A multilayer composite film for outdoor mini LED display screen and a preparation method thereof

Abstract

The application relates to the technical field of display packaging, and discloses a multilayer composite film for an outdoor Mini LED display screen and a preparation method thereof.The composite film comprises, in sequence from the side close to a light-emitting chip to the light-emitting side along the thickness direction, a light extraction control layer, a light spectrum control layer, a viewing angle compensation layer and a surface functional layer.The light extraction control layer reduces total reflection loss and improves light extraction efficiency through refractive index matching and micro-nano structure; the light spectrum control layer realizes ambient light suppression through multilayer interference filtering or selective absorption design; the viewing angle compensation layer optimizes the angle distribution of emitted light through a microlens array; and the surface functional layer provides scratch resistance, stain resistance and ultraviolet protection.The composite film can also comprise a seam compensation structure in an edge area.The application realizes the outdoor display effect of high light efficiency, high contrast, wide viewing angle and no seam, can be widely applied to the field of outdoor Mini LED display screens and the like, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of display packaging technology, and in particular to a multilayer composite film for outdoor Mini LED displays and its preparation method. Background Technology

[0002] As Mini LED display technology expands into outdoor large screens, traffic guidance screens, advertising media, and other fields, the requirements for display effects are becoming increasingly stringent. Outdoor displays face challenges such as strong ambient light interference, the need for wide viewing angles, and visual seams caused by multi-module splicing, which place higher demands on the optical performance of packaging materials.

[0003] In the prior art, Mini LED packaging mainly adopts the following schemes: (1) single-layer transparent potting compound, which only provides basic protection and has no optical control function; (2) simple diffusion film, which can improve uniformity but has low light extraction efficiency; (3) black coating encapsulation, which can improve contrast but sacrifice brightness. For example, patent CN202410324804.0 discloses a three-layer composite film structure (adhesive layer + PET + black coating), which is mainly used to eliminate splicing seams, but does not optimize the light extraction efficiency and viewing angle characteristics.

[0004] However, the existing technology has the following technical defects: (1) Low light extraction efficiency: The light emitted by the Mini LED chip will undergo total internal reflection and waveguide loss inside the encapsulation layer. According to the optical principle, when light shines from a high refractive index chip (GaN-based material, refractive index about 2.4) to a low refractive index encapsulation material (organosilicon, refractive index about 1.4~1.5), the critical angle of total internal reflection is small, and a large amount of light is confined inside the chip and cannot be emitted. The light extraction efficiency of the traditional encapsulation structure is usually only 60%~70%. (2) Poor ambient light suppression capability: Under strong outdoor ambient light, the contrast of the display screen drops sharply. The existing technology mostly uses black light-absorbing materials, which can suppress reflection but also absorb the emitted light, causing brightness loss, and cannot achieve selective optical control of "high absorption of ambient light and high transmission of emitted light". (3) Poor viewing angle characteristics: The traditional encapsulation film is an isotropic structure, and the emitted light is distributed in a Lambertian pattern. The brightness and color drift under wide viewing angle are serious, which makes it difficult to meet the multi-angle viewing needs of outdoor large screens. (4) Insufficient visual compensation at seams: When splicing multiple modules, the optical discontinuity in the seam area results in obvious dark bands or bright lines. Existing technologies rely on complex electronic compensation algorithms, which are costly and have high hardware requirements, and their effectiveness is limited.

[0005] Although existing research has proposed multi-layer optical film structures, such as interference filters and microlens arrays, they are mostly used in backlight modules or general optical components. They have failed to systematically design for the special needs of Mini LED outdoor displays, especially failing to integrate multiple optical functions such as light extraction, ambient light suppression, viewing angle adjustment, and seam compensation into a single encapsulation film structure. Summary of the Invention

[0006] The purpose of this invention is to provide a multilayer composite film for outdoor Mini LED displays and its preparation method, so as to solve the problems of low light extraction efficiency, poor ambient light suppression, poor viewing angle characteristics and insufficient visual compensation of splicing seams in the prior art, and achieve high light efficiency, high contrast, wide viewing angle and seamless outdoor display effect.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A multilayer composite film for outdoor Mini LED displays, wherein the multilayer composite film is a one-piece structure, comprising, along the thickness direction from the side closest to the light-emitting chip to the light-emitting side, the following components:

[0009] The light that comes into contact with the light-emitting chip is extracted from the control layer;

[0010] A spectral modulation layer disposed on the light extraction modulation layer;

[0011] A viewing angle compensation layer disposed on the spectral modulation layer;

[0012] A surface functional layer disposed above the view compensation layer.

[0013] Preferably, the light extraction control layer comprises a refractive index matching material and / or a micro / nano structure surface;

[0014] The refractive index of the refractive index matching material is between the refractive index of the light-emitting surface of the light-emitting chip and the refractive index of the packaging material. Preferably, the refractive index of the refractive index matching material is 1.5~1.8.

[0015] The surface of the micro / nano structure is one of a periodically or randomly distributed microlens array, a pyramid structure, and a moth-eye structure, with a characteristic size of 0.1~10μm.

[0016] Preferably, the light extraction control layer further includes a transparent resin filled with high-refractive-index nanoparticles;

[0017] The high refractive index nanoparticles are selected from one of titanium oxide, zirconium oxide and zinc oxide, with a particle size of 10~100nm and a mass fraction of 10%~40%.

[0018] Preferably, the spectral modulation layer is composed of alternating layers of high refractive index and low refractive index, and the number of layers in the spectral modulation layer is 4 to 20.

[0019] The high refractive index layer is made of one of titanium oxide, niobium oxide, and silicon nitride, with a refractive index of 1.8 to 2.5.

[0020] The material of the low refractive index layer is selected from silicon oxide, magnesium fluoride and fluoropolymers, and has a refractive index of 1.3 to 1.5.

[0021] Preferably, the spectral modulation layer is a selective absorption layer comprising a light-absorbing dye or a light-absorbing pigment;

[0022] The thickness of the selective absorption layer is 1~10μm;

[0023] The light-absorbing dye or pigment is selected from one or more of perylene dyes, phthalocyanine dyes, and anthraquinone dyes, with a mass fraction of 0.5% to 5%.

[0024] Preferably, the viewing angle compensation layer is a microlens array layer, with the lens unit diameter being 10~100μm and the arrangement period being 10~200μm.

[0025] Preferably, the surface functional layer comprises an anti-scratch resin, a hydrophobic and oleophobic additive, and a UV absorber;

[0026] The scratch-resistant resin is a polyurethane acrylate or a silicone-modified acrylate;

[0027] The hydrophobic and oleophobic additive is a fluorinated compound or an organosilicon compound;

[0028] The ultraviolet absorber is a benzotriazole or hindered amine compound.

[0029] Preferably, the composite film further includes a seam compensation structure disposed in the edge region; the seam compensation structure is an optical microstructure formed in the edge region of the composite film.

[0030] Preferably, the seam compensation structure is selected from one of the gradient refractive index region, microprism array, and local light diffusion region, and its width is 0.1~5mm, which matches the seam width of adjacent modules, and is used to compensate for the visual discontinuity of the seam when multiple modules are spliced.

[0031] An outdoor Mini LED display module includes:

[0032] Circuit board;

[0033] Multiple Mini LED chips are arrayed on the circuit substrate; the multiple Mini LED chips and the circuit substrate are covered with a multilayer composite film.

[0034] The light extraction control layer of the multilayer composite film and the light-emitting surface of the Mini LED chip are in direct contact or indirect contact through an optical matching layer.

[0035] The method for preparing the above-mentioned multilayer composite film includes:

[0036] Step S1: Fabrication of the light extraction control layer: A light extraction control layer with a preset refractive index and / or micro / nano structure is formed on a temporary support substrate by coating, imprinting or etching processes;

[0037] Step S2: Preparation of spectral modulation layer: A spectral modulation layer is formed on the light extraction modulation layer by vacuum deposition, coating or multilayer co-extrusion process;

[0038] Step S3: Fabrication of the viewing angle compensation layer: A viewing angle compensation layer is formed on the spectral modulation layer by imprinting a microlens array;

[0039] Step S4: Prepare the surface functional layer: Coat the viewing angle compensation layer with a resin containing anti-scratch, hydrophobic, oleophobic and UV absorption functions, and cure it;

[0040] Step S5 (optional): Form a seam compensation structure in the edge area of ​​the composite film by local embossing or inkjet printing process;

[0041] Step S6: Peel off the temporary support substrate to obtain the multilayer composite film.

[0042] Preferably, in step S1, the coating speed is 5~20m / min, the wet coating thickness is 15~50μm, the imprinting temperature is 40~90℃, the pressure is 0.5~2.0MPa, and the curing ultraviolet light wavelength is 365nm with an energy density of 800~2000mJ / cm².

[0043] In step S2, vacuum coating is performed using magnetron sputtering or plasma-enhanced chemical vapor deposition (PECVD), with a deposition temperature ≤100℃ and a background vacuum degree ≤5×10~4Pa;

[0044] In step S3, the coating speed is 5~15 m / min, and the curing energy density is 500~1500 mJ / cm³. 2 ;

[0045] In step S4, the coating speed is 5~20m / min, the curing temperature is 80~120℃ or the UV energy density is 800~2000mJ / cm²;

[0046] In step S5, the inkjet printing droplet volume is 1~10pL, and the positioning accuracy is ±10μm.

[0047] The present invention has the following advantages and effects compared with the prior art:

[0048] (1) Significantly improved light extraction efficiency: By matching the refractive index of the light extraction control layer and designing the micro-nano structure, the total internal reflection loss of the chip's emitted light at the packaging interface is reduced. The refractive index matching layer reduces the refractive index difference between the chip and the packaging layer, expanding the critical angle for total internal reflection; the micro-nano structure provides additional light extraction paths. The synergistic effect of the two can improve the light extraction efficiency by more than 30%, enabling outdoor displays to achieve higher brightness with the same power consumption.

[0049] (2) Strong ambient light suppression capability: The spectral modulation layer achieves selective optical modulation of "high transmittance of emitted light and high absorption / reflection of ambient light" through multi-layer interference filtering or selective absorption design. Under strong outdoor ambient light, the contrast of the display screen can be improved by 2 to 3 times, significantly improving the daytime viewing effect.

[0050] (3) Optimization of viewing angle characteristics: The viewing angle compensation layer is designed with a microlens array to make the intensity distribution of the emitted light uniform in a wide angle range, which can improve the brightness uniformity in a ±60° viewing angle range to more than 85%, and eliminate the drastic drift of brightness and chromaticity with the viewing angle.

[0051] (4) Visual compensation of seams: The seam compensation structure in the edge area adjusts the light propagation characteristics of the seam area through optical microstructures, so that it is consistent with the optical performance of the chip area, thereby achieving visual "invisibility" of the seam without the need for complex electronic compensation algorithms.

[0052] (5) Multifunctional integration: Multiple optical functions such as light extraction, spectral control, viewing angle compensation, and surface protection are integrated into a single multilayer composite film, simplifying the display module structure and reducing assembly costs.

[0053] (6) Outdoor environmental adaptability: The surface functional layer provides scratch resistance, anti-fouling and anti-ultraviolet protection, ensuring that the composite film maintains stable optical performance during long-term outdoor use. Attached Figure Description

[0054] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0055] Figure 1 A cross-sectional structural diagram of the multilayer composite membrane provided in an embodiment of the present invention;

[0056] Figure 2 This is a schematic diagram of the micro / nano structure of the light extraction control layer provided in an embodiment of the present invention;

[0057] Figure 3A schematic diagram of the multilayer interference filter structure of the spectral modulation layer provided in an embodiment of the present invention;

[0058] Figure 4 This is a schematic diagram of the microlens array structure of the view compensation layer provided in an embodiment of the present invention;

[0059] Figure 5 This is a process flow diagram for preparing the multilayer composite film provided in an embodiment of the present invention.

[0060] Explanation of reference numerals in the figures: (a) Top view of the microprism array; (b) Side view of the microprism array; 100, light extraction control layer; 200, spectral control layer; 300, viewing angle compensation layer; 400, surface functional layer; 110, high refractive index resin matrix; 120, high refractive index nanoparticles; 130, microlens array; 210, high refractive index layer; 220, low refractive index layer. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0062] It should be noted that the numerical ranges involved in the following embodiments are merely illustrative of preferred embodiments of the present invention. Those skilled in the art can adjust the specific parameters through conventional experiments based on the teachings of the present invention and in combination with specific application requirements to achieve the purpose of the present invention.

[0063] Example 1

[0064] This embodiment provides a multilayer composite film for outdoor Mini LED displays, the structure of which is as follows: Figure 1 As shown, from bottom to top (from the chip side to the light-emitting side), the layers are: light extraction control layer 100, spectral control layer 200, viewing angle compensation layer 300, and surface functional layer 400.

[0065] (I) Material and structural design of each layer

[0066] (1) Light is used to extract the control layer 100, such as Figure 2 As shown:

[0067] This layer is designed to combine refractive index matching and micro / nano structure for dual light extraction enhancement, reducing total internal reflection loss of emitted light at the packaging interface and improving light extraction efficiency.

[0068] Matrix resin 110: High refractive index silicone resin, refractive index 1.55, purchased from Dow Corning Incorporated, USA, product model code OE-6630;

[0069] High refractive index nanoparticles 120: Zirconia nanoparticles (ZrO2) with a refractive index of 2.1 and a particle size of 30 nm, purchased from Daiichi Rare Element Chemical Industry Co., Ltd. of Japan, product model code UEP-30, mass fraction 25%, used to increase the composite refractive index to 1.65.

[0070] Micro / nano structure 130: A hexagonal close-packed microlens array is imprinted on the surface of the layer (away from the chip side), with a lens unit diameter of 5μm, a height of 2μm, and a period of 5μm;

[0071] Layer thickness: 20μm.

[0072] This layer, through refractive index matching and the anti-reflection effect of the microlens structure, can reduce the total internal reflection loss of the chip's emitted light by more than 50% and improve the light extraction efficiency by 30%.

[0073] (2) Spectral modulation layer 200, such as Figure 3 As shown:

[0074] This layer is designed as a multi-layer interference filter structure to selectively transmit the emission wavelength of the Mini LED chip and reflect or absorb ambient light.

[0075] Structure: A total of 12 layers are stacked alternately, consisting of a high refractive index layer 210 (TiO2, refractive index 2.4) and a low refractive index layer 220 (SiO2, refractive index 1.46). The optical thickness of each layer is designed to be 1 / 4 of the center wavelength of the corresponding band.

[0076] Specific design: For RGB three-color Mini LED displays, three high-transmittance zones are designed: red light (620~650nm), green light (520~550nm), and blue light (450~480nm), with transmittance ≥92% for each zone; transmittance for other zones (400~700nm excluding the above three zones) is ≤15%.

[0077] Preparation method: Each layer was sequentially deposited on the light extraction control layer 100 using plasma-enhanced chemical vapor deposition (PECVD). The deposition parameters are shown below:

[0078] Background vacuum: 3×10 -4 Pa;

[0079] Deposition temperature: 90℃;

[0080] TiO2 layer: TiCl4 precursor flow rate 10 sccm, O2 flow rate 50 sccm, RF power 200W, deposition rate 0.8nm / s, the deposition time of each layer is automatically stopped according to optical monitoring (the endpoint is 1 / 4 wavelength optical thickness), and the actual deposition time of each layer is about 35~45s;

[0081] SiO2 layer: precursor SiH4 flow rate 15 sccm, N2O flow rate 60 sccm, RF power 150W, deposition rate 0.5nm / s, deposition time per layer approximately 55~70s;

[0082] It has a total of 12 layers and a total thickness of approximately 2.5 μm.

[0083] The transmittance of this layer is high in the red, green and blue emission bands, but low in other bands.

[0084] (3) View compensation layer 300, such as Figure 4 As shown:

[0085] This layer is designed as a microlens array structure to control the angular distribution of emitted light and improve brightness and color uniformity over a wide viewing angle.

[0086] Matrix resin 320: UV-curable acrylate resin, refractive index 1.52, purchased from Mitsubishi Chemical Corporation, Japan, product name UV-ACRYL R-685;

[0087] Microlens structure 310: A hexagonal close-packed array of convex lenses is imprinted on the surface of the layer (away from the chip side), with a lens unit diameter of 30μm, a radius of curvature of 25μm, and a period of 30μm;

[0088] Layer thickness: 20μm (including the thickness of the substrate layer).

[0089] This microlens array can make the intensity distribution of the emitted light uniform within a horizontal viewing angle range of ±60°.

[0090] (4) Surface functional layer 400:

[0091] This layer provides scratch resistance, stain resistance, and UV protection.

[0092] Matrix resin: silicone-modified polyurethane acrylate, hardness 2H, purchased from BASF, Germany, product name Laromer® LR 9020;

[0093] Hydrophobic and oleophobic additive: Fluorinated acrylate copolymer, purchased from Chemours, USA, product name Capstone® ST-100, 2% by mass, to achieve a water contact angle of 108° and an oil contact angle of 48°.

[0094] UV absorber: Benzotriazole compound, purchased from BASF, Germany, product name Tinuvin® 384-2, mass fraction 1.5%, used to block ultraviolet rays with wavelengths less than 380nm;

[0095] Layer thickness: 8μm.

[0096] This layer protects the underlying optical structure from outdoor environmental damage.

[0097] (ii) Preparation method, such as Figure 5 As shown:

[0098] Step S1: Coat the photorelease control layer 100 of the resin composition (containing high refractive index silicone resin, zirconia nanoparticles and photoinitiator) onto a new PET release film (thickness 50μm, surface release force 20~30g / in) at a coating speed of 10m / min, wet thickness 25μm, using 365nm ultraviolet light at 300mJ / cm². 2 After pre-curing with the correct dosage, a microlens array structure is formed on the surface using nanoimprinting technology. The imprinting temperature is 60℃, the pressure is 1.0MPa, and the holding time is 10s. Then, it is subjected to 365nm ultraviolet light again with a higher energy density of 1000mJ / cm². 2 Completely cured.

[0099] Step S2: TiO2 and SiO2 layers are sequentially deposited on the light extraction control layer 100 using PECVD technology to form a 12-layer interference filter structure spectral control layer 200. The deposition parameters are as described above, and the deposition time for each layer is adjusted according to optical monitoring.

[0100] Step S3: A UV-curable acrylate resin with a viewing angle compensation layer 300 is coated onto the spectral control layer 200 at a coating speed of 8 m / min and a wet thickness of 25 μm. A microlens array is formed using a microlens mold under a pressure of 0.8 MPa and a holding time of 15 s. 365 nm UV light is used with an energy density of 800 mJ / cm². 2 Demold after curing.

[0101] Step S4: Coat the surface functional layer 400 with the resin composition (silicone-modified polyurethane acrylate, fluorinated additives, UV absorber, and photoinitiator) on the viewing angle compensation layer 300 at a coating speed of 12 m / min and a wet thickness of 10 μm using 365 nm UV light at an energy density of 1200 mJ / cm². 2 It solidifies to form a surface protective layer.

[0102] Step S5: This embodiment does not include a seam compensation structure.

[0103] Step S6: Peel off the PET release film to obtain a multilayer composite film with a total thickness of approximately 50.5 μm.

[0104] Example 2

[0105] This embodiment is basically the same as Embodiment 1, except that the spectral control layer 200 adopts a selective absorption layer design and a seam compensation structure is added. The materials, structures and preparation methods of the other layers (light extraction control layer 100, viewing angle compensation layer 300, and surface functional layer 400) are the same as those in Embodiment 1.

[0106] (1) Spectral modulation layer 200 (selective absorption type):

[0107] This layer is used to replace the multilayer interference filter structure in Example 1. It achieves selective absorption of ambient light by adding specific dyes, while maintaining high transmittance of the red, green and blue emission bands of the Mini LED chip.

[0108] Material composition:

[0109] Matrix resin: transparent acrylic resin (refractive index 1.52);

[0110] Selective absorption dyes: A compound system is used, specifically:

[0111] High transmittance dye in the red light band: Perylene dye, trade name Lumogen® Red 300, absorption peak at approximately 580nm;

[0112] High transmittance dyes in the green light band: Phthalocyanine dyes (transmittance in the green light region, absorption peak located around 650nm);

[0113] High transmittance dyes in the blue light band: Anthraquinone dyes (transmit in the blue light region, with an absorption peak of about 560nm).

[0114] Each dye has a mass fraction of 1%, and the total dye mass fraction is 3%.

[0115] Layer thickness: 5μm.

[0116] Function Description:

[0117] This absorption layer effectively absorbs non-display wavelengths in ambient light (especially interference light between the three main red, green, and blue peaks), thereby improving ambient light contrast. Simultaneously, because the dye has high transmittance in its corresponding emission wavelength, it does not affect the chip's emission efficiency. This layer is directly deposited on the light extraction control layer 100 using a solution coating + thermal curing process (80℃ / 5min), eliminating the need for vacuum deposition equipment and reducing manufacturing costs.

[0118] (ii) Joint compensation structure

[0119] To eliminate bright or dark lines caused by abrupt changes in the refractive index at the edge of the encapsulation film when splicing multiple Mini LED display modules, this embodiment sets a gradient refractive index transition zone (1.0 mm wide) at the edge area of ​​the multilayer composite film.

[0120] Implementation method:

[0121] During the fabrication of the light extraction control layer 100, within a 1.0 mm width range at the edge of the film layer, the mass fraction of high-refractive-index nanoparticles (zirconia) was linearly reduced from 25% in the central region to 10% along the edge direction through partitioned coating or gradient inkjet printing. Correspondingly, the refractive index in the affected area linearly decreased from 1.65 to 1.55. The gradient change rate was 0.10 / mm.

[0122] Function Description:

[0123] This gradient structure eliminates optical abrupt changes between the film layer and air or adjacent module encapsulation materials, making brightness differences at the seam visually imperceptible. The seam compensation layer and the light extraction control layer are simultaneously imprinted, without adding any extra steps.

[0124] (III) Explanation of Adjustments to Preparation Method

[0125] The preparation method in this embodiment is basically the same as that in Example 1, with only the following adjustments:

[0126] Step S2 (Spectral modulation layer deposition): The above dye / resin mixture is then applied by spin coating or slit coating, and a 5μm thick absorption layer is formed after thermal curing.

[0127] Step S1 (Optical Extraction Control Layer Forming): Before micro-nano structure imprinting, a concentration gradient distribution of zirconium oxide nanoparticles is formed in the edge region of the PET release film through a multi-channel liquid supply system, and then imprinting and curing are performed.

[0128] The remaining steps (S3, S4, S6) are completely consistent with those in Example 1.

[0129] (iv) Description of technical effects

[0130] This embodiment retains most of the optical and protective advantages of Embodiment 1:

[0131] Reduce total internal reflection loss by optically extracting the modulation layer;

[0132] Improve wide-view uniformity through a view compensation layer;

[0133] The surface functional layer achieves scratch resistance, stain resistance, and UV aging resistance.

[0134] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A multilayer composite film for outdoor Mini LED displays, characterized in that, The multilayer composite film is a single-piece structure, comprising, along the thickness direction from the side closest to the light-emitting chip to the light-emitting side, the following components: The light that comes into contact with the light-emitting chip is extracted from the control layer; A spectral modulation layer disposed on the light extraction modulation layer; A viewing angle compensation layer disposed on the spectral modulation layer; A surface functional layer disposed above the view compensation layer.

2. The multilayer composite film according to claim 1, characterized in that, The light extraction control layer includes a refractive index matching material and / or a micro / nano structure surface; The refractive index of the refractive index matching material is between the refractive index of the light-emitting surface of the light-emitting chip and the refractive index of the encapsulation material. Preferably, the refractive index of the refractive index matching material is 1.5 to 1.

8. The micro / nano structure surface is one of a periodically or randomly distributed microlens array, a pyramid structure, and a moth-eye structure, and the characteristic size of the micro / nano structure surface is 0.1~10μm.

3. The multilayer composite film according to claim 2, characterized in that, The light extraction control layer also includes a transparent resin filled with high-refractive-index nanoparticles; The high refractive index nanoparticles are selected from one of titanium oxide, zirconium oxide and zinc oxide, the particle size of the high refractive index nanoparticles is 10~100nm, and the mass fraction of the high refractive index nanoparticles is 10%~40%.

4. The multilayer composite film according to claim 1, characterized in that, The spectral modulation layer is composed of alternating layers of high refractive index and low refractive index, and the number of layers in the spectral modulation layer is 4 to 20. The high refractive index layer is made of one of titanium oxide, niobium oxide, and silicon nitride, and the refractive index of the high refractive index layer is 1.8 to 2.

5. The material of the low refractive index layer is selected from silicon oxide, magnesium fluoride and fluoropolymers, and the refractive index of the low refractive index layer is 1.3 to 1.

5.

5. The multilayer composite film according to claim 1, characterized in that, The spectral modulation layer is a selective absorption layer comprising light-absorbing dyes or light-absorbing pigments; The thickness of the selective absorption layer is 1~10μm; The light-absorbing dye or pigment is selected from one or more of perylene dyes, phthalocyanine dyes, and anthraquinone dyes; the mass fraction of the light-absorbing dye or pigment is 0.5% to 5%.

6. The multilayer composite film according to claim 1, characterized in that, The viewing angle compensation layer is a microlens array layer, the diameter of the lens unit of the microlens array is 10~100μm, and the arrangement period of the microlens array is 10~200μm.

7. The multilayer composite film according to claim 1, characterized in that, The surface functional layer includes an anti-scratch resin, a hydrophobic and oleophobic additive, and a UV absorber; The scratch-resistant resin is a polyurethane acrylate or a silicone-modified acrylate; The hydrophobic and oleophobic additive is a fluorinated compound or an organosilicon compound; The ultraviolet absorber is a benzotriazole or hindered amine compound.

8. The multilayer composite film according to claim 1, characterized in that, The composite film also includes a seam compensation structure disposed in the edge region; the seam compensation structure is an optical microstructure formed in the edge region of the composite film.

9. An outdoor Mini LED display module, characterized in that, The outdoor Mini LED display module includes: Circuit board; A plurality of Mini LED chips are arrayed on the circuit substrate; the plurality of Mini LED chips and the circuit substrate are covered with the multilayer composite film as described in any one of claims 1 to 8; The light extraction control layer of the multilayer composite film and the light-emitting surface of the Mini LED chip are in direct contact or indirect contact through an optical matching layer.

10. A method for preparing a multilayer composite film according to any one of claims 1 to 8, characterized in that, The preparation method includes: Step S1: Fabrication of the light extraction control layer: A light extraction control layer with a preset refractive index and / or micro / nano structure is formed on a temporary support substrate by coating, imprinting or etching processes; Step S2: Preparation of spectral modulation layer: A spectral modulation layer is formed on the light extraction modulation layer by vacuum deposition, coating or multilayer co-extrusion process; Step S3: Fabrication of the viewing angle compensation layer: A viewing angle compensation layer is formed on the spectral modulation layer by imprinting a microlens array; Step S4: Prepare the surface functional layer: Coat the viewing angle compensation layer with a resin containing anti-scratch, hydrophobic, oleophobic and UV absorption functions, and cure it; Step S5 (optional): Form a seam compensation structure in the edge area of ​​the composite film by local embossing or inkjet printing process; Step S6: Peel off the temporary support substrate to obtain the multilayer composite film.

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