A multi-layer structure, a preparation method thereof, and an application thereof

Abstract

The present invention discloses a multi-layer structure, a preparation method and an application thereof. The multi-layer structure includes: a substrate layer; a resin layer based on a fluoropolymer; and a polymer layer located between the substrate layer and the resin layer; the polymer layer contains an adjacent dihydroxy polymer, and the adjacent dihydroxy polymer includes 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, and the prepared multi-layer structure has a low oxygen transmission rate and a stable structure. As a backsheet of a photovoltaic cell, it has excellent weather resistance and durability. #imgabs0#

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer material preparation. Specifically, it 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 ultraviolet-resistant 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 to facilitate 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. Since the adhesion between the fluorine-containing polymer and the substrate is poor and the compounding is difficult, the existing compounding methods include high-pressure extrusion or casting methods, 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 the quality of the product and little improvement in the 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 and it has no contribution to the oxygen permeability.

[0004] Therefore, how to prepare a multi-layer structure with weather resistance, durability and low oxygen permeability 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 high-energy surface substances such as glass, metal, and polyester materials to generate strong hydrogen bonds and is rich in strong adhesiveness; at the same time, the polymer layer formed by the adjacent dihydroxy polymer has the characteristics of strong water resistance and low oxygen transmission rate, and is particularly suitable for bonding polyester materials and fluorine-containing polymers to manufacture a composite multi-layer structure, 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;

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

[0010] A polymer layer located between a substrate layer and a resin layer

[0011] The polymer layer contains an adjacent dihydroxy polymer, and the adjacent dihydroxy polymer comprises structural units represented by formula (I) and formula (II):

[0012]

[0013] 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.

[0014] 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):

[0015]

[0016] 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;

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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 cIdentical or different and each independently selected from C 1-6 alkyl groups.

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

[0022] Exemplarily, the vicinal dihydroxy polymer contains structural units represented by formula (I), formula (II), formula (III), formula (IV) and formula (V).

[0023] According to an embodiment of the present invention, the number average molecular weight of the vicinal dihydroxy polymer is 2,000 to 200,000, exemplarily 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.

[0024] Preferably, in the vicinal 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.

[0025] Preferably, in the vicinal dihydroxy polymer, b is an integer between 0 and 200.

[0026] Preferably, in the vicinal 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.

[0027] Preferably, in the vicinal dihydroxy polymer, d is an integer between 0 and 100.

[0028] Preferably, in the vicinal dihydroxy polymer, e is an integer between 0 and 2,000.

[0029] Preferably, in the vicinal 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.

[0030] Preferably, in the vicinal 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.

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

[0032] According to the present invention, the multi-layer structure sequentially includes a fluoropolymer-based resin layer, a polymer layer, a substrate layer, a polymer layer, and a fluoropolymer-based resin layer.

[0033] 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)acrylates, polyurethanes, polysulfones, polyethersulfones, polyphenylsulfones, polyphenylene sulfides, polyether ketones, polyimides, polycarbonates, polyvinyl chlorides, polyacrylonitriles, nitrile rubbers, hydrogenated nitrile rubbers, polystyrenes, styrene and butadiene block copolymers (SBS), hydrogenated products of styrene and butadiene block copolymers (SEBS), polyvinyl alcohols, ionomers, polyamides, polyethylene terephthalates (PET), polyethylene naphthalates (PEN), and polybutylene terephthalates (PBT).

[0034] Exemplarily, the shape of the substrate can be a plate, a block, etc., preferably a plate.

[0035] Exemplarily, the metal can be aluminum, iron, or copper.

[0036] Exemplarily, the substrate is a single-layer board, a stacked board, and a co-extruded product of PET, PEN, or PBT.

[0037] 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, anchor agent treatment, coupling agent treatment, heat treatment, or chemical activation treatment using boron trifluoride, sulfuric acid, caustic soda, etc.

[0038] 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 fluorine-containing monomer selected from vinylidene fluoride (VDF), vinyl fluoride (VF), tetrafluoroethylene (TFE), hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE), trifluoroethylene, hexafluoroisobutene, perfluorobutylethylene, perfluoro(methyl vinyl ether) (PMVE), perfluoro(ethyl vinyl ether) (PEVE), perfluoropropyl vinyl ether (PPVE), perfluoromethyl vinyl ether (PMVE), perfluoro-2,2-dimethyl-1,3-dioxolane (PDD), and perfluoro-2-methylene-4-1,3-dioxolane (PMD), a copolymer of two or more of the fluorine-containing monomers, or a mixture thereof. A copolymer containing vinylidene fluoride is preferred, for example, a copolymer formed by the polymerization reaction of two fluorine-containing monomers, VDF and HFP.

[0039] According to the present invention, the weight-average molecular weight of the fluoropolymer is 50,000 - 1,500,000, and exemplarily it is 50,000, 100,000, 150,000, 200,000, 500,000, 1,000,000 or 15,000,000.

[0040] According to the present invention, the melting point of the fluoropolymer is 80°C - 180°C.

[0041] According to the present invention, at least one of the following can be added to the resin layer based on the fluoropolymer: the adjacent dihydroxy polymer, polycarbonate, PVC, ABS, styrene-maleic anhydride copolymer, polyacrylonitrile, polystyrene, polysulfone, polyethersulfone, poly(meth)acrylate, polyester, polyurethane, polyurea, polyamide, polyphenylene sulfide (PPS) or silicone resin.

[0042] 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, and the functional groups include but are not limited to at least one of carboxyl group, sulfonic acid group, aziridinyl group, urea group, imide group, phosphoric acid (ester) group, cyano group, imino group, acid anhydride group, amine group, epoxy group, hydroxyl group, ester group, and in particular, it is selected from at least one of carboxyl group, sulfonic acid group, acid anhydride group, amine group, epoxy group, hydroxyl group, cyano group, ester group.

[0043] According to the present invention, the resin layer can 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.

[0044] According to the present invention, the above-mentioned fluoropolymer can also be added to the polymer layer, and the addition amount of the fluoropolymer is less than 90% of the weight of the adjacent dihydroxy polymer.

[0045] According to the present invention, the thickness of the resin layer and the polymer layer is 0.1 - 10,000 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, 10,000 μm.

[0046] The present invention also provides a method for preparing the above multi-layer structure, and the method includes:

[0047] Stacking a substrate, a polymer layer containing the adjacent dihydroxy polymer, and a resin layer based on the fluoropolymer in sequence, and hot pressing to obtain the multi-layer structure (hot pressing method); or,

[0048] Apply the adjacent dihydroxy polymer solution onto the substrate layer to form a polymer layer on the substrate layer, and then coat a fluoropolymer-based resin layer or resin solution on the polymer layer, and optionally heat and dry to obtain the multi-layer structure (solution coating method).

[0049] 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; the hot pressing time is 1 - 100 minutes.

[0050] According to the present invention, in the solution coating method, the drying temperature is 80 - 200 °C; the drying time is 1 - 100 minutes.

[0051] Exemplarily, the polymer solution is prepared by dissolving an adjacent dihydroxy polymer in a solvent.

[0052] Exemplarily, the resin solution is prepared by dissolving the raw materials for preparing the resin layer including a fluoropolymer in a solvent.

[0053] According to the present invention, the concentration of the adjacent dihydroxy polymer in the polymer solution is 0.1 wt% - 50 wt%, exemplarily 10 wt%.

[0054] According to the present invention, the concentration of the fluoropolymer in the resin solution is 0.1 wt% - 80 wt%, exemplarily 20 wt%.

[0055] Exemplarily, the raw materials for preparing the resin layer include a fluoropolymer, and may also include at least one of the adjacent dihydroxy polymer, 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.

[0056] 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.

[0057] 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.

[0058] As an exemplary embodiment of the present invention, the method for preparing the multi-layer structure is specifically as follows:

[0059] Stack the substrate layer, polymer layer, and resin layer in sequence, and then press at 80 - 200 °C and 0.15 - 5 MPa for 1 - 100 min to obtain the multi-layer structure.

[0060] As an exemplary embodiment of the present invention, the method for preparing the multi-layer structure is specifically as follows:

[0061] A polymer solution is coated on the substrate layer to form a polymer layer on the substrate layer; optionally, after drying, a resin solution is coated on the polymer layer, and after drying to remove the solvent, a multi-layer structure is obtained.

[0062] The present invention also provides the application of the above multi-layer structure as a backsheet of a photovoltaic cell.

[0063] Advantages of the present invention:

[0064] 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 low oxygen transmission rate and a stable structure. As a backsheet of a photovoltaic cell, it has excellent weather resistance and durability.

[0065] Term definitions and explanations

[0066] Unless otherwise specified, the terms and descriptions in the context of the present invention have the meanings described below.

[0067] More than refers to more than 3.

[0068] The term "C 1-12 alkyl" should be understood to mean 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.

[0069] The term "C 6-20 aryl" should be understood to preferably mean a monocyclic, bicyclic or tricyclic hydrocarbon ring having 6 to 20 carbon atoms that is monovalent aromatic or partially aromatic, preferably "C 6-14 aryl". The term "C 6-14"Aryl" shall preferably be understood to represent a monocyclic, bicyclic or tricyclic hydrocarbon ring that is monovalent, aromatic or partially aromatic and has 6, 7, 8, 9, 10, 11, 12, 13 or 14 carbon atoms ("C 6-14 aryl"), in particular 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 fluorenyl, or a ring having 14 carbon atoms ("C 14 aryl"), such as anthracenyl. When the C 6-20 aryl is substituted, it can be mono-substituted or multi-substituted. Also, there is no restriction on the substitution site, for example, it can be ortho-substituted, para-substituted or meta-substituted. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 FIG. is a cross-sectional view of the multilayer structure in Example 1.

[0071] Figure 2 FIG. is a cross-sectional view of the multilayer structure in Example 8.

[0072] Wherein: 101, substrate layer; 102, polymer layer; 103, resin layer based on fluoropolymer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0073] 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.

[0074] Unless otherwise specified, the raw materials and reagents used in the following embodiments are commercially available products or can be prepared by known methods.

[0075] Preparation of Vicinal Dihydroxy Polymer

[0076] Preparation Example 1

[0077] Preparation of Vicinal Dihydroxy Polymer SBSOH:

[0078] 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.

[0079] Step 1: Synthesis of styrene-butadiene block copolymer SBS by the method disclosed in "Synthetic Rubber Industry Handbook" (edited by Zhao Xutao and Liu Dahua, 2nd edition, Chemical Industry Press, 2006): Using 1,3-butadiene and styrene as raw materials, cyclohexane as a solvent, and sec-butyllithium as a catalyst for polymerization to obtain SBS;

[0080] Step 2: 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 the double bonds in the polymer molecular structure undergo epoxidation reaction to prepare an epoxidized polymer solution;

[0081] Step 3: Then, add 70% aqueous perchloric acid solution to the epoxidized polymer solution, the epoxy groups are ring-opened to adjacent dihydroxy groups, and the reactants are washed with water and dried to obtain adjacent dihydroxy polymer SBSOH.

[0082] The molar proportion results of the adjacent dihydroxy structural units of the SBSOH sample are shown in Table 1 below.

[0083] SBSOH-1, SBSOH-2, SBSOH-3, and SBSOH-4 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.

[0084] Table 1

[0085] 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 SBSOH-4 92300 2.9 0.66

[0086] 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 obtained by 1 calculation from the 1H-NMR test results.

[0087] Preparation Example 2

[0088] Preparation of adjacent dihydroxy polymer PBOH:

[0089] The adjacent dihydroxy polymer PBOH contains the structures of formulas (I) to (IV), and R1, R2, R3, R4, R5, and R6 are hydrogen;

[0090] Using 1,3-butadiene as a raw material, referring to the method disclosed in Example 1 of CN110964131A, the PBOH samples shown in Table 2 are prepared.

[0091] 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.

[0092] The number-average molecular weight and the molar ratio of adjacent dihydroxy structural units of the PBOH sample are shown in Table 2.

[0093] Table 2

[0094] 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

[0095] In Table 2, the ratios of a, b, c, d and (a + c) / (a + b + c + d) are calculated from the 1 1H-NMR test results.

[0096] Example 1

[0097] A multi-layer structure as Figure 1 shown, the multi-layer structure has 3 layers, which are a substrate layer 101, a polymer layer 102 and a fluoropolymer-based resin layer 103 in sequence. The preparation method is as follows:

[0098] 1), Substrate preparation

[0099] 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.

[0100] 2), Coating of adjacent dihydroxy polymer

[0101] A 10 wt% DMF solution of adjacent dihydroxy polymer PBOH-1 is coated on the surface of the alkali-treated PET with a KTQ-II coater, the coating thickness is 20 μm, and it is dried at 200 °C for 10 minutes to form a polymer coating on the surface of the substrate layer.

[0102] 3), Coating of fluoropolymer-based resin

[0103] 20 parts of PVDF (Solvay 6020, weight-average molecular weight 680,000, melting point 170 - 175 °C) 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 fluoropolymer-based resin coating solution.

[0104] The fluoropolymer-based resin coating solution is coated on the polymer coating, the coating thickness is 30 μm, and it is dried at 200 °C for 10 minutes to obtain a multi-layer structure.

[0105] Example 2

[0106] PBOH-2 is used instead of PBOH-1, and the rest is the same as in Example 1.

[0107] Example 3

[0108] Replace PBOH-1 with PBOH-3, and the rest is the same as in Example 1.

[0109] Example 4

[0110] Replace PBOH-1 with SBSOH-1, and the rest is the same as in Example 1.

[0111] Example 5

[0112] Replace PBOH-1 with SBSOH-2, and the rest is the same as in Example 1.

[0113] Example 6

[0114] Replace PBOH-1 with SBSOH-3, and the rest is the same as in Example 1.

[0115] Example 7

[0116] (1) Preparation of adjacent dihydroxy polymer film

[0117] A DMF solution of 10 wt% PBOH-2 was coated on a polyethylene plate; vacuum dried at 120 °C for 30 min to obtain an adjacent dihydroxy polymer film with a thickness of 100 μm, i.e., the polymer layer.

[0118] (2) Preparation of PVDF film

[0119] A DMF solution of 20 wt% PVDF (Solvay 6020) was coated on a polyethylene plate; vacuum dried at 120 °C for 30 min to obtain a PVDF film with a thickness of 100 μm, i.e., the resin layer.

[0120] (3) Preparation of multi-layer structure

[0121] A 1 mm thick PET film was air-dried according to the surface treatment method of Example 1.

[0122] The PET film, adjacent dihydroxy polymer film and PVDF film were stacked neatly in sequence. The two sides of the stacked composite film were sandwiched with flat stainless steel plates, and a pressure of 3 MPa was applied at 160 °C for 2 minutes to obtain a multi-layer structure.

[0123] The oxygen permeability rates of the adjacent dihydroxy polymer film, PVDF film and multi-layer structure in Example 7 were tested; the test results are shown in Table 4.

[0124] Example 8

[0125] Prepare as Figure 2The multi-layer structure shown, the multi-layer structure has 5 layers, which are successively a fluoropolymer-based resin layer 103, a polymer layer 102, a substrate layer 101, a polymer layer 102, and a fluoropolymer-based resin layer 103. The preparation method is the same as that of Example 1, except that in step 2), the adjacent dihydroxy polymer is coated on both surfaces of the PET sheet, and in step 3), the fluoropolymer-based resin is coated on the two polymer coatings formed on both surfaces of the PET sheet, thereby forming a 5-layer structure as shown in Figure 2 shown.

[0126] Comparative Example 1

[0127] 1), Substrate preparation

[0128] A PET sheet with a specification of 5 cm × 5 cm × 1 mm was 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.

[0129] 2), Coating of fluoropolymer-based resin

[0130] 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 fluoropolymer-based resin coating solution.

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

[0132] Comparative Example 2

[0133] 1), Substrate preparation

[0134] A PET sheet with a model of 5 cm × 5 cm × 1 mm was immersed in a 20% KOH solution at 80 °C, taken out after 1 minute, washed with deionized water, and dried to obtain alkali-treated PET.

[0135] 2), Coating of fluoropolymer-based resin

[0136] 20 parts of modified PVDF (Solvay 5130, that is, acrylic acid-modified PVDF, weight average molecular weight 1,300,000, melting point 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 a fluoropolymer-based resin coating solution.

[0137] The resin coating solution of the fluoropolymer was coated on a PET plate with a coating thickness of 30 μm and dried at 200 °C for 10 minutes to obtain a multilayer structure.

[0138] In Examples 1-7 and Comparative Examples 1-2, the test methods for the performance parameters of the multilayer structure were as follows:

[0139] 1. 180° peel strength

[0140] It was determined with reference to the test method for 180° peel strength of adhesives in GB / T 2790-1995.

[0141] 2. Adhesion test

[0142] The standard cross-cut test was carried out with reference to ASTM D3359. A grid of 100 squares with a side length of 1 mm was formed by cutting at intervals of 11 columns and 11 rows with a utility knife. The surface of the squares was adhered with transparent tape, and the surface state peeled off together with the tape was detected and evaluated.

[0143] Grade 1: No surface peeling;

[0144] Grade 2: Peeling area < 5%;

[0145] Grade 3: Peeling area 5 - 15%;

[0146] Grade 4: Peeling area 15 - 35%;

[0147] Grade 5: Peeling area 35 - 65%;

[0148] Grade 6: Complete peeling.

[0149] 3. After placing the multilayer structure under the conditions of 85% humidity and 85 °C for 48 h, the 180° peel strength and adhesion of the multilayer structure were tested again.

[0150] 4. Oxygen permeability test

[0151] It was determined with reference to GB / T 19789-2021 "Test method for oxygen permeability of plastic films and sheets for packaging materials - Coulometer detection method".

[0152] The oxygen permeability was tested using a Labthink C230M tester.

[0153] The test results are shown in Table 3 and Table 4.

[0154] Table 3

[0155]

[0156] Table 4 Oxygen permeability results of the adjacent dihydroxy polymer film, PVDF film and multilayer structure in Example 7

[0157]

[0158] As can be seen from Table 3 and Table 4 above, the adjacent dihydroxy polymer has strong adhesion to the resin layer and the substrate PET layer, making the multi-layer structure prepared by the present invention have a stable structure and low oxygen permeability; as a backplane of a photovoltaic cell, it has excellent weather resistance and durability.

[0159] 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 substitutions, 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; A resin layer based on a fluoropolymer; And A polymer layer located between the substrate layer and the resin layer, The polymer layer contains an adjacent dihydroxy polymer, and the adjacent dihydroxy polymer contains structural units represented by formula (I) and formula (II): ； Formula (I); ； Formula (II); 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; The adjacent dihydroxy polymer further includes 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 each independently selected from H, C 1-8 alkyl; b and d are the same or different and are each independently an integer 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 Formula (I) to Formula (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, characterized in that In the adjacent dihydroxy polymer, a is an integer between 0 and 3,000, and a and c are not both 0; 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.

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

0.

6. The multi-layer structure according to claim 1, characterized in that, The multilayer structure sequentially includes a substrate layer, a polymer layer, and a resin layer based on a fluoropolymer.

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

8. The multilayer structure according to claim 1, wherein, The substrate is one or a mixture of metals, wood, glass, ceramics, cellulose, poly(meth)acrylates, copolymers of styrene and (meth)acrylates, 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, hydrogenated products of block copolymers of styrene and butadiene, polyvinyl alcohols, ionomers, polyamides, polyethylene terephthalates, polyethylene naphthalate, polybutylene terephthalate; The fluoropolymer is a homopolymer or copolymer of vinyl fluoride, a homopolymer and copolymer of vinylidene fluoride, or a mixture thereof.

9. The multi-layer structure according to claim 8, wherein 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.

10. The multilayer structure according to claim 1, wherein The weight-average molecular weight of the fluoropolymer is 50,000 - 1,500,000.

11. A method for preparing the multi-layer structure according to any one of claims 1 to 10, characterized in that, The method includes: Stacking the substrate, the polymer layer containing the adjacent dihydroxy polymer, and the resin layer based on the fluoropolymer in sequence, and hot pressing to prepare the multilayer structure, and this method is called the hot pressing method; or, The adjacent dihydroxy polymer solution is coated on a substrate layer to form a polymer layer on the substrate layer, and then a fluoropolymer-based resin layer or resin solution is coated on the polymer layer, and optionally heated and dried to obtain the multi-layer structure. This method is called the solution coating method.

12. The preparation method according to claim 11, 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.

13. The preparation method according to claim 11, characterized in that, In the solution coating method, the drying temperature is 80 - 200 °C; the drying time is 1 - 100 minutes.

14. The preparation method according to claim 11, wherein, In the solution coating method, the concentration of the adjacent dihydroxy polymer in the polymer solution is 0.1 wt% - 50 wt%.

15. The preparation method according to claim 11, characterized in that, In the solution coating method, the concentration of the fluoropolymer in the resin solution is 0.1 wt% - 80 wt%.

16. Use of the multi-layer structure according to any one of claims 1 to 10, characterized in that, Used as the backsheet of a photovoltaic cell.

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