A multi-layer structure, its preparation method and application

Abstract

The present invention discloses a multi-layer structure, a preparation method and an application thereof. The multi-layer structure includes: a substrate layer; and a fluoropolymer-based resin layer, wherein the fluoropolymer-based resin layer contains an adjacent dihydroxy polymer, and the adjacent dihydroxy polymer contains structural units represented by formula (I) and formula (II), wherein R1, R2, R3, R4, R5 and R6 are the same or different and are independently selected from H, C 1‑8 alkyl; a and c are the same or different and are independently integers greater than or equal to 0, and a and c are not 0 at the same time. The adjacent dihydroxy polymer of the present invention has strong adhesion to the resin layer and the substrate layer, the structure of the prepared multi-layer structure is stable, the oxygen barrier performance is enhanced, and it has excellent weather resistance and durability as a backsheet of a photovoltaic cell. #imgabs0#

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer material preparation, and specifically relates to a multi-layer structure, a preparation method and an application thereof, which are used as outdoor materials with excellent weather resistance and oxygen barrier properties, especially as the backsheet of a photovoltaic cell. Background Art

[0002] Objects that are long-term exposed to the outdoors and subjected to sunlight irradiation often require strong weather resistance and durability. For this purpose, light-resistant materials or substances are usually attached to the surface of the object, such as coating with anti-ultraviolet compounds or fluorine-containing polymers with good weather resistance.

[0003] A photovoltaic cell is a device that converts solar energy into electrical energy and is long-term exposed to outdoor sunlight irradiation for the absorption and utilization of sunlight. Therefore, the components used in photovoltaic cells need to have excellent weather resistance, durability and low oxygen permeability; especially for the backsheet, PET with relatively high strength and low cost is usually used as the substrate, and a fluorine-containing polymer with strong weather resistance (such as PVDF) is attached to its surface. Due to the poor adhesion between the fluorine-containing polymer and the substrate, it is difficult to compound. Currently, the existing compounding methods include high-pressure extrusion or casting, or modifying the fluorine-containing polymer to increase its adhesiveness, or adding other components that are compatible with the fluorine-containing polymer and have adhesiveness to the substrate, such as adding (meth)acrylate polymers. The extrusion or casting operation causes thermal shock and deformation of the substrate, resulting in a decline in product quality and little improvement in weather resistance; modifying the fluorine-containing polymer or adding other adhesive components can improve the adhesion to the substrate to a certain extent, but the improvement amplitude is not large.

[0004] Therefore, how to prepare a multi-layer structure with weather resistance and durability is an urgent problem to be solved. Summary of the Invention

[0005] In order to improve the above technical problems, the present invention provides a multi-layer structure, a preparation method and an application thereof. The multi-layer structure includes an adjacent dihydroxy polymer, which contacts with high-energy surface substances such as glass, metal, polyester materials, etc., to generate strong hydrogen bonds and is rich in strong adhesion; the adjacent dihydroxy polymer is combined with polyester materials, fluorine-containing polymers, etc. to increase the adhesion to the substrate, enhance the oxygen barrier performance of the composite multi-layer structure, and can be applied to the manufacture of weather-resistant and durable multi-layer structures, such as the backsheet of a photovoltaic cell.

[0006] The technical solution of the present invention is as follows:

[0007] A multi-layer structure, which includes:

[0008] A substrate layer; and

[0009] A resin layer based on a fluorine-containing polymer

[0010] The fluoropolymer-based resin layer contains adjacent dihydroxy polymers, and the adjacent dihydroxy polymers contain structural units represented by formula (I) and formula (II):

[0011]

[0012] In formula (I) and formula (II), R1, R2, R3, R4, R5 and R6 are the same or different and are independently selected from H, C 1-8 alkyl; a and c are the same or different and are independently integers greater than or equal to 0, and a and c are not both 0 at the same time.

[0013] According to an embodiment of the present invention, the adjacent dihydroxy polymer may further include structural units represented by formula (III), formula (IV) and / or formula (V):

[0014]

[0015] In formula (III) and formula (IV), R1, R2, R3, R4, R5 and R6 are the same or different and are independently selected from H, C 1-8 alkyl; b and d are the same or different and are independently integers greater than or equal to 0;

[0016] In formula (V), R 19 is selected from unsubstituted, or optionally substituted by one, two or more R c substituted C 6-20 aryl; each R c is the same or different and is independently selected from C 1-12 alkyl; e is an integer greater than or equal to 0.

[0017] According to an embodiment of the present invention, in formula (I) to formula (II), R1, R2, R3, R4, R5 and R6 are the same or different and are independently selected from H, C 1-6 alkyl.

[0018] According to an embodiment of the present invention, in formula (III) and formula (IV), R1, R2, R3, R4, R5 and R6 are the same or different and are independently selected from H, C 1-6 alkyl.

[0019] According to an embodiment of the present invention, in formula (V), R 19 is selected from unsubstituted, or optionally substituted by one, two or more R c substituted C 6-14 aryl; each R c is the same or different and is independently selected from C 1-6 alkyl.

[0020] Exemplarily, the adjacent dihydroxy polymer contains structural units represented by formula (I), formula (II), formula (III), and formula (IV).

[0021] Exemplarily, the adjacent dihydroxy polymer contains structural units represented by formula (I), formula (II), formula (III), formula (IV), and formula (V).

[0022] According to an embodiment of the present invention, the number-average molecular weight of the adjacent dihydroxy polymer is 2,000 to 200,000, and exemplarily is 2,000, 5,000, 6,700, 7,560, 10,000, 14,500, 15,000, 20,000, 50,000, 62,500, 67,700, 92,300, 100,000, 143,000, 150,000, 200,000.

[0023] Preferably, in the adjacent dihydroxy polymer, a is an integer between 0 and 3,000, and a and c are not both 0; preferably, a is an integer between 50 and 2,000.

[0024] Preferably, in the adjacent dihydroxy polymer, b is an integer between 0 and 200.

[0025] Preferably, in the adjacent dihydroxy polymer, c is an integer between 0 and 3,000, and a and c are not both 0. Preferably, c is an integer between 0 and 300.

[0026] Preferably, in the adjacent dihydroxy polymer, d is an integer between 0 and 100.

[0027] Preferably, in the adjacent dihydroxy polymer, e is an integer between 0 and 2,000.

[0028] Preferably, in the adjacent dihydroxy polymer, (a + c) / (a + b + c + d) ≥ 0.5, preferably 0.6 to 1.0. For example, it is 0.5, 0.6, 0.66, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.97, 0.98, or 1.

[0029] Preferably, in the adjacent dihydroxy polymer, e / (a + b + c + d) is selected from 0 to 5.0; exemplarily, it is 0, 1, 1.5, 2, 2.5, 2.9, 3, 3.5, 4, 4.5, 5.

[0030] According to the present invention, the multilayer structure sequentially includes a substrate layer and a resin layer based on a fluoropolymer.

[0031] According to the present invention, the multilayer structure sequentially includes a resin layer based on a fluoropolymer, a substrate layer, and a resin layer based on a fluoropolymer.

[0032] According to the present invention, the substrate is one or a mixture of metals, woods, glasses, ceramics, celluloses, copolymers of poly(meth)acrylates, styrene and (meth)acrylate, polyurethanes, polysulfones, polyethersulfones, polyphenylsulfones, polyphenylene sulfides, polyether ketones, polyimides, polycarbonates, polyvinyl chlorides, polyacrylonitriles, nitrile rubbers, hydrogenated nitrile rubbers, polystyrenes, block copolymers of styrene and butadiene (SBS), hydrogenated products of block copolymers of styrene and butadiene (SEBS), polyvinyl alcohols, ionomers, polyamides, polyethylene terephthalates (PET), polyethylene naphthalates (PEN), and polybutylene terephthalates (PBT).

[0033] Exemplarily, the shape of the substrate can be a plate, a block, etc., and preferably a plate.

[0034] Exemplarily, the metal can be aluminum, iron, or copper.

[0035] Exemplarily, the substrate is a single-layer board, a stacked board, and a co-extruded product of PET, PEN, or PBT.

[0036] According to the present invention, the surface of the substrate layer can be subjected to at least one surface treatment selected from plasma treatment, corona treatment, primer treatment, anchoring agent treatment, coupling agent treatment, heat treatment, or chemical activation treatment using boron trifluoride, sulfuric acid, caustic soda, etc.

[0037] According to the present invention, the fluoropolymer is a homopolymer or copolymer of vinyl fluoride, a homopolymer and copolymer of vinylidene fluoride, or a mixture thereof. Exemplarily, the fluoropolymer is a homopolymer of at least one fluoromonomer selected from vinylidene fluoride (VDF), vinyl fluoride (VF), tetrafluoroethylene (TFE), hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE), trifluoroethylene, hexafluoroisobutene, perfluorobutyl ethylene, perfluoro(methyl vinyl ether) (PMVE), perfluoro(ethyl vinyl ether) (PEVE), perfluoropropyl vinyl ether (PPVE), perfluoromethyl vinyl ether (PMVE), perfluoro-2,2-dimethyl-1,3-dioxolene (PDD), and perfluoro-2-methylene-4-1,3-dioxolane (PMD), a copolymer of two or more of the above fluoromonomers, or a mixture thereof. Preferred are homopolymers and copolymers of vinylidene fluoride (VDF), such as a copolymer formed by the polymerization reaction of two fluoromonomers, VDF and HFP.

[0038] According to the present invention, the weight-average molecular weight of the fluoropolymer is 50,000 - 1,500,000, and exemplarily is 50,000, 100,000, 150,000, 200,000, 500,000, 1,000,000, or 15,000,000.

[0039] According to the present invention, the melting point of the fluoropolymer is 80°C - 180°C.

[0040] According to the present invention, at least one of polycarbonate, PVC, ABS, styrene-maleic anhydride copolymer, polyacrylonitrile, polystyrene, polysulfone, polyethersulfone, poly(meth)acrylate, polyester, polyurethane, polyurea, polyamide, polyphenylene sulfide (PPS), or silicone resin can be added to the resin layer based on the fluoropolymer.

[0041] According to the present invention, in the resin layer of the fluoropolymer, the fluoropolymer can introduce functional groups through molecular chains to improve the adhesion ability. The functional groups include but are not limited to at least one of carboxyl group, sulfonic acid group, aziridinyl group, ureido group, imide group, phosphoric acid (ester) group, cyano group, imino group, acid anhydride group, amino group, epoxy group, hydroxyl group, and ester group. In particular, it is selected from at least one of carboxyl group, sulfonic acid group, acid anhydride group, amino group, epoxy group, hydroxyl group, cyano group, and ester group.

[0042] According to the present invention, the resin layer may further include pigments, fillers, and UV stabilizers. The pigments or fillers are, for example, titanium dioxide, silicon dioxide, kaolin, montmorillonite, alumina, calcium carbonate, barium carbonate, or carbon black; the UV stabilizers are, for example, benzophenone, benzotriazole, and derivatives of triazine.

[0043] According to the present invention, in the resin layer, the addition amount of the adjacent dihydroxy polymer is 10 - 120 wt% of the fluoropolymer. Exemplarily, it is 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, 100 wt%, 110 wt%, or 120 wt%.

[0044] According to the present invention, the thickness of the resin layer is 0.1 - 10000 μm. Exemplarily, it is 0.1 μm, 1 μm, 20 μm, 50 μm, 100 μm, 200 μm, 400 μm, 500 μm, 600 μm, 800 μm, 1000 μm, 5000 μm, 8000 μm, 10000 μm.

[0045] The present invention also provides a method for preparing the above multi-layer structure, and the method includes:

[0046] Stacking the substrate and the resin layer based on the fluoropolymer containing the adjacent dihydroxy polymer in sequence, and performing hot pressing to obtain the multi-layer structure (hot pressing method); or,

[0047] Coating the resin solution based on the fluoropolymer containing the adjacent dihydroxy polymer on the substrate layer, and heating and drying to obtain the multi-layer structure (solution coating method).

[0048] According to the present invention, in the hot pressing method, the heating temperature is 80 - 200 °C; the applied pressure is 0.15 - 5 MPa; and the hot pressing time is 1 - 100 minutes.

[0049] According to the present invention, in the solution coating method, the drying temperature is 80 - 200 °C; and the drying time is 1 - 100 minutes.

[0050] Exemplarily, the resin solution is prepared by dissolving raw materials for preparing the resin layer, including a fluoropolymer and an adjacent dihydroxy polymer, in a solvent.

[0051] According to the present invention, the concentration of the fluoropolymer in the resin solution is 0.1 wt% - 80 wt%, exemplarily 19 wt% or 20 wt%. The concentration of the adjacent dihydroxy polymer in the resin solution is 0.1 wt% - 50 wt%, exemplarily 10 wt%. In addition, the addition amount of the adjacent dihydroxy polymer is 10 - 120 wt% of the fluoropolymer.

[0052] Exemplarily, the raw materials for preparing the resin layer include a fluoropolymer, and may further include at least one of polycarbonate, PVC, ABS, styrene - maleic anhydride copolymer, polyacrylonitrile, polystyrene, polysulfone, polyethersulfone, poly(meth)acrylate, polyester, polyurethane, polyurea, polyamide, polyphenylene sulfide (PPS), or silicone resin, pigment, filler, UV stabilizer.

[0053] Exemplarily, the solvent is selected from one or a mixture of ethanol, tetrahydrofuran, acetone, methyl ethyl ketone (MEK), DMF, DMAc, NMP, γ - butyrolactone, dioxane, DMSO, etc.

[0054] Exemplarily, in the solution coating method, there is no particular limitation on the coating method, including any method that can form a uniform coating. For example, direct coating, spin coating, etc.

[0055] As an exemplary embodiment of the present invention, the method for preparing the multi - layer structure is specifically as follows:

[0056] The substrate layer and the resin layer are sequentially laminated and then pressed at 80 - 200 °C and 0.15 - 5 MPa for 1 - 100 min to obtain the multi - layer structure.

[0057] As an exemplary embodiment of the present invention, the method for preparing the multi - layer structure is specifically as follows:

[0058] A resin solution based on a fluoropolymer is coated on the substrate layer, and after drying to remove the solvent, a resin layer is formed on the substrate layer to obtain the multi - layer structure.

[0059] The present invention also provides an application of the above-mentioned multi-layer structure, which is used as a backsheet of a photovoltaic cell.

[0060] Advantages of the present invention:

[0061] The adjacent dihydroxy polymer of the present invention has strong adhesion to the resin layer and the substrate layer, and the prepared multi-layer structure has a stable structure. As a backsheet of a photovoltaic cell, it has excellent weather resistance and durability.

[0062] Term definitions and explanations

[0063] Unless otherwise specified, the terms and descriptions in the context of the present invention have the meanings described below.

[0064] More than refers to more than 3.

[0065] The term "C 1-12 alkyl" should be understood to represent a straight-chain or branched-chain saturated monovalent hydrocarbon group having 1 to 12 carbon atoms. For example, "C 1-8 alkyl" represents straight-chain and branched-chain alkyl groups having 1, 2, 3, 4, 5, 6, 7 or 8 carbon atoms, and "C 1-6 alkyl" represents straight-chain and branched-chain alkyl groups having 1, 2, 3, 4, 5 or 6 carbon atoms. The alkyl groups are, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, 2-methylbutyl, 1-methylbutyl, 1-ethylpropyl, 1,2-dimethylpropyl, neopentyl, 1,1-dimethylpropyl, 4-methylpentyl, 3-methylpentyl, 2-methylpentyl, 1-methylpentyl, 2-ethylbutyl, 1-ethylbutyl, 3,3-dimethylbutyl, 2,2-dimethylbutyl, 1,1-dimethylbutyl, 2,3-dimethylbutyl, 1,3-dimethylbutyl or 1,2-dimethylbutyl, etc. or their isomers.

[0066] The term "C 6-20 aryl" should be understood to preferably represent a monocyclic, bicyclic or tricyclic hydrocarbon ring having 6 to 20 carbon atoms and being monovalent aromatic or partially aromatic, preferably "C 6-14 aryl". The term "C 6-14 aryl" should be understood to preferably represent a monocyclic, bicyclic or tricyclic hydrocarbon ring having 6, 7, 8, 9, 10, 11, 12, 13 or 14 carbon atoms and being monovalent aromatic or partially aromatic ("C 6-14 aryl"), especially a ring having 6 carbon atoms ("C6 aryl"), such as phenyl; or biphenyl, or a ring having 9 carbon atoms ("C9 aryl"), such as indanyl or indenyl, or a ring having 10 carbon atoms ("C 10 aryl"), such as tetrahydronaphthyl, dihydronaphthyl or naphthyl, or a ring having 13 carbon atoms ("C 13"Aryl"), such as a fluorenyl group, or a ring having 14 carbon atoms ("C 14 aryl"), such as an anthracenyl group. When the C 6-20 aryl is substituted, it may be mono-substituted or multi-substituted. Moreover, there is no restriction on the substitution site, for example, it may be ortho-substituted, para-substituted or meta-substituted. Brief Description of the Drawings

[0067] Figure 1 It is a cross-sectional view of the multi-layer structure in Example 1.

[0068] Figure 2 It is a cross-sectional view of the multi-layer structure in Example 9.

[0069] Wherein: 101, substrate layer; 102, resin layer based on a fluoropolymer. Detailed Description of the Invention

[0070] The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only illustrative of and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0071] Unless otherwise specified, the raw materials and reagents used in the following embodiments are all commercially available products or can be prepared by known methods.

[0072] Preparation of Vicinal Dihydroxy Polymer

[0073] Preparation Example 1

[0074] Preparation of vicinal dihydroxy polymer SBSOH:

[0075] The vicinal dihydroxy polymer SBSOH contains the structures of formulas (I) to (V), where R1, R2, R3, R4, R5 and R6 are hydrogen, and R 19 is a benzene ring.

[0076] First step: Synthesize the block copolymer SBS of styrene and butadiene according to the method disclosed in "Synthetic Rubber Industry Handbook" (edited by Zhao Xutao and Liu Dahua, second edition, Chemical Industry Press, 2006): Using 1,3-butadiene and styrene as raw materials, cyclohexane as a solvent, and sec-butyl lithium as a catalyst for polymerization to obtain SBS;

[0077] Second step: Using formic acid as a catalyst, dissolve the block copolymer SBS prepared in the first step in a mixed solution of cyclohexane and dichloroethane, add 30% hydrogen peroxide to the mixed solution, and an epoxidation reaction occurs on the double bonds in the polymer molecular structure to prepare an epoxidized polymer solution;

[0078] Step 3: Then, add 70% aqueous perchloric acid solution to the epoxidized polymer solution. The epoxy groups are ring-opened to adjacent dihydroxy groups. The reactants are washed with water and dried to obtain adjacent dihydroxy polymer SBSOH.

[0079] The molar proportion results of the adjacent dihydroxy structural units of the SBSOH samples are shown in Table 1 below.

[0080] SBSOH-1, SBSOH-2, and SBSOH-3 are all prepared by the method in Preparation Example 1. By adjusting the contents of butadiene and styrene, SBSOH with different proportions of adjacent dihydroxy structural units and number-average molecular weights as shown in Table 1 below are prepared.

[0081] Table 1

[0082] SBSOH Number-average molecular weight e / (a + b + c + d) (a + c) / (a + b + c + d) SBSOH-1 6700 3.0 0.70 SBSOH-2 14500 3.0 0.66 SBSOH-3 67700 1 0.60

[0083] In Table 1, the ratios of a, b, c, d, and e and (a + c) / (a + b + c + d), e / (a + b + c + d) are 1 obtained by calculating from the 1H-NMR test results.

[0084] Preparation Example 2

[0085] Preparation of adjacent dihydroxy polymer PBOH:

[0086] The adjacent dihydroxy polymer PBOH contains the structures of formulas (I) to (IV), and R1, R2, R3, R4, R5, and R6 are hydrogen;

[0087] Using 1,3-butadiene as the raw material, referring to the method disclosed in Example 1 of CN110964131A, the PBOH samples shown in Table 2 are prepared.

[0088] PBOH-1, PBOH-2, and PBOH-3 are all prepared by the method in Preparation Example 2. By adjusting the content of 1,3-butadiene, PBOH with different proportions of adjacent dihydroxy structural units and number-average molecular weights are prepared.

[0089] The number-average molecular weights and the molar proportion values of the adjacent dihydroxy structural units of the PBOH samples are shown in Table 2.

[0090] Table 2

[0091] PBOH Number-average molecular weight (a + c) / (a + b + c + d) PBOH-1 7560 0.97 PBOH-2 62500 0.95 PBOH-3 143000 0.98

[0092] In Table 2, the ratios of a, b, c, d and (a + c) / (a + b + c + d) are 1 obtained by calculating from the 1H-NMR test results.

[0093] Example 1

[0094] A kind of asFigure 1 The multi-layer structure shown, the multi-layer structure has 2 layers, namely a substrate layer 101 and a fluoropolymer-based resin layer 102 in sequence, and its preparation method is as follows:

[0095] 1), Substrate preparation

[0096] A PET sheet with a specification of 5 cm × 5 cm × 1 mm is immersed in a 20% KOH solution at 80 °C, taken out after 1 minute, washed with deionized water, and dried to obtain an alkali-treated PET sheet.

[0097] 2), Coating of fluoropolymer-based resin

[0098] 20 parts of PVDF (Solvay 6020, weight average molecular weight 680,000, melting point 170 - 175 °C), 4 parts of adjacent dihydroxy polymer PBOH-1 are dissolved in 62 parts of DMF to form a solution; 18 parts of titanium dioxide (DuPont TiPure R-902+) are added to the solution and mixed evenly to obtain a resin coating solution of fluoropolymer.

[0099] The resin coating solution of fluoropolymer is coated on the treated PET sheet, the coating thickness is 30 μm, and it is dried at 200 °C for 10 minutes to obtain a multi-layer structure.

[0100] Example 2

[0101] Replace PBOH-1 with PBOH-2, and the rest is the same as Example 1.

[0102] Example 3

[0103] Replace PBOH-1 with PBOH-3, and the rest is the same as Example 1.

[0104] Example 4

[0105] Replace PBOH-1 with SBSOH-1, and the rest is the same as Example 1.

[0106] Example 5

[0107] Replace PBOH-1 with SBSOH-2, and the rest is the same as Example 1.

[0108] Example 6

[0109] Replace PBOH-1 with SBSOH-3, and the rest is the same as Example 1.

[0110] Example 7

[0111] The dosage of PBOH-2 is 20 parts, and the rest is the same as Example 2.

[0112] Example 8

[0113] (1) Preparation of PVDF and adjacent dihydroxy polymer composite film

[0114] 20 parts of PVDF (Solvay 6020) and 4 parts of PBOH-2 were dissolved in DMF to prepare a solution with a concentration of 20 wt%, and coated on a polyethylene plate; dried in vacuum at 120 °C for 30 min to obtain a PVDF composite film with a thickness of 100 μm, that is, the resin layer.

[0115] (2) Preparation of multi-layer structure

[0116] A 1 mm thick PET film was air-dried according to the surface treatment method of Example 1.

[0117] The PET film and the PVDF composite film were stacked neatly in sequence, and flat stainless steel plates were clamped on both sides of the stacked composite film. Under a pressure of 3 MPa at 160 °C, after pressing for 2 minutes, a multi-layer structure was obtained.

[0118] Example 9

[0119] Prepare a multi-layer structure as Figure 2 shown. The multi-layer structure has 3 layers, which are a resin layer 102 based on a fluoropolymer, a substrate layer 101, and a resin layer 102 based on a fluoropolymer in sequence. The preparation method is the same as that of Example 1, except that in step 2), the resin of the fluoropolymer is coated on both surfaces of the PET sheet, so as to form a 3-layer structure as Figure 2 shown.

[0120] Comparative Example 1

[0121] 1), Substrate preparation

[0122] A PET sheet with a specification of 5 cm × 5 cm × 1 mm was immersed in an 80 °C, 20% KOH solution, taken out after 1 min, washed with deionized water, and air-dried to prepare an alkali-treated PET sheet.

[0123] 2), Coating of resin based on fluoropolymer

[0124] 20 parts of PVDF (Solvay 6020, weight average molecular weight 680,000, melting point 170-175 °C) were dissolved in 62 parts of DMF to form a solution; 18 parts of titanium dioxide (DuPont TiPure R-902+) were added to the solution and mixed evenly to obtain a resin coating solution of the fluoropolymer.

[0125] The resin coating solution of the fluoropolymer was coated on the PET plate, and the coating thickness was 30 μm. It was dried at 200 °C for 10 minutes to obtain a multi-layer structure.

[0126] Comparative Example 2

[0127] 1), Substrate preparation

[0128] The PET sheet with the specification of 5 cm × 5 cm × 1 mm was impregnated into the 20% KOH solution at 80 °C, taken out after 1 min, washed with deionized water, and dried to prepare the PET sheet treated with the alkali solution.

[0129] 2), Resin coating based on fluoropolymer

[0130] 20 parts of modified PVDF (Solvay 5130, that is, acrylic acid modified PVDF, weight average molecular weight of 1.3 million, melting point of 158 - 166 °C) were dissolved in 62 parts of DMF to form a solution; 18 parts of titanium dioxide (DuPont TiPure R-902+) were added to the solution and mixed evenly to obtain the resin coating solution of fluoropolymer.

[0131] The resin coating solution of fluoropolymer was coated on the PET board with a coating thickness of 30 μm and dried at 200 °C for 10 minutes to obtain the multi-layer structure.

[0132] In Examples 1 - 8 and Comparative Examples 1 - 2, the test methods for the performance parameters of the multi-layer structure were as follows:

[0133] 1. 180° peel strength

[0134] It was determined with reference to the test method for 180° peel strength of adhesives in GB / T 2790 - 1995.

[0135] 2. Adhesion test

[0136] The standard cross-cut test was carried out with reference to ASTM D3359. The surface was cut with a utility knife at intervals of 11 columns and 11 rows to form a 100-grid pattern of 1 mm squares. The surface of the grid was adhered with transparent tape, and the surface state peeled off together with the tape was detected and evaluated.

[0137] Grade 1: No surface peeling;

[0138] Grade 2: Peeling area < 5%;

[0139] Grade 3: Peeling area 5 - 15%;

[0140] Grade 4: Peeling area 15 - 35%;

[0141] Grade 5: Peeling area 35 - 65%;

[0142] Grade 6: Complete peeling.

[0143] 3. After the multi-layer structure was placed at 85% humidity and 85 °C for 48 h, the 180° peel strength and adhesion of the multi-layer structure were tested again.

[0144] The test results are shown in Table 3.

[0145] Table 3

[0146]

[0147] As can be seen from Table 3 above, the fluoropolymer-based resin layer containing adjacent dihydroxy polymers has strong adhesion to the substrate PET layer, making the structure of the multi-layer structure prepared by the present invention stable; as a backsheet of a photovoltaic cell, it has excellent weather resistance and durability.

[0148] Above, the embodiments of the present invention have been described by way of example. However, the protection scope of the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A multi-layer structure, characterized in that, It includes: a substrate layer; and a fluoropolymer-based resin layer, wherein the fluoropolymer-based resin layer contains an adjacent dihydroxy polymer, and the adjacent dihydroxy polymer comprises structural units represented by formula (I) and formula (II): ； Formula (I); ； Formula (II); In Formula (I) to Formula (II), R1, R2, R3, R4, R5 and R6 are the same or different and are independently selected from H, C 1-8 alkyl; a and c are the same or different and are independently integers greater than or equal to 0, and a and c are not both 0 at the same time; The adjacent dihydroxy polymer further comprises structural units represented by formula (III), formula (IV) and / or formula (V): ； Formula (III); Formula (IV); Formula (V); In formula (III) and formula (IV), R1, R2, R3, R4, R5 and R6 are the same or different and are independently selected from H, C 1-8 alkyl; b and d are the same or different and are independently integers greater than or equal to 0; In formula (V), R 19 is selected from unsubstituted, or optionally substituted by one, two or more R c substituted C 6-20 aryl; each R c is the same or different and is independently selected from C 1-12 alkyl; e is an integer greater than or equal to 0; In the adjacent dihydroxy polymer, (a + c) / (a + b + c + d) ≥ 0.

5.

2. The multi-layer structure according to claim 1, wherein In formulas (I) to (II), R1, R2, R3, R4, R5, and R6 are the same or different and are each independently selected from H, C 1-6 alkyl; In Formula (III) and Formula (IV), R1, R2, R3, R4, R5 and R6 are the same or different and are each independently selected from H, C 1-6 alkyl; In formula (V), R 19 is selected from unsubstituted, or optionally substituted by one, two or more R c substituted C 6-14 aryl; each R c is the same or different and is independently selected from C 1-6 alkyl.

3. The multi-layer structure according to claim 1, characterized in that, The number average molecular weight of the adjacent dihydroxy polymer is 2,000 to 200,000.

4. The multi-layer structure according to claim 1, wherein In the adjacent dihydroxy polymer, a is an integer between 0 and 3,000, and a and c are not both 0.

5. The multi-layer structure according to claim 4, wherein a is an integer between 50 and 2,000.

6. The multi-layer structure according to claim 1, wherein In the adjacent dihydroxy polymer, b is an integer between 0 and 200; In the adjacent dihydroxy polymer, c is an integer between 0 and 3,000, and a and c are not both 0; In the adjacent dihydroxy polymer, d is an integer between 0 and 100; In the adjacent dihydroxy polymer, e is an integer between 0 and 2,000.

7. The multi-layer structure according to claim 6, wherein c is an integer between 0 and 300.

8. The multi-layer structure according to claim 1, wherein In the adjacent dihydroxy polymer, e / (a + b + c + d) is selected from 0 to 5.

0.

9. The multi-layer structure according to claim 1, wherein The multilayer structure sequentially includes a substrate layer and a fluoropolymer-based resin layer.

10. The multi-layer structure according to claim 1, wherein The multilayer structure sequentially includes a fluoropolymer-based resin layer, a substrate layer and a fluoropolymer-based resin layer.

11. The multi-layer structure according to claim 1, wherein The substrate is one or a mixture of metal, wood, glass, ceramic, cellulose, poly(meth)acrylate, copolymer of styrene and (meth)acrylate, polyurethane, polysulfone, polyethersulfone, polyphenylsulfone, polyphenylene sulfide, polyether ketone, polyimide, polycarbonate, polyvinyl chloride, polyacrylonitrile, nitrile rubber, hydrogenated nitrile rubber, polystyrene, block copolymer of styrene and butadiene, hydrogenated product of block copolymer of styrene and butadiene, polyvinyl alcohol, ionomer, polyamide, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate.

12. The multilayer structure according to claim 1, wherein The fluoropolymer is a homopolymer or copolymer of vinyl fluoride, a homopolymer and copolymer of vinylidene fluoride, or a mixture thereof.

13. The multi-layer structure according to claim 12, characterized in that, The fluoropolymer is a homopolymer of at least one fluoromonomer selected from vinylidene fluoride, vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, trifluoroethylene, hexafluoroisobutene, perfluorobutyl ethylene, perfluoroethyl vinyl ether, perfluoropropyl vinyl ether, perfluoromethyl vinyl ether, perfluoro-2,2-dimethyl-1,3-dioxolane and perfluoro-2-methylene-4-1,3-dioxolane, a copolymer of two or more of the above fluoromonomers, or a mixture thereof.

14. The multi-layer structure according to claim 1, characterized in that, The weight average molecular weight of the fluoropolymer is 50,000 - 1,500,000.

15. The multi-layer structure according to claim 1, wherein In the fluoropolymer-based resin layer, the addition amount of the adjacent dihydroxy polymer is 10 - 120 wt% of the fluoropolymer.

16. A method for preparing the multilayer structure according to any one of claims 1-15, characterized in that, The method includes: The substrate and the fluoropolymer-based resin layer containing the vicinal dihydroxy polymer are laminated in sequence and hot-pressed to obtain the multi-layer structure, i.e., the hot-pressing method; or, The resin solution of the fluoropolymer-based resin containing the vicinal dihydroxy polymer is coated on the substrate layer and heated and dried to obtain the multi-layer structure, i.e., the solution coating method.

17. The preparation method according to claim 16, characterized in that, In the hot-pressing method, the heating temperature is 80 - 200 °C; the applied pressure is 0.15 - 5 MPa; the hot-pressing time is 1 - 100 minutes; In the solution coating method, the drying temperature is 80 - 200 °C; the drying time is 1 - 100 minutes; In the solution coating method, in the resin solution, the addition amount of the vicinal dihydroxy polymer accounts for 10 - 120 wt% of the weight of the fluoropolymer; In the solution coating method, the concentration of the fluoropolymer in the resin solution is 0.1 wt% - 80 wt%.

18. Use of the multilayer structure according to any one of claims 1-15, characterized in that, It is used as the backsheet of a photovoltaic cell.

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