Multilayer composite hot spot self-triggering flame-retardant photovoltaic encapsulant film and preparation method thereof

Abstract

The present application belongs to the technical field of photovoltaic module encapsulation material, and particularly relates to a multilayer composite hot spot self-triggering flame-retardant photovoltaic encapsulation adhesive film and a preparation method thereof. The adhesive film comprises, in order from the glass side to the cell side of the photovoltaic module, a composite outer light-heat conversion functional layer, a core layer arc separation flame-retardant layer and a bottom layer adhesive weatherproof protective layer. The matrix resin of the outer light-heat conversion functional layer is EVA resin, and the outer light-heat conversion functional layer comprises light-heat conversion nano particles and heat-conducting fillers. The core layer arc separation flame-retardant layer is a porous film layer with a microporous structure, and the matrix resin is POE resin, which comprises an aluminum hypophosphite-based halogen-free composite temperature-sensitive flame retardant, perfluorohexanone microcapsules and an adhesive containing hydrolysable silane groups. The average pore size of the micropores is 5-15 microns, and the porosity is 10%-20%. The matrix resin of the bottom layer adhesive weatherproof protective layer is EVA resin, and the bottom layer adhesive weatherproof protective layer comprises a halogen-free composite flame retardant. The perfluorohexanone microcapsules release perfluorohexanone when the wall material is broken at 170-190 DEG C.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic module encapsulation material technology, specifically relating to a multilayer composite hot spot self-triggered flame-retardant photovoltaic encapsulation film and its preparation method. Background Technology

[0002] When photovoltaic modules are used outdoors for extended periods, they are prone to hot spot effects due to factors such as shading, microcracks, and poor welding. Local temperatures can reach over 200°C, leading not only to a sharp decrease in module power but also potentially causing backsheet burnout or even fire. Traditional EVA or POE encapsulation films primarily serve adhesive, light transmission, and insulation protection functions, but they lack the ability to actively detect and suppress hot spots.

[0003] Most existing flame-retardant films adopt passive flame-retardant technology, which achieves the flame-retardant effect by adding a large amount of halogen or inorganic flame retardants. This has three major drawbacks: First, there is an inherent contradiction between the amount of flame retardant added and the light transmittance and adhesion. Usually, when the amount of flame retardant added exceeds 10%, the visible light transmittance of the film drops to below 88%, and the adhesion strength to the battery cell decreases by more than 30%. Second, the passive flame-retardant response is delayed. It only decomposes and takes effect when the temperature rises above 250°C, which cannot prevent the thermal runaway propagation in the early stage of hot spots. Third, it cannot effectively block the high-voltage arc caused by hot spots, which can easily ignite the backsheet material.

[0004] Therefore, overcoming the limitation that flame-retardant films cannot simultaneously achieve low-temperature response and optical performance is a technical problem that urgently needs to be solved in this field.

[0005] It should be noted that the information disclosed in this background section is only for understanding the background technology of the present application concept, and therefore, the above description is not considered to constitute prior art information. Summary of the Invention

[0006] This disclosure provides at least one multilayer composite hot spot self-triggered flame-retardant photovoltaic encapsulating film and its preparation method.

[0007] In a first aspect, embodiments of this disclosure provide a flame-retardant photovoltaic encapsulation film, comprising, sequentially from the glass side toward the photovoltaic module to the cell side, a composite outer photothermal conversion functional layer, a core flame-retardant arc-shielding layer, and a bottom adhesive weather-resistant protective layer; the matrix resin of the outer photothermal conversion functional layer is EVA resin, and the outer photothermal conversion functional layer includes photothermal conversion nanoparticles and thermally conductive fillers; the core flame-retardant arc-shielding layer is a porous film layer with a microporous structure, the matrix resin of the core flame-retardant arc-shielding layer is POE resin, and the core flame-retardant arc-shielding layer includes aluminum hypophosphite-based halogen-free... The composition includes a composite thermosensitive flame retardant, perfluorohexanone microcapsules, and an adhesive containing hydrolyzable silane groups; the average pore size of the micropores is 5–15 μm, and the porosity is 10%–20%; the base resin of the bottom adhesive weather-resistant protective layer is EVA resin, and the bottom adhesive weather-resistant protective layer includes a halogen-free composite flame retardant; wherein, the outer photothermal conversion functional layer is used for light absorption, photothermal conversion, and rapid heat conduction, the core flame-retardant arc-blocking layer is used for thermosensitive triggering release of extinguishing media, charring flame retardancy, and arc blocking, and the bottom adhesive weather-resistant protective layer is used for adhesive weather resistance and secondary flame retardant protection.

[0008] In one optional embodiment, the photothermal conversion nanoparticles are selected from one or more of graphene nanosheets, carbon nanotubes, black phosphorus nanosheets, and core-shell photothermal composite nanoparticles.

[0009] In one optional embodiment, the core-shell photothermal composite nanoparticles are formed by combining hexagonal boron nitride powder and black phosphorus nanosheets, wherein the mass ratio of hexagonal boron nitride powder to black phosphorus nanosheets is 1 to 4:1, preferably 2:1; and the particle size of the core-shell photothermal composite nanoparticles is 15 to 30 nm.

[0010] In one optional embodiment, the thermally conductive filler is at least one of hexagonal boron nitride, aluminum nitride, aluminum oxide, magnesium oxide, and silicon nitride.

[0011] Preferably, the thermally conductive filler includes sheet-like thermally conductive filler and / or spherical thermally conductive filler to form a continuous thermally conductive network in the outer photothermal conversion functional layer, thereby improving the efficiency of heat signal transmission from the hot spot region to the core layer.

[0012] In one optional embodiment, the perfluorohexanone microcapsules use urea-formaldehyde resin or melamine resin as the wall material and perfluorohexanone as the core material. The microcapsule particle size is 3-10 μm. The perfluorohexanone microcapsules release perfluorohexanone when the wall material ruptures at 170-190°C.

[0013] In one optional embodiment, the halogen-free composite flame retardant is a compound of a phosphorus-nitrogen flame retardant and a metal hydroxide. The phosphorus-nitrogen flame retardant is selected from one or more of ammonium polyphosphate, melamine polyphosphate, melamine cyanurate, and hypophosphite; the metal hydroxide is selected from one or two of aluminum hydroxide and magnesium hydroxide. The phosphorus-nitrogen flame retardant promotes char formation and gas-phase flame retardancy, while the metal hydroxide absorbs heat, cools the gas, and releases moisture to dilute the combustible gas.

[0014] In one optional embodiment, the mass ratio of the phosphorus-nitrogen flame retardant to the metal hydroxide is 1 to 5:1.

[0015] In one optional embodiment, the outer photothermal conversion functional layer has a thickness of 60–300 μm and is composed of the following raw materials in parts by weight: 100 parts EVA resin, 2–4 parts photothermal conversion nanoparticles, 3–8 parts thermally conductive filler, 0.6–1.2 parts crosslinking agent, 0.3–0.8 parts silane coupling agent, 0.15–0.3 parts antioxidant, 0.1–0.2 parts ultraviolet absorber, and 0.1–0.3 parts light stabilizer.

[0016] In one optional embodiment, the core flame-retardant arc-blocking layer has a thickness of 90–220 μm and is composed of the following raw materials in parts by weight: 100 parts POE resin, 4.5–7.0 parts aluminum hypophosphite-based halogen-free composite thermosensitive flame retardant, 1.5–3.0 parts melamine cyanurate, 0.3–0.8 parts nano-silica charring agent, 0.8–1.5 parts adhesive, 1.5–2.5 parts perfluorohexanone microcapsules, and 0.1–0.3 parts heat stabilizer; wherein the adhesive is a modified polyolefin adhesive or polyethylene grafted maleic anhydride.

[0017] In one optional embodiment, the thickness of the bottom adhesive weather-resistant protective layer is 60-300 μm, and it is composed of the following raw materials in parts by weight: 100 parts of EVA resin, 1.5-2.5 parts of halogen-free composite flame retardant, 0.4-0.8 parts of crosslinking agent, 0.5-1.0 parts of silane coupling agent, 0.2-0.5 parts of antioxidant, and 0.1-0.3 parts of light stabilizer.

[0018] Secondly, this disclosure also provides a method for preparing a flame-retardant photovoltaic encapsulating film as described above, comprising the following steps: weighing the EVA resin, photothermal conversion nanoparticles, thermally conductive filler, and additives of the outer photothermal conversion functional layer according to the specified ratio, and mixing them at room temperature and high speed to obtain an outer layer mixture; weighing the solid raw materials of the core flame-retardant arc-blocking layer according to the specified ratio, and mixing the POE resin, aluminum hypophosphite-based halogen-free composite temperature-sensitive flame retardant, melamine cyanurate, nano-silica char-forming agent, adhesive, and heat stabilizer uniformly at 40-50°C, cooling to below 20°C, adding perfluorohexanone microcapsules, and stirring at low speed until uniform. The core layer premix is ​​obtained by uniform mixing. The core layer premix is ​​fed into an extruder, and supercritical CO2 fluid or chemical foaming agent is injected into the melting section to form a microporous structure, thus obtaining the core layer mixture. The EVA resin, halogen-free composite flame retardant, crosslinking agent, silane coupling agent, antioxidant, and light stabilizer for the bottom layer bonding weather-resistant protective layer are weighed according to the formula and mixed evenly to obtain the bottom layer mixture. The outer layer mixture, core layer mixture, and bottom layer mixture are added to the barrel of a three-layer co-extrusion casting equipment, and the overall melt extrusion temperature is controlled at 120-135℃. After casting, cooling, traction, and winding, flame-retardant photovoltaic encapsulation film is obtained.

[0019] In one optional embodiment, the chemical foaming agent is azodicarbonamide, and the addition amount is 0.2% to 0.5% of the total weight of the core layer raw materials; the injection amount of the supercritical CO2 fluid is 0.3% to 0.8% of the mass of the core layer premix.

[0020] In one optional embodiment, the extrusion temperature of the three-layer co-extrusion casting equipment is distributed in a gradient along the direction from the feed section to the die head, with the temperature of the feed section being 115-120°C, the temperature of the plasticizing section being 125-130°C, and the temperature of the die head being 130-135°C.

[0021] The beneficial effects of this invention are that the multilayer composite hot spot self-triggered flame-retardant photovoltaic encapsulation film constructs a multi-level linkage functional gradient of "light absorption / photothermal conversion - rapid heat conduction - temperature-sensitive triggering - fire extinguishing and flame retardancy - arc isolation". Among them, the outer layer photothermal nanoparticles absorb and convert stray light and near-infrared light in the hot spot area, and form a rapid heat conduction network with thermally conductive fillers, so as to transmit the heat signal to the core flame-retardant and arc-isolation layer in a timely manner. The perfluorohexanone microcapsules in the core layer rupture within a preset temperature range of 170-190°C to release perfluorohexanone fire extinguishing medium, and work synergistically with aluminum hypophosphite-based halogen-free composite temperature-sensitive flame retardant, melamine cyanurate and nano silica to achieve gas phase flame suppression, condensed phase char formation and arc isolation. The bottom layer forms a secondary flame-retardant barrier close to the cell side through the compounding of phosphorus nitrogen flame retardant and metal hydroxide, thereby realizing hot spot self-triggered active protection. In addition, the bottom layer adhesive weather-resistant protective layer ensures reliable adhesion to the cell and glass, and gives the film excellent resistance to damp heat and ultraviolet aging. While maintaining a visible light transmittance of over 91%, this film reduces the hot spot power attenuation of the module from approximately 6% to less than 3%, while achieving UL94 V-0 flame retardancy and possessing self-extinguishing arc capability, resulting in a comprehensive improvement in overall performance.

[0022] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained through the structures particularly pointed out in the description and the drawings.

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the structure of a multilayer composite hot spot self-triggered flame-retardant photovoltaic encapsulation film provided in an embodiment of this disclosure.

[0026] In the picture: 1. Outer photothermal conversion functional layer; 2. Core flame-retardant arc-blocking layer; 3. Bottom adhesive weather-resistant protective layer. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] As used herein, the phrases “in one embodiment,” “according to one embodiment,” “in some embodiments,” etc., generally refer to the fact that a particular feature, structure, or characteristic following the phrase can be included in at least one embodiment of this disclosure. Therefore, a particular feature, structure, or characteristic can be included in more than one embodiment of this disclosure, such that these phrases do not necessarily refer to the same embodiment. As used herein, the terms “example,” “exemplary,” etc., are used to “serve as an example, instance, or illustration.” Any implementation, aspect, or design described herein as “example” or “exemplary” is not necessarily to be construed as preferred or superior to other implementations, aspects, or designs. Rather, the use of the terms “example,” “exemplary,” etc., is intended to present concepts in a specific manner.

[0029] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0030] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0031] Please see Figure 1This disclosure provides a flame-retardant photovoltaic encapsulation film, which sequentially comprises a composite outer photothermal conversion functional layer, a core flame-retardant arc-shielding layer, and a bottom adhesive weather-resistant protective layer along the glass side facing the photovoltaic module to the cell side. The base resin of the outer photothermal conversion functional layer is EVA resin, and the outer photothermal conversion functional layer includes photothermal conversion nanoparticles and thermally conductive fillers. The core flame-retardant arc-shielding layer is a porous film layer with a microporous structure, and the base resin of the core flame-retardant arc-shielding layer is POE resin, and the core flame-retardant arc-shielding layer includes an aluminum hypophosphite-based halogen-free composite. The product comprises a temperature-sensitive flame retardant, perfluorohexanone microcapsules, and an adhesive containing hydrolyzable silane groups; the average pore size of the micropores is 5–15 μm, and the porosity is 10%–20%; the base resin of the bottom adhesive weather-resistant protective layer is EVA resin, and the bottom adhesive weather-resistant protective layer includes a halogen-free composite flame retardant; wherein, the outer photothermal conversion functional layer is used for light absorption, photothermal conversion, and rapid heat conduction; the core flame-retardant arc-blocking layer is used for temperature-sensitive triggering release of extinguishing media, charring flame retardancy, and arc blocking; and the bottom adhesive weather-resistant protective layer is used for adhesive weather resistance and secondary flame retardant protection.

[0032] In some embodiments, specifically, the photothermal conversion nanoparticles are selected from one or more of graphene nanosheets, carbon nanotubes, black phosphorus nanosheets, and core-shell photothermal composite nanoparticles.

[0033] Preferably, the core-shell photothermal composite nanoparticles are composed of hexagonal boron nitride powder and black phosphorus nanosheets in a mass ratio of 2:1, and the particle size is 15-30 nm; the carbon-based nanoparticle photothermal particles are carbon nanotubes or graphene nanosheets.

[0034] In some embodiments, specifically, the thermally conductive filler is at least one of hexagonal boron nitride powder and nano-alumina.

[0035] In some embodiments, specifically, the aluminum hypophosphite-based halogen-free composite thermosensitive flame retardant is a composite of aluminum hypophosphite and organically modified montmorillonite, wherein the mass ratio of aluminum hypophosphite to organically modified montmorillonite is 10:1 to 5:1.

[0036] In some embodiments, specifically, the perfluorohexanone microcapsules use urea-formaldehyde resin or melamine resin as the wall material and perfluorohexanone as the core material, with a microcapsule particle size of 3-10 μm. The perfluorohexanone microcapsules release perfluorohexanone when the wall material ruptures at 170-190°C.

[0037] In some embodiments, specifically, the thickness of the outer photothermal conversion functional layer is 60–300 μm, and it is composed of the following raw materials in parts by weight: 100 parts EVA resin, 2–4 parts photothermal conversion nanoparticles, 3–8 parts thermally conductive filler, 0.6–1.2 parts crosslinking agent, 0.3–0.8 parts silane coupling agent, 0.15–0.3 parts antioxidant, 0.1–0.2 parts ultraviolet absorber, and 0.1–0.3 parts light stabilizer.

[0038] Specifically, the outer photothermal conversion functional layer uses EVA resin as the matrix and adds photothermal conversion nanoparticles and thermally conductive fillers, which can efficiently convert incident invisible light and some stray light into heat energy, and conduct it to the core layer through a thermally conductive network, realizing early detection and rapid transmission of hot spot signals; at the same time, crosslinking agents, antioxidants, ultraviolet absorbers and light stabilizers are added to ensure the weather resistance and structural stability of the outer layer.

[0039] In some embodiments, specifically, the core flame-retardant arc-blocking layer has a thickness of 90–220 μm and is composed of the following raw materials in parts by weight: 100 parts POE resin, 4.5–7.0 parts aluminum hypophosphite-based halogen-free composite thermosensitive flame retardant, 1.5–3.0 parts melamine cyanurate, 0.3–0.8 parts nano-silica charring agent, 0.8–1.5 parts adhesive, 1.5–2.5 parts perfluorohexanone microcapsules, and 0.1–0.3 parts heat stabilizer; the adhesive is a modified polyolefin adhesive or polyethylene grafted maleic anhydride.

[0040] Specifically, the core flame-retardant arc-blocking layer is the core functional layer of this invention. Using POE resin as the matrix, it employs a microporous structure design: on one hand, the micropores can divide the arc channel and reduce the arc energy density, achieving physical arc blocking; on the other hand, the compounded aluminum hypophosphite-based halogen-free composite temperature-sensitive flame retardant, melamine cyanurate, and nano-silica charring agent can rapidly form a dense carbon layer at high temperatures, blocking heat and oxygen transfer. Simultaneously, perfluorohexanone microcapsules are introduced. When the hot spot temperature rises to 170–190°C, the microcapsule wall material ruptures due to heat, releasing gaseous perfluorohexanone, which rapidly extinguishes the initial flame through a dual effect of chemical inhibition and physical cooling. Furthermore, by adding a special adhesive to form a covalent bond interface, the migration and precipitation of the core layer functional filler are effectively inhibited, improving the long-term stability of the film.

[0041] In one optional embodiment, the thickness of the bottom adhesive weather-resistant protective layer is 60-300 μm, and it is composed of the following raw materials in parts by weight: 100 parts of EVA resin, 1.5-2.5 parts of halogen-free composite flame retardant, 0.4-0.8 parts of crosslinking agent, 0.5-1.0 parts of silane coupling agent, 0.2-0.5 parts of antioxidant, and 0.1-0.3 parts of light stabilizer.

[0042] Specifically, the bottom adhesive weather-resistant protective layer uses EVA resin as the matrix and adds a low amount of halogen-free composite flame retardant to help improve the overall flame retardancy without affecting the adhesive performance. By optimizing the ratio of silane coupling agent and antioxidant, the long-term reliable adhesion between the film and glass and battery cells is ensured, while giving it excellent resistance to damp heat and ultraviolet aging.

[0043] This disclosure also provides a method for preparing a flame-retardant photovoltaic encapsulating film as described above, comprising the following steps: weighing EVA resin, photothermal conversion nanoparticles, thermally conductive filler, crosslinking agent, silane coupling agent, antioxidant, ultraviolet absorber and light stabilizer according to the specified ratio, and mixing them at room temperature and high speed to obtain an outer photothermal conversion functional layer mixture; Weigh out the solid raw materials of the core layer flame retardant arc barrier according to the formula. Mix the POE resin, aluminum hypophosphite-based halogen-free composite temperature-sensitive flame retardant, melamine cyanurate, nano silica charring agent, binder containing hydrolyzable silane groups and heat stabilizer at 40-50℃. After cooling to below 20℃, add perfluorohexanone microcapsules and stir at low speed to obtain the core layer premix. The core layer premix is ​​fed into an extruder, and supercritical CO2 fluid is injected into the melting section, or a chemical foaming agent is added to the core layer raw material to form a microporous structure through physical or chemical foaming, thereby obtaining the core layer mixture; wherein, the chemical foaming agent is preferably azodicarbonamide, and the addition amount is 0.2% to 0.5% of the total weight of the core layer raw material; the injection amount of supercritical CO2 fluid is 0.3% to 0.8% of the mass of the core layer premix; Weigh out EVA resin, halogen-free composite flame retardant, crosslinking agent, silane coupling agent, antioxidant and light stabilizer according to the formula, mix them evenly to obtain the bottom layer adhesive weather-resistant protective layer mixture; wherein, the halogen-free composite flame retardant can be prepared in advance by compounding phosphorus nitrogen flame retardant and metal hydroxide according to a set mass ratio; The outer layer mixture, core layer mixture, and bottom layer mixture are respectively added to the barrel of a three-layer co-extrusion casting equipment. The overall melt extrusion temperature is controlled at 120-135°C. The mixture undergoes simultaneous melt bonding, casting, cooling, traction, and winding through a die to obtain the flame-retardant photovoltaic encapsulating film. In some embodiments, specifically, the chemical foaming agent is azodicarbonamide, added at 0.2%-0.5% of the total weight of the core layer raw materials; the amount of supercritical CO2 fluid injected is 0.3%-0.8% of the mass of the core layer premix.

[0044] In some embodiments, specifically, the extrusion temperature of the three-layer co-extrusion casting equipment is distributed in a gradient along the direction from the feed section to the die head, with the temperature of the feed section being 115-120°C, the temperature of the plasticizing section being 125-130°C, and the temperature of the die head being 130-135°C. Example

[0045] The multilayer composite hot spot self-triggered flame-retardant photovoltaic encapsulating film structure of this embodiment is as follows: Figure 1 As shown, it consists of an outer photothermal conversion functional layer 1, a core flame-retardant arc-blocking layer 2, and a bottom adhesive weather-resistant protective layer 3. The total thickness is approximately 320 μm, with the outer layer being 80 μm, the core layer 160 μm, and the bottom layer 80 μm.

[0046] The outer photothermal conversion functional layer formulation is as follows: 100 parts of EVA resin (Shenghong Sirbang UE2825, VA content 28%), 2 parts of carbon-based nanoparticles (graphene nanosheets, Suzhou Carbon-Feng Graphene Technology Co., Ltd.), 4 parts of hexagonal boron nitride powder (Dandong Rijin Technology Co., Ltd., particle size 1-5μm), 4 parts of nano alumina (Xuancheng Jingrui New Materials Co., Ltd., 30nm), 0.8 parts of crosslinking agent (diisopropylbenzene peroxide, Shanghai Gaoqiao Petrochemical), 0.5 parts of silane coupling agent (KH-570, Nanjing Shuguang Chemical Group), 0.2 parts of antioxidant (BASF Irganox 1010), 0.15 parts of ultraviolet absorber (BASF Tinuvin 327), and 0.2 parts of light stabilizer (BASF Tinuvin 770).

[0047] Core layer flame retardant arc barrier formulation: 100 parts POE resin (Dow Chemical ENGAGE 8669), 6.0 parts aluminum hypophosphite-based halogen-free composite thermosensitive flame retardant (aluminum hypophosphite to organic modified montmorillonite mass ratio 8:1; aluminum hypophosphite sourced from Jinan Taixing Fine Chemical Co., Ltd., organic modified montmorillonite brand DK4, Zhejiang Fenghong Clay Chemical Co., Ltd.), 2.0 parts melamine cyanurate (Shouguang Weidong Chemical Co., Ltd.), 0.5 parts nano silica charring agent (Evonik AEROSIL R972), 1.2 parts binder (polyethylene grafted maleic anhydride PE-g-MAH, Keais BF320), 1.8 parts perfluorohexanone microcapsules (wall material urea-formaldehyde resin, particle size approximately 5μm, core material perfluorohexanone purity ≥99%, sourced from Shanghai Weihua New Materials Technology Co., Ltd.), and 0.2 parts heat stabilizer (Ca-Zn composite heat stabilizer, German Bear brand MC9700KA1). The core layer is formed using a supercritical CO2 physical foaming process to create micropores with an average pore size of 10 μm and a porosity of 12%.

[0048] The formulation of the bottom bonding weather-resistant protective layer is as follows: 100 parts of EVA resin (same as the outer layer Sirbon UE2825), 2.0 parts of phosphorus-nitrogen halogen-free composite flame retardant (components are ammonium polyphosphate and aluminum hydroxide compound, weight ratio 3:1), 0.5 parts of crosslinking agent (dicumyl peroxide, Shanghai Gaoqiao Petrochemical), 0.8 parts of silane coupling agent (KH-560, Nanjing Shuguang), 0.3 parts of antioxidant (BASF, Irganox 1010), and 0.18 parts of light stabilizer (BASF, Tinuvin 770).

[0049] The preparation method of the composite encapsulating film includes the following steps: Weigh the EVA resin and all additives according to the outer layer formula, put them into a high-speed mixer and mix them at room temperature for 30 minutes to obtain the outer layer mixture, and discharge it for later use. According to the core layer formulation, materials other than perfluorohexanone microcapsules are put into a mixer and mixed for 15 minutes at a temperature of 50-60°C. After cooling to room temperature, microcapsules are added and the mixture is stirred at low speed for 15 minutes to obtain a core layer premix. The core layer premix is ​​fed into a twin-screw extruder, and supercritical CO2 is injected into the melting section at 0.5 wt% at a barrel temperature of 120-130°C to form a microporous melt and obtain a core layer mixture. Weigh all materials according to the bottom formula and put them into a high-speed mixer to mix evenly; The outer layer mixture, core layer mixture, and bottom layer mixture are added to the three barrels of the three-head three-layer co-extrusion casting equipment. The extrusion temperature is set to 128℃. The mixture is simultaneously melted and cast through the die head, cooled by the rapid cooling roller, and then pulled and wound to obtain the finished film. Example

[0050] The multilayer composite hotspot self-triggered flame-retardant photovoltaic encapsulation film structure in this embodiment is the same as that in Embodiment 1, consisting of an outer photothermal conversion functional layer, a core flame-retardant arc-shielding layer, and a bottom adhesive weather-resistant protective layer. The total thickness is approximately 320 μm, of which the outer photothermal conversion functional layer is 80 μm thick, the core flame-retardant arc-shielding layer is 160 μm thick, and the bottom adhesive weather-resistant protective layer is 80 μm thick.

[0051] The difference between this embodiment and Embodiment 1 is that the outer photothermal conversion functional layer uses a combination of core-shell photothermal composite nanoparticles and sheet-like hexagonal boron nitride thermally conductive filler, and the core flame-retardant arc-proof layer uses melamine resin wall material perfluorohexanone microcapsules, and constructs a microporous structure through chemical foaming to further reflect the multi-level linkage effect of photothermal absorption, rapid heat transfer, temperature-sensitive triggering release and arc-proof flame retardancy.

[0052] The outer photothermal conversion functional layer formulation is as follows: 100 parts EVA resin, 3.0 parts core-shell photothermal composite nanoparticles, 5.0 parts sheet-like hexagonal boron nitride powder, 2.0 parts nano-alumina, 0.8 parts crosslinking agent, 0.5 parts silane coupling agent KH-570, 0.2 parts antioxidant, 0.15 parts ultraviolet absorber, and 0.2 parts light stabilizer. The core-shell photothermal composite nanoparticles are composed of hexagonal boron nitride powder and black phosphorus nanosheets at a mass ratio of 2:1, with a particle size of 15–30 nm. The black phosphorus nanosheets enhance near-infrared and stray light absorption and achieve photothermal conversion, while the hexagonal boron nitride shell improves particle dispersion and thermal conductivity continuity within the EVA matrix.

[0053] The core layer flame-retardant arc-shielding layer formulation is as follows: 100 parts POE resin, 5.5 parts aluminum hypophosphite-based halogen-free composite thermosensitive flame retardant (the mass ratio of aluminum hypophosphite to organically modified montmorillonite is 6:1), 2.2 parts melamine cyanurate, 0.6 parts nano-silica charring agent, 1.0 part polyethylene-grafted maleic anhydride, 2.0 parts perfluorohexanone microcapsules, 0.1 parts heat stabilizer, and 0.3 parts chemical foaming agent azodicarbonamide. The perfluorohexanone microcapsules use melamine resin as the wall material and perfluorohexanone as the core material, with a particle size of approximately 8 μm. The wall material ruptures at 170–190°C, releasing perfluorohexanone.

[0054] The formulation of the bottom adhesive weather-resistant protective layer is the same as that in Example 1.

[0055] In preparation, each raw material was weighed according to the outer layer formula and mixed at room temperature and high speed to obtain the outer layer mixture. According to the core layer formula, POE resin, aluminum hypophosphite-based halogen-free composite thermosensitive flame retardant, melamine cyanurate, nano-silica charring agent, polyethylene grafted maleic anhydride, heat stabilizer, and azodicarbonamide were mixed evenly. After cooling, perfluorohexanone microcapsules were added and stirred at low speed to obtain the core layer premix. The core layer premix was fed into an extruder, and the temperature was controlled during extrusion to decompose the azodicarbonamide and form a microporous structure. The average pore size of the resulting core layer micropores was approximately 8–12 μm, and the porosity was approximately 13%. The preparation of the bottom layer mixture was the same as in Example 1. The outer layer mixture, core layer mixture, and bottom layer mixture were added separately to the barrel of a three-layer co-extrusion casting equipment. The overall extrusion temperature was controlled at 130°C. The mixture was simultaneously melted and laminated through a die, cast, cooled, drawn, and wound to obtain the multi-layer composite hot-spot self-triggered flame-retardant photovoltaic encapsulation film of this embodiment.

[0056] Under simulated hot spot conditions, the outer core-shell photothermal composite nanoparticles first absorb stray light and near-infrared light and convert them into local thermal signals. The sheet-like hexagonal boron nitride and nano-alumina form a heat-conducting network, which rapidly transmits the thermal signals to the core layer. The perfluorohexanone microcapsules in the core layer rupture in the range of 170-190℃ to release the fire extinguishing medium. Perfluorohexanone physically cools the initial flame and inhibits free radicals. At the same time, the aluminum hypophosphite-based halogen-free composite temperature-sensitive flame retardant and melamine cyanurate synergistically promote char formation. Nano-silica enhances the density of the char layer, and the microporous structure divides the arc channel and reduces the arc energy density, thereby forming a gradient linkage protection of "light absorption / photothermal conversion - rapid heat conduction - temperature-sensitive triggering - fire extinguishing and flame retardancy - arc isolation". Example

[0057] The multilayer composite hotspot self-triggered flame-retardant photovoltaic encapsulating film structure of this embodiment is the same as that of Embodiment 1, consisting of an outer photothermal conversion functional layer, a core flame-retardant arc-blocking layer, and a bottom adhesive weather-resistant protective layer. The difference between this embodiment and Embodiment 1 is that this embodiment increases the thickness of the outer and bottom layers and adjusts the ratio of photothermal conversion nanoparticles to thermally conductive fillers in the outer layer, so that the film maintains good light transmittance and adhesion performance while further enhancing the lateral heat uniformity of the hotspot area and the flame-retardant protection capability of the bottom layer.

[0058] In this embodiment, the total thickness of the adhesive film is approximately 400 μm, of which the outer photothermal conversion functional layer has a thickness of 120 μm, the core flame-retardant arc-blocking layer has a thickness of 160 μm, and the bottom adhesive weather-resistant protective layer has a thickness of 120 μm.

[0059] The outer photothermal conversion functional layer formulation is as follows: 100 parts EVA resin, 2.5 parts graphene nanosheets, 0.5 parts carbon nanotubes, 4.5 parts hexagonal boron nitride powder, 3.0 parts nano-alumina, 0.9 parts crosslinking agent, 0.6 parts silane coupling agent KH-570, 0.2 parts antioxidant, 0.15 parts ultraviolet absorber, and 0.2 parts light stabilizer. The graphene nanosheets and carbon nanotubes form a point-line-surface composite photothermal absorption structure, which can enhance the photothermal response of local hot spots; the hexagonal boron nitride powder and nano-alumina form a continuous thermal conduction path, which can quickly guide heat to the core layer and reduce local heat accumulation.

[0060] The core layer flame-retardant and arc-shielding layer formulation is the same as in Example 1, namely 100 parts POE resin, 6.0 parts aluminum hypophosphite-based halogen-free composite thermosensitive flame retardant, 2.0 parts melamine cyanurate, 0.5 parts nano-silica charring agent, 1.2 parts polyethylene grafted maleic anhydride, 1.8 parts perfluorohexanone microcapsules, and 0.2 parts heat stabilizer. The core layer is formed with micropores using a supercritical CO2 physical foaming process, with an average pore size of approximately 10 μm and a porosity of approximately 12%. The perfluorohexanone microcapsules release perfluorohexanone upon wall rupture at 170–190°C.

[0061] The formulation of the bottom adhesive weather-resistant protective layer is as follows: 100 parts EVA resin, 2.3 parts halogen-free composite flame retardant, 0.6 parts crosslinking agent, 0.9 parts silane coupling agent KH-560, 0.3 parts antioxidant, and 0.2 parts light stabilizer. The halogen-free composite flame retardant is a mixture of ammonium polyphosphate, melamine polyphosphate, and aluminum hydroxide, with a mass ratio of 2:1:1. Ammonium polyphosphate and melamine polyphosphate promote expansion into char and release inert gases, while aluminum hydroxide decomposes upon heating, absorbing heat and releasing moisture, thus helping to lower the bottom layer temperature and inhibit the spread of flames towards the battery cell side.

[0062] During preparation, by adjusting the output of each extruder and the flow rate ratio of the distributor in the three-layer co-extrusion casting equipment, the outer layer, core layer and bottom layer are respectively formed with layer thicknesses of 120μm, 160μm and 120μm; the overall extrusion temperature is controlled at 128℃, and the multilayer composite hot spot self-triggered flame retardant photovoltaic encapsulation film of this embodiment is obtained through synchronous melting and lamination, casting, cooling, traction and winding of the die head.

[0063] In this embodiment, the outer layer enhances light absorption and photothermal conversion efficiency through graphene nanosheets and carbon nanotubes, and improves thermal diffusion rate through hexagonal boron nitride and nano-alumina. The core layer achieves temperature-sensitive triggered fire extinguishing through perfluorohexanone microcapsules, gas-phase flame suppression and condensed-phase charring through an aluminum hypophosphite-based flame retardant system and melamine cyanurate, and arc isolation through a microporous structure. The bottom layer further constructs a flame-retardant barrier close to the cell side through a phosphorus-nitrogen flame retardant compounded with aluminum hydroxide. Thus, the film forms a functional gradient with a stepwise response from the glass side to the cell side: the outer layer is responsible for hot spot signal capture and heat transfer, the core layer is responsible for active fire extinguishing and arc isolation, and the bottom layer is responsible for adhesion, weather resistance, and secondary flame-retardant protection. Example

[0064] This embodiment provides an outer layer-enhanced thermally conductive multilayer composite hot spot self-triggered flame-retardant photovoltaic encapsulation film to illustrate the influence of different types of photothermal conversion nanoparticles and thermally conductive fillers on multi-level linkage protection performance.

[0065] In this embodiment, the total thickness of the adhesive film is approximately 340 μm, of which the outer photothermal conversion functional layer is 90 μm thick, the core flame-retardant arc-blocking layer is 170 μm thick, and the bottom adhesive weather-resistant protective layer is 80 μm thick.

[0066] The outer photothermal conversion functional layer formulation is as follows: 100 parts EVA resin, 2.0 parts carbon nanotubes, 1.0 part core-shell photothermal composite nanoparticles, 3.0 parts spherical aluminum nitride powder, 3.0 parts hexagonal boron nitride powder, 0.8 parts crosslinking agent, 0.5 parts silane coupling agent KH-570, 0.2 parts antioxidant, 0.15 parts ultraviolet absorber, and 0.2 parts light stabilizer. The core-shell photothermal composite nanoparticles are composed of hexagonal boron nitride powder and black phosphorus nanosheets at a mass ratio of 2:1. Carbon nanotubes mainly construct one-dimensional photothermal absorption and heat conduction channels, while the core-shell photothermal composite nanoparticles enhance near-infrared photothermal conversion efficiency. Spherical aluminum nitride and hexagonal boron nitride together construct a point-to-surface combined heat-conducting network.

[0067] The core layer flame-retardant arc-shielding layer formulation is as follows: 100 parts POE resin, 6.5 parts aluminum hypophosphite-based halogen-free composite thermosensitive flame retardant (the mass ratio of aluminum hypophosphite to organically modified montmorillonite is 7:1), 2.5 parts melamine cyanurate, 0.7 parts nano-silica charring agent, 1.3 parts modified polyolefin binder, 2.2 parts perfluorohexanone microcapsules, and 0.2 parts heat stabilizer. The perfluorohexanone microcapsules use urea-formaldehyde resin as the wall material, have a particle size of approximately 6 μm, and release perfluorohexanone at 170–190°C. The core layer is formed using a supercritical CO2 physical foaming process to create a microporous structure. The supercritical CO2 injection amount is 0.6% of the core layer premix mass, resulting in an average micropore diameter of approximately 9 μm and a porosity of approximately 15%.

[0068] The formulation of the bottom adhesive weather-resistant protective layer is as follows: 100 parts EVA resin, 2.0 parts halogen-free composite flame retardant, 0.5 parts crosslinking agent, 0.8 parts silane coupling agent KH-560, 0.3 parts antioxidant, and 0.18 parts light stabilizer. The halogen-free composite flame retardant is a mixture of ammonium polyphosphate and magnesium hydroxide in a mass ratio of 3:1.

[0069] The preparation method includes: weighing EVA resin, carbon nanotubes, core-shell photothermal composite nanoparticles, spherical aluminum nitride, hexagonal boron nitride, and various additives according to the outer layer formula, and mixing them at high speed to obtain the outer layer mixture; mixing POE resin, aluminum hypophosphite-based halogen-free composite thermosensitive flame retardant, melamine cyanurate, nano-silica charring agent, modified polyolefin adhesive, and heat stabilizer according to the core layer formula at 40-50℃, cooling to below 20℃, adding perfluorohexanone microcapsules, and stirring at low speed to obtain the core layer premix; feeding the core layer premix into a twin-screw extruder, injecting supercritical CO2 into the melting section to form a microporous core layer melt; and mixing all the raw materials of the bottom layer evenly to obtain the bottom layer mixture. Subsequently, the three mixtures were added to a three-layer co-extrusion casting equipment. The temperature of the feeding section was controlled at 115-120°C, the temperature of the plasticizing section was controlled at 125-130°C, and the temperature of the die head was controlled at 130-135°C. After co-extrusion casting, cooling, traction, and winding, the film of this embodiment was obtained.

[0070] The functional linkage process in this embodiment is as follows: the carbon nanotubes and black phosphorus-based core-shell particles in the outer layer preferentially absorb stray light and near-infrared light in the hot spot area and convert them into heat energy. The spherical aluminum nitride and hexagonal boron nitride form a continuous thermally conductive framework, which enables the heat to be quickly transferred to the core layer. After the microcapsules in the core layer reach the trigger temperature, they release perfluorohexanone, which rapidly reduces the local temperature and inhibits the combustion free radical chain reaction. The aluminum hypophosphite-based flame retardant, organic modified montmorillonite, melamine cyanurate, and nano-silica together form an expanded and dense halogen-free flame-retardant carbon layer. The microporous structure further extends the arc path, divides the arc channel, and reduces the heat penetration rate. The phosphorus-nitrogen flame retardant and magnesium hydroxide in the bottom layer provide heat absorption and cooling and carbonization protection, thereby achieving active protection with a step-by-step response. Example

[0071] This embodiment provides a bottom-reinforced flame-retardant multilayer composite hot spot self-triggered flame-retardant photovoltaic encapsulating film to illustrate the synergistic enhancement effect of the bottom-layer halogen-free composite phosphorus-nitrogen flame retardant and metal hydroxide composite on overall fire extinguishing, flame retardant and arc protection.

[0072] In this embodiment, the total thickness of the adhesive film is approximately 360 μm, of which the outer photothermal conversion functional layer is 90 μm thick, the core flame-retardant arc-blocking layer is 160 μm thick, and the bottom adhesive weather-resistant protective layer is 110 μm thick.

[0073] The outer photothermal conversion functional layer is formulated as follows: 100 parts EVA resin, 2.0 parts graphene nanosheets, 1.0 part core-shell photothermal composite nanoparticles, 4.0 parts hexagonal boron nitride powder, 3.0 parts nano alumina, 0.8 parts crosslinking agent, 0.5 parts silane coupling agent KH-570, 0.2 parts antioxidant, 0.15 parts ultraviolet absorber, and 0.2 parts light stabilizer.

[0074] The core layer flame-retardant and arc-shielding layer formulation is as follows: 100 parts POE resin, 5.8 parts aluminum hypophosphite-based halogen-free composite thermosensitive flame retardant (the mass ratio of aluminum hypophosphite to organically modified montmorillonite is 8:1), 2.0 parts melamine cyanurate, 0.5 parts nano-silica charring agent, 1.2 parts polyethylene-grafted maleic anhydride, 2.0 parts perfluorohexanone microcapsules, 0.2 parts heat stabilizer, and 0.25 parts azodicarbonamide. The perfluorohexanone microcapsules use melamine resin as the wall material, have a particle size of approximately 7 μm, and release perfluorohexanone at 170–190°C. The core layer forms a microporous structure through chemical foaming, with an average pore size of approximately 10–14 μm and a porosity of approximately 16%.

[0075] The formulation of the bottom adhesive weather-resistant protective layer is as follows: 100 parts EVA resin, 2.5 parts halogen-free composite flame retardant, 0.6 parts crosslinking agent, 0.9 parts silane coupling agent KH-560, 0.3 parts antioxidant, and 0.2 parts light stabilizer. The halogen-free composite flame retardant is a compound of phosphorus-nitrogen flame retardant and metal hydroxide. The phosphorus-nitrogen flame retardant is a mixture of ammonium polyphosphate and melamine cyanurate, and the metal hydroxide is a mixture of aluminum hydroxide and magnesium hydroxide. The mass ratio of ammonium polyphosphate, melamine cyanurate, aluminum hydroxide, and magnesium hydroxide is 2:1:1:1.

[0076] In preparation, the outer layer mixture, core layer premix, and bottom layer mixture are mixed according to the above formula. All raw materials except the perfluorohexanone microcapsules are added to the core layer premix first, and mixed evenly at 40–50°C. After the system cools to below 20°C, the perfluorohexanone microcapsules are added and mixed at a low speed to prevent premature rupture of the microcapsules during mixing. Subsequently, the three layers are added to a three-layer co-extrusion casting machine, with the overall melt extrusion temperature controlled at 120–135°C. After casting, cooling, traction, and winding, the film of this embodiment is obtained.

[0077] In this embodiment, the bottom layer constructs a phosphorus-nitrogen synergistic flame-retardant system using ammonium polyphosphate and melamine cyanurate. At high temperatures, this system forms a phosphoric acid-based dehydrated char structure and releases non-flammable gases. Aluminum hydroxide and magnesium hydroxide decompose upon heating, absorbing heat and releasing moisture, thus reducing the local temperature on the cell side and diluting the concentration of flammable gases. The core layer's perfluorohexanone microcapsules provide active fire suppression upon trigger release, while the core layer's charring system and microporous structure provide flame-retardant and arc-blocking functions. The bottom layer's composite flame-retardant system acts as a secondary protective barrier near the cell side, inhibiting the further propagation of flames and arcs towards the cell side. Therefore, this embodiment forms a more complete gradient protection chain between the outer layer's photothermal capture and heat conduction, the core layer's temperature-sensitive fire suppression and arc-blocking, and the bottom layer's flame-retardant protection.

[0078] The above Examples 1 to 5 respectively controlled the types of photothermal conversion nanoparticles in the outer layer, the types of thermally conductive fillers, the proportion of temperature-sensitive flame retardant in the core layer, the micropore formation method, the composition of the halogen-free composite flame retardant in the bottom layer, and the layer thickness gradient.

[0079] Example 1 uses graphene nanosheets combined with boron nitride / alumina thermally conductive filler to embody a basic photothermal conversion-thermal conduction-temperature-sensitive triggering structure; Example 2 uses black phosphorus / boron nitride core-shell photothermal composite nanoparticles to enhance the absorption of near-infrared and stray light; Example 3 improves the heat uniformity and secondary flame retardancy of the hot spot area by increasing the thickness of the outer and bottom layers and introducing a graphene nanosheet / carbon nanotube composite photothermal system; Example 4 describes the construction of a highly efficient photothermal-thermal network using carbon nanotubes, core-shell photothermal composite nanoparticles, aluminum nitride, and hexagonal boron nitride. Example 5 strengthens the flame-retardant barrier on the side of the battery cell by compounding the underlying phosphorus-nitrogen flame retardant with aluminum hydroxide and magnesium hydroxide.

[0080] Each embodiment revolves around a gradient multi-level linkage mechanism of "light absorption / photothermal conversion - rapid heat conduction - temperature-sensitive triggering - fire extinguishing and flame retardant - arc isolation", enabling the film to capture and transmit heat signals in the early stage of hot spot, release perfluorohexanone fire extinguishing medium when the temperature reaches the trigger range, and suppress thermal runaway and arc propagation through core layer charring, microporous arc isolation and bottom flame retardant barrier.

[0081] Comparative Example 1 This comparative example uses a traditional EVA encapsulating film with the following formulation: 100 parts EVA resin (Shenghong Sirbang UE2825), 0.5 parts dicumyl peroxide, 0.8 parts silane coupling agent KH-560, 0.3 parts antioxidant Irganox 1010, and 0.18 parts light stabilizer Tinuvin 770. The preparation process is the same as in Example 1, yielding a single-layer EVA film with a total thickness of 320 μm.

[0082] Performance testing: Lamination method: Lamination set temperature: 148℃, vacuum time: 6min, lamination time: 10min. After lamination, the following tests were performed: peel strength, light transmittance, component power and arc self-extinguishing. Samples were prepared and tested according to the peel strength and transmittance test methods provided in GB / T 29848-2013 "Ethylene-vinyl acetate copolymer (EVA) film for photovoltaic module encapsulation". Test the UL94 flame retardancy rating according to IEC 60695-11-10:2013 "Fire hazard testing - Part 11-10: Test flame 50W horizontal and vertical flame test method" and GB / T 2408-2008 "Determination of flammability of plastics - Horizontal and vertical methods"; A simulated hot spot arc test was conducted according to IEC 62271-200:2020 "High voltage switchgear and controlgear - Part 200: AC metal-enclosed switchgear and controlgear with rated voltage of 1 kV and above and 52 kV and below", and the arc self-extinguishing time after the power supply was cut off was recorded. The module underwent 2000 hours of accelerated aging under damp heat according to IEC TS 62804-1:2025 "Detection of potential induced degradation in photovoltaic (PV) modules - Part 1: Crystalline silicon photovoltaic modules" to test the maximum power degradation rate of the module. Under simulated hot spot irradiation, the time required for the film to trigger the self-triggering function of the hot spot was tested, and the thermal response time was recorded. The critical temperature for rupture of perfluorohexanone microcapsules was determined by differential scanning calorimetry (DSC), and the rupture temperature was recorded.

[0083] Table 1

[0084] As shown in Table 1, Examples 1-5 all exhibited good visible light transmittance, flame retardant properties, adhesive properties, and hot spot response capabilities. Compared with Comparative Example 1, Examples 1-5 were able to achieve temperature-sensitive triggering and autonomous arc extinguishing under hot spot conditions, indicating that an effective synergistic protection mechanism is formed between the outer photothermal conversion functional layer, the core flame-retardant arc-blocking layer, and the bottom adhesive weather-resistant protective layer of the present invention.

[0085] Example 4: Because the outer layer is composed of carbon nanotubes, core-shell photothermal composite nanoparticles, aluminum nitride and hexagonal boron nitride, a more efficient photothermal absorption and rapid heat conduction network can be formed, thus further shortening the thermal response time and reducing the arc self-extinguishing time.

[0086] Example 5: Because the bottom layer uses a phosphorus-nitrogen flame retardant compounded with aluminum hydroxide and magnesium hydroxide, a composite flame retardant barrier is formed near the battery cell side, which absorbs heat and cools down, expands into carbon, and dilutes in the gas phase. Therefore, while maintaining good adhesion performance, the overall flame retardant and arc protection capabilities of the film are further improved.

[0087] Examples 1-5 all achieved the UL94 V-0 flame retardant rating, and their power attenuation after damp heat aging was lower than that of Comparative Example 1. This indicates that while improving flame retardancy and arc blocking capabilities, the present invention did not significantly sacrifice the weather resistance and adhesion reliability of the encapsulating film. Overall, the present invention achieves proactive protection against hot spots, electric arcs, and initial combustion risks of photovoltaic modules through a gradient multi-level linkage design of "light absorption / photothermal conversion—rapid heat conduction—temperature-sensitive triggering—fire extinguishing and flame retardancy—arc blocking".

[0088] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A flame-retardant photovoltaic encapsulating film, characterized in that, Along the glass side facing the photovoltaic module to the cell side, it includes a composite outer photothermal conversion functional layer, a core flame-retardant arc-blocking layer, and a bottom adhesive weather-resistant protective layer. The base resin of the outer photothermal conversion functional layer is EVA resin, and the outer photothermal conversion functional layer includes photothermal conversion nanoparticles and thermally conductive fillers. The core flame-retardant arc-proof layer is a porous membrane layer with a microporous structure. The matrix resin of the core flame-retardant arc-proof layer is POE resin. The core flame-retardant arc-proof layer includes an aluminum hypophosphite-based halogen-free composite thermosensitive flame retardant, perfluorohexanone microcapsules, and an adhesive containing hydrolyzable silane groups. The average pore size of the micropores is 5–15 μm, and the porosity is 10%–20%. The base resin of the bottom adhesive weather-resistant protective layer is EVA resin, and the bottom adhesive weather-resistant protective layer includes a halogen-free composite flame retardant. The outer photothermal conversion functional layer is used for light absorption, photothermal conversion and rapid heat conduction; the core flame-retardant arc-blocking layer is used for temperature-sensitive triggering release of extinguishing medium, charring flame retardancy and arc blocking; and the bottom adhesive weather-resistant protective layer is used for adhesive weather resistance and secondary flame-retardant protection.

2. The flame-retardant photovoltaic encapsulating film as described in claim 1, characterized in that, The photothermal conversion nanoparticles are selected from one or more of graphene nanosheets, carbon nanotubes, black phosphorus nanosheets, and core-shell photothermal composite nanoparticles.

3. The flame-retardant photovoltaic encapsulating film as described in claim 2, characterized in that, The core-shell photothermal composite nanoparticles are formed by combining hexagonal boron nitride powder and black phosphorus nanosheets, wherein the mass ratio of hexagonal boron nitride powder to black phosphorus nanosheets is 1 to 4:

1. The core-shell photothermal composite nanoparticles have a particle size of 15–30 nm.

4. The flame-retardant photovoltaic encapsulating film as described in claim 1, characterized in that, The thermally conductive filler is selected from one or more of hexagonal boron nitride, aluminum nitride, aluminum oxide, magnesium oxide, and silicon nitride.

5. The flame-retardant photovoltaic encapsulating film according to claim 1, characterized in that, The perfluorohexanone microcapsules use urea-formaldehyde resin or melamine resin as the wall material and perfluorohexanone as the core material. The microcapsule particle size is 3-10 μm. The perfluorohexanone microcapsules release perfluorohexanone when the wall material ruptures at 170-190°C.

6. The flame-retardant photovoltaic encapsulating film as described in claim 1, characterized in that, The halogen-free composite flame retardant is a compound of phosphorus-nitrogen flame retardant and metal hydroxide.

7. The flame-retardant photovoltaic encapsulating film as described in claim 6, characterized in that, The phosphorus-nitrogen flame retardant is selected from one or more of ammonium polyphosphate, melamine polyphosphate, melamine cyanurate, and hypophosphite; The metal hydroxide is selected from one or two of aluminum hydroxide and magnesium hydroxide.

8. The flame-retardant photovoltaic encapsulating film as described in claim 6, characterized in that, The mass ratio of the phosphorus-nitrogen flame retardant to the metal hydroxide is 1 to 5:

1.

9. The flame-retardant photovoltaic encapsulating film as described in claim 1, characterized in that, The outer photothermal conversion functional layer has a thickness of 60–300 μm and is composed of the following raw materials in parts by weight: 100 parts EVA resin, 2–4 parts photothermal conversion nanoparticles, 3–8 parts thermally conductive filler, 0.6–1.2 parts crosslinking agent, 0.3–0.8 parts silane coupling agent, 0.15–0.3 parts antioxidant, 0.1–0.2 parts ultraviolet absorber, and 0.1–0.3 parts light stabilizer.

10. The flame-retardant photovoltaic encapsulating film as described in claim 1, characterized in that, The core flame-retardant arc-blocking layer has a thickness of 90–220 μm and is composed of the following raw materials in parts by weight: 100 parts POE resin, 4.5–7.0 parts aluminum hypophosphite-based halogen-free composite thermosensitive flame retardant, 1.5–3.0 parts melamine cyanurate, 0.3–0.8 parts nano silica charring agent, 0.8–1.5 parts adhesive, 1.5–2.5 parts perfluorohexanone microcapsules, and 0.1–0.3 parts heat stabilizer; The adhesive is a modified polyolefin adhesive or polyethylene grafted with maleic anhydride.

11. The flame-retardant photovoltaic encapsulating film as described in claim 1, characterized in that, The thickness of the bottom adhesive weather-resistant protective layer is 60-300 μm, and it is composed of the following raw materials in parts by weight: 100 parts of EVA resin, 1.5-2.5 parts of halogen-free composite flame retardant, 0.4-0.8 parts of crosslinking agent, 0.5-1.0 parts of silane coupling agent, 0.2-0.5 parts of antioxidant, and 0.1-0.3 parts of light stabilizer.

12. A method for preparing a flame-retardant photovoltaic encapsulating film as described in any one of claims 1-11, characterized in that, Includes the following steps: Weigh the EVA resin, photothermal conversion nanoparticles, thermally conductive filler and additives for the outer photothermal conversion functional layer according to the formula, and mix them at room temperature and high speed to obtain the outer layer mixture. Weigh out the solid raw materials of the core layer flame retardant arc barrier according to the formula. Mix POE resin, aluminum hypophosphite-based halogen-free composite temperature-sensitive flame retardant, melamine cyanurate, nano silica charring agent, binder, and heat stabilizer evenly at 40-50°C. After cooling to below 20°C, add perfluorohexanone microcapsules and stir evenly at low speed to obtain the core layer premix. Feed the core layer premix into an extruder and inject supercritical CO2 fluid or add chemical foaming agent in the melting section to form a microporous structure to obtain the core layer mixture. Weigh out the EVA resin, halogen-free composite flame retardant, crosslinking agent, silane coupling agent, antioxidant and light stabilizer for the bottom layer bonding weather-resistant protective layer according to the formula, mix them evenly to obtain the bottom layer mixture. The outer layer mixture, core layer mixture, and bottom layer mixture are added to the barrel of a three-layer co-extrusion casting equipment. The overall melt extrusion temperature is controlled at 120-135℃. After casting, cooling, traction, and winding, flame-retardant photovoltaic encapsulation film is obtained.

13. The preparation method according to claim 12, characterized in that, The chemical foaming agent is azodicarbonamide, and the amount added is 0.2% to 0.5% of the total weight of the core layer raw materials; The injection rate of the supercritical CO2 fluid is 0.3% to 0.8% of the mass of the core premix.

14. The preparation method according to claim 12, characterized in that, The extrusion temperature of the three-layer co-extrusion casting equipment is distributed in a gradient along the direction from the feeding section to the die head. The temperature of the feeding section is 115-120℃, the temperature of the plasticizing section is 125-130℃, and the temperature of the die head is 130-135℃.

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