Preparation method and application of polyvinylidene fluoride film capable of improving dripping performance

Abstract

The invention discloses a preparation method of a polyvinylidene fluoride film capable of improving dripping performance, which comprises the following steps: (1) under the action of an initiator, carrying out copolymerization reaction on a fluorine-containing compound monomer and a vinylidene fluoride monomer to obtain a vinylidene fluoride copolymer; the fluorine-containing compound monomers are at least two of hexafluoropropylene, 3, 3, 3-trifluoropropene, trifluoroethylene, chlorotrifluoroethylene, fluorinated ethylene and perfluoroalkyl vinyl ether, and the fluorine-containing compound monomers are at least two of hexafluoropropylene, 3, 3, 3-trifluoropropylene, trifluoroethylene, chlorotrifluoroethylene, fluorinated ethylene and perfluoroalkyl vinyl ether; and (2) preparing the polyvinylidene fluoride copolymer into the polyvinylidene fluoride film through a co-extrusion tape casting method or a co-extrusion blow molding method. According to the preparation method, the fluorine-containing compound monomer and the vinylidene fluoride monomer are subjected to a copolymerization reaction, the anti-aging performance of the fluorine-containing compound monomer is fully utilized so as to achieve the purpose of long-term outdoor use, and meanwhile, the embossing treatment and surface treatment procedures in the preparation method are combined, so that the dripping performance of the polyvinylidene fluoride film is improved.

Description

Technical Field

[0001] This invention relates to the field of fluoropolymer technology, specifically to a method for preparing and applying a polyvinylidene fluoride film with improved dripping properties. Background Technology

[0002] Agricultural film refers to the general term for plastic films used in agricultural production. It can be used to cover farmland, increase soil temperature, maintain soil moisture, promote seed germination and rapid seedling growth, and suppress weed growth. It has a significant effect on improving the growing environment of crops. It mainly includes greenhouse film and mulch film. Greenhouse film is mainly used for covering greenhouses to increase the temperature and humidity of the crop growing environment; mulch film is mainly used for covering farmland to suppress weed growth and increase soil temperature.

[0003] Polyvinylidene fluoride (PVDF) has shown great potential in the field of high-end agricultural films due to its excellent weather resistance, mechanical strength, and chemical stability. The high bond energy and low surface energy of the CF bonds in the PVDF molecular chain result in extremely low surface tension and strong hydrophobicity. However, its inherent strong hydrophobicity leads to poor "dripping properties," which has become a major technical bottleneck for its application in agricultural greenhouse films.

[0004] To improve the anti-dripping properties of PVDF films, two main technical approaches are physical blending and surface modification. Physical blending modification is currently the most mainstream and easily industrialized method, the core of which is to directly mix hydrophilic polymers or functional additives into the PVDF resin. Chinese patent document CN106147088A discloses a high-performance anti-dripping and anti-fogging PVDF composite greenhouse film containing the following components by mass percentage: 55%~80% PVDF resin, 19%~40% PMMA resin, 0.5%~2% light scattering agent, 0.5%~1.5% anti-fogging agent, and the balance being anti-dripping agent. The introduction of PMMA improves the overall hydrophilicity of the blend, and the anti-dripping agent migrates to the film surface, reducing the contact angle between water droplets and the film surface and promoting water droplet spreading.

[0005] Patent document CN209314405U discloses an agricultural film with polyvinylidene fluoride as the base material, with polyvinylidene fluoride as the intermediate base layer and polyethylene as the upper and lower surface films; the intermediate base layer, the upper surface film and the lower surface film are bonded together with polyurethane adhesive, and the initial drip time of the agricultural film is 300 s.

[0006] In summary, existing technologies have effectively endowed PVDF films with basic anti-dripping properties through blending hydrophilic resins and anti-dripping agents. However, further improving the anti-dripping performance of the films remains a key challenge in actual production. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a method for preparing polyvinylidene fluoride (PVDF) films with improved drip-proofing properties. This method involves copolymerizing fluorinated monomers with PVDF monomers, fully utilizing the anti-aging properties of the fluorinated monomers, and combining this with embossing and surface treatment processes in the preparation method to enhance the drip-proofing properties of the PVDF film.

[0008] A method for preparing a polyvinylidene fluoride film with improved anti-dripping properties includes the following steps: (1) Under the action of an initiator, a fluorinated compound monomer is copolymerized with vinylidene fluoride monomer (VDF) to obtain a vinylidene fluoride copolymer; wherein the fluorinated compound monomer is at least two of hexafluoropropylene (HFP), 3,3,3-trifluoropropylene (TFP), trifluoroethylene, trifluorochloroethylene (CTFE), fluorinated ethylene, and perfluoroalkyl vinyl ether; (2) Polyvinylidene fluoride (PVDF) film is prepared by co-extrusion casting or co-extrusion blow molding of vinylidene fluoride copolymer.

[0009] In response to the poor anti-drip properties of general agricultural films on the market, which require frequent repairs, and the drawbacks of ordinary polyvinylidene fluoride (PVDF) films being susceptible to abrasion and short-term failure, and considering the limitations of single PVDF monomer polymerization, this invention utilizes a copolymerization reaction between fluorinated monomers and PVDF monomers. This fully leverages the anti-aging properties of the fluorinated monomers to achieve long-term outdoor use. Simultaneously, it addresses the issues of reduced surface treatment efficiency due to crystallization and shrinkage after homopolymerization of PVDF films, which affects subsequent anti-drip coating processing efficiency, deformation of PVDF materials after anti-drip coating, and poor adhesion between the fluorinated film surface and the anti-drip agent due to the high rigidity of PVDF films, thus improving the anti-drip properties of PVDF films.

[0010] Preferably, in step (1), the mass ratio of the fluorinated compound monomer to the vinylidene fluoride monomer is 1:15~50.

[0011] Preferably, in step (1), the fluorinated compound monomer is hexafluoropropylene and 3,3,3-trifluoropropylene.

[0012] In this invention, the main purpose of using HFP monomer is to improve low-temperature flexibility, reduce the difference in elongation at break between the transverse and longitudinal directions of the polyvinylidene fluoride film, improve impact resistance and tear resistance, and reduce the resilience of the copolymer. The purpose of using TFP monomer is to improve light transmittance, increase melting point, and increase surface hardness of the copolymer. The selection of the above monomers, combined with the embossing and surface treatment in the subsequent co-extrusion casting or co-extrusion blow molding process, can effectively improve the retention effect of the dripping agent on the surface of the finished film, extend the service life, reduce the cost of later maintenance and repair, and achieve the effect of long-term use.

[0013] More preferably, the mass ratio of hexafluoropropylene to 3,3,3-trifluoropropylene is 1~2:1~2.

[0014] Preferably, in step (1), the initiator is a peroxide, peroxydicarbonate, peroxydicarbonate, or azo compound; wherein, the inorganic peroxide can be a persulfate, such as sodium persulfate, potassium persulfate, or ammonium persulfate; the organic peroxide can be an alkyl peroxide, a dialkyl peroxide, a diacyl peroxide, a peroxydicarbonate, or a peroxy ester, or a mixture thereof; the peroxy ester initiator is tert-amyl peroxypentanoate, tert-butyl peroxypentanoate, or succinate peroxide; the initiator of the azo compound can be an azo initiator, such as 2,2'-azobis(2-methylpropanediamine) dihydrochloride.

[0015] More preferably, the amount of the initiator added is 0.01 to 10 wt% of the total mass of the fluorinated compound monomer and the vinylidene fluoride monomer.

[0016] More preferably, the amount of the initiator added is 0.05 to 10 wt% of the total mass of the fluorinated compound monomer and the vinylidene fluoride monomer.

[0017] Preferably, in step (1), the temperature of the copolymerization reaction is 30~70 ℃ and the pressure is 2~6 MPa.

[0018] Preferably, in step (1), the viscosity of the vinylidene fluoride copolymer is ≥1500 Pa·s.

[0019] More preferably, the viscosity of the vinylidene fluoride copolymer is ≥1700 Pa·s.

[0020] More preferably, the viscosity of the vinylidene fluoride copolymer is 1700~2500 Pa·s. Preferably, in step (2), the co-extrusion casting method includes the following steps: granulation → single-layer or multi-layer extrusion → casting → cooling and shaping and embossing → thickness measurement → online surface treatment → online dripping anti-fogging agent coating → drying → winding; The co-extrusion blow molding method includes the following steps: granulation → single-layer or multi-layer extrusion → blow molding → cooling and shaping → thickness measurement → traction → preheating → embossing → online surface treatment → online anti-fogging agent coating → drying → winding. In the single-layer or multi-layer extrusion process, the die head temperature is 200~250 ℃; the metering section temperature is 200~245 ℃; the compression section temperature is 190~235 ℃; and the feeding section temperature is 170~200 ℃.

[0021] More preferably, the temperature of the die head is 210~250 ℃; the temperature of the metering section is 210~245 ℃; the temperature of the compression section is 200~235 ℃; and the temperature of the feeding section is 185~200 ℃.

[0022] More preferably, the temperature of the die head is 225~250 ℃; the temperature of the metering section is 230~245 ℃; the temperature of the compression section is 210~230 ℃; and the temperature of the feeding section is 195~200 ℃.

[0023] More preferably, in the single-layer or multi-layer extrusion process, the screw diameter is 100 mm and the length-to-diameter ratio is 35~44.

[0024] More preferably, in the casting process, the casting stretch ratio is 2 to 2.5.

[0025] More preferably, in the blow molding process, the blow-up ratio of the blown film is 2 to 5.

[0026] More preferably, in the co-extrusion casting method or co-extrusion blow molding method, the embossing depth of the embossing process is 5~100 μm.

[0027] More preferably, in the co-extrusion casting method or co-extrusion blow molding method, corona treatment is used in the online surface treatment process. Generally, in the co-extrusion casting method, corona or plasma surface treatment is performed on the film immediately after the embossing and thickness measurement processes are completed on the main forming roller; for the co-extrusion blow molding method, corona or plasma surface treatment is performed on the film immediately after the online heating embossing process is completed after the film weight measurement process.

[0028] In this invention, an embossing process is added to both the co-extrusion casting method and the co-extrusion blow molding method. The purpose is to provide a suitable storage space for the anti-drip agent (generally using commercially available ELECT AG-150 or ELECT AG-189 from Takemoto Oils Co., Ltd.), reduce the chance and amount of wear on the anti-drip layer caused by hard objects, so as to work in conjunction with the surface corona treatment. This helps to reduce wear and reduce the amount of anti-drip agent used. At the same time, it can also form a firmly bonded anti-drip layer on the surface of the polyvinylidene fluoride film, and together with the anti-drip agent's own function of adsorbing vapor to fill the porous gaps of the inorganic adhesive, it can extend the anti-drip and anti-fogging function.

[0029] The present invention also provides a polyvinylidene fluoride film prepared by the above preparation method.

[0030] Preferably, the thickness of the polyvinylidene fluoride film is 80~150 μm.

[0031] Preferably, the initial dripping time of the polyvinylidene fluoride film is ≤350 s, and the dripping failure time is ≥50 days.

[0032] The present invention also provides the application of the above-mentioned polyvinylidene fluoride film in the preparation of agricultural films.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes the anti-aging properties of fluorinated monomers through copolymerization with vinylidene fluoride monomers to achieve long-term outdoor use. At the same time, the embossing and surface treatment processes in the preparation method improve the anti-dripping properties of the polyvinylidene fluoride film. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited to the following embodiments.

[0035] All raw materials used in this invention are commercially available.

[0036] Example 1 (1) Add 6.4 kg of deionized water and 0.209 g of sodium 10-oxoundecyl sulfate (surfactant) to a 10-liter stainless steel reactor. Purge the mixture with nitrogen and stir for 30 minutes. Heat the reactor to 65 °C. Add 0.376 kg of vinylidene fluoride, 0.012 kg of hexafluoropropylene, and 0.012 kg of 3,3,3-trifluoropropylene to the reactor (wherein the mass ratio of vinylidene fluoride / hexafluoropropylene / 3,3,3-trifluoropropylene is 94 / 3 / 3). The reaction conditions were stabilized at 65 °C and 4 MPa. Then, 0.026 kg of ammonium persulfate initiator was added to initiate the polymerization reaction. Subsequently, a mixture of vinylidene fluoride / hexafluoropropylene / 3,3,3-trifluoropropylene in a 94 / 3 / 3 ratio was continuously added to maintain the pressure, with a replenishment amount of 0.4 kg (containing 0.376 kg of vinylidene fluoride, 0.012 kg of hexafluoropropylene, and 0.012 kg of 3,3,3-trifluoropropylene). After 6 hours, all feed was stopped and the reactor was cooled. The reaction was cooled to room temperature, and residual gases were vented. Stirring was stopped, the reactor was further cooled, and the generated polymer was removed, washed with deionized water, and dried to obtain 0.363 kg of vinylidene fluoride copolymer A. The melt viscosity was measured using ASTM D4440 at 230 °C and 100 s⁻¹. -1 Rheological measurements were performed, and the viscosity of vinylidene fluoride copolymer A was 1935 Pa·s.

[0037] (2) After pre-drying 10,000 g of vinylidene fluoride copolymer A from step (1), it was extruded and granulated in a twin-screw extruder at 185 ℃ and added to a single-screw extruder. The temperatures of the three sections of the single-screw extruder were controlled as follows: metering section temperature 235 ℃; compression section temperature 225 ℃; feeding section temperature 195 ℃; die head temperature 250 ℃; long-life filter connection area temperature 235 ℃; die head temperature 225 ℃; forming cooling roller temperature 65 ℃; embossing depth 35~40 μm; screw speed adjusted to 50 rpm; traction rate 28.0 m / min; corona surface treatment power 3 kW; film surface energy adjusted to 50 mN / m. Then it immediately passed through a coating tank. The anti-dripping agent in the tank was ELECUTT AG-189 from Takemoto Oils Co., Ltd., diluted to 1 wt% with deionized water. It was then passed through an electric heating oven, where the temperatures of the three zones were 50 ℃, 65 ℃, 75 ℃, 85 ℃, 95 ℃, 1 ... After drying at 70 ℃ and 90 ℃, the film surface can be wound up to obtain a 100 μm thick polyvinylidene fluoride film.

[0038] Example 2 The preparation method is the same as in Example 1, except that in step (1), the mass ratio of vinylidene fluoride: hexafluoropropylene: 3,3,3-trifluoropropylene is 94:2:4, and the viscosity of the obtained vinylidene fluoride copolymer is 2000 Pa·s.

[0039] Example 3 The preparation method is the same as in Example 1, except that in step (1), the mass ratio of vinylidene fluoride: hexafluoropropylene: 3,3,3-trifluoropropylene is 94:4:2, and the viscosity of the obtained vinylidene fluoride copolymer is 1900 Pa·s.

[0040] Example 4 The preparation method is the same as in Example 1, except that in step (1), the mass ratio of vinylidene fluoride:hexafluoropropylene:3,3,3-trifluoropropylene is 98:1:1, and the viscosity of the obtained vinylidene fluoride copolymer is 2100 Pa·s.

[0041] Example 5 The preparation method is the same as in Example 1, except that in step (1), the mass ratio of vinylidene fluoride: hexafluoropropylene: 3,3,3-trifluoropropylene is 96:2:2, and the viscosity of the obtained vinylidene fluoride copolymer is 1890 Pa·s.

[0042] Comparative Example 1 The preparation method is the same as in Example 1, except that no fluorinated monomer is added in step (1) to prepare vinylidene fluoride homopolymer, and the viscosity of the obtained vinylidene fluoride homopolymer is 2100 Pa·s.

[0043] Performance testing Test method for dripping performance: Refer to GB / T 4455-2019 Polyethylene blown greenhouse film for agricultural use.

[0044] Table 1: Results of dripping performance test of polyvinylidene fluoride films in Examples 1-5 The above examples demonstrate that the addition of more non-VDF monomers can accelerate the initial dripping time, which helps agricultural films to quickly eliminate fog. Hexafluoropropylene has a weaker promoting effect on initial dripping time than 3,3,3-trifluoropropylene. It is generally believed that hexafluoropropylene is superior to 3,3,3-trifluoropropylene in lowering the polymer melting point. This leads to greater deformation of fluoropolymer films containing more hexafluoropropylene during molding and processing, resulting in a delayed initial dripping time. However, hexafluoropropylene is superior to 3,3,3-trifluoropropylene in terms of drip failure time. It can be considered that greater film deformation helps prolong the accumulation of the dripping agent, indirectly improving the dripping effect. Generally, the initial dripping time of commonly used agricultural films is within 420 seconds, and the dripping failure time is more than 8 days to be considered qualified. The agricultural film of this application is far superior to ordinary commercially available agricultural films in these two indicators.

[0045] The above description is merely 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 foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a polyvinylidene fluoride film with improved anti-dripping properties, characterized in that, Includes the following steps: (1) Under the action of an initiator, a fluorinated compound monomer and a vinylidene fluoride monomer are copolymerized to obtain a vinylidene fluoride copolymer; wherein the fluorinated compound monomer is at least two of hexafluoropropylene, 3,3,3-trifluoropropylene, trifluoroethylene, trifluorochloroethylene, fluorinated ethylene, and perfluoroalkyl vinyl ether. (2) Polyvinylidene fluoride film is prepared by co-extrusion casting or co-extrusion blow molding of vinylidene fluoride copolymer.

2. The method for preparing polyvinylidene fluoride film with improved anti-dripping properties according to claim 1, characterized in that, In step (1), the mass ratio of the fluorinated compound monomer to the vinylidene fluoride monomer is 1:15~50.

3. The method for preparing polyvinylidene fluoride film with improved anti-dripping properties according to claim 1, characterized in that, In step (1), the fluorinated monomers are hexafluoropropylene and 3,3,3-trifluoropropylene.

4. The method for preparing polyvinylidene fluoride film with improved anti-dripping properties according to claim 3, characterized in that, The mass ratio of hexafluoropropylene to 3,3,3-trifluoropropylene is 1~2:1~2.

5. The method for preparing polyvinylidene fluoride film with improved anti-dripping properties according to claim 1, characterized in that, In step (1), the viscosity of the vinylidene fluoride copolymer is ≥1500 Pa·s.

6. The method for preparing polyvinylidene fluoride film with improved anti-drip properties according to claim 1, characterized in that, In step (1), the temperature of the copolymerization reaction is 30~70 ℃ and the pressure is 2~6 MPa.

7. The method for preparing polyvinylidene fluoride film with improved anti-dripping properties according to claim 1, characterized in that, In step (2), the co-extrusion casting method includes the following steps: granulation → single-layer or multi-layer extrusion → casting → cooling and shaping and embossing → thickness measurement → online surface treatment → online anti-fogging agent coating → drying → winding; The co-extrusion blow molding method includes the following steps: granulation → single-layer or multi-layer extrusion → blow molding → cooling and shaping → thickness measurement → traction → preheating → embossing → online surface treatment → online anti-fogging agent coating → drying → winding. In the single-layer or multi-layer extrusion process, the die head temperature is 200~250 ℃; the metering section temperature is 200~245 ℃; the compression section temperature is 190~235 ℃; and the feeding section temperature is 170~200 ℃.

8. The method for preparing polyvinylidene fluoride film with improved anti-dripping properties according to claim 1, characterized in that, In step (2), the embossing depth of the embossing process in the co-extrusion casting method or co-extrusion blow molding method is 5~100 μm.

9. A polyvinylidene fluoride film prepared by any one of the preparation methods according to claims 1 to 8.

10. The polyvinylidene fluoride film according to claim 9, characterized in that, The initial dripping time of the polyvinylidene fluoride film is ≤350 s, and the dripping failure time is ≥50 days.

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