CN116814193A

CN116814193A - Adhesive suitable for solar cells, and preparation and use thereof

Info

Publication number: CN116814193A
Application number: CN202310452315.9A
Authority: CN
Inventors: 孙幸幸; 霍力垚; 杜丽君; 吴君毅
Original assignee: Changshu 3f Zhonghao New Chemical Materials Co ltd; Shanghai Huayi Sanaifu New Material Co ltd
Current assignee: Changshu 3f Zhonghao New Chemical Materials Co ltd; Shanghai Huayi Sanaifu New Material Co ltd
Priority date: 2023-04-25
Filing date: 2023-04-25
Publication date: 2023-09-29
Also published as: WO2024222232A1

Abstract

The present application provides an adhesive suitable for solar cells and its preparation and use. The adhesive includes a copolymer containing copolymerized structural units derived from the following monomers: monomer A, Fluorinated monomer; Monomer B, a vinyl ester monomer; and optionally Monomer C, a C1-C8 fluorine-free olefin monomer. The adhesive of the present application exhibits excellent peel strength and UV aging resistance, and solar cells manufactured using the adhesive can exhibit excellent long-term sealing performance and device working life.

Description

Adhesive suitable for solar cells, and preparation and use thereof

Technical Field

The application relates to the field of solar cells, in particular to a copolymerization type binder suitable for a solar cell, and a synthesis method and application thereof.

Background

Solar cells have been receiving more and more attention and industrialization in recent years as a device using renewable energy, but the current solar cells still have a number of technical defects to be further improved so as to meet the requirements of market expansibility, low cost and higher device performance in the market.

Improvements in solar cells have focused on their individual components, such as adhesives for the manufacture of solar panels, and in particular adhesives for their backsheets, are one of the subjects of intense research. The back plate is a photovoltaic packaging material which is used on the back surface of the solar cell module and is directly contacted with the external environment in a large area, and the back plate needs to have excellent performances of weather resistance, electric insulation resistance, water vapor barrier and the like. The solar cell back sheet most commonly used in the market at present is a back sheet with a three-layer composite structure, wherein the upper layer and the lower layer of the back sheet are fluorine-containing polymer films, such as polyvinyl fluoride (PVF) or polyvinylidene fluoride (PVDF), and the base layer is mostly a polymer film without fluorine, such as polyethylene terephthalate (PET), but the surface energy of the fluorine-containing film is low, so that the fluorine-containing film is difficult to be compounded with the PET film with high surface energy of the base layer, and the three-layer material needs to be compounded by adopting an adhesive bonding mode, so that the solar cell back sheet is prepared. The adhesive conventionally used at present has limited bonding strength with the fluoropolymer film of the back plate and is easy to age, so that the fluoropolymer film is easy to peel from the substrate layer without fluorine material, and the durability requirement of 25 years cannot be met in performance.

In order to overcome the problems of the adhesive strength and weather resistance of the fluorine film and the adhesive, researchers have carried out various experiments such as modification of various components of materials, treatment by physical or chemical means, surface modification, etc., but the actual effect is quite unsatisfactory, and thus, the art has not been able to develop an adhesive material which can truly solve the problems. It is therefore highly desirable to develop a binder having high adhesion and high bond strength to fluoropolymer films, while also exhibiting excellent weatherability under outdoor prolonged ultraviolet irradiation.

Disclosure of Invention

The present inventors have conducted intensive studies with respect to the above problems, and have succeeded in developing an adhesive material, thereby effectively solving the problems of the prior art which have been urgently solved for a long time.

In a first aspect the application provides an adhesive comprising a copolymer comprising copolymerized structural units derived from:

monomer A: a fluoromonomer represented by formula I;

in formula I, R ₁ 、R ₂ And R is ₃ 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;

monomer B: monomers of formula II:

in formula II, R ₄ 、R ₅ And R is ₆ 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, C2-C12 alkenyloxy; r is R ₇ Selected from: hydrogen, fluorine, C1-C18 alkyl; and

optional monomer C: a C1-C8 fluorine-free olefin monomer represented by formula III;

in formula III, R ₈ 、R ₉ 、R ₁₀ And R is ₁₁ 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.

According to one embodiment of the first aspect of the application, the monomer a is present in an amount of 1 to 40 mole%, based on the total molar amount of all comonomers in the copolymer. According to another embodiment of the first aspect of the application, the monomer B is present in an amount of 60 to 99 mole%, based on the total molar amount of all comonomers in the copolymer. According to another embodiment of the first aspect of the application, the monomer C is present in an amount of 0 to 5 mole%, based on the total molar amount of all comonomers in the copolymer.

According to another embodiment of the first aspect of the application, the monomer a is selected from at least one of the following: tetrafluoroethylene, hexafluoropropylene, perfluoro-1-butene, perfluoro-2-butene, perfluoro-isobutylene, perfluoro-1-n-pentene, perfluoro-2-n-pentene, perfluoro-isopentene, perfluoro-1-hexene, perfluoro-2-methyl-2-pentene, and trifluoro-chloroethylene.

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

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

According to another embodiment of the first aspect of the application, the copolymer has a number average molecular weight Mn of 20,000-1,000,000.

In a second aspect the application provides a process for the synthesis of the adhesive of the application, which comprises carrying out the polymerization of the monomers a, B and optionally C in a polymerization reactor.

According to one embodiment of the second aspect of the application, the polymerization reactor further has therein at least one of the following components when carrying out the polymerization reaction: water, a dispersing agent, a stabilizing agent and an initiator. According to another embodiment of the second aspect of the present application, the polymerization is carried out at a temperature of 55 to 100℃and a pressure of 0.6 to 2.8 MPa.

In a third aspect the present application provides a backsheet comprising one or more fluoropolymer films and one or more matrix layers of a material different from the material of the fluoropolymer films, the one or more matrix layers being bonded to the fluoropolymer films using an adhesive and the adhesive being an adhesive according to the present application.

A fourth aspect of the present application provides a solar cell comprising a transparent protective sheet, a cell sheet, a back sheet and a frame, the back sheet being a back sheet according to the present application.

Drawings

Various embodiments of the present application are discussed in the following paragraphs with reference to the drawings. It is to be noted, however, that the embodiments shown in the drawings and described in detail below are only some of the preferred embodiments of the application, the scope of which is defined by the claims and not limited to these preferred embodiments. In addition, for the purposes of clarity, the reactors and various components shown in the figures of the specification are not drawn to true scale.

FIG. 1 shows a cross-sectional view of a back plate according to one embodiment of the application;

fig. 2 shows a schematic view of a solar cell according to an embodiment of the application.

Detailed Description

"Range" is disclosed herein in the form of lower and upper limits. There may be one or more lower limits and one or more upper limits, respectively. The 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 ranges. All ranges that can be defined in this way are inclusive and combinable, i.e., any lower limit can be combined with any upper limit to form a range. For example, ranges of 60-120 and 80-110 are listed for specific parameters, with the understanding that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3,4 and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.

In the present application, unless otherwise indicated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed throughout, and "0-5" is simply a shorthand representation of a combination of these values.

In the present application, all the embodiments mentioned herein and the preferred embodiments may be combined with each other to form new technical solutions, if not specifically described.

In the present application, all technical features mentioned herein and preferred features may be combined with each other to form new technical solutions, if not specifically stated.

In the present application, the term "comprising" as referred to herein means open or closed unless otherwise specified. For example, the term "comprising" may mean that other components not listed may also be included, or that only listed components may be included.

In the present application, the terms "solar cell", "solar panel", "solar cell module", "photovoltaic panel" and "photovoltaic module" are used interchangeably to refer to solar cells manufactured by the techniques of the present application.

In the present application, by "polymerized/copolymerized structural units derived from a monomer" is meant structural units formed as part of the copolymer backbone by addition polymerization of the monomer via carbon-carbon double bonds in its molecule, the original composition, substituents and structure of the monomer being retained within the copolymer structural units it forms, but it is also possible for suitable changes to occur by chemical reactions. For example, the vinyl ester monomer represented by formula II may undergo hydrolysis in a small amount during or after polymerization so that the ester groups pendant to the main chain therein become hydroxyl groups pendant to the main chain.

Monomer C is an optional component in the present application, so that the comonomer used in preparing the copolymer of the present application may include only monomer A and monomer B, without monomer C; it is also possible that the comonomers used in the preparation of the copolymers of the application comprise monomers A, B and C at the same time.

According to one embodiment of the application, the monomer a is a fluoromonomer having the structure shown in formula I:

according to one embodiment of the application, in formula I, R ₁ 、R ₂ And R is ₃ 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. According to another embodiment of the application, in formula I, R ₁ 、R ₂ And R is ₃ 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, partially fluorinated or perfluorinated C2-C10 alkenyl. According to another embodiment of the application, in formula I, R ₁ 、R ₂ And R is ₃ 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 the application, in formula IWherein R is ₁ 、R ₂ And R is ₃ 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.

In the present application, when a group or compound is described as "fully fluorinated", "fully fluoro", "perfluorinated" or "perfluorinated", it is meant that all hydrogen atoms in the group or compound that are attached to carbon atoms through c—h bonds have been replaced with fluorine in 100% total. When a group or compound is described as "partially fluorinated" or "partially fluorinated," it is meant that a portion of the hydrogen atoms attached to the carbon atoms through C-H bonds in the group or compound are replaced with fluorine, e.g., the ratio of hydrogen atoms replaced with fluorine atoms may be 2 to 95%, alternatively 5 to 90%, alternatively 10 to 85%, alternatively 15 to 80%, alternatively 20 to 75%, alternatively 25 to 70%, alternatively 30 to 65%, alternatively 35 to 60%, alternatively 40 to 55%, alternatively 45 to 50%, based on the total number of hydrogen atoms attached to the carbon atoms through C-H bonds in the group or compound.

According to a specific embodiment of the application, said monomer a is selected from at least one of the following: tetrafluoroethylene, hexafluoropropylene, perfluoro-1-butene, perfluoro-2-butene, perfluoro-isobutylene, perfluoro-1-n-pentene, perfluoro-2-n-pentene, perfluoro-isopentene, perfluoro-1-hexene, perfluoro-2-methyl-2-pentene, and trifluorochloroethylene; more specifically, the monomer a may be tetrafluoroethylene.

According to one embodiment of the application, the molar content of the monomer a may be 1 to 40 mol%, for example 5 to 38 mol%, or 7 to 36 mol%, or 8 to 35 mol%, or 10 to 32 mol%, or 12 to 30 mol%, or 15 to 28 mol%, or 18 to 26 mol%, or 20 to 24 mol%, or 22 to 23 mol%, or may be within a numerical range obtained by combining any two of the above-mentioned end values with each other, based on the total molar amount of all monomers used to prepare the copolymer.

According to one embodiment of the application, the monomer B is a vinyl ester monomer having the structure shown in formula II:

according to another embodiment of the application, in formula II, R ₄ 、R ₅ And R is ₆ 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, C2-C12 alkenyloxy; r is R ₇ Selected from: hydrogen, fluorine, C1-C18 alkyl. According to another embodiment of the application, in formula II, R ₄ 、R ₅ And R is ₆ 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, C2-C10 alkenyloxy; r is R ₇ Selected from: hydrogen, fluorine, C1-C16 alkyl. According to another embodiment of the application, in formula II, R ₄ 、R ₅ And R is ₆ 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, C2-C8 alkenyloxy; r is R ₇ Selected from: hydrogen, fluorine, C1-C12 alkyl. According to another embodiment of the application, in formula II, R ₄ 、R ₅ And R is ₆ 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, C2-C6 alkenyloxy; r is R ₇ Selected from: hydrogen, C1-C6 alkyl.

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

According to one embodiment of the application, the molar content of the monomer B may be 60 to 99 mol%, for example 62 to 98 mol%, or 65 to 96 mol%, or 68 to 95 mol%, or 70 to 92 mol%, or 72 to 90 mol%, or 74 to 86 mol%, or 75 to 85 mol%, or 78 to 82 mol%, or 79 to 80 mol%, or may be within a numerical range obtained by combining any two of the above-mentioned end values with each other, based on the total molar amount of all monomers used to prepare the copolymer.

According to one embodiment of the present application, when the monomer C is further contained in the copolymer, the monomer C may be a C1-C8 olefin monomer having a structure represented by formula III, particularly a C1-C8 olefin monomer containing no fluorine.

In formula III, R ₈ 、R ₉ 、R ₁₀ And R is ₁₁ 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. According to another embodiment of the application, in formula III, R ₈ 、R ₉ 、R ₁₀ And R is ₁₁ 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. According to another embodiment of the application, in formula III, R ₈ 、R ₉ 、R ₁₀ And R is ₁₁ 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. According to another embodiment of the application, in formula III, R ₈ 、R ₉ 、R ₁₀ And R is ₁₁ 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.

According to one embodiment of the application, said monomer C is selected from at least one of the following: ethylene, propylene, n-butene, isobutylene, butadiene, 1-pentene, cyclobutene, 2-pentene, isopentene, isoprene, cyclopentadiene, styrene; for example, the monomer C may be ethylene.

According to one embodiment of the application, the molar content of monomer C may be from 0 to 5 mol%, for example from 0.5 to 4.5 mol%, or from 1 to 4 mol%, or from 1.5 to 3.5 mol%, or from 2 to 3 mol%, or from 2.2 to 2.5 mol%, or may be within the numerical range obtained by combining any two of the above endpoints with each other, based on the total molar amount of all monomers used to prepare the copolymer.

According to one embodiment of the application, the molecular weight (in terms of number average molecular weight Mn) of the copolymer may 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 may be within a numerical range obtained by combining any two of the above-mentioned end values with each other. The number average molecular weight may be characterized using techniques known in the art, for example, end group analysis, membrane permeation, etc., and the molecular weight of the copolymer may be determined using commercially available molecular weight meters, according to the instructions of the instrument or standard methods by the methods described above.

According to another embodiment of the application, the copolymer product produced according to the application has an intrinsic viscosity of 0.6-3.0dL/g, for example, 0.8-2.8dL/g, or 1.0-2.5dL/g, or 1.2-2.3dL/g, or 1.5-2.0dL/g, or 1.6-1.8dL/g, or can be within the numerical range obtained by combining any two of the above-mentioned end values with each other. The intrinsic viscosity can be measured using equipment, procedures and formulas known in the art, and for example, the copolymer intrinsic viscosity can be measured according to standard methods of GB/T1548-2016, STAS 7614-1988, and the like.

The present application also provides a process for preparing the copolymer, which comprises carrying out the polymerization of the monomers A, B and optionally C in a polymerization reactor.

In accordance with one embodiment of the present application, in the polymerization reaction, one or more other components, such as water, a dispersant, a stabilizer, an initiator, etc., may be used in addition to the above-described polymerization monomers. The water may be distilled water, deionized water, double distilled water or ultrapure water, preferably deionized water is used. The water may be used in an amount of 50 to 200 parts by weight, for example, 70 to 180 parts by weight, or 80 to 160 parts by weight, or 90 to 140 parts by weight, or 100 to 130 parts by weight, or 110 to 128 parts by weight, or 120 to 125 parts by weight, or may be within a numerical range obtained by combining any two of the above-mentioned end values with each other, based on 100 parts by weight of the total weight of all monomers used for carrying out the reaction.

The dispersants are useful for improving the dispersibility of the starting materials, intermediate products, and end products in the reaction system to promote the reaction to proceed uniformly throughout the reactor, and exemplary dispersants for use in the polymerization reaction system of the present application include perfluorinated carboxylic acid salts, particularly ammonium salts of perfluorinated carboxylic acids, such as ammonium perfluorooctanoate. The dispersant may be used in an amount of 0.01 to 20 parts by weight, for example, 0.05 to 15 parts by weight, or 0.1 to 12 parts by weight, or 0.12 to 10 parts by weight, or 0.15 to 5 parts by weight, or 0.18 to 2 parts by weight, or 0.20 to 1 part by weight, or 0.25 to 0.6 part by weight, or 0.30 to 0.50 part by weight, or may be within a numerical range obtained by combining any two of the above-mentioned end values with each other, based on 100 parts by weight of the total amount of all monomers used for the reaction.

The stabilizer is used to provide stable process conditions in the reactor during the polymerization reaction, thereby improving the stability of the reaction system, and preferably a stabilizer which is stable in performance, does not adversely affect the polymerization reaction, and is easily separated after the completion of the polymerization reaction. Examples of the stabilizer include paraffin wax, resin microspheres, and the like. The stabilizer may be used in an amount of 1 to 50 parts by weight, for example, 2 to 45 parts by weight, or 3 to 40 parts by weight, or 4 to 35 parts by weight, or 5 to 30 parts by weight, or 6 to 25 parts by weight, or 7 to 20 parts by weight, or 8 to 15 parts by weight, or 8.2 to 10 parts by weight, or may be within a numerical range obtained by combining any two of the above-mentioned end values with each other, based on 100 parts by weight of the total amount of all monomers used for the reaction.

The initiator is used to provide free radicals to initiate the free radical polymerization of the monomers of the present application and may be any of a variety of peroxide-based initiators known in the art, such as succinic peroxide, ammonium persulfate, hydrogen peroxide, t-butyl hydroperoxide, potassium persulfate, benzoyl peroxide t-butyl peroxide, methyl ethyl ketone peroxide, and the like. The initiator may be used in an amount of 0.001 to 1 part by weight, for example, 0.005 to 0.8 part by weight, or 0.01 to 0.6 part by weight, or 0.012 to 0.5 part by weight, or 0.015 to 0.2 part by weight, or 0.018 to 0.1 part by weight, or 0.019 to 0.08 part by weight, or 0.020 to 0.06 part by weight, or 0.021 to 0.04 part by weight, or may be within a numerical range obtained by combining any two of the above-mentioned end values with each other, based on 100 parts by weight of the total monomers used for the reaction.

According to one embodiment of the application, the polymerization is carried out under an inert atmosphere, for example under a nitrogen atmosphere or a rare gas atmosphere, for example under a nitrogen atmosphere.

According to another embodiment of the application, the polymerization of the monomer feed is initiated in the reactor by first removing oxygen by evacuating the reactor. For example, the reaction vessel may be evacuated before the polymerization reaction starts to remove oxygen therefrom as much as possible, and the monomers for copolymerization may be charged into the reaction vessel simultaneously with or after the evacuation and the deoxidation. According to one embodiment of the application, the oxygen content in the gas phase in the reaction vessel is made less than 30ppm, alternatively less than 20ppm, alternatively less than 10ppm by means of a vacuumized deoxygenation operation prior to the start of the copolymerization reaction, said proportions being based on the total gas volume in the gas phase in the reaction vessel.

According to one embodiment of the present application, the polymerization reaction may be carried out at a temperature of 55 to 100 ℃, for example, the reaction temperature may be 58 to 90 ℃, or 60 to 80 ℃, or 60 to 70 ℃, or 60 to 65 ℃. According to another embodiment of the present application, the polymerization reaction may be carried out at a pressure of 0.6 to 2.8MPa, for example, the reaction pressure may be 0.8 to 2.7MPa, or may be 1 to 2.5MPa, or 1.2 to 2.4MPa, or 1.5 to 2.3MPa, or 1.8 to 2.2MPa, or 2.0 to 2.1MPa. According to one embodiment of the application, the pressure is provided by the gaseous polymeric monomer feed taking part in the polymerization reaction, which may be provided, for example, by one or more of monomer a, monomer B and optionally monomer C, while the pressure contributed by the other gases (e.g. oxygen or air) is negligible. According to one embodiment of the present application, the pressure in the reaction vessel used to carry out the copolymerization reaction is provided by the monomer a, or by the monomer a and the monomer C, or by the monomer a and the monomer B, or by the monomer a, the monomer B and the monomer C.

According to some embodiments of the application, the copolymer of the application may be used directly as a binder, i.e. the binder consists of the copolymer without other components. According to another embodiment of the present application, the adhesive may contain other additives as needed in addition to the copolymer of the present application, for example, examples of additives that may be used in the adhesive of the present application may include one or more of the following: diluents, lubricants, heat stabilizers, ultraviolet stabilizers, antioxidants, processing aids, dispersants, compatibilizers, coupling agents, tackifiers, fillers, impact modifiers, flame retardants, antistatic agents, conductive agents, pigments, colorants, plasticizers, processing aid oils, antimicrobial agents, and the like.

The adhesive of the present application can simultaneously exhibit good adhesive strength to fluoropolymer parts as well as non-fluoropolymer parts and thus can be used to join together parts of two different materials as described above, thereby producing a device or apparatus having excellent adhesive strength. According to one exemplary embodiment, the adhesive of the present application may be used to manufacture a back sheet of a solar cell.

According to one embodiment of the application, the backsheet of the solar cell comprises one or more fluoropolymer films and one or more matrix layers of a material different from the material of the fluoropolymer films, which are bonded together with the fluoropolymer films using the adhesive of the application. According to one embodiment of the present application, the fluoropolymer film of the back sheet may contain various fluoropolymers such as polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), etc., as needed, while the polymer contained in the base layer may be a non-fluorine-containing polymer such as polyethylene terephthalate (PET), etc. According to one embodiment of the application, the adhesive of the application may be disposed between the fluoropolymer film and the base layer in any continuous pattern, discrete pattern or complete layer to bond the two together, preferably applied between the two in a complete adhesive layer. The adhesive layer may be prepared by extruding, casting, pouring, etc. the adhesive of the present application.

For example, fig. 1 shows a cross-sectional view of a backsheet according to the application, which in the embodiment shown in fig. 1 comprises two fluoropolymer films on both sides and a substrate layer in the middle, which are bonded to both sides of the substrate layer, respectively, with the adhesive layer according to the application.

The back sheet of the present application can be used in solar cell modules and provides excellent adhesive strength (peel strength) and weather resistance (oxidation resistance, uv degradation resistance, discoloration resistance).

Fig. 2 shows a schematic view of an exemplary solar cell comprising, in order from top to bottom, the following components: frame, transparent protection piece, first glued membrane, battery piece, second glued membrane, backplate and terminal box. The design of these components other than the back sheet is known in the art, for example, the transparent protective sheet may be a glass sheet having high light transmittance, two adhesive films are used to seal the transparent protective sheet and the back sheet to the battery sheet, one conventional example of an adhesive film is a film prepared using ethylene-vinyl acetate (EVA) resin, the battery sheet is a component for converting sunlight into electric energy, and the generated electric energy is transmitted to an external electric energy storage and transmission device via a junction box. According to another embodiment of the application, one or both of the adhesive films in the solar cell may also be formed using the adhesive of the application; for example, a second adhesive film between the back sheet and the battery sheet can also be prepared using the adhesive of the present application, with which the adhesive of the present application can simultaneously exhibit excellent adhesive strength to a fluoropolymer film (e.g., a fluoropolymer film located on the outside of the back sheet) and other non-fluorine containing materials (e.g., a battery sheet, more specifically, a substrate or current collector of a battery sheet) to achieve desired adhesive strength, service life, and weather resistance.

The application is described below in terms of specific examples for the purpose of better understanding of the content of the application. It should be understood that these embodiments are merely illustrative and not limiting. The reagents used in the examples were commercially available as usual unless otherwise indicated. The methods and conditions used in the examples are conventional methods and conditions unless otherwise specified.

Examples

In the following examples, the copolymers of the present application are prepared and compared to the properties of conventional polymer binder materials of the prior art. The following examples are only specific examples of the present application, but the technical features of the present application are not limited thereto. Any simple changes, equivalent substitutions or other modifications made on the basis of the present application to solve the substantially same technical problems and substantially the same technical effects are included in the scope of the present application.

The paraffin wax used in the following examples was purchased from Jiangsu Yijiu, tetrafluoroethylene was produced by Shanghai Sanyi New Material Co., ltd, vinyl acetate was purchased from Chuanwei, and the other reagents (ammonium perfluorooctanoate, succinic peroxide and ammonium persulfate) were all analytically pure reagents, and were used directly without further purification, and the water used was deionized water.

Example 1: synthesis of tetrafluoroethylene-vinyl acetate copolymer

A50L stainless steel reaction vessel was used as the polymerization reactor, wherein the rotational speed of the stirrer was set to 500 revolutions per minute. Adding 30kg of deionized water, 12kg of vinyl acetate and 1kg of paraffin into a reactor, sealing the reactor, adding 150g of ammonium perfluorooctanoate aqueous solution with concentration of 20wt%, vacuumizing the reactor by using a vacuum pump, injecting tetrafluoroethylene to 0.2MPa into the reactor after vacuumizing the reactor, vacuumizing the reactor by using the vacuum pump, repeating the above process for three times, testing the oxygen content in the reactor, if the oxygen content is less than 20ppm, the oxygen content is qualified, and if the oxygen content is not qualified, continuing the cycle of vacuumizing-filling tetrafluoroethylene until the oxygen content in the reactor is qualified. After the oxygen content in the reaction kettle is qualified, the reaction kettle is heated to 60 ℃, gas-phase tetrafluoroethylene is input into the reaction kettle through a gas inlet, so that the pressure in the reaction kettle reaches 2.0MPa, at the moment, 5g of succinic peroxide and 0.12g of aqueous solution containing 0.12g of ammonium persulfate are added into the reaction kettle through a feed port, and the polymerization reaction is started. Tetrafluoroethylene gas was introduced into the reaction vessel during the reaction so that the pressure in the vessel was maintained at 2.0MPa and the temperature was maintained at 60 ℃. 60g of the ammonium perfluorooctanoate solution is continuously added into the reaction kettle in a continuous mode through a liquid adding port in the reaction process. Stopping the reaction until the feeding amount of tetrafluoroethylene reaches 12kg, recovering the gas phase monomer, cooling and discharging, and separating paraffin to obtain the copolymerization product emulsion. The emulsion was coagulated by stirring at room temperature in a coagulation tank at a stirring speed of 450rpm, the product was washed with water, and dried to obtain copolymer product powder. The molar ratio of tetrafluoroethylene to vinyl acetate in the copolymer product was 25 as measured by nuclear magnetic resonance: 75, and the Mn of the copolymer was 21.2 ten thousand as measured by gel permeation chromatography.

The powder was extruded in an extrusion laboratory from Potop company at 200℃and the extrudate was cast, cooled, slit and wound to give a film having a thickness of 400. Mu.m.

Example 2: synthesis of tetrafluoroethylene-vinyl acetate-ethylene copolymer

A50L stainless steel reaction vessel was used as the polymerization reactor, wherein the rotational speed of the stirrer was set to 500 revolutions per minute. Adding 30kg of deionized water, 12kg of vinyl acetate and 1kg of paraffin into a reactor, sealing the reactor, adding 150g of ammonium perfluorooctanoate aqueous solution with concentration of 20wt%, vacuumizing the reactor by using a vacuum pump, injecting tetrafluoroethylene to 0.2MPa into the reactor after vacuumizing the reactor, vacuumizing the reactor by using the vacuum pump, repeating the above process for three times, testing the oxygen content in the reactor, if the oxygen content is less than 20ppm, the oxygen content is qualified, and if the oxygen content is not qualified, continuing the cycle of vacuumizing-filling tetrafluoroethylene until the oxygen content in the reactor is qualified. Mixing gaseous tetrafluoroethylene and ethylene in a molar ratio of 10:1 by using a compression pump to form mixed raw material gas, heating the reaction kettle to 60 ℃ after the oxygen content in the reaction kettle is qualified, inputting the mixed raw material gas into the reaction kettle through a gas inlet to enable the pressure in the reaction kettle to reach 2.0MPa, and adding an aqueous solution containing 5g of succinic peroxide and 0.12g of ammonium persulfate into the reaction kettle through a feed port at the moment to enable the polymerization reaction to start. The mixed raw material gas is introduced into the reaction kettle during the reaction period, so that the pressure in the kettle is maintained at 2.0MPa, and the temperature is maintained at 60 ℃. 60g of the ammonium perfluorooctanoate solution is continuously added into the reaction kettle in a continuous mode through a liquid adding port in the reaction process. Stopping the reaction until the feeding amount of the mixed raw material gas reaches 12kg, recovering the gas phase monomer, cooling and discharging, and separating paraffin to obtain the copolymer emulsion. The emulsion was coagulated by stirring at room temperature in a coagulation tank at a stirring speed of 450rpm, the product was washed with water, and dried to obtain copolymer product powder.

The molar ratio of tetrafluoroethylene to vinyl acetate to ethylene in the copolymer product was determined to be 21:76.6:2.4 by nuclear magnetic resonance techniques and the Mn of the copolymer was determined to be 28.8 ten thousand by gel permeation chromatography techniques.

Comparative example 1:

in this comparative example 1, an ethylene-vinyl acetate copolymer (vinyl acetate content 33 mol%) which is a commercial product available from the company of the petrifaction was extruded in an extruder as described in example 1 at a temperature of 90℃and the extrudate was subjected to casting, cooling, slitting, and winding to form a film having a thickness of 400. Mu.m.

Example 3

In this example 3, the properties of the materials (polymer films) produced in examples 1-2 and comparative example 1 were characterized using the following techniques.

(1) The adhesion strength properties were tested according to the national standard GB/T2790 "180 peel strength test method for Adhesives Flexible Material vs. rigid Material". Specifically, a PVDF film of 1mm thickness purchased from the company Sanafrican new materials Co., ltd. In Shanghai was cut to a size of 100 mm. Times.100 mm, the polymer film prepared in examples 1-2 and comparative example 1 was cut to a size of 100 mm. Times.100 mm, respectively, and laminated on the PVDF film, and the laminate of the two films was fed to a laminator for lamination. The laminate structure after lamination was measured on a tensile machine at a speed of 100mm/min and tensile strength values were recorded.

(2) The ultraviolet aging test was conducted according to the GB/T19394-2003 test method.

Specifically, a PVDF film of 1mm thickness purchased from the company Sanafrican new materials Co., ltd. In Shanghai was cut to a size of 100 mm. Times.100 mm, the polymer film prepared in examples 1-2 and comparative example 1 was cut to a size of 100 mm. Times.100 mm, respectively, and laminated on the PVDF film, and the laminate of the two films was fed to a laminator for lamination. The laminated structure after lamination is sent into an ultraviolet irradiation box and is irradiated with light with the wavelength of 280nm to 400nm at the temperature of 60 ℃ to 120kWh/m ² Is irradiated for 720 hours.

The yellowness index is calculated before and after irradiation according to the yellowness of the test sample of national standard "Plastic yellow index test method" GB2409 respectively.

The test results are summarized in table 1 below:

table 1: characterization results of adhesive films

Sample numbering	Adhesive strength with fluorine film (N/cm)	Yellowing index delta YI after ultraviolet aging
			Example 1	138	1.1
Example 2	118	2.3
			Comparative example 1	76	4.2

From the performance detection indexes, the adhesive film has the advantages of high peeling strength and good ultraviolet aging resistance. In addition, examples 1-2 and comparative example 1 each exhibited excellent adhesive strength (high peel strength) to PET (non-fluoropolymer material, commonly used as a base layer of a solar cell backsheet). The adhesives of examples 1-2 of the present application are significantly better than prior art adhesives due to their excellent bond strength and better radiation aging resistance to both the non-fluoropolymer substrate layer and the PVDF film, and are more suitable for use in the manufacture of solar module backsheets and packages.

Claims

1. An adhesive comprising a copolymer comprising copolymerized structural units derived from:

monomer A: a fluoromonomer represented by formula I;

monomer B: monomers of formula II:

2. The adhesive of claim 1 wherein said monomer a is present in an amount of 1 to 40 mole percent, said monomer B is present in an amount of 60 to 99 mole percent, and said monomer C is present in an amount of 0 to 5 mole percent, based on the total molar amount of all comonomers in said copolymer.

3. The adhesive of claim 1, wherein the monomer a is selected from at least one of the following: tetrafluoroethylene, hexafluoropropylene, perfluoro-1-butene, perfluoro-2-butene, perfluoro-isobutylene, perfluoro-1-n-pentene, perfluoro-2-n-pentene, perfluoro-isopentene, perfluoro-1-hexene, perfluoro-2-methyl-2-pentene, and trifluoro-chloroethylene.

4. The adhesive of claim 1, wherein the monomer B is selected from at least one of the following: vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl stearate.

5. The adhesive of claim 1, wherein the monomer C is selected from at least one of the following: ethylene, propylene, n-butene, isobutylene, butadiene, 1-pentene, cyclobutene, 2-pentene, isopentene, isoprene, cyclopentadiene, styrene.

6. The adhesive of any one of claims 1-5 wherein the copolymer has a number average molecular weight Mn of 20,000-1,000,000.

7. A process for the synthesis of the adhesive of any of claims 1-6, comprising carrying out the polymerization of the monomers a, B and optionally C in a polymerization reactor.

8. The method of claim 7, wherein the polymerization reactor further has therein at least one of the following components when performing the polymerization reaction: water, a dispersing agent, a stabilizing agent and an initiator; and is also provided with

The polymerization reaction is carried out at a temperature of 55-100 ℃ and a pressure of 0.6-2.8 MPa.

9. A backsheet comprising one or more fluoropolymer films and one or more matrix layers of a material different from the material of the fluoropolymer films, the one or more matrix layers being bonded to the fluoropolymer films using an adhesive, characterized in that the adhesive is the adhesive of any one of claims 1-6.

10. A solar cell comprising a transparent protective sheet, a cell sheet, a back sheet, and a frame, the back sheet being the back sheet of claim 9.