A polyvinylidene fluoride greenhouse film and a preparation method thereof

Abstract

This invention belongs to the technical field of agricultural greenhouse film materials, specifically relating to a polyvinylidene fluoride (PVDF) greenhouse film and its preparation method. The resin raw material for film formation is a compound of copolymer PVDF resin I and copolymer PVDF resin II; wherein the copolymer PVDF resin I accounts for 10-30% by weight, and the copolymer PVDF resin II accounts for 70-90% by weight. The preparation of this PVDF greenhouse film involves compounding two different copolymer PVDF resins in a certain proportion as film-forming resin raw materials to obtain a single PVDF greenhouse film. The resulting greenhouse film is isotropic, with right-angle tear strength ≥250KN / m in both the MD and TD directions, significantly improving tear strength and processing performance, making it suitable for high-end facility agriculture.

Description

Technical Field

[0001] This invention belongs to the field of agricultural greenhouse film materials technology, specifically relating to a polyvinylidene fluoride greenhouse film and its preparation method. Background Technology

[0002] Existing greenhouse films are mainly made of polyolefins through extrusion blow molding. The mechanical properties, light transmittance, dustproof and other aging resistance of the films all decline rapidly with the increase of service life, generally less than 3 years. Even with integrated coating, multi-layer co-extrusion and grafting technologies, the longest service life is less than 5 years, leading to frequent replacement of greenhouse films.

[0003] Fluoropolymers, with their outstanding weather resistance, light transmittance, superhydrophobicity, and mechanical properties, have opened up new avenues for ultra-long-life greenhouse films. AGC Corporation of Japan pioneered the invention of fluoropolymer greenhouse films with a lifespan exceeding 15 years.

[0004] Patent CN111031786A discloses an agricultural fluoropolymer film made of ethylene-tetrafluoroethylene (ETFE) copolymer. Patent CN1715314A discloses a fluorinated copolymer film of ethylene-tetrafluoroethylene-hexafluoropropylene-fluoroalkyl vinyl ether tetroxide (ETFE), suitable for agricultural greenhouses and building covering films. However, ETFE resin is expensive and is prepared using cast film technology, with a width of less than 2.4 meters, which increases the cost of its installation in greenhouse coverings.

[0005] Polyvinylidene fluoride (PVDF) is widely used in solar backsheet films due to its outstanding weather resistance. However, its tendency to orient along the extrusion direction and its poor longitudinal tear resistance limit its application in greenhouse films. Arkema's patent CN102821595A discloses a multilayer fluorinated film containing at least three layers of PVDF film with different crystallinities, ranging from 1 to 7 meters in width. This significantly improves the film's UV stability and tear strength, making it suitable for large-scale greenhouse covering, extending its service life, and reducing production costs. However, the widest PVDF film prepared is 7 meters, and its tear resistance in the MD and TD directions is still insufficient, limiting its application in larger-scale greenhouse films. Summary of the Invention

[0006] The purpose of this invention is to provide a polyvinylidene fluoride greenhouse film and its preparation method, addressing the problems of insufficient tear resistance in the MD direction and insufficient blown film width of existing PVDF fluoropolymer films.

[0007] This invention uses two PVDF blends with different monomer ratios as film-forming raw materials to produce the same film. The resulting polyvinylidene fluoride greenhouse film is isotropic, and the right-angle tear strength in both the MD and TD directions is ≥250KN / m, which significantly improves the tear strength and processing performance.

[0008] The polyvinylidene fluoride greenhouse film has a width of over 10m, a lifespan of over 15 years, a light transmittance of ≥93%, a tensile breaking stress of ≥35MPa, and a tensile breaking strain of ≥300%, making it suitable for high-end facility agriculture.

[0009] The technical solution of the present invention is as follows: a polyvinylidene fluoride greenhouse film, wherein the resin raw material for film formation is composed of copolymer PVDF resin I and copolymer PVDF resin II; wherein the copolymer PVDF resin I accounts for 10-30% by weight and the copolymer PVDF resin II accounts for 70-90% by weight.

[0010] The copolymer PVDF resin I is composed of 89-95% vinylidene fluoride comonomer units, 4-7% hexafluoropropylene comonomer units, and 1-4% perfluoroalkyl vinyl ether comonomer units.

[0011] The copolymer PVDF resin II is composed of 83-86% vinylidene fluoride comonomer units, 10-13% hexafluoropropylene comonomer units, and 1-4% perfluoroalkyl vinyl ether comonomer units.

[0012] Furthermore, the melt index of the copolymer PVDF resin I is 5-20 g / 10 min (tested at 230°C and 5 kg); the melt index of the copolymer PVDF resin II is 2-10 g / 10 min (tested at 230°C and 5 kg).

[0013] Furthermore, the perfluoroalkyl vinyl ether comonomer is selected from at least one of perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and perfluoropropyl vinyl ether monomers.

[0014] The above-mentioned polyvinylidene fluoride greenhouse film has a width of 10-16m, a lifespan of ≥15 years, a light transmittance of ≥93%, a tensile breaking stress of ≥35MPa, a tensile breaking strain of ≥300%, and a right-angle tear resistance of ≥250KN / m in both the MD and TD directions.

[0015] The above-mentioned method for preparing polyvinylidene fluoride greenhouse film includes the following steps: (1) Prepare resin emulsion I or resin suspension I according to the composition of the copolymerized PVDF resin I.

[0016] Resin emulsion II or resin suspension II was prepared according to the composition of the copolymerized PVDF resin II described above.

[0017] The resin emulsion can be prepared using conventional emulsion polymerization technology, and the resin suspension can be prepared using conventional suspension polymerization technology.

[0018] (2) Weigh out resin emulsion I and resin emulsion II according to their respective weight ratios and mix them evenly to obtain a copolymer PVDF resin mixed emulsion.

[0019] Alternatively, resin suspension I and resin suspension II can be mixed evenly to obtain a copolymer PVDF resin mixed suspension.

[0020] (3) The copolymer PVDF resin mixture emulsion obtained in step (2) is coagulated, washed, dried and granulated; or the copolymer PVDF resin mixture suspension is washed, dried and granulated; to obtain copolymer PVDF resin mixture particles composed of copolymer PVDF resin I and copolymer PVDF resin II.

[0021] (4) The polyvinylidene fluoride greenhouse film is prepared by extruding and blowing the copolymer PVDF resin mixed particles obtained in step (3).

[0022] The blown film processing temperature is 170-250℃; the blow-up ratio is controlled at 2.0-3.5; and the traction speed is 5-10 m / min. The resulting film has better and more uniform longitudinal and transverse elongation and tear strength, avoiding the problems of low transverse elongation and poor tear performance.

[0023] In this invention, the blown film processing temperature is 190-230℃, more preferably 190-220℃.

[0024] The beneficial effects of the present invention are as follows: The film-forming resin raw material of the polyvinylidene fluoride greenhouse film of the present invention is composed of two different copolymer PVDF resins compounded in proportion. The PVDF greenhouse film made using the film-forming resin raw material is isotropic, and the right-angle tear strength in both the MD and TD directions is ≥250KN / m, which significantly improves the tear strength and improves the processing performance.

[0025] The obtained polyvinylidene fluoride greenhouse film has a width of over 10m and a lifespan of over 15 years; the light transmittance of the film is ≥93%, and the light transmittance remains basically unchanged with the change of film thickness; the tensile breaking stress is ≥35MPa, and the tensile breaking strain is ≥300%, making it suitable for high-end facility agriculture. Attached Figure Description

[0026] Figure 1 The spectrum of PVDF resin I described in Example 1 was obtained using FTIR testing.

[0027] Figure 2 The spectrum of PVDF resin II described in Example 1 is obtained by FTIR testing.

[0028] Figure 3These are wide-angle X-ray scattering test images of PVDF greenhouse films in Examples 1-4.

[0029] Figure 4 These are wide-angle X-ray scattering test images of PVDF greenhouse films, as shown in Comparative Examples 1-8. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments, but these embodiments do not limit the implementation of the present invention. All parts of each material in the following embodiments and comparative examples are expressed as weight percentages.

[0031] 1. The test methods for each performance index are shown in Table 1.

[0032] Table 1 Test Methods

[0033] 2. The specific preparation steps of the PVDF resin obtained by emulsion polymerization used in the examples and comparative examples are as follows: Polymerization: Deionized water was added to the reactor, along with a compound dispersant of sodium dodecyl sulfate / polyethylene glycol stearate. The reactor was evacuated to remove oxygen until the oxygen content was ≤20 ppm. The reactor was heated to 80±3℃, and the initial mixed monomers were introduced into the reactor until the reaction pressure reached 4.0±0.1 MPa. Potassium persulfate was added as the initial initiator to initiate the reaction. The initiator and mixed monomers were replenished to maintain a constant reactor pressure. Ethyl propionate, a molecular weight regulator, was added to the reactor. When the reaction weight reached the predetermined weight, the addition of initiator, monomers, and molecular weight regulator was stopped, and the reaction was halted, yielding a PVDF copolymer emulsion.

[0034] Post-processing: The post-processing steps for PVDF emulsion include coagulation, washing, drying, and granulation. The process parameters are as follows: Coagulation is carried out using a high-speed stirring mechanical demulsification method to demulsify the PVDF emulsion; after demulsification, plate and frame filter press-washing is performed, repeated 5 times, with the washing water temperature controlled at 70±2℃; after washing, airflow drying is used, with the inlet temperature set at 120℃ and the outlet temperature set at 80℃; the dried powder is granulated using a twin-screw granulator at a granulation temperature of 170-200℃.

[0035] 3. The specific steps for preparing the suspension polymerized PVDF resin used in the examples are as follows: Polymerization: Deionized water, polyvinyl alcohol as dispersant, ethyl acetate as molecular weight regulator, and disodium hydrogen phosphate as pH regulator are added to a reactor. The reactor is evacuated to remove oxygen until the oxygen content is ≤20 ppm. The reactor is heated to 80±3℃, and the initial mixed monomers are introduced into the reactor until the reaction pressure reaches 6.0±0.3 MPa. Diisopropyl peroxide (IPP) is added as the initial initiator to initiate the reaction. The initiator and mixed monomers are replenished to maintain a constant reactor pressure. When the reaction weight reaches the predetermined weight, the addition of initiator and monomers is stopped, and the reaction is stopped, yielding a PVDF copolymer suspension.

[0036] Post-processing: The post-processing steps for PVDF suspension include washing, drying, and granulation. The process parameters are as follows: the PVDF suspension is subjected to plate and frame filter press-washing, repeated 3 times, and the washing water temperature is controlled at 70±2℃. After washing, the powder is dried by airflow with an inlet temperature set at 120℃ and an outlet temperature set at 80℃. The dried powder is then granulated using a twin-screw granulator at a granulation temperature of 170-200℃.

[0037] Example 1 The polyvinylidene fluoride greenhouse film is formed by a resin raw material composed of copolymer PVDF resin I and copolymer PVDF resin II.

[0038] The copolymer PVDF resin I accounts for 10% by weight, and the copolymer PVDF resin II accounts for 90% by weight.

[0039] The copolymerized PVDF resin I is composed of 95% vinylidene fluoride comonomer units, 4% hexafluoropropylene comonomer units, and 1% perfluoropropyl vinyl ether comonomer units. The melt flow index is 5.5 g / 10 min (tested at 230°C and 5 kg).

[0040] The copolymerized PVDF resin II is composed of 86% vinylidene fluoride monomer units, 11% hexafluoropropylene comonomer units, and 3% perfluoropropyl vinyl ether comonomer units. Its melt flow index is 2.5 g / 10 min (tested at 230°C and 5 kg).

[0041] The specific steps for preparing the polyvinylidene fluoride greenhouse film are as follows: (1) Resin emulsion I and resin emulsion II were prepared according to the respective compositions of the copolymer PVDF resin I and copolymer PVDF resin II.

[0042] (2) Weigh out resin emulsion I and resin emulsion II according to their respective weight ratios and mix them evenly to obtain a copolymer PVDF resin mixed emulsion.

[0043] (3) The copolymer PVDF resin emulsion obtained in step (2) is coagulated, washed, dried and granulated to obtain copolymer PVDF resin mixed particles composed of copolymer PVDF resin I and copolymer PVDF resin II.

[0044] (4) The polyvinylidene fluoride greenhouse film is prepared by extruding and blowing the copolymer PVDF resin mixed particles obtained in step (3).

[0045] The specific temperatures for blown film processing are as follows: 180℃ for zone 1 of the extruder, 190℃ for zone 2 of the extruder, 200℃ for zone 3 of the extruder, 210℃ for zone 4 of the extruder, 210℃ for the connector, and 220℃ for the die head.

[0046] The inflation ratio is controlled at 2.5, and the traction speed is 8 m / min.

[0047] The final product is a PVDF greenhouse film with a width of 12m and a thickness of 100μm. After 4500 hours of UV aging, the tensile breaking stress remains at 67%, meeting the requirement of a lifespan of over 15 years.

[0048] Example 2 The difference from Example 1 is that the copolymer PVDF resin I accounts for 30% by weight and the copolymer PVDF resin II accounts for 70% by weight.

[0049] The others are the same as in Example 1.

[0050] The final product is a PVDF greenhouse film with a width of 12m and a thickness of 100μm. After 4500 hours of UV aging, the tensile breaking stress remains at 72%, meeting the requirement of a lifespan of over 15 years.

[0051] Example 3 The difference from Example 1 is that the copolymer PVDF resin I accounts for 15% by weight and the copolymer PVDF resin II accounts for 85% by weight.

[0052] The copolymerized PVDF resin I is composed of 89% vinylidene fluoride comonomer units, 7% hexafluoropropylene comonomer units, and 4% perfluoromethyl vinyl ether comonomer units. The melt flow index is 18.0 g / 10 min (tested at 230°C and 5 kg).

[0053] The copolymerized PVDF resin II is composed of 83% vinylidene fluoride monomer units, 13% hexafluoropropylene comonomer units, and 4% perfluoromethyl vinyl ether comonomer units. The melt flow index is 8.5 g / 10 min (tested at 230°C and 5 kg).

[0054] The others are the same as in Example 1.

[0055] The final product is a PVDF greenhouse film with a width of 12m and a thickness of 100μm. After 4500 hours of UV aging, the tensile breaking stress remains at 70%, meeting the requirement of a lifespan of over 15 years.

[0056] Example 4 Unlike Example 1, the copolymer PVDF resin I accounts for 20% by weight and the copolymer PVDF resin II accounts for 80% by weight.

[0057] The copolymerized PVDF resin I is composed of 92% vinylidene fluoride comonomer units, 6% hexafluoropropylene comonomer units, and 2% perfluoropropyl vinyl ether comonomer units. Its melt flow index is 13.5 g / 10 min (tested at 230°C and 5 kg).

[0058] The copolymerized PVDF resin II is composed of 85% vinylidene fluoride monomer units, 13% hexafluoropropylene comonomer units, and 2% perfluoropropyl vinyl ether comonomer units. Its melt flow index is 7.5 g / 10 min (tested at 230°C and 5 kg).

[0059] The copolymerized PVDF is produced by suspension polymerization, resulting in a suspension, and the post-processing does not involve agglomeration.

[0060] The others are the same as in Example 1.

[0061] The final product is a PVDF greenhouse film with a width of 12m and a thickness of 100μm. After 4500 hours of UV aging, the tensile breaking stress remains at 70%, meeting the requirement of a lifespan of over 15 years.

[0062] Comparative Example 1 The difference from Example 2 is that the copolymerized PVDF resin I is composed of 97% vinylidene fluoride comonomer units, 2% hexafluoropropylene comonomer units, and 1% perfluoropropyl vinyl ether comonomer units. The melt index is 5.5 g / 10 min (tested at 230°C and 5 kg).

[0063] The others are the same as in Example 2.

[0064] Comparative Example 2 The difference from Example 1 is that the copolymer PVDF resin I accounts for 40% by weight and the copolymer PVDF resin II accounts for 60% by weight.

[0065] The others are the same as in Example 1.

[0066] Comparative Example 3 The difference from Example 1 is that the polyvinylidene fluoride greenhouse film is formed using only copolymerized PVDF resin I as the resin raw material.

[0067] The others are the same as in Example 1.

[0068] Comparative Example 4 The difference from Example 1 is that the polyvinylidene fluoride greenhouse film is formed by using only copolymerized PVDF resin II as the resin raw material.

[0069] The others are the same as in Example 1.

[0070] Comparative Example 5 The difference from Example 2 is that the PVDF copolymer resin II used in this comparative example has a composition of 83% vinylidene fluoride comonomer units and 17% hexafluoropropylene comonomer units. The melt index is 8.5 g / 10 min (tested at 230°C and 5 kg).

[0071] The others are the same as in Example 2.

[0072] Comparative Example 6 The difference from Example 2 is that the PVDF copolymer used in this comparative example has a composition of 89% vinylidene fluoride comonomer units, 7% hexafluoropropylene comonomer units, and 4% perfluoropropyl vinyl ether comonomer units. The melt index is 18.0 g / 10 min (tested at 230°C and 5 kg).

[0073] The others are the same as in Example 2.

[0074] Comparative Example 7 The difference from Example 1 is that in the preparation method of the polyvinylidene fluoride greenhouse film, step (4) controls the blow-up ratio to be 4.0.

[0075] The others are the same as in Example 1.

[0076] Comparative Example 8 The difference from Example 1 is that in the preparation method of the polyvinylidene fluoride greenhouse film, the traction speed in step (4) is 12 m / min.

[0077] The others are the same as in Example 1.

[0078] The performance of the greenhouse films obtained in each embodiment and comparative example is shown in Table 2.

[0079] Table 2. Membrane performance indicators

[0080] Experimental Example 1 I. Experimental Objective: To characterize the structure of PVDF resin I and PVDF resin II.

[0081] II. Experimental Methods: FTIR was used to test PVDF resin I and PVDF resin II described in Example 1, and the resulting spectra are shown below. Figure 1 (PVDF resin I) and Figure 2 (PVDF resin II).

[0082] Experimental Example 2 I. Experimental Objective: To determine the performance of PVDF greenhouse films of different thicknesses.

[0083] II. Experimental Methods: Using the film-forming resin raw material formulation described in Example 1, PVDF films with thicknesses of 80μm, 100μm, 120μm, and 150μm were prepared according to the preparation method described therein.

[0084] III. Performance is as follows:

[0085] It is evident that PVDF films of different thicknesses exhibit similar performance.

[0086] Experimental Example 3 I. Experimental Objective: To test the orientation degree of PVDF greenhouse film.

[0087] II. Experimental Methods: Wide-angle X-ray scattering (WAXS) was used to test the orientation degree of PVDF film to determine whether the film is anisotropic in the MD and TD directions.

[0088] III. Experimental Results: Figure 3 From the 2D images, the greenhouse film results obtained by this invention are all unoriented and are isotropic.

[0089] Depend on Figure 4 From the 2D images, the greenhouse films obtained in Comparative Examples 3, 4, 6, 7, and 8 clearly show orientation, indicating anisotropy.

Claims

1. A polyvinylidene fluoride greenhouse film characterized by, The resin raw material for forming the greenhouse film is composed of copolymer PVDF resin I and copolymer PVDF resin II; wherein, the copolymer PVDF resin I accounts for 10-30% by weight and the copolymer PVDF resin II accounts for 70-90% by weight. The composition of the copolymer PVDF resin I is 89-95% vinylidene fluoride comonomer units, 4-7% hexafluoropropylene comonomer units and 1-4% perfluoroalkyl vinyl ether comonomer units. The copolymer PVDF resin II is composed of 83-86% vinylidene fluoride comonomer units, 10-13% hexafluoropropylene comonomer units, and 1-4% perfluoroalkyl vinyl ether comonomer units.

2. The polyvinylidene fluoride greenhouse film according to claim 1, characterized in that, The melt flow index of the copolymerized PVDF resin I was tested at 230℃ and 5kg and was 5-20g / 10min.

3. The polyvinylidene fluoride greenhouse film according to claim 1, characterized in that, The melt flow index of the copolymerized PVDF resin II was tested at 230℃ and 5kg and was 2-10g / 10min.

4. The polyvinylidene fluoride greenhouse film according to claim 1, characterized in that, The perfluoroalkyl vinyl ether comonomer is selected from at least one of perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and perfluoropropyl vinyl ether monomers.

5. The polyvinylidene fluoride greenhouse film according to any one of claims 1 to 4, characterized in that, The width of the greenhouse film is 10-16m, the lifespan of the greenhouse film is ≥15 years, the light transmittance is ≥93%, the tensile breaking stress is ≥35MPa, the tensile breaking strain is ≥300%, and the right-angle tear resistance in both the MD and TD directions is ≥250KN / m.

6. A method of producing a polyvinylidene fluoride greenhouse film as claimed in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Prepare resin emulsion I or resin suspension I according to the composition of the copolymerized PVDF resin I described above; Resin emulsion II or resin suspension II were prepared according to the composition of the copolymer PVDF resin II described above. (2) Weigh out resin emulsion I and resin emulsion II according to their respective weight ratios and mix them evenly to obtain a copolymer PVDF resin mixed emulsion. Alternatively, resin suspension I and resin suspension II can be mixed evenly to obtain a copolymer PVDF resin mixed suspension; (3) The copolymerized PVDF resin emulsion obtained in step (2) is coagulated, washed, dried and granulated; Alternatively, the copolymerized PVDF resin mixture suspension may be washed, dried, and granulated. A copolymer PVDF resin mixture granule composed of copolymer PVDF resin I and copolymer PVDF resin II was prepared. (4) The polyvinylidene fluoride greenhouse film is prepared by extruding and blowing the copolymer PVDF resin mixed particles obtained in step (3).

7. The method for preparing polyvinylidene fluoride greenhouse film according to claim 6, characterized in that, In step (4), the blown film processing temperature is 170-250℃; the blow-up ratio is controlled at 2.0-3.5, and the traction speed is 5-10m / min.

8. The method for preparing polyvinylidene fluoride greenhouse film according to claim 7, characterized in that, The processing temperature of blown film in step (4) is 190-230℃.

9. The method for preparing polyvinylidene fluoride greenhouse film according to claim 8, characterized in that, The processing temperature of blown film in step (4) is 190-220℃.

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