PTFE bacteria-removing filter membrane, its preparation method and use

Abstract

The application discloses a PTFE bacteria-removing filter membrane and a preparation method and application thereof. The filter membrane comprises a main body, a first outer surface and a second outer surface of the main body are substantially symmetrical, surface nodes and surface fibers for forming a porous structure are included on the outer surfaces of the filter membrane, and the adjacent surface nodes are connected through the surface fibers. The IPA bubble point of the filter membrane is 0.12-0.35 MPa. The thickness of the filter membrane is 30-80 microns. The SEM average width of the surface fibers is 80-350 nm, and the SEM average length of the surface fibers is 0.9-2.5 microns. Under the joint action of the suitable membrane hole size, the suitable membrane thickness size, the suitable membrane structure and the suitable length and the suitable coarse fiber of the surface fibers, the sufficient interception of bacteria is ensured, the ideal bacteria capturing effect is realized, and a large flux is obtained. The filter membrane also has high mechanical strength, can bear high pressure during filtration, has strong stability and long service life. The filter membrane is used for liquid bacteria removal and / or gas bacteria removal, and has a wide application range.

Description

Technical Field

[0001] This invention relates to the field of membrane materials technology, and more specifically to a PTFE antibacterial filter membrane, its preparation method, and its applications. Background Technology

[0002] In the 1960s, 0.45 μm pore size filter membranes were considered "sterilizing" liquid filters and were successfully applied to the sterilization filtration of injectable drugs. These filters were challenge-tested using Serratia marcescens. In a paper published in 1960, Dr. Frances Bowman of the United States observed that "culture media filtered through 0.45 μm filters were sterilized by a certain substance that could..." 4 ~10 6 pcs / cm 2 Repeated contamination by microorganisms that could penetrate the pore size of the filter membrane under challenge levels led to the development of the ASTM F-838 standard. This challenge level became the standard method for validating liquid sterile filters. The bacteria capable of penetrating a 0.45 μm filter membrane are *Pseudomonas deficientis*, with a size of 0.3–0.4 μm. Subsequently, the first new sterile filter was developed. For ease of definition, the pore size of this filter was reduced from the original 0.45 μm to half that at 0.225 μm, and later simplified to 0.22 μm, thus opening a new chapter in sterile filters.

[0003] In the early 1980s, based on the ASTM F-838 standard method for bacterial retention, Millipore in the United States pioneered the first truly sterile filter, based on a polyvinylidene fluoride (PVDF) membrane. Currently, the main materials used for filter membranes include nylon, polyethersulfone (PES), PVDF, and polytetrafluoroethylene (PTFE). Compared to other materials, PTFE plays a crucial role in biopharmaceuticals and other fields due to its excellent thermal stability, chemical corrosion resistance, and resistance to strong acids and alkalis, resulting in a significant demand gap both domestically and internationally. Currently, PTFE filter membranes are typically prepared using the methods disclosed in US patents US3953566 and US4187390. This preparation method mainly includes the following steps: mixing PTFE dispersion resin with kerosene as a lubricant, extruding the mixture into a paste, and removing the lubricant; then stretching the mixture unidirectionally or bidirectionally below the melting point of PTFE to obtain the PTFE filter membrane.

[0004] US Patent Application No. US08 / 690924 discloses a microporous polytetrafluoroethylene membrane, which mainly consists of a series of interconnected nodes made of protofibrils. These nodes are typically arranged in parallel, highly elongated, and have an aspect ratio of 25:1 or greater. The nodes are extremely thin and long, resulting in a unique combination of high airflow and high strength, ensuring that the product of the Fraser number and the ball burst rate is at least 100. Furthermore, the membrane exhibits good uniformity, optical transparency, and operability.

[0005] Furthermore, Chinese Patent Application No. 2020115811067 discloses a PTFE porous membrane, its preparation method, and its uses. This porous membrane has a thickness of 10-100 μm, an average pore size of 1-20 μm (relatively large pore size), and a porosity of 60-90%. On the membrane cross-section parallel to the membrane thickness direction, it contains primary nodes, which are granular structures. Several primary nodes are stacked to form nodes (at this point, the nodes on the cross-section can be considered as elongated structures). Adjacent nodes are connected by a first fiber, and primary nodes on the same node are connected by a second fiber. The average particle size of the primary nodes is 0.5-2.5 μm. This membrane structure allows the porous membrane to not only have high tensile strength and good mechanical properties, but also a high flow rate, fast filtration speed, and low time cost; it is suitable for filtering stripping solutions and etching solutions in semiconductor manufacturing processes.

[0006] However, such porous PTFE membranes cannot be used as filter membranes because their pores are relatively large, making it impossible to guarantee efficient retention of bacteria. To ensure efficient bacterial retention, researchers generally employ various methods to reduce the pore size of PTFE membranes. However, when the overall pore size of the membrane decreases, the overall flux of the membrane drops significantly (for example, if the pore size is reduced to half, the flux may become one-quarter or even lower). Furthermore, small-pore filter membranes are particularly prone to clogging, making it impossible to filter the corresponding fluid for an extended period, resulting in a shorter lifespan. Therefore, such PTFE filter membranes cannot meet the needs of practical applications, meaning they still cannot be used as sterilization membranes.

[0007] To improve membrane flux, some technicians have researched and concluded that making the membrane nodes very fine or even eliminating them, while also using finer fibers, can increase the overall porosity of the membrane and thus improve the overall flux. This approach can maintain good flux while ensuring retention efficiency. However, this method also has a problem: the mechanical strength of the filter membrane is relatively low (the fibers are prone to breakage without the support of nodes), making it unable to withstand high pressure during filtration, and its stability is not strong, resulting in a short service life. Especially in actual use, the filter membrane usually needs to be folded, and the folds of the filter membrane are easily damaged during long-term filtration. Filter membranes with very fine surface fibers are even more easily damaged during filtration, making it impossible to achieve efficient sterilization for a long time.

[0008] The existence of the above-mentioned problems greatly limits the development of antibacterial membranes. Summary of the Invention

[0009] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a PTFE sterilization filter membrane, its preparation method and uses. This filter membrane not only has high bacterial retention efficiency, but also high throughput and excellent mechanical strength, making it particularly suitable for liquid sterilization and / or gas sterilization, with a wide range of applications.

[0010] To achieve the above objectives, the present invention provides the following technical solution: a PTFE antibacterial filter membrane, comprising a body having a non-directional tortuous pathway within the body, one side surface of the body being a first outer surface, and the other side surface of the body being a second outer surface, the first outer surface and the second outer surface being substantially symmetrical; each side outer surface of the filter membrane includes surface nodes and surface fibers for forming a porous structure, and adjacent surface nodes are connected by surface fibers;

[0011] The cross-section of the main body includes several support points and support fibers, and adjacent support points are connected by support fibers; the support points have a granular structure.

[0012] The filter membrane has an IPA bubble point of 0.12-0.35 MPa and a thickness of 30-80 μm.

[0013] The surface fibers have an average SEM width of 80-350 nm and an average SEM length of 0.9-2.5 μm.

[0014] Preferably, the filter membrane has an IPA bubble point of 0.15-0.30 MPa; a thickness of 35-70 μm; an average SEM width of 100-320 nm for the surface fibers; and an average SEM length of 1.1-2.2 μm for the surface fibers.

[0015] In the main structure of the polytetrafluoroethylene filter membrane provided by this invention, it can be found that there is no skin structure (dense structure). Each outer surface has a certain fiber structure, and these fibers intertwine to form pores of a certain size (each outer surface is a porous structure). Further research shows that the two outer surfaces of the main body (the first outer surface and the second outer surface) are basically symmetrical. In this invention, symmetry means that the fiber structure and pore size of the two outer surfaces of the main body are basically the same (on the outer surface of the membrane, the relatively thick fiber entities are called surface nodes, and the relatively thin fiber entities are called surface fibers; since the two outer surfaces are symmetrical, the characteristics (length and thickness) of the corresponding surface fibers and surface nodes are basically the same). Therefore, any one of the outer surfaces of this invention can be used as the liquid inlet surface without special requirements. When processing the filter membrane, the process is more convenient, and there is no situation of "reversed liquid inlet and outlet surfaces".

[0016] As is well known, the length and width of surface fibers are important factors affecting the characteristic properties of PTFE filter membranes, such as pore size, tensile strength, and flux. Surface fibers essentially refer to the distance between two adjacent surface nodes. Generally, if the surface fibers are too fine (too small in diameter), the overall mechanical strength of the membrane is likely to be too low; while if the surface fibers are too coarse (too large in diameter), the overall porosity of the membrane is likely to be too low, resulting in low membrane flux. At the same time, when the surface fibers are too long, the overall pores of the membrane are too large, which cannot efficiently retain bacteria and will also reduce the mechanical strength of the membrane to some extent. Conversely, when the surface fibers are too short, the membrane pores are relatively small, resulting in low membrane flux.

[0017] Compared to existing technologies that achieve high retention efficiency and high flux through minimizing membrane pore size and minimizing surface knots, this invention achieves higher flux and filtration speed by making the membrane pores relatively large, with an IPA bubble point of 0.12-0.35 MPa (the IPA bubble point is used to characterize the overall pore size of the membrane). This larger pore size facilitates higher flux (filtration rate). Furthermore, the membrane of this invention has a sponge-like structure with non-directional tortuous pathways within its main body. These non-directional tortuous pathways refer to irregularly oriented groove structures and / or discretely distributed pore structures, and these pathways are interconnected. The membrane structure, with its interconnected pores and tortuous pathways, enhances the membrane's ability to retain bacteria in the fluid. Furthermore, the membrane's thickness is 30-80 μm (when the membrane thickness is too small, its mechanical strength is low; simultaneously, the filtration time is too short, making effective filtration impossible; when the membrane thickness is too large, the filtration time is too long, resulting in excessive time costs). This combination of pore size, tortuous pathways, and suitable thickness further ensures the membrane's mechanical strength, flux, and bacterial retention. Simultaneously, several granular support points exist on the membrane's cross-section, further improving its mechanical strength without significantly affecting its flux.

[0018] Further research revealed that for the antibacterial filter membrane of this invention, when the membrane surface has surface fibers of suitable length (average SEM length 0.9-2.5 μm) and suitable thickness (average SEM width 80-350 nm), and because the two outer surfaces of the filter membrane are basically symmetrical, the lower layer fibers will be interleaved and stacked with the upper layer fibers (between adjacent layers) in the membrane structure, thereby improving the retention efficiency. This further ensures that the filter membrane still has high retention efficiency even when the membrane pores are relatively large. Ultimately, with suitable membrane pore size, suitable membrane thickness, and suitable membrane structure (two outer surfaces), the desired retention efficiency is achieved. The combined effect of symmetrical and tortuous pathways and appropriately sized surface fibers of suitable length and coarseness ensures sufficient retention of bacteria, achieving ideal bacterial capture. Simultaneously, the surface fibers of this fineness have minimal impact on membrane flux, and due to the relatively large overall pore size of the filter membrane, it still maintains a high flux. Furthermore, the surface fibers of this fineness are not easily broken, ensuring high mechanical strength, enabling the filter membrane to withstand high pressure during filtration, exhibiting strong stability and a long service life. Even when the filter membrane is folded during actual use, it is not easily damaged, enabling long-term, efficient, and rapid sterilization.

[0019] Generally, the larger the overall pore size of the membrane, the lower the bubble point; conversely, the smaller the overall pore size, the higher the bubble point. The bubble point is an important performance characteristic of polymer filter membranes. It is determined by reading the pressure at which continuous bubbling begins in the middle of the membrane. The methods for testing the bubble point are well-known in the art. For example, the procedures for these tests are explained in detail in ASTM F316-70 and ANS / ASTM F316-70 (re-approved in 1976), which are incorporated herein by reference.

[0020] The test solution used in this invention is IPA (isopropanol). The bubble point of the filter membrane in this invention is 0.12-0.35 MPa. Its relatively small bubble point indicates that the overall pore size of the filter membrane is relatively large, which is beneficial for the high throughput of the sterilization filter membrane. In addition, because the membrane pores of this invention are relatively large, they are not easily clogged. When sterilizing various fluids, the fluid can pass through the filter membrane quickly and stably. Furthermore, due to the inherent characteristics of the PTFE membrane and its low dissolution (no additives are added during the preparation process), it is ensured that the effective substances of the drug solution are not significantly affected after passing through the filter membrane, and it has a wide range of applications.

[0021] The measurement of various surface morphology parameters of the filter membrane (such as the average width and length of surface fibers under SEM, and the average length of surface nodes under SEM) can be performed by characterizing the membrane structure using a scanning electron microscope, followed by measurement using computer software (such as Matlab, NIS-Elements, etc.) or manually, and then performing corresponding calculations. During membrane fabrication, in the direction perpendicular to the membrane thickness (if the membrane is a flat sheet, this direction is planar; if the membrane is a hollow fiber membrane, this direction is perpendicular to the radius), its characteristics, such as pore size distribution, are roughly uniform and consistent. Therefore, the average pore size of the entire plane can be reflected by measuring the average pore size of a portion of the corresponding plane. In actual measurement, the membrane surface can be characterized first using an electron microscope to obtain the corresponding SEM image, and a certain area, such as 1 μm, can be selected. 2 (1μm x 1μm) or 25μm 2 (5μm x 5μm) or 100μm 2(10μm x 10μm), the specific area size depends on the actual situation. Then, the length and width of the surface fibers and the length and width of the surface nodes on this area are measured by appropriate computer software or manually. Then, the average SEM length and average SEM width of the surface fibers and the average SEM width of the surface nodes in this area are calculated. This value can be used as the corresponding feature value on the outer surface. Of course, those skilled in the art can also obtain the above parameters by other measurement methods. The above measurement methods are for reference only. The thickness of the membrane can be obtained by characterizing the morphology of the membrane structure using a scanning electron microscope and then measuring and calculating it by computer software (such as Matlab, NIS-Elements, etc.) or manually.

[0022] As a further improvement of the present invention, the average compactness Q of the membrane body is 35%-85%, and the average compactness Q is calculated by the following formula: Q = D 实 / D×100%;

[0023] In the above formula, D 实 D is the sum of the thicknesses of all entities along the thickness direction of the membrane body, where each entity includes the support point and the support fiber, and D is the thickness of the membrane body.

[0024] Further research revealed that the antibacterial filter membrane of this invention is relatively dense, meaning that in the thickness direction of the membrane, the solid parts are basically stacked together, without particularly large pores, thus forming many tortuous pathways, which further ensures the membrane's retention efficiency. To reflect the density of the filter membrane, this invention uses the characteristic of average compactness Q. Average compactness refers to the ratio of the sum of the thicknesses of all solid parts in the thickness direction of the membrane body to the membrane thickness. The magnitude of this ratio reflects the area occupied by the solid parts in the thickness direction of the membrane body; the larger the ratio, the higher the density of the membrane. In this invention, the average compactness S of the membrane body is 35%-85% (preferably, the average compactness S is 45%-80%), which further demonstrates that in the thickness direction of the antibacterial filter membrane, the support points and support fibers are basically tightly packed together, forming relatively tortuous pathways, thus ensuring that the membrane has greater mechanical strength and higher retention efficiency. However, the average compactness will not be too high, and a certain gap is necessary to ensure that the membrane flux is large and the filtration resistance is not too high.

[0025] The average compactness of the sterilization filter membrane in this application can be measured by characterizing the membrane structure using a scanning electron microscope (SEM), followed by measurement using computer software (such as Matlab, NIS-Elements, etc.) or manually, and then performing corresponding calculations. In actual measurement, the membrane cross-section (a section cut along the fiber length direction on the membrane surface, which is the direction of membrane travel and longitudinal stretching) can be characterized using an SEM to obtain the corresponding SEM image. Multiple sites (at least three) can be selected, and a straight line parallel to the thickness direction can be drawn along each site. The length of the solid portion (support points and supporting fibers) along this line can be measured and then divided by the overall membrane thickness to obtain the compactness at that site. The average compactness Q of the membrane can then be obtained. It should be noted that fibers within the pores are not included in the solid portion because they are not actually fibers at the cross-section, but rather fibers near the cross-section.

[0026] As a further improvement of the present invention, the length direction of the surface nodes is substantially perpendicular to the length direction of the surface fibers; the basis weight of the filter membrane is 18-45 g / m³. 2 Preferably, the basis weight of the filter membrane is 22-35 g / m³. 2 The aspect ratio of the surface fibers is 4-16.

[0027] Basis weight, also known as areal density, can be understood as the content of solid portion on the outer surface of the sterilizing membrane. In existing technologies, by making the fibers very fine, the basis weight of the filter membrane is greatly reduced, resulting in excessively low mechanical strength. However, the present invention has a suitable basis weight, which further ensures that the filter membrane has high mechanical strength without affecting the flux (when the basis weight of the filter membrane is too high, it indicates that there is too much solid portion on the membrane surface, the surface pore area ratio is too low, the flux will also be greatly reduced, and the pressure loss will be greatly increased). In the present invention, the length direction of the surface nodes is basically perpendicular to the length direction of the surface fibers, and the surface fibers and surface nodes are relatively ordered, not disordered. This is more conducive to the stacking of the lower and upper fibers, ensuring the retention efficiency. Furthermore, through the combined effect of basis weight and overall membrane pore size, the sterilizing filter membrane is guaranteed to have good mechanical strength and high flux.

[0028] Further research revealed that the aspect ratio (the ratio of the length to the width of the surface fibers) also affects the flux and mechanical properties of the filter membrane to some extent. When the aspect ratio is too large, the surface fibers are prone to breakage during fluid filtration (compared to surface nodes, surface fibers are relatively thin and easily break), thus affecting retention efficiency. This is especially true for the outer surface, which serves as the inlet surface; the probability of surface fiber breakage increases significantly when fluid passes through it instantaneously. Conversely, the aspect ratio cannot be too small, as this would make the surface fibers too coarse, greatly increasing the resistance to fluid flow through the filter membrane. A suitable aspect ratio further ensures a longer service life for the filter membrane during filtration. Simultaneously, with surface fibers of a suitable aspect ratio on the membrane surface, the lower fibers in the membrane structure achieve a more ideal staggered stacking with the upper fibers, resulting in a more tortuous flow channel, which is more conducive to improving the retention efficiency for bacteria. This further ensures that the filter membrane still maintains high retention efficiency even when the membrane pores are relatively large.

[0029] As a further improvement of the present invention, the average SEM length of the surface nodes is 0.6-3.0 μm, and the average SEM diameter of the surface nodes is 250-900 nm. Preferably, the average SEM length of the surface nodes is 0.8-2.6 μm, and the average SEM diameter of the surface nodes is 300-800 nm.

[0030] On the outer surface of the membrane, relatively coarse fibers are called surface knots. The length and width (diameter) of the surface knots have a certain influence on the porosity and pore size of the membrane surface, which in turn affects the overall mechanical strength, flux, and retention efficiency of the membrane. In the prior art, for surface knots, one approach is to make the surface knots both coarse and long (often greater than 20 μm in length), while another approach is to have as few knots as possible on the outer surface. In this invention, it is desirable for a certain number of knots to appear on the surface, but the length of the surface knots is relatively short, with an average SEM length of 0.6 μm-3. 0μm; with this length, large membrane pores are not formed, and the pore size is relatively suitable, which is conducive to ensuring sufficient retention of bacteria; furthermore, the average SEM diameter of the surface nodes is 250-900nm, and the surface nodes are neither too coarse nor too fine. With the effect of surface nodes of this length and width, the stability of the membrane pores can be maintained for a long time, ensuring that the filter membrane has good mechanical strength and is easy to process; and it can ensure that bacteria are retained sufficiently during long-term filtration, while having little impact on the basic changes in flux, so that the filter membrane still has good flux.

[0031] As a further improvement of the present invention, the aspect ratio of the surface nodes is 1.2-8; the average SEM area of ​​the surface nodes is 0.5-2 μm. 2The ratio of the average SEM length of the surface node to the average SEM length of the surface fiber is 1.03-3; the ratio of the average SEM width of the surface node to the average SEM width of the surface fiber is 2-5.

[0032] Further research revealed that controlling the aspect ratio of surface nodes, the ratio of the average SEM length of surface nodes to the average SEM length of surface fibers, and the ratio of the average SEM width of surface nodes to the average SEM width of surface fibers are all beneficial to further improving the various properties of the membrane. Of course, the control of these parameters is only suitable for the sterilization membrane of this invention, and is not suitable for other sterilization membranes or even PTFE filter membranes. In this invention, by controlling the aspect ratio of surface nodes to 1.5-6, the filter membrane can obtain a suitable pore size under the action of surface nodes with such an aspect ratio, and at the same time, the surface and even the whole have good porosity, thereby ensuring that the sterilization membrane of this invention has high retention efficiency and high flux.

[0033] Meanwhile, the length of the surface nodes in this invention is not very long, but is appropriately longer than the length of the surface fibers. This structural design is conducive to obtaining a relatively ideal membrane pore size, and also makes it more conducive to the interlacing of fibers between the upper and lower layers. Even if the membrane pores are slightly larger, it still has a high retention efficiency for bacteria. Furthermore, the surface nodes are slightly thicker than the surface fibers, and the width of both is controlled within an appropriate range, which is more conducive to ensuring the mechanical strength and flux of the membrane.

[0034] Furthermore, the surface node structure in this invention is not as elongated or thick as that in the prior art; that is, the area of ​​the surface nodes is not too large. Studies have shown that the average SEM area of ​​the surface nodes on the outer surface is 0.5-2 μm. 2 This surface node area size ensures the membrane's mechanical strength and impact resistance, preventing the impact of the feed liquid from affecting the membrane's performance. At the same time, it has a small impact on the membrane flux, allowing the sterilization filter membrane to still have a large flux.

[0035] As a further improvement of the present invention, the hole area ratio of the first outer surface is 25-55%;

[0036] On the first outer surface, the ratio between the sum of the surface node areas and the sum of the surface fiber areas is 0.5-0.9.

[0037] In this invention, the pore area ratio of the first outer surface is 25-55%. Such a pore area ratio further ensures that the membrane has high tensile strength and compressive strength. This pore area ratio, combined with the thickness and length of the surface fibers, ensures that the first outer surface can withstand high pressure for a long time when used as a liquid inlet surface. Even if it encounters a sudden impact of fluid (such as power failure), the membrane pores will not collapse. It can adapt to various harsh working conditions and has a wide range of applications. At the same time, it can also enable the filter membrane to have a high flow rate, allowing the fluid to pass through the filter membrane quickly and filter more fluid in a shorter time.

[0038] Meanwhile, the present invention also discovered that the ratio between the sum of the surface node areas and the sum of the surface fiber areas also has a certain impact on the tensile strength and flow rate of the membrane. In the present invention, it is preferable that the sum of the surface fiber areas is slightly larger than the sum of the surface node areas, which is more conducive to forming tortuous pathways. That is, even with slightly larger membrane pores, it still has a high retention efficiency for bacteria, making the filter membrane fully usable as a sterilization membrane and meeting the needs of practical applications.

[0039] Since the distribution of surface nodes and surface fibers on any outer surface of the membrane is roughly uniform and consistent, the ratio of the sum of the surface node areas to the sum of the surface fiber areas in a corresponding region can be used to reflect the overall ratio of the surface node area to the surface fiber area on that plane. In actual measurement, the outer surface of the membrane can be characterized using an electron microscope to obtain a corresponding SEM image. Because the distribution of surface nodes and surface fibers on the outer surface of the membrane is roughly uniform, a certain area, such as 1 μm, can be selected. 2 (1μm multiplied by 1μm) or 100μm 2 (10μm multiplied by 10μm), the specific area size depends on the actual situation, and then use the corresponding computer software or manual measurement to measure the sum of the surface node areas and the sum of the surface fiber areas to obtain the corresponding ratio; of course, those skilled in the art can also obtain the above parameters through other measurement methods, and the above measurement methods are for reference only.

[0040] As a further improvement of the present invention, the average SEM spacing between adjacent surface fibers is 200-600 nm; the ratio of the average SEM spacing between adjacent surface fibers to the average SEM width of the surface fibers is 1.5-6. Preferably, the average SEM spacing between adjacent surface fibers is 250-550 nm; the ratio of the average SEM spacing between adjacent surface fibers to the average SEM width of the surface fibers is 1.8-5.

[0041] Further research revealed that the gaps between adjacent surface fibers allow fluid to pass through. Therefore, the distance between adjacent surface fibers also affects the overall pore size of the membrane. Excessive distance leads to a larger overall pore size, hindering efficient bacterial retention. Conversely, insufficient distance affects membrane flux. In this invention, the average SEM spacing between adjacent surface fibers is 200-600 nm, a suitable spacing. Combined with surface fibers of a certain thickness and length, this further enhances the membrane's high retention efficiency and high flux. Furthermore, by setting the ratio of the average SEM spacing to the average SEM width of the surface fibers to 1.5-6, this ratio better ensures the mechanical strength and stability of the sterilization membrane, enabling long-term efficient sterilization while minimizing pressure loss. In practical industrial applications, this results in high energy conversion efficiency, high economic value, and a more environmentally friendly approach.

[0042] As a further improvement of the present invention, on any side of the outer surface of the filter membrane, the difference between the maximum and minimum SEM width of the surface nodes is 100-800 μm; the uniformity coefficient of the SEM width of the surface nodes is 10%-35%; the uniformity coefficient of the surface nodes = the standard deviation of the surface nodes / the average value of the surface nodes. The smaller the uniformity coefficient, the more uniform the feature. In the present invention, the surface nodes are relatively uniform in size, which is beneficial to the various performance characteristics of the filter membrane.

[0043] As a further improvement of the present invention, the uniformity coefficient of the surface node SEM length is greater than the uniformity coefficient of the surface node SEM width, and the difference between the two is 10-40%.

[0044] In this invention, the thickness of the surface nodes is relatively uniform, while the length of the surface nodes does not need to be so uniform. Some surface nodes are longer, and some are shorter. The coefficient of variation of the surface node width is less than the coefficient of variation of the surface node length. This is because surface nodes, as entanglement points of multi-strand fibers, affect the strength of the filter membrane. Larger entanglement points indicate an increase in the number of fibers involved in the entanglement, resulting in greater strength, but large surface nodes reduce flux. If all entanglement points are small, the number of fibers involved in the entanglement will decrease, thus increasing flux, but decreasing strength. By using surface nodes of varying lengths, the filter membrane can simultaneously achieve both strength and flux, and this structure provides a good balance.

[0045] As a further improvement of the present invention, the SEM average diameter of the support point is 150-650 nm, and the ratio of its SEM average diameter to film thickness is 0.006-0.014. Preferably, the SEM average diameter of the support point is 200-600 nm.

[0046] In the main cross-sectional structure of the sterilization membrane of this invention, there are several granular structures, which we call support points. These support points are connected by support fibers, and there are certain gaps between adjacent support fibers. These gaps form pathways to facilitate fluid passage. Compared with the support fibers, these support points are relatively thick, with an average SEM diameter of 150-650 nm. This thickness of support points helps to give the sterilization membrane high mechanical strength. On the other hand, the relatively large number of these support points, and the connection between adjacent support points through support fibers, together form many tortuous pathways. This thickness of support points ensures the stability of each pathway, making it less likely to collapse or shrink during filtration. This allows for long-term and efficient retention of bacteria, ensuring sufficient bacterial capture while maintaining high flux and low pressure loss in the filter membrane.

[0047] As is well known, the fluid filtration process is mainly completed in the thickness direction of the membrane. The fluid passes through the membrane from one surface and exits from the other surface. The support point can be regarded as a relatively dense area with low porosity within the membrane cross-section, while the support fiber is an area with higher porosity within the membrane cross-section. When the size of the support point is too large, it will cause considerable resistance to the fluid flow and affect the fluid flow velocity within the membrane, resulting in lower membrane flux and greater pressure loss. Conversely, when the support point is too small, the mechanical strength of the sterilization membrane is too low. Research has found that when the ratio of the average SEM diameter of the support point to the membrane thickness is 0.006-0.014, there is a suitable ratio, and the support point is relatively small, which can ensure both membrane strength and high flux.

[0048] In this invention, the SEM average diameter of the support point is the thickness of the support point. The SEM average diameter of the support point can be obtained by characterizing the morphology of the membrane cross-section structure using a scanning electron microscope, and then measuring the diameter of the support point using computer software (such as Matlab, NIS-Elements, etc.) or manually, thereby further calculating the corresponding SEM average diameter. Of course, it is understood that those skilled in the art can also obtain the above parameters through other measurement methods.

[0049] As a further improvement of the present invention, on the cross-section of the membrane, the average spacing between adjacent support points in the thickness direction is 1.5-4 μm, and the ratio of the average spacing to the thickness is 2%-10%.

[0050] Further observation revealed that the distance between adjacent support points is relatively small, indicating a relatively large number of support points on the membrane cross-section. These support points are connected by support fibers, and the combined effect of numerous support points and fibers creates a complex network of pathways. The appropriate size of the support points and the suitable spacing between adjacent support points ensure the stability of each pathway, preventing them from collapsing or shrinking during filtration. This allows for long-term and efficient retention of bacteria, ensuring sufficient bacterial capture while maintaining high flux and low pressure loss in the filter membrane.

[0051] In this invention, adjacent support points refer to two support points that are adjacent in the same thickness direction. The determination of adjacent support points can be achieved by first characterizing the membrane cross-section with an electron microscope to obtain the corresponding SEM image; then drawing a straight line parallel to the thickness direction, determining several support points on the line, and then calculating the spacing between adjacent support points and taking the average value; to avoid randomness, it is necessary to draw several lines and test several sets to obtain the average spacing between the corresponding adjacent support points in the thickness direction.

[0052] As a further improvement of the present invention, the SEM average length of the supporting fiber is 800-2200 nm, and the SEM average diameter of the supporting fiber is 80-260 nm; the ratio of the SEM average length of the supporting fiber to the film thickness is 1%-6%. Preferably, the SEM average length of the supporting fiber is 1000-2000 nm, and the SEM average diameter of the supporting fiber is 90-250 nm.

[0053] Adjacent support points are connected by support fibers, and there are gaps between the support fibers to allow fluid to pass through. Therefore, the length and width of the support fibers further affect the overall mechanical strength, retention efficiency, and dirt holding capacity of the sterilization membrane. When the support fibers are too short, there will be too many support points on the membrane cross-section, resulting in greater resistance, pressure loss, and energy consumption when the fluid passes through the sterilization membrane. It will also lead to fewer pores in the membrane (lower porosity), which in turn results in lower dirt holding capacity and flux. When the support fibers are too long, the overall pore size of the membrane will be too large, affecting the retention efficiency. However, when the supporting fibers are too thin, the overall mechanical strength of the membrane is insufficient. Furthermore, when the fluid flows inside the membrane, the supporting fibers are prone to breakage, and the membrane pores may collapse, making stable filtration impossible for extended periods. Additionally, when the supporting fibers are too thin, they easily adsorb various effective substances from the fluid, resulting in a low yield of these substances. Conversely, when the supporting fibers are too thick, the fluid flow velocity within the membrane becomes too low, and the flow time becomes too long. Therefore, this invention further ensures flux, retention efficiency, and mechanical strength by using supporting fibers of suitable length and thickness, which, in conjunction with the size of the support points, also contribute to these characteristics.

[0054] Furthermore, the ratio of the average SEM length of the supporting fiber to the membrane thickness in this invention is 1%-6%, which further ensures that the supporting fiber has a suitable length, ensuring that the filter membrane can fully retain various bacteria in the fluid without affecting the flow rate; this is beneficial for the filter membrane to have high retention efficiency and fast flow rate.

[0055] The present invention measures the SEM average length and SEM average diameter of the supporting fibers by characterizing the membrane cross-section using a scanning electron microscope, followed by measurement and calculation using computer software (such as Matlab, NIS-Elements, etc.) or manually. The overall SEM average length and average diameter of the cross-section are reflected by measuring the SEM average length and average diameter of the corresponding area. In actual measurement, the membrane cross-section can be characterized first using an electron microscope to obtain the corresponding SEM image, and a certain area, such as 1 μm, can be selected. 2 (1μm x 1μm) or 25μm 2 (5μm x 5μm), the specific area size depends on the actual situation. Then, the SEM length and SEM diameter of the supporting fibers on this area are measured by appropriate computer software or manually. Then, the average SEM length and average SEM diameter of the supporting fibers in this area are calculated to obtain the average SEM length and average SEM diameter of the supporting fibers on the membrane cross section. Of course, those skilled in the art can also obtain the above parameters by other measurement methods. The above measurement methods are for reference only.

[0056] As a further improvement of the present invention, the filter membrane has an LRV greater than 7 against Pseudomonas degenerates; under conditions of pressure of 0.03 MPa and temperature of 20°C, the time required for 50 ml of water to pass through the 47 mm diameter filter membrane is 18-35 s; the porosity of the filter membrane is 55-85%; the transverse tensile strength and longitudinal tensile strength of the filter membrane are both 10-60 MPa; and the transverse elongation and longitudinal elongation of the filter membrane are both greater than 40%.

[0057] In the bacterial retention challenge experiment of the filter membrane of the present invention, Pseudomonas aeruginosa (ATCC 19146) with a bacterial diameter of 0.3-0.4 μm was used and tested according to the standard of ASTM F838-2015ae1. The test results showed that the filter membrane had an LRV greater than 7 for Pseudomonas aeruginosa, which can fully capture bacteria and meet the needs of practical applications.

[0058] For filter membranes, flux is crucial. If the flux of a filter membrane is too low, it lacks practical value and cannot meet the needs of actual applications. Through flow rate testing of the filter membrane of this invention, it was found that 50ml of water takes only 18-35 seconds to pass through a 47mm diameter filter membrane. This short time indicates that the sterilization membrane has a fast flow rate and rapid filtration speed, enabling it to filter a large amount of fluid within a certain time. It has high economic efficiency per unit time and is suitable for liquid and gas sterilization, especially for air and liquid filtration in the pharmaceutical industry.

[0059] Testing revealed that the porosity of the filter membrane of this invention is 55%-85% (preferably 60%-80%), resulting in a high dirt-holding capacity, the ability to trap more impurity particles, and a long service life. Furthermore, the combination of a large pore size and high porosity ensures a high flux and low pressure loss, thus meeting the needs of practical applications. Commonly used porosity testing methods include mercury intrusion porosimetry, density method, and wet-dry membrane weighing method. This application uses the wet-dry membrane weighing method for measurement. Of course, those skilled in the art can obtain the above parameters through other measurement methods; the above measurement methods are for reference only.

[0060] Tensile strength is a crucial indicator for evaluating the mechanical strength of a filter membrane. Under certain conditions, a higher tensile strength indicates better mechanical strength. Tensile strength refers to the membrane's ability to withstand parallel tensile forces. During testing, the membrane sample is subjected to a tensile load until failure. Based on the maximum tensile load at failure and the change in membrane sample size (length), the tensile strength and elongation at break can be calculated. Tensile strength and elongation at break can be measured using a universal tensile testing machine. The testing methods for tensile strength are well-known in the field; for example, ASTM D790 or ISO 178 details the procedures for tensile strength testing. In this invention, the PTFE antibacterial filter membrane exhibits both transverse and longitudinal tensile strengths of 10-60 MPa, with transverse and longitudinal elongation rates exceeding 40%. This demonstrates that the filter membrane of this invention possesses high tensile strength and elongation at break, exhibiting good mechanical properties, good toughness, high industrial practical value, suitability for various processing methods, and a wide range of applications.

[0061] In addition, the present invention also provides a method for preparing a PTFE antibacterial filter membrane, comprising the following steps:

[0062] A. Mixing: Mix and stir the polytetrafluoroethylene dispersion resin and lubricant until a paste is obtained;

[0063] B. Blank making: The above paste is pre-pressed into a cylindrical blank;

[0064] C. Extrusion: The preform obtained in step B is extruded to form a flat strip-shaped matrix;

[0065] D. Drying: The strip-shaped substrate is dried to allow the lubricant to evaporate;

[0066] E. Longitudinal stretching: The dried strip matrix is ​​stretched longitudinally at a temperature of 150-250℃ and a stretching ratio of 2-10 times to obtain the first strip matrix.

[0067] F. Lateral stretching: The first strip matrix is ​​laterally stretched at a temperature of 150-300℃, a stretching ratio of 26-50 times, and a stretching rate of no more than 100% / s to obtain the second matrix.

[0068] G. First heat setting: The second substrate is placed in an environment with a temperature of 330-390℃ for the first heat setting, and the heat setting time is 0.2-3 minutes to obtain the filter membrane semi-finished product;

[0069] H. Second heat setting: The filter membrane semi-finished product is placed in an environment with a temperature of 330-390℃ for a second heat setting. During the second heat setting, the longitudinal shrinkage rate and transverse shrinkage rate of the filter membrane semi-finished product are controlled so that the shrinkage rate in the membrane thickness direction is greater than 20%. The second heat setting time is 5-20 minutes to obtain the filter membrane.

[0070] As a further improvement of the present invention, the polytetrafluoroethylene dispersion resin has a number average molecular weight of 4 million to 12 million and a crystallinity of over 90%; the lubricant is at least one of lubricating oil, palm oil, naphthenic oil, white oil, aviation kerosene, degreased kerosene, and paraffin wax; step A, mixing, specifically refers to mixing and stirring the polytetrafluoroethylene dispersion resin and the lubricant at a weight ratio of 1:0.1 to 1:0.3, and then placing them in an environment with a temperature of 35-50°C for 8-24 hours to obtain a paste.

[0071] As a further improvement of the present invention, the strip substrate obtained in step C is calendered so that the thickness of the calendered strip substrate is 60-85% of the thickness of the strip substrate before calendering; the longitudinal shrinkage rate and transverse shrinkage rate of the second substrate are controlled during the first heat setting so that the shrinkage rate in the film thickness direction is 3-18%; during the second heat setting process, the thickness shrinkage rate of the filter membrane semi-finished product is 25%-45%.

[0072] As a further improvement of the present invention, the longitudinal stretching rate in step E is 8-75% / s, and the ratio of the longitudinal stretching rate to the transverse stretching rate is 0.3-0.8.

[0073] Preferably, the transverse stretching rate in step F is 25-95%.

[0074] As a further improvement of the present invention, the ratio of the transverse stretching ratio to the longitudinal stretching ratio is 3.5-12; the temperature during transverse stretching is 20-60°C higher than the temperature during longitudinal stretching.

[0075] In preparing the PTFE sterilization filter membrane of the present invention, the raw material polytetrafluoroethylene dispersion resin and lubricant are first mixed and stirred. The number average molecular weight of the polytetrafluoroethylene dispersion resin is 4 million to 12 million. Since the filter membrane prepared by the present invention is used for sterilization, its pore size will not be too large. When the number average molecular weight is too small, the mechanical strength of the filter membrane will be too low. When the number average molecular weight is too large, it is not easy to form a filter membrane with high porosity, which will lead to a low flux of the filter membrane. By selecting a polytetrafluoroethylene dispersion resin with a certain number average molecular weight, it is beneficial to make the prepared polytetrafluoroethylene filter membrane have sufficient mechanical strength and flux. The crystallinity of the polytetrafluoroethylene dispersion resin used is all above 90%. Such high crystallinity polytetrafluoroethylene resin is more conducive to producing the fiber structure (correspondingly coarse and fine surface fibers and surface nodes) required by the present invention, thereby facilitating the acquisition of a PTFE sterilization filter membrane with high tensile strength and high flow rate.

[0076] The lubricant is at least one of lubricating oil, palm oil, naphthenic oil, white oil, aviation kerosene, degreased kerosene, and paraffin wax. The lubricant can be a single substance or a mixture of several of the above substances. By selecting a suitable lubricant, the polytetrafluoroethylene (PTFE) dispersion resin can be easily processed to obtain the desired membrane structure. Preferably, the weight ratio of PTFE dispersion resin to lubricant in this invention is 1:0.1-1:0.3. This weight ratio further ensures uniform mixing of the lubricant and PTFE, facilitating subsequent processing. Excessive lubricant can lead to residues even after drying and other processes. Furthermore, it can result in insufficient fiberization and low mechanical strength of the film during film formation, failing to meet the requirements of practical applications.

[0077] After the polytetrafluoroethylene (PTFE) dispersion resin and lubricant are mixed evenly, they are placed in an oven at a temperature of 35-50℃ for 8-24 hours to obtain a paste. The purpose of maturation is to ensure that the PTFE dispersion resin and lubricant are mixed more evenly, and that the lubricant is evenly dispersed in the PTFE dispersion resin, which facilitates subsequent preform extrusion. Next, the paste is pre-pressed into a cylindrical preform. Then, the preform is extruded by placing it into an extruder to form a flat strip matrix.

[0078] Preferably, the extruded strip matrix is ​​calendered so that the thickness of the calendered strip matrix is ​​30-70% of the thickness of the strip matrix before calendering. After calendering, the thickness of the strip matrix will be appropriately reduced, which is conducive to the generation of a certain force between the resin particles, and to the full fusion of the fibers in the thickness direction. With the synergistic effect of subsequent transverse and longitudinal stretching, first heat setting and second heat setting, the PTFE antibacterial filter membrane required by the present invention can be formed, and the filter membrane has an ideal membrane pore and fiber structure. Then, drying is performed: the calendered strip matrix is ​​placed in an oven to dry so that the lubricant evaporates, wherein the drying temperature is 100-250℃.

[0079] Then, longitudinal stretching is performed. The dried strip matrix is ​​stretched longitudinally on a film stretching machine at a temperature of 150-250℃ and a stretching ratio of 2-10 times to obtain the first strip matrix. Preferably, the longitudinal stretching rate is 8%-75% / s. The stretching rate (including longitudinal and transverse stretching rates) is specifically achieved by the distance between the rollers and the speed difference between the rollers. During the longitudinal stretching process, nodes and fibers begin to split. Since the activation energy of PTFE resin for fiber formation is very low, a relatively high stretching temperature is required (but the temperature cannot be too high) to easily form an ideal fiber structure, which, in conjunction with the subsequent transverse stretching, forms a suitable membrane pore size to facilitate bacterial retention. A longitudinal stretching temperature of 150-250℃ is preferable. If the longitudinal stretching temperature is too high, the uniformity of the film formation will be very poor. If the longitudinal stretching temperature is below 150℃, the degree of fiberization of the membrane will be insufficient, and an ideal surface fiber and high porosity filter membrane cannot be formed, resulting in a low final flux and high pressure drop.

[0080] After longitudinal stretching, transverse stretching is performed directly without any heat setting. This is because heat setting at this stage would lock the structure, resulting in elongated, large-area surface nodes that are almost parallel to each other. Direct transverse stretching, however, allows for the formation of shorter, less coarse nodes on the membrane surface, ensuring the membrane pores are not excessively large (achieving the desired pore size). In this invention, the transverse stretching temperature is 150-300℃, the stretching ratio is 26-50 times, and the stretching rate is no more than 100% / s. As a key aspect of this invention, a higher stretching ratio and temperature are required during transverse stretching. The transverse stretching rate is relatively slow (which is beneficial for separating the fibers and increasing porosity), thus facilitating the acquisition of surface fibers of suitable thickness and ideal membrane pore size. Preferably, the ratio of longitudinal stretching rate to transverse stretching rate is 0.3-0.8, ensuring that the transverse stretching rate is not too slow, the surface fibers and surface are not too coarse, and the diameters of the support points and supporting fibers are not too large, thus guaranteeing membrane flux. The ratio of transverse stretching ratio to longitudinal stretching ratio is 3.5-12. The temperature during transverse stretching is 20-60°C higher than the temperature during longitudinal stretching. The transverse stretching ratio and temperature are not too high, further obtaining an ideal membrane structure while ensuring the uniformity of fibers and membrane pores, thereby further ensuring the retention of bacteria.

[0081] The second substrate, after being stretched laterally, undergoes a first heat setting at 330-390℃ for 0.2-3 minutes, which can be considered a preliminary setting. This preliminary setting time should not be too long, primarily serving as initial fusion setting and stress relaxation (eliminating internal stress caused by incoordination in the material's microstructure deformation). This results in a film with high mechanical strength and a long service life. However, the first heat setting time should not be too long, as this can easily lead to excessive fiber fusion, resulting in uneven pore size and fiber uniformity. Preferably, during the first heat setting process, the film should also be stretched to control the longitudinal and transverse shrinkage rates of the second substrate, ensuring a thickness shrinkage rate of 3-18%. This reduces the surface shrinkage rate of the second substrate during the first heat setting (ensuring that surface fibers and nodes are not too coarse), while also causing some shrinkage in the thickness direction, leading to fiber fusion and filamentation, which facilitates the formation of support points and fibers of suitable thickness.

[0082] Finally, a second heat setting is performed, which takes a longer time, ranging from 5 to 20 minutes. During this second heat setting, the semi-finished filter membrane needs to be stretched taut to keep it under tension. This limits the longitudinal and transverse shrinkage of the surface, resulting in shrinkage primarily in the thickness direction, with a thickness shrinkage rate greater than 20%, ideally 25%-45%. Through this extended second heat setting, recrystallization occurs, and the fibers in the thickness direction are fully fused (coalesced), while the fibers in the surface direction are not fully fused (coalesced), thus obtaining a filter membrane with suitable fiber structure, thickness, and pore size.

[0083] Through the combined action of the first and second heat setting, the membrane is fully set, resulting in a filter membrane with good dimensional stability and high strength. This membrane also has high bacterial retention efficiency and high throughput, making it suitable for a wide range of applications.

[0084] As a further improvement of the present invention, a PTFE sterilization filter membrane is used for liquid sterilization and / or gas sterilization.

[0085] Because PTFE filter membranes are resistant to acids and alkalis, they have a wide range of applications. Furthermore, the manufacturing process contains virtually no additives, resulting in low leaching during filtration and preventing impact on the effective substances in the fluid. Additionally, PTFE filter membranes are essentially neutral and uncharged, making them less prone to adsorbing proteins and ensuring high yields. They are suitable for sterilization of various gases, such as in respirators and fermenters, as well as for liquid sterilization, and are commonly used to filter various pharmaceutical solutions with organic solvents.

[0086] The beneficial effects of this invention are as follows: The PTFE sterilization filter membrane provided by this invention comprises a main body with non-directional tortuous pathways within it. One side surface of the main body is a first outer surface, and the other side surface is a second outer surface, wherein the first and second outer surfaces are substantially symmetrical. Each outer surface of the filter membrane includes surface nodes and surface fibers for forming a porous structure, with adjacent surface nodes connected by surface fibers. The filter membrane has an IPA bubble point of 0.12-0.35 MPa and a suitable pore size. The filter membrane thickness is 30-80 μm. The average SEM width of the surface fibers is 80-350 nm, and the average SEM length of the surface fibers is 0.9-2.5 μm. The membrane exhibits suitable pore size, suitable membrane thickness, and suitable... The membrane structure (symmetrical two outer surfaces and tortuous pathways) and the combined effect of surface fibers of suitable length and coarseness ensure sufficient retention of bacteria, achieving ideal bacterial capture. Simultaneously, the surface fibers of such fineness have minimal impact on membrane flux, and due to the relatively large overall pore size of the filter membrane, it still maintains a high flux. Furthermore, the surface fibers of such fineness are not prone to breakage, ensuring high mechanical strength, enabling the filter membrane to withstand high pressure during filtration, and exhibiting strong stability and a long service life. This filter membrane is suitable for liquid and / or gas sterilization, with a wide range of applications. In addition, this invention provides a method for preparing this filter membrane, which is convenient, rapid, effective, simple to operate, environmentally friendly, and suitable for large-scale promotion. Attached Figure Description

[0087] Figure 1 The image shows a scanning electron microscope (SEM) image of the liquid inlet surface of the PTFE filter membrane prepared in Example 1, with a magnification of 1000×.

[0088] Figure 2 The image shown is a further magnified scanning electron microscope (SEM) image of the liquid inlet surface of the PTFE filter membrane prepared in Example 1, with a magnification of 5000×.

[0089] Figure 3 The image shows a scanning electron microscope (SEM) image of the liquid outlet surface of the PTFE filter membrane prepared in Example 1, with a magnification of 1000×.

[0090] Figure 4 The image shown is a further magnified scanning electron microscope (SEM) image of the liquid outlet surface of the PTFE filter membrane prepared in Example 1, with a magnification of 5000×.

[0091] Figure 5 The image shows a scanning electron microscope (SEM) image of the longitudinal section of the PTFE filter membrane prepared in Example 1, with a magnification of 5000×.

[0092] Figure 6The image shown is a further magnified scanning electron microscope (SEM) image of the longitudinal section of the PTFE filter membrane prepared in Example 1, with a magnification of 2000×. Detailed Implementation

[0093] To more clearly illustrate the overall concept of this application, detailed descriptions are provided below using examples. Unless otherwise specified, the raw materials and equipment used in the preparation of the PTFE antibacterial filter membrane in the following examples are commercially available. The structural morphology of the PTFE antibacterial filter membrane was characterized using a Hitachi S-5500 scanning electron microscope.

[0094] Example 1: A method for preparing a PTFE antibacterial filter membrane, comprising the following steps:

[0095] A. Mixing: The polytetrafluoroethylene dispersion resin and lubricant are mixed and stirred at a weight ratio of 1:0.3, and then placed in an environment at 48°C for 20 hours to mature, thereby obtaining a paste; the polytetrafluoroethylene dispersion resin has a number average molecular weight of 10 million and a crystallinity of over 90%; the lubricant is lubricating oil.

[0096] B. Blank making: The above paste is pre-pressed into a cylindrical blank;

[0097] C. Extrusion: The blank obtained in step B is extruded to form a flat strip matrix; the strip matrix is ​​then rolled so that the thickness of the rolled strip matrix is ​​70% of the thickness of the strip matrix before rolling.

[0098] D. Drying: The strip-shaped substrate is dried to allow the lubricant to evaporate;

[0099] E. Longitudinal stretching: The dried strip matrix is ​​longitudinally stretched at a temperature of 220℃ and a stretching ratio of 8 times to obtain the first strip matrix; the longitudinal stretching rate is 60% / s.

[0100] F. Lateral stretching: The first strip matrix is ​​laterally stretched at a temperature of 280°C, a stretching ratio of 44 times, and a stretching rate of 80% / s to obtain the second matrix.

[0101] G. First heat setting: The second substrate is placed in an environment with a temperature of 370°C for the first heat setting for 1 minute to obtain a filter membrane semi-finished product; During the first heat setting, the longitudinal shrinkage rate and transverse shrinkage rate of the second substrate are controlled so that the shrinkage rate in the membrane thickness direction is 8%;

[0102] H. Second heat setting: The filter membrane semi-finished product is placed in an environment with a temperature of 380℃ for a second heat setting. During the second heat setting, the longitudinal shrinkage rate and transverse shrinkage rate of the filter membrane semi-finished product are controlled so that the shrinkage rate in the membrane thickness direction is 30%. The second heat setting time is 10 minutes to obtain the filter membrane.

[0103] Example 2: A method for preparing a PTFE antibacterial filter membrane, comprising the following steps:

[0104] A. Mixing: The polytetrafluoroethylene dispersion resin and lubricant are mixed and stirred at a weight ratio of 1:0.25, and then placed in an environment at a temperature of 45°C for 18 hours to obtain a paste; the polytetrafluoroethylene dispersion resin has a number average molecular weight of 9 million and a crystallinity of over 90%; the lubricant is palm oil.

[0105] B. Blank making: The above paste is pre-pressed into a cylindrical blank;

[0106] C. Extrusion: The blank obtained in step B is extruded to form a flat strip matrix; the strip matrix is ​​then rolled so that the thickness of the rolled strip matrix is ​​60% of the thickness of the strip matrix before rolling.

[0107] D. Drying: The strip-shaped substrate is dried to allow the lubricant to evaporate;

[0108] E. Longitudinal stretching: The dried strip matrix is ​​longitudinally stretched at a temperature of 210℃ and a stretching ratio of 7 times to obtain the first strip matrix; the longitudinal stretching rate is 50% / s.

[0109] F. Lateral stretching: The first strip matrix is ​​laterally stretched at a temperature of 260°C, a stretching ratio of 40 times, and a stretching rate of 70% / s to obtain the second matrix.

[0110] G. First heat setting: The second substrate is placed in an environment with a temperature of 360°C for the first heat setting, and the heat setting time is 1.2 minutes to obtain a filter membrane semi-finished product; during the first heat setting, the longitudinal shrinkage rate and transverse shrinkage rate of the second substrate are controlled so that the shrinkage rate in the membrane thickness direction is 10%;

[0111] H. Second heat setting: The filter membrane semi-finished product is placed in an environment with a temperature of 370℃ for a second heat setting. During the second heat setting, the longitudinal shrinkage rate and transverse shrinkage rate of the filter membrane semi-finished product are controlled so that the shrinkage rate in the membrane thickness direction is 32%. The second heat setting time is 12 minutes to obtain the filter membrane.

[0112] Example 3: A method for preparing a PTFE antibacterial filter membrane, comprising the following steps:

[0113] A. Mixing: The polytetrafluoroethylene dispersion resin and lubricant are mixed and stirred at a weight ratio of 1:0.2, and then placed in an environment at a temperature of 42°C for 15 hours to mature, thereby obtaining a paste; the polytetrafluoroethylene dispersion resin has a number average molecular weight of 8 million and a crystallinity of over 90%; the lubricant is naphthenic oil.

[0114] B. Blank making: The above paste is pre-pressed into a cylindrical blank;

[0115] C. Extrusion: The blank obtained in step B is extruded to form a flat strip matrix; the strip matrix is ​​then rolled so that the thickness of the rolled strip matrix is ​​55% of the thickness of the strip matrix before rolling.

[0116] D. Drying: The strip-shaped substrate is dried to allow the lubricant to evaporate;

[0117] E. Longitudinal stretching: The dried strip matrix is ​​longitudinally stretched at a temperature of 200℃ and a stretching ratio of 6 times to obtain the first strip matrix; the longitudinal stretching rate is 40% / s.

[0118] F. Lateral stretching: The first strip matrix is ​​laterally stretched at a temperature of 240°C, a stretching ratio of 36 times, and a stretching rate of 60% / s to obtain the second matrix.

[0119] G. First heat setting: The second substrate is placed in an environment with a temperature of 350°C for the first heat setting for 1.5 minutes to obtain a filter membrane semi-finished product; During the first heat setting, the longitudinal shrinkage rate and transverse shrinkage rate of the second substrate are controlled so that the shrinkage rate in the membrane thickness direction is 12%;

[0120] H. Second heat setting: The filter membrane semi-finished product is placed in an environment with a temperature of 360°C for a second heat setting. During the second heat setting, the longitudinal shrinkage rate and transverse shrinkage rate of the filter membrane semi-finished product are controlled so that the shrinkage rate in the membrane thickness direction is 34%. The second heat setting time is 14 minutes to obtain the filter membrane.

[0121] Example 4: A method for preparing a PTFE antibacterial filter membrane, comprising the following steps:

[0122] A. Mixing: The polytetrafluoroethylene dispersion resin and lubricant are mixed and stirred at a weight ratio of 1:0.15, and then placed in an environment at 38°C for 12 hours to mature, thereby obtaining a paste; the polytetrafluoroethylene dispersion resin has a number average molecular weight of 6 million and a crystallinity of over 90%; the lubricant is white oil.

[0123] B. Blank making: The above paste is pre-pressed into a cylindrical blank;

[0124] C. Extrusion: The blank obtained in step B is extruded to form a flat strip matrix; the strip matrix is ​​then rolled so that the thickness of the rolled strip matrix is ​​45% of the thickness of the strip matrix before rolling.

[0125] D. Drying: The strip-shaped substrate is dried to allow the lubricant to evaporate;

[0126] E. Longitudinal stretching: The dried strip matrix is ​​longitudinally stretched at a temperature of 180℃ and a stretching ratio of 5 times to obtain the first strip matrix; the longitudinal stretching rate is 30% / s.

[0127] F. Lateral stretching: The first strip matrix is ​​laterally stretched at a temperature of 220°C, a stretching ratio of 32 times, and a stretching rate of 50% / s to obtain the second matrix.

[0128] G. First heat setting: The second substrate is placed in an environment with a temperature of 340°C for the first heat setting for 2 minutes to obtain a filter membrane semi-finished product; During the first heat setting, the longitudinal shrinkage rate and transverse shrinkage rate of the second substrate are controlled so that the shrinkage rate in the membrane thickness direction is 14%;

[0129] H. Second heat setting: The filter membrane semi-finished product is placed in an environment with a temperature of 350℃ for a second heat setting. During the second heat setting, the longitudinal shrinkage rate and transverse shrinkage rate of the filter membrane semi-finished product are controlled so that the shrinkage rate in the membrane thickness direction is 36%. The second heat setting time is 15 minutes to obtain the filter membrane.

[0130] Example 5: A method for preparing a PTFE antibacterial filter membrane, comprising the following steps:

[0131] A. Mixing: Polytetrafluoroethylene dispersion resin and lubricant are mixed and stirred at a weight ratio of 1:0.1, and then placed in an environment at 36°C for 10 hours to mature, thereby obtaining a paste; the number average molecular weight of the polytetrafluoroethylene dispersion resin is 5 million, and the crystallinity is above 90%; the lubricant is aviation kerosene; B. Preforming: The above paste is pre-pressed into a cylindrical preform;

[0132] C. Extrusion: The blank obtained in step B is extruded to form a flat strip matrix; the strip matrix is ​​then rolled so that the thickness of the rolled strip matrix is ​​35% of the thickness of the strip matrix before rolling.

[0133] D. Drying: The strip-shaped substrate is dried to allow the lubricant to evaporate;

[0134] E. Longitudinal stretching: The dried strip matrix is ​​longitudinally stretched at a temperature of 160℃ and a stretching ratio of 4 times to obtain the first strip matrix; the longitudinal stretching rate is 20% / s.

[0135] F. Lateral stretching: The first strip matrix is ​​laterally stretched at a temperature of 200°C, a stretching ratio of 30 times, and a stretching rate of 40% to obtain the second matrix.

[0136] G. First heat setting: The second substrate is placed in an environment with a temperature of 335°C for the first heat setting for 2.5 minutes to obtain a filter membrane semi-finished product; During the first heat setting, the longitudinal shrinkage rate and transverse shrinkage rate of the second substrate are controlled so that the shrinkage rate in the membrane thickness direction is 16%;

[0137] H. Second heat setting: The filter membrane semi-finished product is placed in an environment with a temperature of 350℃ for a second heat setting. During the second heat setting, the longitudinal shrinkage rate and transverse shrinkage rate of the filter membrane semi-finished product are controlled so that the shrinkage rate in the membrane thickness direction is 38%. The second heat setting time is 18 minutes to obtain the filter membrane.

[0138] Example 6

[0139] Based on Example 1, the number-average molecular weight of the polytetrafluoroethylene dispersion resin in step A was adjusted to 14 million, and the lubricant was adjusted to degreased kerosene; the longitudinal stretching rate in step E was adjusted to 10% / s; the transverse stretching temperature in step F was adjusted to 260℃, and the transverse stretching rate was adjusted to 12% / s (the ratio of the longitudinal stretching rate to the transverse stretching rate was 0.83); all other preparation conditions remained unchanged, and the corresponding filter membrane was obtained.

[0140] Example 7

[0141] Based on Example 1, the number-average molecular weight of the polytetrafluoroethylene dispersion resin in step A was adjusted to 2 million, and the lubricant was adjusted to paraffin wax; the longitudinal stretching rate in step E was adjusted to 80% / s; the transverse stretching temperature in step F was adjusted to 240℃, and the transverse stretching rate was adjusted to 100% / s (the ratio of the longitudinal stretching rate to the transverse stretching rate was 0.8); all other preparation conditions remained unchanged, and the corresponding filter membrane was obtained.

[0142] Example 8

[0143] Based on Example 1, the crystallinity of the polytetrafluoroethylene dispersion resin in step A was adjusted to 80, and the lubricant was changed to paraffin wax; the longitudinal stretching rate in step E was adjusted to 50% / s; the transverse stretching temperature in step F was adjusted to 235℃, and the transverse stretching rate was adjusted to 75% / s (the ratio of the longitudinal stretching rate to the transverse stretching rate was 0.67); all other preparation conditions remained unchanged, and the corresponding filter membrane was obtained.

[0144] Comparative Example 1

[0145] Based on Example 1, the longitudinal stretching temperature in step E was set to 130°C, the longitudinal stretching ratio was set to 3 times, and the longitudinal stretching rate was set to 90% / s; the transverse stretching temperature in step F was set to 140°C, the transverse stretching ratio was set to 15 times, and the transverse stretching rate was set to 150% / s; all other preparation conditions remained unchanged, and the corresponding filter membrane was obtained.

[0146] Comparative Example 2

[0147] Based on Example 1, in step G, the longitudinal and transverse shrinkage rates of the second substrate are not controlled during the first heat setting, and the first heat setting time is adjusted to 0.5 min. In step H, during the second heat setting, the longitudinal and transverse shrinkage rates of the filter membrane semi-finished product are not controlled, so that the membrane will shrink significantly in the planar direction and the shrinkage in the membrane thickness direction will be greatly reduced. In addition, the second heat setting temperature is adjusted to 375°C and the time is adjusted to 2 min. With the other conditions unchanged, the corresponding filter membrane is obtained.

[0148] Structural characterization: The surface and cross-sectional morphology of the filter membranes obtained in each embodiment and comparative example were characterized by scanning electron microscopy to obtain the corresponding data;

[0149] Table 1: Corresponding characteristics of surface fibers and surface nodes

[0150]

[0151]

[0152] Table 2

[0153]

[0154] Table 3: Corresponding characteristics of support points and support fibers

[0155]

[0156] As can be seen from the tables above, the PTFE filter membranes prepared in Examples 1-8 of the present invention all have ideal node and fiber structures, which are beneficial to the polytetrachloroethylene filter membrane having high tensile strength, high flux and sufficient retention of bacteria.

[0157] Various tests were performed on the filter membranes prepared in Examples 1-8 and Comparative Examples 1 and 2 to obtain the corresponding parameters such as IPA bubble point, thickness, average compactness Q, LRV against defective Pseudomonas, flow rate, porosity and tensile strength.

[0158] Table 4

[0159] Sample IPA bubble point / MPa Thickness / μm Average compactness Q / % <![CDATA[Grammage g / m 2 > LRV Flow rate / s Example 1 0.16 65 45 25 ＞7 20 Example 2 0.20 55 50 27 ＞7 22 Example 3 0.24 50 55 31 ＞7 24 Example 4 0.28 45 60 33 ＞7 28 Example 5 0.30 40 68 35 ＞7 32 Example 6 0.20 60 48 29 ＞7 34 Example 7 0.12 70 40 21 ＞7 18 Example 8 0.17 64 42 23 ＞7 21 Comparative Example 1 0.60 50 80 48 ＞7 80 Comparative Example 2 0.10 75 28 16 4.5 15

[0160] Table 5

[0161]

[0162] As shown in Tables 4 and 5, the filter membranes prepared in Examples 1 to 8 have ideal structures (such as pore size, thickness, average compactness, and basis weight), which makes the filter membranes not only highly efficient in removing bacteria, but also have high flux, good tensile strength, and high mechanical strength, making them suitable for various processing and with a wide range of applications. The filter membrane in Comparative Example 1, by making the pores smaller, ensures the retention efficiency, but its flux is significantly reduced, which cannot meet the needs of practical applications. As for Comparative Example 2, because the shrinkage rate in the thickness direction was not guaranteed during heat setting, the final filter membrane has insufficient compactness, larger pores, poor bacterial retention efficiency, and cannot be used as a sterilization membrane.

[0163] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A PTFE antibacterial filter membrane, characterized in that: The filter membrane includes a main body with non-directional tortuous pathways. One side surface of the main body is a first outer surface, and the other side surface of the main body is a second outer surface. The first and second outer surfaces are substantially symmetrical. Each side surface of the filter membrane includes surface nodes and surface fibers for forming a porous structure, and adjacent surface nodes are connected by surface fibers. The cross-section of the main body includes several support points and support fibers, and adjacent support points are connected by support fibers; the support points have a granular structure. The filter membrane has an IPA bubble point of 0.12-0.35 MPa and a thickness of 30-80 μm. The surface fibers have an average SEM width of 80-350 nm and an average SEM length of 0.9-2.5 μm. The average SEM length of the surface nodes is 0.6-3.0 μm, and the average SEM diameter of the surface nodes is 250-900 nm. The filter membrane has an LRV greater than 7 for defective Pseudomonas.

2. The PTFE sterilization filter membrane according to claim 1, characterized in that: The average compactness Q of the membrane body is 35%-85%, and the average compactness Q is calculated by the following formula: Q=D 实 / D×100%; In the above formula, D 实 D is the sum of the thicknesses of all entities along the thickness direction of the membrane body, where each entity includes the support point and the support fiber, and D is the thickness of the membrane body.

3. The PTFE antibacterial filter membrane according to claim 1, characterized in that: The length direction of the surface node is substantially perpendicular to the length direction of the surface fiber; The basis weight of the filter membrane is 18-45 g / m³. 2 ; The aspect ratio of the surface fibers is 4-16.

4. The PTFE sterilization filter membrane according to claim 1, characterized in that: The basis weight of the filter membrane is 22-35 g / m³. 2 .

5. The PTFE sterilization filter membrane according to claim 1, characterized in that: The aspect ratio of the surface nodes is 1.2-8; The average SEM area of ​​the surface nodes is 0.5-2 μm. 2 ; The ratio of the average SEM length of the surface node to the average SEM length of the surface fiber is 1.03-3; The ratio of the average SEM width of the surface node to the average SEM width of the surface fiber is 1.5-7.

6. The PTFE sterilization filter membrane according to claim 1, characterized in that: The porosity of the first outer surface is 25%-55%; On the first outer surface, the ratio between the sum of the surface node areas and the sum of the surface fiber areas is 0.5-0.

9.

7. The PTFE antibacterial filter membrane according to claim 1, characterized in that: The average SEM spacing between adjacent surface fibers is 200-600 nm; the ratio of the average SEM spacing between adjacent surface fibers to the average SEM width of the surface fibers is 1.5-6.

8. The PTFE antibacterial filter membrane according to claim 1, characterized in that: On any side of the outer surface of the filter membrane, the difference between the maximum and minimum SEM width of the surface nodes is 100-800 μm; the uniformity coefficient of the SEM width of the surface nodes is 10%-35%. The surface node uniformity coefficient = the standard deviation of the surface nodes / the average value of the surface nodes.

9. The PTFE antibacterial filter membrane according to claim 1, characterized in that: The uniformity coefficient of the surface node SEM length is greater than the uniformity coefficient of the surface node SEM width, and the difference between the two is 10%-40%.

10. The PTFE sterilization filter membrane according to claim 1, characterized in that: The average SEM diameter of the support point is 150-650 nm, and the ratio of its average SEM diameter to film thickness is 0.006-0.

014.

11. The PTFE sterilization filter membrane according to claim 1, characterized in that: On the cross-section of the membrane, the average spacing between adjacent support points in the thickness direction is 1.5-4 μm, and the ratio of this average spacing to the thickness is 2%-10%.

12. The PTFE sterilization filter membrane according to claim 1, characterized in that: The average SEM length of the supporting fiber is 800-2200 nm, and the average SEM diameter of the supporting fiber is 80-260 nm. The ratio of the average SEM length of the supporting fiber to the film thickness is 1%-6%.

13. The PTFE antibacterial filter membrane according to claim 1, characterized in that: Under a pressure of 0.03 MPa and a temperature of 20°C, it takes 15-35 seconds for 50 ml of water to pass through a filter membrane with a diameter of 47 mm. The porosity of the filter membrane is 55-85%; The filter membrane has a transverse tensile strength and a longitudinal tensile strength of 10-60 MPa. The transverse and longitudinal tensile ratios of the filter membrane are both greater than 40%.

14. A method for preparing a PTFE antibacterial filter membrane according to any one of claims 1 to 13, characterized in that: Includes the following steps: A. Mixing: Mix and stir the polytetrafluoroethylene dispersion resin and lubricant until a paste is obtained; B. Blank making: The above paste is pre-pressed into a cylindrical blank; C. Extrusion: The preform obtained in step B is extruded to form a flat strip-shaped matrix; D. Drying: The strip-shaped substrate is dried to allow the lubricant to evaporate; E. Longitudinal stretching: The dried strip matrix is ​​stretched longitudinally at a temperature of 150-250℃ and a stretching ratio of 2-10 times to obtain the first strip matrix. F. Lateral stretching: The first strip matrix is ​​laterally stretched at a temperature of 150-300℃, a stretching ratio of 26-50 times, and a stretching rate of no more than 100% / s to obtain the second matrix. G. First heat setting: The second substrate is placed in an environment with a temperature of 330-390℃ for the first heat setting, and the heat setting time is 0.2-3 minutes to obtain the filter membrane semi-finished product; H. Second heat setting: The semi-finished filter membrane is placed in an environment with a temperature of 330-390℃ for a second heat setting. During the second heat setting, the longitudinal shrinkage rate and transverse shrinkage rate of the semi-finished filter membrane are controlled so that the shrinkage rate in the membrane thickness direction is greater than 20%. The second heat setting time is 5-20 minutes to obtain the filter membrane.

15. The method for preparing a PTFE antibacterial filter membrane according to claim 14, characterized in that: The polytetrafluoroethylene dispersion resin has a number average molecular weight of 4 million to 12 million and a crystallinity of over 90%. The lubricant is at least one of the following: lubricating oil, palm oil, naphthenic oil, white oil, aviation kerosene, degreased kerosene, and paraffin wax; Step A, mixing, specifically refers to mixing and stirring the polytetrafluoroethylene dispersion resin and lubricant at a weight ratio of 1:0.1-1:0.3, then placing it in an environment with a temperature of 35-50℃ for 8-24 hours to obtain a paste.

16. The method for preparing a PTFE antibacterial filter membrane according to claim 14, characterized in that: The strip-shaped substrate obtained in step C is calendered so that the thickness of the calendered strip-shaped substrate is 30%-70% of the thickness of the strip-shaped substrate before calendering; During the first heat setting, the longitudinal and transverse shrinkage rates of the second substrate are controlled to achieve a film thickness shrinkage rate of 3%-18%. During the second heat setting process, the thickness shrinkage rate of the filter membrane semi-finished product is 25%-45%.

17. The method for preparing a PTFE antibacterial filter membrane according to claim 14, characterized in that: In step E, the longitudinal stretching rate is 8-75% / s, and the ratio of the longitudinal stretching rate to the transverse stretching rate is 0.3-0.

8.

18. The method for preparing a PTFE antibacterial filter membrane according to claim 14, characterized in that: The ratio of the transverse stretching ratio to the longitudinal stretching ratio is 3.5-12; The temperature during transverse stretching is 20-60°C higher than the temperature during longitudinal stretching.

19. The use of a PTFE antibacterial filter membrane as described in any one of claims 1-13, characterized in that: The PTFE sterilization filter membrane is used for liquid sterilization and / or gas sterilization.

Images