Equipment and process for preparing polyvinylidene fluoride membranes by phase inversion method

Abstract

This invention relates to the field of filter membrane preparation technology, specifically disclosing an equipment and process for preparing polyvinylidene fluoride (PVDF) membranes via phase inversion. The equipment includes a stirring and dissolving tank, a spinning tank, a core liquid tank, a spinneret, a first gel bath, a second gel bath, a winding device, and a control system. The stirring and dissolving tank and the spinning tank are connected via a first conveying assembly. Before spinning, this invention eliminates all air bubbles in the casting solution through the combined action of a mechanical stirring defoaming mechanism and a vibration defoaming mechanism in the spinning tank. This not only improves the quality of the subsequent spinning castings but also eliminates the need for a vacuum system. When the casting spinning traction speed changes, the fork-type telescopic adjustment frame can be adjusted via a telescopic drive component, thereby regulating the traction distance of the casting in the non-solvent or non-solvent mixture during traction. This ensures that the exchange rate between solvent and non-solvent in the casting remains the same, guaranteeing consistent product quality and performance.

Description

Technical Field

[0001] This invention relates to the field of filter membrane preparation technology, and specifically discloses an apparatus and process for preparing polyvinylidene fluoride membranes by phase inversion method. Background Technology

[0002] Compared with traditional water treatment processes, membrane separation technology has advantages such as small footprint, low energy consumption, high-quality effluent, good treatment effect, and minimal environmental impact, making it an emerging technology for solving contemporary water resource and environmental problems. Polyvinylidene fluoride (PVDF) membranes are filter membrane materials with impact resistance, abrasion resistance, and chemical stability. The immersion precipitation phase inversion (NIPS) method is currently the most widely used preparation process for PVDF membranes and other hollow fiber membranes.

[0003] Utility model patent application number 2022202233699 discloses a hollow fiber membrane spinning machine, which is also equipment for preparing polyvinylidene fluoride membranes by the immersion precipitation phase inversion method. It includes a vacuum pump, a pneumatic pump, a membrane liquid feeding device, a core liquid feeding device, a spinning device, a condensation tank assembly, a guide wheel assembly, and a collection tank. The membrane liquid feeding device and the core liquid feeding device are connected to the vacuum pump and the pneumatic pump, respectively. The spinning device is located below the membrane liquid feeding device and the core liquid feeding device. The condensation tank assembly is located below the spinning device, and the collection tank is located at the end of the condensation tank away from the spinning device. A take-up wheel is installed in the collection tank. The guide wheel assembly is adapted to guide the spun fibers at the outlet of the spinning device to the take-up wheel for winding. An oscillating device is installed above the collection tank, located on the side of the take-up wheel closer to the condensation tank. The oscillating device is adapted to drive the cast membrane to move laterally back and forth. This hollow fiber membrane spinning machine has some shortcomings when used for the phase inversion method to prepare polyvinylidene fluoride membranes. Firstly, when polyvinylidene fluoride (PVDF) and film-forming additives are dissolved together in a solvent, air bubbles are present in the solution. Traditional methods for removing these bubbles involve vacuum degassing, which not only requires a vacuum system for the entire equipment, resulting in a complex structure and higher requirements for equipment sealing, but also fails to completely eliminate air bubbles in the solution. The presence of these bubbles affects the quality of the subsequently obtained PVDF cast film. Secondly, if the spinning speed changes during the spinning process, the contact time between the cast film and the non-solvent or non-solvent mixture in the coagulation bath changes, leading to different amounts of solvent and non-solvent exchange in the cast film. Simultaneously, the traction tension of the cast film changes, making it impossible to guarantee consistent cast film performance. Therefore, addressing the aforementioned shortcomings of existing hollow fiber membrane spinning machines used for the phase inversion method of PVDF membrane preparation, this application proposes a phase inversion method for PVDF membrane preparation that effectively solves the above-mentioned technical problems. Summary of the Invention

[0004] The purpose of this invention is to provide an equipment and process for preparing polyvinylidene fluoride (PVDF) membranes by phase inversion, so as to overcome the shortcomings of existing hollow fiber membrane spinning machines in the process of preparing PVDF membranes by phase inversion.

[0005] This invention is achieved through the following technical solution:

[0006] An apparatus for preparing polyvinylidene fluoride (PVDF) membranes by phase inversion includes a stirring and dissolving tank, a spinning tank, a core liquid tank, a spinneret, a first gel bath, a second gel bath, a winding device, and a control system. The stirring and dissolving tank and the spinning tank are connected by a first conveying assembly, the spinning tank and the spinneret are connected by a second conveying assembly, and the core liquid tank and the spinneret are connected by a third conveying assembly.

[0007] The spinning tank is equipped with a mechanical stirring and defoaming mechanism inside, and a vibration defoaming mechanism is provided at the lower end of the spinning tank. The mechanical stirring and defoaming mechanism includes a first motor located at the top of the spinning tank. The lower end of the first motor is connected to a defoaming rotating shaft extending into the spinning tank. The lower end of the defoaming rotating shaft is provided with a connecting plate. Several liquid-dispensing plates are evenly connected to the connecting plate. Each liquid-dispensing plate has a row of defoaming rods at both its upper and lower ends. The vibration defoaming mechanism includes several strips evenly fixed to the bottom wall of the spinning tank. Each strip is connected to a defoaming spring. A pneumatic vibrator is provided at the lower end of the outer wall of the spinning tank, which is aligned with each strip.

[0008] The spinneret is fixedly installed on the upper left side of the first gel bath. Several guide rollers are installed in the first gel bath. A speed measuring roller is installed on the upper right side of the first gel bath, and a sensor is installed at one end of the speed measuring roller. Feed rollers and discharge rollers are respectively installed on the upper left and right sides of the second gel bath. A horizontally arranged fork-type telescopic adjustment frame is installed inside the second gel bath. Four leaching rollers are installed at the upper end of the fork-type telescopic adjustment frame, and three impregnation rollers are installed at the lower end. The four leaching rollers and three impregnation rollers are staggered. A telescopic drive component is fixed to the lower end of one side of the second gel bath. The end of the telescopic drive component that extends into the second gel bath is connected to a connecting frame. The connecting frame is connected to the lower end of the fork-type telescopic adjustment frame. A sliding column is connected to the lower end of the other side of the fork-type telescopic adjustment frame. Horizontal sliding grooves that interact with the sliding column are provided on the front and rear inner walls of the second gel bath.

[0009] As a further provision of the above solution, the winding device includes a base, on which a winding frame is provided, and a winding roller suspended in the air is rotatably connected to the upper end of the winding frame. A winding motor is connected to the end of the winding roller, and a support seat is slidably provided on the winding frame located at the suspended end of the winding roller.

[0010] As a further provision of the above scheme, a crossbeam parallel to the winding roller is fixed on the winding frame located above the winding roller. A U-shaped seat is slidably arranged on the side of the crossbeam facing the second gel bath. A guide rod is rotatably arranged in the U-shaped seat. Multiple guide wheels are evenly spaced on the guide rod. A reciprocating screw is rotatably arranged on the crossbeam. The total pitch of the thread grooves on the reciprocating screw is equal to the distance between two adjacent guide wheels. A screw nut matching the reciprocating screw is provided on the back of the U-shaped seat.

[0011] As a further provision of the above scheme, the end of the reciprocating screw extending out of the winding frame is connected to a first pulley, the end of the winding roller extending out of the winding frame is provided with a second pulley, and a transmission belt is provided between the first pulley and the second pulley.

[0012] As a further feature of the above solution, the cross-sectional shape of the liquid-dispensing plate is a vertically arranged V-shape, and the defoaming rod is U-shaped and fixedly connected to the upper or lower end of the liquid-dispensing plate.

[0013] As a further feature of the above solution, the strip is in the shape of an arc that fits against the bottom wall of the spinning tank, and the movable end of the defoaming spring is connected to a defoaming needle end that extends toward the central axis of the spinning tank.

[0014] As a further provision of the above scheme, a second motor is provided at the upper end of the stirring and dissolving tank. The motor shaft of the second motor is connected to a stirring shaft that extends into the stirring and dissolving tank. Multiple stirring rods are connected to the upper end of the stirring shaft, and a scraper that fits against the inner wall of the stirring and dissolving tank is connected to the lower end. A solvent inlet pipe and a material inlet pipe are provided at the upper end of the stirring and dissolving tank.

[0015] As a further provision of the above scheme, the first conveying component, the second conveying component and the third conveying component all include a conveying pipe, the conveying pipes in the second conveying component and the third conveying component are equipped with metering pumps, and the conveying pipes in the first conveying component are equipped with a material conveying pump.

[0016] As a further feature of the above solution, a filter is also provided on the conveying pipe in the second conveying assembly.

[0017] This invention also discloses a phase inversion method for preparing polyvinylidene fluoride membranes using the above-mentioned equipment, comprising the following steps:

[0018] S1: Pre-input control molding into the control system, and control the specific extension and retraction amount of the telescopic drive component based on the speed of the speed measuring roller fed back by the sensor.

[0019] S2: Add polyvinylidene fluoride and film-forming additives into a stirring and dissolving tank, stir and dissolve, and then transfer the casting solution to a spinning tank;

[0020] S3: Start the mechanical stirring defoaming mechanism and the vibration defoaming mechanism to fully defoam the casting liquid in the spinning tank. After defoaming is completed, simultaneously introduce the casting liquid and core liquid into the spinneret according to the set ratio.

[0021] S4: The cast film filaments ejected from the spinneret are first solidified in the first gel bath, and then enter the second gel bath and are immersed in a non-solvent or non-solvent mixture, so that the solvent and non-solvent in the cast film undergo rapid exchange, resulting in phase separation to form the final product, which is then wound and collected.

[0022] Beneficial effects:

[0023] 1) The equipment for preparing polyvinylidene fluoride membrane by phase inversion method disclosed in this invention first prepares casting solution through a stirring dissolution tank, and then transfers the casting solution to a spinning tank. Before spinning, the mechanical stirring defoaming mechanism and the vibration defoaming mechanism in the spinning tank can completely eliminate the air bubbles in the casting solution. This not only improves the quality of the subsequent spinning and casting, but also eliminates the need for a vacuum system in the entire device, reducing the sealing requirements of the entire equipment. This effectively simplifies the entire equipment and reduces equipment and operating costs.

[0024] 2) The present invention also provides a fork-type telescopic adjustment frame, a telescopic drive component, an leaching roller, and an impregnation roller in the second gel bath. When the rotation speed of the speed measuring roller changes, it indicates that the casting sheet spinning traction speed changes. At this time, the fork-type telescopic adjustment frame can be changed by the action of the telescopic drive component, thereby adjusting the traction travel distance of the casting sheet in the non-solvent or non-solvent mixture during the traction process, so that the amount of exchange between the solvent and non-solvent in the casting sheet remains the same. At the same time, the adjustment of the fork-type telescopic adjustment frame can also adaptively adjust the tension during the casting sheet traction process, which greatly improves the quality and performance consistency of the final product.

[0025] 3) The present invention further improves the design of the winding device. When multiple cast film filaments are pulled, the rotation of the winding roller is synchronized with the reciprocating screw. Then, through the action between the reciprocating screw and the screw nut, the U-shaped seat can move back and forth along the crossbeam, thereby enabling the cast film filaments to be evenly wound onto the winding roller, effectively preventing the cast film filaments from winding and tangling, and improving the winding effect of the cast film filaments. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a three-dimensional structural diagram of the device of the present invention from a first angle;

[0028] Figure 2 This is a three-dimensional structural diagram of the device of the present invention from a first angle;

[0029] Figure 3 This is a three-dimensional structural diagram of the interior of the stirring and dissolving tank in this invention;

[0030] Figure 4 This is a three-dimensional structural diagram of the interior of the spinning tank in this invention;

[0031] Figure 5 For the present invention Figure 4 Enlarged structural diagram at point A;

[0032] Figure 6 This is a three-dimensional structural diagram of the interior of the first gel bath in this invention;

[0033] Figure 7 This is a three-dimensional structural diagram of the second gel bath in this invention;

[0034] Figure 8 This is a three-dimensional structural diagram of the fork-type telescopic adjustment frame, impregnation roller, telescopic drive component, etc. in this invention.

[0035] Figure 9 This is a three-dimensional structural diagram of the winding device in Embodiment 2 of the present invention from a first angle;

[0036] Figure 10 This is a two-dimensional structural diagram of the winding device in Embodiment 2 of the present invention from a second angle.

[0037] in:

[0038] 1-Stirring and dissolving tank, 101-Second motor, 102-Stirring shaft, 103-Stirring rod, 104-Scraper, 105-Solvent inlet pipe, 106-Material inlet pipe;

[0039] 2-Spinning tank, 201-Mechanical stirring and defoaming mechanism, 202-Vibration defoaming mechanism, 2011-First motor, 2012-Defoaming shaft, 2013-Connecting plate, 2014-Liquid dispensing plate, 2015-Defoaming rod, 2021-Strip plate, 2022-Defoaming spring component, 2023-Pneumatic vibrator, 2024-Defoaming needle tip;

[0040] 3-Core liquid tank, 4-Spinneret;

[0041] 5-First gel bath, 501-Guide roller, 502-Speed ​​measuring roller;

[0042] 6-Second gel bath, 601-Feed roller, 602-Discharge roller, 603-Fork-type telescopic adjustment frame, 604-Immersion roller, 605-Immersion roller, 606-Telescopic drive component, 607-Connecting frame, 608-Sliding column, 609-Transverse chute;

[0043] 7-Rewinding device, 701-Base, 702-Rewinding frame, 703-Rewinding roller, 704-Support seat, 705-Crossbeam, 706-U-shaped seat, 707-Guide rod, 708-Guide wheel, 709-Reciprocating screw, 710-Screw nut, 711-First pulley, 712-Second pulley, 713-Drive belt.

[0044] 8-Transfer pipe, 9-Metering pump, 10-Feed pump. Detailed Implementation

[0045] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0046] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The following will refer to the appendix... Figures 1-10 This application will be described in detail with reference to the embodiments.

[0047] Example 1

[0048] Example 1 discloses an apparatus for preparing polyvinylidene fluoride membranes by a phase inversion method, as shown in the attached diagram. Figure 1 and attached Figure 2 The main body of the equipment includes a stirring and dissolving tank 1, a spinning tank 2, a core liquid tank 3, a spinneret 4, a first gel bath 5, a second gel bath 6, a winding device 7, and a control system (not shown in the figure). The spinneret 4, the first gel bath 5, the second gel bath 6, and the winding device 7 are arranged sequentially from left to right. The stirring and dissolving tank 1 is connected to the spinning tank 2 via a first conveying assembly, the spinning tank 2 is connected to the spinneret 4 via a second conveying assembly, and the core liquid tank 3 is connected to the spinneret 4 via a third conveying assembly. Specifically, the first, second, and third conveying assemblies all include conveying pipes 8. Metering pumps 9 are installed on the conveying pipes 8 in the second and third conveying assemblies, and a feed pump 10 is installed on the conveying pipe 8 in the first conveying assembly.

[0049] Reference Appendix Figure 3A second motor 101 is installed at the upper end of the stirring and dissolving tank 1. The motor shaft of the second motor 101 is connected to a stirring shaft 102 that extends into the stirring and dissolving tank 1. Multiple stirring rods 103 are connected to the upper end of the stirring shaft 102, and scrapers 104 that fit against the inner wall of the stirring and dissolving tank 1 are connected to its lower end. A solvent inlet pipe 105 and a material inlet pipe 106 are also provided at the upper end of the stirring and dissolving tank 1. During operation, polyvinylidene fluoride and film-forming additives are poured into the tank and dissolved in the solvent to form a casting solution. The dissolved casting solution is then conveyed to the spinning tank 2 through a first conveying assembly.

[0050] Reference Appendix Figure 4 and attached Figure 5 A mechanical stirring and defoaming mechanism 201 is installed inside the spinning tank 2, and a vibration defoaming mechanism 202 is also installed at the lower end of the spinning tank 2. The mechanical stirring and defoaming mechanism 201 includes a first motor 2011 installed at the top of the spinning tank 2. The lower end of the first motor 2011 is connected to a defoaming rotating shaft 2012 extending into the spinning tank 2. A connecting plate 2013 is installed at the lower end of the defoaming rotating shaft 2012. Several liquid-dispensing plates 2014 are evenly connected to the connecting plate 2013. In this figure, there are three liquid-dispensing plates 2014. The cross-sectional shape of the liquid-dispensing plates 2014 is a vertically arranged V-shape. Then, a row of defoaming rods 2015 are provided at the upper and lower ends of each liquid-dispensing plate 2014. The defoaming rods 2015 are U-shaped and are fixedly connected to the upper or lower end of the liquid-dispensing plate 2014. When the mechanical stirring and defoaming mechanism 201 is running, the first motor 2011 is used as the power source to make the liquid-dispensing plate 2014 rotate at the bottom of the casting liquid. During the rotation, because the cross-sectional shape of the liquid-dispensing plate 2014 is a vertically set V-shape, the casting liquid flows along the liquid-dispensing plate 2014 to the upper and lower ends. Then, through the action of the U-shaped defoaming rod 2015, the air bubbles in the casting liquid can be broken and eliminated.

[0051] The vibration defoaming mechanism 202 includes several strips 2021 uniformly fixed to the bottom wall of the spinning tank 2, and each strip 2021 is arc-shaped and fits against the bottom wall of the spinning tank 2. A defoaming spring 2022 is connected to each strip 2021, and a pneumatic vibrator 2023, aligned with each strip 2021, is located at the lower end of the outer wall of the spinning tank 2. To improve the effect of the defoaming spring 2022 on breaking bubbles inside the casting solution during high-frequency vibration, a defoaming needle end 2024 extending towards the central axis of the spinning tank 2 is connected to the movable end of the defoaming spring 2022. This allows the defoaming spring 2022 to effectively break bubbles that are difficult to puncture through the defoaming needle end 2024 during high-frequency vibration, thereby eliminating all bubbles in the casting solution.

[0052] Reference Appendix Figure 1 and attached Figure 6 The spinneret 4 is fixedly installed at the upper left end of the first gel bath 5, and the conveying pipes 8 in the second and third conveying assemblies are connected to the spinneret 4. In addition, to prevent impurities in the casting solution from entering the spinneret 4 and causing blockage or affecting the quality of the cast sheet, a filter (not shown in the figure) is also installed on the conveying pipe 8 in the second conveying assembly. Several guide rollers 501 are installed in the first gel bath 5, and a speed measuring roller 502 is installed at the upper right end of the first gel bath 5. A sensor (not shown in the figure) is installed at one end of the speed measuring roller 502, and this sensor is connected to the control system wires to provide real-time feedback on the traction speed of the cast sheet.

[0053] Reference Appendix Figure 7 and attached Figure 8 Feed rollers 601 and discharge rollers 602 are respectively arranged on the left and right sides of the upper end of the second gel bath 6. A horizontally arranged fork-type telescopic adjustment frame 603 is installed inside the second gel bath 6. Four leaching rollers 604 are arranged at the upper end of the fork-type telescopic adjustment frame 603, and three impregnation rollers 605 are arranged at the lower end, with the four leaching rollers 604 and three impregnation rollers 605 staggered. During operation, the cast sheet can shuttle back and forth between the four leaching rollers 604 and three impregnation rollers 605, while the non-solvent or non-solvent mixture in the second gel bath 6 can cover the three impregnation rollers 605.

[0054] A telescopic drive component 606 is fixed to the lower end of one side of the second gel bath 6. This telescopic drive component 606 can be a cylinder or a screw jack. A connecting frame 607 is connected to the end of the telescopic drive component 606 that extends into the second gel bath 6. The connecting frame 607 is connected to the lower end of the fork-type telescopic adjustment frame 603. Finally, a sliding column 608 is connected to the lower end of the other side of the fork-type telescopic adjustment frame 603, and transverse sliding grooves 609 that interact with the sliding column 608 are provided on the front and rear inner walls of the second gel bath 6. When the casting traction speed changes, the control system can adjust the fork-type telescopic adjustment frame 603 by controlling the extension or retraction of the telescopic drive component 606, thereby adjusting the traction travel distance of the casting in the non-solvent or non-solvent mixture during traction, so that the amount of solvent and non-solvent exchange in the casting remains the same.

[0055] Reference Appendix Figure 9 The winding device 7 includes a base 701, on which a winding frame 702 is mounted. A suspended winding roller 703 is rotatably connected to the upper end of the winding frame 702. A winding motor (not shown in the figure) is connected to the end of the winding roller 703. A support seat 704 is slidably mounted on the winding frame 702 at the suspended end of the winding roller 703. Finally, the cast sheet drawn from the second gel bath 6 is drawn onto the winding roller 703 for collection.

[0056] Example 2

[0057] Example 2 discloses an improved design of a phase inversion method for preparing polyvinylidene fluoride membranes based on Example 1. The similarities with Example 1 will not be described again. The main feature is that when the cast sheet is in the shape of membrane filaments, multiple membrane filaments will intertwine and become entangled when being wound on the winding roller 703, which cannot guarantee the winding quality.

[0058] Reference Appendix Figure 9 and attached Figure 10 In this embodiment 2, the winding device 7 includes a base 701, a winding frame 702 is provided on the base 701, a winding roller 703 is rotatably connected to the upper end of the winding frame 702, a winding motor is connected to the end of the winding roller 703, and a support seat 704 is slidably provided on the winding frame 702 located at the suspended end of the winding roller 703.

[0059] Meanwhile, a crossbeam 705 parallel to the take-up roller 703 is fixed on the take-up frame 702 located above the take-up roller 703. A U-shaped seat 706 is slidably arranged on the side of the crossbeam 705 facing the second gel bath 6. A guide rod 707 is rotatably arranged in the U-shaped seat 706. Multiple guide wheels 708 are evenly spaced on the guide rod 707. A reciprocating screw 709 is rotatably arranged on the crossbeam 705. The total pitch of the thread groove on the reciprocating screw 709 is equal to the distance between two adjacent guide wheels 708. A screw nut 710 matching the reciprocating screw 709 is provided on the back of the U-shaped seat 706.

[0060] Finally, in order to ensure that the left and right swinging is synchronized during the traction and winding of the film filament and the collection process, this embodiment 2 also has a first pulley 711 connected to the end of the reciprocating screw 709 extending out of the winding frame 702, a second pulley 712 provided at the end of the roller shaft of the winding roller 703 extending out of the winding frame 702, and a transmission belt 713 provided between the first pulley 711 and the second pulley 712.

[0061] In this embodiment 2, when the winding device 7 winds up the cast film filaments, the reciprocating screw 709 rotates synchronously through the action of the transmission belt 713, the first pulley 711, and the second pulley 712. Then, through the action between the reciprocating screw 709 and the screw nut 710, the U-shaped seat 706 can reciprocate along the crossbeam 705, and the distance of the reciprocating movement is equal to the distance between two adjacent guide wheels 708. This allows the cast film filaments to be evenly wound onto the winding roller 703, effectively preventing the cast film filaments from winding and tangling, and improving the collection effect.

[0062] Example 3

[0063] Example 3 discloses a process for preparing polyvinylidene fluoride membranes using the phase inversion method described in Example 1 or Example 2, which includes the following steps:

[0064] Step 1: Input the control molding in advance into the control system, and control the specific extension and retraction amount of the telescopic drive component 606 according to the speed of the speed measuring roller 502 fed back by the sensor.

[0065] Step 2: Add polyvinylidene fluoride and film-forming additives together into a stirring and dissolving tank 1. The film-forming additives can be high molecular weight additives (such as polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol) and low molecular weight additives (such as surfactants, diethylene glycol dimethyl ether, inorganic salts, propionic acid, alcohols). Stir for 60 minutes to dissolve and obtain a casting solution. Then transfer the casting solution to a spinning tank 2.

[0066] Step 3: Simultaneously start the mechanical stirring defoaming mechanism 201 and the vibration defoaming mechanism 202, so that the casting liquid is defoamed for 30 minutes under the action of the two. After the defoaming is completed, the casting liquid and the core liquid in the core liquid tank 3 are simultaneously introduced into the spinneret 4 according to the set ratio.

[0067] Step 4: The cast film filaments ejected from the spinneret 4 will first solidify in the first gel bath 5, and then enter the second gel bath 6 and be immersed in a non-solvent or non-solvent mixture, so that the solvent and non-solvent in the cast film will exchange rapidly, resulting in phase separation and forming the final product. The finished product is then wound and collected on the take-up roller.

[0068] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An apparatus for preparing polyvinylidene fluoride (PVDF) membranes by a phase inversion method, comprising a stirring and dissolving tank (1), a spinning tank (2), a core liquid tank (3), a spinneret (4), a first gel bath (5), a second gel bath (6), a winding device (7), and a control system, characterized in that, The stirring and dissolving tank (1) and the spinning tank (2) are connected by a first conveying assembly, the spinning tank (2) and the spinneret (4) are connected by a second conveying assembly, and the core liquid tank (3) and the spinneret (4) are connected by a third conveying assembly. The spinning tank (2) is equipped with a mechanical stirring defoaming mechanism (201) inside, and a vibration defoaming mechanism (202) is provided at the lower end of the spinning tank (2). The mechanical stirring defoaming mechanism (201) includes a first motor (2011) located at the top of the spinning tank (2). The lower end of the first motor (2011) is connected to a defoaming rotating shaft (2012) extending into the spinning tank (2). The lower end of the defoaming rotating shaft (2012) is provided with a connecting plate (2013). A plurality of liquid-dispensing plates (2014) are evenly connected to the spinning tank (2). Each of the liquid-dispensing plates (2014) has a row of defoaming rods (2015) at both the upper and lower ends. The vibration defoaming mechanism (202) includes a plurality of strips (2021) evenly fixed on the bottom wall of the spinning tank (2). Each of the strips (2021) is connected to a defoaming spring (2022). The lower end of the outer wall of the spinning tank (2) is provided with a pneumatic vibrator (2023) aligned with each strip (2021). The spinneret (4) is fixedly installed on the upper left side of the first gel bath (5). Several guide rollers (501) are installed in the first gel bath (5). A speed measuring roller (502) is installed on the upper right side of the first gel bath (5), and a sensor is installed at one end of the speed measuring roller (502). Feed rollers (601) and discharge rollers (602) are respectively installed on the upper left and right sides of the second gel bath (6). A horizontally arranged fork-type telescopic adjustment frame (603) is installed inside the second gel bath (6). Four leaching rollers (604) are installed at the upper end of the fork-type telescopic adjustment frame (603), and four leaching rollers (604) are installed at the lower end. The second gel bath (6) is provided with three impregnation rollers (605) and four leaching rollers (604) and three impregnation rollers (605) are staggered. A telescopic drive (606) is fixed to the lower end of one side of the second gel bath (6). The end of the telescopic drive (606) that extends into the second gel bath (6) is connected to a connecting frame (607). The connecting frame (607) is connected to the lower end of a fork-type telescopic adjustment frame (603). A sliding column (608) is connected to the lower end of the other side of the fork-type telescopic adjustment frame (603). A transverse sliding groove (609) that interacts with the sliding column (608) is provided on the front and rear inner walls of the second gel bath (6). The cross-sectional shape of the liquid-dispensing plate (2014) is a vertically arranged V-shape, and the shape of the defoaming rod (2015) is U-shaped and is fixedly connected to the upper or lower end of the liquid-dispensing plate (2014). The strip (2021) is in an arc shape that fits against the bottom wall of the spinning tank (2), and the movable end of the defoaming spring (2022) is connected to a defoaming needle end (2024) extending toward the central axis of the spinning tank (2).

2. The apparatus for preparing polyvinylidene fluoride membrane by phase inversion method according to claim 1, characterized in that, The winding device (7) includes a base (701), on which a winding frame (702) is provided. A winding roller (703) is rotatably connected to the upper end of the winding frame (702), and a winding motor is connected to the end of the winding roller (703). A support seat (704) is slidably provided on the winding frame (702) located at the suspended end of the winding roller (703).

3. The apparatus for preparing polyvinylidene fluoride membrane by phase inversion method according to claim 2, characterized in that, A beam (705) parallel to the take-up roller (703) is fixed on a take-up frame (702) located above the take-up roller (703). A U-shaped seat (706) is slidably arranged on the side of the beam (705) facing the second gel bath (6). A guide rod (707) is rotatably arranged in the U-shaped seat (706). Multiple guide wheels (708) are evenly spaced on the guide rod (707). A reciprocating screw (709) is rotatably arranged on the beam (705). The total pitch of the thread groove on the reciprocating screw (709) is equal to the distance between two adjacent guide wheels (708). A screw nut (710) matching the reciprocating screw (709) is provided on the back of the U-shaped seat (706).

4. The apparatus for preparing polyvinylidene fluoride membrane by phase inversion method according to claim 3, characterized in that, The end of the reciprocating screw (709) extending out of the winding frame (702) is connected to a first pulley (711), and the end of the winding roller (703) extending out of the winding frame (702) is provided with a second pulley (712). A transmission belt (713) is provided between the first pulley (711) and the second pulley (712).

5. The apparatus for preparing polyvinylidene fluoride membrane by phase inversion method according to claim 1, characterized in that, The upper end of the stirring and dissolving tank (1) is provided with a second motor (101), the motor shaft of the second motor (101) is connected to a stirring shaft (102) that extends into the stirring and dissolving tank (1), the upper end of the stirring shaft (102) is connected to a plurality of stirring rods (103), and the lower end is connected to a scraper (104) that fits against the inner wall of the stirring and dissolving tank (1). The upper end of the stirring and dissolving tank (1) is provided with a solvent inlet pipe (105) and a material inlet pipe (106).

6. The apparatus for preparing polyvinylidene fluoride membrane by phase inversion method according to claim 1, characterized in that, The first conveying assembly, the second conveying assembly and the third conveying assembly all include a conveying pipe (8). The conveying pipe (8) in the second conveying assembly and the third conveying assembly are equipped with a metering pump (9). The conveying pipe (8) in the first conveying assembly is equipped with a material pump (10).

7. The apparatus for preparing polyvinylidene fluoride membrane by phase inversion method according to claim 6, characterized in that, A filter is also provided on the conveying pipe (8) in the second conveying assembly.

8. A process for preparing polyvinylidene fluoride membranes by phase inversion using the equipment described in any one of claims 1-7, characterized in that, Includes the following steps: S1: Input the control molding in advance in the control system, and control the specific extension amount of the telescopic drive (606) according to the speed of the speed measuring roller (502) fed back by the sensor; S2: Add polyvinylidene fluoride and film-forming additives together into a stirring and dissolving tank (1), stir and dissolve, and then transfer the casting solution to a spinning tank (2); S3: Start the mechanical stirring defoaming mechanism (201) and the vibration defoaming mechanism (202) to fully defoam the casting liquid in the spinning tank (2). After defoaming, the casting liquid and core liquid are simultaneously introduced into the spinneret (4) according to the set ratio. S4: The cast film filaments ejected from the spinneret (4) are first solidified in the first gel bath (5), and then enter the second gel bath (6) and are immersed in a non-solvent or non-solvent mixture, so that the solvent and non-solvent in the cast film are rapidly exchanged, resulting in phase separation to form the final product, and then the finished product is wound and collected.

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