Amphiphilic block polymer nanospheres, methods of making and uses thereof

Abstract

The present application provides an amphiphilic block polymer nanosphere, a preparation method and an application. The amphiphilic block polymer nanosphere comprises a hydrophobic polymer core, a fluorine-containing crosslinked shell layer covering at least part of the outer surface of the hydrophobic polymer core, and a thermally responsive segment polymer arm and a reactive adhesive segment polymer arm grafted to at least part of the outer surface of the fluorine-containing crosslinked shell layer. The photovoltaic encapsulation adhesive film comprising the amphiphilic block polymer nanosphere of the present application can simultaneously have high adhesion and high barrier properties.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic materials, and in particular to an amphiphilic block polymer nanosphere, its preparation method, and its application. Background Technology

[0002] Photovoltaic encapsulation films are the core encapsulation materials for photovoltaic modules, widely used in the manufacture of new photovoltaic modules such as monocrystalline silicon, polycrystalline silicon, perovskite tandem cells, and heterojunction cells. They undertake the core functions of bonding and fixing, environmental barrier, optical coupling, and electrical insulation. As photovoltaic modules develop towards higher efficiency and longer lifespan, the market is placing higher performance demands on photovoltaic encapsulation films. These films not only need to maintain high adhesive strength over long periods in extreme environments such as high humidity, high temperature, and ultraviolet radiation, but also require low gas permeability to meet the 25-30 year service life requirements of photovoltaic modules.

[0003] Existing technologies mainly improve the performance of photovoltaic encapsulation films through three pathways, but all have significant drawbacks. The first type is high-adhesion encapsulation film technology. This technology adds a large amount of silane coupling agents, tackifying resins, and inorganic nanoparticles to matrix resins such as ethylene-vinyl acetate copolymer (EVA) and polyolefin elastomer (POE). While this can improve the initial adhesive strength and mechanical properties of the photovoltaic encapsulation film, the silane coupling agents and tackifying resins easily migrate to the surface of the photovoltaic encapsulation film under humid and hot aging conditions, causing uneven distribution of components within the photovoltaic encapsulation film, damaging its density, and thus reducing its barrier properties. Furthermore, the tackifying resin will hydrolyze and volatilize over long-term use, leading to further degradation of the photovoltaic encapsulation film. The first type is the continuous degradation of the film's adhesiveness; the second type is high-barrier encapsulant film technology, which adds layered nanofillers to the photovoltaic encapsulant film to improve its barrier properties. However, nanofillers reduce the adhesive strength of the photovoltaic encapsulant film, and after long-term use and aging, they will agglomerate and settle, causing the barrier performance of the photovoltaic encapsulant film to deteriorate; the third type is simple compounded bifunctional encapsulant film technology, which adds both tackifiers and barrier fillers to the photovoltaic encapsulant film. However, the synergy between tackifiers and barrier fillers is poor, and problems such as tackifiers damaging the barrier network and barrier fillers weakening the adhesive interface are prone to occur, resulting in the adhesiveness and barrier properties canceling each other out.

[0004] In summary, existing technologies cannot simultaneously achieve both high adhesion and high barrier properties in photovoltaic encapsulation films, thus failing to meet the development requirements of high efficiency and long lifespan for photovoltaic modules. Therefore, there is a need to provide a photovoltaic encapsulation film that combines both high adhesion and high barrier properties. Summary of the Invention

[0005] The first aspect of the present invention provides an amphiphilic block polymer nanosphere, which, when applied to a photovoltaic encapsulation film, can enable the photovoltaic encapsulation film to possess both high adhesion and high barrier properties.

[0006] A second aspect of the present invention provides a method for preparing amphiphilic block polymer nanospheres, which can prepare the above-mentioned amphiphilic block polymer nanospheres.

[0007] A third aspect of the present invention provides a photovoltaic encapsulation film comprising the above-mentioned amphiphilic block polymer nanospheres, wherein the photovoltaic encapsulation film of the present invention has both high adhesion and high barrier properties.

[0008] A fourth aspect of the present invention provides a photovoltaic module including the photovoltaic encapsulating film described above, wherein the photovoltaic module of the present invention has a long service life.

[0009] A first aspect of the present invention provides an amphiphilic block polymer nanosphere comprising a hydrophobic polymer core, a fluorinated cross-linked shell coating at least a portion of the outer surface of the hydrophobic polymer core, and thermally responsive polymer arms and reactive adhesive polymer arms grafted onto at least a portion of the outer surface of the fluorinated cross-linked shell.

[0010] The amphiphilic block polymer nanospheres described above, wherein the thermally responsive polymer arms comprise poly(N-isopropylacrylamide).

[0011] The reactive adhesive polymer arm comprises poly(methacrylate-copolymer-glycidyl methacrylate).

[0012] The hydrophobic polymer core comprises polystyrene-copoly-divinylbenzene and / or polymethyl methacrylate-copoly-divinylbenzene, and at least a portion of the surface and interior of the hydrophobic polymer core comprises epoxy groups.

[0013] The amphiphilic block polymer nanospheres described above, wherein the hydrophobic polymer core has a particle size of 50~200 nm;

[0014] The thickness of the fluorinated cross-linked shell is 5~10 nm.

[0015] A second aspect of the present invention provides a method for preparing the above-mentioned amphiphilic block polymer nanospheres, comprising:

[0016] Synthesize the hydrophobic polymer core;

[0017] At least a portion of the surface of the hydrophobic polymer core is coated with a fluorinated crosslinked shell formed by copolymerization of fluorinated monomers and crosslinking agents;

[0018] At least a portion of the surface of the fluorinated crosslinked shell is grafted with thermally responsive polymer arms and reactive adhesive polymer arms.

[0019] The method for preparing amphiphilic block polymer nanospheres as described above includes:

[0020] A first raw material system comprising a first monomer and divinylbenzene is subjected to a first polymerization reaction to obtain a first emulsion comprising the hydrophobic polymer core;

[0021] A second polymerization reaction is carried out on a second raw material system comprising the first emulsion, dodecafluoroheptyl methacrylate and pentaerythritol triacrylate to obtain a second emulsion comprising the hydrophobic polymer core and a fluorinated crosslinked shell located on at least a portion of the surface of the hydrophobic polymer core.

[0022] A third polymerization reaction is carried out on a third raw material system comprising the second emulsion, a reversible addition-fragmentation chain transfer agent, N-isopropylacrylamide, methacrylic acid, and glycidyl methacrylate, to form thermally responsive polymer arms and reactive adhesive polymer arms on at least a portion of the surface of the fluorinated crosslinked shell.

[0023] The first monomer includes methyl methacrylate or styrene.

[0024] The preparation method of amphiphilic block polymer nanospheres as described above, wherein the first raw material system further includes a second monomer with a molar percentage of 1-5%, the second monomer comprising epoxy groups; and / or,

[0025] In the first polymerization reaction, the temperature is 70~80℃ and the time is 6~8h;

[0026] In the second polymerization reaction, the temperature is 75~85℃ and the time is 4~6h;

[0027] In the third polymerization reaction, the temperature is 55~65℃ and the time is 8~12h.

[0028] A third aspect of the present invention provides a photovoltaic encapsulating film comprising the aforementioned amphiphilic block polymer nanospheres.

[0029] In the photovoltaic encapsulation film described above, the mass fraction of the amphiphilic block polymer nanospheres in the photovoltaic encapsulation film is 3 to 10.

[0030] The photovoltaic encapsulating film as described above further comprises, by weight parts: 80-120 parts of matrix resin, 0.6-1.2 parts of main crosslinking agent, 0.3-0.8 parts of co-crosslinking agent, 0.2-0.8 parts of silane coupling agent, 0.3-1.0 parts of UV additive, 0.1-0.3 parts of antioxidant, and 0.05-0.2 parts of deacidifying agent.

[0031] A fourth aspect of the present invention provides a photovoltaic module, wherein the photovoltaic encapsulating film described above is included.

[0032] This invention designs an amphiphilic block polymer nanosphere having a hydrophobic polymer core, a fluorinated cross-linked shell covering at least a portion of the outer surface of the hydrophobic polymer core, and thermally responsive polymer arms and reactive adhesive polymer arms grafted onto at least a portion of the outer surface of the fluorinated cross-linked shell. This amphiphilic block polymer nanosphere is then placed within a photovoltaic encapsulation film, solving the problem in existing photovoltaic encapsulation films that cannot simultaneously possess high adhesion and high barrier properties. When this photovoltaic encapsulation film is applied to photovoltaic modules, it can extend the service life of the photovoltaic modules. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. 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. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0034] Existing photovoltaic encapsulation films cannot simultaneously possess both high adhesion and high barrier properties. The inventors discovered in their research that by adding an amphiphilic block polymer nanosphere with a "core-shell-polymer arm" structure to the photovoltaic encapsulation film, the photovoltaic encapsulation film can achieve both high adhesion and high barrier properties.

[0035] A first aspect of the present invention provides an amphiphilic block polymer nanosphere comprising a hydrophobic polymer core, a fluorinated cross-linked shell coating at least a portion of the outer surface of the hydrophobic polymer core, and thermally responsive polymer arms and reactive adhesive polymer arms grafted onto at least a portion of the outer surface of the fluorinated cross-linked shell.

[0036] Specifically, in the amphiphilic block polymer nanospheres of the present invention, the hydrophobic polymer core can play a hydrophobic barrier role, and the fluorinated cross-linked shell can enhance the structural stability of the amphiphilic block polymer nanospheres, while providing anchoring points for the thermally responsive polymer arms and the reactive adhesive polymer arms. The thermally responsive polymer arms can change their morphology according to temperature changes, and the reactive adhesive polymer arms can interact with specific materials to achieve strong adhesion. Through the synergistic effect of the hydrophobic polymer core, the fluorinated cross-linked shell, and the thermally responsive and reactive adhesive polymer arms in the amphiphilic block polymer nanospheres of the present invention, the amphiphilic block polymer nanospheres possess excellent structural stability, environmental responsiveness, and adhesion ability.

[0037] Photovoltaic modules typically consist of a cover plate (including glass or a backsheet), a photovoltaic encapsulating film, and solar cells. The photovoltaic encapsulating film is positioned closer to one side of the solar cells, while the cover plate is positioned further away. In existing technologies, the adhesiveness of the photovoltaic encapsulating film refers to the interfacial adhesion between the encapsulating film and the substrates of the photovoltaic module (including the cover plate and solar cells). Good adhesion ensures that all components of the photovoltaic module are tightly bonded together, guaranteeing the structural stability of the photovoltaic module and preventing failures such as delamination or peeling under long-term use or external stress. The barrier properties of the photovoltaic encapsulating film refer to its ability to prevent external moisture, acidic gases, and other corrosive substances from penetrating the interior of the photovoltaic module. Excellent barrier properties reduce the aging effects of corrosive substances on the photovoltaic module, thereby extending its service life.

[0038] When the amphiphilic block polymer nanospheres of the present invention are used in photovoltaic encapsulation films, the hydrophobic polymer core and the fluorinated cross-linked shell are dispersed together in the matrix resin of the photovoltaic encapsulation film. The hydrophobic properties of the hydrophobic polymer core can reduce water vapor adsorption. The fluorinated cross-linked shell has a dense cross-linked structure, and the fluorine atoms give the fluorinated cross-linked shell a low surface energy characteristic. The low surface energy characteristic can significantly reduce the adsorption between the fluorinated cross-linked shell and water molecules. The hydrophobic polymer core and the fluorinated cross-linked shell form a dense three-dimensional network in the photovoltaic encapsulation film. The "maze effect" of the three-dimensional network is used to extend the penetration path of corrosive substances such as water vapor and acidic gases. At the same time, the low surface energy characteristic of the fluorinated cross-linked shell is used to inhibit water vapor penetration, thereby improving the barrier properties of the photovoltaic encapsulation film.

[0039] Photovoltaic module assembly typically employs a lamination process. Under the high-temperature conditions of this lamination process, the structure of the thermally responsive polymer arms grafted onto at least part of the outer surface of the fluorinated cross-linked shell in amphiphilic block polymer nanospheres changes from curling to stretching. This causes the reactive adhesive polymer arms to migrate to the interface between the photovoltaic encapsulation film and the cover plate, solar cells, or other substrates. The active functional groups contained in these reactive adhesive polymer arms can undergo chemical reactions such as esterification and etherification with the hydroxyl groups on the substrate surface to form stable covalent bonds. The strong bonding properties of these covalent bonds enhance the adhesion of the photovoltaic encapsulation film, thereby strengthening the interfacial adhesion between the photovoltaic encapsulation film and the substrate.

[0040] When the photovoltaic encapsulation film includes the amphiphilic block polymer nanospheres of the present invention, the barrier properties of the photovoltaic encapsulation film are borne by the hydrophobic polymer core and the fluorinated cross-linked shell of the amphiphilic block polymer nanospheres; while the adhesive properties of the photovoltaic encapsulation film are jointly achieved by the thermally responsive polymer arms and the reactive adhesive polymer arms of the amphiphilic block polymer nanospheres. This allows the photovoltaic encapsulation of the present invention to have both excellent barrier properties and excellent adhesive properties, effectively solving the problem in the prior art where the adhesive and barrier properties of photovoltaic encapsulation films cancel each other out due to the migration of small molecule additives and the enrichment of nanofiller interfaces.

[0041] Furthermore, in existing technologies, photovoltaic encapsulation films require the addition of a large amount of additives to balance adhesion and barrier properties. The extensive use of these additives increases the haze of the photovoltaic encapsulation film, reduces its light transmittance, and consequently degrades its optical performance. This invention, through the formation of stable covalent bonds between the reactive adhesive polymer arms in amphiphilic block polymer nanospheres and the substrate surface, ensures the long-term stability of the adhesion of the photovoltaic encapsulation film. At the same time, it eliminates the need for the addition of a large amount of additives, enabling the photovoltaic encapsulation film to maintain optical performance while exhibiting superior adhesion.

[0042] In some embodiments, the photovoltaic encapsulating film comprising the amphiphilic block polymer nanospheres of the present invention has a water vapor transmission rate of less than 10 g / m³ at a temperature of 40°C and a relative humidity of 90%. 2 Furthermore, the water vapor transmission rate can be reduced to 5 g / m². 2 • Day or less.

[0043] Initial peel strength refers to the peel force per unit width between the photovoltaic encapsulating film and the substrate (such as glass) of a photovoltaic module when the encapsulating film is peeled from the substrate in its initial state without any aging treatment, according to the prescribed test standards. A higher initial peel strength indicates better adhesion of the photovoltaic encapsulating film. In some embodiments, the initial peel strength between the photovoltaic encapsulating film, including the amphiphilic block polymer nanospheres of this invention, and the glass is greater than 100 N / cm, and further, the initial peel strength is 120 N / cm. After aging the photovoltaic module in an environment of 85°C and 85% relative humidity for 5000 hours, the peel strength retention rate between the photovoltaic encapsulating film and the glass in the photovoltaic module is still above 85%, while the peel strength retention rate of existing photovoltaic encapsulating films under the same aging test conditions is usually less than 50%.

[0044] In some embodiments of the present invention, the thermally responsive polymer arm comprises poly(N-isopropylacrylamide), which has a low critical dissolution temperature (about 32°C) and whose molecular chain contains both hydrophilic amide groups and hydrophobic isopropyl groups. At room temperature storage and the melt extrusion temperature of the photovoltaic encapsulation film, the amide groups form hydrogen bonds with water molecules in the surrounding environment, causing the thermally responsive polymer arms to become hydrophilic and curl up, encapsulating the reactive adhesive polymer arms and ensuring the integrity of the three-dimensional network in the photovoltaic encapsulation film. The reactive adhesive polymer arms include poly(methacrylic acid-copoly-glycidyl methacrylate). Poly(methacrylic acid-copoly-glycidyl methacrylate) contains abundant carboxyl groups (-COOH) and epoxy groups. At the lamination process temperature, the hydrogen bonding between the molecular chains of the thermally responsive polymer arms is disrupted, and the hydrophobic effect of the isopropyl groups becomes dominant, causing the thermally responsive polymer arms to change from a hydrophilic state to a hydrophobic state and extend. This propels the reactive adhesive polymer arms to migrate to the interface between the photovoltaic encapsulation film and the substrate, where the carboxyl groups and epoxy groups in the reactive adhesive polymer arms react chemically with the hydroxyl groups on the substrate surface to form stable covalent bonds, improving the adhesion of the photovoltaic encapsulation film.

[0045] In some embodiments of the present invention, the hydrophobic polymer core comprises polystyrene-copoly-divinylbenzene and / or polymethyl methacrylate-copoly-divinylbenzene, and at least a portion of the surface and interior of the hydrophobic polymer core comprises epoxy groups.

[0046] Specifically, the hydrophobic polymer core may include polystyrene-co-divinylbenzene, polymethyl methacrylate-co-divinylbenzene, or both. Polystyrene-co-divinylbenzene and / or polymethyl methacrylate-co-divinylbenzene impart excellent hydrophobicity to the hydrophobic polymer core, reducing water vapor adsorption and providing a substrate for the fluorinated crosslinked shell. The epoxy groups on the surface and inside the hydrophobic polymer core can react with the active groups in the fluorinated crosslinked shell, enhancing the bonding force between the hydrophobic polymer core and the fluorinated crosslinked shell, resulting in greater stability of the amphiphilic block polymer nanospheres and thus providing superior barrier properties for the photovoltaic encapsulation film.

[0047] In some implementations, the melt extrusion temperature of the photovoltaic encapsulating film is less than 90°C;

[0048] In some implementations, the lamination process is carried out at a temperature of 140-150°C.

[0049] In some embodiments of the present invention, when the particle size of the hydrophobic polymer core is 50-200 nm, the amphiphilic block polymer nanospheres including the hydrophobic polymer core can be stably and uniformly dispersed in the photovoltaic encapsulation film without agglomeration. They synergistically construct a dense and continuous three-dimensional network with the fluorinated cross-linked shell, maximizing the "maze effect" and extending the penetration path of corrosive substances such as water vapor and acidic gases. At the same time, it can also ensure the optical performance of the photovoltaic encapsulation film itself, giving the photovoltaic encapsulation film better barrier properties.

[0050] In some embodiments of the present invention, when the thickness of the fluorinated crosslinked shell is 5~10nm, on the one hand, a uniform and dense coating layer can be formed on the surface of the hydrophobic polymer core, giving full play to the low surface energy characteristics and forming a continuous three-dimensional network with the hydrophobic polymer core; on the other hand, the compatibility between the amphiphilic block polymer nanospheres and the matrix resin in the photovoltaic encapsulation film can be maintained, thereby giving the photovoltaic encapsulation film better barrier properties.

[0051] A second aspect of the present invention provides a method for preparing the above-mentioned amphiphilic block polymer nanospheres, comprising:

[0052] Synthesize hydrophobic polymer cores;

[0053] At least a portion of the surface of the hydrophobic polymer core is coated with a fluorinated crosslinked shell formed by copolymerization of fluorinated monomers and crosslinking agents;

[0054] At least a portion of the surface of the fluorinated cross-linked shell is grafted with thermally responsive polymer arms and reactive adhesive polymer arms.

[0055] Specifically, a hydrophobic polymer core is first synthesized, and then a fluorinated monomer and a crosslinking agent are copolymerized with the hydrophobic polymer core to coat the surface of the hydrophobic polymer core with a fluorinated crosslinked shell. Then, a thermally responsive polymer and a reactive adhesive polymer are grafted onto the surface of the fluorinated crosslinked shell to form thermally responsive polymer arms and reactive adhesive polymer arms, ultimately obtaining the amphiphilic block polymer nanospheres of the present invention.

[0056] The preparation method of the amphiphilic block polymer nanospheres of the present invention, through stepwise synthesis of hydrophobic polymer core, coating with fluorinated cross-linked shell, and grafting of thermally responsive polymer arms and reactive adhesive polymer arms, can ensure that the hydrophobic polymer core, fluorinated cross-linked shell, thermally responsive polymer arms and reactive adhesive polymer arms of the amphiphilic block polymer nanospheres can all exist stably and play their respective roles. Thus, it is ensured that when the amphiphilic block polymer nanospheres are applied to photovoltaic encapsulation films, the photovoltaic encapsulation films can have both high barrier properties and high adhesion.

[0057] In some embodiments of the present invention, the preparation method of amphiphilic block polymer nanospheres includes:

[0058] A first raw material system comprising a first monomer, divinylbenzene, and glycidyl methacrylate is subjected to a first polymerization reaction to obtain a first emulsion comprising a hydrophobic polymer core.

[0059] A second polymerization reaction is carried out on a second raw material system comprising a first emulsion, dodecafluoroheptyl methacrylate and pentaerythritol triacrylate to obtain a second emulsion comprising a hydrophobic polymer core and a fluorinated crosslinked shell located on at least a portion of the surface of the hydrophobic polymer core.

[0060] A third polymerization reaction is carried out on a third raw material system comprising a second emulsion, a reversible addition-fragmentation chain transfer agent, N-isopropylacrylamide, methacrylic acid, and glycidyl methacrylate to form a thermally responsive polymer arm and a reactive adhesive polymer arm on at least a portion of the surface of the fluorinated crosslinked shell.

[0061] The first monomer includes methyl methacrylate or styrene.

[0062] Specifically, during the first polymerization reaction, the unsaturated double bonds in the first monomer break and copolymerize with the double bonds of divinylbenzene. The divinylbenzene molecule contains two polymerizable double bonds. During the polymerization process, the first monomer and divinylbenzene crosslink to form a hydrophobic polymer core. After the first polymerization reaction is completed, the generated hydrophobic polymer core is dispersed in the reaction system to obtain the first emulsion.

[0063] In the second polymerization reaction, the crosslinking agent can be pentaerythritol triacrylate, ethylene glycol dimethacrylate, or both pentaerythritol triacrylate and ethylene glycol dimethacrylate. The unsaturated bonds of dodecafluoroheptyl methacrylate and the crosslinking agent break, and copolymerization occurs on the surface of the hydrophobic polymer core, thereby forming a fluorinated crosslinked shell on the surface of the hydrophobic polymer core to obtain the second emulsion.

[0064] Some double bonds in dodecafluoroheptyl methacrylate and the crosslinking agent failed to fully participate in the second polymerization reaction and remained on the surface of the fluorinated crosslinked shell, providing anchoring sites for covalent bonding in the third polymerization reaction. In the third polymerization reaction, the active groups in the reversible addition-fragmentation chain transfer agent molecule can undergo addition reactions with the double bonds remaining on the surface of the fluorinated crosslinked shell, and are covalently bonded to the surface of the fluorinated crosslinked shell, becoming chain transfer sites for the third polymerization reaction. N-isopropylacrylamide monomers polymerize at the chain transfer sites to form the first polymer chain. The reversible addition-fragmentation chain transfer agent effectively inhibits the disordered crosslinking of the first polymer chain, and the growth rate of the first polymer chain is controllable, eventually forming a thermally responsive polymer arm grafted onto the surface of the fluorinated crosslinked shell. At the same time, methacrylic acid monomers and glycidyl methacrylate monomers undergo copolymerization reactions, forming the second polymer chain through alternating or block linkages. Finally, under the action of the reversible addition-fragmentation chain transfer agent, reactive adhesive polymer arms are formed, resulting in the amphiphilic block polymer nanospheres of the present invention.

[0065] The preparation method of the amphiphilic block polymer nanospheres of the present invention is simple and highly controllable. It can accurately construct a structure consisting of a hydrophobic polymer core, a fluorinated cross-linked shell coating the surface of the hydrophobic polymer, and thermally responsive polymer arms and reactive adhesive polymer arms grafted onto the surface of the fluorinated cross-linked shell. Furthermore, it eliminates the need for complex separation and purification steps, ensuring that the amphiphilic block polymer nanospheres have high purity. When these amphiphilic block polymer nanospheres are used in photovoltaic encapsulation films, they can enhance the barrier and adhesive properties of the photovoltaic encapsulation films.

[0066] In some embodiments of the present invention, when the first raw material system further includes glycidyl methacrylate with a molar percentage of 1-5%, glycidyl methacrylate can participate in copolymerization during the first polymerization reaction and introduce epoxy groups into the interior and surface of the generated hydrophobic polymer core; during the second polymerization reaction, the epoxy groups can react with the unsaturated bonds in dodecafluoroheptyl methacrylate and the crosslinking agent, and tightly connect the hydrophobic polymer core and the fluorinated crosslinked shell through covalent bonds, thereby enhancing the bonding force between the hydrophobic polymer core and the fluorinated crosslinked shell while ensuring the hydrophobicity of the hydrophobic polymer core, thus making the amphiphilic block polymer nanospheres have better stability.

[0067] In some embodiments of the present invention, when the temperature is 70-80°C and the time is 6-8 hours in the first polymerization reaction, the first monomer, divinylbenzene and glycidyl methacrylate can react more fully, thereby increasing the yield of the hydrophobic polymer core.

[0068] In some embodiments of the present invention, when the temperature is 75~85°C and the time is 4~6h in the second polymerization reaction, the surface of the hydrophobic polymer core can be fully coated with a fluorinated cross-linked shell and form a dense three-dimensional network with the hydrophobic polymer core, so that the photovoltaic encapsulation film including the amphiphilic block polymer nanospheres of the present invention has better barrier properties.

[0069] In some embodiments of the present invention, in the third polymerization reaction, when the temperature is 55~65°C and the time is 8~12h, the reversible addition-fragmentation chain transfer agent has higher activity, which can ensure that the thermally responsive polymer arm and the reactive adhesive polymer arm grow fully and are grafted onto the surface of the fluorinated crosslinked shell, ultimately obtaining the amphiphilic block polymer nanospheres of the present invention.

[0070] In some embodiments, the first polymerization reaction also includes an emulsifier. The present invention does not particularly limit the emulsifier; it can be any emulsifier commonly used in the art. For example, sodium dodecyl sulfate can be an emulsifier.

[0071] In some embodiments, the first polymerization reaction and the second polymerization reaction further include an initiator. The present invention does not particularly limit the initiator; it can be any initiator commonly used in the art. For example, potassium persulfate can be an initiator.

[0072] In some implementations, the pH of the second emulsion needs to be adjusted to neutral before the third polymerization reaction.

[0073] In some embodiments, the third polymerization reaction includes a first-stage polymerization reaction and a second-stage polymerization reaction, wherein the first-stage polymerization reaction yields a thermally responsive polymer arm and the second-stage polymerization reaction yields a reactive adhesive polymer arm.

[0074] In some embodiments, the amphiphilic block polymer nanospheres of the present invention can be prepared by including the following steps:

[0075] In a reaction vessel, styrene, divinylbenzene, glycidyl methacrylate, emulsifier and initiator are dissolved in deionized water to carry out the first polymerization reaction, resulting in a first emulsion containing a hydrophobic polymer core.

[0076] A mixture of dodecafluoroheptyl methacrylate and pentaerythritol triacrylate and an initiator are simultaneously added dropwise to the first emulsion to carry out a second polymerization reaction, resulting in a second emulsion with a hydrophobic polymer core and a fluorinated crosslinked shell located on at least part of the surface of the hydrophobic polymer core.

[0077] The pH of the second emulsion was adjusted to neutral, and a reversible addition-fragmentation chain transfer agent and N-isopropylacrylamide were added to carry out a first-stage polymerization reaction. Then, methacrylic acid and glycidyl methacrylate were added sequentially to carry out a second-stage polymerization reaction, forming thermally responsive polymer arms and reactive adhesive polymer arms on at least a portion of the surface of the fluorinated crosslinked shell. Finally, the emulsion was demulsified, washed, and freeze-dried to obtain amphiphilic block polymer nanospheres.

[0078] A third aspect of the present invention provides a photovoltaic encapsulating film comprising the aforementioned amphiphilic block polymer nanospheres. The amphiphilic block polymer nanospheres of the present invention comprise a hydrophobic polymer core, a fluorinated cross-linked shell coating at least a portion of the surface of the hydrophobic polymer core, and thermally responsive polymer arms and reactive adhesive polymer arms grafted onto at least a portion of the surface of the fluorinated cross-linked shell. The hydrophobic polymer core and the fluorinated cross-linked shell can form a three-dimensional network, enhancing the barrier properties of the photovoltaic encapsulating film. The thermally responsive polymer arms and the reactive adhesive polymer arms can be covalently bonded to the substrate of the photovoltaic module during the lamination process, resulting in excellent adhesion of the photovoltaic encapsulating film. Through the synergistic effect of the hydrophobic polymer core, the fluorinated cross-linked shell, the thermally responsive polymer arms, and the reactive adhesive polymer arms, the photovoltaic encapsulating film of the present invention possesses both high adhesion and high barrier properties.

[0079] In some embodiments of the present invention, when the mass fraction of amphiphilic block polymer nanospheres in the photovoltaic encapsulation film is 3 to 10 parts, the photovoltaic encapsulation film can have better adhesion and barrier properties while saving costs, and its addition amount is much lower than the conventional amount of 20 to 30 parts of functional filler in the prior art.

[0080] In some embodiments of the present invention, when the photovoltaic encapsulation film further comprises 80-120 parts by weight of matrix resin, 0.6-1.2 parts by main crosslinking agent, 0.3-0.8 parts by co-crosslinking agent, 0.2-0.8 parts by silane coupling agent, 0.3-1.0 parts by UV additive, 0.1-0.3 parts by antioxidant, and 0.05-0.2 parts by acid remover, the components can work synergistically to make the overall performance of the photovoltaic encapsulation film more excellent.

[0081] Specifically, the high content of matrix resin serves as the basic framework material for photovoltaic encapsulation films, providing the necessary flexibility and mechanical support for molding and ensuring the uniform dispersion and function of other functional components. The decomposition temperature of the main crosslinking agent is well-matched with the lamination process, and the combined use of the main crosslinking agent and the co-crosslinking agent can improve the density and toughness of the crosslinking network in the photovoltaic encapsulation film, giving it good mechanical properties. Silane coupling agents can further enhance the interfacial compatibility and adhesion strength between the photovoltaic encapsulation film and the substrate in the photovoltaic module. UV additives and antioxidants can improve the photovoltaic encapsulation film's resistance to UV aging and oxidation, delaying yellowing and embrittlement during use. Acid removers can effectively remove acidic substances such as acetic acid generated during the use of photovoltaic encapsulation films.

[0082] In this invention, the amount of silane coupling agent added is much lower than the conventional amount of 2-3 parts of silane coupling agent used in the prior art.

[0083] The present invention does not impose any particular limitation on the matrix resin. The matrix resin can be any matrix resin commonly used in the art. For example, the matrix resin can be an ethylene-vinyl acetate copolymer (EVA, vinyl acetate content 28%~33%) and / or a polyolefin elastomer (POE, octene content >20%). Further, the matrix resin can be obtained by blending EVA with high vinyl acetate content and POE in a mass ratio of 7:3.

[0084] The present invention does not particularly limit the main crosslinking agent, and can be any main crosslinking agent commonly used in the art. For example, the main crosslinking agent can be tert-butyl peroxide-2-ethylhexyl carbonate (TBEC).

[0085] The present invention does not specifically limit the co-crosslinking agent, and can be any co-crosslinking agent commonly used in the art. For example, the co-crosslinking agent can be a mixture of triallyl isocyanurate (TAIC) and 1,2-polybutadiene.

[0086] The present invention does not specifically limit the silane coupling agent, and can be any silane coupling agent commonly used in the art. For example, the silane coupling agent can be γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560).

[0087] The present invention does not specifically limit the UV auxiliary agent, and it can be a commonly used UV auxiliary agent in the art. For example, the UV auxiliary agent can be a compound containing benzotriazole UV absorbers (such as Tinuvin 326), hindered amine light stabilizers (HALS, such as Tinuvin 770) and vitamin E.

[0088] The present invention does not specifically limit the antioxidants, and can be any antioxidants commonly used in the art. For example, the antioxidant can be a composite system of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010) and tris(2,4-di-tert-butylphenyl) phosphite (antioxidant 168).

[0089] The present invention does not specifically limit the deacidifying agent, and can be any deacidifying agent commonly used in the art. For example, the deacidifying agent can be calcium stearate or magnesium oxide.

[0090] The present invention does not impose any particular limitation on the preparation method of photovoltaic encapsulating film, and can use any method commonly used in the art for preparing photovoltaic encapsulating film.

[0091] In some embodiments, the photovoltaic encapsulating film of the present invention can be prepared by including the following steps:

[0092] The matrix resin was premixed in a high-speed mixer, and then amphiphilic block polymer nanospheres (ABPNs) powder, antioxidant, UV additive and deacidifier were added in sequence and mixed to obtain a premix.

[0093] The premix is ​​transferred to the main feed port of an internal mixer or twin-screw extruder. The main crosslinking agent, co-crosslinking agent and silane coupling agent are precisely injected into the premix through the side feed port for melting treatment to obtain the melt.

[0094] After the molten material is filtered through a 200-mesh filter, it is extruded through a T-die, calendered by a three-roll calender, and cooled by a cooling roller to form a photovoltaic encapsulation film.

[0095] After covering the surface of the photovoltaic encapsulation film with a release film, it is rolled up, cured at room temperature, and then slit and packaged.

[0096] The premixing time is 2-3 minutes;

[0097] The mixing time is 5-8 minutes;

[0098] During the melting process, the temperature is 85~90℃;

[0099] The thickness of the photovoltaic encapsulating film is 0.3~0.6mm;

[0100] The maturation time is 24~48 hours.

[0101] A fourth aspect of the present invention provides a photovoltaic module comprising the photovoltaic encapsulating film described above.

[0102] Specifically, the photovoltaic module of the present invention includes a first cover plate, a first photovoltaic encapsulating film, a solar cell, a second photovoltaic encapsulating film, and a second cover plate stacked sequentially. The photovoltaic encapsulating film of the present invention can be the first photovoltaic encapsulating film, the second photovoltaic encapsulating film, or both. The first cover plate can be glass or a back sheet, and the second cover plate can be glass or a back sheet. It should be noted that the first cover plate and the second cover plate cannot both be back sheets.

[0103] The photovoltaic module of the present invention includes the above-mentioned photovoltaic encapsulating film, which has high barrier properties and high adhesion, thus improving the stability and weather resistance of the photovoltaic module, thereby extending the service life of the photovoltaic module and meeting the needs of long-term outdoor use of the photovoltaic module.

[0104] The present invention does not specifically limit the type of photovoltaic module, and can be any photovoltaic module commonly used in the art. For example, the photovoltaic module of the present invention can be a perovskite solar cell photovoltaic module, a heterojunction solar cell photovoltaic module, or a bifacial double-glass solar cell photovoltaic module.

[0105] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0106] Example 1

[0107] The method for preparing the photovoltaic module in this embodiment includes:

[0108] (1) Preparation of amphiphilic block polymer nanospheres

[0109] (a) In a reactor, 40g styrene, 4g divinylbenzene, 1.5g glycidyl methacrylate (GMA, accounting for about 3% of the total molar amount of monomers), 2.5g sodium dodecyl sulfate (SDS, emulsifier) ​​and 0.4g potassium persulfate were dissolved in deionized water to carry out the first polymerization reaction at a temperature of 75°C for 8 hours to obtain the first emulsion;

[0110] (b) A mixture consisting of 15 mL of dodecyl fluoroheptyl methacrylate and 1.2 g of pentaerythritol triacrylate (PETA) and 0.2 g of potassium persulfate (dissolved in 10 mL of water) were simultaneously added dropwise to the first emulsion. The mass ratio of dodecyl fluoroheptyl methacrylate, pentaerythritol triacrylate and potassium persulfate in the mixture was 90:7.2:1.2. The second polymerization reaction was carried out at 75 °C for 5 h to obtain the second emulsion.

[0111] (c) The pH of the second emulsion was adjusted to neutral using a 5% sodium bicarbonate (NaHCO3) aqueous solution. 0.15 g of a reversible addition-fragmentation chain transfer agent and 5 g of N-isopropylacrylamide (NIPAM) were added. The reversible addition-fragmentation chain transfer agent was S-dodecyl-S'-(α,α'-dimethyl-α''-acetic acid) trithiocarbonate (DDMAT). A first-stage polymerization reaction was carried out at 60 °C for 6 h. Then, 2 g of methacrylic acid and 4 g of glycidyl methacrylate were added sequentially for a second-stage polymerization reaction, and the reaction was continued at 60 °C for 6 h. Finally, the emulsion was demulsified, washed, and freeze-dried to obtain amphiphilic block polymer nanospheres (ABPNs) powder. In the amphiphilic block polymer nanospheres, the particle size of the hydrophobic polymer core was 195 nm, and the thickness of the fluorinated cross-linked shell was 8 nm.

[0112] (2) Preparation of photovoltaic encapsulating film

[0113] (a) 100 parts of matrix resin were premixed in a high-speed mixer for 3 min, wherein the mass ratio of EVA to POE in the matrix resin was 7:3, the VA content in EVA was 30%, and the octyl content in POE was >20%; then 5 parts of amphiphilic block polymer nanospheres (ABPNs) powder, 0.2 parts of antioxidant (a composite antioxidant composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1), 0.6 parts of UV additive (a compound composed of Tinuvin 326, Tinuvin 770 and vitamin E in a mass ratio of 1:1:0.5), and 0.1 parts of deacidifying agent (calcium stearate) were added sequentially and mixed for 6 min to obtain a premix.

[0114] (b) Transfer the premix to the main feed port of the twin-screw extruder, and precisely inject 0.9 parts of the main crosslinking agent (TBEC), 0.5 parts of the co-crosslinking agent (a mixture of TAIC and 1,2-polybutadiene in a mass ratio of 1:1) and 0.5 parts of the silane coupling agent (KH-560) into the premix through the side feed port. Melt the mixture at 88°C to obtain the melt.

[0115] (c) After the molten material is filtered through a 200-mesh filter, it is extruded through a T-die, calendered by a three-roll calender and cooled by a cooling roller to form a photovoltaic encapsulation film with a thickness of 0.5 mm;

[0116] (d) After covering the surface of the photovoltaic encapsulation film with a release film, roll it up and cure it at room temperature for 36 hours, and then cut and package it.

[0117] (3) Preparation of photovoltaic modules

[0118] Two 3.2mm thick, 300mm×300mm ultra-white patterned tempered glass sheets were used as the first and second cover plates, along with a 156mm×156mm monocrystalline silicon solar cell. The sheets were stacked in the following order: first cover plate, first photovoltaic encapsulating film, solar cell, second photovoltaic encapsulating film, second cover plate (glass), to obtain a laminated assembly. The laminated assembly was placed in a laminator, and a vacuum was drawn to <1 mbar. Lamination was then performed at 145℃ for a total of 15 minutes. After cooling, the assembly was removed to obtain the photovoltaic module.

[0119] Example 2

[0120] The method for preparing the photovoltaic module in this embodiment is basically the same as that in Embodiment 1, except that:

[0121] (2) Preparation of photovoltaic encapsulating film

[0122] (a) Add 5 parts of amphiphilic block polymer nanospheres (ABPNs) powder.

[0123] Comparative Example 1

[0124] The preparation method of the photovoltaic module in this comparative example is basically the same as that in Example 1, except that:

[0125] No step (1);

[0126] (2) Preparation of photovoltaic encapsulating film

[0127] (a) Without adding amphiphilic block polymer nanospheres;

[0128] (b) Add 2.5 parts of silane coupling agent (KH-560);

[0129] Performance testing

[0130] The photovoltaic modules of the embodiments and comparative examples were subjected to the following tests:

[0131] (1) Water vapor transmission rate test

[0132] Instrumentation: PERMATRAN-W 3 / 34 water vapor transmission rate tester (MOCON, USA).

[0133] Test standard: Refer to the method in GB / T 21529-2008.

[0134] Test Procedure: The photovoltaic module is clamped in the test chamber, with one side providing a high humidity environment of 90% RH and the other side circulated with a dry carrier gas. The system automatically monitors and calculates the steady-state rate of water vapor passing through the sample to the electrolysis sensor, and directly outputs the water vapor transmission rate (WVTR) value.

[0135] Test conditions: temperature 40.0±0.5℃, relative humidity of the test chamber 90±2%; the photovoltaic module under test was a circular module with a diameter of 80mm, and three parallel data points were obtained for each test group. The test results are shown in Table 1.

[0136] Table 1

[0137]

[0138] (2) Initial peel strength test

[0139] Instrumentation: Instron 5967 universal testing machine, equipped with a 90° peeling fixture.

[0140] Test standard: Refer to the method in GB / T 2790-1995.

[0141] Sample preparation: The photovoltaic encapsulation film to be tested (25mm wide × 100mm long) is sandwiched between two clean 3.2mm ultra-white glass sheets (50mm wide × 150mm long), and placed in a small laminator. It is then laminated at 145℃ under vacuum for 15 minutes to produce a sandwich structure sample with a laminated structure of "glass, photovoltaic encapsulation film, glass".

[0142] Test conditions: Room temperature (23±2℃), peeling speed 100 mm / min.

[0143] Test Procedure: Peel approximately 25mm off one end of the sample and fix it to the upper and lower clamps of the testing machine. Start the testing machine to perform the peeling, and record the average force value during the stable peeling phase (approximately 50mm stroke). Divide this average force value by the film width (25mm) to obtain the peel strength (N / cm). Average the value of 5 samples tested in each group. The test results are shown in Table 2.

[0144] Table 2

[0145]

[0146] Water vapor transmission rate reflects the barrier properties of photovoltaic encapsulation film; the lower the water vapor transmission rate, the better the barrier properties of photovoltaic encapsulation film. Initial peel strength reflects the adhesive properties of photovoltaic encapsulation film; the higher the initial peel strength, the better the adhesive properties of photovoltaic encapsulation film.

[0147] As shown in Tables 1-2, the water vapor transmission rate and initial peel strength of the photovoltaic encapsulation films in Examples 1-2 are superior to those in Comparative Example 1. This is because the photovoltaic encapsulation films of the present invention incorporate amphiphilic block polymer nanospheres. These nanospheres have a hydrophobic polymer core, a fluorinated crosslinked layer as a shell, and thermally responsive polymer arms and reactive adhesive polymer arms. The hydrophobic polymer core and the fluorinated crosslinked shell form a uniform and dense three-dimensional network within the film, which can extend the water vapor permeation path and significantly reduce the water vapor transmission rate of the photovoltaic encapsulation film. Simultaneously, the thermally responsive polymer arms impart good temperature response characteristics and dispersion stability to the amphiphilic block polymer nanospheres, ensuring their uniform distribution during photovoltaic encapsulation film processing and lamination, thus guaranteeing the structural stability of the photovoltaic encapsulation film. Furthermore, the active functional groups on the reactive adhesive polymer arms can chemically react with the hydroxyl groups on the surface of the photovoltaic module substrate to form stable covalent bonds, improving the interfacial bonding force between the photovoltaic encapsulation film and the photovoltaic module substrate, thereby increasing the initial peel strength of the photovoltaic encapsulation film.

[0148] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. An amphiphilic block polymer nanosphere, characterized in that, It includes a hydrophobic polymer core, a fluorinated cross-linked shell covering at least a portion of the outer surface of the hydrophobic polymer core, and thermally responsive polymer arms and reactive adhesive polymer arms grafted onto at least a portion of the outer surface of the fluorinated cross-linked shell.

2. The amphiphilic block polymer nanospheres according to claim 1, characterized in that, The thermally responsive polymer arm comprises poly(N-isopropylacrylamide); and / or, The reactive adhesive polymer arm comprises poly(methacrylate-copoly-glycidyl methacrylate); and / or, The hydrophobic polymer core comprises polystyrene-copoly-divinylbenzene and / or polymethyl methacrylate-copoly-divinylbenzene, and at least a portion of the surface and interior of the hydrophobic polymer core comprises epoxy groups.

3. The amphiphilic block polymer nanospheres according to claim 1 or 2, characterized in that, The hydrophobic polymer core has a particle size of 50~200 nm; and / or, The thickness of the fluorinated cross-linked shell is 5~10 nm.

4. A method for preparing the amphiphilic block polymer nanospheres according to any one of claims 1-3, characterized in that, include: Synthesize the hydrophobic polymer core; At least a portion of the surface of the hydrophobic polymer core is coated with a fluorinated crosslinked shell formed by copolymerization of fluorinated monomers and crosslinking agents; At least a portion of the surface of the fluorinated crosslinked shell is grafted with thermally responsive polymer arms and reactive adhesive polymer arms.

5. The method for preparing amphiphilic block polymer nanospheres according to claim 4, characterized in that, include: A first raw material system comprising a first monomer and divinylbenzene is subjected to a first polymerization reaction to obtain a first emulsion comprising the hydrophobic polymer core. A second polymerization reaction is carried out on a second raw material system comprising the first emulsion, dodecyl fluoroheptyl methacrylate and a crosslinking agent to obtain a second emulsion comprising the hydrophobic polymer core and a fluorinated crosslinked shell located on at least a portion of the surface of the hydrophobic polymer core; A third polymerization reaction is carried out on a third raw material system comprising the second emulsion, a reversible addition-fragmentation chain transfer agent, N-isopropylacrylamide, methacrylic acid, and glycidyl methacrylate, to form thermally responsive polymer arms and reactive adhesive polymer arms on at least a portion of the surface of the fluorinated crosslinked shell. The first monomer includes methyl methacrylate or styrene; The crosslinking agent includes pentaerythritol triacrylate and / or ethylene glycol dimethacrylate.

6. The method for preparing amphiphilic block polymer nanospheres according to claim 5, characterized in that, The first raw material system also includes glycidyl methacrylate at a molar percentage of 1-5%; and / or, In the first polymerization reaction, the temperature is 70~80℃ and the time is 6~8h; and / or, In the second polymerization reaction, the temperature is 75~85℃ and the time is 4~6h; and / or, In the third polymerization reaction, the temperature is 55~65℃ and the time is 8~12h.

7. A photovoltaic encapsulating film, characterized in that, Including the amphiphilic block polymer nanospheres according to any one of claims 1-6.

8. The photovoltaic encapsulating film according to claim 7, characterized in that, In the photovoltaic encapsulation film, the mass fraction of the amphiphilic block polymer nanospheres is 3 to 10.

9. The photovoltaic encapsulating film according to claim 7 or 8, characterized in that, The photovoltaic encapsulation film further comprises, by weight, 80-120 parts of matrix resin, 0.6-1.2 parts of main crosslinking agent, 0.3-0.8 parts of co-crosslinking agent, 0.2-0.8 parts of silane coupling agent, 0.3-1.0 parts of UV additive, 0.1-0.3 parts of antioxidant, and 0.05-0.2 parts of deacidifying agent.

10. A photovoltaic module, characterized in that, Includes the photovoltaic encapsulating film according to any one of claims 7-9.

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