High-brightness interference-eliminating optical diaphragm

Abstract

The high-brightness interference-eliminating optical film comprises a diffusion film (500), an upper prism film (100) and a lower prism film (200), a plurality of prism structures (201) arranged in parallel are formed on the upper prism film (100) and the lower prism film (200), the diffusion film (500) at least comprises an anisotropic diffusion layer (501), ellipsoidal PMMA particles (511) are dispersed in the anisotropic diffusion layer (501), and the ellipsoidal PMMA particles (511) are uniformly distributed in the anisotropic diffusion layer (501). The ellipsoidal PMMA particles (511) are oriented and arranged along the stretching direction; the thickness of the anisotropic diffusion layer (501) is 30-60 [mu] m. According to the utility model, through the arrangement of the diffusion film comprising the anisotropic diffusion layer, the high brightness of light transmission can be maintained, the transverse scattering of light can be enhanced under the condition that the brightness is not reduced, the interference is effectively eliminated, and the contradiction that the high brightness and the interference elimination are difficult to harmonize in the prior art is solved.

Description

Technical Field

[0001] This utility model relates to a high-brightness anti-interference optical film. Background Technology

[0002] The backlight module of a liquid crystal display includes various optical films with different functions. For example, the relevant prior art is described in detail in CN 101354455 A, CN106199788 A, CN 104698518 A, and CN 112630875 B.

[0003] For example, a DPP composite film is disclosed in CN 115963662 B, a previous application filed by the applicant, such as... Figure 1 As shown, the DPP composite film includes a diffusion film 500, an upper prism film 100, a lower prism film 200, and a first adhesive layer 310 and a second adhesive layer 410 that bond the three together. Multiple parallel prism structures 201 are formed on both the upper prism film 100 and the lower prism film 200. The diffusion film 500 includes a substrate layer 51 at the bottom and a microsphere scattering layer 52 coated on top of the substrate layer 51.

[0004] Figure 1 For ease of understanding, the diagram shows that the prism structures 201 on the upper prism film 100 and the lower prism film 200 are arranged in parallel directions. However, in real products, in most cases, the prism structures on the two prism films are arranged at a certain angle. For example, the prism structures on the two prism films are placed orthogonally (such as one in the X direction and the other in the Y direction).

[0005] Prism structures on the same prism film are generally arranged parallel to each other, resulting in periodic repetition of each prism structure on a spatial scale. This leads to overlap in the spatial frequency distribution of prism structures between two prism films. The more regular the periodicity of the prism structure arrangement, the more severe the spatial frequency overlap. When the prism structures of two prism films intersect at an angle, especially when the angles are orthogonal, this spatial frequency overlap easily forms a striped pattern. This striped pattern is not "optical interference" in the traditional sense, but rather a "beat frequency" phenomenon caused by the superposition of two periodic structures, commonly referred to as moiré patterns formed by spatial frequency interference in the field of liquid crystal displays.

[0006] One solution to eliminate these interference fringes is to disrupt the regular arrangement of the prism fringes, thereby eliminating the regular brightness variations caused by the regular arrangement of the prism fringes, and thus reducing or eliminating the interference fringes generated by the prism sheet. This is described in detail in the applicant's previous application, CN 104698518 A. However, the manufacturing of prism fringes cannot completely avoid repetition, and as display sizes increase, this periodic structural superposition cannot be completely avoided.

[0007] Another approach is to mitigate interference fringes using a diffusion film. The scattering layer on the diffusion film disperses the concentrated light, resulting in a wider angular distribution of light passing through the prism film. This "dispersion" blurs the structural correspondence between the prisms, thus weakening the contrast of the interference fringes; however, if the diffusion effect is insufficient, interference may still be visible. The diffusion film essentially disperses some of the light that could otherwise be focused forward, reducing brightness enhancement efficiency. Maximizing the diffusion capability would reduce overall luminance, while large-size displays require higher luminance. Therefore, there is an irreconcilable contradiction between eliminating interference by improving diffusion capability and increasing film luminance. Summary of the Invention

[0008] The technical problem to be solved by this application is to provide a high-brightness anti-interference optical film to reduce or avoid the problems mentioned above.

[0009] To address the aforementioned technical problems, this application proposes a high-brightness anti-interference optical film, comprising a diffusion film, an upper prism film, and a lower prism film. Multiple parallel prism structures are formed on both the upper and lower prism films. The diffusion film includes at least one anisotropic diffusion layer, within which ellipsoidal PMMA microparticles are dispersed. These ellipsoidal PMMA microparticles are oriented along the stretching direction. The thickness of the anisotropic diffusion layer is 30-60 μm.

[0010] Preferably, the ellipsoidal PMMA microparticles have a major axis diameter of 6-10 μm and a minor axis diameter of 2-5 μm.

[0011] Preferably, the surface of the anisotropic diffusion layer is coated with a subwavelength scattering structure layer, in which PMMA nanoparticles with a particle size of 50-300 nm are dispersed; the thickness of the subwavelength scattering structure layer is 3-5 μm.

[0012] This invention, by incorporating a diffusion film with an anisotropic diffusion layer, maintains high light transmission brightness while enhancing lateral light scattering without reducing brightness, effectively eliminating interference and resolving the inherent contradiction between high brightness and interference reduction in existing technologies. Furthermore, this invention can further add a subwavelength scattering structure layer to the surface of the anisotropic diffusion layer, which can further enhance the effectiveness of suppressing interference fringes on top of the existing high brightness and interference reduction limits. Moreover, the emission angle transition of the scattered light is more uniform, thus achieving the dual goals of optical uniformity and fringe reduction while maintaining the high brightness of the thin film. Attached Figure Description

[0013] The accompanying drawings are intended only to illustrate and explain this application and do not limit the scope of this application.

[0014] Figure 1 The diagram shown is a structural schematic of a DPP composite membrane disclosed in the prior art.

[0015] Figure 2 The diagram shown is a structural schematic of a high-brightness anti-interference optical film according to a specific embodiment of this application.

[0016] Figure 3 The diagram shown is a structural schematic of a high-brightness anti-interference optical film according to another specific embodiment. Detailed Implementation

[0017] To provide a clearer understanding of the technical features, objectives, and effects of this application, specific embodiments are now described with reference to the accompanying drawings. Identical components are denoted by the same reference numerals.

[0018] based on Figure 1 The present application proposes an improved high-brightness anti-interference optical film, which, in contrast to the prior art shown, is a high-brightness anti-interference optical film. Figure 1 Similar to the prior art, the high-brightness anti-interference optical film of this application also includes a diffusion film 500, an upper prism film 100, a lower prism film 200, and a first adhesive layer 310 and a second adhesive layer 410 that bond the three together. Multiple parallel prism structures 201 are formed on both the upper prism film 100 and the lower prism film 200. Unlike the prior art, this invention improves the diffusion film 500, as shown in the specific improved structure below. Figure 2 , 3 As shown.

[0019] For ease of understanding, this application is as follows: Figure 2 Only the improved diffusion film 500 is shown in the image. The structures of the upper prism film 100 and lower prism film 200 of this invention can be referenced. Figure 1 To understand.

[0020] Figure 1 In the prior art diffusion film 500, the microbead scattering layer 52 contains PMMA microbeads, which can diffuse light, increase product haze to shield bright spots, increase the product viewing angle, and weaken the contrast of interference fringes. However, as described in the background art, the microbead scattering layer 52 actually reduces the overall brightness of the film, thus only weakening the interference fringes is possible, not eliminating them. In the case of high brightness requirements for large-size displays, especially when the backlight system uses a high-density Mini-LED light source, interference fringes are more likely to appear and the contrast is more pronounced. Relying solely on the microbead scattering layer 52 cannot solve the technical problem of interference elimination and will also reduce the overall brightness.

[0021] In view of this, the present invention proposes an improved high-brightness anti-interference optical film, comprising: Figure 2 The diffusion film 500 shown includes at least one anisotropic diffusion layer 501.

[0022] The anisotropic diffusion layer 501 is composed of a PET matrix and ellipsoidal PMMA microparticles 511 dispersed within it. The ellipsoidal PMMA microparticles 511 are oriented along the stretching direction to enhance light scattering in the direction parallel to the film surface and maintain high transmittance in the perpendicular direction. In one specific embodiment, the major axis particle size of the ellipsoidal PMMA microparticles 511 is 6-10 μm, and the minor axis particle size is 2-5 μm. In another specific embodiment, the thickness of the anisotropic diffusion layer 501 is 30-60 μm. In yet another specific embodiment, the mass content of the ellipsoidal PMMA microparticles in the anisotropic diffusion layer is 10-18 wt%.

[0023] Ellipsoidal PMMA microparticles 511 possess an asymmetric structure between their major and minor axes. When blended within a PET matrix, they are randomly distributed and non-directional in the unstretched film. However, if the film is unidirectionally stretched in a molten or softened state at high temperatures, the stretching force causes the major axes of the ellipsoidal microparticles to align and rotate along the stretching direction. Figure 2 As shown, the oriented arrangement of ellipsoidal microparticles gives the film an anisotropic structural characteristic. The ellipsoidal microparticles approximately form a linearly arranged microlens array in the stretching direction. This microstructure has higher transmittance along the short axis and stronger scattering along the long axis, resulting in direction-selective directional scattering. In liquid crystal backlight modules, light needs to penetrate the diffusion film as perpendicularly as possible to enter the LCD panel; if the diffusion film scatters too strongly, it will cause the light angle to shift and the brightness to decrease. The anisotropic diffusion layer has higher transmittance in the vertical direction (along the short axis), which means higher light concentration and less brightness loss. Therefore, compared with traditional isotropic scattering diffusion films, it can maintain a higher peak brightness and has higher luminance. At the same time, the anisotropic diffusion layer has stronger random light scattering in the lateral direction (along the long axis), which can effectively disrupt the periodic light path of the two superimposed prism films, thereby eliminating interference fringes.

[0024] by Figure 1 The existing composite membrane shown is used as a comparative example. Figure 1 The ordinary diffusion membrane 500 shown is replaced with Figure 2 The diffusion film shown includes an anisotropic diffusion layer 501, and three embodiments are designed based on this alternative structure.

[0025] Example 1

[0026] The thickness of the anisotropic diffusion layer is 30 μm, and the mass content of the ellipsoidal PMMA particles dispersed inside the layer is 10 wt%. The size of the ellipsoidal PMMA particles is: major axis diameter 6 μm and minor axis diameter 2 μm.

[0027] Example 2

[0028] The thickness of the anisotropic diffusion layer is 40 μm, and the mass content of the ellipsoidal PMMA particles dispersed inside the layer is 15 wt%. The size of the ellipsoidal PMMA particles is: major axis diameter 8 μm and minor axis diameter 3 μm.

[0029] Example 3

[0030] The thickness of the anisotropic diffusion layer is 60 μm, and the mass content of the ellipsoidal PMMA particles dispersed inside the layer is 18 wt%. The size of the ellipsoidal PMMA particles is: major axis diameter 10 μm and minor axis diameter 5 μm.

[0031] Comparative Example

[0032] A standard diffusion film with a thickness of 50 μm contains 10 μm spherical particles, with a mass content of 15 wt% in the layer.

[0033] Brightness enhancement is based on standard white field test conditions (5000K backlight, center measurement); fringe suppression is a subjective-objective combined score, with 10 being "fringe completely invisible to the naked eye" and 0 being "obvious interference fringes".

[0034] As can be seen from the comparison, this utility model, by setting a diffusion film containing an anisotropic diffusion layer, can maintain the high brightness of light transmission and enhance the lateral scattering of light without reducing the brightness, effectively eliminating interference and solving the contradiction between high brightness and interference elimination that is difficult to reconcile in the prior art.

[0035] Furthermore, the high-brightness light obtained by the two prism films will produce some transmission loss after being diffused laterally through the anisotropic diffusion layer 501 of the diffusion film 500. Although the directional arrangement of ellipsoidal PMMA particles 511 in the anisotropic diffusion layer 501 can offset this loss, the anisotropic diffusion layer 501 is only of practical value if the brightness value is not reduced. Therefore, the ability of the anisotropic diffusion layer 501 to suppress interference fringes has a certain upper limit. Exceeding this upper limit will reduce the brightness value.

[0036] For example, in low-cost display applications where visual requirements are not extremely stringent (such as ordinary backlighting rather than professional display applications), a diffusion film 500 with only one anisotropic diffusion layer 501 can meet the requirements for high brightness and interference suppression, as shown in Examples 1-3, especially Examples 2 and 3. However, in high-end display scenarios that require both high contrast and high uniformity, especially when using high-density Mini-LED light sources, higher angular stability is required, such as for ultra-wide viewing angles. Since interference fringes are more pronounced under high contrast, a single anisotropic diffusion layer 501 is insufficient to suppress the visibility of the fringes. In this case, an additional diffusion structure needs to be added on top of the anisotropic diffusion layer 501.

[0037] Therefore, as Figure 3 As shown, this invention coats a subwavelength scattering structure layer 502 onto the surface of an anisotropic diffusion layer 501. The subwavelength scattering structure layer 502 comprises an optically transparent coating containing dispersed PMMA nanoparticles 521 with a particle size of 50-300 nm. The PMMA nanoparticles 521 are randomly arranged along the film surface direction, forming a surface layer with a subwavelength-scale undulating structure after curing. This further suppresses interference fringes and improves the uniformity of the angular distribution of emitted light. In one specific embodiment, the volume fraction of PMMA nanoparticles 521 in the subwavelength scattering structure layer 502 is 5-8 vol%. In another specific embodiment, the thickness of the subwavelength scattering structure layer 502 is 1-2 μm. The optically transparent coating is preferably an acrylic emulsion containing a UV curing agent.

[0038] The working principle of the subwavelength scattering structure layer is as follows: the irregular arrangement and slight aggregation of particles in the coating create surface roughness and undulations, causing phase disturbances in light waves as they pass through the surface; the optical path coherence condition required for interference is disrupted; as a result, the fringe contrast is "blurred" or "dissolved," i.e., the anti-fringe effect. This is equivalent to adding a slightly frosted layer to a mirror, disrupting its reflective fringes without significantly reducing transmittance. When the particle size in the coating is much smaller than the wavelength of visible light (400nm), Rayleigh scattering is triggered; when the particle size is close to the wavelength of visible light, Mie scattering is triggered. Figure 1 The existing microbead scattering layer 52 shown contains PMMA microbeads of mixed sizes, which simultaneously trigger Rayleigh and Mie scattering.

[0039] When the PMMA nanoparticles (50-300nm) used in the coating are located precisely in the transition region between Rayleigh scattering and Mie scattering mechanisms, a subwavelength scattering structure is formed. This subwavelength scattering structure can produce gentle, multi-angle emitted light. This "soft diffusion" effect allows light to focus vertically while spreading smoothly in the angular direction, thereby improving the uniformity of the emission angle distribution. Compared to macroscopic optical structures (such as prisms or columnar scattering), the angular distribution of this subwavelength scattering structure has a more natural transition, without causing brightness hotspots or shadow bands. Compared to the case where Rayleigh and Mie scattering are triggered simultaneously, the subwavelength scattering structure of this invention has higher light scattering efficiency, resulting in less brightness loss. It can assist in interference cancellation while maintaining greater luminance.

[0040] Example 4

[0041] Based on the anisotropic diffusion layer in Example 1, a subwavelength scattering structure layer is added. The PMMA nanoparticles dispersed in the subwavelength scattering structure layer have a particle size of 50 nm and a volume fraction of 5 vol%. The thickness of the subwavelength scattering structure layer is 1 μm.

[0042] Example 5

[0043] Based on the anisotropic diffusion layer in Example 2, a subwavelength scattering structure layer is added. The PMMA nanoparticles dispersed in the subwavelength scattering structure layer have a particle size of 150 nm and a volume fraction of 6 vol%. The thickness of the subwavelength scattering structure layer is 1.5 μm.

[0044] Example 6

[0045] Based on the anisotropic diffusion layer in Example 3, a subwavelength scattering structure layer is added. The PMMA nanoparticles dispersed in the subwavelength scattering structure layer have a particle size of 300 nm and a volume fraction of 8 vol%. The thickness of the subwavelength scattering structure layer is 2 μm.

[0046] The brightness increase values ​​are all calculated based on comparative ratios.

[0047] This invention, by adding a subwavelength scattering structure layer to the surface of the anisotropic diffusion layer, further enhances the effectiveness of suppressing interference fringes while maintaining high brightness and interference suppression limits. Moreover, the transition of the scattered light's exit angle is more uniform, with negligible luminous flux loss. The subwavelength scattering structure layer functions to "soften the interference behavior of light" and "smooth the angular transition of light." By disrupting coherence through microscale structures, it achieves the dual goals of optical uniformity and fringe removal while maintaining the film's high brightness.

[0048] The following is a reference to the appendix. Figure 1-3 The preparation method of the high-brightness anti-interference optical film of this invention is further described below. As shown in the figure, the preparation method of the high-brightness anti-interference optical film of this application includes the following steps.

[0049] For example Figure 2 The diffusion film with the structure shown is prepared by the following steps: PET chips and ellipsoidal PMMA microparticles 511 are weighed and fed into a twin-screw extruder for blending, and then extruded through a die to form a thick sheet. During the extrusion process, the temperature of the cooling roller is controlled at 40-60℃ to ensure that the ellipsoidal PMMA microparticles do not undergo significant changes. The thick sheet is then subjected to unidirectional stretching to orient the ellipsoidal PMMA microparticles 511 along the stretching direction, thereby obtaining an anisotropic diffusion layer 501 with anisotropic light diffusion characteristics; the stretching ratio is 3-4 times, and the stretching temperature is 90-110℃. After stretching, the film is cut at a 45° angle between the length direction and the stretching direction, and then wound up to obtain a diffusion film composed of anisotropic diffusion layers for later use. Finally, the prepared diffusion film is composited with two prism films in a conventional manner to form a high-brightness anti-interference optical film.

[0050] In this process, a specific cutting direction is deliberately chosen after stretching, so that the length direction of the diffusion film forms a 45° angle with the stretching direction. When the diffusion film is combined with the prism film, the major axis of the ellipsoidal PMMA particles in the anisotropic diffusion layer of the diffusion film can form a 45° angle with the prism structure direction of the prism film, thus obtaining the most ideal anti-interference fringe direction. The working principle is as follows: because the ellipsoidal PMMA particles are oriented along their major axis (i.e., along the stretching direction) through unidirectional stretching, light is mainly scattered along this direction. If the main scattering direction of the light is parallel or perpendicular to the prism structure, it may cause directional enhancement and overlap, which may induce new interference fringes. However, cutting the diffusion film at a certain angle (not 0 degrees or 90 degrees) with the stretching direction ensures that the main scattering direction forms a non-0-degree or non-90-degree angle with the prism structure during recombination. At this point, for the entire composite film system, the directional high-frequency components that might have caused interference coupling are dispersed or homogenized. When observed by the human eye, the interference fringes are stretched in space and the energy distribution is broadened, resulting in a reduced or even completely invisible interference effect. If the cutting angle is 45°, the main scattering direction of the diffusion film, relative to the two mutually perpendicular and overlapping prism structures, is located precisely in the middle of the angle between the two prism structures. That is, the 45° cut makes the scattering distribution diagonal, forming a complementary relationship with the prism's converging direction. Therefore, it can maximize the avoidance of brightness loss, achieve the optimal scattering angle distribution, and possess the most uniform lateral brightness transition. This diagonal composite can be achieved through a simple 45° cut; the operation is extremely simple, requires no additional requirements for subsequent composite equipment, is very low-cost, yet yields optimal results.

[0051] Furthermore, regarding Figure 3 The diffusion film with the structure shown is further prepared by the following steps: PMMA nanoparticles 521 are dispersed in an acrylic emulsion system containing a UV curing agent to form a coating by ultrasonic dispersion and stirring; the coating is applied to one side surface of a cut anisotropic diffusion layer 501 using a doctor blade; and the coating is cured by UV irradiation, thereby forming a subwavelength scattering structure layer 502 with a subwavelength scale scattering structure on the surface of the anisotropic diffusion layer 501. The film is then wound up to obtain a diffusion film 500 composed of the anisotropic diffusion layer and the subwavelength scattering structure layer for later use. Finally, the prepared diffusion film 500 is composited with two prism films in a conventional manner to form a high-brightness anti-interference optical film.

[0052] Those skilled in the art should understand that although this application is described by way of multiple embodiments, not every embodiment contains only one independent technical solution. This description is merely for clarity, and those skilled in the art should understand the specification as a whole and consider the technical solutions involved in each embodiment as being able to be combined with each other to form different embodiments to understand the scope of protection of this application.

[0053] The above description is merely an illustrative embodiment of this application and is not intended to limit the scope of this application. Any equivalent changes, modifications, and combinations made by those skilled in the art without departing from the concept and principles of this application shall fall within the scope of protection of this application.

Claims

1. A high-brightness anti-interference optical film, comprising a diffusion film (500), an upper prism film (100) and a lower prism film (200), a plurality of prism structures (201) are formed on the upper prism film (100) and the lower prism film (200) in parallel, characterized in that, The diffusion film (500) comprises at least one anisotropic diffusion layer (501), wherein ellipsoidal PMMA microparticles (511) are dispersed in the anisotropic diffusion layer (501), and the ellipsoidal PMMA microparticles (511) are arranged in the stretching direction; the thickness of the anisotropic diffusion layer (501) is 30-60 μm.

2. The high-brightness antireflection optical film of claim 1, wherein The long axis particle size of the ellipsoidal PMMA microparticles (511) is 6-10 μm, and the short axis particle size is 2-5 μm.

3. The high-brightness antireflection optical film of claim 1 or 2, wherein The surface of the anisotropic diffusion layer (501) is coated with a subwavelength scattering structure layer (502), wherein PMMA nanoparticles (521) with a particle size of 50-300 nm are dispersed in the structure layer (502); the thickness of the subwavelength scattering structure layer (502) is 3-5 μm.

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