A brightness enhancement film and a composite brightness enhancement film

Abstract

This invention relates to the field of optical thin film technology, and in particular to a brightness enhancement film and a composite brightness enhancement film, comprising a substrate layer and a prism structure layer attached to one surface of the substrate layer. The prism structure layer is composed of several M-shaped prism protrusions and triangular protrusions. The M-shaped prism protrusions adopt an asymmetrical gradient design, with the angle between their third hypotenuse and base successively decreasing or increasing along the first direction. The triangular protrusions are isosceles right triangles and are arranged with the M-shaped prism protrusions according to a set rule. This invention significantly reduces the probability of moiré pattern formation by optimizing the prism structure design, while improving front brightness and balancing production efficiency and cost control. The composite brightness enhancement film achieves multi-level light control through the superposition of two brightness enhancement films, further optimizing the display effect.

Description

Technical Field

[0001] This utility model belongs to the field of optical thin film technology, and in particular relates to a brightness enhancement film and a composite brightness enhancement film. Background Technology

[0002] Liquid crystal displays (LCDs), as the mainstream display technology, are widely used in various electronic devices. Since LCDs themselves do not emit light, they rely on a backlight module to provide a uniform and high-brightness light source to achieve their display function. In the backlight module, a brightness enhancement film, as a key optical film, uses its surface microprism structure to regulate light, refocusing scattered light into the central viewing angle range, thereby significantly improving brightness when viewed directly and reducing the loss of light at low angles. Traditional brightness enhancement films typically employ a long strip-shaped microprism structure with an isosceles triangular cross-section. Through refraction, total internal reflection, and multiple refraction effects on the prism sides, they effectively control the angle of the emitted light, achieving a brightness enhancement effect. However, this regularly arranged prism structure is prone to optical interference with the periodic arrangement of the LCD panel pixel units. When the spacing between them is close or there is a specific angular relationship, moiré patterns are formed, leading to a decrease in image sharpness and affecting display quality. As display technology advances towards higher resolution, the pixel spacing of LCD panels continues to shrink, significantly increasing the interference sensitivity between traditional prism structures and pixel units. The moiré pattern problem becomes increasingly prominent, becoming a significant factor restricting display quality.

[0003] In existing technologies, some patents propose solutions to improve moiré patterns, such as reducing the consistency with the pixel arrangement of the liquid crystal panel by increasing the irregularity of the prism structure, thereby reducing the probability of moiré patterns appearing. However, these designs are often too cumbersome and random, involving multiple variables, resulting in difficult mold processing, long production cycles, and uncontrollable costs. Furthermore, simply pursuing the irregularity of the prism structure may affect the optical performance of the brightness enhancement film, leading to problems such as brightness loss or uneven brightness distribution. Therefore, how to effectively suppress moiré patterns while maintaining optical performance, and simplifying the structural design to improve production efficiency and reduce costs, has become an urgent technical challenge.

[0004] This invention addresses the aforementioned problems by proposing a novel brightness enhancement film and composite brightness enhancement film design. By introducing an asymmetric "M"-shaped prism structure with gradient bottom corners, combined with the alternating arrangement of regular prisms, the irregularity of the prism structure is improved while optimizing optical control capabilities. This effectively suppresses moiré patterns while ensuring uniformity of luminance and brightness distribution. This design not only solves the moiré pattern problem of traditional brightness enhancement films in high-resolution displays but also reduces mold processing difficulty and production costs, providing a new solution for the development of display technology. Utility Model Content

[0005] This utility model relates to a brightness enhancement film and a composite brightness enhancement film, which effectively suppresses moiré patterns by optimizing the prism structure design, while improving front brightness and balancing production efficiency and cost control. The brightness enhancement film includes a substrate layer and a prism structure layer attached to one surface of the substrate layer; the prism structure layer is composed of several M-shaped prism protrusions and triangular protrusions, wherein the M-shaped prism protrusions adopt a unique asymmetrical gradient design, combined with isosceles right-angled triangular protrusions to achieve multi-level light control.

[0006] This utility model achieves the above-mentioned objective through the following technical solution: a brightness enhancement film, comprising a substrate layer and a prism structure layer attached to one side surface of the substrate layer; the prism structure layer includes a plurality of M-shaped prism protrusions arranged along a first direction, and in cross-section, the M-shaped prism protrusions include a first inclined side, a second inclined side, a third inclined side, a fourth inclined side, and a bottom edge that are sequentially adjacent to form a closed shape, the bottom edge being in contact with the surface of the substrate layer, the extension line of the third inclined side passing through the adjacent point of the first inclined side and the bottom edge, and the extension line of the second inclined side passing through the adjacent point of the fourth inclined side and the bottom edge; the length and height of the bottom edge of the M-shaped prism protrusions remain constant along the first direction; the included angle α between the third inclined side and the bottom edge decreases or increases sequentially along the first direction.

[0007] Furthermore, the M-shaped prism protrusions are continuously arranged along the first direction; the M-shaped prism protrusions extend to the required length along the second direction, and the first direction is perpendicular to the second direction.

[0008] Furthermore, the M-shaped prism protrusions are arranged at equal intervals, and a triangular protrusion is provided between every two adjacent M-shaped prism protrusions; the triangular protrusion is an isosceles right triangle, and the height and base length of the triangular protrusion are equal to those of the M-shaped prism protrusion; the M-shaped prism protrusions and the triangular protrusions are arranged continuously.

[0009] Furthermore, the prism structure layer also includes a plurality of triangular protrusions arranged at equal intervals, the plurality of M-shaped prism protrusions forming an M-shaped prism protrusion unit, and an M-shaped prism protrusion unit is disposed between any two adjacent triangular protrusions; the triangular protrusions are isosceles right triangles, and the height and base length of the triangular protrusions are equal to those of the M-shaped prism protrusions; the M-shaped prism protrusions and the triangular protrusions are arranged continuously.

[0010] Furthermore, all M-shaped prism protrusions are arranged symmetrically around the centerline of the prism structure layer.

[0011] Furthermore, the first hypotenuse, the second hypotenuse and its extension, and the base form a triangle, forming a first triangle group along the first direction; the fourth hypotenuse, the third hypotenuse and its extension, and the base form a triangle, forming a second triangle group along the opposite direction of the first direction; the first triangle group and the second triangle group are centrally symmetrical and their bases coincide, thereby forming the plurality of M-shaped prism protrusions.

[0012] Furthermore, the range of the included angle α between the third hypotenuse and the base is: 27°≤α<45°.

[0013] Furthermore, the first inclined side and the second inclined side are set at an angle and form a first peak, and the third inclined side and the fourth inclined side are set at an angle and form a second peak; the first peak, the second peak and the bottom side are equidistant from each other, and this vertical distance is the height of the M-shaped prism protrusion.

[0014] Furthermore, a trough of the M-shaped prism protrusion is formed at the adjacent point between the second and third inclined sides; the distance between any two adjacent troughs of the M-shaped prism protrusion is denoted as the prism spacing P, where P is greater than or equal to 21 μm.

[0015] Furthermore, the refractive index of the prism structure layer is greater than or equal to 1.58; the material of the substrate layer is selected from one or more combinations of polyethylene terephthalate, polycarbonate, polymethyl methacrylate, polystyrene or polyamide resin, and its thickness ranges from 20 to 100 μm.

[0016] Another objective of this invention is to provide a composite brightness enhancement film, which includes a first brightness enhancement film and a second brightness enhancement film with the same structure as the above-mentioned brightness enhancement film and stacked together. The prism protrusion in the first brightness enhancement film extends at an angle to the prism protrusion in the second brightness enhancement film. An adhesive layer is provided at the bottom of the first brightness enhancement film, and the first brightness enhancement film is stacked on top of the second brightness enhancement film through the adhesive layer.

[0017] In the technical solution of this utility model, the M-shaped prism protrusion is designed with an asymmetrical gradient structure. By successively decreasing or increasing the angle α between the third hypotenuse and the base along the first direction, a highly irregular optical microstructure is formed. Compared with the traditional isosceles triangular prism structure, this design significantly reduces the interference effect between the pixel unit and the prism array, thereby reducing the generation of moiré patterns. The triangular protrusion, as an auxiliary optical structure, is arranged alternately with the M-shaped prism protrusion, enabling hierarchical control of incident light at different angles. This improves the brightness of the front surface while avoiding luminance loss due to excessive randomization.

[0018] Furthermore, the geometric parameters of the M-shaped prism protrusion are clearly defined. For example, the first hypotenuse, the second hypotenuse and its extension, and the base form a triangle, creating a first triangle group along the first direction; the fourth hypotenuse, the third hypotenuse and its extension, and the base form a triangle, creating a second triangle group along the opposite direction of the first direction; the first triangle group and the second triangle group are centrally symmetrical and their bases coincide. This design ensures the height consistency of the M-shaped prism protrusion, while the gradual change in the included angle α enhances the complexity of the optical structure, enabling light to be efficiently converged in multiple directions.

[0019] Specifically, the refractive index of the prism structure layer is greater than or equal to 1.58. This value range is set based on practical application requirements to ensure the propagation efficiency and reflection effect of light within the prism structure layer. Furthermore, the substrate layer is made of one or more combinations of polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), polystyrene (PS), or polyamide resin (PA), with PET being preferred. Its thickness ranges from 20 to 100 μm to balance optical performance and mechanical strength.

[0020] Furthermore, in the composite brightness enhancement film, the superposition of the first and second brightness enhancement films is achieved by adjusting the angle between the length extension directions of the prism protrusions. Specifically, the length extension directions of the prism protrusions in the first and second brightness enhancement films are set at a 90° angle. This orthogonal design can further optimize light distribution, significantly improve front brightness, and reduce the probability of moiré patterns. The first brightness enhancement film is fixed above the second brightness enhancement film by an adhesive layer. The thickness and material selection of the adhesive layer need to be determined according to the specific optical performance requirements.

[0021] This invention solves the moiré pattern problem in traditional brightness enhancement films through an innovative prism structure design, while simultaneously considering optical performance, production efficiency, and cost control, thus possessing broad application prospects. By combining the M-shaped prism protrusion with the isosceles right-angled triangular protrusion, it achieves the dual functions of wide-angle light convergence and paraxial light correction, further improving front brightness and display uniformity. Furthermore, the asymmetric "M"-shaped equal-height prism structure involves fewer variables, simplifying mold processing, shortening processing time, reducing the risk of uncontrollable costs, and facilitating large-scale production.

[0022] Compared with existing technologies, the beneficial effects of this utility model's brightness enhancement film and composite brightness enhancement film are as follows: First, the asymmetric gradient M-shaped prism protrusion design improves the irregularity of the prism structure and reduces the probability of moiré patterns. Second, by alternating the asymmetric "M"-shaped equal-height prism structure with isosceles right-angled triangular protrusions, a balance is achieved between enhancing front brightness and suppressing moiré patterns, while avoiding the brightness loss caused by excessive randomization in traditional designs. Third, the asymmetric "M"-shaped equal-height prism involves fewer variables, simplifying processing and reducing costs. Finally, the combination design of the M-shaped prism protrusions and triangular protrusions enables multi-level light control, adapting to the needs of high-resolution display technology. Attached Figure Description

[0023] Figure 1 This is a three-dimensional structural diagram of the brightness enhancement film in Embodiment 1 of this utility model;

[0024] Figure 2 This is a schematic diagram of the cross-section of the brightness enhancement film in Embodiment 1 of this utility model;

[0025] Figure 3 This is a partial structural schematic diagram of the cross-section of the brightness enhancement film in Embodiment 1 of this utility model;

[0026] Figure 4 This is a schematic diagram of the M-shaped prism protrusion in Embodiment 1 of this utility model;

[0027] Figure 5 This is a schematic diagram illustrating the design process of the M-shaped prism protrusion in Embodiment 1 of this utility model;

[0028] Figure 6 This is a schematic diagram of the brightness enhancement film in Embodiment 3 of this utility model;

[0029] Figure 7 This is a schematic diagram of the brightness enhancement film in Embodiment 4 of this utility model;

[0030] Figure 8 This is a schematic diagram of the composite brightening film in Embodiment 5 of this utility model;

[0031] The numbers in the diagram represent:

[0032] 100, 200, 300 - Brightening film; 400 - Composite brightening film;

[0033] 1-Substrate layer;

[0034] 2-Prism structure layer, 21-M-type prism protrusion, 211-First oblique side, 212-Second oblique side, 213-Third oblique side, 214-Fourth oblique side, 215-Bottom side, 216-First peak, 217-Second peak, 23-M-type prism protrusion unit. Detailed Implementation

[0035] Example 1:

[0036] Please refer to Figures 1-5 This embodiment is a brightness enhancement film 100, which includes a substrate layer 1 and a prism structure layer 2 attached to one side surface of the substrate layer 1; the prism structure layer 2 includes a plurality of M-shaped prism protrusions 21, all of which are symmetrically arranged about the center line OO' of the prism structure layer 2; the M-shaped prism protrusions 21 are continuously arranged from the starting point A of the substrate layer 1 along a first direction to the ending point B of the substrate layer 1; the M-shaped prism protrusions 21 extend along a second direction to the required length, wherein the first direction is perpendicular to the second direction.

[0037] In cross-section, the M-shaped prism protrusion 21 includes a first inclined side 211, a second inclined side 212, a third inclined side 213, a fourth inclined side 214, and a bottom edge 215, which are sequentially adjacent to form a closed shape. The bottom edge 215 is bonded to the surface of the substrate layer 1. The extension of the third inclined side 213 passes through the adjacent point C between the first inclined side 211 and the bottom edge 215, and the extension of the second inclined side 212 passes through the adjacent point D between the fourth inclined side 214 and the bottom edge 215. The length of the bottom edge of the M-shaped prism protrusion 21 remains constant along the first direction. The angle α between the third inclined side 213 and the bottom edge 215 decreases sequentially along the first direction starting from the starting point A, for example... Figure 3 In the order α1>α2>α3>α4>α5; or the angle β between the second hypotenuse 212 and the base 215 decreases sequentially from the endpoint B along the opposite direction of the first direction, for example Figure 3 The order of β1>β2>β3>β4>β5 is given. This gradient design significantly reduces the interference effect between the pixel unit and the prism array, thereby reducing the generation of moiré patterns.

[0038] In this embodiment, the first hypotenuse 211, the second hypotenuse 212 and their extensions, and the base 215 form a triangle, forming a first triangle group S1 along the first direction; the fourth hypotenuse 214, the third hypotenuse 213 and their extensions, and the base 215 form a triangle, forming a second triangle group S2 along the opposite direction of the first direction; the first triangle group S1 and the second triangle group S2 are centrally symmetrical and their bases coincide, thereby forming a plurality of M-shaped prism protrusions 21, and the plurality of M-shaped prism protrusions 21 are centrally symmetrically arranged about the center line OO' of the prism structure layer 2, therefore... Figure 3 In this design, α1=β1, α2=β2, α3=β3, α4=β4, and α5=β5. This centrally symmetrical design not only ensures the consistency of optical performance but also enhances the light-gathering effect.

[0039] In this embodiment, 27°≤α<45°; 27°≤β<45°.

[0040] In this embodiment, the first hypotenuse 211 and the second hypotenuse 212 are set at an angle and form a first peak 216, and the third hypotenuse 213 and the fourth hypotenuse 214 are set at an angle and form a second peak 217. The vertical distances between the first peak 216, the second peak 217 and the bottom edge 215 are equal and equal to the height H of the M-shaped prism protrusion 21. The height H of the M-shaped prism protrusion 21 remains constant along the first direction.

[0041] At the point E where the second hypotenuse 212 and the third hypotenuse 213 meet, a trough of the M-shaped prism protrusion 21 is formed. The distance between any two adjacent troughs of the M-shaped prism protrusion 21 is the prism spacing P, which is greater than or equal to 21 μm. The spacing P varies with the base angles α and β of the M-shaped prism protrusion 21. This spacing setting ensures that light can be efficiently focused in multiple directions.

[0042] The refractive index of prism structure layer 2 is greater than or equal to 1.58. The specific value of the refractive index of prism structure layer 2 needs to be adjusted according to the actual application scenario, but it should always meet the requirement of being greater than or equal to 1.58.

[0043] The substrate layer 1 is made of one or more of polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), polystyrene (PS), and polyamide resin (PA). PET is preferred. The thickness of the substrate layer 1 is 20~100µm. This thickness range ensures a balance between optical performance and mechanical strength. The function of the substrate layer 1 is to provide stable support for the prism structure layer 2 while ensuring the flexibility and durability of the overall structure.

[0044] Example 2:

[0045] This embodiment is a brightness enhancement film, and its structure is basically the same as that of Embodiment 1. The difference is that the included angle α between the third inclined side 213 and the bottom side 215 increases sequentially along the first direction; or the included angle β between the second inclined side 212 and the bottom side 215 increases sequentially in the opposite direction of the first direction.

[0046] Example 3:

[0047] Please refer to Figure 6This embodiment is a brightness enhancement film 200, whose structure is basically the same as that of Embodiment 1 or Embodiment 2. The difference is that the M-shaped prism protrusions 21 are not arranged continuously, but at equal intervals, and a triangular protrusion 22 is provided between every two adjacent M-shaped prism protrusions 21. The triangular protrusion 22 is an isosceles right triangle, and the height and base length of the triangular protrusion 22 are the same as those of the M-shaped prism protrusions 21. The M-shaped prism protrusions 21 are arranged at equal intervals, and the interval is the same as the base length of the M-shaped prism protrusions 21, so that the M-shaped prism protrusions 21 and the triangular protrusions 22 together form a prism structure layer 2 with continuously arranged protrusions.

[0048] This embodiment adds triangular protrusions 22 between the M-shaped prism protrusions 21, combining the M-shaped protrusions and isosceles right-angled triangular protrusions into a hybrid prism structure design. This results in more precise optical control capabilities within the brightness enhancement film. Specifically:

[0049] (1) The M-shaped prism protrusion 21 is mainly responsible for the convergence of wide-angle light; the triangular protrusion 22, as an "auxiliary prism", is mainly used for secondary correction of small-angle scattered light, supplementing the blind spot of the M-shaped structure for the control of paraxial light; the two are arranged alternately to form a "main-auxiliary" optical path optimization, so that incident light at different angles is efficiently converted into vertical outgoing light, further improving the front brightness (gain can reach 1.5~2 times), realizing multi-level light control and improving axial brightness;

[0050] (2) The M-shaped prism protrusion 21 adopts a central symmetric design to balance the light distribution in the horizontal / vertical direction, but may cause micro-brightness fluctuations due to periodic arrangement; inserting the triangular protrusion 22 can destroy the strict periodicity of the M-shaped prism protrusion 21, disrupt the light interference mode, thereby suppressing moiré fringes and brightness patches, making the screen display more uniform.

[0051] (3) The M-shaped prism protrusion 21 alone may not be able to achieve 100% effective utilization of light energy due to limited optical control angle, back reflection loss and process sensitivity. Therefore, in this embodiment, the luminance can be compensated to the greatest extent by interlacing the triangular protrusions 22, while avoiding the appearance of moiré patterns.

[0052] Example 4:

[0053] Please refer to Figure 7 This embodiment is a brightness enhancement film 300, which includes a substrate layer 1 and a prism structure layer 2 disposed on the substrate layer 1. The prism structure layer 2 includes triangular protrusions 22 arranged at equal intervals and M-shaped prism protrusion units 23 arranged between two adjacent triangular protrusions 22. The M-shaped prism protrusion unit 23 includes at least two M-shaped prism protrusions 21, and the geometric parameter variation rules of the M-shaped prism protrusions 21 are the same as those in Embodiment 1 or Embodiment 2.

[0054] The height and base length of the M-shaped prism protrusion 21 remain constant along the first direction. The triangular protrusion 22 is an isosceles right triangle. The triangular protrusion 22 has the same height and base length as the M-shaped prism protrusion 21.

[0055] In this embodiment, the M-shaped prism protrusion unit 23 includes three M-shaped prism protrusions 21. In other embodiments, there may be two, four or more M-shaped prism protrusions 21.

[0056] In this embodiment, in any M-shaped prism protrusion unit 23, the included angle α between the third hypotenuse 213 and the bottom side 215 decreases sequentially along the first direction, for example... Figure 7 In the first direction, α1>α2>α3; or the angle β between the second hypotenuse 212 and the base 215 decreases sequentially in the opposite direction to the first direction, for example... Figure 7 In the equation, β1 > β2 > β3; and α1 = β1, α2 = β2, α3 = β3. The triangular protrusions 22 and the M-shaped prism protrusions 21 are continuously arranged to form a prism structure layer 2 with continuously arranged protrusions. This design further optimizes the light distribution and significantly improves the brightness of the front surface.

[0057] Example 5:

[0058] Please refer to Figure 8 This embodiment is a composite brightness enhancement film 400, which includes a first brightness enhancement film 41 and a second brightness enhancement film 42 with the same structure as in Embodiment 1, Embodiment 2, Embodiment 3, or Embodiment 4, stacked together. The first brightness enhancement film 41 includes a first substrate layer 411 and a first prism layer 412 attached to the first substrate layer 411. The second brightness enhancement film 42 includes a second substrate layer 421 and a second prism layer 422 attached to the second substrate layer 421. The structures of the first prism layer 412 and the second prism layer 422 are the same as the prism structure layer 2 in Embodiment 1, Embodiment 2, Embodiment 3, or Embodiment 4, but the extension direction of the protrusions in the first prism layer 412 is at an angle to the extension direction of the protrusions in the second prism layer 412. In this embodiment, the angle is 90°. This orthogonal design can further optimize the light distribution, significantly improve the front brightness, and reduce the probability of moiré patterns.

[0059] An adhesive layer 43 is provided at the bottom of the first brightness enhancement film 41, and the first brightness enhancement film 41 is stacked on top of the second brightness enhancement film 42 through the adhesive layer 43.

[0060] In practical applications, the brightness enhancement film and composite brightness enhancement film of this invention are suitable for optical films in LCD backlight modules. By combining asymmetric gradient M-shaped prism protrusions with isosceles right-angled triangular protrusions, multi-level light control is achieved to meet the needs of high-resolution display technology. The substrate layer 1 is selected from one or more combinations of polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), polystyrene (PS), or polyamide resin (PA), preferably PET, with a thickness ranging from 20 to 100 μm to balance optical performance and mechanical strength. The refractive index of the prism structure layer 2 is greater than or equal to 1.58. This value range is set based on practical application requirements to ensure the propagation efficiency and reflection effect of light within the prism structure layer.

[0061] In summary, this invention solves the moiré pattern problem in traditional brightness enhancement films through an innovative prism structure design, while simultaneously considering optical performance, production efficiency, and cost control. In the specific implementation process, the material and thickness of the substrate layer 1 are first determined based on the actual application scenario. Then, the prism structure layer 2 is processed to meet the geometric parameter requirements. During processing, it is necessary to ensure the height consistency of the M-shaped prism protrusions 21 and the gradual change characteristics of the included angle α, while controlling the prism spacing P and refractive index. For the composite brightness enhancement film 400, the stacking method of the first brightness enhancement film 41 and the second brightness enhancement film 42 also needs to be adjusted to achieve optimal optical performance. Through the above steps, the final brightness enhancement film and composite brightness enhancement film can meet the needs of high-resolution display technology and have broad application prospects.

[0062] For those skilled in the art, various modifications and improvements can be made without departing from the inventive concept of this utility model, and these modifications and improvements all fall within the protection scope of this utility model.

Claims

1. A brightness enhancement film, characterized in that: It includes a substrate layer and a prism structure layer attached to one surface of the substrate layer; the prism structure layer includes a plurality of M-shaped prism protrusions arranged along a first direction. In cross-section, the M-shaped prism protrusions include a first inclined side, a second inclined side, a third inclined side, a fourth inclined side, and a bottom edge that are sequentially adjacent to form a closed shape. The bottom edge is in contact with the surface of the substrate layer. The extension line of the third inclined side passes through the adjacent point of the first inclined side and the bottom edge, and the extension line of the second inclined side passes through the adjacent point of the fourth inclined side and the bottom edge. The length and height of the bottom edge of the M-shaped prism protrusions remain constant along the first direction. The included angle α between the third inclined side and the bottom edge decreases or increases sequentially along the first direction.

2. The brightening film as described in claim 1, characterized in that: The M-shaped prism protrusions are continuously arranged along a first direction; the M-shaped prism protrusions extend to the required length along a second direction, wherein the first direction is perpendicular to the second direction.

3. The brightening film as described in claim 1, characterized in that: The M-shaped prism protrusions are arranged at equal intervals, and a triangular protrusion is provided between every two adjacent M-shaped prism protrusions; the triangular protrusion is an isosceles right triangle, and the height and base length of the triangular protrusion are equal to those of the M-shaped prism protrusion; the M-shaped prism protrusions and the triangular protrusions are arranged continuously.

4. The brightening film as described in claim 1, characterized in that: The prism structure layer also includes a plurality of triangular protrusions arranged at equal intervals. The plurality of M-shaped prism protrusions form an M-shaped prism protrusion unit, and an M-shaped prism protrusion unit is arranged between any two adjacent triangular protrusions. The triangular protrusions are isosceles right triangles, and the height and base length of the triangular protrusions are equal to those of the M-shaped prism protrusions. The M-shaped prism protrusions and the triangular protrusions are arranged continuously.

5. The brightening film as described in claim 1, characterized in that: All M-shaped prism protrusions are arranged symmetrically around the centerline of the prism structure layer.

6. The brightening film according to any one of claims 1 to 4, characterized in that: The first hypotenuse, the second hypotenuse and its extension, and the base form a triangle, forming a first triangle group along the first direction; the fourth hypotenuse, the third hypotenuse and its extension, and the base form a triangle, forming a second triangle group along the opposite direction of the first direction; the first triangle group and the second triangle group are centrally symmetrical and their bases coincide, thereby forming the plurality of M-shaped prism protrusions.

7. The brightening film according to any one of claims 1 to 4, characterized in that: The included angle α between the third hypotenuse and the base is in the range of 27°≤α<45°.

8. The brightening film according to any one of claims 1 to 4, characterized in that: The first hypotenuse and the second hypotenuse are set at an angle and form a first peak, and the third hypotenuse and the fourth hypotenuse are set at an angle and form a second peak; the first peak, the second peak and the bottom edge are equidistant from each other, and this vertical distance is the height of the M-shaped prism protrusion.

9. The brightening film according to any one of claims 1 to 4, characterized in that: The second inclined side and the third inclined side form a trough of the M-shaped prism convexity at their adjacent points; the distance between any two adjacent troughs of the M-shaped prism convexity is denoted as the prism spacing P, where P is greater than or equal to 21 μm.

10. The brightening film according to any one of claims 1 to 4, characterized in that: The refractive index of the prism structure layer is greater than or equal to 1.58; the material of the substrate layer is selected from one or more combinations of polyethylene terephthalate, polycarbonate, polymethyl methacrylate, polystyrene or polyamide resin, and its thickness ranges from 20 to 100 μm.

11. A composite brightening film, characterized in that: It includes a first brightness enhancement film and a second brightness enhancement film with the same structure as any one of claims 1 to 4, which are stacked together. The prism protrusion in the first brightness enhancement film extends at an angle to the prism protrusion in the second brightness enhancement film. An adhesive layer is provided at the bottom of the first brightness enhancement film, and the first brightness enhancement film is stacked on top of the second brightness enhancement film through the adhesive layer.

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