Functional film as well as preparation method and application thereof

Abstract

The invention provides a functional film and a preparation method and application thereof, and belongs to the technical field of functional films. The functional film comprises a base material layer and a closed cavity embedded in the base material layer. The functional film provided by the invention only comprises one base material layer, and is lighter and thinner, lower in optical absorption and better in heat transfer performance; and compared with a laminated structure, the film has the advantages of no interface mismatching risk, low cost, no laminated interface, avoidance of layering caused by moisture permeation in a high-temperature and high-humidity environment, high environmental aging resistance, simple preparation method and no need of lamination. In the field of solar cells, the functional film disclosed by the invention can improve the power generation efficiency, long-term service life and environmental tolerance of a solar module by improving the structural stability of heat dissipation and packaging, and has good application space in precise optical devices due to the characteristics of lightness, thinness, flexibility and non-heterogeneity in the field of displays.

Description

Technical Field

[0001] The present invention relates to the technical field of functional films, and in particular to a functional film and a preparation method and application thereof. Background Art

[0002] Optical functional films play a vital role in many modern technological fields, such as improving energy conversion efficiency, optimizing information display effects, and realizing new optoelectronic devices. Especially in the fields of solar photovoltaics and information display, which have high requirements for optical performance, material stability and cost-effectiveness, the demand for advanced optical film structures is becoming increasingly urgent.

[0003] In the field of solar photovoltaics, there are a lot of gaps between the cells of a solar cell and between the cells and the frame. Therefore, gap films are set in the gaps to improve light utilization.

[0004] There are currently several structures of gap membranes: (1) Traditional glazed glass: Traditional glazed glass improves light utilization through diffuse reflection, but has problems such as low reflection efficiency and high burst rate, and there is a strong trend of being replaced by microprism structure; (2) Mainstream microprism coating structure: Mainstream microprism coating structure achieves light reflection by coating a metal reflective film (such as aluminum film) on the microprism structure; (3) Diffuse reflection film based on material modification: Mesoporous composite materials are applied to gap membranes to improve the reflectivity of special bands, but the structural innovation is insufficient; (4) Laminated structure containing optical cavity, the optical cavity is sealed by laminating a double-layer structure, and the optical function is achieved by the refractive index difference between the double-layer structure substrate and the optical cavity in the laminated structure.

[0005] With the trend toward lighter and more flexible photovoltaic modules and the increasing demand for power density and long-term reliability, the development of new gap membrane technologies that combine efficient light utilization, excellent weather resistance, structural stability, and low cost has become an important issue that needs to be urgently addressed in the industry.

[0006] At the same time, in the field of light-guiding display devices, high-performance optical films are also an indispensable core component of modern display panels. These optical films are used to achieve a variety of key functions in backlight modules, including improved light efficiency, light uniformity, viewing angle control, color enhancement, polarization management, and screen protection. The continuous pursuit of thinner, lighter, more flexible display devices with higher image quality (such as high brightness, wide color gamut, high contrast), and lower power consumption poses severe and ongoing challenges to the precise structural design, material selection, and manufacturing processes of these optical films. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a functional film and its preparation method and application. The functional film provided by the present invention comprises only one layer of base material, has low cost, and is simple to prepare without lamination.

[0008] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0009] The present invention provides a functional film, comprising a base material layer and a closed cavity embedded in the base material layer, wherein the closed cavity is sealed by forming an integrated sealing structure in situ of the base material layer.

[0010] Preferably, the sealing of the closed cavity is achieved by material rebound and / or material backflow of the base material layer.

[0011] Preferably, the matrix material layer comprises an optically transparent material.

[0012] Preferably, the functional film further includes a gradient refractive index layer.

[0013] Preferably, the surface of the base material layer has a microstructure.

[0014] Preferably, the surface of the base material layer is further provided with an additional functional layer, and the additional functional layer includes one or more of a coating, a film and a surface structure.

[0015] Preferably, the closed cavity contains contents, and the contents include fluid and / or solid.

[0016] The present invention also provides a method for preparing the functional film described in the above technical solution, comprising the following steps:

[0017] forming a front cavity structure having an opening on the surface of the base material layer;

[0018] The functional membrane is obtained by forming an integrated sealing structure in situ at the opening of the front cavity structure using the material of the base material layer itself to seal the front cavity structure.

[0019] The present invention also provides the application of the functional film described in the above technical solution or the functional film prepared by the preparation method described in the above technical solution in the field of solar cells.

[0020] The present invention also provides the use of the functional film described in the above technical solution or the functional film prepared by the preparation method described in the above technical solution in the field of light-guiding display devices.

[0021] The present invention provides a functional film comprising a base material layer and a closed cavity embedded in the base material layer.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The functional film provided by the present invention forms an integrated closed structure in situ through the base material, eliminating the physical interface between different layer structures existing in the traditional laminated structure. Therefore, it fundamentally avoids failure modes such as interface delamination and cracking caused by weak interface adhesion, material thermal mismatch or moisture penetration, and significantly improves the structural stability and service life of the functional film in harsh environments (such as long-term outdoor operation of solar panels and repeated bending of flexible display devices).

[0024] In addition, since the sealing is a natural continuation or highly compatible combination of the matrix material layer, it avoids light scattering, absorption or refractive index mutation that may be caused by the heterogeneous interface, which is conducive to maintaining excellent optical properties (such as high transmittance and uniform optical response).

[0025] In addition, the functional film of the present invention is a single base material layer, which has significant advantages over multi-layer lamination in terms of lightness, flexibility, reduced material costs and simplification of some manufacturing processes. It has lower optical absorption and better heat transfer performance, and therefore has good application space in the fields of solar cells and optical displays. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the functional membrane structure including a closed cavity;

[0027] Figure 2 Schematic diagram of the structure of the base material layer before reflow;

[0028] Figure 3 Schematic diagram of the surface microstructure of the epitaxial removable template and the functional film before rebounding in the rebound area;

[0029] Figure 4 A schematic diagram of a functional membrane structure including a functional material layer for a removable template;

[0030] Figure 5 This is a simulation diagram of the optical transmittance of the film with a laminated structure in Comparative Example 1;

[0031] Figure 6 This is a simulation diagram of the optical transmittance of the functional film in Example 1 of the present invention;

[0032] Figure 7 This is a luminous flux test chart of a film with a laminated structure in Comparative Example 1;

[0033] Figure 8 This is a luminous flux test diagram of the functional film in Example 1. DETAILED DESCRIPTION

[0034] The present invention provides a functional film, comprising a base material layer and a closed cavity embedded in the base material layer, wherein the closed cavity has at least one predetermined optical function with respect to capturing incident light and / or capturing internal reflected light.

[0035] In the present invention, the functional film has no lamination interface, avoids delamination caused by moisture penetration in high temperature and high humidity environments, has high resistance to environmental aging, and has the advantage of being lightweight. The functional film of the present invention only includes a layer of base material, which is lighter and thinner, has lower optical absorption, and better heat transfer performance; and compared with the laminated structure, there is no risk of interface mismatch, low cost, no lamination interface, avoids delamination caused by moisture penetration in high temperature and high humidity environments, has high resistance to environmental aging, and the preparation method is simple and does not require lamination. In the field of solar cells, the functional film of the present invention can improve the power generation efficiency, long-term working life and environmental tolerance of solar modules by improving heat dissipation and the structural stability of packaging. In the field of displays, its lightness, flexibility and non-heterogeneity make it have a good application space in precision optical devices.

[0036] The functional film of the present invention is a single-layer structure. Compared to the laminated structures of the prior art, the functional film provided by the present invention does not require lamination, so its "top layer" is thinner than that of laminated structures. The optical advantages are reflected in the thin top layer and the reduced number of interfaces: the thin top layer reduces the material's absorption and scattering of light, improving light transmittance, while also optimizing off-axis performance and reducing the change in path length when light is incident at an oblique angle. Fewer interfaces (such as replacing a multilayer structure such as PET-adhesive-PET-air with PET-air) can reduce Fresnel reflection losses and scattering sources, thereby improving total transmittance, reducing haze and stray light, and improving image clarity or signal-to-noise ratio in optical applications.

[0037] In the present invention, the optical function is preferably obtained and constituted by the internal structure of the embedded closed cavity and the size, material, position and / or alignment of the contents of the closed cavity.

[0038] In the present invention, when the surface of the functional film has a microstructure and / or an additional functional layer having an optical function, the optical function is preferably also obtained and constituted by the microstructure and the additional functional layer having an optical function.

[0039] In the present invention, the design space of the closed cavity is free. Through the synergistic advantage of material and structure, a functional layer is preferably deposited on the cavity wall to enhance the comprehensive optical benefits. The material of the functional layer preferably includes TiO2 or SiO2-TiO2 composite layer.

[0040] In the present invention, the closed cavity is preferably obtained by at least one of embossing, stamping, photolithography, molding, casting and removable template, more preferably a removable template. Compared with stamping, the removable template can form a closed cavity structure with a small cavity opening and a large cavity.

[0041] In the present invention, it is preferred to blend the material of the removable template with the substrate by pre-embedding the template removal mechanism and the material rebound and / or material reflux mechanism of the matrix material layer, thereby achieving precise control and stable packaging of the closed cavity structure, providing a new technical path for improving the efficiency of functional membrane components.

[0042] In one embodiment of the present invention, the base material layer is preferably embedded with a soluble material (such as polyvinyl alcohol, PVA) during the molding process. After the base material is solidified, the soluble material is dissolved to form an embedded cavity, and then combined with the substrate rebound mechanism to obtain the closed cavity.

[0043] In the present invention, the closed cavity is preferably obtained by co-extrusion casting. In a specific embodiment of the present invention, the base material layer and the removable template are preferably co-extruded by a co-extrusion device to form an integrated structure to obtain the closed cavity.

[0044] In the present invention, the template design of the removable template preferably includes a deformation compensation design to compensate for cavity deformation during the process environment.

[0045] In the present invention, the material of the removable template and the material of the base material layer are preferably chemically stable.

[0046] In the present invention, the number of the closed cavities is preferably greater than one, and the multiple closed cavities preferably have the same function or at least multiple functions designed together.

[0047] In the present invention, the geometric form of the closed cavity preferably includes a protrusion, a ridge, a recess, a binary form, an inclined form, a square form, a triangular form, a grating pixel form, a trapezoidal form or a lens form.

[0048] In the present invention, the height of the closed cavity is preferably 10 to 65 μm, and specifically can be 10, 20, 30, 40, 50, 55, 60 or 65 μm.

[0049] In the present invention, the closed cavity is preferably closed by a self-sealing layer, and the self-sealing layer is preferably formed by material rebound and / or material reflow from the base material layer, and preferably an interlocking / optical microstructure is formed between the base material layer and the self-sealing layer. In a specific embodiment of the present invention, the closed cavity is obtained by a removable template, and the closed cavity is achieved by material rebound of the base material layer. The removable template is preferably a partially epitaxial template, and the epitaxial region guides the substrate to rebound at the cavity opening to form an interlocking / optical microstructure. During the process, the removable template is controlled to rebound until the cavity is closed after removal (and cleaning).

[0050] In the present invention, the “rebound” in the material rebound is based on the elastic recovery of the material of the bulk material layer. The self-sealing layer formed by the material rebound means that after the front cavity structure with an opening is formed by embossing, mold removal or sacrificial template removal, the base material layer undergoes elastic recovery deformation at the opening by virtue of its inherent elastic properties, thereby shrinking or closing the opening to form a self-sealing layer. In a specific embodiment of the present invention, the base material layer preferably comprises a shape memory polymer, and through a preset programming step, under a specific external stimulus (such as temperature change), the base material layer around the front cavity structure with an opening undergoes a preset shape recovery to achieve self-sealing of the opening. In another embodiment of the present invention, the base material layer generates internal residual stress during the molding process, which is released after the opening is formed. The release of the internal residual stress may synergistically promote the self-sealing of the opening.

[0051] In the present invention, the material reflow to form a self-sealing layer refers to the process of locally heating or other energy input to the opening edge area of ​​the front cavity structure with an opening, so that the material of the base material layer is softened, melted and flows in the area. Driven by surface tension or capillary force, the molten material of the base material layer bridges and closes the opening, and after cooling and solidification, a closed cavity integrated with the base material layer is formed. The capillary force helps to prevent the molten material of the base material layer from collapsing into the closed cavity and promotes the bridging and closing of the opening.

[0052] In the present invention, the material reflow preferably utilizes a focused laser beam to precisely irradiate the opening edge region of the front cavity structure (laser fusion), causing the matrix material layer to locally melt in this region. The molten material flows and resolidifies under the action of surface tension, thereby sealing the opening and forming a closed cavity integral with the matrix material layer. In the present invention, the laser fusion has the characteristics of non-contact, high precision, and localized heating, and is suitable for the precise sealing of tiny openings. By regulating the laser parameters of the laser fusion (including power, pulse width, and scanning path), precise control of the melting area and the sealing process can be achieved.

[0053] In the present invention, the functional film preferably further comprises a gradient refractive index layer (GRIN layer), wherein the material of the GRIN layer is preferably the same as that of the base material layer, with only a difference in material density. In the present invention, the GRIN layer is preferably formed during a laser fusion process.

[0054] In the present invention, the interaction between the laser and the matrix material layer during the laser fusion process may also produce a slight change in the refractive index around the fused region, bringing additional optical functionality to the device. The monolithic structure (comprising a matrix material layer and a closed cavity embedded within the matrix material layer) makes the region of refractive index change around the closed cavity an integral part of the optical design, rather than an interface effect. Unlike laminated structures, this eliminates the need to manufacture a separate GRIN layer (e.g., using a laser to seal the opening while simultaneously generating a refractive index gradient GRIN layer in the surrounding matrix material layer). This GRIN effect can be adjusted by controlling the laser parameters, thereby achieving unique optical functionality directly integrated with the closed cavity.

[0055] In the present invention, the material rebound and material reflow preferably occur simultaneously, such as when the rebound and reflow occur simultaneously under thermal assistance. The material rebound has the problems of incomplete closure, weak interface bonding force, and insufficient long-term stability. If the material reflow closes a larger initial opening, it may require a higher temperature, a longer heating time, or face challenges such as collapse of the molten material, uneven flow, and impact on flatness. Combining the material rebound and material reflow can maximize strengths and minimize weaknesses, improve efficiency, and make the process window wider.

[0056] In the present invention, the material rebound and material reflow preferably occur simultaneously, which can achieve more complete sealing at a relatively low temperature (preferably 90-170°C, specifically 90, 130 or 170°C) and a shorter time (preferably 2-30s, specifically 2, 10, 20 or 30s), and reduce the thermal impact or deformation caused by large-scale reflow. During the simultaneous occurrence of the material rebound and material reflow, it is preferred to apply a small auxiliary pressure (more preferably 0.01-0.3MPa, specifically 0.01, 0.05, 0.1, 0.2 or 0.3MPa) to help ensure close contact and fusion of the rebound / reflow interface.

[0057] In the present invention, the surface of the base material layer preferably has a microstructure, that is, the self-sealing layer preferably has a functional surface microstructure. The microstructure is the in-situ microstructure of the base material layer, which can be obtained when preparing the base material layer or in the process of in-situ sealing.

[0058] In the present invention, the matrix material layer is preferably arranged in a gap structure between solar cells and / or between cells and a frame, or is arranged as a layer structure located above / below the gap between solar cells and / or between cells and a frame.

[0059] In the present invention, the base material layer preferably comprises an optically transparent material.

[0060] In the present invention, the material of the base material layer preferably includes one or more of ethylene-vinyl acetate copolymer (EVA), polyethylene terephthalate (PET), polyolefin elastomer (POE) and modified materials thereof.

[0061] In the present invention, the base material layer preferably includes a rebound region and / or a rigid region, wherein the elastic modulus of the rebound region and / or the rigid region is different from that of the non-rebound region and / or the rigid region of the base material layer. In a specific embodiment of the present invention, the base material layer is provided with a rebound region at the opening of the closed cavity. The differentiated elastic modulus setting facilitates the self-sealing of the closed cavity opening.

[0062] In the present invention, the surface of the base material layer is preferably further provided with an additional functional layer, and the additional functional layer preferably includes one or more of a coating, a film and a surface structure. The coating and the film are preferably planar structures, the coating is chemically bonded, and the film is obtained by multi-layer lamination, such as including hot pressing bonding. The surface structure is preferably a non-planar structure to play an optical role.

[0063] In the present invention, the additional functional layer preferably includes but is not limited to an optical functional layer, a mechanical functional layer, a self-cleaning layer and a weather-resistant functional layer. Specifically, the coating is preferably an anti-reflective coating, more preferably a nano-scale silica / titanium dioxide composite coating, and the film is preferably a composite film with optical-aging dual properties, more preferably an inner layer of an acrylate anti-reflective coating containing a UV absorber, and an outer layer of a silica-alumina wear-resistant layer.

[0064] In the present invention, the base material layer and the closed cavity preferably have different refractive indices.

[0065] In the present invention, the closed cavity includes contents, which preferably include fluid and / or solid. The contents are preferably introduced into the closed cavity before the closed cavity is closed.

[0066] In the present invention, the fluid preferably includes air.

[0067] In the present invention, the solid preferably includes one or more of a temperature-sensitive material, a photosensitive material and a functional material.

[0068] In the present invention, the temperature-sensitive material and the photosensitive material independently include poly(N-isopropylacrylamide) (PNIPAM) and / or a paraffin-based complex, which can achieve dynamic regulation of the closed cavity.

[0069] In the present invention, the functional material preferably includes TiO2, which can constitute the internal microstructure of the closed cavity, form a synergistic optical benefit with the closed cavity structure, and balance light transmittance, reflection gain and mechanical properties.

[0070] The present invention also provides a method for preparing the functional film described in the above technical solution, comprising the following steps:

[0071] Opening the base material to obtain a front cavity structure with an opening;

[0072] The front cavity structure is sealed to form a closed cavity, thereby obtaining the functional membrane.

[0073] The present invention opens the base material to obtain a front cavity structure with an opening.

[0074] The present invention preferably obtains the front cavity structure by at least one of embossing, stamping, photolithography, molding, casting or removable template.

[0075] In the present invention, at least one of the enclosed cavities is obtained by removing the removable template, and the removable template is preferably removed by at least one of template etching, degradation, phase change, or absorption. In a specific embodiment of the present invention, a functional film is prepared by synergistically using multiple template removal methods.

[0076] In the present invention, the etching substrate of the template etching preferably includes CaCO3 micro-nano particles and / or ZnO micro-nano particles.

[0077] In the present invention, the front cavity structure is preferably obtained by removing a removable template, and the removal process is preferably a multi-stage removal process. By adjusting the reaction conditions, sudden environmental changes are avoided, which is conducive to the gradual release of gas, avoidance of mist (gas and product mixing) generation, thoroughness of removal and stability of the cavity structure.

[0078] After the removal of the removable template is completed, a post-cleaning process is preferably further included to obtain the front cavity structure.

[0079] In the present invention, the etching rate ratio of the material of the removable template to the base material is preferably >100:1.

[0080] In the present invention, the material of the removable template is preferably a green material, more preferably polylactic acid (PLA degradable material) or photoresist, and the photoresist is a laser degradable polymer.

[0081] After obtaining the front cavity structure, the present invention seals the front cavity structure to form a closed cavity, thereby obtaining the functional membrane.

[0082] In the present invention, the sealing preferably includes material rebound and / or material reflow of the base material layer, and more preferably includes applying heat pressure at the opening of the front cavity structure to promote the rebound of the base material layer. The present invention does not particularly limit the specific parameters of the heat pressing, and methods familiar to those skilled in the art can be used.

[0083] In the present invention, the process of directional stretching is preferably further included before sealing to optimize the wall surface of the closed cavity and avoid surface unevenness that affects optical efficiency.

[0084] The functional film of the present invention is a closed cavity integrally formed in a single-layer base material layer. The lamination process is preferably omitted in the preparation method, and there is no risk of interface mismatch.

[0085] The present invention also provides the application of the functional film described in the above technical solution or the functional film prepared by the preparation method described in the above technical solution in the field of solar cells.

[0086] The present invention also provides a solar cell, comprising the functional film described in the above technical solution or the functional film prepared by the preparation method described in the above technical solution, which is used to improve the light efficiency of the gap between solar cells and / or between cells and frames, and the functional film serves as an integrated fixing component of the solar cell.

[0087] In the field of solar cells, the functional film of the present invention can improve the power generation efficiency, long-term working life and environmental tolerance of solar modules by improving heat dissipation and structural stability of packaging.

[0088] In the present invention, the typical application structure of the functional film in the field of photovoltaic modules preferably includes:

[0089] When the functional film of the present invention is applied to a solar cell module, it can be used as an integrated gap film.

[0090] In the present invention, the solar cell module preferably includes a stacked structure from top to bottom: tempered glass, an upper encapsulation film, a plurality of solar cells arranged in parallel, a lower encapsulation film and a backplane, and the functional film is arranged between two adjacent solar cells, or / and in the gap between the solar cell and the module frame.

[0091] In the present invention, the functional film is completely embedded and encapsulated inside the packaging layer composed of the upper packaging film and the lower packaging film. The base material layer of the functional film is preferably the same as or highly compatible with the packaging film. After hot lamination, the functional film and the packaging film are melted into one to form an integral packaging structure without obvious interface.

[0092] The present invention also provides the use of the functional film described in the above technical solution or the functional film prepared by the preparation method described in the above technical solution in the field of light-guiding display devices.

[0093] In the field of displays, the functional film of the present invention can ensure display effects and device life by optimizing heat dissipation, and ensure functional stability of optical films and product durability through structural integrity, thereby improving display quality, extending service life, and promoting lighter, thinner and more flexible designs.

[0094] In the present invention, the typical application structure of the functional film in the field of light guide display preferably includes:

[0095] When the functional film of the present invention is applied to a light-guiding display device, it can constitute a new integrated light guide plate (LGP). The functional film is located in the backlight module of the display. The functional film is preferably integrated into the backlight module of the display device as a light guide plate.

[0096] The present invention also provides an edge-entry backlight module, which preferably includes a reflective sheet, a light guide plate, a lower diffuser, a prism sheet and an upper diffuser. The side of the edge-entry backlight module is also provided with an LED light source. The light guide plate is the functional film described in the present invention. The functional film itself is used as a light guide plate, replacing the traditional solid acrylic or PC light guide plate.

[0097] The present invention has no particular limitation on the specific manner of the application, and any manner familiar to those skilled in the art may be used.

[0098] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0099] Those skilled in the art will appreciate that the optimal value of the opening size described in the embodiment is closely related to the specific base material selected (e.g., its thermophysical properties such as melt viscosity and surface tension) and the laser process parameters used (e.g., laser power, spot size, scanning speed, pulse width, etc.). Therefore, the 3 μm opening size described in this embodiment is merely a feasible and preferred example under specific material and process conditions, and should not be understood as the sole limitation on the scope of protection of the present invention. Those skilled in the art can adjust and determine other appropriate opening sizes through conventional experimental means based on the different material systems and process equipment used to achieve the integrated closed structure of the present invention.

[0100] Those skilled in the art will appreciate that the thickness of the base material (conventional thicknesses include 25, 38, 50, 75, 100, 125, 188, 250 μm) can have a significant effect on its effective mechanical properties and its thermomechanical response during local laser processing. Although the inherent material properties (such as chemical composition, glass transition temperature) remain consistent for a given grade of polymer such as PET, changes in film thickness can affect parameters such as bending stiffness, heat dissipation characteristics, and laser-induced thermal stress distribution. For example, a thinner film may exhibit greater flexibility, but may also be more susceptible to thermal deformation or have different heat dissipation capabilities than a thicker film of the same material. Conversely, a thicker film has a greater heat capacity, which changes the temperature gradient achieved during laser irradiation, the size of the molten pool, and the subsequent cooling rate.

[0101] Example 1

[0102] Optical-grade PET film (the optical-grade PET film model is AGO8 PETMO1, purchased from Shanghai Qisheng Electronic Technology Co., Ltd., using TD direction, with a refractive index of 1.56) is selected as the substrate material, and photoresist is selected as the removable template.

[0103] Preparation steps: (1) Remove the removable template to prepare a front cavity structure with an opening, the opening size of the front cavity structure is 3μm; (2) Reflow the material and seal the front cavity structure: a. Use a focused ultraviolet picosecond laser (wavelength 355nm, pulse width 10ps, repetition frequency 1MHz); b. Control the laser spot size (5μm), scanning speed (100mm / s) and laser average power to make the laser beam scan along the edge of the microchannel opening; c. The PET film undergoes local and rapid melting under laser irradiation, and the molten PET flows driven by surface tension and capillary force, bridging and sealing the opening. d. After the laser is removed, the molten PET quickly cools and solidifies, completely fusing with the base material PET material to form a closed cavity. The height of the closed cavity is 10μm, the distance from the top of the closed cavity to the top of the functional film (i.e., the "top layer" thickness) is 2μm, and the distance from the bottom of the closed cavity to the bottom of the functional film (i.e., the "bottom layer" thickness) is 10μm.

[0104] Results: A closed cavity with an integrated laser-fused closed structure embedded in a single-layer PET film was obtained, and a GRIN layer (gradient layer) was observed in the laser action area. The gradient layer had a uniform transition and was caused by the local density change caused by the interaction between the laser and the material.

[0105] Figure 1 Schematic diagram of the functional membrane structure containing a closed cavity. Figure 2 Schematic diagram of the structure of the base material layer before reflow.

[0106] Example 2

[0107] The substrate material is an optical-grade POE film with a thickness of 100 μm, and the removable template is a photoresist.

[0108] Preparation steps: (1) removing the removable template to prepare a front cavity structure with an opening, wherein the opening size of the front cavity structure is 3 μm; (2) material rebound and material reflow to close the front cavity structure: a. using a heater array manufactured using micro-electromechanical system technology, applying 130°C (this temperature is higher than the softening point of the POE film but far below its rapid degradation temperature) and a pressure of 0.05 MPa to the front cavity structure to assist the contact and flow of the base material layer; b. the POE film rebounds and reflows under heating (2s), thereby achieving the closure of the front cavity structure and forming a closed cavity.

[0109] The result: a closed cavity embedded in a single-layer POE film. This embodiment uses material rebound to rapidly shrink the opening, reducing the gap required for subsequent material reflow. This allows for a more complete seal at a relatively low temperature (130°C) or in a short time (2 seconds), minimizing the thermal impact or deformation caused by large-scale reflow. A slight auxiliary pressure (0.05 MPa) helps ensure close contact and fusion at the rebound / reflow interface.

[0110] Example 3

[0111] The base material is an optical-grade PET film with a thickness of 100 μm (the optical-grade PET film model is AGO8PETMO1, purchased from Shanghai Qisheng Electronic Technology Co., Ltd., using the MD direction), and the epitaxial removable template is a PLA degradable material. The elasticity of the PET film in Example 3 is higher than that of the PET film in Example 1.

[0112] Figure 3 Schematic diagram of the surface microstructure of the epitaxial removable template and the functional film before rebound in the rebound area.

[0113] Preparation steps: (1) removing the epitaxial removable template to prepare a front cavity structure with an opening, wherein the opening size of the front cavity structure is 3 μm; (2) material rebounds to close the front cavity structure: a. using a heater array manufactured using micro-electromechanical system technology, applying a heating temperature of 120°C to the front cavity structure, the modified PET film rebounds under heating, thereby closing the front cavity structure and forming a closed cavity.

[0114] The results: A closed cavity embedded in a single layer of PET film was obtained, with its opening sealed by the rebound of the substrate material. At the closed cavity or its edges, guided by the epitaxial removable template, a pre-defined interlocking structure (enhancing the mechanical stability of the seal) was formed, along with an optical microstructure. This optical microstructure could be controlled by manipulating the epitaxial region structure.

[0115] Example 4

[0116] The base material is an optical-grade POE film with a thickness of 100 μm, the removable template is a photoresist, and the removable template includes a functional material layer TiO2.

[0117] Preparation steps: (1) removing the removable template to prepare a front cavity structure with an opening, wherein the opening size of the front cavity structure is 3 μm; (2) material rebound and material reflow to close the front cavity structure: a. using a heater array manufactured by micro-electromechanical system technology, applying 130°C (this temperature is higher than the softening point of the POE film but far below its rapid degradation temperature) and a pressure of 0.05 MPa to the front cavity structure to assist the contact and flow of the base material layer; b. the POE film rebounds and reflows under heating (10 s), thereby achieving the closure of the front cavity structure and forming a closed cavity.

[0118] Figure 4 Schematic diagram of the functional film structure of a removable template including a functional material layer TiO2.

[0119] Results: A closed cavity embedded in a single-layer POE film was obtained, and the functional film included a functional material layer of TiO2.

[0120] Example 5

[0121] The base material is a polyolefin elastomer with a thickness of 100 μm.

[0122] Preparation steps: (1) A soluble material (PVA) is embedded in the base material layer during the molding process. After the base material is solidified, the soluble material is dissolved to form a front cavity structure with an opening, and the opening size of the front cavity structure is 3 μm; (2) Material rebound and material reflow to close the front cavity structure: a. A heater array manufactured using micro-electromechanical system technology is used to apply 135°C (this temperature is higher than the softening point of polyolefin elastomer but far lower than its rapid degradation temperature) and a pressure of 0.05 MPa to the front cavity structure to assist the contact and flow of the base material layer; b. The polyolefin elastomer rebounds and reflows under heating (30s), thereby achieving the closure of the front cavity structure and forming a closed cavity.

[0123] Example 6

[0124] A solar cell employs the functional film prepared in Example 1 as an integrated fixture component for improving the optical efficiency of the gap between solar cells. During the packaging process of the solar cell assembly, the optically functional area of ​​the functional film is positioned within the gap. The enclosed cavity within the functional film and the gradient refractive index structure formed around it effectively redirect sunlight incident on the gap to the active photosensitive area of ​​adjacent solar cells through reflection, refraction, or scattering.

[0125] Example 7

[0126] A flexible light-guiding display device is provided. The functional film prepared in Example 1 is integrated into a backlight module of the display device as a light-guiding film to obtain a light-guiding display device that is light, thin and flexible.

[0127] Comparative Example 1

[0128] The film, formed by the laminated structure and containing a closed cavity structure, comprises two material layers (both optical-grade PET films as described in Example 1), laminated together to form a laminated structure. An optically functional cavity is formed at the interface between the two material layers. The cavity height is 10 μm, the distance from the top of the cavity to the top of the film (i.e., the "top layer" thickness) is 10 μm, and the distance from the bottom of the cavity to the bottom of the film (i.e., the "bottom layer" thickness) is 10 μm.

[0129] Figure 5 This is a simulation diagram of the optical transmittance of a film with a laminated structure in Comparative Example 1. Figure 6 This is a simulation diagram of the optical transmittance of the functional film in Example 1 of the present invention. It can be seen that the functional film of the present invention has higher light transmittance and better off-axis performance.

[0130] Luminous flux test results

[0131] Figure 7 This is a luminous flux test chart of the film with a laminated structure of Comparative Example 1. The minimum luminous flux is 0, the maximum is 6267.9 W, the average is 237.13 W, the total luminous flux is 59.283 W, the luminous flux / emitted luminous flux is 0.21876, and there are 298 incident light rays. Figure 8 This is a luminous flux test chart of the functional film of Example 1. The minimum luminous flux is 0, the maximum is 6267.9W, the average is 264.42W, the total luminous flux is 66.106W, the luminous flux / emitted luminous flux is 0.24393, and there are 344 incident light rays. It can be seen that the functional film provided by the present invention has a higher luminous flux.

[0132] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation thereto. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications shall also be considered within the scope of protection of the present invention.

Claims

1. A functional film, characterized in that: It comprises a base material layer and a closed cavity embedded in the base material layer, wherein the closed cavity is sealed by forming an integrated sealing structure in situ of the base material layer.

2. The functional film according to claim 1, characterized in that The closed cavity is closed by material rebound and / or material backflow of the base material layer.

3. The functional film according to claim 1 or 2, characterized in that The base material layer includes an optically transparent material.

4. The functional film according to claim 1, characterized in that The functional film further includes a gradient refractive index layer.

5. The functional film according to claim 1, characterized in that The surface of the base material layer has a microstructure.

6. The functional film according to claim 1 or 5, characterized in that The surface of the base material layer is further provided with an additional functional layer, and the additional functional layer includes one or more of a coating, a film and a surface structure.

7. The functional film according to claim 1, characterized in that The closed cavity contains contents, which include fluid and / or solid.

8. The method for preparing a functional film according to any one of claims 1 to 7, characterized in that: The following steps are involved: forming a front cavity structure having an opening on the surface of the base material layer; The functional membrane is obtained by forming an integrated sealing structure in situ at the opening of the front cavity structure using the material of the base material layer itself to seal the front cavity structure.

9. Use of the functional film according to any one of claims 1 to 7 or the functional film prepared by the preparation method according to claim 8 in the field of solar cells.

10. Use of the functional film according to any one of claims 1 to 7 or the functional film prepared by the preparation method according to claim 8 in the field of light-guiding display devices.

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