An encapsulated ultrasonic transducer and an extraction method for a wet porous membrane

Abstract

The application provides a kind of encapsulated ultrasonic transducer and a kind of wet porous membrane extraction method, belong to lithium ion battery membrane preparation technical field.The encapsulated ultrasonic transducer provided by the application adopts stainless steel shell and flange to form airtight space, realizes the encapsulation of the outside of the rear end and front cover plate of half-wavelength sandwich type piezoelectric transducer, ensures that each ultrasonic transducer can independently act on extraction liquid, directly contacts and couples with extraction liquid through the setting of amplitude lever probe, the vibration transmission path is short, the energy utilization rate is higher, the sound field distribution is more uniform, and the cavitation effect is stronger.The amplitude lever probe can form a concentrated and stable excitation surface, can form a controllable strong ultrasonic field on the surface of the base film, avoid the problems of sound field blind area, local overheating or uneven cavitation easily occurred in the built-in ultrasonic transducer, and further improve the extraction efficiency of the membrane.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery separator preparation technology, and in particular to an extraction method for encapsulating an ultrasonic transducer and a wet porous separator. Background Technology

[0002] With the development of new energy vehicles and energy storage, the demand for lithium-ion batteries is increasing. As an important component of lithium-ion batteries, the demand and production capacity of porous separators are also showing a continuous growth trend. Currently, separators are mainly prepared through wet processes. The preparation process mainly involves mixing polyolefin resin, white oil, and antioxidants into a uniform slurry, forming a thin film on a substrate through casting or coating, and then stretching, extracting, shaping, and slitting to obtain the final product. Among these steps, extraction is the key process in wet separator preparation, achieving microporous structure formation, removing processing aids, and ensuring the ion conductivity and electrolyte wettability of the separator. It directly determines the separator's porosity, pore size structure, and final electrochemical performance.

[0003] An ultrasonic transducer is a device that converts electromagnetic energy into mechanical energy (sound energy) and electrical energy into high-frequency (typically 20-100kHz) mechanical vibration, which can be used to assist extraction. A common sandwich-type ultrasonic transducer mainly consists of a piezoelectric ceramic plate, electrodes, a front cover plate, a rear cover plate, and pre-tightening bolts. Its basic principle is to introduce ultrasonic waves into a liquid or solution, using the mechanical vibration and cavitation effect generated by the sound waves to accelerate the mass transfer process between the target substance and the solvent, thereby significantly improving extraction efficiency. To ensure the isolation of the ultrasonic transducer from the liquid, multiple ultrasonic transducers are usually evenly attached to the inner surface of a sealed steel plate, which is then placed inside the extraction solution. When the ultrasonic transmitting device is working, the internal ultrasonic transducers emit ultrasonic waves, causing cavitation effects in the extraction solution around the steel plate, increasing substance diffusion and improving the extraction efficiency of substances in the solution. However, there are some problems with the setting of this ultrasonic transducer, which will reduce the extraction efficiency and increase the amount of extractant used: (1) Multiple ultrasonic transducers emit sound waves with the same frequency and phase on the same plane at the same time. The solvent will also form reflected sound waves. After the sound waves are superimposed, a fixed standing wave field will be formed in the liquid. The sound intensity in the antinode is extremely high and the cavitation is strong; while the sound intensity in the node is almost zero and there is no cavitation; (2) There are individual differences and coupling differences between multiple ultrasonic transducer array elements, which will cause their actual frequencies to differ. However, since all ultrasonic transducers are fixed on the same axis, the system will track the overall average resonance point, making it difficult for the ultrasonic transducers to work in the best state. The ultrasonic transducers with lower actual frequencies or those that have malfunctioned and stopped will become the load of the normally working ultrasonic transducers, greatly reducing the electroacoustic conversion efficiency; (3) In the steel plate structure, the sound waves will not only be transmitted vertically into the liquid, but will also propagate laterally along the plane of the steel plate (Lamb wave). The waves emitted by adjacent ultrasonic transducers will interfere with each other and cancel each other in the steel plate. A large amount of energy is difficult to propagate into the liquid, but is converted into the mechanical internal energy of the steel plate, generating heat. Summary of the Invention

[0004] The purpose of this invention is to provide an encapsulated ultrasonic transducer and an extraction method for a wet porous membrane. The encapsulated ultrasonic transducer provided by this invention is used for the extraction of wet porous membranes, resulting in better cavitation and higher extraction efficiency.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: An encapsulated ultrasonic transducer includes a stainless steel housing and a half-wavelength sandwich piezoelectric transducer; The front end of the half-wavelength sandwich piezoelectric transducer includes a front cover plate 5, a flange 6, and an amplitude transformer probe 9 arranged sequentially; the front cover plate 5, the flange (6), and the amplitude transformer probe (9) are an integrated structural component; The stainless steel shell is a cylindrical shell with one end open; the stainless steel shell is sleeved on the rear end of the half-wavelength sandwich piezoelectric transducer and the outside of the front cover plate 5, and is fixed to the flange 6 to form a sealed structure.

[0006] Preferably, the open end of the stainless steel housing and the flange 6 are provided with matching threaded holes 8; the stainless steel housing and the flange 6 are fastened together by bolts passing through the threaded holes 8.

[0007] Preferably, the contact surface between the open end and the flange 6 is provided with a sealing groove 7.

[0008] Preferably, the sealing groove 7 is filled with a sealing ring; the sealing ring includes a perfluoroether rubber or a polytetrafluoroethylene-coated fluororubber O-ring.

[0009] Preferably, the flange 6 is disposed at the node of the half-wavelength sandwich piezoelectric transducer.

[0010] This invention also provides an extraction method using a wet porous membrane, comprising the following steps: The porous membrane base film after casting and stretching is subjected to a first extraction, a second extraction, a third extraction, a fourth extraction, a fifth extraction, and a sixth extraction in sequence; the extracting solution for the first, second, third, fourth, fifth, and sixth extractions is a dichloromethane-white oil solution; the mass fraction of dichloromethane in the first, second, third, fourth, fifth, and sixth extractions is 90%, 95%, 98%, 99.5%, 99.8%, and 100%, respectively; the extraction time for the first, second, third, fourth, fifth, and sixth extractions is the same, which is 8-10 s; the fifth extraction is performed under the condition of ultrasonication of the encapsulated ultrasonic transducer as described in any one of claims 1 to 7.

[0011] Preferably, the fifth extraction is carried out in an extraction tank, and the top of the stainless steel shell of the encapsulated ultrasonic transducer is fixed in the extraction tank. The vertical distance between the radiation surface of the encapsulated ultrasonic transducer and the center of the porous diaphragm base film is 48~52mm.

[0012] The present invention provides an encapsulated ultrasonic transducer, comprising a stainless steel housing and a half-wavelength sandwich piezoelectric transducer; the front end of the half-wavelength sandwich piezoelectric transducer includes a front cover plate, a flange, and an amplitude transformer probe arranged sequentially; the front cover plate (5), the flange (6), and the amplitude transformer probe (9) are integrated structural components; the stainless steel housing is a cylindrical shell with one end open; the stainless steel housing is sleeved on the rear end of the half-wavelength sandwich piezoelectric transducer and the outside of the front cover plate, and is fixed with the flange to form a sealed structure. The encapsulated ultrasonic transducer provided by this invention uses a stainless steel shell and flange to form a sealed space, achieving encapsulation of the rear end of the half-wavelength sandwich piezoelectric transducer and the outer side of the front cover plate. This ensures that each ultrasonic transducer can act independently on the extraction liquid. By setting an amplitude transformer probe to directly contact and couple with the extraction liquid, the vibration transmission path is short, avoiding ultrasonic attenuation caused by the shell and cavity obstruction when the ultrasonic transducer is built-in. This results in higher energy utilization, a more uniform sound field distribution, and a stronger cavitation effect. It avoids the problems of uneven cavitation and low electroacoustic conversion efficiency caused by multiple ultrasonic transducers being sealed and fixed on a central axis simultaneously. Furthermore, the amplitude transformer probe 9 can form a concentrated and stable excitation surface, enabling the formation of a controllable strong ultrasonic field on the base membrane surface. This avoids the sound field blind zone, local overheating, or uneven cavitation problems that are common with built-in ultrasonic transducers, further improving the extraction efficiency of the diaphragm. Example results show that when the ultrasonic transducer provided by this invention is used for the extraction of wet porous diaphragms, after being ultrasonically treated with the fifth extraction liquid for 10 seconds, the oil content of the diaphragm can be as low as 0.77%. Attached Figure Description

[0013] Figure 1 This is a structural diagram of a half-wavelength sandwich piezoelectric transducer according to an embodiment of the present invention; wherein, 1 is a pre-tightening bolt, 2 is the transducer rear cover plate, 3 is the piezoelectric ceramic, 4 is the electrode, 5 is the front cover plate, 6 is the flange, 7 is the sealing groove, 8 is the threaded hole, and 9 is the amplitude transformer probe. Figure 2 The diagram shows the change in cavitation radius of the encapsulated ultrasonic transducer of this invention under different ultrasonic frequencies in dichloromethane extractant. Figure 3 The diagram shows the change in cavitation radius of the encapsulated ultrasonic transducer of this invention under ultrasonic action at different sound pressure amplitudes in dichloromethane extractant. Figure 4 Experimental test diagrams showing the extraction of porous membrane substrates using the encapsulated ultrasonic transducer of this invention under different dichloromethane extractants, frequencies, power levels, and lift-off distances: Figure 5 This is a schematic diagram of the fifth extraction process using a wet porous membrane according to an embodiment of the present invention; Figure 6 The graph shows the content of white oil in the porous membrane base membrane after extraction in each extraction tank in Example 2 and Comparative Examples 1-5 of the present invention; Figure 7 The graph shows the content of white oil in the porous membrane base membrane after extraction in each extraction tank in Example 2 and Comparative Examples 5-10 of the present invention. Figure 8 The graph shows the content of white oil in the porous membrane base membrane after extraction in each extraction tank in Example 3 and Comparative Examples 11-15 of the present invention. Figure 9 The graph shows the content of white oil in the porous membrane base membrane after extraction in each extraction tank in Example 4 and Comparative Examples 16-19 of the present invention. Figure 10 This is a graph showing the content of white oil in the porous membrane base membrane after extraction in each extraction tank of Comparative Examples 20-23 of the present invention. Detailed Implementation

[0014] This invention provides an encapsulated ultrasonic transducer, comprising a stainless steel housing and a half-wavelength sandwich piezoelectric transducer; The front end of the half-wavelength sandwich piezoelectric transducer includes a front cover plate 5, a flange 6, and an amplitude transformer probe 9 arranged sequentially; the front cover plate (5), flange (6), and amplitude transformer probe (9) are integrated structural components; The stainless steel shell is a cylindrical shell with one end open; the stainless steel shell is sleeved on the rear end of the half-wavelength sandwich piezoelectric transducer and the outside of the front cover plate 5, and is fixed to the flange 6 to form a sealed structure.

[0015] The encapsulated ultrasonic transducer provided by this invention includes a stainless steel housing, which is a cylindrical shell open at one end. This invention uses a stainless steel housing to encapsulate the front end of a half-wavelength sandwich piezoelectric transducer, enabling the half-wavelength sandwich piezoelectric transducer to be used long-term in a liquid environment. It allows the unencapsulated amplitude transformer probe to directly contact and couple with the extraction liquid, resulting in a shorter vibration transmission path. This avoids ultrasonic attenuation caused by the housing and cavity obstruction when the ultrasonic transducer is fully integrated, leading to higher energy utilization, a more uniform sound field distribution, and stronger cavitation effect.

[0016] In one embodiment of the present invention, the open end of the stainless steel housing is provided with a threaded hole 8. The present invention defines the threaded hole to allow the open end of the stainless steel housing to be fastened to the flange with bolts. The present invention does not have a special limitation on the specifications of the threaded hole 8; any threaded hole specification well known in the art can be used to fix the stainless steel housing and the flange 6 to form a sealing structure.

[0017] In one embodiment of the present invention, a sealing groove 7 is provided on the contact surface between the open end and the flange. The sealing groove 7 consists of a groove formed on the flange and a corresponding groove formed on the flange; the sealing groove 7 is filled with a sealing ring; the sealing ring may include perfluoroether rubber or polytetrafluoroethylene-coated fluororubber O-rings.

[0018] In one embodiment of the present invention, a circular hole may be formed at the sealing end of the stainless steel housing. The present invention does not have a special limitation on the circular hole; any circular hole specification known in the art can be used to lead out the wires of the half-wavelength sandwich piezoelectric transducer and connect them to the excitation power supply. In one embodiment of the present invention, the wires of the half-wavelength sandwich piezoelectric transducer are led out and then sealed. The present invention does not have a special limitation on the sealing; any sealing method known in the art can be used to seal the half-wavelength sandwich piezoelectric transducer after the wires are led out. The present invention does not have a special limitation on the specifications of the stainless steel housing; any stainless steel housing specification known in the art can be used to fit the front end of the half-wavelength sandwich piezoelectric transducer.

[0019] The encapsulated ultrasonic transducer provided by this invention also includes a half-wavelength sandwich piezoelectric transducer. This invention uses a half-wavelength sandwich piezoelectric transducer to assist extraction, thereby improving the extraction efficiency of the porous membrane substrate.

[0020] As one embodiment of the present invention, the half-wavelength sandwich piezoelectric transducer provided by the present invention includes a rear end and a front end; the present invention does not have a special limitation on the rear end of the half-wavelength sandwich piezoelectric transducer, and a rear end of a half-wavelength sandwich piezoelectric transducer well known in the art can be used. In the embodiments of the present invention, such as Figure 1 As shown, the rear end may include a pre-tightening bolt 1, a transducer rear cover plate 2, a piezoelectric ceramic 3, and an electrode 4 arranged sequentially.

[0021] like Figure 1 As shown, the front end of the half-wavelength sandwich piezoelectric transducer provided by the present invention includes a front cover plate 5.

[0022] This invention does not impose a special limitation on the diameter of the front cover plate 5; any diameter suitable for the art can be used. Similarly, this invention does not impose a special limitation on the thickness of the front cover plate 5, as long as the thickness of the front cover plate 5 and the overall thickness of the flange 6 are equal to half the wavelength of the acoustic wave of the half-wavelength sandwich piezoelectric transducer. In one embodiment of this invention, the front cover plate 5 can be made of titanium alloy. In another embodiment of this invention, pre-tightening bolts 1 can be used to sequentially fasten the transducer rear cover plate 2, piezoelectric ceramic 3, electrode 4, and front cover plate 5 together.

[0023] In this invention, the stainless steel housing is fitted over the rear end of the half-wavelength sandwich piezoelectric transducer and the outer side of the front cover plate 5. In one embodiment, a gap may be left between the stainless steel housing and the rear end of the half-wavelength sandwich piezoelectric transducer. This invention does not impose any specific limitations on this gap; using a gap distance well-known in the art can avoid the housing constraining and damping the transducer's vibration, thus ensuring resonant stability.

[0024] like Figure 1 As shown, the front end of the half-wavelength sandwich piezoelectric transducer provided by the present invention also includes a flange 6 connected to the front cover plate 5; the front cover plate 5 and the flange 6 are an integrated structural component.

[0025] In one embodiment of the present invention, the flange 6 can be disposed at the node of the half-wavelength sandwich piezoelectric transducer. In another embodiment, the position of the flange 6 can be determined using finite element simulation analysis. The position where the displacement is 0 in the half-wavelength sandwich piezoelectric transducer model is the node position. The present invention does not impose special limitations on the thickness and diameter of the flange 6, as long as the thickness and diameter of the flange 6 are such that the flange is located at the transducer vibration node. In another embodiment, the flange 6 can be provided with threaded holes 8, which match the threaded holes 8 on the open end of the stainless steel shell. The present invention does not impose special limitations on the specifications, location, distribution, and number of the threaded holes 8. Using the well-known sealing groove 7 and threaded hole 8 specifications, the stainless steel shell and flange 6 can be fixed together to form a sealing structure.

[0026] In one embodiment of the present invention, a groove is provided on the flange 6, and the groove on the flange 6 is correspondingly provided with the groove on the open end of the stainless steel shell to form a sealing groove 7.

[0027] In this invention, the stainless steel housing and the flange 6 are fixed together to form a sealed structure. This fixing can be achieved by using bolts to fasten the stainless steel housing and the flange 6 through the threaded holes 8. This invention achieves encapsulation of the rear end of the half-wavelength sandwich piezoelectric transducer and the outer side of the front cover plate 5 by defining a sealed structure between the stainless steel housing and the flange 6.

[0028] like Figure 1 As shown, the front end of the half-wavelength sandwich piezoelectric transducer provided by the present invention also includes an amplitude rod probe 9 disposed below the flange 6. The front cover plate (5), flange (6) and amplitude rod probe (9) are an integrated structural component.

[0029] In one embodiment of the present invention, the amplitude transformer probe 9 can be a frustum structure. In another embodiment of the present invention, the diameter of the amplitude transformer probe can be determined using an impedance matching method, specifically: according to... Calculate the load impedance (Taking dichloromethane as the extractant as an example), where and These are the density and speed of sound of dichloromethane, respectively. The area of ​​the probe's end face that extends into the liquid is given. Only the real part of the radiation impedance is calculated here, while the imaginary mass load is ignored. according to = , calculate ,in, and These are the major circle diameter and minor circle diameter of the amplitude transformer probe, respectively. Where is the area of ​​the front cover plate; G is the theoretical magnification factor; the setting of G can be calculated based on the amplitude of the half-wavelength sandwich piezoelectric transducer itself and the target amplitude, and the target amplitude can be set to 10~30μm; the small circle diameter of the amplitude transformer probe can be set to the required diameter, thus obtaining... In one embodiment of the present invention, the diameter change of the amplitude transformer probe 9 can be a circular arc transition.

[0030] The encapsulated ultrasonic transducer provided by this invention uses a stainless steel shell and flange to form a sealed space, achieving encapsulation of the rear end of the half-wavelength sandwich piezoelectric transducer and the outer side of the front cover plate. This ensures that each ultrasonic transducer can act independently on the extraction liquid. By setting an amplitude transformer probe to directly contact and couple with the extraction liquid, the vibration transmission path is short, avoiding ultrasonic attenuation caused by the shell and cavity obstruction when the ultrasonic transducer is built-in. This results in higher energy utilization, more uniform sound field distribution, and stronger cavitation effect. It avoids the problems of uneven cavitation and low electroacoustic conversion efficiency caused by multiple ultrasonic transducers being sealed and fixed on a central axis at the same time. Moreover, the amplitude transformer probe can form a concentrated and stable excitation surface, which can form a controllable strong ultrasonic field on the base membrane surface, avoiding the sound field blind zone, local overheating, or uneven cavitation problems that are prone to occur in built-in ultrasonic transducers, further improving the extraction efficiency of the diaphragm.

[0031] This invention also provides an extraction method using a wet porous membrane, comprising the following steps: The porous membrane substrate, after casting and stretching, was subjected to a first extraction, a second extraction, a third extraction, a fourth extraction, a fifth extraction, and a sixth extraction in sequence; the extracts for the first, second, third, fourth, fifth, and sixth extractions were all dichloromethane-white oil solutions; the mass fractions of dichloromethane in the first, second, third, fourth, fifth, and sixth extractions were 90%, 95%, 98%, 99.5%, 99.8%, and 100%, respectively; as one embodiment of the present invention, the extracts for the first, second, third, fourth, fifth, and sixth extractions could be... The extracts for the first, second, third, fourth, fifth, and sixth extractions are all dichloromethane-white oil solutions, which are ensured by supplementing with additional dichloromethane. The mass fractions of dichloromethane in the first, second, third, fourth, fifth, and sixth extractions are 90%, 95%, 98%, 99.5%, 99.8%, and 100%, respectively. The extraction times for the first, second, third, fourth, fifth, and sixth extractions are the same, ranging from 8 to 10 seconds. The fifth extraction is performed under the condition of ultrasonication using the encapsulated ultrasonic transducer as described in any one of claims 1 to 7.

[0032] In one embodiment of the present invention, the porous membrane base film after casting and stretching is fixed before extraction. The present invention does not impose any particular limitation on the fixing process; any fixing method well-known in the art can be used to fix the porous membrane base film to ensure that it remains flat and stretched during the extraction process.

[0033] In this invention, the extractants for the first, second, third, fourth, fifth, and sixth extractions are all dichloromethane-white oil solutions. This invention, by limiting the extractant to a dichloromethane-white oil solution, leverages the excellent solubility of white oil, allowing it to penetrate the microporous structure of the porous membrane and fully dissolve and remove the adsorbed and retained white oil from the pores, thus achieving efficient removal and cleaning of white oil from the membrane.

[0034] In this invention, the mass fraction of dichloromethane in the dichloromethane-white oil solution during the first extraction, second extraction, third extraction, fourth extraction, fifth extraction and sixth extraction is 90%, 95%, 98%, 99.5%, 99.8% and 100% respectively.

[0035] In this invention, the extraction times for the first, second, third, fourth, fifth, and sixth extractions are the same; each extraction takes 8-10 seconds. This invention ensures that the porous membrane base membrane receives sufficient mass transfer time at each extraction stage by limiting the extraction times to the same duration, thus ensuring that the dissolution and diffusion of white oil are fully carried out in each extraction. Furthermore, it facilitates process control and continuous production. The consistent extraction time for each stage facilitates synchronous operation and uniform cycle time, simplifies process flow control, and promotes automated, continuous membrane extraction production, thereby improving the stability and operability of the equipment.

[0036] In one embodiment of the present invention, the porous membrane base film can be sequentially subjected to a first extraction, a second extraction, a third extraction, a fourth extraction, a fifth extraction, and a sixth extraction via rollers. The present invention does not impose any particular limitation on the arrangement of the rollers; any roller arrangement known in the art can be used. The present invention also does not impose any particular limitation on the rollers; any rollers known in the art capable of transporting the porous membrane base film can be used.

[0037] In this invention, the first, second, third, fourth, fifth, and sixth extractions are each performed in an independent extraction tank. The fifth extraction tank contains the encapsulated ultrasonic transducer described in the above-mentioned technical solution. Figure 5 As shown, the top of the stainless steel shell of the encapsulated ultrasonic transducer is fixed to the extraction tank, and the vertical distance between the radiating surface of the encapsulated ultrasonic transducer and the center of the porous diaphragm base membrane is 48-52 mm. This invention ensures the ultrasonic transducer's ultrasonic-assisted function is maximized and extraction efficiency is improved by limiting the installation of the encapsulated ultrasonic transducer in the fifth extraction tank and limiting the vertical distance between the excitation surface of the encapsulated ultrasonic transducer and the center of the porous diaphragm base membrane. This invention does not impose any special limitations on the installation of the encapsulated ultrasonic transducer; it can be installed in the desired position using a method well-known in the art. This invention does not impose any special limitations on the number of encapsulated ultrasonic transducers installed; it can be installed using a number well-known in the art to ensure that the ultrasound is directly transmitted to the extraction liquid and that multiple devices can vibrate independently.

[0038] In one embodiment of the present invention, the frequency of the encapsulated ultrasonic transducer can be 20 kHz; the power of the encapsulated ultrasonic transducer can be 60 kHz. The present invention, by limiting the frequency of the encapsulated ultrasonic transducer to ensure the generation of a stable and moderate cavitation effect and microjets, enhances the penetration of dichloromethane into the membrane pores, rapidly extracts and removes white oil from the porous base membrane, and improves extraction efficiency.

[0039] In one embodiment of the present invention, the frequency and power of the encapsulated ultrasonic transducer can be determined by solving the equations of motion of ultrasonic cavitation bubbles, as shown below. Figures 2-3 As shown. Figure 2 The graph shows the change of cavitation radius of the half-wavelength sandwich piezoelectric transducer of the present invention under different ultrasonic frequencies in dichloromethane extractant. As can be seen from the graph, the cavitation radius is the largest when the ultrasonic frequency is 20kHz. Therefore, the ultrasonic frequency can be set to 20kHz. Figure 3 The graph shows the change in cavitation radius of the half-wavelength sandwich piezoelectric transducer of the present invention under ultrasonic action at different sound pressure amplitudes (i.e., power) in dichloromethane extractant. As can be seen from the graph, the cavitation radius is the largest when the ultrasonic power is 60W, so the ultrasonic power can be set to 60W.

[0040] As one embodiment of the present invention, the fifth extraction process flow chart of the wet porous membrane is as follows: Figure 5 As shown, firstly, the porous membrane base film is cut and fixed. Then, the frequency and power of the half-wavelength sandwich piezoelectric transducer are controlled to be 20kHz and 60W, respectively. The half-wavelength sandwich piezoelectric transducer is then encapsulated and installed in the fifth extraction tank, with a vertical distance of 50mm from the center of the porous membrane base film. The ultrasonic time during the extraction process is limited to 8-10s. In one embodiment of the invention, the frequency, power, and vertical distance from the center of the porous membrane base film of the half-wavelength sandwich piezoelectric transducer can be determined through simulation experiments. Specifically, the porous membrane base film can be extracted with the half-wavelength sandwich piezoelectric transducer in extraction solutions of different frequencies, different powers, and different concentrations. The results are shown below. Figure 4 As shown in the figure, by analyzing the oil content of the porous membrane base membrane after extraction with a half-wavelength sandwich piezoelectric transducer in extractants of different frequencies, powers, and concentrations, the frequency and power of the half-wavelength sandwich piezoelectric transducer were determined to be 20kHz and 60W, respectively. Considering the influence of the half-wavelength sandwich piezoelectric transducer on the porous membrane base membrane, the vertical distance between the transducer and the center of the porous membrane base membrane was determined to be 50mm.

[0041] This invention installs a packaged ultrasonic transducer in the extraction tank of the fifth extraction process and limits the vertical distance between the excitation surface of the packaged ultrasonic transducer and the porous membrane base film, as well as the ultrasonic frequency, ultrasonic power, and ultrasonic time. This allows the packaged ultrasonic transducer to form a concentrated and stable excitation surface during the extraction process, thereby creating a controllable strong ultrasonic field on the base film surface and improving extraction efficiency.

[0042] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0043] Example 1 An encapsulated ultrasonic transducer, comprising a stainless steel housing and a half-wavelength sandwich piezoelectric transducer; like Figure 1 As shown, the front end of the half-wavelength sandwich piezoelectric transducer includes a front cover plate 5, a flange 6, and an amplitude transformer probe 9 arranged sequentially; the front cover plate 5, the flange 6, and the amplitude transformer probe 9 are integrated structural components. The stainless steel shell is a cylindrical shell with one end open; the stainless steel shell is sleeved on the rear end of the half-wavelength sandwich piezoelectric transducer and the outside of the front cover plate 5, and is fixed with the flange 6 to form a sealed structure. like Figure 1 As shown, the rear end of the half-wavelength sandwich piezoelectric transducer is composed of a pre-tightening bolt 1, a transducer rear cover plate 2, a piezoelectric ceramic 3, and an electrode 4; the pre-tightening bolt 1 sequentially fastens the transducer rear cover plate 2, the piezoelectric ceramic 3, the electrode 4, and the front cover plate 5 into one unit; The stainless steel housing has a threaded hole 8 at its open end, and a sealing groove 7 is provided on the contact surface between the open end and the flange. The flange 6 may have a threaded hole 8, which matches the threaded hole 8 at the open end of the stainless steel housing. A groove is formed on the flange 6, and this groove corresponds to the groove at the open end of the stainless steel housing to form the sealing groove 7. The stainless steel housing and the flange 6 are fastened together with bolts through the threaded hole 8. A sealing ring is filled in the sealing groove 7; the sealing ring is made of perfluoroether rubber. The flange 6 has a thickness of 5mm; the flange 3 has a diameter of 100mm; the amplitude transformer probe 4 has a frustum structure that is wider at the top and narrower at the bottom; the large circle diameter of the amplitude transformer probe 9 is 50mm; the small circle diameter of the amplitude transformer probe 9 is 20mm; the height of the amplitude transformer probe 9 is the difference between half the wavelength and the distance from the front cover plate node to the top; the sealing groove 7 is a semi-cylindrical groove with a diameter of 2mm; the sealing groove 7 is located at a diameter of 90mm on the circular surface of the flange; the threaded hole 8 is M4; the threaded hole 8 is located at a diameter of 70mm on the circular surface of the flange.

[0044] Example 2 The 100mm×100mm porous membrane substrate, after casting and stretching, was sequentially passed through six extraction tanks at a speed of 1.67m / s using a roller. The extraction solution was a dichloromethane-white oil solution. The mass fractions of dichloromethane in the dichloromethane-white oil solution in the six extraction tanks were 90%, 95%, 98%, 99.5%, 99.8%, and 100%, respectively. The extraction time in each extraction tank was 10s.

[0045] One encapsulated ultrasonic transducer as described in Example 1 is suspended in the extractant of the fifth extraction tank. The wires are led out of the extraction tank through a sealing structure, which is integrated with the transducer encapsulation structure. The installation position of the encapsulated ultrasonic transducer is such that the vertical distance between the excitation surface of the encapsulated ultrasonic transducer and the center of the porous diaphragm base film is 50 mm. The extraction time for each extraction is 10 s. The encapsulated ultrasonic transducer operates continuously. The frequency of the ultrasound is 20 kHz. The power of the ultrasound is 60 W.

[0046] Example 3 The difference between this embodiment and embodiment 2 is that the roller speed of 1.67 m / s is replaced with 1.85 m / s; the extraction time in each extraction tank is 9 s; the ultrasonic time of the encapsulated ultrasonic transducer is 9 s, and the rest is the same as in embodiment 2.

[0047] Example 4 The difference between this embodiment and embodiment 2 is that the roller speed of 1.67 m / s is replaced with 2.08 m / s; the extraction time in each extraction tank is 8 s; the ultrasonic time of the encapsulated ultrasonic transducer is 8 s, and the rest is the same as in embodiment 2.

[0048] Comparative Example 1 The difference between this comparative example and Example 2 is that the encapsulated ultrasonic transducer described in Example 1 is replaced by the encapsulated ultrasonic transducer described in Example 1 being installed in the extract of the fifth extraction, while the rest is the same as Example 2.

[0049] Comparative Example 2 The difference between this comparative example and Example 2 is that the encapsulated ultrasonic transducer described in Example 1 is replaced by the encapsulated ultrasonic transducer described in Example 1 being installed in the extract of the fifth extraction, while the rest is the same as Example 2.

[0050] Comparative Example 3 The difference between this comparative example and Example 2 is that the encapsulated ultrasonic transducer described in Example 1 is replaced by the encapsulated ultrasonic transducer described in Example 1 being installed in the extract of the fifth extraction, while the rest is the same as Example 2.

[0051] Comparative Example 4 The difference between this comparative example and Example 2 is that the encapsulated ultrasonic transducer described in Example 1 is replaced by the encapsulated ultrasonic transducer described in Example 1 being installed in the extract of the fifth extraction, while the rest is the same as Example 2.

[0052] Comparative Example 5 The difference between this comparative example and Example 2 is that the encapsulated ultrasonic transducer described in Example 1 was not installed; otherwise, it is the same as Example 2.

[0053] Comparative Example 6 The difference between this comparative example and Example 2 is that the ultrasonic time of the encapsulated ultrasonic transducer is 9 seconds, while the rest is the same as in Example 2.

[0054] Comparative Example 7 The difference between this comparative example and Example 2 is that the ultrasonic time of the encapsulated ultrasonic transducer is 8 seconds, while the rest is the same as in Example 2.

[0055] Comparative Example 8 The difference between this comparative example and Example 2 is that the ultrasonic time of the encapsulated ultrasonic transducer is 7 seconds, while the rest is the same as in Example 2.

[0056] Comparative Example 9 The difference between this comparative example and Example 2 is that the ultrasonic time of the encapsulated ultrasonic transducer is 6 seconds, while the rest is the same as in Example 2.

[0057] Comparative Example 10 The difference between this comparative example and Example 2 is that the ultrasonic time of the encapsulated ultrasonic transducer is 5 seconds, while the rest is the same as in Example 2.

[0058] Comparative Example 11 The difference between this comparative example and Example 3 is that the ultrasonic time of the encapsulated ultrasonic transducer is 8 seconds, while the rest is the same as in Example 3.

[0059] Comparative Example 12 The difference between this comparative example and Example 3 is that the ultrasonic time of the encapsulated ultrasonic transducer is 7 seconds, while the rest is the same as in Example 3.

[0060] Comparative Example 13 The difference between this embodiment and embodiment 3 is that the ultrasonic time of the encapsulated ultrasonic transducer is 6 seconds, while the rest is the same as in embodiment 8.

[0061] Comparative Example 14 The difference between this comparative example and Example 3 is that the ultrasonic time of the encapsulated ultrasonic transducer is 5 seconds, while the rest is the same as in Example 3.

[0062] Comparative Example 15 The difference between this comparative example and Example 3 is that the encapsulated ultrasonic transducer described in Example 1 was not installed; otherwise, it is the same as Example 3.

[0063] Comparative Example 16 The difference between this comparative example and Example 4 is that the ultrasonic time of the encapsulated ultrasonic transducer is 7 seconds, while the rest is the same as in Example 4.

[0064] Comparative Example 17 The difference between this comparative example and Example 4 is that the ultrasonic time of the encapsulated ultrasonic transducer is 6 seconds, while the rest is the same as in Example 4.

[0065] Comparative Example 18 The difference between this comparative example and Example 4 is that the ultrasonic time of the encapsulated ultrasonic transducer is 5 seconds, while the rest is the same as in Example 4.

[0066] Comparative Example 19 The difference between this comparative example and Example 4 is that the encapsulated ultrasonic transducer described in Example 1 was not installed; otherwise, it is the same as Example 4.

[0067] Comparative Example 20 The difference between this comparative example and Example 2 is that the roller speed of 1.67 m / s is replaced with 2.38 m / s; the extraction time in each extraction tank is 7 s; the ultrasonic time of the encapsulated ultrasonic transducer is 7 s, and the rest is the same as Example 2.

[0068] Comparative Example 21 The difference between this comparative example and comparative example 20 is that the ultrasonic time of the encapsulated ultrasonic transducer is 6s, while the rest is the same as that of comparative example 20.

[0069] Comparative Example 22 The difference between this comparative example and comparative example 20 is that the ultrasonic time of the encapsulated ultrasonic transducer is 5s, while the rest is the same as that of comparative example 20.

[0070] Comparative Example 23 The difference between this comparative example and comparative example 20 is that the encapsulated ultrasonic transducer described in Example 1 was not installed; otherwise, it is the same as comparative example 20.

[0071] The content of white oil in the porous membrane base membrane after extraction in each extraction tank of Examples 2 and 1-5 was tested using a forced-air drying oven and an analytical balance. The results are as follows: Figure 6As shown in the figure, after the fifth extraction, the oil content of white oil in the porous membrane base membrane of Example 2 of the present invention is 0.18%; while the oil content of white oil in the porous membrane base membranes of Comparative Examples 1-5 after the fifth extraction is 2.86%, 2.73%, 1.55%, and 1.16%, respectively. This indicates that the oil content of white oil in the porous membrane base membrane of Example 2 of the present invention is low after extraction.

[0072] The content of white oil in the porous membrane base membrane after extraction in each extraction tank of Examples 2 and Comparative Examples 5-10 was tested using a forced-air drying oven and an analytical balance. The results are as follows: Figure 7 As shown in the figure, after the fifth extraction in Example 2 of the present invention, the oil content of white oil in the porous membrane base is 0.77%; while in Comparative Examples 5-10, the oil content of white oil in the porous membrane base after the fifth extraction is 2.78%, 1.28%, 1.33%, 1.44%, 2.21%, and 2.57%, respectively. This indicates that, with an oil content ≤1% as the standard, the oil content of white oil in the porous membrane base after the fifth extraction in Example 2 of the present invention is less than 1%, thus the sixth extraction can be omitted, saving extraction time and extractant.

[0073] The content of white oil in the porous membrane base membrane after extraction in each extraction tank of Examples 3 and Comparative Examples 11-15 was tested using a forced-air drying oven and an analytical balance. The results are as follows: Figure 8 As shown in the figure, after the sixth extraction in Example 3 of the present invention, the oil content of white oil in the porous membrane base membrane is 0.8%; while in Comparative Examples 11-15, the oil content of white oil in the porous membrane base membrane after the sixth extraction is 1.03%, 1.04%, 0.97%, 1.35%, and 1.45%, respectively. This indicates that, with an oil content ≤1% as the standard, the porous membrane base membrane of Example 3 of the present invention, after a 9s ultrasonic extraction and a sixth extraction, with a total extraction time of 54s, has an oil content of less than 1% of white oil, thus saving extraction time.

[0074] The content of white oil in the porous membrane base membrane after extraction in each extraction tank of Examples 4 and Comparative Examples 16-19 was tested using a forced-air drying oven and an analytical balance. The results are as follows: Figure 9 As shown in the figure, in Example 4 of the present invention, after the sixth extraction, the oil content of white oil in the porous membrane base membrane was 1%; while in Comparative Examples 16-19, the oil content of white oil in the porous membrane base membrane after the sixth extraction was 1.03%, 1.36%, 1.65%, and 3.27%, respectively. This indicates that, with an oil content ≤1% as the standard, in Example 6 of the present invention, after an ultrasonic time of 8 seconds and a sixth extraction, the oil content of white oil in the porous membrane base membrane was 1% after a total extraction time of 48 seconds, saving extraction time.

[0075] The content of white oil in the porous membrane base membrane after extraction in each extraction cell of Comparative Examples 20-23 was tested using a forced-air drying oven and an analytical balance. The results are as follows: Figure 10 As shown in the figure, the oil content of white oil in the porous membrane base membranes of Comparative Examples 20-23 after the sixth extraction was 1.8%, 2.06%, 1.93%, and 2.5%, respectively. This indicates that an oil content ≤1% is considered acceptable. In Example 6 of this invention, after ultrasonic extraction for 5, 6, and 7 seconds, and a total extraction time of 42 seconds, the oil content of white oil in the porous membrane base membrane was greater than 1%, which does not meet the standard.

[0076] In summary, the encapsulated ultrasonic transducer provided by this invention is used for extraction of wet porous membranes, resulting in better cavitation and higher extraction efficiency.

[0077] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An encapsulated ultrasonic transducer, comprising a stainless steel housing and a half-wavelength sandwich piezoelectric transducer; The front end of the half-wavelength sandwich piezoelectric transducer includes a front cover plate (5), a flange (6), and an amplitude transformer probe (9) arranged sequentially; the front cover plate (5), the flange (6), and the amplitude transformer probe (9) are an integrated structural component; The stainless steel shell is a cylindrical shell with one end open; the stainless steel shell is sleeved on the rear end of the half-wavelength sandwich piezoelectric transducer and the outside of the front cover plate (5), and is fixed with the flange (6) to form a sealed structure.

2. The encapsulated ultrasonic transducer according to claim 1, characterized in that, The stainless steel housing has matching threaded holes (8) on its open end and on the flange (6); the stainless steel housing and the flange (6) are fastened together by bolts passing through the threaded holes (8).

3. The encapsulated ultrasonic transducer according to claim 2, characterized in that, The contact surface between the open end and the flange (6) is provided with a sealing groove (7).

4. The encapsulated ultrasonic transducer according to claim 3, characterized in that, The sealing groove (7) is filled with a sealing ring; the sealing ring includes a perfluoroether rubber or a polytetrafluoroethylene-coated fluororubber O-ring.

5. The encapsulated ultrasonic transducer according to any one of claims 1 to 4, characterized in that, The flange (6) is located at the node of the half-wavelength sandwich piezoelectric transducer.

6. An extraction method using a wet porous membrane, comprising the following steps: The porous membrane base film after casting and stretching is subjected to a first extraction, a second extraction, a third extraction, a fourth extraction, a fifth extraction, and a sixth extraction in sequence; the extracting solution for the first, second, third, fourth, fifth, and sixth extractions is a dichloromethane-white oil solution; the mass fraction of dichloromethane in the first, second, third, fourth, fifth, and sixth extractions is 90%, 95%, 98%, 99.5%, 99.8%, and 100%, respectively; the extraction time for the first, second, third, fourth, fifth, and sixth extractions is the same, which is 8-10 s; the fifth extraction is performed under the condition of ultrasonication of the encapsulated ultrasonic transducer as described in any one of claims 1 to 5.

7. The extraction method according to claim 6, characterized in that, The fifth extraction is carried out in the extraction tank. The top of the stainless steel shell of the encapsulated ultrasonic transducer is fixed in the extraction tank. The vertical distance between the radiation surface of the encapsulated ultrasonic transducer and the center of the porous diaphragm base film is 48~52mm.

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