Film system structure of DBEF brightness enhancement film

Abstract

A DBEF brightness enhancement film system structure disclosed by the present invention comprises a plurality of reflection units stacked in sequence, each reflection unit comprises a plurality of groups of film layer structures stacked in sequence, each group of film layer structure comprises a first film layer and a second film layer, and the refractive indexes of the first film layer and the second film layer are different; in the same reflection unit, the thickness of the film layer structure is the same; the thickness of the film layer structure is different between different reflection units. According to the invention, two materials with different refractive indexes are alternately stacked to form the reflection unit, the thickness of two stacked film layers is improved and designed on the basis of the reflection unit, and then a plurality of reflection units with film layer structures with different thicknesses are stacked, so that the reflection unit is formed. The obtained film system structure transmits P light and keeps high reflectivity for S light in the whole visible light wave band, the brightening effect can be achieved, and the requirement of a DBEF brightening film is met.

Description

Technical Field

[0001] The present invention relates to the technical field of display film system structures, and in particular to a DBEF brightness enhancement film system structure. Background Art

[0002] Liquid crystal displays (LCDs) are currently the most predominant optoelectronic information terminal devices. Their display principle utilizes polarized liquid crystals to modulate polarized light to achieve image display. The backlight source is the source of the display's light energy. The emitted light can be decomposed into two components with mutually perpendicular polarization directions: "P light (parallel polarized light)" and "S light (vertically polarized light)." However, after passing through the polarizing film, the "S" light is completely blocked, resulting in a 50% loss of backlight energy. The transmitted "P" light is continuously reflected and absorbed by other components such as the liquid crystals. Ultimately, only approximately 10% of the light is projected onto the display screen, resulting in weak LCD panel brightness. To address this issue, a brightness enhancement film, a crucial optical component, has been introduced into the LCD backlight module. Its unique structural design effectively improves light utilization efficiency, thereby boosting display brightness.

[0003] LCD brightness enhancement films can be categorized by their structure, including focusing prisms, microlenses, and reflective polarizers (DBEF). DBEF's brightness enhancement strategy differs from traditional focusing products. Its primary principle is based on Bragg diffraction. It utilizes a unique multi-layered structure to continuously reflect and depolarize S light, then re-decompose it into P light components before reintroducing them into the transmitted light path, achieving a brighter display.

[0004] Due to the complex structure and challenging molding challenges of DBEF films, detailed descriptions of these films are currently lacking in published literature. To balance practicality, the brightness-enhancing films are kept thin, resulting in subtle differences in thickness between adjacent layers. Determining the thickness of each layer is crucial in influencing the optical performance of the model during design. Determining the specific layer stacking structure remains a core issue currently under investigation. Over the years, several researchers have made progress in studying the structure of DBEF films. Li Y et al. systematically investigated the factors influencing Bragg reflection and explored methods for achieving broadband reflection. Kim T et al. proposed a simplified reflective structure based on a birefringent polymer matrix, but this only achieved high reflectivity within a narrow bandwidth. Pan S et al. proposed a method for generating giant birefringence using subwavelength silicon gratings. By exploiting the significant refractive index difference between the two materials, a relatively thin film structure was constructed, but this did have some impact on the transmission of P-light. Li M et al. developed a periodically alternating PC / PMMA multilayer material and investigated the effect of periodicity on optical properties within a specific wavelength range.

[0005] The above studies explored the effects of different structural stacking on optical properties, but failed to provide a film structure that can achieve basic transmission of P light and maintain high reflectivity for S light in the entire visible light band.

[0006] In view of this, this application is hereby filed. Summary of the Invention

[0007] The present invention provides a DBEF brightening film system structure. First, two materials with different refractive indices are alternately stacked to form a reflective unit. Based on the reflective unit, the thickness of the two stacked film layers is improved and designed, and then multiple reflective units with film layer structures with different thicknesses are stacked. The obtained film system structure transmits P light and maintains a high reflectivity for S light in the entire visible light band, which can achieve a brightening effect and meet the needs of DBEF brightening film.

[0008] The present invention is achieved through the following technical solutions: In a first aspect, the present invention provides a DBEF brightness enhancement film system structure, comprising a plurality of reflective units stacked in sequence, The reflective unit includes a plurality of film layer structures stacked in sequence, each film layer structure includes a first film layer and a second film layer, and the refractive indexes of the first film layer and the second film layer are different; Within the same reflective unit, the thickness of the film layer structure is the same; The thickness of the film layer structure is different between different reflective units.

[0009] The present invention first forms a reflective unit by alternately stacking two materials with different refractive indices. Based on the reflective unit, the thickness of the two stacked film layers is improved and designed, and then multiple reflective units with film layer structures with different thicknesses are stacked. The obtained film system structure transmits P light and maintains a high reflectivity for S light in the entire visible light band, which can achieve a brightening effect and meet the requirements of DBEF brightening film.

[0010] In a specific embodiment, the reflection unit is (a H b L ) T express; Where T represents the stacking period of the film structure, H Indicates the base thickness of film layer 1, L represents the reference thickness of the second film layer, a represents the ratio of the first film layer in the reflective unit to the corresponding reference thickness, and b represents the ratio of the second film layer in the reflective unit to the corresponding reference thickness; The sum of a and b is different between different reflection units.

[0011] By improving the thickness of the first film layer and the second film layer in different reflection units, the film layer structures of different reflection units in the film system structure show different thicknesses, so as to obtain a film system structure with a high reflectivity of S light covering different wavelength bands.

[0012] In a specific embodiment, along the stacking direction of the reflection units, between different reflection units, the thickness of the film layer structure increases or decreases.

[0013] In a specific embodiment, between different reflection units, the ratio of the thickness of the first film layer to the thickness of the second film layer in the film layer structure is different.

[0014] In a specific embodiment, the reference thickness of the first film layer H and The reference thickness of the second film layer L is equal, 0 < a < 2, 0 < b < 2, that is, between different reflection units, the ratio of a to b is different. Preferably, the ratio of a to b is greater than 0 and less than 2.

[0015] The present invention finds that when the thickness ratio of the first film layer and the second film layer changes, it will cause the high reflectivity of the reflection unit for S light to cover different wavelength bands. Therefore, the present invention selects to stack multiple reflection units with different thickness ratios of the first film layer and the second film layer to obtain a variable thickness ratio stacked film system structure, which can meet the requirement of high reflectivity of S light covering the entire visible light band.

[0016] Among them, the variable thickness ratio stacked film system structure can be expressed as (a1 H b1 L ) T (a2 H b2 L ) T (a3 H b3 L ) T (a4 H b4 L ) T (a5 H b5 L ) T ……(a i H b i L ) T , a i / b i has different values, [[ID=6ii]] H=L .

[0017] In a specific embodiment, between different reflection units, b has the same value. Along the stacking direction of the reflection units, between different reflection units, the value of a increases or decreases. Preferably, the value of b is 1, 0 < a < 2.

[0018] In a specific implementation, the value of a increases or decreases by the same amount.

[0019] In a specific embodiment, the ratio of a to b is the same between different reflective units, preferably 1, and along the stacking direction of the reflective units, the thickness of the film layer structure increases or decreases by the same amount of Δd between different reflective units.

[0020] The present invention finds that when the thickness ratio of film layer one to film layer two remains unchanged between different reflective units, reflective units of different thicknesses can be obtained by simultaneously and equally changing the thickness of film layer one and film layer two, and stacking up multiple reflective structures with equal gradient thickness changes to obtain a layer gradient stacked film system structure, which can meet the demand for high reflectivity of S light covering the entire visible light band.

[0021] Among them, the layer gradient stacked film structure can be expressed as (a1 H b1 L ) T (a1+Δd) H (b1+Δd) L ) T (a1+2Δd) H (b1+2Δd) L ) T (a1+3Δd) H (b1+3Δd) L ) T (a1+4Δd) H (b1+4Δd) L ) T ...((a1+iΔd) H (b1+iΔd) L ) T 。

[0022] In a specific embodiment, in the reflective unit, the stacking period T of the film structure ranges from 10 to 50, and the T value is the same between different reflective units. In the reflective unit, as the stacking period of the film structure increases, the reflectivity of the reflective unit can be improved, and the visible light band in the range of 450-650nm is basically covered. The continuous increase in the stacking period of the film structure has little effect on the reflectivity, and the profitability is low. Therefore, considering the manufacturing process of the film system, the stacking period is preferably .

[0023] In a specific embodiment, the stacking period N of the reflective units is ≥8.

[0024] In a specific embodiment, the film layer 1 is made of polyethylene naphthalate PEN, which is anisotropic after processing and has a certain degree of uniaxial orientation on the film plane. The film layer 1 has a different refractive index in the biaxial orientation, that is, the refractive index has different values in the x-axis and y-axis directions. , ; The second film layer is made of polyethylene naphthalate copolymer, which is isotropic after processing and has the same refractive index in biaxial orientation. The present invention forms a reflective unit by alternately stacking two materials, which can realize the functions of basically transmitting P light and mainly reflecting S light.

[0025] In a specific embodiment, n2 is greater than n1, preferably n1=1.4, n2=1.6~1.8.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. The embodiment of the present invention provides a DBEF brightness enhancement film system structure. It uses two materials with different refractive indices to alternately stack to form a reflective unit. Based on the reflective unit, the thickness of the two stacked film layers is improved and designed. Then, multiple reflective units with film layers of different thicknesses are stacked. The resulting film system transmits P light and maintains a high reflectivity for S light throughout the entire visible light band, achieving a brightening effect and meeting the requirements of DBEF brightness enhancement film. 2. A DBEF brightness enhancement film system structure provided by an embodiment of the present invention stacks multiple reflective units with different thickness ratios of film layer 1 and film layer 2 to obtain a variable thickness ratio stacked film system structure, which can meet the requirement of high reflectivity of S light covering the entire visible light band; 3. A DBEF brightening film system structure provided by an embodiment of the present invention limits the thickness ratio of film layer 1 to film layer 2 to be constant. By simultaneously and equally varying the thickness of film layer 1 and film layer 2, reflective units of varying thicknesses are obtained. Multiple reflective structures with film layer thicknesses varying in equal gradients are stacked to form a layer-gradient stacked film system structure, which can meet the requirement for high reflectivity of S light covering the entire visible light band. 4. A DBEF brightening film system structure provided in an embodiment of the present invention is stacked in two different ways, namely, a film system structure A obtained by stacking eight reflective units with different thickness ratios and a film system structure B obtained by stacking eight reflective units with gradient changes in the film layers, both of which can meet the high reflection of S light in the visible light band. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without making any creative efforts.

[0028] Figure 1 The embodiment 1 of the present invention provides the following embodiments with different refractive indices: Optical properties of the reflective unit; Figure 2 The optical characteristics of the reflective units with different stacking periods T provided in Example 2 of the present invention; Figure 3 The optical characteristics of the reflective unit with different film thickness ratios provided in Example 3 of the present invention; Figure 4 The optical characteristics of the reflective unit with different film thickness ratios provided in Example 3 of the present invention; Figure 5 The optical characteristics of the variable thickness ratio stacked film structure with different stacking numbers provided in Example 4 of the present invention; Figure 6 The optical properties of the variable thickness ratio stacked film structure provided in Example 5 of the present invention and the N8 film structure provided in Example 4; Figure 7 The optical properties of the layer gradient stacked film structure with different Δd provided in Example 6 of the present invention; Figure 8 The optical properties of the film structure A provided in Example 5 and the film structure B provided in Example 6 of the present invention; Figure 9 The film structure A provided in Example 5 of the present invention is at different incident angles. Optical properties under Figure 10 The film structure B provided in Example 6 of the present invention is at different incident angles. The optical properties of . DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples and drawings. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0030] In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that these specific details are not necessarily required to practice the present invention. In other embodiments, well-known construction materials or methods are not specifically described to avoid obscuring the present invention.

[0031] Throughout this specification, references to "one embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present invention. Therefore, appearances of the phrases "one embodiment," "an embodiment," "an example," or "an example" in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, or characteristics may be combined in one or more embodiments or examples in any suitable combinations and / or subcombinations. Furthermore, it will be understood by those of ordinary skill in the art that the figures provided herein are for illustrative purposes only and are not necessarily drawn to scale. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0032] In the description of the present invention, the terms "front", "back", "left", "right", "up", "down", "vertical", "horizontal", "high", "low", "inside", "outside", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limiting the scope of protection of the present invention.

[0033] Example 1 An embodiment of the present invention provides a reflection unit, which is represented by ( HL ) 20 , H Indicates the optical reference thickness of the PEN film (one quarter of the reference light wavelength). L represents the reference optical thickness of the PEN copolymer film layer. The PEN film layers are alternately stacked with a stacking period of T = 20. The refractive index n1 of the PEN copolymer film layer is 1.4, and the biaxial refractive indices of the PEN film layer are n1 = 1.4 and n2 = 1.6-1.8, respectively. In this embodiment, specific values for the reference optical thickness of the PEN film layer and the reference optical thickness of the PEN copolymer film layer are not given. Persons skilled in the art will be able to select and design these values based on actual product requirements.

[0034] Figure 1 The reference wavelength is , in the case of vertical incidence, that is With different refractive indices The optical characteristics of the reflective unit are shown in the figure. As can be seen, the reflective unit, formed by alternating layers of two materials, can reflect S light within a certain range of the reference wavelength. As the refractive index n2 increases—that is, the difference Δn between n1 and n2—the reflectivity of the reflective structure increases, and the wavelength range covered by the high reflectivity also expands. For n2 = 1.6-1.8, the reflection of S light within the reference wavelength range can reach over 90%.

[0035] The film layer of the present invention adopts the traditional multi-coextrusion molding method. During this process, stretching will cause molecular chain orientation, resulting in changes in the refractive index in various directions, thereby producing birefringence. Therefore, due to the limitations of the PEN material structure and processing technology, the refractive index change caused by the stretching process is generally around 0.3, and n2 cannot be increased indefinitely. Therefore, considering all factors, the optimal value of n2 can be selected as 1.7.

[0036] Example 2 An embodiment of the present invention provides a reflection unit, which is represented by ( HL ) T , H Indicates the optical reference thickness of the PEN film layer, L Denotes the base optical thickness of a PEN copolymer film layer stacked alternately with a stacking period of T. The refractive index of the PEN copolymer film is n1 = 1.4, and the biaxial refractive indices of the PEN film are n1 = 1.4 and n2 = 1.7. T = 10-50.

[0037] Figure 2 The reference wavelength is , in the case of vertical incidence, that is The optical properties of reflective units with different stacking periods T are shown in the figure. As can be seen from the figure, the reflectivity of the reflective structure increases with the number of stacked layers, reaching its maximum value at a period of T = 20, almost covering the 450-650nm range. Thereafter, the reflectivity increases only slightly with increasing period T. Considering the film fabrication process, the minimum number of film layers should be used to achieve the desired function, so a stacking period T of 20 is preferred.

[0038] Example 3 The embodiment of the present invention provides a reflection unit, which is represented by (a HL ) 20 , H Indicates the optical reference thickness of the PEN film layer, L Indicates the reference optical thickness of the PEN copolymer film layer, H=L, a represents the ratio Φ of the PEN film thickness to the optical reference thickness, ranging from 0 to 2. The PEN film layers and the PEN copolymer film layers are alternately stacked with a stacking period T = 20. The refractive index n1 of the PEN copolymer film layer is 1.4, and the biaxial refractive indices of the PEN film layer are n1 = 1.4 and n2 = 1.7, respectively.

[0039] Figure 3 and Figure 4 The reference wavelength is , under vertical incidence, the optical characteristics of the reflective unit with different PEN film layer and PEN copolymer film layer thickness ratio Φ. Figure 3 As can be seen from the figure, as the thickness ratio increases, the high reflectivity band moves from short wavelength to long wavelength, and the covered band gradually becomes wider. When Φ increases from 0.5 to 1.5, the high reflectivity band moves from 392-434nm to 656-724nm, and the width of the high reflectivity band also increases from 0.5 to 1.5. Increased to However, when the thickness Φ=2.0, the high reflection band reappears in the short wave region, and the coverage band is larger than When the Figure 6 As shown in the figure, when the thickness ratio increases exponentially to 3-9 times, it is clearly found that the high-reflection band coverage area becomes increasingly narrow. Therefore, in this embodiment, Φ<2 is preferred. The reflective unit provided in this embodiment can achieve a film structure with different high-reflection band coverage areas by varying the thickness ratio of the PEN film layer to the PEN copolymer film layer.

[0040] Example 4 An embodiment of the present invention provides a variable thickness ratio stacked film structure, which is formed by stacking multiple reflective units with different film thickness ratios as described in Example 3. Specifically, with a reflective unit with a thickness ratio of 1 as a reference, reflective units with thickness ratios less than 1 and greater than 1 are stacked towards both ends of 1. This embodiment provides four film structures with a stacking number N of reflective units of 5-8, which are specifically represented as follows:

[0041] Figure 5 The reference wavelength is , under normal incidence, the optical properties of a variable thickness ratio stacked film structure with different stacking numbers. As can be seen from the figure, as the number of stacks increases, the high reflectivity band of the film structure for S light gradually widens. When the number of stacks N = 5-7, some high reflectivity bands are still not covered. As the number of stacks N increases to 8, the film structure basically achieves high reflectivity coverage of the entire visible light band. Therefore, the preferred stacking number N of reflective units in the film structure is preferably 8.

[0042] Example 5 In the technology of Example 4, Figure 5 It can be seen that the reflectivity of the N8 film structure is about 95% near the wavelength of 450nm, and there is still room for improvement.

[0043] Therefore, an embodiment of the present invention provides a variable thickness ratio stacked film structure. The thickness ratio of each reflective unit in the film structure is further improved so that the thickness ratios of different reflective units are changed by an equal amount with a difference of 1.5, thereby obtaining a film structure A, which is specifically represented as follows:

[0044] Figure 6 Figure 2 shows the optical properties of the variable thickness ratio stacked film structure of this embodiment and the N8 film structure of Example 4. It can be seen that by limiting the variation of the thickness ratio of the reflective units in the film structure of this embodiment, the reflectivity can be maintained above 98% at a short wavelength near 450nm. At the same time, the reflectivity curve is relatively more stable across the entire visible light band, and the resulting film structure can better meet performance requirements.

[0045] Example 6 An embodiment of the present invention provides a layer gradient stacked film structure, which is formed by stacking a plurality of reflective units, wherein the reflective unit is represented by (a H a L ) 20 , H Indicates the optical reference thickness of the PEN film layer, L represents the reference optical thickness of the PEN copolymer film layer, and a represents the ratio of the thickness of the PEN film layer or PEN copolymer film layer to the corresponding optical reference thickness, ranging from 0 to 2. The PEN film layers and the PEN copolymer film layers are alternately stacked with a stacking period of T = 20. The refractive index of the PEN copolymer film layer is n1 = 1.4, and the biaxial refractive indices of the PEN film layer are n1 = 1.4 and n2 = 1.7, respectively.

[0046] The thickness ratio of the film layers remains constant between different reflective units, while the thicknesses of the PEN and PEN copolymer films vary by equal amounts. This means that the thickness of a varies by equal amounts of Δd, with Δd ranging from 0 to 0.2. The layer-gradient film structure is stacked by taking a reflective unit with an a value of 1 as the base, and stacking reflective units with equal amounts of Δd towards either end of 1.

[0047] Where Δd is 0.1, N=8, and the layer gradient film structure B is obtained, which is specifically expressed as follows:

[0048] Figure 7The optical properties of layer-gradient stacked film structures with different Δd values are shown in the figure. As can be seen from the figure, when Δd = 0, the film structure (HL) is 160, which is equivalent to simply increasing the period of the basic reflective unit, and its high reflectivity coverage band does not expand. When Δd = 0.05, the high reflectivity coverage band expands to 450-700nm. It is not until Δd = 0.1 that high reflectivity is achieved across the entire visible light band. As Δd continues to increase, the reflectivity curve develops some low reflectivity troughs, and the high reflectivity region narrows, resulting in a decrease in optical properties. Therefore, Δd is preferably 0.1, and the optical properties of the resulting film structure B meet the performance requirements.

[0049] The optical properties of the film structure A formed by stacking reflective units with different thickness ratios in Example 5 and the film structure B formed by stacking reflective units with gradient film layer changes in Example 6 were compared. Figure 8 As shown, film structure A and film structure B can meet the requirements of high reflectivity in the entire visible light band.

[0050] While the reflectivity of film structure A fluctuates slightly across the entire visible light band, it consistently remains above 98%. The reflectivity of film structure B is relatively stable overall, with only noticeable fluctuations in the short-wavelength region of 420nm, where the reflectivity drops to 94.5%. Film structure A performs even better in terms of reflectivity. Overall, both film systems established by this invention can meet practical needs.

[0051] In addition, the film structure A formed by stacking the reflective units with different thickness ratios in Example 5 is The optical properties of the embodiment 6 are compared with those of the embodiment 1 under different incident angles. The optical properties of the following are compared. Figure 9 and Figure 10 As shown, with the incident angle As the incidence increases, the high-reflection coverage bandwidth of the two film structures gradually narrows, and the high-reflection band tends to shift toward the shorter wavelength direction. This is because the effective optical thickness of the film structure decreases when the incident light is oblique.

[0052] Further analysis revealed that the film structure A exhibited a more significant response difference to the change of the incident angle than the film structure B. That is, as the incident angle increases, the film structure A moves more toward the short-wave direction. In the case of The reflectivity in the vicinity drops sharply, while the film structure B still maintains a relatively high reflectivity level.

[0053] In general, the two film structures have different reflection characteristic curves in the visible light band. The reflectivity of film structure A remains very high in the entire visible light band. Although film structure B has obvious fluctuations in the short-wave region, both can well meet the high reflection of S light in the visible light band. After considering the oblique incidence of the light source, due to the reduction of the effective optical thickness of the film structure, the reflection range of the two film systems has a certain degree of shift to the short wave. In this case, film structure B performs better in terms of band coverage and incident angle adaptability. The layer gradient stacking film structure is also more practical than the variable thickness stacking film structure. In subsequent film processing and manufacturing, film structures with different stacking methods can be selected according to actual needs.

[0054] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A DBEF brightening film system structure, characterized in that: It includes a plurality of reflective units stacked in sequence, The reflective unit includes a plurality of film layer structures stacked in sequence, each film layer structure includes a first film layer and a second film layer, and the refractive indexes of the first film layer and the second film layer are different; Within the same reflective unit, the thickness of the film layer structure is the same; The thickness of the film layer structure is different between different reflective units.

2. The DBEF brightness enhancement film system structure according to claim 1, characterized in that: The reflection unit is (a H b L ) T express; Where T represents the stacking period of the film structure, H Indicates the base thickness of film layer 1, L represents the reference thickness of the second film layer, a represents the ratio of the first film layer in the reflective unit to the corresponding reference thickness, and b represents the ratio of the second film layer in the reflective unit to the corresponding reference thickness; The sum of a and b is different between different reflection units.

3. The DBEF brightness enhancement film system structure according to claim 2, characterized in that: Along the stacking direction of the reflective units, the thickness of the film layer structure increases or decreases between different reflective units.

4. The DBEF brightness enhancement film system structure according to claim 2, characterized in that: The ratio of the thickness of the first film layer to the thickness of the second film layer in the film layer structure is different between different reflective units.

5. The DBEF brightness enhancement film system structure according to claim 4, characterized in that: Reference thickness of the first film layer H and Reference thickness of the second film layer L Equal, 0 < a < 2, 0 < b < 2, and the ratio of a to b is different between different reflection units.

6. The DBEF brightness enhancement film structure according to claim 2, characterized in that: The ratio of a to b is the same between different reflective units, and along the stacking direction of the reflective units, the thickness of the film layer structure increases or decreases by the same amount between different reflective units.

7. The DBEF brightness enhancement film system structure according to claim 2, characterized in that: In the reflection unit, the stacking period T of the film layer structure ranges from 10 to 50, and the T value is the same among different reflection units.

8. The DBEF brightness enhancement film structure according to claim 1, characterized in that: The stacking period of the reflection unit is ≥8.

9. The DBEF brightness enhancement film structure according to claim 1, characterized in that: The biaxial orientation refractive index of the film layer 1 is different, and the biaxial orientation refractive index of the film layer 2 is the same; the biaxial orientation refractive indexes of the film layer 1 are n1 and n2 respectively, the biaxial orientation refractive index of the film layer 2 is n1, and n2 is greater than n1.

10. The DBEF brightness enhancement film system structure according to claim 1, characterized in that: The first film layer is made of polyethylene naphthalate (PEN), and the second film layer is made of polyethylene naphthalate copolymer.

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