A modified PVDF thin film and its preparation method, and a solar cell backsheet.

Abstract

The present invention relates to a modified PVDF film and a preparation method, a solar cell backboard, the backboard comprising a polyethylene terephthalate (PET) layer and a modified polyvinylidene fluoride layer located on both sides of the PET layer, wherein the modified polyvinylidene fluoride film layer located inside is used for bonding with the EVA (ethylene-vinyl acetate) adhesive film of a solar cell module. The present invention mainly blends polyvinylidene fluoride with a hydroxyl-containing polymer ethylene-vinyl alcohol copolymer (EVOH) having good barrier properties, and adds a certain compatibilizer to increase the compatibility of the two, and the hydroxyl group of the ethylene-vinyl alcohol copolymer can react chemically with the organic group of the EVA adhesive film, thereby increasing the bonding ability with EVA, and the method is simple to operate, low cost, and has strong bonding ability.

Description

Technical Field

[0001] The invention belongs to the technical field of photovoltaic components, and in particular relates to a modified PVDF film and a preparation method thereof, and a solar cell back plate. Background Art

[0002] Solar cell backsheet is an important packaging material for photovoltaic modules. It isolates the modules from the external environment, achieves electrical insulation, and enables the modules to operate outdoors for a long time. The quality of the backsheet is closely related to the reliability and service life of the modules. At present, the most commonly used solar cell backsheet is KPK (PVDF / PET / PVDF) backsheet. As a double-sided fluorine-containing composite backsheet, it has excellent resistance to environmental erosion, UV aging and moisture and heat. At the same time, it has obvious cost advantages over the widely used TPT (PVF / PET / PVF) backsheet in the market. Therefore, with the continuous expansion of the solar energy market, its demand is also increasing. However, the surface tension of polyvinylidene fluoride film is poor and it is difficult to bond with EVA film, which limits the widespread application of polyvinylidene fluoride in solar cell backsheets.

[0003] In view of the problems such as poor surface tension of polyvinylidene fluoride film and poor adhesion to EVA film, the commonly used surface modification method is corona, that is, the arc is formed by high-voltage discharge between capacitors to cause physical and chemical changes on the surface of the material, thereby reducing the surface energy of the polyvinylidene fluoride film surface, and then increasing the adhesion to the EVA film. Other methods include grafting acrylic acid or siloxane on the surface of polyvinylidene fluoride. For example, patent CN 111435688 B uses oxygen plasma to bombard the surface of polyvinylidene fluoride film, and then grafts siloxane on the surface of polyvinylidene fluoride by spraying, and uses the amino functional group of siloxane to react with the organic group of EVA, thereby achieving efficient adhesion to EVA. However, the adhesion between polyvinylidene fluoride and EVA film after corona will gradually decrease with the increase of storage time, and surface grafting of hydroxyl or acrylic acid will reduce the water vapor barrier capacity of polyvinylidene fluoride film. Therefore, it is urgent to develop a modified polyvinylidene fluoride film that increases the adhesion to EVA film without losing the water vapor barrier capacity of the film. Summary of the invention

[0004] Purpose of the invention: To address the problems and deficiencies in the prior art, a modified PVDF film and a preparation method, and a solar cell backplane are proposed.

[0005] The present invention introduces EVOH into a polyvinylidene fluoride matrix, and adds a certain compatibilizer to increase the compatibility of polyvinylidene fluoride and EVOH to obtain better mechanical strength. The hydroxyl groups in the EVOH polymer can react chemically with the organic groups in EVA to enhance the adhesion. In addition, EVOH has good water vapor barrier properties and can be widely used in the fields of solar back panels.

[0006] To achieve the above object, a method for preparing a modified polyvinylidene fluoride film according to the present invention is characterized in that it comprises the following steps:

[0007] A method for preparing a modified PVDF film comprises the following steps:

[0008] S1: uniformly mixing dried polyvinylidene fluoride particles, ethylene-vinyl alcohol copolymer particles, a compatibilizer, an antioxidant and an ultraviolet light absorber in a high-speed mixer, and melt-granulating in a twin-screw extruder to obtain a modified polyvinylidene fluoride special material;

[0009] S2: forming the modified polyvinylidene fluoride special material into a modified polyvinylidene fluoride thick film;

[0010] S3 biaxially stretches the modified polyvinylidene fluoride thick film to obtain a modified PVDF thin film.

[0011] Furthermore, the mass ratio of the polyvinylidene fluoride particles to the ethylene-vinyl alcohol copolymer particles is 9-7:1-3.

[0012] Furthermore, the compatibilizer is radiation-grafted polyvinylidene fluoride of acrylic acid or maleic anhydride, and the added ratio of acrylic acid or maleic anhydride is 5wt% to 10wt% of the polyvinylidene fluoride.

[0013] Furthermore, the antioxidant is antioxidant 1010 or antioxidant 168, and the ultraviolet light absorber is 2-hydroxy-4-octyloxybenzophenone, 2-(2-hydroxy-5-benzyl)benzotriazole, or monobenzoic acid resorcinol ester.

[0014] Furthermore, the ratio of the antioxidant to the ultraviolet light absorber is 1 wt% to 2 wt% of the total mass of the polyvinylidene fluoride particles and the ethylene-vinyl alcohol copolymer particles.

[0015] Furthermore, the polyvinylidene fluoride thick film is formed by hot pressing film forming with a flat vulcanizer and tape casting, and the thickness of the thick film is not less than 0.05 mm.

[0016] Furthermore, the biaxial stretching is simultaneous biaxial stretching, the simultaneous biaxial stretching temperature is 100-120° C., the stretching speed is 30-50 mm / s, and the stretching ratio is 1.5-4.

[0017] Furthermore, the compatibilizer is a special material of polyvinylidene fluoride grafted glycidyl methacrylate or polyvinylidene fluoride grafted maleic anhydride, and the addition ratio thereof is 5wt% to 10wt% of the polyvinylidene fluoride particles.

[0018] Furthermore, before S1, the step of preparing the compatibilizer includes:

[0019] Putting dried polyvinylidene fluoride particles, glycidyl methacrylate, benzoyl peroxide, and 9-vinyl anthracene into a twin-screw extruder for melt reaction extrusion granulation to obtain the polyvinylidene fluoride grafted glyceryl methacrylate special material, wherein the addition ratio of benzoyl peroxide and 9-vinyl anthracene is 0.025% to 0.15% of the total mass of glycidyl methacrylate and polyvinylidene fluoride; the mass ratio of polyvinylidene fluoride to glycidyl methacrylate is 90 to 97:3 to 10;

[0020] Alternatively, dried polyvinylidene fluoride particles, maleic anhydride, benzoyl peroxide, and 9-vinyl anthracene are melt-reacted and extruded in a twin-screw extruder to obtain the polyvinylidene fluoride grafted maleic anhydride special material, wherein the addition ratio of benzoyl peroxide and 9-vinyl anthracene is 0.025% to 0.15% of the total mass of maleic anhydride (MAH) and polyvinylidene fluoride; and the mass ratio of polyvinylidene fluoride to maleic anhydride is 90 to 97:3 to 10.

[0021] According to another aspect of the present invention, the present invention provides a polyvinylidene fluoride film prepared by the above method and a solar cell back panel comprising the film.

[0022] The above technical scheme conceived by the present invention is compared with the existing technical scheme: the hydrophilicity of PVDF and the adhesion of EVA film are improved. Since EVOH contains more hydroxyl groups on the molecular chain, it can significantly reduce the surface energy of PVDF film when blended with PVDF. Moreover, the hydroxyl groups of EVOH molecular chain can react with the organic groups of EVA film to undergo alcoholysis reaction, which can significantly improve the adhesion of PVDF and EVA film. Moreover, EVOH, as one of the three high barrier molecular materials, has excellent barrier properties and can significantly improve the water vapor barrier capacity of PVDF when blended with PVDF. However, PVDF and EVOH have poor compatibility. The present invention improves the mechanical properties of the material by adding melt-grafted glycidyl methacrylate or maleic anhydride to achieve reactive compatibility. The present invention further improves the water vapor barrier and mechanical properties of PVDF film through a synchronous biaxial stretching process. By optimizing the stretching ratio, stretching temperature and stretching speed, a modified PVDF film with high water vapor barrier and excellent mechanical properties can be obtained, which can be widely used in the bonding of the inner layer of the solar cell back panel and the EVA film. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of a method for preparing a modified PVDF film in an embodiment provided by the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments.

[0025] A method for preparing a modified PVDF film comprises the following steps:

[0026] S1: Dry polyvinylidene fluoride particles, ethylene-vinyl alcohol copolymer particles, compatibilizer, antioxidant and ultraviolet light absorber are mixed evenly in a high-speed mixer, and melt-granulated in a twin-screw extruder to obtain a modified polyvinylidene fluoride special material.

[0027] S2: forming the modified polyvinylidene fluoride special material into a modified polyvinylidene fluoride thick film;

[0028] S3 biaxially stretches the modified polyvinylidene fluoride thick film to obtain a modified PVDF thin film.

[0029] Furthermore, the mass ratio of the polyvinylidene fluoride particles to the ethylene-vinyl alcohol copolymer particles is 9-7:1-3.

[0030] The principle of the mass ratio of polyvinylidene fluoride to ethylene-vinyl alcohol copolymer being 9-7:1-3 is that:

[0031] Since polyvinylidene fluoride and ethylene-vinyl alcohol copolymer are incompatible, the higher the proportion of ethylene-vinyl alcohol copolymer added, the higher the proportion of compatibilizer added, and the corresponding stretch ratio should be lower. When the proportion of compatibilizer added is certain, the higher the mass ratio and the higher the stretch ratio, the film will break. The higher the mass ratio and the higher the stretch ratio, the better the corresponding tensile strength and water vapor barrier properties.

[0032] Furthermore, the compatibilizer is radiation-grafted polyvinylidene fluoride of acrylic acid or maleic anhydride, and the added ratio of acrylic acid or maleic anhydride is 5wt% to 10wt% of the polyvinylidene fluoride.

[0033] Furthermore, the antioxidant is antioxidant 1010 or antioxidant 168, and the ultraviolet light absorber includes: 2-hydroxy-4-octyloxybenzophenone, 2-(2-hydroxy-5-benzyl)benzotriazole, and monobenzoic acid resorcinol ester.

[0034] Furthermore, the ratio of the antioxidant to the ultraviolet light absorber is 1 wt% to 2 wt% of the total mass of the polyvinylidene fluoride particles and the ethylene-vinyl alcohol copolymer particles.

[0035] Furthermore, the polyvinylidene fluoride thick film is formed by hot pressing film forming with a flat vulcanizer and tape casting, and the thickness of the thick film is not less than 0.05 mm.

[0036] Furthermore, the biaxial stretching is simultaneous biaxial stretching, the simultaneous biaxial stretching temperature is 100-120° C., the stretching speed is 30-50 mm / s, and the stretching ratio is 1.5-4.

[0037] Furthermore, the compatibilizer is a special material of polyvinylidene fluoride grafted glycidyl methacrylate or polyvinylidene fluoride grafted maleic anhydride, and the addition ratio thereof is 5wt% to 10wt% of the polyvinylidene fluoride particles.

[0038] Furthermore, before S1, the step of preparing the compatibilizer includes:

[0039] Putting dried polyvinylidene fluoride particles, glycidyl methacrylate, benzoyl peroxide, and 9-vinyl anthracene into a twin-screw extruder for melt reaction extrusion granulation to obtain the polyvinylidene fluoride grafted glyceryl methacrylate special material, wherein the addition ratio of benzoyl peroxide and 9-vinyl anthracene is 0.025% to 0.15% of the total mass of glycidyl methacrylate and polyvinylidene fluoride; the mass ratio of polyvinylidene fluoride to glycidyl methacrylate is 90 to 97:3 to 10;

[0040] Alternatively, dried polyvinylidene fluoride particles, maleic anhydride, benzoyl peroxide, and 9-vinyl anthracene are melt-reacted and extruded in a twin-screw extruder to obtain the polyvinylidene fluoride grafted maleic anhydride special material, wherein the addition ratio of benzoyl peroxide and 9-vinyl anthracene is 0.025% to 0.15% of the total mass of maleic anhydride (MAH) and polyvinylidene fluoride; and the mass ratio of polyvinylidene fluoride to maleic anhydride is 90 to 97:3 to 10.

[0041] According to another aspect of the present invention, the present invention provides a polyvinylidene fluoride film prepared by the above method and a solar cell back panel comprising the film.

[0042] The above technical scheme conceived by the present invention is compared with the existing technical scheme: the hydrophilicity of PVDF and the adhesion of EVA film are improved. Since EVOH contains more hydroxyl groups on the molecular chain, it can significantly reduce the surface energy of PVDF film when blended with PVDF. Moreover, the hydroxyl groups of EVOH molecular chain can react with the organic groups of EVA film to undergo alcoholysis reaction, which can significantly improve the adhesion of PVDF and EVA film. Moreover, EVOH, as one of the three high barrier molecular materials, has excellent barrier properties and can significantly improve the water vapor barrier capacity of PVDF when blended with PVDF. However, PVDF and EVOH have poor compatibility. The present invention improves the mechanical properties of the material by adding melt-grafted glycidyl methacrylate or maleic anhydride to achieve reactive compatibility. The present invention further improves the water vapor barrier and mechanical properties of PVDF film through a synchronous biaxial stretching process. By optimizing the stretching ratio, stretching temperature and stretching speed, a modified PVDF film with high water vapor barrier and excellent mechanical properties can be obtained, which can be widely used in the bonding of the inner layer of the solar cell back panel and the EVA film.

[0043] The present invention is further described in detail below in conjunction with the embodiments.

[0044] Embodiment 1:

[0045] A modified polyvinylidene fluoride film is prepared according to the following steps:

[0046] (1) Mix dried polyvinylidene fluoride particles, ethylene-vinyl alcohol copolymer particles, polyvinylidene fluoride with melt-grafted glycidyl methacrylate as a compatibilizer, antioxidant 1010, and ultraviolet light absorber monobenzoic acid resorcinol ester in a high-speed mixer, and melt granulate in a twin-screw extruder. The mass ratio of polyvinylidene fluoride to ethylene-vinyl alcohol copolymer is 90:10; the compatibilizer is 5wt% of the polyvinylidene fluoride, and the antioxidant 1010 and ultraviolet light absorber monobenzoic acid resorcinol ester are 1wt% of the total mass of polyvinylidene fluoride and ethylene-vinyl alcohol copolymer;

[0047] (2) forming a 0.4 mm thick film by tape casting the modified polyvinylidene fluoride particles obtained in step (1);

[0048] (3) The modified polyvinylidene fluoride thick film obtained in step (2) is simultaneously biaxially stretched at 120° C. to prepare a biaxially oriented polyvinylidene fluoride film at a stretching speed of 50 mm / s and a stretching ratio of 4.0.

[0049] Embodiment 2:

[0050] A modified polyvinylidene fluoride film is prepared according to the following steps:

[0051] (1) Mix dried polyvinylidene fluoride particles, ethylene-vinyl alcohol copolymer particles, polyvinylidene fluoride with melt-grafted glycidyl methacrylate as a compatibilizer, antioxidant 1010, and ultraviolet light absorber monobenzoic acid resorcinol ester in a high-speed mixer, and melt granulate in a twin-screw extruder. The mass ratio of polyvinylidene fluoride and ethylene-vinyl alcohol copolymer is 70:30; the compatibilizer is 10wt% of the polyvinylidene fluoride, and the antioxidant 1010 and ultraviolet light absorber monobenzoic acid resorcinol ester are 1wt% of the total mass of polyvinylidene fluoride and ethylene-vinyl alcohol copolymer;

[0052] (2) forming a 0.4 mm thick film by tape casting the modified polyvinylidene fluoride particles obtained in step (1);

[0053] (3) The modified polyvinylidene fluoride thick film obtained in step (2) is simultaneously biaxially stretched at 120° C. to prepare a biaxially oriented polyvinylidene fluoride film at a stretching speed of 50 mm / s and a stretching ratio of 4.0.

[0054] Embodiment 3:

[0055] A modified polyvinylidene fluoride film is prepared according to the following steps:

[0056] (1) Mix dried polyvinylidene fluoride particles, ethylene-vinyl alcohol copolymer particles, polyvinylidene fluoride with melt-grafted maleic anhydride as a compatibilizer, antioxidant 1010, and ultraviolet light absorber monobenzoic acid resorcinol ester in a high-speed mixer, and melt granulate in a twin-screw extruder. The mass ratio of polyvinylidene fluoride and ethylene-vinyl alcohol copolymer is 90:10; the compatibilizer is 5wt% of the polyvinylidene fluoride, and the antioxidant 1010 and the ultraviolet light absorber monobenzoic acid resorcinol ester are 1wt% of the total mass of polyvinylidene fluoride and ethylene-vinyl alcohol copolymer;

[0057] (2) forming a 0.4 mm thick film by hot pressing the modified polyvinylidene fluoride particles obtained in step (1) using a flat plate vulcanizer;

[0058] (3) The modified polyvinylidene fluoride thick film obtained in step (2) is simultaneously biaxially stretched at 120° C. to prepare a biaxially oriented polyvinylidene fluoride film at a stretching speed of 50 mm / s and a stretching ratio of 4.0.

[0059] Embodiment 4:

[0060] A modified polyvinylidene fluoride film is prepared according to the following steps:

[0061] (1) Mix dried polyvinylidene fluoride particles, ethylene-vinyl alcohol copolymer particles, polyvinylidene fluoride with melt-grafted methacrylate glycerol as a compatibilizer, antioxidant 168, and ultraviolet light absorber monobenzoic acid resorcinol ester in a high-speed mixer, and melt granulate in a twin-screw extruder. The mass ratio of polyvinylidene fluoride to ethylene-vinyl alcohol copolymer is 70:30; the compatibilizer is 10wt% of the polyvinylidene fluoride, and the antioxidant 168 and ultraviolet light absorber monobenzoic acid resorcinol ester are 2wt% of the total mass of polyvinylidene fluoride and ethylene-vinyl alcohol copolymer;

[0062] (2) forming a 0.05 mm thick film by hot pressing the modified polyvinylidene fluoride particles obtained in step (1) using a flat plate vulcanizer;

[0063] (3) The modified polyvinylidene fluoride thick film obtained in step (2) is simultaneously biaxially stretched at 120° C. to prepare a biaxially oriented polyvinylidene fluoride film, with a stretching speed of 50 mm / s and a stretching ratio of 1.5.

[0064] Embodiment 5:

[0065] A modified polyvinylidene fluoride film is prepared according to the following steps:

[0066] (1) Mix dried polyvinylidene fluoride particles, ethylene-vinyl alcohol copolymer particles, polyvinylidene fluoride with melt-grafted maleic anhydride as a compatibilizer, antioxidant 1010, and ultraviolet light absorber 2-(2-hydroxy-5-benzyl)benzotriazole in a high-speed mixer, and melt granulate in a twin-screw extruder. The mass ratio of polyvinylidene fluoride to ethylene-vinyl alcohol copolymer is 80:20; the compatibilizer is 5wt% of polyvinylidene fluoride, and the antioxidant 1010 and ultraviolet light absorber 2-(2-hydroxy-5-benzyl)benzotriazole are 1wt% of polyvinylidene fluoride;

[0067] (2) forming a 0.3 mm thick film by tape casting the modified polyvinylidene fluoride particles obtained in step (1);

[0068] (3) The modified polyvinylidene fluoride thick film obtained in step (2) is simultaneously biaxially stretched at 110° C. to prepare a biaxially oriented polyvinylidene fluoride film at a stretching speed of 30 mm / s and a stretching ratio of 3.0.

[0069] Embodiment 6:

[0070] A modified polyvinylidene fluoride film is prepared according to the following steps:

[0071] (1) Mix dried polyvinylidene fluoride particles, ethylene-vinyl alcohol copolymer particles, polyvinylidene fluoride with melt-grafted maleic anhydride as a compatibilizer, antioxidant 1010, and ultraviolet light absorber 2-hydroxy-4-n-octyloxybenzophenone in a high-speed mixer, and melt granulate in a twin-screw extruder. The mass ratio of polyvinylidene fluoride to ethylene-vinyl alcohol copolymer is 80:20; the compatibilizer is 10wt% of the polyvinylidene fluoride, and the antioxidant 1010 and ultraviolet light absorber 2-hydroxy-4-n-octyloxybenzophenone are 1wt% of the total mass of polyvinylidene fluoride and ethylene-vinyl alcohol copolymer;

[0072] (2) forming a 0.2 mm thick film by hot pressing the modified polyvinylidene fluoride particles obtained in step (1) using a flat plate vulcanizer;

[0073] (3) The modified polyvinylidene fluoride thick film obtained in step (2) is simultaneously biaxially stretched at 120° C. to prepare a biaxially oriented polyvinylidene fluoride film at a stretching speed of 50 mm / s and a stretching ratio of 4.0.

[0074] Comparative Example 1:

[0075] Prepare polyvinylidene fluoride film as a comparative sample according to the following steps:

[0076] (1) Dry polyvinylidene fluoride particles, polymethyl methacrylate particles, antioxidant 1010, and ultraviolet light absorber monobenzoic acid resorcinol ester are mixed uniformly in a high-speed mixer, and melt granulated in a twin-screw extruder. The mass ratio of polyvinylidene fluoride to ethylene-vinyl alcohol copolymer is 70:30; the antioxidant 1010 and the ultraviolet light absorber monobenzoic acid resorcinol ester are 1wt% of the total mass of polyvinylidene fluoride and ethylene-vinyl alcohol copolymer;

[0077] (2) The modified polyvinylidene fluoride particles obtained in step (1) are formed into a 25 μm film by a tape casting method.

[0078] Comparative Example 2:

[0079] Prepare polyvinylidene fluoride film as a comparative sample according to the following steps:

[0080] (1) Dry polyvinylidene fluoride particles, ethylene-vinyl alcohol copolymer particles, antioxidant 1010, and ultraviolet light absorber monobenzoic acid resorcinol ester are mixed uniformly in a high-speed mixer, and melt granulated in a twin-screw extruder. The mass ratio of polyvinylidene fluoride to ethylene-vinyl alcohol copolymer is 70:30; the antioxidant 1010 and ultraviolet light absorber monobenzoic acid resorcinol ester are 1wt% of the total mass of polyvinylidene fluoride and ethylene-vinyl alcohol copolymer;

[0081] (2) forming a 0.1 mm thick film by hot pressing the modified polyvinylidene fluoride particles obtained in step (1) using a flat plate vulcanizer;

[0082] (3) The modified polyvinylidene fluoride thick film obtained in step (2) is simultaneously biaxially stretched at 120° C. to prepare a biaxially oriented polyvinylidene fluoride film, with a stretching speed of 50 mm / s and a stretching ratio of 2.

[0083] The preparation of the solar cell backsheet of the embodiment and the comparative example is carried out according to the following steps:

[0084] The middle layer is a polyPET support layer, the outer layer is a PVDF film, the inner layer is a modified PVDF film prepared using the patent of the present invention or a comparative PVDF film, and the thickness of the PVDF film and PET bonded by an adhesive is (300±10μm).

[0085] The tensile properties of the PVDF films (thickness of about 25 μm) of the examples and comparative examples were tested in accordance with GBT1040-1992 standard at a tensile rate of 25 mm / min.

[0086] Adhesion with EVA: The test method is peel strength test. Use a knife to cut a 1cm wide strip between the back panel and the EVA, and make sure to cut through it. Use a tensile testing machine to pull the peeling layer in a 180° direction at a speed of 100mm / min. Take points when the material is peeled off at a uniform speed and take the minimum value. The peel strength between the EVA and the back panel is determined to be 40N / cm to be qualified.

[0087] Water vapor transmission rate test: According to GB / T 21529-2008 standard, the test was conducted using the W3 / 330 water vapor transmission rate test system. The test area was 108 mm x 108 mm, the test temperature was 40°C, the test humidity was 90%, and three samples were tested for each solar cell back panel to take the average value.

[0088] The test results of the film's tensile properties, the test results of the water vapor transmission rate of the solar cell back sheet, and the test results of the EVA adhesion are shown in Table 1:

[0089] Table 1

[0090]

[0091] It can be seen from the table that the modified PVDF film prepared in the example has good mechanical properties, the solar cell backsheet prepared from the modified PVDF film has good adhesion to the EVA film, and has good water vapor barrier properties.

[0092] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a modified PVDF film, characterized in that: The following steps are involved: S1: uniformly mixing dried polyvinylidene fluoride particles, ethylene-vinyl alcohol copolymer particles, a compatibilizer, an antioxidant and an ultraviolet light absorber in a high-speed mixer, and melt-granulating the mixture in a twin-screw extruder to obtain a modified polyvinylidene fluoride special material; S2: forming the modified polyvinylidene fluoride special material into a modified polyvinylidene fluoride thick film; S3 biaxially stretching the modified polyvinylidene fluoride thick film to obtain a modified PVDF film; The compatibilizer is a special material of polyvinylidene fluoride grafted glycidyl methacrylate or polyvinylidene fluoride grafted maleic anhydride, and its addition ratio is 5wt% to 10wt% of the polyvinylidene fluoride particles; The polyvinylidene fluoride thick film is formed by hot pressing film forming and tape casting on a flat vulcanizing machine, and the thickness of the thick film is not less than 0.05 mm; The biaxial stretching is synchronous biaxial stretching, the synchronous biaxial stretching temperature is 100-120° C., the stretching speed is 30-50 mm / s, and the stretching ratio is 1.5-4.

2. The method for preparing the modified PVDF film according to claim 1, characterized in that: The mass ratio of the polyvinylidene fluoride particles to the ethylene-vinyl alcohol copolymer particles is 9-7:1-3.

3. The method for preparing the modified PVDF film according to claim 1, characterized in that: Before S1, the steps to make the compatibilizer include: Putting dried polyvinylidene fluoride particles, glycidyl methacrylate, benzoyl peroxide, and 9-vinyl anthracene into a twin-screw extruder for melt reaction extrusion granulation to obtain the polyvinylidene fluoride grafted glyceryl methacrylate special material, wherein the addition ratio of benzoyl peroxide and 9-vinyl anthracene is 0.025% to 0.15% of the total mass of glycidyl methacrylate and polyvinylidene fluoride; the mass ratio of polyvinylidene fluoride to glycidyl methacrylate is 90 to 97:3 to 10; Alternatively, dried polyvinylidene fluoride particles, maleic anhydride, benzoyl peroxide, and 9-vinyl anthracene are melt-reacted and extruded in a twin-screw extruder to obtain the polyvinylidene fluoride grafted maleic anhydride special material, wherein the addition ratio of benzoyl peroxide and 9-vinyl anthracene is 0.025% to 0.15% of the total mass of maleic anhydride (MAH) and polyvinylidene fluoride; and the mass ratio of polyvinylidene fluoride to maleic anhydride is 90 to 97:3 to 10.

4. The method for preparing the modified PVDF film according to claim 1, characterized in that: The antioxidant is antioxidant 1010 or antioxidant 168, and the ultraviolet light absorber includes: 2-hydroxy-4-n-octyloxybenzophenone, 2-(2-hydroxy-5-benzyl)benzotriazole, and monobenzoic acid resorcinol ester.

5. The method for preparing the modified PVDF film according to claim 1 or 4, characterized in that: The ratio of the antioxidant to the ultraviolet light absorber is 1 wt% to 2 wt% of the total mass of the polyvinylidene fluoride particles and the ethylene-vinyl alcohol copolymer particles.

6. A modified PVDF film, characterized in that: The preparation method is described in any one of claims 1 to 5.

7. A solar cell back sheet, characterized in that: It comprises three layers, wherein the outer layer is a polyvinylidene fluoride film, the middle supporting layer is polyethylene terephthalate, and the inner layer is the modified PVDF film as claimed in claim 6.

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