the light guide plate. Each prism has a plurality of prism strips arranged side-by-side and facing away from the structured optical film, wherein the extension direction of the prism strips on one prism is different from the extension direction of the prism strips on another prism. The present invention also provides a display device including the backlight module.

Description

Technical Field

[0001] This invention relates to an optical device, and more particularly to a backlight module and display device. Prior Technology

[0002] Existing backlight modules typically incorporate diffusers to homogenize light. Common diffusers contain multiple scattering particles that disperse light, thus homogenizing it. However, these diffusers with scattering particles are often used for masking and have low optical directivity, compromising the high directivity of the light guide plate. Improving directivity requires reducing the diffuser's haze, but this worsens the masking effect. While brightness enhancers are beneficial for increasing luminance, the haze of the upper and lower diffusers used in the backlight module affects luminance and optical appearance, making it difficult to further improve the luminance of existing backlight modules. Therefore, maintaining masking capabilities while increasing light-gathering angle and directivity has become a key design focus for backlight modules. Summary of the Invention

[0003] Therefore, the purpose of this invention is to provide a backlight module that improves the light-gathering and directivity of the light emission angle.

[0004] The backlight module of this invention includes a light guide plate, a light source, a structured optical film, two prisms, and a reflective sheet located below the light guide plate. The light guide plate has a light-incident surface and a light-exit surface connected to the light-incident surface. The light source is disposed corresponding to the light-incident surface of the light guide plate. The structured optical film is disposed corresponding to the light-exit surface of the light guide plate and includes a body, a plurality of prisms arranged side-by-side on the body and facing the light-exit surface, and a plurality of optical structures disposed on the 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 structures. The two prisms are stacked on the structured optical film. Each of the prisms has a plurality of prism strips arranged side by side and facing away from the structured optical film, wherein the extension direction of the prism strips on one prism is different from the extension direction of the prism strips on another prism.

[0005] Another object of the present invention is to provide a display device comprising a backlight module as described above, and a display panel disposed on the backlight module.

[0006] The advantage of this invention lies in that the light emitted from the light source first passes through the prism of the structured optical film, thereby improving its directivity. Then, through the optical structure of the structured optical film, the energy is concentrated at the position where the light is split by the prism, while simultaneously maintaining concealing properties. In this way, the structured optical film can still promote concentrated light emission while maintaining concealing capabilities. Finally, the diagonal mirror is used to concentrate and focus the split light energy, thereby improving the light collection and brightness of the backlight module. Simple Explanation of the Diagram

[0007] Figure 1 is an exploded perspective view, showing a preferred embodiment of the backlight module of the present invention; Figure 2 is a side view diagram, used to illustrate Figure 1 from a side perspective; Figure 3A is a schematic diagram, which is an enlarged view of the area shown in the box in Figure 2; Figure 3B is a schematic diagram illustrating another embodiment different from Figure 3A; Figure 3C is a schematic diagram illustrating yet another embodiment different from that in Figure 3A; Figure 3D is a schematic diagram illustrating yet another embodiment different from Figure 3A; Figure 4 is a graph illustrating the relationship between the refractive index ratio of a prism and a structured optical film and luminance. Figure 5 is a graph illustrating the relationship between the ratio of the prism angle of the structured optical film to the roughness of the reflective sheet and the luminance. Figure 6 is a side view schematic diagram illustrating the use of different types of reflective sheets in this backlight module; Figure 7 is a graph illustrating the relationship between the ratio of the prism angle of the structured optical film to the roughness of the diffuser and the brightness. Figure 8 is a side view schematic diagram, illustrating that the bottom surface of a light guide plate of the backlight module has a plurality of light guide structures; Figure 9 is a graph illustrating the relationship between the viewing angle and luminance of the light guide structure of the light guide plate; Figure 10 is a schematic diagram of the simulated effect, illustrating the spatial luminance distribution of the backlight module of the present invention, corresponding to different light-receiving angles; Figure 11 is a side view schematic diagram, which is a preferred embodiment of the display device of the present invention; Figure 12 is a schematic diagram illustrating how moiré fringes are formed; Figure 13 is a curve graph illustrating the relationship between moiré fringe spacing and luminance; Figure 14 is a side view schematic diagram, illustrating that the depths of the structured optical film and the microstructures on the prism are randomly distributed; Figure 15 is a top view illustrating how the prisms on the two prisms deflect to reduce moiré fringes. Figure 16 is a top view schematic diagram illustrating the phenomenon where the optical structure on the structured optical film forms a deflection to reduce moiré fringes; Figure 17 is a top view schematic diagram illustrating the phenomenon where optical structures on the structured optical film deflect to reduce moiré fringes, wherein the arrangement of the optical structures differs from that in Figure 16; Figure 18 is a top view illustrating the deflection of prisms on the structured optical film to reduce moiré fringes; and Figure 19 is a side view schematic diagram, illustrating that a first surface of the structured optical film has a plurality of upwardly convex arcuate regions, and each of the arcuate regions is provided with a plurality of the optical structures; Figure 20 is a schematic diagram of a simulation effect, illustrating the luminance distribution of the incident light source; and Figure 21 is a schematic diagram of a simulation effect, illustrating the luminance distribution of the emitted light source. Implementation

[0008] The features and technical content of the related patent applications of this invention will be clearly presented in the following detailed description of the preferred embodiments with reference to the accompanying drawings. Before proceeding with the detailed description, it should be noted that similar elements are represented by the same numbers. The directional terms mentioned in the following embodiments, such as up, down, left, right, front, back, bottom, and top, are only for reference to the accompanying drawings. Therefore, the directional terms used are for illustrative purposes and not for limiting the invention.

[0009] In the following description, the terms "about," "substantially," "roughly," or "same" generally indicate a range within 10%, 5%, 3%, 2%, 1%, or 0.5% of a given value. The quantities given here are approximate, meaning that the terms "about," "substantially," "roughly," or "same" may be implied even without specific mention of them.

[0010] Referring to Figures 1 and 2, a preferred embodiment of the backlight module of the present invention is shown, comprising a light guide plate 2, a light source 3, a structured optical film 4, two prisms 5, and a diffuser 6. The light guide plate 2 has a light-incident surface 21 and a light-emitting surface 22 connecting the light-incident surface 21. The light source 3 is disposed corresponding to the light-incident surface 21 of the light guide plate 2 and has a plurality of light-emitting elements 31 arranged along the light-incident surface 21. The structured optical film 4 is located between the prisms 5 and the light-emitting surface 22. The prisms 5 are located between the diffuser 6 and the structured optical film 4 and are stacked on the structured optical film 4. At least two adjacent optical films of the structured optical film 4 and the two prisms 5 are integrally formed. In the embodiments shown in Figures 1 and 2, the structured optical film 4 and the prism 5 adjacent to the structured optical film 4 are an integral structure.

[0011] The structured optical film 4 is disposed opposite to the light-emitting surface 22 of the light guide plate 2, and includes a body 41, a plurality of prisms 42 arranged side by side on the body 41 and facing the light-emitting surface 22, and a plurality of optical structures 43 disposed on the body 41 and facing away from the light-emitting surface 22 of the light guide plate 2. The prisms 42 are located between the light-emitting surface 22 and the optical structures 43, and the 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 5 has a plurality of prism strips 51 arranged side by side and facing away from the structured optical film 4, wherein the extension direction E1 of the prism strip 51 on one prism 5 is different from the extension direction E2 of the prism strip 51 on another prism 5. In the embodiment shown in Figure 1, the prism strip 51 of the upper prism 5 extends along the extension direction E1, while the prism strip 51 of the lower prism 5 extends along the extension direction E2, and the extension direction E1 is perpendicular to the extension direction E2.

[0012] The backlight module disclosed in this embodiment primarily allows the light emitted from the light source 3 to first pass through the prism 42 of the structured optical film 4, thereby improving its directivity. However, this results in a problem where the energy is not easily concentrated due to fogging. The optical structure 43 of the structured optical film 4 then maintains this concealing effect. In this way, the structured optical film 4 can still promote concentrated light emission while maintaining its concealing ability. Finally, the diagonal mirror 51 is used to concentrate the split light energy, thereby improving the light gathering performance 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 avoids the problem of uneven light emission caused by adsorption between stacked optical films.

[0013] In this embodiment, the structured optical film 4 and the adjacent prism 51 are integrally formed, thus avoiding the adverse effects on the prism 42 and the optical structure 43 caused by relative misalignment between the optical films. In some embodiments, the two prisms 5 may also be integrally formed. In other embodiments, the structured optical film 4 and the two prisms 5 may be integrally formed, further ensuring no relative positional misalignment among the three components and facilitating assembly. The optical films are bonded together with adhesive after fabrication; the bonding method is understood by those skilled in the art and will not be described further.

[0014] Referring to Figures 2 and 3A, the following explanation describes how the optical structure 43 of the structured optical film 4 generates 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. The light from the light source 3 enters the body 41 through the prism 42 and then exits the structured optical film 4 through the optical structure 43 to maintain the concealing effect. The concealing effect is mainly due to the fact that each optical structure 43 has multiple side surfaces 431a, which can deflect the light through the side surfaces 431a and guide it to multiple light-emitting directions, avoiding excessive concentration of light energy directly above the optical structure 43, thereby generating a concealing effect. Referring to Figure 3A, in this embodiment, the central line L of each optical structure 43 is perpendicular to the body 41 of the structured optical film 4. Each optical structure 43 is a quadrangular pyramid structure with four sides 431a. Each side 431a is a composite surface formed by joining a first layer unit 431b and a second layer unit 431c along the extension direction of the central line L. Each surface unit has a normal. The angle between the normal of the surface unit in the same layer surrounding the central line L and the central line L is the same. The angle between the normal of the surface unit in different layers along the central line L and the central line L is different. It should be noted that the "normal" referred to here is a line perpendicular to the first layer unit 431b and the second layer unit 431c, respectively. More specifically, each first layer unit 431b has a normal N1, and each second layer unit 431c has a normal N2. The normal N1 of each first layer unit 431b has an angle θ1 with the central line L, and the normal N2 of each second layer unit 431c has an angle θ2 with the central line L. In each of the first layer units 431b, the angle θ1 between the normal N1 and the central line L is the same. Similarly, in each of the second layer units 431c, the angle θ2 between the normal N2 and the central line L is the same, but the angles θ1 and θ2 are different. This means that the first layer units 431b and the second layer units 431c are inclined planes with different degrees of inclination. In some embodiments, the angle θ1 between the normal N1 and the central line L of the surface unit closer to the vertex 430 is smaller than the angle θ2 between the normal N2 and the central line L of the surface unit farther from the vertex 430, thus forming inclined planes with different degrees of inclination. This allows light to be refracted and reflected by the inclined planes with different degrees of inclination, enabling the light to be dispersed as much as possible in all directions, reducing the concentration of light at a specific angle or directly above. This allows the light to travel in different directions upon emission, achieving the purpose of homogenizing the light and increasing its luminosity.Furthermore, in this embodiment, the included angle θ1 of the first layer unit 431b near the vertex 430 of each optical structure 43 is smaller than the included angle θ2 of the second layer unit 431c farther from the vertex 430. That is, the angle between the normal of the surface unit and the central line L decreases as the distance from the prism 5 increases. This simplifies the manufacturing process, increases the yield, and reduces the risk of poor process yield caused by an overly sharp vertex 430. If the optical structure 43 adopts a recessed structure design, the thickness of the structured optical film 4 can be further reduced.

[0015] Please refer to Figure 3B, which discloses an embodiment different from that in Figure 3A. The main difference is that the angle θ1 between the normal N1 of the first layer unit 431b, which is closer to the vertex 430, and the central line L is greater than the angle θ2 between the normal N2 of the second layer unit 431c, which is farther from the vertex 430, and the central line L. In other words, the angle between the normal of the surface unit and the central line L increases with the distance from the prism 5. This design can more effectively reduce scratches from the stacked films above.

[0016] Please refer to Figure 3C, which discloses an embodiment different from that in Figure 3A. Each optical structure 43 has a central line L, a platform 432, and a plurality of side surfaces 433 surrounding the central line L. The central line L is perpendicular to the body 41 of the structured optical film 4. The side surfaces 433 connect the platform 432 to the body 41 of the structured optical film 4. This design primarily uses a trapezoidal tool to fabricate the microstructure within the mold, creating a platform shape corresponding to the platform 432 of each optical structure 43. Therefore, tool wear can be reduced at the platform, maintaining tool life and ensuring the stability of the microstructure formation.

[0017] Please refer to Figure 3D, which reveals another embodiment different from Figure 3A. Each optical structure 43 has a central line L and a plurality of side surfaces 431a surrounding the central line L. The central line L is perpendicular to the body 41 of the structured optical film 4. Each side surface 431a is a composite surface formed by joining two or more surface units along the extension direction of the central line L. The surface units 431b closer to the vertex 430 are curved surfaces, while the surface units 431c farther from the vertex 430 are sloped surfaces. This design is similar to that of Figure 3C, but it primarily uses an R-shaped tool to create the microstructure within the mold, resulting in an arc-shaped position of the microstructure corresponding to the curved surface of each optical structure 43 closer to the vertex 430. Therefore, tool wear can be reduced at the curved surface, maintaining tool life and ensuring the stability of the microstructure's formation.

[0018] The following further explains how the present invention can improve luminance through the following methods. First, the luminance produced 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 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 indices is greater than or equal to 1.08, the luminance can be maintained above 100% and steadily increases with the increase of the refractive index. When the ratio of the refractive indices 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 5 is 1.62, and the refractive index of the structured optical film 4 is 1.55, which can maintain the luminance at around 100%. In this case, the luminance can at least maintain its original value, without producing the adverse effect of reduced luminance.

[0019] Referring to Figures 1 and 2, the backlight module also includes a reflective sheet 7a located below the light guide plate 2. The ratio of the angle of the prism 42 of the structured optical film 4 to the roughness of the reflective sheet 7a is between 700 and 900, inclusive. In this embodiment, the reflective sheet 7a is selected from silver reflective sheets with a roughness of 0.1. This type of reflective sheet needs to be paired with a smaller prism 42 prism angle; for example, the angle of each prism 42 prism angle is between 70° and 90°, inclusive. Preferably, the angle of each prism 42 prism angle is 80°, which provides the optimal 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 of the absolute values ​​of the distances from each point on the actual contour of the measured surface to the centerline of the contour within the sampling length. Since the centerline average surface roughness (generally referred to simply as roughness, Ra) is well-known to those skilled in the art, it will not be elaborated upon here. As shown in Figure 5, firstly, the luminance produced by the backlight module disclosed in Figures 1 and 2 is set to 100%. By maintaining the ratio of the prism angle of the prism 42 to the roughness of the reflective sheet 7a between 700 and 900, the luminance can be maintained above 100%.

[0020] In addition to the reflective reflector 7a, another type of diffuser reflector can also be used. Referring to Figure 6, in some embodiments, the backlight module also includes a diffuser reflector 7b located below the light guide plate 2. The ratio of the angle of the prism 42 of the structured optical film 4 to the roughness of the diffuser 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 larger prism 42 prism angle, for example, the angle of each prism 42 prism angle is greater than 80° and less than or equal to 100°. Preferably, the angle of each prism 42 prism angle is 90°, which provides the optimal brightness enhancement effect. As shown in Figure 7, firstly, the brightness produced by the backlight module disclosed in Figures 1 and 2 is set to 100%. By maintaining the ratio of the prism angle of prism 42 to the roughness of the reflective sheet 7a between 200 and 250, the luminance can be maintained at over 100%. Through the above design, a suitable reflective sheet can be matched according to the prism angle of prism 42 to maintain optimal luminance.

[0021] 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 connected to each other. The light-facing surface 241 faces the light-tracing direction of the light source 3, and a light-receiving angle 243 is formed between the light-facing surface 241 and the bottom surface 23. The light-receiving angle 243 is less than or equal to 20°. As shown in Figure 9, firstly, when the light-receiving angle 243 is set to 5°, the backlight module produces a luminance of approximately 100%. When the light-receiving angle 243 is less than or equal to 20°, the light can be concentrated between the viewing angles of 70° and 80°, and the luminance in this range can mostly be maintained above 60%. When the light-receiving angle 243 is greater than 35°, regardless of the viewing angle, no light concentration effect is produced, and the luminance is below 60%, which is insufficient to maintain good luminance. Even at viewing angles between 70° and 80°, the luminance still fails to exceed 60%. Refer to Figure 10, which is a spatial luminance distribution diagram corresponding to the backlight module shown in Figure 8. It should be noted that the spatial luminance distribution diagram is a computer simulation diagram, and it was originally a color diagram, but is presented as a grayscale diagram in this case. In addition, the vertical and horizontal axes of Figure 10 both represent angles, and the center of the intersection of the vertical and horizontal axes can represent the central axis of the light-emitting surface 22 of the light guide plate 2. Generally speaking, the larger the light-receiving angle 243, the more the energy is dispersed, which is less conducive to luminance. Therefore, the backlight module of the present invention further limits the light-receiving angle 243 to be less than or equal to 20°. In Figure 10, when the light-receiving angle 243 is 20°, energy concentration can be observed on both sides of the central axis. As the light-receiving angle 243 gradually decreases, the energy concentration on both sides of the central axis becomes more pronounced, and the luminance is further improved. Therefore, it can be seen that the light-guiding structure 24 is formed on the bottom surface 23 of the light guide plate 2, and the light-receiving angle 243 of the light-guiding structure 24 can effectively improve luminance at a specific angle. Conversely, if the light-receiving angle gradually increases, for example to 35°, there will be an adverse effect of a 10% decrease in luminance. It should be noted that in Figure 10, the light-guiding structure 24 is a concave design; in some embodiments, the light-guiding structure 24 can also be a convex design, which can also achieve the effect of improving luminance.

[0022] As shown in Figure 11, a display panel 8 is disposed on the backlight module, which is the display device of the present invention. It should be noted that the display panel 8 can also be disposed on the backlight module shown in Figure 2 or Figure 6.

[0023] Furthermore, since both the prism 42 of the structured optical film 4 and the prism strip 51 on one of the prism plates 5 are strip-shaped structures, they are prone to interference at a constant angle and frequency, resulting in moiré patterns. Moiré patterns are primarily a visual effect of magnification or reduction produced by overlapping or rotating two or more different sets of stripes. The principle is that two sets of patterns with similar spatial frequencies interfere with each other, resulting in a lower frequency (wider spacing) pattern being displayed.

[0024] Referring to Figure 12 and in conjunction with Figure 2, in some embodiments, the prisms 42 of the structured optical film 4 have a non-zero included angle θ with the prism strips 51 on one of the prism plates 5. There is a prism spacing T1 between each adjacent prism 42 and a prism strip spacing T2 between each adjacent prism strip 51. These prisms 42 and prism strips 51 combine to form a complex number of moiré fringes. There is a moiré fringe spacing P between each adjacent moiré fringe, which must satisfy the following relationship: P = The moiré fringe spacing P is less than 250 mm. As shown in Figure 13, firstly, the luminance produced by the backlight module disclosed in Figures 1 and 2 is set to 100%. When the moiré fringe spacing P is less than 250 mm, the luminance can be effectively improved, maintaining a luminance of over 100%.

[0025] In addition to the above, the present invention proposes several solutions to avoid the generation of moiré fringes. The first solution is to make the heights of the structured optical film 4 and the prism structure of the prism plate 5 randomly distributed. Referring to FIG14, as previously described, the structured optical film 4 has a prism 42 and an optical structure 43, while the prism plate 5 has prism strips 51. In this embodiment, at least one of the heights of the prism 42 of the structured optical film 4, the heights (or depths) of the optical structure 43, and the heights of the prism strips 51 of the second optical film 5 are randomly distributed. Due to the viewing angle, it can be seen in FIG14 that the depth of the optical structure 43, or the height of the prism strips 51 adjacent to the structured optical film 4, exhibits irregular random variations. In this way, the original rules governing the interference between the prism 42 and the optical structure 43 of the structured optical film 4 can be disrupted, thus mitigating the moiré fringe phenomenon. Alternatively, the height or depth of the prism 42 and the optical structure 43 of the structured optical film 4, as well as the prism 51 of the second optical film 5, can be randomly changed, which can also reduce the risk of moiré fringe formation.

[0026] The second solution involves slightly deflecting each diaphragm or microstructure on it. In the first approach, as shown in Figure 15, each prism 5 has a first edge 501 and a second edge 502 that are perpendicular to each other. In the two prisms 5, the extension direction E1 of the prism strip 51 (solid line in Figure 15) of one prism 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 prism 5 has a second angle α2 with the second edge 502. In this embodiment, the extension directions E1 and E2 are substantially nearly perpendicular. 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 values. Since the prism strips 51 or 51' of the prism 5 are slightly deflected, it is less likely to produce moiré fringes that interfere with each other at an angle with the prism 42 and the optical structure 43' of the approximately parallel structured optical film 4.

[0027] In the second approach, as shown in Figure 16, 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 such 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 forms an angle of adjustment UA. Alternatively, as shown in Figure 17, the line L1 is inclined at approximately 45 degrees and forms an angle of adjustment UA. The adjustment angle UA is not 0, and its absolute value is between 3° and 5°, including the endpoint values. Because the optical structures 43 of the structured optical film 4 are slightly deflected, it is less likely to produce angular interference moiré fringes with the approximately parallel prism strips 51 or prism strips 51' of the prism 5.

[0028] In the third method, referring to Figure 18, the extension direction D1 of the prism 42 of the structured optical film 4 is substantially parallel to the extension direction E1 of the prism strip 51 on one of the prism plates 5 located far from the structured optical film 4. There is a lower adjustment angle DA between the extension direction D1 of the prism 42 of the structured optical film 4 and an edge of the structured optical film 4 parallel to the extension direction E1. This lower adjustment angle DA is not 0, and its absolute value is between 3° and 5°, including the endpoint value. Because the prism 42 of the structured optical film 4 undergoes a small deflection, it is less likely to produce angular interference moiré fringes with the approximately parallel prism strips 51 or prism strips 51' of the prism plate 5.

[0029] In addition, in some embodiments, when the present invention is used in conjunction with a reflective reflector, the refractive index of the structured optical film 4 is between 1.4 and 1.6, including the endpoint value. When the refractive index is less than 1.4, the light emission angle of the structured optical film 4 will be more oblique and away from the positive direction. Conversely, when the refractive index is greater than 1.6, the light emission angle of the structured optical film 4 will be more collimated and biased towards the positive direction. Both will produce unsuitable light emission angles, which are not easily used by the prism 5 above and will result in poor light emission efficiency.

[0030] 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 apex angle. The ratio of the prism angle to the apex angle is between 0.636 and 1.5. Since the size of the prism angle determines the beam splitting effect of the structured optical film 4 when emitting light, and the size of the apex angle of each optical structure 43 determines the orthogonal angle of the structured optical film 4 when emitting light, when using a reflective reflector in this invention, the ratio of the prism angle to the apex angle must be selected between 0.636 and 1.5 to produce a suitable beam splitting effect and orthogonal angle, so as to provide better light emission efficiency for the prism 5 above.

[0031] In practical applications, within the aforementioned ratio range, the prism angle of each prism 42 is between 70° and 120°, including the endpoints. The size of this prism angle determines the spectral splitting effect of the structured optical film 4 during light emission. When the prism angle is smaller, the spectral splitting effect is more pronounced, and the light emission areas are separated further apart. When the prism angle is larger, the spectral splitting effect is less pronounced, and the light emission areas are separated closer together and more concentrated. Specifically, when the prism angle is less than 70°, the light emission areas of the structured optical film 4 will be separated too far apart. Conversely, when the prism angle is greater than 120°, the light emission areas of the structured optical film will be separated too closely. Both will produce unsuitable spectral splitting effects, making them difficult to utilize with the prism 5 above, resulting in poor light emission efficiency.

[0032] The apex angle of each optical structure 43 is between 80° and 110°, including the endpoint value. The size of the apex angle of each optical structure 43 determines the light emission angle of the structured optical film 4. Specifically, when the apex angle is less than 80°, the light emission angle will be more positive; conversely, when the apex angle is greater than 110°, the light emission angle will be further away from the positive direction. Both will result in unsuitable light emission angles that are not easily utilized by the upper prism 5, resulting in poor light emission efficiency.

[0033] With the above design, when using a reflective reflector, the incident light pattern shown in Figure 20 can be converted into the outgoing light pattern shown in Figure 21, resulting in a more symmetrical beam splitting effect with the half-width at half-maximum (HWHM) closer to the center. In practical design, the peak luminance of the incident light rays toward each prism 42 of the structured optical film 4 is between 3° and 15°, including the endpoint values. The HWHM of the luminance is between 34° and 54° in a first direction (X-axis), including the endpoint values, and between 13° and 33° in a second direction (Y-axis), including the endpoint values. The first and second directions are orthogonal to each other. Therefore, the incident light pattern when using a reflective reflector is more concentrated and more positively biased. When the incident light rays do not conform to the aforementioned range, the efficiency of the outgoing light from the structured optical film 4 will be poor, resulting in reduced luminance and a skewed positive viewing angle.

[0034] In other words, only when a suitable incident light pattern conforming to the aforementioned range enters the structured optical film 4 will a suitable emitted light pattern be generated. The detailed numerical range is as follows: the peak position of the emitted light from each optical structure 43 of the structured optical film 4 is between 20° and 40°, including the endpoint value, and the half-width at half-maximum (FWHM) of the luminance is between 15° and 25° (symmetric on both the first X-axis and the second Y-axis), including the endpoint value. Similarly, when the emitted light does not conform to the aforementioned range, it is not easily utilized by the upper prism 5, resulting in poor efficiency of the emitted light from the prism 5, causing reduced luminance and adverse effects such as a skewed viewing angle.

[0035] The above describes the application of this invention in conjunction with a reflective reflector. A reflective reflector generally refers to a silver-plated reflector, which has a distinct mirror effect. It can reflect incident light at an incident angle to the mirror surface, and then reflect it back at the same incident angle. Polished metal objects can very effectively reflect light in a mirror-like manner. The reflective material used in mirrors is typically aluminum or silver.

[0036] When this invention is used in conjunction with a diffuse reflective sheet, different situations arise. A diffuse reflective sheet generally refers to a white-surfaced reflective sheet with a significant diffuse reflection effect. It allows incident light to reach the white surface at an incident angle and then reflect it at an angle within a certain range. The white surface can be achieved by applying a matte coating. Matte coatings essentially exhibit complete diffuse reflection, and surfaces made of non-absorbent powders (such as plaster) can become near-perfect diffuse reflective sheets.

[0037] Because diffuse reflection produces angular reflection within a certain range, the viewing angle is relatively divergent and the beam splitting effect is not obvious. Therefore, the structured optical film 4 is needed to produce a more concentrated light effect. The means to achieve this is to design a smaller apex angle for each of the optical structures 43, a smaller prism angle for each of the prisms 42, and a larger refractive index for the structured optical film 4 when using diffuse reflections, compared to a reflective reflector. Details are as follows:

[0038] In some embodiments, when the present invention is used in conjunction with a diffuser, 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 emission angle of the structured optical film 4 will be more oblique, moving away from the positive direction. Conversely, when the refractive index is greater than 1.7, the light emission angle of the structured optical film 4 will be more collimated, leaning towards the positive direction. Both result in unsuitable light emission angles, making it difficult to utilize the prism 5 above and producing poor light emission efficiency. Compared to when a reflective sheet is used, 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 produce a more concentrated light effect from the structured optical film 4.

[0039] When using a diffuser-type reflector in conjunction with this invention, the ratio of the prism angle to the apex angle must be selected between 0.6 and 1.57 to produce a suitable beam splitting effect and positive viewing angle, thereby providing better light extraction efficiency for the upper prism 5. In practical application, the prism angle of each prism 42 is between 60° and 110°, including the endpoint value. When the prism angle is less than 60°, the light extraction areas of the structured optical film 4 will be too far apart; conversely, when the prism angle is greater than 110°, the light extraction areas of the structured optical film will be too close together. Both will produce unsuitable beam splitting effects, making it difficult for the upper prism 5 to utilize and resulting in poor light extraction efficiency. The apex angle of each optical structure 43 is between 70° and 100°, including the endpoint value. When the apex angle is less than 70°, the light emission angle becomes more positive; conversely, when the prism angle is greater than 100°, the light emission angle deviates further from the positive direction. Both result in unsuitable light emission angles, making them difficult to utilize with the upper prism 5 and leading to poor light emission efficiency. Compared to using a reflective reflector, the prism angle of each prism 42 is between 70° and 120° (inclusive), and the apex angle of each optical structure 43 is between 80° and 110° (inclusive). In this embodiment, smaller prism angles and apex angles are used to create a more concentrated light effect on the structured optical film 4.

[0040] With the above design, when a diffuser is used, the peak luminance of the incident light rays toward each of the prisms 42 of the structured optical film 4 is between 7° and 15°, including the endpoint values. The half-width at half-maximum (FWHM) of the luminance is between 36° and 56° in a first direction (X-axis), including the endpoint values, and between 16° and 26° in a second direction (Y-axis), including the endpoint values. The first and second directions are orthogonal to each other. Therefore, the incident light pattern is wider and further away from the positive direction when using a diffuser. When the incident light rays do not conform to the aforementioned range, the efficiency of the emitted light from the structured optical film 4 will be poor, resulting in reduced luminance and a skewed positive viewing angle.

[0041] In other words, only when a suitable incident light pattern conforming to the aforementioned range enters the structured optical film 4 will a suitable emitted light pattern be generated. The detailed numerical range is as follows: the peak position of the emitted light from each optical structure 43 of the structured optical film 4 is between 20° and 40°, including the endpoint value, and the half-width at half-maximum (FWHM) of the luminance is between 20° and 30° (the first X-axis and the second Y-axis are both symmetrical), including the endpoint value. Similarly, when the emitted light does not conform to the aforementioned range, it is not easily utilized by the upper prism 5, resulting in poor efficiency of the emitted light from the prism 5, causing adverse effects such as reduced luminance and skewed viewing angle.

[0042] In summary, whether it is the first solution where the heights of the structured optical film 4 and the prism structure 5 are randomly distributed, or the second solution where each film or the microstructure on the film is slightly deflected, both are intended to allow for greater variation in the travel angle of light as it passes through the structured optical film 4 and the second optical film 5, thereby reducing interference and the generation of moiré fringes.

[0043] Furthermore, to avoid adsorption between the stacked optical films, the present invention also proposes another solution. Referring to Figure 19, the 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 disposed on the first surface 411. The first surface 411 has a plurality of upwardly convex arcuate regions 412, and a plurality of optical structures 43 are disposed in each arcuate region 412, and the central lines L of the optical structures 43 are not parallel to each other. The body 41 can be formed by coating a UV adhesive layer on a substrate layer, forming an upwardly convex arcuate surface on the UV adhesive layer, and then imprinting the shape of the optical structure 43. After the UV adhesive layer is cured, the shape of each arcuate region 412 being provided with a plurality of optical structures 43 is formed. With this design, the first surface 411 of the structured optical film 4 is raised rather than completely flat, which can reduce the phenomenon of easy adsorption between the structured optical film 4 and the prism 5 located above it, and avoid uneven light emission caused by mutual adsorption between the structured optical film 4 and the prism 5 located above it.

[0044] The backlight module of this invention primarily allows the light emitted by the light source 3 to first pass through the prism 42 of the structured optical film 4, thereby improving its directivity. Then, it passes through the optical structure 43 of the structured optical film 4 to maintain its shielding effect. In this way, the structured optical film 4 can still concentrate the light emission while maintaining its shielding capability. Finally, the diagonal mirror 51 concentrates the split light energy, thereby improving the light emission angle, light concentration, and directivity of the backlight module. Furthermore, at least two adjacent optical films are integrated into a single structure. This not only improves assembly convenience but also avoids the problem of uneven light emission caused by adsorption between stacked optical films, and also avoids the adverse effects of relative misalignment between optical films on the optical structure. Furthermore, by combining different refractive indices of optical films, pairing the prism 42 of the structured optical film 4 with different types of reflective sheets, setting the light guide structure 24 of the light guide plate 2, and forming a specific spacing of moiré fringes, the brightness can be further enhanced while producing a concealing effect, thereby improving the brightness and light emission uniformity of the backlight module. On the other hand, the prism 42 of the structured optical film 4, the optical structure 43, and the prism 51 of the second optical film 5 can all have their height or depth randomly changed, or be slightly deflected, to reduce the risk of moiré fringes. Additionally, the first surface 411 of the structured optical film 4 can be made to have a convex shape rather than a completely flat surface, which can reduce the phenomenon of easy adhesion between it and the prism 5 located above.

[0045] However, the above description is only a preferred embodiment of the present invention and should not be construed as limiting the scope of the present invention. Any simple equivalent changes and modifications made in accordance with the scope of the patent application and the description of the invention shall still fall within the scope of the patent of the present invention.

[0046] 2: Light guide plate 21: Light-receiving surface 22: Exposed surface 23: Bottom 24: Light guide structure 241: Sunlit side 242: Non-light-facing surface 243: Light-reducing angle 3: Light source 31: Light-emitting components 4: Structured optical films 401: First side 402: Second side 41:Ontology 411: First Surface 412: Curved area 42: Prism 43: Optical Structure 430: Vertex 431a: Side view 431b: First-level unit 431c: Second-level unit 432: Platform 433: Side View 5: Prism Lens 501: First Edge 502: Second Edge 51: Prism Strip 6: Diffusion sheet 7a: Reflective reflector 7b: Diffuser reflector 8: Display panel E1, E2: Extension direction L: Central Line L1: Connection N1, N2: Normal lines θ, θ1, θ2: included angles α1: First angle α2: Second angle UA: Adjust angle DA: Adjust angle downwards

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 disposed corresponding to the light incident surface of the light guide plate; a structured optical film disposed corresponding to the light emitting surface of the light guide plate, and including a body, a plurality of prisms arranged side-by-side on the body and facing the light emitting surface, and a plurality of optical structures disposed 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; two prisms are stacked on the structured optical film, wherein each prism has a plurality of parallel prism strips facing away from the structured optical film, wherein the extension direction E1 of the prism strips on one prism is different from the extension direction E2 of the prism strips on the other prism; and a reflective sheet located below the light guide plate; The incident light rays toward each of the prisms of the structured optical film have a peak brightness position between 3° and 15°, including the endpoint value, and a half-width at half-maximum (WHM) angle between 34° and 54° in a first direction, including the endpoint value, and between 13° and 33° in a second direction, including the endpoint value. The first direction and the second direction are orthogonal to each other. The outgoing light rays from each of the optical structures of the structured optical film have a peak brightness position between 20° and 40°, including the endpoint value, and a WHM angle between 15° and 25°, including the endpoint value.

2. The backlight module as described in claim 1, wherein, Each of the optical structures has a central line and a vertex, the central line being perpendicular to the body of the structured optical film, and the vertex being located on the central line.

3. The backlight module as described in claim 2, wherein, Each of the optical structures further has a plurality of side surfaces surrounding the central line, each side surface being a composite surface formed by joining two or more surface units along the extension direction of the central line, each surface unit having a normal, the angle between the normal of the surface unit closer to the vertex and the central line being greater than the angle between the normal of the surface unit farther from the vertex and the central line.

4. The backlight module as described in claim 1, 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 being perpendicular to the body of the structured optical film, the side surfaces connecting the platform to the body of the structured optical film.

5. The backlight module as described in claim 1, wherein, Each of the optical structures has a central line, a vertex located on the central line, and a plurality of side surfaces surrounding the central line, the central line being perpendicular to the body of the structured optical film. Each of the side surfaces is a composite surface formed by joining two or more surface units along the extension direction of the central line, wherein the surface unit closer to the vertex is a curved surface and the surface unit farther from the vertex is a sloped surface.

6. The backlight module as described in claim 1, wherein, The refractive index of the structured optical film is between 1.4 and 1.6, including the endpoint values. Each of the prisms of the structured optical film has a prism angle, and each of the optical structures of the structured optical film has a vertex angle. The ratio of the prism angle to the vertex angle is between 0.636 and 1.

5.

7. The backlight module as described in claim 6, wherein, The prism angle of each prism is between 70° and 120°, including the endpoint value, and the apex angle of each optical structure is between 80° and 110°, including the endpoint value.

8. The backlight module as described in claim 2, wherein, Each of the optical structures further has a plurality of side surfaces surrounding the central line, each side surface being a composite surface formed by joining two or more surface units along the extension direction of the central line, each surface unit having a normal, the angle between the normal of the surface unit closer to the vertex and the central line being smaller than the angle between the normal of the surface unit farther from the vertex and the central line.

9. A display device comprising a backlight module as described in any one of claims 1 to 8, and a display panel disposed on the backlight module.

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