Optical film assembly, backlight module and display device

Abstract

An optical film assembly (200) configured to guide light from a light guide plate (110) of a backlight module (100) is provided. The optical film assembly (200) includes a lower prism sheet (220) and an upper prism sheet (230). The lower prism sheet (220) has a plurality of lower prism structures (221) extending along a first direction (D1). The upper prism sheet (230) is disposed above the lower prism sheet (220) and has a plurality of upper prism structures (231) extending along a second direction (D2) different from the first direction (D1). The second direction (D2) and an extension direction (A1) of a light incident surface (111) of the light guide plate (110) have an included angle in a range of 25 degrees to 50 degrees, or 130 degrees to 155 degrees.

Description

[Technical Field]

[0001] The present disclosure relates to a film assembly and its applications, and more particularly to a film assembly applicable to a backlight module, and a backlight module and a display device using the film assembly. [Background technology]

[0002] A typical backlight module mainly includes a light guide plate and a plurality of optical films, and the optical films refract light emitted from the light guide plate to emit the light at a front viewing angle. However, such a backlight module cannot be applied to an anti-peeping display product. Therefore, how to achieve a good anti-peeping effect by changing the combination design of the optical film and the light guide plate has been a goal that those skilled in the art are actively working to achieve. Summary of the Invention

[0003] Therefore, an object of the present disclosure is to provide an optical film assembly, and a backlight module and a display device using the film assembly, which is designed to maintain the amount of light emitted from the front viewing angle of the light beam while reducing stray light emitted from the side of the light beam.

[0004] In accordance with the above-mentioned object of the present disclosure, there is provided an optical film assembly configured to guide light rays from a light guide plate of a backlight module. The optical film assembly includes a lower prism sheet and an upper prism sheet. The lower prism sheet has a plurality of lower prism structures extending along a first direction. The upper prism sheet is disposed above the lower prism sheet and has a plurality of upper prism structures extending along a second direction different from the first direction. The second direction and the extension direction of the light incident surface of the light guide plate form an included angle ranging from 25 degrees to 50 degrees, or from 130 degrees to 155 degrees.

[0005] According to one embodiment of the present disclosure, the first direction and the extending direction of the light incident surface of the light guide plate form an angle in the range of 115 degrees to 140 degrees, or in the range of 220 degrees to 245 degrees.

[0006] According to one embodiment of the present disclosure, the first direction and the second direction are perpendicular to each other.

[0007] According to one embodiment of the present disclosure, the above optical film assembly further includes a lower diffusion sheet disposed below the lower prism sheet, the lower diffusion sheet including a plurality of diffusion particles, and these diffusion particles cause the lower diffusion sheet to have a haze of 50% or more and 60% or less.

[0008] According to one embodiment of the present disclosure, the optical film assembly further includes an upper diffusion sheet disposed above the upper prism sheet, wherein the upper diffusion sheet includes a plurality of diffusion particles, and the diffusion particles cause the upper diffusion sheet to have a haze of 30% or less.

[0009] According to one embodiment of the present disclosure, the optical film assembly further includes a lower diffusion sheet and an upper diffusion sheet, wherein the haze ratio of the lower diffusion sheet to the upper diffusion sheet is 1.6 or more and 6 or less.

[0010] According to one embodiment of the present disclosure, the lower diffusion sheet is disposed below the lower prism sheet, and the upper diffusion sheet is disposed above the upper prism sheet. After light from the light guide plate passes through the lower diffusion sheet, the lower prism sheet, the upper prism sheet, and the upper diffusion sheet in sequence, some of the light exits the upper diffusion sheet in the front viewing direction and some of the light exits the upper diffusion sheet in the side viewing direction, and the ratio of the amount of light exiting in the side viewing direction to the amount of light exiting in the front viewing direction is less than 0.07.

[0011] According to one embodiment of the present disclosure, the front viewing direction is parallel to the light output normal of the upper diffusion sheet, and the side viewing direction and the light output normal form an angle greater than 45 degrees.

[0012] According to one embodiment of the present disclosure, each of the lower prism structures and each of the upper prism structures is a strip-like structure.

[0013] In accordance with the above object of the present disclosure, there is further provided a backlight module, which includes a light guide plate, a light source, and the above optical film assembly. The light guide plate has a light incident surface and a light exit surface. The light source is disposed adjacent to the light incident surface. The optical film assembly is disposed above the light exit surface.

[0014] Based on the above object of the present disclosure, there is further provided a display device, which includes a light guide plate, a light source, the above optical film assembly, and a display panel. The light guide plate has a light incident surface and a light exit surface. The light source is disposed adjacent to the light incident surface. The optical film assembly is disposed above the light exit surface. The display panel is disposed above the optical film assembly.

[0015] As can be seen from the above, the optical film assembly of the present disclosure mainly satisfies the optical needs of an anti-peeping display by designing the included angle between the extension direction of the upper prism structure of the upper prism sheet and the light incident surface in accordance with the change in the included angle between the extension direction of the lower prism structure of the lower prism sheet and the light incident surface, while maintaining the amount of light emitted from the front viewing angle and reducing the amount of light emitted from the side viewing angle. Furthermore, when combined with a diffusion sheet of a different haze, the combination of the upper prism sheet and the lower prism sheet of the present disclosure can also achieve the effect of reducing stray light emitted from the side viewing angle. [Brief explanation of the drawings]

[0016] For a more complete understanding of the embodiments and their advantages, reference is now made to the following description taken in conjunction with the drawings, in which:

[0017] [Figure 1] 1 is a schematic diagram illustrating a backlight module according to a first embodiment of the present disclosure. [Figure 2]FIG. 2 is a front view showing a lower prism sheet according to the first embodiment of the present disclosure. [Figure 3] FIG. 2 is a front view showing an upper prism sheet according to the first embodiment of the present disclosure. [Figure 4] FIG. 4 is a comparison diagram showing the output luminance at a front viewing angle and the output luminance at a side viewing angle produced by the included angle design of the upper prism sheet according to the first embodiment of the present disclosure. [Figure 5] FIG. 2 is a side view showing a lower diffusion sheet according to the first embodiment of the present disclosure. [Figure 6] FIG. 10 is a schematic diagram illustrating a backlight module according to a second embodiment of the present disclosure. [Figure 7] 1 is a schematic diagram illustrating a display device according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0018] 1 is a schematic diagram illustrating a backlight module according to a first embodiment of the present disclosure. The backlight module 100 of this embodiment mainly includes a light guide plate 110, a light source 120, and an optical film assembly 200. The light source 120 mainly provides light to the light guide plate 110, and the optical film assembly 200 is disposed in front of the light guide plate 110. The optical film assembly 200 mainly reduces the amount of light emitted from the light guide plate 110 at a side viewing angle and maintains the amount of light emitted from the light guide plate 110 at a front viewing angle, thereby allowing the backlight module 100 to be used in anti-peeping display products.

[0019] 1 , the light guide plate 110 has a light incident surface 111 and a light exit surface 112. The light source 120 is disposed adjacent to the light incident surface 111, and light emitted from the light source 120 enters the light guide plate 110 through the light incident surface 111 and then exits through the light exit surface 112 of the light guide plate 110. In this embodiment, the optical film assembly 200 includes a lower diffusion sheet 210, a lower prism sheet 220, and an upper prism sheet 230, which are stacked in order in front of the light exit surface 112 of the light guide plate 110.

[0020] 2 and 3 are front views illustrating a lower prism sheet and an upper prism sheet according to a first embodiment of the present disclosure. In this embodiment, the lower prism sheet 220 includes a plurality of lower prism structures 221, each of which is a strip-shaped structure extending along a first direction D1. An included angle α is formed between the first direction D1 and the extension direction A1 of the light incident surface 111 of the light guide plate 110. The upper prism sheet 230 includes a plurality of upper prism structures 231, each of which is a strip-shaped structure extending along a second direction D2, where the second direction D2 is different from the first direction D1. An included angle β is formed between the second direction D2 and the extension direction A1 of the light incident surface 111 of the light guide plate 110. In this embodiment, the included angle β is within a range of 25 degrees to 50 degrees, or 130 degrees to 155 degrees. As a result, the light rays emitted from the light output surface 112 of the light guide plate 110 pass through the lower diffusion sheet 210, the lower prism sheet 220, and the upper prism sheet 230 in that order, and then some of the light rays (e.g., light ray L1 in FIG. 1) exit from the upper prism sheet 230 along the front viewing direction (also called the front viewing angle), and other light rays (e.g., light ray L2 in FIG. 1) exit from the upper prism sheet 230 along the side viewing direction (also called the side viewing angle). For example, when a user faces the backlight module 100 shown in FIG. 1, the user looks straight ahead at the center position of the backlight module 100. At this time, if an extension line P1 passing through this center position is defined on the light output surface of the backlight module 100, a side viewing direction is defined on a plane P2 (plane P2 includes the hatched area in FIG. 1) formed by the extension line P1 and the front viewing direction. Here, the front viewing direction means that the light ray is parallel to the normal direction of the upper prism sheet 230, and the side viewing direction means a direction that forms an included angle θ with the front viewing direction on the plane P2.

[0021] 4, which is a comparison diagram of the output brightness at a front viewing angle and the output brightness at a side viewing angle produced by the design of the included angle of the upper prism sheet according to the first embodiment of the present disclosure. As can be seen from FIG. 4, when the included angle β of the upper prism sheet 230 is within the range of 25 to 50 degrees, or 130 to 155 degrees (i.e., within the range selected by the dashed-line frame in FIG. 4), the entire backlight module 100 can produce output brightness at a large front viewing angle and output brightness at a small side viewing angle. As a result, the ratio of the amount of light emitted from the side viewing direction to the amount of light emitted from the front viewing direction (also referred to as the side viewing angle output ratio) is small, for example, less than 0.07. This means that the amount of light emitted in the side direction can be reduced by designing the included angle β of the upper prism sheet 230 within the range of 25 to 50 degrees, or 130 to 155 degrees.

[0022] Also, referring to Tables 1 and 2 below, Tables 1 and 2 show the output results of light rays L1 and L2 according to the combination of the included angle α of the lower prism sheet 220 and the included angle β of the upper prism sheet 230.

[0023] Table 1 JPEG0007808691000001.jpg47161

[0024] Table 2 JPEG0007808691000002.jpg47161

[0025] As can be seen from Tables 1 and 2 above, when the included angle β of the upper prism sheet 230 is in the range of 25° to 50°, or 130° to 155°, the side viewing angle light output ratio is less than 10%, or even less than 7%, which can meet the needs of anti-spying products. It can be seen from this that the included angle α of the lower prism sheet 220 can be designed to be in the range of 115° to 140°, or 220° to 245°, or the second direction D2 of the upper prism structure 231 of the upper prism sheet 230 and the first direction D1 of the lower prism structure 221 of the lower prism sheet 220 can be made perpendicular to each other, thereby achieving the effect of reducing the side viewing angle light output ratio.

[0026] 5 is a side view of a lower diffusion sheet according to a first embodiment of the present disclosure. In one embodiment, the lower diffusion sheet 210 includes a plurality of diffusion particles 211. The lower diffusion sheet 210 of the present disclosure can reduce stray light emitted primarily from a side viewing angle (i.e., an included angle θ between the front viewing direction and the side viewing direction greater than 45 degrees). Here, stray light refers to light rays diffused by the diffusion particles and having no specific directionality. When parallel light L3 enters the lower diffusion sheet 210, some of the light rays (e.g., light ray L4) pass through the lower diffusion sheet 210 parallel, while the other light rays (e.g., light ray L5) are scattered by the diffusion particles 211 and pass through the lower diffusion sheet 210. The deviation angle of light ray L5 from parallel light ray L3 is greater than 2.5 degrees. The ratio of the transmittance of scattered light ray L5 passing through the lower diffusion sheet 210 to the sum of the transmittances of light ray L4 and light ray L5 can be defined as the haze of the lower diffusion sheet 210. In this embodiment, the lower diffusion sheet 210 has a haze of 50% to 60%. A haze of 0% for the lower diffusion sheet 210 can achieve a low side-viewing angle light output ratio, but cannot satisfy the uniformity requirement for light near the light-incident side of the light output surface. A haze of 90% for the lower diffusion sheet 210 can achieve a low side-viewing angle light output ratio, but cannot satisfy the output brightness requirement for the front-viewing angle. Furthermore, the amount of stray light measured at side-viewing angles is high, which impairs the anti-peeping effect of the product. Therefore, a haze of 50% to 60% for the diffusion sheet 210 not only satisfies the anti-peeping objective of the product, but also reduces stray light at side-viewing angles. In addition, in conventional backlight modules, a high haze lower diffusion sheet (e.g., a 90% haze lower diffusion sheet) is prone to generating a lot of stray light, but in the present disclosure, by using a low haze lower diffusion sheet of 50% to 60%, the optical appearance required by customers can be met while reducing the generation of stray light and further meeting the requirements of anti-peeping products.

[0027] The backlight module of the present disclosure may have different structural designs. Also, FIG. 6 is a schematic diagram of a backlight module according to a second embodiment of the present disclosure. The structure of the backlight module 300 of this embodiment is substantially the same as the structure of the backlight module 100 shown in FIG. 1 , except that the backlight module 300 further includes an upper diffusion sheet 440. As shown in FIG. 6 , the backlight module 300 mainly includes a light guide plate 310, a light source 320, and an optical film assembly 400. The light source 320 mainly provides light to the light guide plate 310, and the optical film assembly 400 is disposed in front of the light guide plate 310. The optical film assembly 400 mainly reduces the amount of light emitted from the light guide plate 310 that exits from a side viewing angle, while maintaining at least the amount of light emitted from the light guide plate 310 that exits from a front viewing angle, thereby enabling the backlight module 300 to be used in anti-peeping display products.

[0028] 6, in this embodiment, optical film assembly 400 includes lower diffusion sheet 410, lower prism sheet 420, upper prism sheet 430, and upper diffusion sheet 440, which are stacked in this order in front of the light output surface of light guide plate 310. The structures of lower prism sheet 420 and upper prism sheet 430 are substantially the same as the structures of lower prism sheet 220 and upper prism sheet 230 shown in FIGS. 1 to 3, and therefore will not be described here. In this embodiment, the effect of the upper diffusion sheet 440 is to ensure that the anti-peeping display product has better optical quality, for example, better uniformity. In particular, the haze of the upper diffusion sheet 440 is lower than that of the lower diffusion sheet 410, thereby ensuring that excessive stray light is not generated in the light rays emitted from the upper diffusion sheet 440, and the product to which the optical film assembly of the present disclosure is applied further meets the anti-peeping properties.

[0029] In this embodiment, the lower diffusion sheet 410 and the upper diffusion sheet 440 include, for example, the diffusion particles 211 shown in FIG. 5 , and these diffusion particles cause the lower diffusion sheet 410 to have a haze of 50% to 60%. The haze of the upper diffusion sheet 440 is lower than that of the lower diffusion sheet 410, for example, 30% or less. Furthermore, Table 3 illustrates that, based on the condition that the included angle between the prism structure of the upper prism sheet 430 and the extension direction of the light incident surface 311 of the light guide plate 310 is in the range of 25° to 50° or 130° to 155°, the amount of stray light generated remains within the acceptable range for an anti-spy product, even when the haze of the lower diffusion sheet 410 and the upper diffusion sheet 440 is changed. Table 3 shows that when the haze of the lower diffusion sheet 410 is in the range of 50% to 60% and the haze of the upper diffusion sheet 440 is 30% or less, little stray light is generated. Furthermore, as can be seen from the results in Table 3, when the haze ratio of the lower diffusion sheet 410 to the upper diffusion sheet 440 is in the range of 1.6 or more and 6 or less, the product can meet the anti-peeping characteristics, generate less stray light, and also have the optical quality of the backlight module of this embodiment, for example, have better uniformity.

[0030] Table 3 JPEG0007808691000003.jpg34161

[0031] Also, please refer to FIG. 7, which is a schematic diagram of a display device according to one embodiment of the present disclosure. The display device 500 of this embodiment includes a backlight module 100 and a display panel 510, as shown in FIG. 1. The display panel 510 is disposed in front of the backlight module 100. The display device 500 can similarly maintain the amount of light emitted at a front viewing angle and reduce the amount of light emitted at a side viewing angle by designing the optical film assembly 200 in the backlight module 100, and therefore, a description thereof will be omitted here. The embodiment of the present invention is illustratively described with respect to the application of the backlight module 100 shown in FIG. 1 to the display device 500, and is not intended to limit the present disclosure. The backlight modules of the other embodiments described above (e.g., the backlight module 300 shown in FIG. 6) can also be applied to display devices to provide similar anti-peeping effects.

[0032] As can be seen from the above embodiments of the present disclosure, the optical film assembly of the present disclosure mainly relies on the design of the included angle between the extension direction of the upper prism structure of the upper prism sheet and the light incident surface, and changes in the included angle between the extension direction of the lower prism structure of the lower prism sheet and the light incident surface to reduce the amount of light emitted from the side viewing angle while maintaining the amount of light emitted from the front viewing angle, thereby meeting the optical needs of anti-peeping displays. Furthermore, when combined with a diffusion sheet of a different haze, the combination of the upper prism sheet and the lower prism sheet of the present disclosure can also achieve the effect of reducing stray light emitted from the side viewing angle.

[0033] Although the embodiments of the present disclosure have been described above, they are not intended to limit the present disclosure, and a person skilled in the art may make some changes and modifications without departing from the spirit and scope of the embodiments of the present disclosure. Therefore, the scope of protection of the embodiments of the present disclosure should be determined based on the scope of protection defined by the appended claims. [Explanation of symbols]

[0034] 100 Backlight Module 110 Light guide plate 111 Light entrance surface 112 Idemitsu surface 120 light source 200 Optical Film Assembly 210 Lower diffusion sheet 211 Diffusion Particles 220 Lower prism sheet 221 Lower Prism Structure 230 Upper prism sheet 231 Upper Prism Structure 300 Backlight Module 310 Light guide plate 311 Light entrance surface 320 light source 400 Optical Film Assembly 410 Lower diffusion sheet 420 Lower prism sheet 430 Upper prism sheet 440 Upper diffusion sheet 500 display device 510 Display Panel A1 Stretching direction D1 1st direction D2 2nd direction L1 ray L2 ray L3 ray L4 ray L5 ray P1 extension line P2 plane α included angle β included angle θ included angle

Claims

1. 1. An optical film assembly configured to guide light rays from a light guide plate of a backlight module, comprising: a lower prism sheet having a plurality of lower prism structures each extending along a first direction and disposed on the light output surface of the light guide plate; an upper prism sheet provided on the opposite side of the lower prism sheet from the light guide plate, the upper prism sheet has a plurality of upper prism structures each extending along a second direction different from the first direction, and has an included angle between the second direction and an extension direction of a light incident surface of the light guide plate, the included angle being in a range of 25 degrees to 50 degrees, or in a range of 130 degrees to 155 degrees, a lower diffusion sheet provided on the lower prism sheet's side facing the light guide plate, and an upper diffusion sheet provided on the upper prism sheet's side facing away from the lower prism sheet, the upper diffusion sheet includes a plurality of diffusion particles; the plurality of diffusion particles cause the upper diffusion sheet to have a haze of less than 30%; a haze ratio of the lower diffusion sheet to the upper diffusion sheet of 1.6 or more and 6 or less; Optical film assembly.

2. The angle between the first direction and the extension direction of the light incident surface of the light guide plate is in the range of 115 degrees to 140 degrees, or in the range of 220 degrees to 245 degrees. The optical film assembly of claim 1 .

3. The first direction and the second direction are perpendicular to each other. The optical film assembly of claim 2 .

4. The lower diffusion sheet includes a plurality of diffusion particles, the lower diffusion sheet has a haze of 50% or more and 60% or less due to the plurality of diffusion particles; The optical film assembly of claim 1 .

5. After the light rays from the light guide plate pass through the lower diffusion sheet, the lower prism sheet, the upper prism sheet and the upper diffusion sheet in order, a portion of the light rays exits from the upper diffusion sheet along the front viewing direction, and another portion of the light rays exits from the upper diffusion sheet along the side viewing direction, a ratio of the amount of light emitted from the side viewing direction to the amount of light emitted from the front viewing direction is less than 0.07; The optical film assembly of claim 1 .

6. a light guide plate having a light entrance surface and a light exit surface; a light source disposed adjacent to the light entrance surface; an optical film assembly according to any one of claims 1 to 5, which is provided above the light exit surface; Including, Backlight module.

7. a light guide plate having a light entrance surface and a light exit surface; a light source disposed adjacent to the light entrance surface; an optical film assembly according to any one of claims 1 to 5, which is disposed above the light exit surface of the light guide plate; a display panel disposed above the optical film assembly; Including, Display device.

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