Adhesives suitable for solar cells and preparation and use thereof

Abstract

This application provides an adhesive suitable for solar cells, its preparation, and its use. The adhesive comprises a copolymer containing copolymeric structural units derived from the following monomers: monomer A, a fluorinated monomer; monomer B, a vinyl ester monomer; and optionally monomer C, a C1-C8 non-fluorinated olefin monomer. The adhesive of this application exhibits excellent peel strength and resistance to UV aging, and solar cells manufactured using this adhesive demonstrate excellent long-term sealing performance and device lifespan.

Description

Technical Field

[0001] This application relates to the field of solar cells, and more specifically to a copolymeric binder suitable for use in solar cells, a method for synthesizing the same, and its applications. Background Technology

[0002] As a device that utilizes renewable energy, solar cells have received increasing attention and have been industrialized in the past decade. However, current solar cells still have many technical shortcomings that need further improvement to meet the market's increasingly higher requirements for market scalability, low cost, and equipment performance.

[0003] Improvements to solar cells focus on their various components, with adhesives used in solar panel manufacturing, particularly those for the backsheet, being a key area of ​​research. The backsheet, placed on the back of the solar module, is a photovoltaic encapsulation material that directly contacts the external environment over a large area, requiring excellent weather resistance, electrical insulation, and water vapor barrier properties. Currently, the most commonly used solar cell backsheets on the market have a three-layer composite structure. The top and bottom layers are fluoropolymer films, such as polyvinylidene fluoride (PVF) or polyvinylidene fluoride (PVDF), while the substrate layer is typically a fluorine-free polymer film, such as polyethylene terephthalate (PET). However, due to the low surface energy of the fluoropolymer film, it is difficult to bond it with the high surface energy of the PET substrate layer. Adhesives are needed to bond the three layers together to create the solar cell backsheet. Currently, conventional adhesives have limited bonding strength with the fluoropolymer film of the backsheet and are prone to aging, leading to easy peeling between the fluoropolymer film and the fluorine-free substrate layer. This results in performance that fails to meet the 25-year durability requirement.

[0004] To overcome the aforementioned issues of adhesion strength and weather resistance between fluoropolymer films and adhesives, researchers have conducted numerous experiments, such as modifying the material components, treating it with physical or chemical methods, and surface modification. However, the actual results have been far from ideal. To date, no adhesive material has been developed in this field that can truly resolve these problems. Therefore, there is an urgent need to develop an adhesive that exhibits high adhesion and bonding strength to fluoropolymer films, while also demonstrating excellent weather resistance under long-term, continuous ultraviolet radiation outdoors. Summary of the Invention

[0005] In response to the above problems, the inventors of this application conducted in-depth research and successfully developed an adhesive material, thereby effectively solving a long-standing problem in the prior art.

[0006] The first aspect of this application provides an adhesive comprising a copolymer containing copolymeric structural units derived from monomers:

[0007] Monomer A: The fluorinated monomer shown in Formula I;

[0008]

[0009] In Formula I, R1, R2 and R3 are each independently selected from: hydrogen, fluorine, chlorine, C1-C12 alkyl, partially fluorinated or perfluorinated C1-C12 alkyl, C3-C12 cycloalkyl, partially fluorinated or perfluorinated C3-C12 cycloalkyl, C6-C12 aryl, partially fluorinated or perfluorinated C6-C12 aryl, C2-C12 alkenyl, partially fluorinated or perfluorinated C2-C12 alkenyl;

[0010] Monomer B: The monomer shown in Formula II:

[0011]

[0012] In Formula II, R4, R5, and R6 are each independently selected from: hydrogen, C1-C12 alkyl, C1-C12 alkoxy, C3-C12 cycloalkyl, C3-C12 cycloalkoxy, C2-C12 alkenyl, C6-C12 aryl, C6-C12 aryloxy, C2-C12 alkenyl, and C2-C12 alkenyloxy; R7 is selected from: hydrogen, fluorine, and C1-C18 alkyl; and

[0013] Optional monomer C: C1-C8 non-fluorinated olefin monomers as shown in Formula III;

[0014]

[0015] In Equation III, R8, R9, R 10 and R 11 Each is independently selected from: hydrogen, C1-C12 alkyl, C1-C12 alkoxy, C3-C12 cycloalkyl, C3-C12 cycloalkoxy, C2-C12 alkenyl, C6-C12 aryl, C6-C12 aryloxy, and C2-C12 alkenyl.

[0016] According to one embodiment of the first aspect of this application, the content of monomer A is 1-40 mol% based on the total molar amount of all comonomers in the copolymer. According to another embodiment of the first aspect of this application, the content of monomer B is 60-99 mol% based on the total molar amount of all comonomers in the copolymer. According to another embodiment of the first aspect of this application, the content of monomer C is 0-5 mol% based on the total molar amount of all comonomers in the copolymer.

[0017] According to another embodiment of the first aspect of this application, the monomer A is selected from at least one of the following: tetrafluoroethylene, hexafluoropropylene, perfluoro-1-butene, perfluoro-2-butene, perfluoroisobutene, perfluoro-1-n-pentene, perfluoro-2-n-pentene, perfluoroisopentene, perfluoro-1-hexene, perfluoro-2-methyl-2-pentene, and trifluorochloroethylene.

[0018] According to another embodiment of the first aspect of this application, the monomer B is selected from at least one of the following: vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl stearate.

[0019] According to another embodiment of the first aspect of this application, the monomer C is selected from at least one of the following: ethylene, propylene, n-butene, isobutene, butadiene, 1-pentene, cyclobutene, 2-pentene, isopentene, isoprene, cyclopentadiene, and styrene.

[0020] According to another embodiment of the first aspect of this application, the number-average molecular weight Mn of the copolymer is 20,000-1,000,000.

[0021] A second aspect of this application provides a method for synthesizing the adhesive of this application, the method comprising carrying out a polymerization reaction of said monomer A, monomer B and optional monomer C in a polymerization reactor.

[0022] According to one embodiment of the second aspect of this application, during the polymerization reaction, the polymerization reactor further comprises at least one of the following components: water, dispersant, stabilizer, and initiator. According to another embodiment of the second aspect of this application, the polymerization reaction is carried out at a temperature of 55-100°C and a pressure of 0.6-2.8 MPa.

[0023] A third aspect of this application provides a backsheet comprising one or more fluoropolymer films and one or more substrate layers, wherein the substrate layer is made of a material different from that of the fluoropolymer film, and the one or more substrate layers are bonded to the fluoropolymer film using an adhesive, wherein the adhesive is the adhesive of this application.

[0024] A fourth aspect of this application provides a solar cell comprising a transparent protective sheet, a cell, a backsheet, and a frame, wherein the backsheet is the backsheet described in this application. Attached Figure Description

[0025] The following paragraphs discuss various embodiments of this application in conjunction with the accompanying drawings. However, it should be noted that the embodiments shown in the drawings and described in detail below are merely some preferred embodiments of this application, and the scope of protection of this application is defined by the claims, and not limited to these preferred embodiments. Furthermore, for clarity, the reactors and various components shown in the accompanying drawings are not drawn to scale.

[0026] Figure 1 A cross-sectional view of a backplate according to one embodiment of this application is shown;

[0027] Figure 2 A schematic diagram of a solar cell according to one embodiment of this application is shown. Detailed Implementation

[0028] The “range” disclosed in this document takes the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges that can be defined in this way are inclusive and composable; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is also expected that ranges of 60-110 and 80-120 are also included. Furthermore, if the minimum range values ​​are listed as 1 and 2, and if the maximum range values ​​are listed as 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0029] In this application, unless otherwise stated, the numerical range "ab" is a shortened representation of any combination of real numbers from a to b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in this document, and "0-5" is simply a shortened representation of these numerical combinations.

[0030] Unless otherwise specified in this application, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0031] Unless otherwise specified, all technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0032] In this application, unless otherwise specified, the term "comprising" as used herein can be either open-ended or closed-ended. For example, "comprising" may mean that it may also include other components not listed, or it may only include the listed components.

[0033] In this application, the terms "solar cell", "solar panel", "solar cell module", "photovoltaic panel" and "photovoltaic module" are used interchangeably and all refer to solar cells manufactured using the technology of this application.

[0034] In this application, the term "polymeric structural unit / copolymeric structural unit derived from a monomer" refers to a structural unit formed by the addition polymerization of the monomer through carbon-carbon double bonds in its molecule, which is part of the copolymer backbone. The original composition, substituents, and structure of the monomer are retained within the copolymer structural unit formed therefrom, but may also undergo appropriate changes through chemical reactions. For example, the vinyl ester monomer represented by Formula II may undergo minor hydrolysis during or after polymerization, causing the ester groups side-attached to the backbone to become hydroxyl groups side-attached to the backbone.

[0035] In this application, monomer C is an optional component. Therefore, the comonomer used in preparing the copolymer of the present invention may include only monomer A and monomer B, without monomer C; or the comonomer used in preparing the copolymer of the present invention may include monomer A, monomer B and monomer C.

[0036] According to one embodiment of this application, monomer A is a fluorinated monomer having the structure shown in Formula I:

[0037]

[0038] According to one embodiment of this application, in Formula I, R1, R2 and R3 are each independently selected from: hydrogen, fluorine, chlorine, C1-C12 alkyl, partially fluorinated or perfluorinated C1-C12 alkyl, C3-C12 cycloalkyl, partially fluorinated or perfluorinated C3-C12 cycloalkyl, C6-C12 aryl, partially fluorinated or perfluorinated C6-C12 aryl, C2-C12 alkenyl, and partially fluorinated or perfluorinated C2-C12 alkenyl. According to another embodiment of this application, in Formula I, R1, R2 and R3 are each independently selected from: hydrogen, fluorine, chlorine, C1-C10 alkyl, partially fluorinated or perfluorinated C1-C10 alkyl, C3-C10 cycloalkyl, partially fluorinated or perfluorinated C3-C10 cycloalkyl, C6-C10 aryl, partially fluorinated or perfluorinated C6-C10 aryl, C2-C10 alkenyl, and partially fluorinated or perfluorinated C2-C10 alkenyl. According to another embodiment of this application, in Formula I, R1, R2 and R3 are each independently selected from: hydrogen, fluorine, chlorine, C1-C8 alkyl, partially fluorinated or perfluorinated C1-C8 alkyl, C3-C8 cycloalkyl, partially fluorinated or perfluorinated C3-C8 cycloalkyl, C6-C8 aryl, partially fluorinated or perfluorinated C6-C8 aryl, C2-C8 alkenyl, partially fluorinated or perfluorinated C2-C8 alkenyl. According to another embodiment of this application, in Formula I, R1, R2 and R3 are each independently selected from: hydrogen, fluorine, chlorine, C1-C6 alkyl, partially fluorinated or perfluorinated C1-C6 alkyl, C3-C6 cycloalkyl, partially fluorinated or perfluorinated C3-C6 cycloalkyl, C6-C7 aryl, partially fluorinated or perfluorinated C6-C7 aryl, C2-C6 alkenyl, partially fluorinated or perfluorinated C2-C6 alkenyl.

[0039] In this application, when a group or compound is described as "fully fluorinated," "fully fluorinated," "perfluorinated," or "perfluorinated," it means that all hydrogen atoms in the group or compound that are bonded to carbon atoms via CH bonds have been 100% replaced by fluorine. When a group or compound is described as "partially fluorinated" or "partially fluorinated," it means that a portion of the hydrogen atoms in the group or compound that are bonded to carbon atoms via CH bonds have been replaced by fluorine. For example, the proportion of hydrogen atoms replaced by fluorine atoms can be 2-95%, or 5-90%, or 10-85%, or 15-80%, or 20-75%, or 25-70%, or 30-65%, or 35-60%, or 40-55%, or 45-50%, all of which are relative to the total number of hydrogen atoms in the group or compound that are bonded to carbon atoms via CH bonds.

[0040] According to a specific embodiment of this application, the monomer A is selected from at least one of the following: tetrafluoroethylene, hexafluoropropylene, perfluoro-1-butene, perfluoro-2-butene, perfluoroisobutene, perfluoro-1-n-pentene, perfluoro-2-n-pentene, perfluoroisopentene, perfluoro-1-hexene, perfluoro-2-methyl-2-pentene, and trifluorochloroethylene; more specifically, the monomer A may be tetrafluoroethylene.

[0041] According to one embodiment of this application, based on the total molar amount of all monomers used to prepare the copolymer, the molar content of monomer A can be 1-40 mol%, for example 5-38 mol%, or 7-36 mol%, or 8-35 mol%, or 10-32 mol%, or 12-30 mol%, or 15-28 mol%, or 18-26 mol%, or 20-24 mol%, or 22-23 mol%, or within the range of values ​​obtained by combining any two of the above endpoints.

[0042] According to one embodiment of this application, monomer B is an ethylene ester monomer having the structure shown in Formula II:

[0043]

[0044] According to another embodiment of this application, in Formula II, R4, R5, and R6 are each independently selected from: hydrogen, C1-C12 alkyl, C1-C12 alkoxy, C3-C12 cycloalkyl, C3-C12 cycloalkoxy, C2-C12 alkenyl, C6-C12 aryl, C6-C12 aryloxy, C2-C12 alkenyl, and C2-C12 alkenyloxy; R7 is selected from: hydrogen, fluorine, and C1-C18 alkyl. According to another embodiment of this application, in Formula II, R4, R5, and R6 are each independently selected from: hydrogen, C1-C10 alkyl, C1-C10 alkoxy, C3-C10 cycloalkyl, C3-C10 cycloalkoxy, C2-C10 alkenyl, C6-C10 aryl, C6-C10 aryloxy, C2-C10 alkenyl, and C2-C10 alkenyloxy; R7 is selected from: hydrogen, fluorine, and C1-C16 alkyl. According to another embodiment of this application, in Formula II, R4, R5, and R6 are each independently selected from: hydrogen, C1-C8 alkyl, C1-C8 alkoxy, C3-C8 cycloalkyl, C3-C8 cycloalkoxy, C2-C8 alkenyl, C6-C8 aryl, C6-C8 aryloxy, C2-C8 alkenyl, and C2-C8 alkenyloxy; R7 is selected from: hydrogen, fluorine, and C1-C12 alkyl. According to another embodiment of this application, in Formula II, R4, R5, and R6 are each independently selected from: hydrogen, C1-C6 alkyl, C1-C6 alkoxy, C3-C6 cycloalkyl, C3-C6 cycloalkoxy, C2-C6 alkenyl, C6-C7 aryl, C6-C7 aryloxy, C2-C6 alkenyl, and C2-C6 alkenyloxy; R7 is selected from: hydrogen and C1-C6 alkyl.

[0045] According to one specific embodiment of this application, the monomer B is selected from at least one of the following: vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl stearate; for example, the monomer B may be vinyl acetate.

[0046] According to one embodiment of this application, based on the total molar amount of all monomers used to prepare the copolymer, the molar content of monomer B can be 60-99 mol%, for example 62-98 mol%, or 65-96 mol%, or 68-95 mol%, or 70-92 mol%, or 72-90 mol%, or 74-86 mol%, or 75-85 mol%, or 78-82 mol%, or 79-80 mol%, or within the range of values ​​obtained by combining any two of the above endpoints.

[0047] According to one embodiment of this application, when the copolymer also contains monomer C, monomer C may be a C1-C8 olefin monomer having the structure shown in Formula III, particularly a fluorine-free C1-C8 olefin monomer.

[0048]

[0049] In Equation III, R8, R9, R 10 and R 11 Each is independently selected from: hydrogen, C1-C12 alkyl, C1-C12 alkoxy, C3-C12 cycloalkyl, C3-C12 cycloalkoxy, C2-C12 alkenyl, C6-C12 aryl, C6-C12 aryloxy, and C2-C12 alkenyl. According to another embodiment of this application, in Formula III, R8, R9, and R... 10 and R 11 Each of the following is independently selected from: hydrogen, C1-C10 alkyl, C1-C10 alkoxy, C3-C10 cycloalkyl, C3-C10 cycloalkoxy, C2-C10 alkenyl, C6-C10 aryl, C6-C10 aryloxy, and C2-C10 alkenyl. According to another embodiment of this application, in Formula III, R8, R9, and R... 10 and R 11 Each is independently selected from: hydrogen, C1-C8 alkyl, C1-C8 alkoxy, C3-C8 cycloalkyl, C3-C8 cycloalkoxy, C2-C8 alkenyl, C6-C8 aryl, C6-C8 aryloxy, and C2-C8 alkenyl. According to another embodiment of this application, in Formula III, R8, R9, and R... 10 and R 11 Each is independently selected from: hydrogen, C1-C6 alkyl, C1-C6 alkoxy, C3-C6 cycloalkyl, C3-C6 cycloalkoxy, C2-C6 alkenyl, C6-C7 aryl, C6-C7 aryloxy, and C2-C6 alkenyl.

[0050] According to a specific embodiment of this application, the monomer C is selected from at least one of the following: ethylene, propylene, n-butene, isobutene, butadiene, 1-pentene, cyclobutene, 2-pentene, isopentenene, isoprene, cyclopentadiene, styrene; for example, the monomer C can be ethylene.

[0051] According to one embodiment of this application, based on the total molar amount of all monomers used to prepare the copolymer, the molar content of monomer C can be 0-5 mol%, for example 0.5-4.5 mol%, or 1-4 mol%, or 1.5-3.5 mol%, or 2-3 mol%, or 2.2-2.5 mol%, or within the range of values ​​obtained by combining any two of the above endpoints.

[0052] According to one embodiment of this application, the molecular weight (as a number-average molecular weight Mn) of the copolymer can be 20,000-1,000,000, for example, 30,000-900,000, or 40,000-800,000, or 50,000-700,000, or 60,000-600,000, or 70,000-500,000, or 80,000-400,000, or 90,000-300,000, or 100,000-200,000, or can be within the range of any combination of the above two end values. The number-average molecular weight can be characterized using techniques known in the art, such as end-group analysis, membrane permeation, etc. A commercially available molecular weight analyzer can be used, and the molecular weight of the copolymer can be detected using the above methods according to the instrument manual or standard methods.

[0053] According to another embodiment of this application, the intrinsic viscosity of the copolymer product obtained by the present invention is 0.6-3.0 dL / g, for example, it can be 0.8-2.8 dL / g, or 1.0-2.5 dL / g, or 1.2-2.3 dL / g, or 1.5-2.0 dL / g, or 1.6-1.8 dL / g, or it can be within the range of any combination of the above two extreme values. The intrinsic viscosity can be detected using equipment, procedures, and formulas known in the art, for example, according to standard methods such as GB / T 1548-2016 and STAS 7614-1988.

[0054] This application also provides a method for preparing the copolymer, the method comprising carrying out a polymerization reaction of the monomer A, monomer B and optional monomer C in a polymerization reactor.

[0055] According to one embodiment of this application, in the polymerization reaction, in addition to the polymerizable monomers described above, one or more other components may be used, such as water, dispersant, stabilizer, initiator, etc. The water may be distilled water, deionized water, redistilled water, or ultrapure water, preferably deionized water. Based on 100 parts by weight of all monomers used in the reaction, the amount of water used may be 50-200 parts by weight, for example, 70-180 parts by weight, or 80-160 parts by weight, or 90-140 parts by weight, or 100-130 parts by weight, or 110-128 parts by weight, or 120-125 parts by weight, or within a range of values ​​obtained by combining any two of the above endpoints.

[0056] The dispersant is used to improve the dispersibility of raw materials, intermediate products, and final products in the reaction system to promote uniform reaction throughout the reactor. Exemplary dispersants used in the polymerization reaction system of this invention include perfluorinated carboxylates, particularly ammonium perfluorinated carboxylates, such as ammonium perfluorooctanoate. The amount of dispersant used can be 0.01-20 parts by weight, for example 0.05-15 parts by weight, or 0.1-12 parts by weight, or 0.12-10 parts by weight, or 0.15-5 parts by weight, or 0.18-2 parts by weight, or 0.20-1 part by weight, or 0.25-0.6 parts by weight, or 0.30-0.50 parts by weight, or within a range of values ​​obtained by combining any two of the above endpoints.

[0057] The stabilizer is used to ensure stable process operating conditions within the reactor during the polymerization reaction, thereby improving the stability of the reaction system. Preferably, a stabilizer with stable performance, which does not negatively impact the polymerization reaction and is easily separable after polymerization is complete is used. Examples of stabilizers include paraffin wax, resin microspheres, etc. Based on 100 parts by weight of all monomers used in the reaction, the amount of stabilizer used can be 1-50 parts by weight, for example, 2-45 parts by weight, or 3-40 parts by weight, or 4-35 parts by weight, or 5-30 parts by weight, or 6-25 parts by weight, or 7-20 parts by weight, or 8-15 parts by weight, or 8.2-10 parts by weight, or within a range obtained by combining any two of the above values.

[0058] The initiator is used to provide free radicals to initiate the free radical polymerization reaction of the monomers of the present invention. The initiator can be any peroxide-based initiator known in the art, such as succinic acid peroxide, ammonium persulfate, hydrogen peroxide, tert-butyl hydrogen peroxide, potassium persulfate, benzoyl peroxide, tert-butyl peroxide, methyl ethyl ketone peroxide, etc. Based on 100 parts by weight of all monomers used in the reaction, the amount of initiator used can be 0.001-1 parts by weight, for example, 0.005-0.8 parts by weight, or 0.01-0.6 parts by weight, or 0.012-0.5 parts by weight, or 0.015-0.2 parts by weight, or 0.018-0.1 parts by weight, or 0.019-0.08 parts by weight, or 0.020-0.06 parts by weight, or 0.021-0.04 parts by weight, or within a range obtained by combining any two of the above values.

[0059] According to one embodiment of this application, the polymerization reaction is carried out under an inert atmosphere, such as a nitrogen atmosphere or a rare gas atmosphere, such as a nitrogen atmosphere.

[0060] According to another embodiment of this application, the reactor is first evacuated to remove oxygen before the monomer feedstock begins polymerization within the reactor. For example, the reactor can be evacuated before the polymerization reaction begins to remove as much oxygen as possible. The monomer for copolymerization is then introduced into the reactor during or after the evacuation process. According to one embodiment of this application, before the copolymerization reaction begins, the oxygen content in the gas phase within the reactor is reduced to less than 30 ppm, less than 20 ppm, or less than 10 ppm through evacuation, based on the total gas volume in the gas phase within the reactor.

[0061] According to one embodiment of this application, the polymerization reaction can be carried out at a temperature of 55-100°C, for example, the reaction temperature can be 58-90°C, or 60-80°C, or 60-70°C, or 60-65°C. According to another embodiment of this application, the polymerization reaction can be carried out at a pressure of 0.6-2.8 MPa, for example, the reaction pressure can be 0.8-2.7 MPa, or 1-2.5 MPa, or 1.2-2.4 MPa, or 1.5-2.3 MPa, or 1.8-2.2 MPa, or 2.0-2.1 MPa. According to one embodiment of this application, the pressure is provided by the gaseous polymerization monomer raw materials participating in the polymerization reaction, for example, by one or more of monomer A, monomer B, and optionally monomer C, while the pressure contributed by other gases (e.g., oxygen or air) is minimal and negligible. According to one embodiment of this application, the pressure inside the reactor used for the copolymerization reaction is provided by monomer A, or by monomer A and monomer C, or by monomer A and monomer B, or by monomer A, monomer B and monomer C.

[0062] According to some embodiments of this application, the copolymer of this application can be used directly as an adhesive, that is, the adhesive is composed of the copolymer without other components. According to another embodiment of this application, in addition to containing the copolymer of this application, the adhesive may also contain other additives as needed. Examples of additives that can be used in the adhesive of this application may include one or more of the following: diluents, lubricants, heat stabilizers, UV stabilizers, antioxidants, processing aids, dispersants, compatibilizers, coupling agents, tackifiers, fillers, impact modifiers, flame retardants, antistatic agents, conductive agents, pigments, colorants, plasticizers, processing aid oils, antibacterial agents, etc.

[0063] The adhesive of this application exhibits good adhesive strength to both fluoropolymer and non-fluoropolymer components, thus enabling it to be used to bond components of two different materials together, thereby producing a device or apparatus with excellent adhesive strength. According to an exemplary embodiment, the adhesive of this application can be used to manufacture the backsheet of a solar cell.

[0064] According to one embodiment of this application, the backsheet of the solar cell includes one or more fluoropolymer films and one or more substrate layers. The material of the substrate layer is different from the material of the fluoropolymer film. The one or more substrate layers are bonded to the fluoropolymer film using the adhesive of this invention. According to one embodiment of this application, the fluoropolymer film of the backsheet may contain various fluoropolymers as needed, such as polyvinylidene fluoride (PVF), polyvinylidene fluoride (PVDF), etc., while the polymer contained in the substrate layer may be a fluorine-free polymer, such as polyethylene terephthalate (PET), etc. According to one embodiment of this application, the adhesive of this invention may be disposed between the fluoropolymer film and the substrate layer in any continuous pattern, discrete pattern, or complete layer to bond the two together, preferably as a complete adhesive layer applied between them. The adhesive layer may be prepared by extrusion, casting, pouring, or other methods using the adhesive of this invention.

[0065] For example Figure 1 A cross-sectional view of a backplate according to this application is shown. Figure 1 In the embodiment shown, the back sheet includes two fluoropolymer films located on both sides and a substrate layer located in the middle. The two fluoropolymer films are respectively bonded to both sides of the substrate layer using the adhesive layer of the present invention.

[0066] The backsheet of this application can be used in solar cell modules and provides excellent adhesive strength (peel strength) and weather resistance (resistance to oxidation, UV degradation, and discoloration).

[0067] Figure 2A schematic diagram of an exemplary solar cell is shown, which includes the following components in order from top to bottom: a frame, a transparent protective sheet, a first encapsulating film, a solar cell, a second encapsulating film, a backsheet, and a junction box. The designs of these components, except for the backsheet, are known in the art. For example, the transparent protective sheet can be a glass sheet with high light transmittance. The two encapsulating films are used to seal the transparent protective sheet and the backsheet to the solar cell. A common example of an encapsulating film is a film made of ethylene-vinyl acetate (EVA) resin. The solar cell is the component used to convert sunlight into electrical energy, which is then transmitted to an external energy storage and transmission device via the junction box. According to another embodiment of this application, one or both of the encapsulating films in the solar cell can also be formed using the adhesives of this application; for example, the second encapsulating film between the backsheet and the solar cell can also be prepared using the adhesives of this application. The adhesives of this application can simultaneously exhibit excellent adhesive strength to fluoropolymer films (e.g., fluoropolymer films located on the outside of the backsheet) and other non-fluorinated materials (e.g., the solar cell, more specifically, the substrate or current collector of the solar cell), thereby achieving the desired adhesive strength, service life, and weather resistance.

[0068] The present application is described below by way of specific embodiments, the purpose of which is to provide a better understanding of the content of the present application. It should be understood that these embodiments are merely illustrative and not restrictive. The reagents used in the embodiments, unless otherwise stated, are commercially available. The methods and conditions used in the embodiments, unless otherwise specified, are conventional methods and conditions.

[0069] Example

[0070] In the following embodiments, the copolymers of the present invention were prepared and their performance was compared with that of conventional polymer adhesive materials of the prior art. The following embodiments are merely specific examples listed in this application, but the technical features of this application are not limited thereto. Any simple changes, equivalent substitutions, or other modifications made based on this application to solve essentially the same technical problem and achieve essentially the same technical effect are covered within the scope of protection of this application.

[0071] In the following examples, the paraffin used was purchased from Jiangsu Yijiu Company, the tetrafluoroethylene was produced by Shanghai Sanaifu New Material Co., Ltd., the vinyl acetate was purchased from Chuanwei Company, and the other reagents (ammonium perfluorooctanoate, succinic acid peroxide and ammonium persulfate) were all analytical grade reagents and were used directly without further purification. The water used was deionized water.

[0072] Example 1: Synthesis of tetrafluoroethylene-vinyl acetate copolymer

[0073] A 50L stainless steel reactor was used as the polymerization reactor, with the stirrer set to 500 rpm. 30 kg of deionized water, 12 kg of vinyl acetate, and 1 kg of paraffin wax were added to the reactor. The reactor was then sealed, and 150 g of a 20 wt% ammonium perfluorooctanoate aqueous solution was added. A vacuum pump was used to evacuate the reactor, and after evacuating the gas, tetrafluoroethylene was injected into the reactor to a pressure of 0.2 MPa. The reactor was then evacuated again, and this process was repeated three times. The oxygen content in the reactor was tested; a content <20 ppm was considered acceptable. If the content was unacceptable, the "vacuuming-tetrafluoroethylene filling" cycle was continued until the oxygen content in the reactor met the acceptable level. After the oxygen content in the reactor reaches the required level, the reactor is heated to 60°C. Gas-phase tetrafluoroethylene is introduced into the reactor through the gas inlet, bringing the pressure inside the reactor to 2.0 MPa. At this point, an aqueous solution containing 5 g of succinic acid peroxide and 0.12 g of ammonium persulfate is added into the reactor through the feeding port, initiating the polymerization reaction. During the reaction, tetrafluoroethylene gas is continuously introduced into the reactor to maintain the pressure at 2.0 MPa and the temperature at 60°C. During the reaction, a total of 60 g of the ammonium perfluorooctanoate solution is continuously added to the reactor through the liquid feeding port. When the tetrafluoroethylene feed reaches 12 kg, the reaction is stopped, the gas-phase monomer is recovered, the product is cooled and discharged, and the paraffin is separated to obtain a copolymer emulsion. This emulsion is stirred and coagulated in a coagulation tank at 450 rpm at room temperature. The product is washed with water and dried to obtain a copolymer product powder. The molar ratio of tetrafluoroethylene to vinyl acetate in the copolymer product was determined to be 25:75 using nuclear magnetic resonance (NMR) technology, and the Mn content of the copolymer was determined to be 212,000 using gel permeation chromatography (GPC).

[0074] The powder was extruded in an extrusion tester purchased from Potop, with the extrusion temperature controlled at 200°C. The extrudate was then processed through casting, cooling, slitting, and winding to produce a film with a thickness of 400 micrometers.

[0075] Example 2: Synthesis of tetrafluoroethylene-vinyl acetate-ethylene copolymer

[0076] A 50L stainless steel reactor was used as the polymerization reactor, with the stirrer set to 500 rpm. 30 kg of deionized water, 12 kg of vinyl acetate, and 1 kg of paraffin wax were added to the reactor. The reactor was then sealed, and 150 g of a 20 wt% ammonium perfluorooctanoate aqueous solution was added. A vacuum pump was used to evacuate the reactor, and after evacuating the gas, tetrafluoroethylene was injected into the reactor to a pressure of 0.2 MPa. The reactor was then evacuated again, and this process was repeated three times. The oxygen content in the reactor was tested; a content <20 ppm was considered acceptable. If the content was unacceptable, the "vacuuming-tetrafluoroethylene filling" cycle was continued until the oxygen content in the reactor met the acceptable level. A compressor pump was used to mix gaseous tetrafluoroethylene and ethylene at a molar ratio of 10:1 to form a mixed feed gas. After the oxygen content in the reactor reached the required level, the reactor was heated to 60°C. The mixed feed gas was then introduced into the reactor through the gas inlet, bringing the pressure inside the reactor to 2.0 MPa. At this point, an aqueous solution containing 5 g of succinic acid peroxide and 0.12 g of ammonium persulfate was added into the reactor through the feeding port, initiating the polymerization reaction. During the reaction, the mixed feed gas was continuously introduced into the reactor to maintain the pressure at 2.0 MPa and the temperature at 60°C. During the reaction, a total of 60 g of ammonium perfluorooctanoate solution was continuously added into the reactor through the liquid feeding port. When the mixed feed gas feed reached 12 kg, the reaction was stopped, the gaseous monomer was recovered, the product was cooled and discharged, and the paraffin was separated to obtain a copolymer emulsion. This emulsion was stirred and coagulated in a coagulation tank at 450 rpm at room temperature. The product was washed with water and dried to obtain a copolymer product powder.

[0077] The molar ratio of tetrafluoroethylene:vinyl acetate:ethylene in the copolymer product was determined to be 21:76.6:2.4 by nuclear magnetic resonance (NMR) and the Mn of the copolymer was determined to be 288,000 by gel permeation chromatography (GPC).

[0078] The powder was extruded in an extrusion tester purchased from Potop, with the extrusion temperature controlled at 200°C. The extrudate was then processed through casting, cooling, slitting, and winding to produce a film with a thickness of 400 micrometers.

[0079] Comparative Example 1:

[0080] In Comparative Example 1, a commercially available ethylene-vinyl acetate copolymer (vinyl acetate content 33 mol%) purchased from Yanshan Petrochemical Company was used. The copolymer resin was extruded in the extruder described in Example 1, with the extrusion temperature controlled at 90°C. The extrudate was then subjected to casting, cooling, slitting, and winding processes to form a film with a thickness of 400 micrometers.

[0081] Example 3

[0082] In this Example 3, the properties of the materials (polymer films) prepared in Examples 1-2 and Comparative Example 1 were characterized using the following techniques.

[0083] (1) The adhesive strength performance was tested according to the national standard GB / T2790 "Test method for 180° peel strength of adhesives, flexible materials versus rigid materials". Specifically, a 1mm thick PVDF film purchased from Shanghai Sanai Fu New Materials Co., Ltd. was cut into 100mm×100mm pieces. The polymer films prepared in Examples 1-2 and Comparative Example 1 were also cut into 100mm×100mm pieces and stacked on the PVDF film. The laminate of the two films was then fed into a laminator for lamination. The laminated structure was then tested on a tensile testing machine at a speed of 100mm / min, and the tensile strength values ​​were recorded.

[0084] (2) Conduct UV aging tests according to the test method of GB / T19394-2003.

[0085] Specifically, a 1mm thick PVDF film purchased from Shanghai Sanai Fu New Materials Co., Ltd. was cut into 100mm × 100mm pieces. Polymer films prepared in Examples 1-2 and Comparative Example 1 were also cut into 100mm × 100mm pieces and stacked on top of the PVDF film. The laminate of the two films was then fed into a laminator for lamination. The laminated structure was then placed in an ultraviolet irradiation chamber and subjected to light with wavelengths from 280nm to 400nm at a temperature of 60°C and a concentration of 120kWh / m². 2 The irradiation intensity was subjected to 720 hours of irradiation.

[0086] The yellowness of the samples was tested before and after irradiation according to the national standard GB2409 "Test Method for Yellow Index of Plastics". The yellowing index was calculated based on the difference before and after irradiation.

[0087] The test results are summarized in Table 1 below:

[0088] Table 1: Characterization results of adhesive films

[0089] Example 1 138 1.1 Example 2 118 2.3 Comparative Example 1 76 4.2

[0090] As can be seen from the above performance test indicators, the adhesive film of the present invention has the advantages of high peel strength and good resistance to ultraviolet aging. Furthermore, Examples 1-2 and Comparative Example 1 all exhibit excellent adhesion strength (high peel strength) to PET (a non-fluoropolymer material, commonly used as the substrate layer of solar cell backsheets). The adhesives of Examples 1-2 of the present invention exhibit excellent adhesion strength to both non-fluoropolymer substrate layers and PVDF films, as well as better resistance to radiation aging, significantly outperforming existing adhesives and making them more suitable for manufacturing solar cell module backsheets and encapsulation.

Claims

1. An adhesive comprising a copolymer composed of copolymeric structural units derived from monomers: Monomer A: Tetrafluoroethylene; Monomer B: Vinyl acetate; Based on the total molar amount of all comonomers in the copolymer, the content of monomer A is 1-40 mol%, and the content of monomer B is 60-99 mol%.

2. The adhesive as claimed in claim 1, characterized in that, The number-average molecular weight Mn of the copolymer is 20,000-1,000,000.

3. A method for synthesizing the adhesive according to any one of claims 1-2, the method comprising carrying out the polymerization reaction of said monomer A and monomer B in a polymerization reactor.

4. The method as described in claim 3, characterized in that, During the polymerization reaction, the polymerization reactor also contains at least one of the following components: water, dispersant, stabilizer, and initiator; and The polymerization reaction is carried out at a temperature of 55-100℃ and a pressure of 0.6-2.8MPa.

5. A backsheet comprising one or more fluoropolymer films and one or more substrate layers, wherein the substrate layer is made of a material different from that of the fluoropolymer film, and the one or more substrate layers are bonded to the fluoropolymer film using an adhesive, characterized in that... The adhesive is the adhesive according to any one of claims 1-2.

6. A solar cell comprising a transparent protective sheet, solar cells, a backsheet, and a frame, wherein the backsheet is the backsheet of claim 5.

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