Polyvinylidene fluoride membrane and preparation method thereof

Abstract

The invention provides a polyvinylidene fluoride membrane and a preparation method thereof. The preparation method comprises the following steps: injecting a polyvinylidene fluoride solution into the surface of a coagulating bath solution through a guide plate with an inclination angle, and curing to form the polyvinylidene fluoride membrane. According to the method, the contact angle of the guide plate, the concentration of the polymer solution, the inclination angle of the guide plate and the width of the liquid storage tank are accurately regulated and controlled, so that spreading instability caused by surface tension is effectively inhibited, and the overall quality of the polyvinylidene fluoride film is further improved; meanwhile, the width of the polyvinylidene fluoride film is controllable, and the requirements of different application scenes can be met. The method for preparing the polyvinylidene fluoride membrane is simple, convenient and low in energy consumption, a high-temperature or low-temperature heat treatment process is not needed, the energy consumption is greatly reduced, and the production efficiency is improved. And the polyvinylidene fluoride film prepared by the method has excellent film forming quality, almost no obvious wrinkled edge exists, and the thickness and the structure of the film show high uniformity.

Description

Technical Field

[0001] The present invention relates to the technical field of high molecular polymer film preparation, in particular to a polyvinylidene fluoride film and a preparation method thereof. Background Art

[0002] Porous polymer membranes offer many advantages, such as being lighter, having a larger surface area, providing sound and heat insulation, allowing materials to pass through faster, and separating materials more efficiently. These advantages make them useful in a wide range of applications, including water purification, industrial separations, energy storage, electronics, and healthcare.

[0003] There are several ways to make this porous plastic film, the three most common ones are:

[0004] 1. Phase separation: This method involves dissolving the polymer in a suitable solvent. A nonsolvent, miscible with the solvent but insoluble in the polymer, is then used to extract the solvent, causing phase separation in the polymer system. During this process, as the nonsolvent is added, the originally homogeneous solution begins to separate into polymer-rich and polymer-poor fractions. As the system solidifies, the polymer-rich fraction forms the basic skeleton of the membrane, while the polymer-poor fraction develops into the pore structure.

[0005] 2. Template method: This method involves mixing a template with predetermined geometric features with a polymer and removing the template after molding to obtain a porous membrane with precise pore size and porosity.

[0006] 3. Melt extrusion / stretching method: First, the polymer is heated to a molten state and extruded through a die to form a primary membrane, and then a continuous or discontinuous pore structure is induced by mechanical stretching operation.

[0007] Although the technology for preparing porous polymer membranes is relatively mature, there is still room for improvement in terms of environmental friendliness, cost-effectiveness and process simplicity. For example, the main problem faced by the phase separation method is the use of a large amount of volatile organic solvents, which not only increases production costs but also causes environmental pollution. In addition, the solvent recovery and treatment process is complicated, which may increase the overall production cost. The main challenge of the template method lies in the selection and removal steps of the template, which often leads to extended production cycles and increased product costs; at the same time, it is difficult to ensure the consistency of all pores. Although the melt extrusion / stretching method is suitable for industrial production, its high energy consumption characteristics cannot be ignored; in addition, in order to achieve a good pore structure, the requirements for processing equipment, processing conditions, etc. are extremely high, which further increases the manufacturing cost.

[0008] In response to the problems of high energy consumption, high cost, difficulty in adjusting the membrane width, and uneven membrane structure in the preparation process of porous polymer membranes, the invention patent (ZL 202310514941.6) proposes a technical solution for self-driven membrane formation on the surface of the coagulation bath. However, in this technology, the parameters of polymer membrane formation, including the properties of the polymer solution, the composition of the coagulation bath, and the control of the injection of the polymer solution into the coagulation bath surface, are too harsh, the quality of the membrane fluctuates greatly, the membrane edge is prone to wrinkles, the width of the membrane is difficult to control, and large-scale continuous production is difficult. Therefore, achieving the adjustability of the membrane width, ensuring the uniformity of the membrane structure, and avoiding the waste caused by wrinkles on the membrane edge during the preparation process are the main challenges facing the current porous polymer membrane preparation technology. Summary of the Invention

[0009] In view of this, the present invention proposes a polyvinylidene fluoride (PVDF) membrane and a preparation method thereof to solve the problem that the existing liquid surface film forming technology causes the PVDF membrane to produce wrinkles and need to be cut, resulting in a large amount of waste, while ensuring the adjustability of the membrane width and the uniformity of the film forming structure.

[0010] In a first aspect, the present invention provides a method for preparing a PVDF membrane, comprising: injecting a PVDF solution onto the surface of a coagulation bath solution through a guide plate having an inclined angle, and forming a PVDF membrane after solidification;

[0011] The PVDF solution is formed by dissolving PVDF powder in an organic solvent, with a mass concentration of 5 to 20 wt%;

[0012] The coagulation bath solution is formed by dissolving an organic solvent in water, and the volume ratio of the organic solvent to the water is 60:40.

[0013] On the basis of the above technical solution, preferably, the organic solvent is selected from one of N,N-dimethylformamide (DMF), N-methylpyrrolidone, dimethylacetamide, dimethyl sulfoxide or cyclohexanone.

[0014] On the basis of the above technical solution, preferably, the guide plate is half immersed in the coagulation bath solution; and the inclination angle is 10° to 40°.

[0015] In the present invention, the water contact angle of the guide plate can be treated by coating a hydrophilic coating, electrochemical oxidation, pickling or plasma treatment, or directly using hydrophilic glass to obtain a guide plate with a water contact angle of 5° to 65°; the preferred recommended method of the present invention is to perform plasma treatment on the guide plate.

[0016] On the basis of the above technical solution, preferably, the guide plate is treated with plasma for 0.5 to 1 minute, and the atmosphere is air.

[0017] On the basis of the above technical solution, preferably, the water contact angle of the guide plate after plasma treatment is 5° to 65°.

[0018] On the basis of the above technical solution, preferably, a liquid storage groove is provided on the guide plate, and the liquid storage groove is used to store the PVDF solution.

[0019] In the present invention, the outlet width of the liquid storage groove can be appropriately adjusted according to actual production needs and is not limited thereto.

[0020] Based on the above technical solution, preferably, the width w of the outlet of the liquid storage groove is 1 to 30 cm, and the height h is 1.5 mm.

[0021] On the basis of the above technical solution, preferably, the guide plate is a float inorganic glass plate or hydrophilic glass.

[0022] In a second aspect, the present invention provides a PVDF membrane prepared by the above preparation method, wherein the PVDF membrane has a width of 2 to 40 cm and has no edge wrinkles.

[0023] The method for preparing a polymer film provided by the present invention has the following beneficial effects compared with the prior art:

[0024] (1) The method for preparing the polymer film of the present invention is simple and has low energy consumption. It does not require high-temperature or low-temperature heat treatment processes, which greatly reduces energy consumption, improves production efficiency, and can achieve large-scale continuous production.

[0025] (2) The polymer membrane prepared by the present invention effectively suppresses the spreading instability caused by surface tension by precisely controlling the contact angle of the guide plate, the concentration of the polymer solution, the inclination angle of the guide plate, and the width of the liquid storage tank, thereby further improving the overall quality of the polymer membrane; at the same time, the width of the polymer membrane is controllable to meet the needs of different application scenarios.

[0026] (3) The polymer film prepared by the present invention has excellent film quality, almost no obvious wrinkled edges, and the thickness and structure of the film show a high degree of uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 This is a front view of the process flow for preparing the PVDF membrane of the present invention;

[0029] Figure 2 A top view of the process flow for preparing the PVDF membrane of the present invention;

[0030] In the figure, 1, liquid storage tank, 2, PVDF solution, 3, guide plate, 4, coagulation bath solution, 5, PVDF liquid flow, 6, spreading liquid layer, 7, solidification line at the edge of the spreading liquid layer, 8, PVDF membrane;

[0031] Figure 3 1 is a picture of the PVDF membrane prepared in Example 1 of the present invention; in the figure, a is an optical photograph of the PVDF membrane prepared in Example 1, and b is a cross-sectional SEM image of different areas of the PVDF membrane prepared in Example 1;

[0032] Figure 4 This is a diagram showing the process of preparing a PVDF membrane according to Example 2 of the present invention; in the figure, a is a schematic diagram showing the hydrophilicity and hydrophobicity of the guide plate surface according to Example 2; b is a photograph of the film-forming process according to Example 2; and c is an optical photograph of the PVDF membrane prepared according to Example 2.

[0033] Figure 5 This is a diagram showing the process of preparing a PVDF membrane according to Example 3 of the present invention; in the figure, a is a photograph of the film-forming process according to Example 3; b is an optical photograph of the PVDF membrane prepared according to Example 3;

[0034] Figure 6 This is a process diagram of preparing a PVDF membrane in Example 4 of the present invention. In the figure, a is a schematic diagram of the hydrophilicity and hydrophobicity of the guide plate surface in Example 4; b is an optical photograph of the PVDF membrane prepared in Example 4;

[0035] Figure 7 This is an optical photograph of the PVDF membrane prepared in Example 5 of the present invention;

[0036] Figure 8 This is a diagram showing the process of preparing a PVDF membrane according to Example 6 of the present invention; in the figure, a is a photograph of the film-forming process according to Example 6; b is an optical photograph of the PVDF membrane prepared according to Example 6;

[0037] Figure 9 This is an optical photograph of the PVDF membrane prepared in Example 7 of the present invention;

[0038] Figure 10 This is an optical photograph of the PVDF membrane prepared in Example 8 of the present invention;

[0039] Figure 11 This is an optical photograph of the PVDF membrane prepared in Example 9 of the present invention;

[0040] Figure 12 This is an optical photograph of the PVDF membrane prepared in Example 10 of the present invention;

[0041] Figure 13 This is an optical photograph of the PVDF membrane prepared in Example 11 of the present invention;

[0042] Figure 14 This is an optical photograph of the PVDF membrane prepared in Comparative Example 1 of the present invention;

[0043] Figure 15 This is a diagram showing the process of preparing a PVDF membrane in Comparative Example 2 of the present invention; in the figure, a is a photograph of the film-forming process of Comparative Example 2; b is an optical photograph of the PVDF membrane prepared in Comparative Example 2;

[0044] Figure 16 This is an optical photograph of the PVDF membrane prepared in Comparative Example 3 of the present invention;

[0045] Figure 17 This is an optical photograph of the PVDF membrane prepared in Comparative Example 4 of the present invention;

[0046] Figure 18 This is an optical photograph of the PVDF membrane prepared in Comparative Example 5 of the present invention;

[0047] Figure 19 This is a process diagram for preparing PVDF membrane in Comparative Example 6 of the present invention; in the figure, a is a photo of the film-forming process of Comparative Example 6; b is an optical photo of the PVDF membrane prepared in Comparative Example 6. DETAILED DESCRIPTION

[0048] Existing methods for forming films on the surface of a coagulation bath involve overly stringent parameters and conditions, resulting in poor film quality, uncontrollable film width, and impracticality for large-scale continuous production. To address this technical problem, the inventors conducted further research and developed the present invention.

[0049] Refer to the attached Figure 1 、 2 The present invention provides a method for preparing a PVDF membrane, comprising: injecting a PVDF solution into the surface of a coagulation bath solution through a guide plate having an inclination angle a, and forming a PVDF membrane after solidification.

[0050] As a specific embodiment of the present invention, the guide plate is half immersed in the coagulation bath solution; and the inclination angle is 10° to 40°.

[0051] Furthermore, the guide plate is treated with plasma, and the water contact angle is 5° to 65°.

[0052] In the present invention, when the polymer solution contacts the coagulation bath surface through the guide plate, the polymer solution first spreads outward on the coagulation bath surface under the action of the surface tension of the coagulation bath solution, forming a uniform liquid film; at the same time, the organic solvent in the spreading liquid film will diffuse into the coagulation bath driven by the concentration difference with the coagulation bath, triggering a phase separation process, and finally solidifying to form a porous polymer film. In this process, the spreading of the polymer forms a thin layer of coagulation bath laminar flow between the spreading interface and the guide plate, causing the coagulation bath to continuously flow from the bulk phase to the spreading interface and move along the film-forming direction. This process can maintain a stable surface tension gradient on the spreading liquid surface, thereby achieving stable spreading, allowing the spreading solution to form a stable spreading area on the coagulation bath surface. This area has a fixed spreading width, thereby continuously forming a porous polymer film with a highly uniform structure at the edge of the spreading liquid film.

[0053] Furthermore, by adjusting the deflector's tilt angle and hydrophilicity, surface tension-induced spreading instability can be suppressed, enhancing spreading stability and reducing wrinkles during film formation, further improving polymer film quality. Furthermore, by adjusting the deflector's water contact angle, polymer solution concentration, tilt angle, and reservoir width, the width of the spreading liquid film can be further controlled, thereby further regulating the polymer film width during the spreading process and enabling the preparation of large-area polymer films.

[0054] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0055] The following are specific examples of the present invention. Unless otherwise specified, the sources of materials involved in the examples are all commercially available conventional products.

[0056] Example 1

[0057] This embodiment provides a method for preparing a PVDF membrane, comprising the following steps:

[0058] A float inorganic glass plate is selected as a guide plate, and the guide plate is plasma treated under air conditions for 1 minute, and the water contact angle of the guide plate is adjusted to 5°; DMF and pure water are evenly mixed in a volume ratio of 60:40 to obtain a coagulation bath solution; PVDF powder is fully dissolved in DMF at 40°C to prepare a 13wt% PVDF solution; the guide plate is semi-immersed and tilted in the coagulation bath, the tilt angle is adjusted to 10°, and a liquid storage groove is set on the guide plate to store the PVDF solution, and the width and height of the liquid storage groove outlet are adjusted to 30cm and 1.5mm; the PVDF solution is injected into the liquid storage groove, and then the liquid storage groove outlet is opened so that the PVDF liquid flow flowing out uniformly, slowly and steadily from the liquid storage groove outlet is simultaneously in contact with the junction of the guide plate and the coagulation bath, and then a PVDF film is formed on the surface of the coagulation bath, such as Figure 3 shown.

[0059] Depend on Figure 3 It can be seen that the PVDF membrane prepared in this embodiment has a width of about 40 cm and has no wrinkles on the edges. At the same time, the membrane thickness and pore structure have good uniformity.

[0060] Example 2

[0061] This embodiment provides a method for preparing a PVDF membrane, comprising the following steps:

[0062] Float inorganic glass plates were selected as guide plates, and the guide plates were plasma treated for 0.5 min under air conditions to adjust the water contact angle of the guide plates to 17°. Figure 4 As shown in a; DMF and pure water are mixed evenly in a volume ratio of 60:40 to obtain a coagulation bath solution; PVDF powder is fully dissolved in DMF at 40°C to prepare a 13wt% PVDF solution; the guide plate is semi-immersed and tilted in the coagulation bath, the tilt angle is adjusted to 10°, and a liquid storage groove is provided on the guide plate to store the PVDF solution, and the width and height of the liquid storage groove outlet are adjusted to 1cm and 1.5mm; the PVDF solution is injected into the liquid storage groove, and then the liquid storage groove outlet is opened so that the PVDF liquid flowing out from the liquid storage groove outlet uniformly, slowly and steadily comes into contact at the junction of the guide plate and the coagulation bath, thereby forming a PVDF film on the surface of the coagulation bath, as shown in FIG. Figure 4 shown.

[0063] Depend on Figure 4 It can be seen that the PVDF membrane prepared in this embodiment has a width of about 2 cm and has no wrinkles on the edges.

[0064] Example 3

[0065] This embodiment provides a method for preparing a PVDF membrane, comprising the following steps:

[0066] A float inorganic glass plate is selected as a guide plate, and the guide plate is plasma treated under air conditions for 0.1 min, and the water contact angle of the guide plate is adjusted to 65°; DMF and pure water are evenly mixed in a volume ratio of 60:40 to obtain a coagulation bath solution; PVDF powder is fully dissolved in DMF at 40°C to prepare a 13wt% PVDF solution; the guide plate is semi-immersed and tilted in the coagulation bath, the tilt angle is adjusted to 10°, and a liquid storage groove is set on the guide plate to store the PVDF solution, and the width and height of the liquid storage groove outlet are adjusted to 1 cm and 1.5 mm; the PVDF solution is injected into the liquid storage groove, and then the liquid storage groove outlet is opened so that the PVDF liquid flow flowing out uniformly, slowly and steadily from the liquid storage groove outlet is simultaneously in contact with the junction of the guide plate and the coagulation bath, and then a PVDF film is formed on the surface of the coagulation bath, such as Figure 5 shown.

[0067] Depend on Figure 5 It can be seen that the PVDF membrane prepared in this embodiment has a width of about 2 cm and has no wrinkles on the edges.

[0068] Example 4

[0069] This embodiment provides a method for preparing a PVDF membrane, comprising the following steps:

[0070] A float inorganic glass plate is selected as a guide plate, and the guide plate is plasma treated under air conditions for 1 minute, and the water contact angle of the guide plate is adjusted to 5°; DMF and pure water are evenly mixed in a volume ratio of 60:40 to obtain a coagulation bath solution; PVDF powder is fully dissolved in DMF at 40°C to prepare a 13wt% PVDF solution; the guide plate is semi-immersed and tilted in the coagulation bath, the tilt angle is adjusted to 25°, and a liquid storage groove is set on the guide plate to store the PVDF solution, and the width and height of the liquid storage groove outlet are adjusted to 1 cm and 1.5 mm; the PVDF solution is injected into the liquid storage groove, and then the liquid storage groove outlet is opened so that the PVDF liquid flow flowing out uniformly, slowly and steadily from the liquid storage groove outlet is simultaneously in contact with the junction of the guide plate and the coagulation bath, and then a PVDF film is formed on the surface of the coagulation bath, such as Figure 6 shown.

[0071] Depend on Figure 6 It can be seen that the PVDF membrane prepared in this embodiment has a width of about 2 cm and has no wrinkles on the edges.

[0072] Example 5

[0073] This embodiment provides a method for preparing a PVDF membrane, comprising the following steps:

[0074] A float inorganic glass plate was selected as a guide plate, and the guide plate was plasma treated under air conditions for 0.5 min, and the water contact angle of the guide plate was adjusted to 17°; DMF and pure water were evenly mixed in a volume ratio of 60:40 to obtain a coagulation bath solution; PVDF powder was fully dissolved in DMF at 40°C to prepare a 13wt% PVDF solution; the guide plate was semi-immersed and tilted in the coagulation bath, the tilt angle was adjusted to 25°, and a liquid storage groove was set on the guide plate to store the PVDF solution, and the width and height of the liquid storage groove outlet were adjusted to 1 cm and 1.5 mm; the PVDF solution was injected into the liquid storage groove, and then the liquid storage groove outlet was opened so that the PVDF liquid flow flowing out uniformly, slowly and steadily from the liquid storage groove outlet was simultaneously in contact with the junction of the guide plate and the coagulation bath, and then a PVDF film was formed on the surface of the coagulation bath, such as Figure 7 shown.

[0075] Depend on Figure 7 It can be seen that the PVDF membrane prepared in this embodiment has a width of about 2 cm and has no wrinkles on the edges.

[0076] Example 6

[0077] This embodiment provides a method for preparing a PVDF membrane, comprising the following steps:

[0078] A float inorganic glass plate is selected as a guide plate, and the guide plate is plasma treated under air conditions for 0.1 min, and the water contact angle of the guide plate is adjusted to 65°; DMF and pure water are evenly mixed in a volume ratio of 60:40 to obtain a coagulation bath solution; PVDF powder is fully dissolved in DMF at 40°C to prepare a 13wt% PVDF solution; the guide plate is semi-immersed and tilted in the coagulation bath, the tilt angle is adjusted to 25°, and a liquid storage groove is set on the guide plate to store the PVDF solution, and the width and height of the liquid storage groove outlet are adjusted to 1 cm and 1.5 mm; the PVDF solution is injected into the liquid storage groove, and then the liquid storage groove outlet is opened so that the PVDF liquid flow flowing out uniformly, slowly and steadily from the liquid storage groove outlet is simultaneously in contact with the junction of the guide plate and the coagulation bath, and then a PVDF film is formed on the surface of the coagulation bath, such as Figure 8 shown.

[0079] Depend on Figure 8 It can be seen that the PVDF membrane prepared in this embodiment has a width of about 2 cm and has no wrinkles on the edges.

[0080] Example 7

[0081] This embodiment provides a method for preparing a PVDF membrane, comprising the following steps:

[0082] A float inorganic glass plate is selected as a guide plate, and the guide plate is plasma treated under air conditions for 1 minute, and the water contact angle of the guide plate is adjusted to 5°; DMF and pure water are evenly mixed in a volume ratio of 60:40 to obtain a coagulation bath solution; PVDF powder is fully dissolved in DMF at 40°C to prepare a 13wt% PVDF solution; the guide plate is semi-immersed and tilted in the coagulation bath, the tilt angle is adjusted to 40°, and a liquid storage groove is set on the guide plate to store the PVDF solution, and the width and height of the liquid storage groove outlet are adjusted to 8cm and 1.5mm; the PVDF solution is injected into the liquid storage groove, and then the liquid storage groove outlet is opened so that the PVDF liquid flow flowing out uniformly, slowly and steadily from the liquid storage groove outlet is simultaneously in contact with the junction of the guide plate and the coagulation bath, and then a PVDF film is formed on the surface of the coagulation bath, such as Figure 9 shown.

[0083] Depend on Figure 9 It can be seen that the PVDF membrane prepared in this embodiment has a width of about 10 cm and has no wrinkles on the edges.

[0084] Example 8

[0085] This embodiment provides a method for preparing a PVDF membrane, comprising the following steps:

[0086] A float inorganic glass plate was selected as a guide plate, and the guide plate was plasma treated under air conditions for 0.5 min, and the water contact angle of the guide plate was adjusted to 17°; DMF and pure water were mixed evenly in a volume ratio of 60:40 to obtain a coagulation bath solution; PVDF powder was fully dissolved in DMF at 40°C to prepare a 13wt% PVDF solution; the guide plate was semi-immersed and tilted in the coagulation bath, the tilt angle was adjusted to 40°, and a liquid storage groove was set on the guide plate to store the PVDF solution, and the width and height of the liquid storage groove outlet were adjusted to 1 cm and 1.5 mm; the PVDF solution was injected into the liquid storage groove, and then the liquid storage groove outlet was opened so that the PVDF liquid flow flowing out evenly, slowly and steadily from the liquid storage groove outlet was simultaneously in contact with the junction of the guide plate and the coagulation bath, and then a PVDF film was formed on the surface of the coagulation bath, such as Figure 10 shown.

[0087] Depend on Figure 10 It can be seen that the PVDF membrane prepared in this embodiment has a width of about 2 cm and has no wrinkles on the edges.

[0088] Example 9

[0089] This embodiment provides a method for preparing a PVDF membrane, comprising the following steps:

[0090] A float inorganic glass plate is selected as a guide plate, and the guide plate is plasma treated under air conditions for 0.1 min, and the water contact angle of the guide plate is adjusted to 65°; DMF and pure water are evenly mixed in a volume ratio of 60:40 to obtain a coagulation bath solution; PVDF powder is fully dissolved in DMF at 40°C to prepare a 13wt% PVDF solution; the guide plate is semi-immersed and tilted in the coagulation bath, the tilt angle is adjusted to 40°, and a liquid storage groove is set on the guide plate to store the PVDF solution, and the width and height of the liquid storage groove outlet are adjusted to 1 cm and 1.5 mm; the PVDF solution is injected into the liquid storage groove, and then the liquid storage groove outlet is opened so that the PVDF liquid flow flowing out uniformly, slowly and steadily from the liquid storage groove outlet is simultaneously in contact with the junction of the guide plate and the coagulation bath, and then a PVDF film is formed on the surface of the coagulation bath, such as Figure 11 shown.

[0091] Depend on Figure 11 It can be seen that the PVDF membrane prepared in this embodiment has a width of about 2 cm and has no wrinkles on the edges.

[0092] Example 10

[0093] This embodiment provides a method for preparing a PVDF membrane, comprising the following steps:

[0094] A float inorganic glass plate was selected as a guide plate, and the guide plate was plasma treated under air conditions for 0.5 min, and the water contact angle of the guide plate was adjusted to 17°; DMF and pure water were evenly mixed in a volume ratio of 60:40 to obtain a coagulation bath solution; PVDF powder was fully dissolved in DMF at 40°C to prepare a 5wt% PVDF solution; the guide plate was semi-immersed and tilted in the coagulation bath, the tilt angle was adjusted to 25°, and a liquid storage groove was set on the guide plate to store the PVDF solution, and the width and height of the liquid storage groove outlet were adjusted to 1 cm and 1.5 mm; the PVDF solution was injected into the liquid storage groove, and then the liquid storage groove outlet was opened so that the PVDF liquid flow flowing out uniformly, slowly and steadily from the liquid storage groove outlet was simultaneously in contact with the junction of the guide plate and the coagulation bath, and then a PVDF film was formed on the surface of the coagulation bath, such as Figure 12 shown.

[0095] Depend on Figure 12 It can be seen that the PVDF membrane prepared in this embodiment has a width of about 2.5 cm and has no wrinkles on the edges.

[0096] Example 11

[0097] This embodiment provides a method for preparing a PVDF membrane, comprising the following steps:

[0098] A float inorganic glass plate was selected as a guide plate, and the guide plate was plasma treated under air conditions for 0.5 min, and the water contact angle of the guide plate was adjusted to 17°; DMF and pure water were mixed evenly in a volume ratio of 60:40 to obtain a coagulation bath solution; PVDF powder was fully dissolved in DMF at 40°C to prepare a 20wt% PVDF solution; the guide plate was semi-immersed and tilted in the coagulation bath, the tilt angle was adjusted to 25°, and a liquid storage groove was set on the guide plate to store the PVDF solution, and the width and height of the liquid storage groove outlet were adjusted to 1 cm and 1.5 mm; the PVDF solution was injected into the liquid storage groove, and then the liquid storage groove outlet was opened so that the PVDF liquid flow flowing out evenly, slowly and steadily from the liquid storage groove outlet was simultaneously in contact with the junction of the guide plate and the coagulation bath, and then a PVDF film was formed on the surface of the coagulation bath, such as Figure 13 shown.

[0099] Depend on Figure 13 It can be seen that the PVDF membrane prepared in this example has a width of about 1.5 cm and has no wrinkles on the edges.

[0100] Comparative Example 1

[0101] This comparative example provides a method for preparing a PVDF membrane, comprising the following steps:

[0102] A float inorganic glass plate was selected as a guide plate, and the guide plate was plasma treated under air conditions for 0.5 min, and the water contact angle of the guide plate was adjusted to 17°; DMF and pure water were evenly mixed in a volume ratio of 60:40 to obtain a coagulation bath solution; PVDF powder was fully dissolved in DMF at 40°C to prepare a 4wt% PVDF solution; the guide plate was semi-submerged and tilted in the coagulation bath, with the tilt angle adjusted to 25°, and a liquid storage groove was set on the guide plate to store the PVDF solution, as shown in FIG. Figure 1 , as shown in 2, and the width of the liquid storage groove outlet is adjusted to 1 cm and the height is 1.5 mm; the PVDF solution is injected into the liquid storage groove, and then the liquid storage groove outlet is opened, so that the PVDF liquid flow flowing out from the liquid storage groove outlet evenly, slowly and steadily contacts the junction of the guide plate and the coagulation bath at the same time, and then a PVDF film is formed on the surface of the coagulation bath, as shown Figure 14 shown.

[0103] Depend on Figure 14 It can be seen that the PVDF membrane prepared in this comparative example is discontinuous.

[0104] Comparative Example 2

[0105] This comparative example provides a method for preparing a PVDF membrane, comprising the following steps:

[0106] A float inorganic glass plate was selected as a guide plate, and the guide plate was plasma treated under air conditions for 0.5 min, and the water contact angle of the guide plate was adjusted to 17°; DMF and pure water were mixed evenly in a volume ratio of 60:40 to obtain a coagulation bath solution; PVDF powder was fully dissolved in DMF at 40°C to prepare a 23wt% PVDF solution; the guide plate was semi-immersed and tilted in the coagulation bath, the tilt angle was adjusted to 25°, and a liquid storage groove was set on the guide plate to store the PVDF solution, and the width and height of the liquid storage groove outlet were adjusted to 1 cm and 1.5 mm; the PVDF solution was injected into the liquid storage groove, and then the liquid storage groove outlet was opened so that the PVDF liquid flow flowing out evenly, slowly and steadily from the liquid storage groove outlet was simultaneously in contact with the junction of the guide plate and the coagulation bath, and then a PVDF film was formed on the surface of the coagulation bath, such as Figure 15 shown.

[0107] Depend on Figure 15 It can be seen that the PVDF membrane prepared in this comparative example has obvious non-directional characteristics, and the PVDF membrane has wrinkled edges, and the membrane quality is low.

[0108] Comparative Example 3

[0109] This comparative example provides a method for preparing a PVDF membrane, comprising the following steps:

[0110] A float inorganic glass plate is selected as a guide plate, and the guide plate is plasma treated under air conditions for 1.5 minutes, and the water contact angle of the guide plate is adjusted to 4°; DMF and pure water are evenly mixed in a volume ratio of 60:40 to obtain a coagulation bath solution; PVDF powder is fully dissolved in DMF at 40°C to prepare a 13wt% PVDF solution; the guide plate is semi-immersed and tilted in the coagulation bath, and the tilt angle is adjusted to 25°, and a liquid storage groove is set on the guide plate to store the PVDF solution, and the width and height of the liquid storage groove outlet are adjusted to 1 cm and 1.5 mm; the PVDF solution is injected into the liquid storage groove, and then the liquid storage groove outlet is opened so that the PVDF liquid flow flowing out uniformly, slowly and steadily from the liquid storage groove outlet is simultaneously in contact with the junction of the guide plate and the coagulation bath, and then a PVDF film is formed on the surface of the coagulation bath, such as Figure 16 shown.

[0111] Depend on Figure 16 It can be seen that the PVDF membrane prepared in this comparative example has obvious wrinkled edges and the membrane quality is low.

[0112] Comparative Example 4

[0113] This comparative example provides a method for preparing a PVDF membrane, comprising the following steps:

[0114] A float inorganic glass plate is selected as a guide plate, and the guide plate is plasma treated under air conditions for 0 min, and the water contact angle of the guide plate is adjusted to 68°; DMF and pure water are evenly mixed in a volume ratio of 60:40 to obtain a coagulation bath solution; PVDF powder is fully dissolved in DMF at 40°C to prepare a 13wt% PVDF solution; the guide plate is semi-immersed and tilted in the coagulation bath, the tilt angle is adjusted to 25°, and a liquid storage groove is set on the guide plate to store the PVDF solution, and the width and height of the liquid storage groove outlet are adjusted to 1 cm and 1.5 mm; the PVDF solution is injected into the liquid storage groove, and then the liquid storage groove outlet is opened so that the PVDF liquid flow flowing out uniformly, slowly and steadily from the liquid storage groove outlet is simultaneously in contact with the junction of the guide plate and the coagulation bath, and then a PVDF film is formed on the surface of the coagulation bath, such as Figure 17 shown.

[0115] Depend on Figure 17 It can be seen that the PVDF membrane prepared in this comparative example has obvious wrinkled edges and the membrane quality is low.

[0116] Comparative Example 5

[0117] This comparative example provides a method for preparing a PVDF membrane, comprising the following steps:

[0118] A float inorganic glass plate was selected as a guide plate, and the guide plate was plasma treated under air conditions for 0.5 min, and the water contact angle of the guide plate was adjusted to 17°; DMF and pure water were evenly mixed in a volume ratio of 60:40 to obtain a coagulation bath solution; PVDF powder was fully dissolved in DMF at 40°C to prepare a 13wt% PVDF solution; the guide plate was semi-immersed and tilted in the coagulation bath, the tilt angle was adjusted to 9°, and a liquid storage groove was set on the guide plate to store the PVDF solution, and the width and height of the liquid storage groove outlet were adjusted to 1 cm and 1.5 mm; the PVDF solution was injected into the liquid storage groove, and then the liquid storage groove outlet was opened so that the PVDF liquid flow flowing out uniformly, slowly and steadily from the liquid storage groove outlet was simultaneously in contact with the junction of the guide plate and the coagulation bath, and then a PVDF film was formed on the surface of the coagulation bath, such as Figure 18 shown.

[0119] Depend on Figure 18 It can be seen that the PVDF membrane prepared in this comparative example has obvious wrinkled edges and the membrane quality is low.

[0120] Comparative Example 6

[0121] This comparative example provides a method for preparing a PVDF membrane, comprising the following steps:

[0122] A float inorganic glass plate was selected as a guide plate, and the guide plate was plasma treated under air conditions for 0.5 min, and the water contact angle of the guide plate was adjusted to 17°; DMF and pure water were mixed evenly in a volume ratio of 60:40 to obtain a coagulation bath solution; PVDF powder was fully dissolved in DMF at 40°C to prepare a 13wt% PVDF solution; the guide plate was semi-immersed and tilted in the coagulation bath, the tilt angle was adjusted to 42°, and a liquid storage groove was set on the guide plate to store the PVDF solution, and the width and height of the liquid storage groove outlet were adjusted to 1 cm and 1.5 mm; the PVDF solution was injected into the liquid storage groove, and then the liquid storage groove outlet was opened so that the PVDF liquid flow flowing out evenly, slowly and steadily from the liquid storage groove outlet was simultaneously in contact with the junction of the guide plate and the coagulation bath, and then a PVDF film was formed on the surface of the coagulation bath, such as Figure 19 shown.

[0123] Depend on Figure 19 It can be seen that the PVDF membrane prepared in this comparative example has obvious wrinkled edges and the membrane quality is low.

[0124] In the present invention, a polymer solution of suitable concentration (5-20 wt%) is selected to pass through a guide plate with a certain inclination angle (10°-40°) and its regulated surface water contact angle (5°-65°), stably flow to the coagulation bath, and continuously spread on the surface of the coagulation bath driven by surface tension to form a uniform polymer liquid film. Stable spreading is the key to forming a high-quality polymer film. Otherwise, it will lead to an unstable spreading process, that is, capillary instability, causing the edge of the spreading liquid film to be disturbed, thereby generating a wrinkled edge. Regulating the concentration of the polymer solution at 5% to 20% helps the polymer solution to spread effectively in the coagulation bath, making the polymer distribution in the formed liquid film more uniform, ensuring the stability of the spreading, and inhibiting the formation of edge wrinkles. On the other hand, adjusting the guide plate's inclination angle between 10° and 40° and the water contact angle between 5° and 65° can ensure the fluidity and stability of the polymer flow, which is conducive to establishing a stable spreading interface, further effectively reducing the edge disturbance of the spreading, and suppressing the formation of edge wrinkles, thereby enabling the continuous and stable formation of uniform polymer films over a large area. Therefore, by regulating the polymer solution concentration, the guide plate's inclination angle, and the guide plate's water contact angle, Examples 1 to 11 of the present invention achieve the preparation of high-quality polymer films with uniform film thickness and wrinkle-free edges.

[0125] In Comparative Example 1, the concentration of the polymer solution is too low, resulting in too low a polymer content in the liquid film formed by spreading, making it impossible to ensure the integrity of the liquid film and forming a discontinuous film. In Comparative Example 2, the concentration of the polymer solution is too high, resulting in too high a polymer content in the liquid film, making it impossible to spread effectively, and therefore the polymer distribution is uneven, forming edge wrinkles. In Comparative Example 3, the water contact angle of the guide plate is too small, resulting in the polymer solution spreading on the guide plate, reducing the liquid flow height of the polymer solution, resulting in unstable spreading, and forming a film with wrinkled edges. In Comparative Example 4, the water contact angle of the guide plate is too large, resulting in the polymer solution being unable to spread on the guide plate, increasing the liquid flow height of the polymer solution, resulting in instability at the contact interface between the polymer solution and the coagulation bath, and forming a film with wrinkled edges. In Comparative Example 5, the inclination angle of the guide plate is too small, which reduces the fluidity of the polymer solution flowing to the coagulation bath interface, is not conducive to the stability of spreading, and forms edge wrinkles. In Comparative Example 6, the inclination angle of the guide plate is too large, which will increase the fluidity of the polymer solution flowing toward the coagulation bath interface, which is not conducive to the stability of spreading, thereby forming edge wrinkles.

[0126] In summary, the polymer membrane prepared by the present invention effectively suppresses spreading instability caused by surface tension through precise control of the guide plate contact angle, polymer solution concentration, guide plate tilt angle, and reservoir width, further improving the overall quality of the polymer membrane. This also allows for controllable polymer membrane width to meet the needs of various application scenarios. The polymer membrane prepared by the present invention exhibits excellent film quality, with virtually no noticeable wrinkled edges and a high degree of uniformity in thickness and structure.

[0127] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a polyvinylidene fluoride film, characterized in that: include: The polyvinylidene fluoride solution is injected onto the surface of the coagulation bath solution through a guide plate with an inclined angle, and a polyvinylidene fluoride film is formed after solidification; The polyvinylidene fluoride solution is formed by dissolving polyvinylidene fluoride powder in an organic solvent, and the mass concentration is 5-20wt%; The coagulation bath solution is formed by dissolving an organic solvent in water, and the volume ratio of the organic solvent to the water is 60:

40.

2. The preparation method according to claim 1, characterized in that The organic solvent is selected from one of N,N-dimethylformamide, N-methylpyrrolidone, dimethylacetamide, dimethyl sulfoxide or cyclohexanone.

3. The preparation method according to claim 1, characterized in that: The guide plate is half immersed in the coagulation bath solution; and the inclination angle is 10° to 40°.

4. The preparation method according to claim 3, characterized in that: The guide plate is treated with plasma for 0.5 to 1 minute in an air atmosphere.

5. The preparation method according to claim 4, characterized in that: The water contact angle of the guide plate after plasma treatment is 5° to 65°.

6. The preparation method according to claim 5, characterized in that: The guide plate is provided with a liquid storage groove, and the liquid storage groove is used to store the polyvinylidene fluoride solution.

7. The preparation method according to claim 6, characterized in that: The outlet width of the liquid storage groove is 1 to 30 cm, and the height is 1.5 mm.

8. A polyvinylidene fluoride film, characterized in that: The polyvinylidene fluoride film is prepared by the preparation method according to any one of claims 1 to 7.

9. The polyvinylidene fluoride film according to claim 8, characterized in that The polyvinylidene fluoride film has a width of 2 to 40 cm and has no edge wrinkles.

10. Use of the polyvinylidene fluoride membrane according to claim 9 in purification equipment, separation equipment and electronic equipment.

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