Polyethylene filter membrane as well as preparation method and application thereof

Abstract

The invention provides a polyethylene filter membrane as well as a preparation method and application thereof, a main body of the polyethylene filter membrane comprises a flow guide area, an adsorption area, an interception area and a non-directional zigzag passage, and the thickness of the adsorption area, the ratio of the thickness of the adsorption area to the thickness of the interception area, the HFE complete bubbling point and the specific surface area of the filter membrane are in reasonable ranges. The SEM average diameter of the flow guide area is larger than that of the adsorption area, and the SEM average diameter of the adsorption area is larger than that of the interception area, so that high flux and high interception efficiency are achieved at the same time, and the filtering device can be efficiently used for filtering photoresist process materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of membrane materials, and particularly relates to a polyethylene filter membrane and a preparation method and application thereof. BACKGROUND

[0002] With the continuous advancement of semiconductor manufacturing processes to higher precision and smaller nodes, the purity requirement of semiconductor lithography process materials as key materials in the pattern transfer process is increasingly high. Impurities in semiconductor lithography process materials include three categories of organic impurities, inorganic impurities and particle impurities. The above impurities have different particle sizes. However, even the presence of a small amount of small-size nanoscale impurities (for example, 2 nm impurities) can cause pattern defects or even device failure. Therefore, before the preparation and use of semiconductor lithography process materials, efficient removal of impurities becomes a key link to ensure process yield.

[0003] Polyethylene filter membranes (UPE) are widely used in the filtration of semiconductor lithography process materials due to their high chemical stability and high mechanical strength. In order to obtain high-purity semiconductor lithography process materials, small-size nanoscale impurities (for example, 2 nm impurities) are usually removed by reducing the pore size of the filter membrane and / or increasing the thickness of the separation layer (in the present application, the retention zone). However, the above-mentioned methods will cause the problem of flux decline of the filter membrane, that is, high retention efficiency and flux cannot be achieved at the same time, which seriously restricts its practicality in actual production.

[0004] Therefore, it is urgent to develop a UPE filter membrane that can achieve high retention efficiency and flux at the same time in the filtration of semiconductor lithography process materials. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a polyethylene filter membrane and a preparation method and application thereof. The filter membrane has non-directional tortuous passages in the main body, and the main body comprises a flow guide zone, an adsorption zone and a retention zone in the thickness direction from the liquid inlet surface to the liquid outlet surface. By adjusting the HFE complete bubble point of the filter membrane to be relatively large (the overall membrane pore is relatively small but not too small), the specific surface area is appropriate, the SEM average pore diameter of the flow guide zone is larger than that of the adsorption zone, the SEM average pore diameter of the adsorption zone is larger than that of the retention zone, the thickness of the adsorption zone is relatively large, and the thickness of the adsorption zone is relatively large compared with the thickness of the retention zone. When used for the filtration of semiconductor lithography process materials, high retention efficiency and flux can be achieved at the same time.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a polyethylene filter membrane, comprising a main body, one side of which is an inlet liquid surface and the other side of which is an outlet liquid surface; the main body has a non-directional tortuous pathway; the HFE complete bubble point of the filter membrane is 0.5 MPa-1.5 MPa; the main body sequentially comprises a guiding zone, an adsorption zone, and a retention zone along its thickness from the inlet liquid surface to the outlet liquid surface; the SEM average pore size of the guiding zone is larger than that of the adsorption zone, and the SEM average pore size of the adsorption zone is larger than that of the retention zone; the specific surface area of ​​the filter membrane is 8 m². 2 / g-20m 2 / g; the thickness of the adsorption zone is not less than 20μm; the ratio of the thickness of the adsorption zone to the thickness of the retention zone is greater than 3.

[0007] Impurities in semiconductor lithography materials can lead to a decrease in semiconductor device yield. Even small amounts of tiny nanoscale impurities (e.g., 2nm impurities) can cause a drop in yield. Therefore, it is necessary to control the impurities in semiconductor lithography materials to extremely low or even zero levels. Filter membranes are frequently used to filter semiconductor lithography materials as an effective means of removing impurities. Those skilled in the art typically improve impurity removal efficiency by reducing the overall pore size of the filter membrane. However, reducing the pore size inevitably leads to a significant decrease in flux, making it impossible to achieve a good balance between removal efficiency and flux. The inventors of this application have discovered through continuous research that, under specific membrane structures, slightly increasing the overall pore size of the filter membrane can still result in a filter membrane with high removal efficiency while simultaneously improving flux.

[0008] Firstly, by adjusting the complete bubble point of the HFE (hydrofluoroether) of the filter membrane to 0.5 MPa-1.5 MPa, the overall pore size of the filter membrane is characterized by its HFE complete bubble point. A higher complete bubble point indicates a smaller overall pore size. This specific bubble point size indicates that the pore size of the filter membrane is relatively small but not excessively small, capable of trapping impurities in photoresist materials ranging from a few nanometers to tens of nanometers. This provides a foundation for ensuring retention efficiency and increasing throughput. Furthermore, by macroscopically controlling the filter membrane structure from the inlet to the outlet... The liquid surface, in its thickness direction, comprises a guiding zone, an adsorption zone, and a retention zone, with the SEM average pore size of the guiding zone being larger than that of the adsorption zone, which in turn is larger than that of the retention zone. In other words, the guiding zone has the largest SEM average pore size, followed by the adsorption zone, and the retention zone has the smallest. The guiding zone, located near the inlet liquid surface, is the first area through which the fluid passes during the filtration of semiconductor photolithography materials. The guiding zone, with its larger pore size, provides numerous and wide fluid pathways. On the one hand, it can reduce the resistance of the semiconductor photolithography process material fluid entering the membrane, ensuring the overall high throughput of the filter membrane. On the other hand, the synergistic effect of the larger pore size of the guiding zone and the non-directional tortuous path in the main body causes the pores to overlap. The size of the nano impurities is larger than the size of the superimposed pores, which can achieve the removal of nano impurities. That is, the relatively large nano impurities (often hundreds of nanometers or large nanometers in diameter) larger than the pore size of the guiding zone membrane and smaller than the pore size of the guiding zone membrane are removed, which can prevent large impurities from entering the adsorption zone or the retention zone and causing deep blockage. It protects the channels of the adsorption zone and the retention zone and indirectly contributes to the overall high throughput of the filter membrane. That is, the guiding zone is the "pre-protection layer" of the throughput. At the same time, since the filter membrane is composed of ultra-high molecular weight polyethylene, it has relatively high strength. Even when the pore size of the guiding zone is relatively large, the guiding zone can withstand the pressure brought by the fluid entering from the liquid inlet surface. It can maintain the integrity of the guiding zone structure when the fluid enters, thus achieving effective filtration for a long time.As one of the key aspects of this invention, the adsorption zone primarily receives fluid from the guiding zone and transports it to the retention zone. Its pore size lies between that of the guiding and retention zones, serving as the main channel for fluid transport and a crucial area for maintaining impurity rejection rates. The adsorption zone possesses a relatively wide fluid pathway (its pore size is larger than that of the retention zone), ensuring a high overall flux of the filter membrane. Simultaneously, the adsorption zone, in conjunction with the non-directional tortuous pathways within the main body, effectively removes nano-impurities larger than the pore size of the adsorption zone and some smaller than the pore size. Furthermore, due to the pore walls within the adsorption zone... It can serve as a carrier for impurity adsorption. By controlling the specific surface area (specific surface area refers to the total surface area of ​​the filter membrane per unit mass) of this invention, the adsorption zone has a relatively large number of pore walls, i.e., a relatively large number of adsorption sites. Under the influence of van der Waals forces, hydrogen bonds, etc., it can adsorb more impurities. In conjunction with the non-directional tortuous pathway inside the adsorption zone, impurities that are not excluded or adsorbed need to turn multiple times in the non-directional tortuous pathway to penetrate the membrane, thus increasing the actual migration path. Moreover, the thickness of the adsorption zone is not less than 20 μm, meaning that the overall path of impurities through the adsorption zone is relatively long. Furthermore, the multiple turning points increase the adsorption of impurities and the number of collisions between impurities and the pore walls. During these collisions, larger aggregates formed between impurities are effectively removed due to the larger pore size of the membrane. Simultaneously, impurities are easily adsorbed or retained due to inertia or spatial constraints when turning or entering branches. These adsorbed or retained nano-impurities on the pore walls reduce the pore size, further removing more impurities. These removed impurities then further hinder the desorbed or retained nano-impurities, preventing them from continuing to flow forward under the influence of the fluid. This allows more tiny nano-impacts (a few nanometers or tens of nanometers) to be retained in the adsorption zone (without needing to reach the retention zone to be retained), achieving a technical effect of 1+1>2. Only a relatively small number of tiny impurities will enter the retention zone, and most of the pores in the retention zone remain in a flowable state after filtration, protecting the channels in the retention zone and ensuring a high overall flux of the membrane. In other words, the adsorption zone is the "core balance layer" between flux and retention. If the filter membrane is directly composed of the flow guiding zone and the retention zone, the fluid flow rate from the flow guiding zone to the retention zone will change abruptly, causing damage to the membrane pores and resulting in low retention efficiency.The pore size of the retention zone is the smallest, which is the core guarantee of retention accuracy. It removes smaller nanoscale impurities in the fluid that are not retained by the adsorption zone, and is the last barrier to retention efficiency. In synergy with the non-directional tortuous pathways within the bulk, it can retain impurities from 1nm to 10nm, acting as the "final gatekeeper" for retention. Furthermore, the ratio of the thickness of the adsorption zone to the thickness of the retention zone is greater than 3, meaning the thickness of the retention zone is relatively small compared to the adsorption zone. This ensures that the flux remains at a high level. If the thickness of the retention zone is too large, even with the presence of the flow-guiding and adsorption zones, the overall flux of the filter membrane will be low.

[0009] Therefore, the main body of this UPE filter membrane contains a flow guiding zone, an adsorption zone, a retention zone, and a non-directional tortuous path. The thickness of the adsorption zone, the ratio of the adsorption zone thickness to the retention zone thickness, the complete bubble point of HFE, and the specific surface area of ​​the filter membrane are all within a reasonable range. Furthermore, the average SEM diameter of the flow guiding zone is greater than that of the adsorption zone, and the average SEM diameter of the adsorption zone is greater than that of the retention zone. This results in the resistance being weakened in the flow guiding zone, and the retention in the adsorption and retention zones being strengthened in a stratified manner. In other words, the flow guiding zone ensures the initial flux, the adsorption zone balances the flux and retention, and the retention zone ensures the retention accuracy, achieving a balance between high flux and high retention efficiency. Therefore, this design is innovative.

[0010] The non-directional tortuous pathways of the present invention refer to randomly oriented groove structures and / or discretely distributed hole structures, and each non-directional tortuous pathway is interconnected.

[0011] The complete bubble point of HFE described in this invention refers to the complete bubble point in an HFE (hydrofluoroether) solution. The test methods are well known in the art, and 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. The complete bubble point of the filter membrane is determined using an HFE solution as the test medium. The pressure at which the filter membrane begins to continuously bubble is the complete bubble point of HFE.

[0012] 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, this direction is perpendicular to the radius), its various characteristics, such as pore size and fiber diameter, are roughly uniform and generally consistent. Therefore, the overall pore size and fiber diameter on a given plane can be reflected by the pore size and fiber diameter in a partial area of ​​that plane. In this invention, the polyethylene filter membrane is a flat sheet membrane.

[0013] In a cross-sectional scanning electron microscope (SEM) image at a magnification of 1000×, the side with the larger pore size is the inlet surface, and the side with the smaller pore size is the outlet surface. In the thickness direction from the inlet surface to the outlet surface, the plane where the pore size first becomes significantly smaller is called plane P1, and the plane where the pore size becomes significantly smaller for the second time is called plane P2. The area between the inlet surface and plane P1 is the flow guiding zone, the area between plane P1 and plane P2 is the adsorption zone, and the area between plane P2 and the outlet surface is the retention zone. The distance from plane P1 to the inlet surface is the thickness of the flow guiding zone, the distance between plane P2 and plane P1 is the thickness of the adsorption zone, and the distance between plane P3 and the outlet surface is the thickness of the retention zone. The test method is to measure the distance between the inlet surface and plane P1, the distance between plane P1 and plane P2, and the distance between plane P2 and the outlet surface on the cross-sectional SEM image of the membrane using computer software (such as Matlab, NIS-Elements, etc.) or manually, so as to obtain the thickness of the flow guiding zone, the thickness of the adsorption zone, and the thickness of the retention zone, respectively.

[0014] The average SEM pore size of the flow guiding region is obtained by characterizing the flow guiding region with a certain magnification, such as 10,000x, 20,000x, or 50,000x scanning electron microscopy. Pores at different locations are then uniformly selected as measurement objects, and the corresponding SEM pore sizes are measured using appropriate computer software (such as Matlab, NIS-Elements, etc.) or manually. The average value is then calculated to obtain the average SEM pore size of the flow guiding region. Similarly, the average SEM pore size of the adsorption region and the average SEM pore size of the retention region can be obtained using the same characterization, measurement, and calculation methods as those for the flow guiding region, except that the characterization object is replaced by the adsorption region or the retention region.

[0015] The specific surface area of ​​the filter membrane described in this invention can be obtained by testing with a fully automated surface and pore analyzer (i.e., BET, Micromeritics ASAP 2460, USA).

[0016] As a further improvement of the present invention, the SEM average pore size of the adsorption region is 100nm-300nm; the thickness of the adsorption region is 25μm-80μm; and / or, the thickness of the filter membrane is 60μm-150μm.

[0017] Our research revealed that by controlling the average SEM pore size of the adsorption region to be 100nm-300nm, which is relatively large, although the pore size of the adsorption region is much larger than the particle size of most impurities in semiconductor photolithography materials, the non-directional tortuous pathways of the adsorption region allow for the removal of some larger impurities that were not trapped by the current-conducting region. Furthermore, these unremoved impurities can still be well retained or adsorbed on and near the pore walls of the adsorption region. Simultaneously, the larger impurities in the adsorption region... Pore ​​size allows for higher flux in the filter membrane. If the SEM average pore size of the adsorption region is less than 100 nm, it is not conducive to further improving the flux of the filter membrane. If the SEM average pore size of the adsorption region is greater than 300 nm, it leads to a decrease in the pore wall surface area and the number of times impurities turn in the adsorption region, which is not conducive to maintaining the retention efficiency. Furthermore, we found that by controlling the thickness of the adsorption region to 25 μm-80 μm, i.e., a relatively thick adsorption region, more adsorption sites can be provided for filtering semiconductor photolithography materials. Additionally, the greater the thickness, the better the flux. The longer impurities in the semiconductor lithography process material remain within the adsorption zone, the higher the probability of collisions between impurities and the pore walls. This also increases the likelihood of impurities redirecting or branching, resulting in more impurities being excluded, adsorbed, or retained, thus improving retention efficiency. Furthermore, the thicker adsorption zone provides greater contaminant holding capacity, ensuring continuous filtration even with semiconductor lithography materials containing high impurity content. The thicker adsorption zone also allows for sufficient pressure reduction of the liquid transitioning from the guide zone to the adsorption zone, reducing pressure when the liquid enters the retention zone. The thickness is already small, resulting in less impact on the pores in the retention area. This allows the pores in the retention area to remain more intact, further ensuring retention efficiency and facilitating the continued use of semiconductor photolithography material filtration. However, if the adsorption area is too thick, it will negatively impact flux maintenance. Furthermore, by controlling the filter membrane thickness between 60μm and 150μm, the membrane as a whole possesses good strength, enabling better and more continuous operation when used for semiconductor photolithography material filtration. If the filter membrane thickness exceeds 150μm, it will negatively impact flux maintenance. This is further enhanced by a specific surface area of ​​8m². 2 / g-20m 2 With the synergistic effect of / g, the filter membrane with a thickness of 60μm-150μm provides a longer mass transfer path and a sufficient adsorption site for the specific surface area, enabling the feed liquid to achieve multi-channel transport in the longer mass transfer path, thereby improving the retention efficiency. At the same time, when the filter membrane is thicker, its fiber skeleton can provide rigid support for the pores of the filter membrane, disperse the membrane stress in the pores, avoid stress concentration in the thickness direction of the filter membrane, and also improve the compressive strength of the filter membrane under the synergistic effect.

[0018] The filter membrane of this invention achieves improved retention efficiency and flux through the synergistic effect of larger pore size and greater thickness in the adsorption zone. This is because the greater thickness compensates for the reduction in adsorption sites (i.e., pore wall surface area) and impurity turning frequency caused by the larger pore size. The larger pore size also compensates for the reduced flux caused by the greater thickness. The larger pore size ensures a wider flow path in the adsorption zone, while the greater thickness provides a longer flow path. In conjunction with the non-directional tortuous path of the adsorption zone, the greater thickness increases both the pore wall area and the number of impurity turning frequencies. In other words, the adsorption zone has both a wider flow path to improve flux and a larger pore wall area and a greater number of impurity turning frequencies. This design achieves simultaneous improvement in flux and retention efficiency. Furthermore, with the synergistic effect of the adsorption zone thickness, filter membrane thickness, and the ratio of the adsorption zone thickness to the retention zone thickness being greater than 3, the thickness of the flow guiding zone of the filter membrane is also relatively large. The flow guiding zone plays a pre-filtration role for semiconductor photolithography materials, which can reduce filtration steps and lower filtration costs. At the same time, the thickness of the retention zone is relatively small, which has little impact on flux. Since the adsorption zone can retain most of the impurities, the small thickness of the retention zone ensures both final retention and membrane flux. In other words, the reasonable design of the thickness of the three layers of the flow guiding zone, adsorption zone, and retention zone can achieve high flux even when the overall filter membrane is relatively thick.

[0019] The thickness of a filter membrane refers to the distance between the liquid surface and the inlet surface. The test method is to measure the distance between the inlet surface and the outlet surface on a cross-sectional SEM image of the membrane using computer software (such as Matlab, NIS-Elements, etc.) or manually, thus obtaining the thickness of the filter membrane.

[0020] As a further improvement of the present invention, the adsorption zone has adsorption zone fibers forming a porous structure, the ratio of the SEM average pore size of the adsorption zone to the SEM average diameter of the adsorption zone fibers is 3-12; the porosity of the adsorption zone is 35%-75%.

[0021] When the filter membrane of this invention is used for filtering semiconductor photolithography materials, since most impurities in the semiconductor photolithography materials are removed in the adsorption region, the ratio of the SEM average pore size of the adsorption region to the SEM average diameter of the fibers in the adsorption region is further adjusted to 3-12. A ratio within this range can form a wider fluid channel, which is beneficial for increasing flux. Simultaneously, the adsorption region has a larger pore wall surface area, more impurity deflection, and more entry branches, which is beneficial for improving retention efficiency. If the ratio of the SEM average pore size of the adsorption region to the SEM average diameter of the fibers in the adsorption region is too large, the fibers in the adsorption region are relatively thin compared to the pores in the adsorption region, resulting in relatively weak support for the pores. When continuously used for filtering semiconductor photolithography materials, this can easily lead to membrane pore collapse, which is detrimental to the continuous use of the filter membrane. Furthermore, the ratio... Excessive porosity can reduce the surface area of ​​the pore walls, the number of times impurities deflect and enter branches, which is detrimental to improving retention efficiency. If the ratio of the average SEM pore size of the adsorption zone to the average SEM diameter of the fibers in the adsorption zone is too small, the fibers will be too densely packed and unable to maintain flux. The porosity of the adsorption zone refers to the ratio of the sum of the areas of all pores on the cross-section of the adsorption zone to the area of ​​the cross-section of the adsorption zone. The larger the ratio, the larger the area of ​​the pores on the cross-section of the adsorption zone, and the more pathways the fluid will have when passing through the adsorption zone, which is beneficial to improving flux. However, the ratio should not be too large. If the porosity ratio of the adsorption zone exceeds 75%, the fiber area on the adsorption zone will be relatively small, which is detrimental to maintaining retention efficiency. Therefore, by controlling the porosity of the adsorption zone to 35%-75%, it is beneficial to both improve flux and maintain retention efficiency.

[0022] When the ratio of the average SEM pore size of the adsorption zone to the average SEM diameter of the fiber in the adsorption zone is 3-12, the pores are ensured to be "useful" (able to flow and retain), and the porosity is 35%-75% to ensure that the pores are "sufficient" (sufficient number and space). With the synergistic effect of the two, the pores in the adsorption zone are both useful and numerous. In addition, with the synergistic effect of non-directional tortuous pathways, the flux and retention efficiency are further improved.

[0023] The method for measuring the average diameter of the fiber in the adsorption region using SEM is to take SEM images of the cross-section of the adsorption region at a magnification of 10,000x, 20,000x, or 50,000x, depending on the magnification required to clearly measure the SEM diameter of the fiber in the adsorption region. A specific area (e.g., 25 μm) of the cross-section of the adsorption region is selected from the SEM image. 2 (5μm*5μm), 4μm 2 (2μm*2μm), 1μm 2(e.g., 1μm*1μm, the specific area size depends on the actual situation) can be used as the test object. It can be measured by computer software (such as Matlab, NIS-Elements, etc.) or manually, and corresponding calculations can be performed. Preferably, the SEM diameter of more than 10 different adsorption zones of the fiber is selected and the average value is calculated, which is the SEM average diameter of the adsorption zone fiber.

[0024] The porosity of the adsorption region is measured by selecting cross-sectional electron micrographs of three or more different adsorption regions (to meet statistical requirements), and then measuring the porosity of each adsorption region using software such as ImageJ. The average value is then calculated, which is the porosity of the adsorption region as described in this invention. Of course, those skilled in the art can also obtain the porosity of the adsorption region using other testing methods.

[0025] As a further improvement of the present invention, the thickness of the retention zone is 3μm-15μm; the ratio of the average SEM pore size of the adsorption zone to the average SEM pore size of the retention zone is 3-10; and / or, the liquid outlet surface includes a plurality of liquid outlet holes, the average SEM pore size of the liquid outlet holes being 15nm-50nm.

[0026] The retention region of the filter membrane in this application is the "final gatekeeper" for retention. The presence of the retention region ensures the removal of extremely small impurities (e.g., 2nm) in the semiconductor photolithography process materials. Because impurities are subjected to exclusion, adsorption, and retention in the adsorption region, most impurities are removed in the adsorption region, with only a very small amount passing through to enter the retention region. Therefore, the thickness of the retention region can be relatively small. Sufficient impurity retention can be achieved when the thickness of the retention region is not less than 3μm. Furthermore, since the retention region has the smallest pore size in the filter membrane, a larger retention region has a greater impact on the overall flux of the filter membrane. By controlling the thickness of the retention region to within 15μm, a high flux is maintained. Therefore, by adjusting the thickness of the retention region to 3μm-15μm, the filter membrane exhibits… To achieve better retention efficiency while maintaining good flux, our research found that when the ratio of the SEM average pore size of the adsorption region to that of the retention region is 3-10, the pore size change during the transition from the adsorption region to the retention region is relatively small. The flow rate of the semiconductor lithography material from the adsorption region to the retention region is also relatively stable, and the membrane pores in the retention region can remain intact during continuous filtration, indirectly ensuring retention. If the ratio of the SEM average pore size of the adsorption region to that of the retention region is greater than 10, on the one hand, the flow rate change of the semiconductor lithography material from the adsorption region to the retention region is large, posing a risk of generating significant turbulence, which could damage the structure of the membrane pores in the retention region and negatively impact retention efficiency; on the other hand, either... If the average SEM pore size of the adsorption zone is too large or the average SEM pore size of the retention zone is too small, it will negatively impact the adsorption zone's ability to retain impurities. (If the average SEM pore size is too large, the number of adsorption sites will decrease, and neither size exclusion impurities nor the amount of retained or adsorbed impurities can be improved.) Conversely, if the average SEM pore size of the retention zone is too small, it will negatively impact flux maintenance. If the ratio of the average SEM pore size of the adsorption zone to that of the retention zone is less than 3, their average SEM pore sizes are relatively similar. A relatively small average SEM pore size in the adsorption zone is detrimental to maintaining the overall flux of the filter membrane, while a relatively large average SEM pore size in the adsorption zone is detrimental to... Maintaining the retention efficiency of the filter membrane: We know that the outlet surface is the last stage where the feed liquid leaves the filter membrane. The pore size of the pores on the outlet surface takes into account both "flow capacity" and "retention control". If the pore size is less than 15nm, the feed liquid entering the retention zone from the adsorption zone cannot be quickly discharged, which is not conducive to maintaining the filter membrane flux. At the same time, it will lead to pressure buildup inside the membrane, which may damage the membrane pore structure in the retention zone and is not conducive to continuous filtration. If the pore size is greater than 50nm, although the feed liquid can be discharged quickly, it cannot effectively intercept smaller particles of impurities that have not been adsorbed by the adsorption zone, which is not conducive to maintaining the retention efficiency. Therefore, by adjusting the pore size of the outlet surface pores to 15-50nm, it is beneficial to the rapid discharge of the feed liquid in the retention zone, the maintenance of flux, and the improvement of retention efficiency.

[0027] If the thickness of the retention zone is simultaneously controlled to be 3μm-15μm and the ratio of the SEM average pore size of the adsorption zone to that of the retention zone is 3-10, then a smaller pore size ratio constructs a low-resistance transition channel from the adsorption zone to the retention zone. The adsorption zone undertakes the functions of "mass transfer + main retention," while the retention zone undertakes the functions of "precise retention + low-resistance output," forming a well-defined retention closed loop, resulting in better retention efficiency and flux of the filter membrane. Furthermore, with the synergistic effect of the SEM average pore size of the outlet pores being 15nm-50nm, the large pore size of the adsorption zone enables low-resistance feeding, quickly transporting the liquid to the retention zone and avoiding resistance buildup in the adsorption zone. The thin layer of small pores in the retention zone achieves precise retention without causing a sharp increase in resistance, ensuring a smooth flow of the liquid to the outlet surface. The pores at the outlet surface then connect with the retention zone. The feed liquid is quickly discharged, completely eliminating the end bottleneck and improving throughput. At the same time, the adsorption zone can filter most impurities, the retention zone can intercept some nano-impurities, and the outlet pores act as a catch-all to intercept nano-impurities that have passed through the retention zone. The retention zone has a larger pore surface area than the adsorption zone. Due to the 3μm-15μm thickness of the retention zone and the non-directional tortuous path, the collision opportunities between nano-impurities and the pore walls are increased. At the same time, due to the large specific surface area of ​​smaller impurities (such as 2nm impurities), the chance of collision with the pores in the retention zone is further increased. When in contact with the inside of the pores, they are adsorbed inside the pores by van der Waals forces or hydrogen bonds. They may also be retained at the corners or branches of the pore walls during the collision process and will not flow out with the feed liquid, thus improving the retention efficiency.

[0028] The average SEM diameter of the liquid outlet pores is obtained by characterizing the liquid outlet surface with a certain magnification, such as 20,000x or 50,000x using a scanning electron microscope. Then, liquid outlet pores at different locations are uniformly selected as measurement objects (preferably more than 10). The corresponding SEM pore diameters are measured using appropriate computer software (such as Matlab, NIS-Elements, etc.) or manually, and the average value is calculated.

[0029] As a further improvement of the present invention, the pore area of ​​the mesopores in the filter membrane accounts for 50%-80% of the total pore area in the filter membrane, wherein the pore size of the mesopores is greater than 2nm and less than or equal to 50nm; the pore area of ​​the micropores in the filter membrane accounts for 1%-10% of the total pore area in the filter membrane, wherein the pore size of the micropores is less than or equal to 2nm; and the porosity of the filter membrane is 40%-80%.

[0030] The porosity of a filter membrane refers to the volume ratio of all pores in the membrane. When used for filtering materials in semiconductor photolithography processes, a higher porosity results in lower resistance to liquid flow and higher throughput. However, the porosity cannot be too high, otherwise it will negatively impact the overall strength of the membrane and may cause structural damage at the start of filtration. Therefore, by controlling the porosity to 40%-80%, the membrane achieves both good strength to ensure continuous filtration of semiconductor photolithography materials and better throughput. Furthermore, based on an overall porosity of 40%-80%, the ratio of mesopore area to micropore area is controlled. Specifically, the proportion of mesopore area (greater than 2nm and less than or equal to 50nm) in the total pore area is controlled to 50%-80%. This means a larger proportion of mesopore area and a slightly larger pore size, resulting in relatively lower mass transfer resistance to the liquid and ensuring better throughput. Simultaneously, the mesopores themselves... By removing large particles larger than 50nm and utilizing non-directional tortuous pathways, the overlapping of membrane pores between mesopores can also remove some impurities smaller than 50nm. Mesopores also have relatively more pore walls. When relatively small-sized impurities that are not removed pass through the pore walls of mesopores, they are adsorbed by van der Waals forces or hydrogen bonds. Some impurities are also retained at the turning or branching points on the surface of the pore walls of mesopores. The larger pore area ratio of mesopores not only ensures better flux of the filter membrane, but also serves as the main force for impurity retention when the filter membrane is used for filtering semiconductor photolithography materials. On the other hand, micropores with a pore size of 2nm or less have a smaller pore area ratio and have a smaller impact on flux. At the same time, they can remove 2nm impurities and achieve precise control over the retention of impurities in photoresist materials, thereby improving retention efficiency. That is, the high pore area ratio of mesopores ensures high flux and pre-retention, while the low pore area ratio of micropores achieves high retention, ultimately achieving a better balance between retention and flux.

[0031] The proportion of the mesopore area and the proportion of the micropore area in the total pore area of ​​the filter membrane described in this invention can be obtained by testing and calculation using a fully automated surface and pore analyzer (i.e., BET, Micromeritics ASAP 2460, USA).

[0032] Commonly used methods for testing porosity include mercury intrusion porosimetry, density method, and wet-dry film weighing method. Of course, those skilled in the art can also obtain the above parameters through other testing methods. The above testing methods are for reference only.

[0033] As a further improvement of the present invention, the XRD crystallinity of the filter membrane is 15%-40%; the average grain size of the filter membrane is 15nm-30nm; and / or, the basis weight of the filter membrane is 20g / m³. 2-45g / m 2 .

[0034] Generally, the higher the XRD crystallinity of a filter membrane, the higher the rigidity of the fiber skeleton. If the rigidity of the fiber skeleton is too high, even a slightly higher filtration pressure in semiconductor photolithography materials can lead to brittle fracture. Therefore, the XRD crystallinity of the filter membrane is controlled to be no greater than 40%. However, if the XRD crystallinity of the filter membrane is too low, the insufficient rigidity of the fiber skeleton can also cause fracture due to insufficient rigidity even a slightly higher filtration pressure in semiconductor photolithography materials. Therefore, the XRD crystallinity of the filter membrane is controlled to be no less than 15%, that is, by controlling the XRD crystallinity of the filter membrane to be between 15% and 40%, even a slightly higher filtration pressure can be guaranteed to ensure continuous filtration when used for filtering semiconductor photolithography materials. At the same time, the amorphousness of this filter membrane is relatively low. The surface energy of the amorphous region is higher due to the irregular entanglement and stacking of molecular chains, resulting in uneven intermolecular forces (large intermolecular spacing in some areas and small intermolecular spacing in others, forming a large number of "energy imbalance sites"). Since the surface energy of the nano-impurities themselves is also high, according to the "principle of minimum energy," the high surface energy nano-impurities will spontaneously migrate to and be adsorbed onto these high surface energy sites in the amorphous region. These adsorption sites can better adsorb nano-impurities. Simultaneously, the flexibility of the amorphous material can encapsulate or retain the adsorbed or retained nano-impurities, preventing desorption and resulting in better retention efficiency. Combined with the synergistic effect of an adsorption region thickness of at least 20 μm, the retention efficiency of the adsorption region is even higher, leading to better overall retention efficiency of the filter membrane. The retention zone retains fewer impurities, better maintaining the pores of the membrane and resulting in lower flux decay. Since the average crystallite size of the filter membrane is 15nm-30nm, belonging to the nanoscale, and the XRD crystallinity is 15%-40%, the filter membrane fibers simultaneously contain crystalline and amorphous regions. This means the crystallites are not tightly bonded but are filled or separated by polymer chains in the amorphous regions. At the interface between the crystallites and amorphous regions, the disordered entanglement of the amorphous molecular chains causes protrusions on the fiber surface, or if the gaps between adjacent crystallites are not completely filled, there will be nanoscale depressions. In other words, the fiber surface has a certain degree of roughness, making it easier for the pore walls of the adsorption zone to adsorb unadsorbed nanoparticles. Impurities are reduced, improving the retention efficiency of the adsorption zone, thus resulting in better overall retention efficiency of the filter membrane. Simultaneously, the retention zone retains fewer impurities, better maintaining the unobstructed flow of the membrane pores and reducing flux decay. Furthermore, in synergy with specific surface area, the crystalline zone stabilizes pore size, providing sufficient adsorption sites. The amorphous zone and nanoscale grain size increase the adsorption capacity of these sites. In other words, the filter membrane has sufficient adsorption sites with better adsorption capacity, resulting in higher retention efficiency. During semiconductor photolithography material filtration, impurities are essentially completely removed as they pass through the flow guiding and adsorption zones, while the membrane pores in the retention zone maintain good flow, further reducing flux decay.

[0035] Because the filter membrane of this invention has a suitable number of pore walls, meaning it has sufficient adsorption sites, its retention efficiency can be guaranteed. Furthermore, by adjusting the basis weight of the filter membrane to be relatively small (i.e., slightly lower fiber mass per unit area), the connectivity between the pores of the filter membrane is improved, resulting in higher flux. However, if the basis weight of the filter membrane is too small, the fiber mass per unit area will be too low, posing a risk of pore collapse when the filter membrane is used for filtering materials in semiconductor photolithography processes. Therefore, the basis weight of the filter membrane is adjusted to 8 μm. 2 / g-20m 2 / g, improving the filter membrane flux while ensuring retention efficiency, and the filter membrane also has good pressure resistance; furthermore, under the synergistic effect of XRD crystallinity, the fibers that make up the filter membrane have a certain rigidity, improving the pressure resistance of the filter membrane, and the filter membrane can be used for continuous filtration of semiconductor photolithography process materials.

[0036] The XRD crystallinity and grain size of the filter membrane can be obtained by X-ray diffraction (Rigaku Ultima IV, Japan).

[0037] Basis weight usually refers to "mass per unit area", also known as areal density. Testing can be performed according to standards JIS L1913:2010 and GB / T451.2-2002. In this application, the basis weight test method involves cutting the film into circular pieces with a diameter of 47 mm, then weighing the pieces using a balance to obtain a mass of M grams. Therefore, the basis weight of the circular piece is M / (π*(47 / (2*1000))). 2 The weight of the present invention is obtained by taking the average value of multiple (preferably more than 3) measurements. Of course, those skilled in the art can also obtain it by other testing methods.

[0038] As a further improvement of the present invention, the ratio of the thickness of the adsorption zone to the thickness of the flow guiding zone is 0.8-2.5; the ratio of the average SEM pore size of the flow guiding zone to the average SEM pore size of the adsorption zone is 2-5; and / or, the liquid inlet surface includes a plurality of liquid inlet holes, and the pore area ratio of the liquid inlet surface is 30%-70%.

[0039] The flow-guiding zone of the filter membrane in this invention mainly serves as a pre-filtration area and improves flux. If the ratio of the average SEM pore size of the flow-guiding zone to the average SEM pore size of the adsorption zone is greater than 5, then either the average SEM pore size of the flow-guiding zone is too large or the average SEM pore size of the adsorption zone is too small. If the average SEM pore size of the flow-guiding zone is too large, the pre-filtration effect will be relatively poor. Some impurities larger than the pore size of the adsorption zone will not be pre-retained in the flow-guiding zone (including exclusion, adsorption, retention, etc.), which may clog the adsorption zone and thus be detrimental to improving the overall flux of the filter membrane. If the SEM average pore size of the adsorption zone is too large, the pre-filtration effect will be relatively poor. If the average pore size (SEM) is too small, the presence of the adsorption zone is detrimental to improving the overall membrane flux. Furthermore, if the ratio of the average SEM pore size of the flow-guiding zone to that of the adsorption zone is too large, significant turbulence will occur when the filtration fluid enters the adsorption zone from the flow-guiding zone. When the membrane is used for filtration, the pores at the interface between the adsorption and flow-guiding zones may collapse, hindering continuous filtration. If the ratio of the average SEM pore size of the flow-guiding zone to that of the adsorption zone is less than 2, then the average SEM pore sizes of the flow-guiding zone and the adsorption zone are relatively close. If... When larger particles of impurities are present, some membrane pores in the flow-guiding zone may become clogged, which is detrimental to maintaining flux. Therefore, by controlling the ratio of the SEM average pore size of the flow-guiding zone to that of the adsorption zone to be 2-5, the filter membrane exhibits better flux while allowing for continuous fluid filtration. Since the thickness of the adsorption zone is not less than 20 μm, by adjusting the ratio of the thickness of the adsorption zone to that of the flow-guiding zone to be 0.8-2.5, meaning the flow-guiding zone is also relatively thick, the flow-guiding zone provides ample low-resistance channel space, resulting in superior flux and relatively... The thick flow-guiding zone enables thorough pre-filtration, trapping larger nanoparticles and reducing the trapping pressure in the adsorption zone. This better preserves the membrane pores in the adsorption zone, resulting in higher flux and superior trapping efficiency. The pore size ratio between the flow-guiding and adsorption zones achieves graded trapping through pre-filtration and deep filtration, while the thickness ratio ensures sufficient space in the adsorption zone for deep trapping of nanoparticles. This synergistic effect forms a complete trapping chain, significantly reducing the trapping pressure in the trapping zone and minimizing flux attenuation while maintaining superior trapping efficiency.

[0040] When the filter membrane of this invention is used for filtering materials in semiconductor photolithography processes, the inlet surface serves as the fluid entry point. The size of its pore area ratio determines the fluid entry speed. A larger pore area ratio means more channels for fluid entry and a faster entry speed. However, if the pore area ratio of the inlet surface is too large, the pressure resistance of the inlet surface will decrease, which is not conducive to continuous filtration. Therefore, by adjusting the pore area ratio of the inlet surface to 30%-70%, sufficient openings are achieved, allowing the fluid to quickly and uniformly enter the membrane interior. Simultaneously, the SEM average pore size in the flow guiding zone and the adsorption zone... The synergistic effect of the SEM average pore size ratio of 2-5 and the ratio of adsorption zone thickness to flow guiding zone thickness of 0.8-2.5 creates a continuous flow path with low-resistance feeding at the inlet surface, low-resistance transport in the flow guiding zone, and retention in the adsorption zone. The paths for low-resistance transport in the flow guiding zone and retention in the adsorption zone are relatively long, improving the flux and retention efficiency of the filter membrane. Furthermore, the synergistic effect of the pore area ratio of 30%-70% at the inlet surface and the XRD crystallinity of the filter membrane of 15%-40% results in better pressure resistance at the inlet surface, which is beneficial for continuous filtration.

[0041] The method for measuring the porosity of the liquid inlet surface involves selecting cross-sectional electron microscope images of three or more different liquid inlet surfaces, then measuring the porosity of each surface using software such as ImageJ, and calculating the average value, which is the porosity of the liquid inlet surface as described in this invention. Of course, those skilled in the art can also obtain the porosity of the liquid inlet surface using other testing methods.

[0042] As a further improvement of the present invention, the flow guiding region has flow guiding region fibers forming a porous structure, and each flow guiding region fiber agglomerates to form a block structure, wherein the SEM average diameter of the block structure is 500nm-900nm; the ratio of the SEM average diameter of the block structure to the SEM average pore size of the flow guiding region is 1.0-1.5.

[0043] The flow-guiding zone is the part of the membrane that first comes into contact with the feed liquid. Since the pore size of the flow-guiding zone is the largest, to obtain a filter membrane with superior pressure resistance, we controlled the morphology and diameter of the fibers in the flow-guiding zone. Firstly, we controlled the flow-guiding zone fibers to be composed of blocky structures formed by the aggregation of individual fibers. These blocky structures stacked together form a "skeleton-pore" system, which provides better support than a single fiber. We also unexpectedly discovered that the uneven structure formed by fiber aggregation makes the surface of the blocky structure rough, increasing the adsorption capacity for nano-impurities, improving the pre-retention capacity of the flow-guiding zone, and thus improving the retention capacity of the filter membrane. This also reduces the retention pressure in the adsorption zone, better maintaining the flow of the membrane pores in the adsorption zone, and indirectly reducing flux attenuation. Secondly, by adjusting the diameter of the block structure to 500nm-900nm, the relatively coarse block structure provides better support, better protecting the membrane pores in the flow guiding zone and maintaining their integrity, thus exhibiting better pressure resistance. In our research, we also found that when the diameter of the block structure is not less than the average SEM pore size of the flow guiding zone, in addition to the block structure being able to stably support the pores in the flow guiding zone, it can also ensure a balance between the proportion of the block structure and the pores in the flow guiding zone. The flow guiding zone has more fluid channels, resulting in better flux of the filter membrane.

[0044] The method for measuring the average diameter of the bulk structure using SEM is to take SEM images of the cross-section of the flow-guiding region at a magnification of 10,000x, 20,000x, or 50,000x, depending on the magnification required to clearly measure the SEM diameter of the bulk structure. A specific area (e.g., 100 μm) of the cross-section of the flow-guiding region is selected from the SEM image. 2 (10μm*10μm), 16μm 2 (4μm*4μm), 4μm 2 (e.g., 2μm*2μm, the specific area size depends on the actual situation) can be used as the test object. It can be measured by computer software (such as Matlab, NIS-Elements, etc.) or manually, and corresponding calculations can be performed. Preferably, more than 10 different block structures are selected for SEM diameter measurement, and the average value is calculated, which is the average SEM diameter of the block structure.

[0045] As a further improvement of the present invention, the filter membrane further includes a flow-enhancing region located between the adsorption region and the retention region. The retention region has retention region fibers forming a porous structure, and the flow-enhancing region has flow-enhancing region fibers forming a porous structure. The flow-enhancing region fibers and the adsorption region fibers are continuous, and the flow-enhancing region fibers and the retention region fibers are continuous. The ratio of the SEM average pore size of the flow-enhancing region to the SEM average pore size of the flow-enhancing region is 0.3-0.7. The SEM average pore size of the flow-enhancing region is greater than the SEM average pore size of the adsorption region.

[0046] In the polyethylene filter membrane main structure provided by this invention, it can be further clearly seen that part of the filter membrane main body includes a flow-enhancing zone between the adsorption zone and the retention zone in the thickness direction from the inlet surface to the outlet surface. Because the fibers in the flow-enhancing zone are continuous with the fibers in the adsorption zone, and also continuous with the fibers in the retention zone, this type of filter membrane constructs a continuous structure of "flow-enhancing zone → adsorption zone → flow-enhancing zone → retention zone". By adjusting the SEM average pore size of the flow-enhancing zone to be larger than that of the adsorption zone, and the ratio of the SEM average pore size of the flow-enhancing zone to that of the flow-enhancing zone to be 0.3-0.7, since the adsorption zone is the main area for impurity retention, the retained impurities can cause an increase in local resistance in the adsorption zone. The presence of the flow-enhancing zone with the aforementioned pore size can divert some fluid, release the resistance of the adsorption zone, avoid the accumulation of local pressure in the adsorption zone, ensure the flux of the adsorption zone, and thus ensure the flux of the filter membrane. Simultaneously, the presence of the flow-enhancing zone slows down the flow rate due to the larger pore size, which can extend the unadsorbed zone. The residence time of impurities trapped in the flow-enhancing zone increases the chance of collision between impurities and the pore walls of the flow-enhancing zone, further trapping impurities not trapped in the adsorption and flow-enhancing zones, reducing the trapping pressure in the trapping zone, thus improving both trapping efficiency and flux. If the ratio of the SEM average pore size of the flow-enhancing zone to the SEM average pore size of the flow-enhancing zone is greater than 0.7, then the SEM average pore size of the flow-enhancing zone is too large. Although it can indeed increase the overall flux of the filter membrane, it will cause flow problems. The SEM average pore size of the enhanced zone differs significantly from that of the retention zone. When fluid flows through the enhanced zone into the retention zone, the large pore size change poses a risk of creating significant turbulence, which can damage the membrane pores at the interface between the enhanced and retention zones. This can compromise the structural integrity of the filter membrane and hinder the maintenance of retention efficiency. If the ratio of the SEM average pore size of the enhanced zone to that of the guided zone is less than 0.3, the pore size of the enhanced zone is relatively small, which is also detrimental to maintaining the filter membrane flux.

[0047] For filter membranes containing flow-enhancing zones, the division of their flow-enhancing, adsorption, flow-enhancing, and retention zones is as follows: In a cross-sectional scanning electron microscope (SEM) image at a magnification of 1000×, in the thickness direction from the inlet surface to the outlet surface, the plane where the pore size first becomes significantly smaller is called plane P1, the plane where the pore size becomes significantly smaller for the second time is called plane P2, and the plane where the pore size first becomes significantly larger is called plane P3. The area between the inlet surface and plane P1 is the flow-enhancing zone, the area between plane P1 and plane P3 is the adsorption zone, the area between plane P3 and plane P2 is the flow-enhancing zone, and the area between plane P2 and the outlet surface is the retention zone. The distance from the inlet surface to plane P1 is the thickness of the flow guiding zone, the distance from plane P1 to plane P3 is the thickness of the adsorption zone, the distance from plane P3 to plane P2 is the thickness of the flow enhancement zone, and the distance from plane P2 to the outlet surface is the thickness of the retention zone. The test method is to measure the distances from the inlet surface to P1, from plane P1 to plane P3, from plane P3 to plane P2, and from plane P2 to the outlet surface on the cross-sectional SEM image of the membrane using computer software (such as Matlab, NIS-Elements, etc.) or manually. This yields the thicknesses of the flow guiding zone, adsorption zone, flow enhancement zone, and retention zone, respectively.

[0048] The average SEM aperture of the flow-enhancing region is obtained by characterizing the flow-enhancing region with a certain magnification, such as 10,000x, 20,000x, or 50,000x using a scanning electron microscope. Holes at different locations are uniformly selected as measurement objects, and the corresponding SEM apertures are measured using appropriate computer software (such as Matlab, NIS-Elements, etc.) or manually. The average value is then calculated to obtain the average SEM aperture of the flow-enhancing region.

[0049] As a further improvement of the present invention, the ratio of the thickness of the adsorption zone to the thickness of the flow-enhancing zone is 1.2-4; the thickness of the flow-enhancing zone is greater than the thickness of the retention zone.

[0050] We know that the thickness of the adsorption region of the filter membrane of this invention is not less than 20 μm. By adjusting the ratio of the thickness of the adsorption region to the thickness of the flow-enhancing region to 1.2-4, and ensuring that the thickness of the flow-enhancing region is greater than the thickness of the retention region, the thickness of the flow-enhancing region within this range satisfies the requirement for a smooth transition while avoiding excessive thickness leading to an excessively long mass transfer path and thus reduced flux. Furthermore, the flow-enhancing region within this thickness range can retain more nano-impurities because, although the pore size of the flow-enhancing region is larger than that of the adsorption region, it is smaller than that of the flow-enhancing region. The thickness of the flow-enhancing zone ensures that it still has a certain number of pore wall surfaces. Through the effects of exclusion and adsorption, it can further retain impurities that have not been retained by the adsorption zone, further reducing the pressure of the retention layer and preventing the flux from decreasing due to impurity blockage. At the same time, by setting the thickness of the flow-enhancing zone to be greater than that of the retention zone, a structure of "thick transition layer + thin retention zone" is formed. The flow-enhancing zone disperses the flow velocity of the liquid with sufficient thickness, preventing high flow velocities from directly impacting the small pores of the retention zone, protecting the integrity of the membrane pores, and ensuring that the retention efficiency is at an excellent level.

[0051] As a further improvement of the present invention, the filter membrane has a retention efficiency of over 90% for 5nm colloidal gold; the water flow rate of the filter membrane is less than 2500s / @50mL@20℃@φ47mm@0.03MPa; the longitudinal tensile strength of the filter membrane is greater than 5MPa, and the transverse tensile strength of the filter membrane is greater than 3.5MPa.

[0052] The SEMI (Semiconductor Equipment and Materials International) C12 standard clearly stipulates that 5nm colloidal gold is used as the standard test medium for nanoscale retention efficiency. This is because 5nm colloidal gold has good monodispersity and its particle size deviation can be controlled within ±5%, which can accurately simulate the key harmful substances of 2nm-10nm in photoresist. Therefore, this invention uses 5nm colloidal gold as the test medium to measure the retention efficiency of the filter membrane. The higher the retention efficiency, the better the filter membrane can remove impurities. In this invention, the polyethylene filter membrane has a retention efficiency of more than 90% for 5nm colloidal gold, which can effectively remove impurities of 2nm-10nm in semiconductor photoresist process materials and has high practical value. The test method using 5nm colloidal gold as the test medium is as follows: (1) Prepare a colloidal gold solution and measure its concentration C using ICP-MS (inductively coupled plasma mass spectrometry). o (2) Pass the colloidal gold solution prepared in step (1) through the polyethylene filter membrane prepared in this invention under constant operating pressure or flow rate, collect the stabilized filtrate after filtration, and measure the concentration C of the stabilized filtrate using ICP-MS. f (3) Calculate the retention efficiency: Retention efficiency (%) = (1-C f / C o )*100%.

[0053] Water flow rate is a core indicator characterizing the water permeability of a filter membrane. It refers to the time required for a certain volume of water to pass through a filter membrane of a specific area under specified temperature and pressure conditions. The magnitude of the water flow rate reflects the speed of filtration; the lower the flow rate, the shorter the time required for water to pass through the filter membrane, the faster the filtration speed, and the higher the flux. In this invention, the water flow rate of the polyethylene filter membrane is less than 2500 s / @50 mL@20℃@φ47 mm@0.03 MPa. The low water flow rate indicates that the polyethylene filter membrane has a fast filtration speed, which can meet the requirements of rapid filtration of semiconductor photoresist process materials, resulting in high economic benefits. The test method for water flow rate can be found in sections 0136-0139 of the specification in patent CN113926322B.

[0054] After mechanical strength testing, the polyethylene filter membrane prepared by this invention has a longitudinal tensile strength greater than 5 MPa and a transverse tensile strength greater than 3.5 MPa, exhibiting excellent mechanical properties and correspondingly good compressive strength, making it highly practical for industrial applications.

[0055] The longitudinal tensile strength mentioned in this invention refers to the tensile strength in the length direction of the membrane, and the transverse tensile strength refers to the tensile strength perpendicular to the length direction of the membrane. Both the transverse tensile strength and the longitudinal tensile strength are measured by a universal tensile testing machine, and the average value is taken after multiple measurements (preferably more than 5 times, the specific number of times depends on the situation).

[0056] A second aspect of the present invention provides a method for preparing a polyethylene filter membrane as described above, comprising the following steps:

[0057] Step 1: Preparation of casting solution:

[0058] Casting solution A is composed of polyethylene resin A1, solvent A2 and non-solvent A3. The solid content of casting solution A is 8%-15%, the weight average molecular weight of polyethylene resin A1 is 300,000-1,500,000, and the mass of solvent A2 accounts for 30%-40% of the total mass of solvent A2 and non-solvent A3.

[0059] Casting solution B is composed of polyethylene resin B1, polyethylene resin B2, solvent B3 and non-solvent B4. The solid content of casting solution B is 12%-18%. Polyethylene resin B1 is UPE with a weight average molecular weight of 1.5 million to 3 million. Polyethylene resin B2 is HDPE with a weight average molecular weight of 300,000 to 1.5 million. The mass of polyethylene resin B1 is 50%-70% of the total mass of polyethylene resin B1 and polyethylene resin B2. The mass of solvent B3 accounts for 10%-30% of the total mass of solvent B3 and non-solvent B4.

[0060] The solid content of the casting solution B is greater than that of the casting solution A;

[0061] Step 2: Extrusion:

[0062] Casting solution A and casting solution B are combined into a two-layer solution structure by flowing through a co-extrusion feed head with two inlets. Then, they are extruded through a flat die to form a molded product with an inlet surface and an outlet surface. The inlet surface is formed by casting solution A and the outlet surface is formed by casting solution B. The die extrusion temperature is 190℃-240℃.

[0063] Step 3: Phase separation process:

[0064] The molded product obtained in step 2 is subjected to phase separation at 5℃-120℃ for 5s-30s to obtain film I; the temperature on both sides of the liquid film is different during phase separation, and the temperature on the liquid inlet side is at least 40℃ higher than the temperature on the liquid outlet side.

[0065] Step 4: Gas quenching optimization treatment:

[0066] The inlet side of the biofilm I obtained in step 3 is circulated with gas for optimization treatment to obtain biofilm II. The gas flow temperature is 50℃-80℃, the gas flow rate is 85m / min-120m / min, and the gas flow direction is parallel to the film thickness direction. The optimization treatment time is 10s-20s.

[0067] Step 5: Extraction;

[0068] The membrane II obtained in step four is extracted with the extraction solution, thereby removing solvent A2, solvent B3, non-solvent A3 and non-solvent B4 from membrane II to obtain the original membrane;

[0069] Step Six: Heat Setting

[0070] The original membrane obtained in step 5 is kept at 80℃-120℃ for 20min-40min to obtain a polyethylene filter membrane.

[0071] As a further improvement of the present invention, the solvent in step one is at least one of paraffin oil, white oil, hydraulic oil, decahydronaphthalene, castor oil extract, and castor oil; the non-solvent in step one is at least one of dimethyl phthalate, dioctyl adipate, ethylene glycol diacetate, dimethyl carbonate, palm oil, and triacetin; and the extract in step five is at least one of dichloromethane, acetone, methanol, ethanol, glycerol, tetrafluoroethane, and isopropanol.

[0072] As a further improvement of the present invention, the molecular weight distribution of polyethylene resin A1 in step one is 1.5-3.5; the density of polyethylene resin B2 in step one is 0.92 g / cm³. 3 -0.96g / cm 3 The difference between the solid content of casting solution B and the solid content of casting solution A is 1.5%-4.5%.

[0073] As a further improvement of the present invention, in step two, the casting liquid A and casting liquid B have the same temperature, and both are 10°C-20°C higher than the die extrusion temperature; before the phase separation treatment in step three, the molded product obtained in step two is further pretreated. The pretreatment is a blowing pretreatment on the liquid inlet side, the blowing pretreatment time is 1s-3s, the temperature is 120°C-150°C, the blowing pretreatment rate is 10m / min-30m / min, and the blowing pretreatment direction is perpendicular to the liquid inlet side.

[0074] As a further improvement of the present invention, during the phase separation process, the liquid outlet side contacts the cooling roller for phase separation, and the liquid inlet side is separated by air blowing. The temperature of the cooling roller is 10℃-20℃; the air blowing speed is 40m / min-80m / min, the air blowing direction is parallel to the liquid inlet surface of the membrane, and the temperature is 80℃-110℃.

[0075] As a further improvement of the present invention, the heat setting in step six includes a primary heat setting and a secondary heat setting, wherein the primary heat setting is held at 80℃-100℃ for 15min-30min; the secondary heat setting is held at 100℃-120℃ for 5min-10min; and / or, the stretch ratio of the filter membrane is 3-6 times.

[0076] This invention is based on the thermally induced phase separation method to prepare polyethylene filter membranes. In the early stages of the research, we attempted to prepare the filter membrane of this invention using a single casting solution under different phase separation conditions, but all attempts failed. When using a single casting solution, either the pore size of the adsorption zone was too small or the pore size of the retention zone was too large, failing to achieve both retention efficiency and flux. However, we succeeded when using two casting solutions with different solid contents and certain phase separation conditions. This is because casting solutions with different solid contents provide an important foundation for the formation of the flow conduction zone, adsorption zone, and retention zone of the filter membrane. In the preparation process, we first prepared a casting solution A with a relatively low solid content and a casting solution B with a relatively high solid content. Casting solution A contains polyethylene resin A1 with a weight average molecular weight of 300,000-1,500,000 and a corresponding solvent system (including solvent A2 and non-solvent A3), wherein the mass of solvent A2 accounts for a certain percentage of the total mass of solvent A2 and non-solvent A3. The amount is 30%-40%; the casting solution B contains UPE with a weight average molecular weight of 1.5 million-3 million, HDPE with a weight average molecular weight of 300,000-1.5 million and the corresponding solvent system (including solvent B3 and non-solvent B4). The mass of UPE is 50%-70% of the total mass of UPE and HDPE, and the mass of solvent B3 accounts for 10%-30% of the total mass of solvent B3 and non-solvent B4. The casting solution A uses a single component of medium-high molecular weight polyethylene as the film-forming material. Its molecular chain entanglement is moderate, which can lay the foundation for the formation of a stable pore skeleton during phase transformation. Since the solid content of casting solution A is low, and the mass ratio of solvent A2 in the solvent system is slightly higher than that of solvent B3 in casting solution B, it is beneficial to slow down the phase separation rate and form larger membrane pores. Finally, after phase separation, gas quenching optimization treatment, extraction and other steps, the main flow guiding zone of the filter membrane is formed.Casting solution B uses a composite of UPE with a weight-average molecular weight of 1.5 million to 3 million and HDPE with a weight-average molecular weight of 300,000 to 1.5 million as the film-forming material. The presence of UPE with a weight-average molecular weight of 1.5 million to 3 million, due to its extremely long molecular chains and high entanglement density, results in a polymer network with high mechanical strength during phase inversion, which can support the small-aperture channels without collapsing or deforming during filtration. The presence of HDPE with a weight-average molecular weight of 300,000 to 1.5 million, whose weight-average molecular weight range is consistent with that of polyethylene resin in casting solution A, can enhance the film-forming properties. The interfacial compatibility between solution A and casting solution B is crucial. During co-extrusion, the molecular chains at the interface can diffuse into each other, preventing defects such as delamination at the boundary between casting solutions A and B in the final filter membrane. Simultaneously, the addition of HDPE can reduce the entanglement of UPE. However, the mass ratio of HDPE to the total mass of HDPE and UPE should not be too high. If the mass ratio of HDPE is too high, it will weaken the rigidity of the fiber network structure; if the mass ratio of HDPE is too low, the interfacial compatibility between casting solutions A and B cannot be guaranteed. Furthermore, the solid content of casting solution B is greater than that of the casting membrane. The solid content of liquid A and the mass percentage of solvent B3 in the solvent system are slightly lower than that of solvent A2 in casting solution A. Liquid A exhibits a faster phase separation rate, which is beneficial for forming relatively small membrane pores. Ultimately, after phase separation, gas quenching optimization, and extraction, it mainly forms the retention and adsorption zones of the filter membrane, or the retention, flow enhancement, and adsorption zones of the filter membrane. (When the overall thickness of the filter membrane is relatively thick, for example, greater than 100 μm, it forms the retention, flow enhancement, and adsorption zones of the filter membrane; when the overall thickness of the filter membrane is relatively thin, for example, less than 100 μm, it forms the retention, flow enhancement, and adsorption zones of the filter membrane.) The filter membrane has a retention zone and an adsorption zone (i.e., the filter membrane does not contain a flow-enhancing zone), and the average SEM pore size of the flow-enhancing zone is larger than that of the adsorption zone, and the average SEM pore size of the adsorption zone is larger than that of the retention zone; preferably, the molecular weight distribution of polyethylene resin A1 in step one is 1.5-3.5. A relatively small molecular weight distribution indicates small differences in molecular chain length, which is beneficial to the uniformity of the entangled network in the casting solution A and the absence of local differences, and is beneficial to the uniformity of pore formation in the molded product during phase separation; preferably, the density of polyethylene resin B2 in step one is 0.92 g / cm³. 3 -0.96g / cm 3The casting solution has better flexibility, which is beneficial for accelerating phase separation. Preferably, the difference between the solid content of casting solution B and casting solution A is 1.5%-4.5%, so that the difference between the solid content of casting solution B and casting solution A is controlled within a certain range. Under the combined influence of phase separation, gas quenching treatment and other conditions, it is beneficial to form a better ratio of pore size of the flow-conducting zone to the adsorption zone and the thickness of the retention zone. Preferably, the casting solution A and casting solution B are at the same temperature, which is more conducive to better interfacial compatibility between casting solution A and casting solution B. Furthermore, by controlling the temperature of casting solution A and casting solution B to be 10℃-20℃ higher than the die extrusion temperature, it is beneficial for casting solution A and casting solution B to maintain good fluidity and smoothly fill the die flow channel. Casting solution A and casting solution B can achieve stable stratified flow, and at the same time, the stability and uniformity of the solution of casting solution A and casting solution B during extrusion are better. Moreover, at higher temperatures, the molecular chains of casting solution A and casting solution B can undergo moderate diffusion and entanglement when passing through the co-extrusion feed head, resulting in better interfacial compatibility.

[0077] The solvent system in casting solution A consists of solvent A2 and non-solvent A3. Solvent A2 is the solvent for the polyethylene resin in casting solution A, meaning that when heated to at most the boiling point of solvent A2, solvent A2 can completely dissolve the polyethylene resin to form a homogeneous solution. Non-solvent A3 is the non-solvent for the polyethylene resin in casting solution A, meaning that when heated to at most the boiling point of non-solvent A3, non-solvent A3 cannot dissolve the polyethylene resin to form a homogeneous solution. The solvent system in casting solution B consists of solvent B3 and non-solvent B4. Solvent B3 is the solvent for the mixed UPE and HDPE polyethylene resin in casting solution B, meaning that when heated to at most the boiling point of solvent B3, solvent B3 can dissolve the mixed UPE and HDPE polyethylene resin to form a homogeneous solution. Non-solvent B4 is the non-solvent for the mixed UPE and HDPE polyethylene resin in casting solution B, meaning that when heated to at most the boiling point of non-solvent B4, non-solvent B4 cannot dissolve the mixed UPE and HDPE polyethylene resin to form a homogeneous solution.

[0078] Next, casting solution A and casting solution B are combined into a two-layer solution structure by flowing through a co-extrusion feed head with two inlets.

[0079] After extrusion through a flat die, a flat liquid film is formed on a carrier (the carrier can be a roller or other carrier). The side of the casting liquid B is attached to the carrier. Since the film-forming material of casting liquid A is polyethylene resin with a weight average molecular weight of 300,000 to 1,500,000, and the film-forming material of casting liquid B contains HDPE with a weight average molecular weight of 300,000 to 1,500,000, their weight average molecular weights are consistent. The interfacial compatibility between casting liquid A and casting liquid B is good. During co-extrusion, the molecular chains at the interface can diffuse into each other, and there will be no delamination between the layers of the filter membrane. At the same time, the extrusion temperature of the die in this invention is 190℃-240℃, which is conducive to the smooth extrusion of casting liquid A and casting liquid B from the die.

[0080] The extruded product undergoes phase separation and curing at temperatures ranging from 5℃ to 120℃. By controlling the temperature of casting solution A (with a relatively lower solid content, i.e., the inlet side) to be at least 40℃ higher than that of casting solution B (with a relatively higher solid content, i.e., the outlet side), the cooling rate of casting solution A is slower than that of casting solution B. Combined with the lower solid content of casting solution A and the higher mass content of solvent A2 in casting solution A, the phase separation rate on the inlet side is slower, mainly forming a larger pore size guiding zone. Meanwhile, the cooling rate on the outlet side is faster, and the temperature of casting solution B is lower than that of solvent B3. Under the synergistic effect of various factors, the phase separation rate on the liquid outlet side is faster, forming a smaller pore size trapping zone near the liquid outlet. After the trapping and phase separation is completed, the low temperature is transferred to the membrane interior through the membrane pores in the trapping zone. Compared to the phase separation rate in the trapping zone, the low temperature is slightly slower, resulting in a slightly larger pore size compared to the trapping zone. This forms the adsorption zone of the filter membrane of this invention, or the adsorption zone and the flow enhancement zone. Combined with gas quenching optimization, the thickness of the adsorption zone of the filter membrane is not less than 20 μm, and the ratio of the adsorption zone thickness to the trapping zone thickness is greater than 3. Preferably, phase separation on the liquid outlet side is achieved through a contact cooling roller, and phase separation on the liquid inlet side is achieved through air blowing. The temperature of the cooling roller is controlled at 10℃-2℃. At 0℃, with a blowing temperature of 80℃-110℃, the difference between the cooling rate on the inlet side and the cooling rate on the outlet side further widens, meaning the difference in phase separation rates between the inlet and outlet sides further widens. Since the blowing direction is parallel to the inlet surface of the membrane, the cooling rate on the inlet side can be further slowed down, resulting in slower phase separation on the inlet side compared to the outlet side. The phase separation on the outlet side has a greater impact on the overall phase separation of the membrane, leading to a thicker adsorption zone, smaller pore size, and correspondingly lower porosity in the adsorption zone. Furthermore, the thickness of the flow guiding zone is smaller, and the pore size is larger. Because the blowing direction is parallel to the inlet surface of the membrane, therefore… The blowing speed can be slightly faster than the pre-phase separation speed, and the slightly faster blowing speed will not damage the membrane. Preferably, the stretch ratio of the filter membrane is 3 to 6 times, which means that the ratio of the rotation speed of the cooling roller to the extrusion speed of the die head is 3 to 6 times. That is, during the operation of the membrane, the external force forces the disordered entangled molecular chains to align along the stretching direction to form a regular chain segment structure, providing a template for crystal growth and improving the crystallinity of the filter membrane. Under the synergistic effect of HDPE and secondary heat setting in the casting solution B, the crystallinity of the filter membrane is within the preferred range. At the same time, the external force during stretching can tear large crystals into small crystals, and the oriented molecular chains limit the excessive growth of crystals, resulting in a crystal size within the preferred range.Preferably, before the phase separation process in step three, the molded product obtained in step two is pre-treated by blowing air onto the liquid inlet side. The blowing temperature is controlled at 120℃-150℃, which is between the phase separation temperature and the die head temperature, thus achieving a pre-cooling effect. This results in a slower cooling rate of the molded product under the combined action of pre-phase separation and phase separation, leading to a slower phase separation rate in the guiding zone. This results in larger and more uniform pores in the guiding zone, and a larger pore area ratio on the liquid inlet side. Simultaneously, the fibers in the guiding zone gradually agglomerate into a blocky structure under the slower phase separation rate and the synergistic effect of the blowing direction and rate. Since the molded product is still relatively soft during pre-phase separation, the blowing pre-treatment rate needs to be kept low. Furthermore, because the pre-treatment time is extremely short, there is essentially no phase separation on the liquid outlet side before it contacts the cooling roller.

[0081] Gas quenching optimization, as a core functional step connecting phase separation treatment and extraction-thermal setting, achieves "precise completion of incomplete phase separation curing + directional reconstruction of pore function" through "directional penetration gas quenching". Firstly, after phase separation in step three, the pores in the flow-guiding and retention zones of film generation I are fully cured, while the pores in the adsorption zone, or adsorption zone and flow-enhancing zone, are in a semi-cured state. These pores exhibit inherent defects such as insufficient pore expansion, incomplete branch pore development, and residual stress on the pore walls. Through a directional design where the gas flow direction is parallel to the film thickness direction, and utilizing the large pore channels in the flow-guiding zone, the gas flow precisely penetrates the flow-guiding zone and acts directionally on the adsorption zone, or adsorption zone and flow-enhancing zone. This achieves precise control and targeted optimization of the adsorption zone, or adsorption zone and flow-enhancing zone. Secondly, the heat carried by the gas can quickly remove residual heat from the adsorption zone, adsorption zone, and flow-enhancing zone, promoting the directional evaporation of the solvent system and driving the semi-curing process. The expansion of the pores provides a "highly efficient mass transfer channel" for subsequent extraction processes, allowing the extractant to quickly penetrate into the membrane and preventing solvent residue. The relatively low gas inlet rate avoids the impact and deformation of the semi-cured pore walls caused by high-speed gas flow. However, the gas inlet rate is not extremely low, allowing for complete expansion and stable curing of the pores in the adsorption zone, or the adsorption zone and the flow enhancement zone, within a short time (10-20 seconds). Simultaneously, the gas flow temperature of 50℃-80℃ precisely matches the critical temperature range for pore expansion and curing in the adsorption zone's semi-cured system, achieving an optimal balance between pore expansion efficiency and structural integrity. Combined with the specific composition and phase separation treatment of casting solutions A and B, the overall specific area of ​​the filter membrane is at a reasonable level, and the HFE bubble point of the filter membrane is within the range of 0.5MPa-1.5MPa. The gases used in the gas quenching optimization treatment include, but are not limited to, nitrogen, argon, and dry air.

[0082] After gas quenching optimization, the green film II is then extracted. The solvent system (solvent A2, solvent B3, non-solvent A3, non-solvent B4) is removed from the green film II through the extraction solution to obtain the original film.

[0083] Finally, the obtained original membrane is kept at 80℃-120℃ for 20min-40min to obtain a polyethylene filter membrane. Preferably, the heat setting includes a primary heat setting and a secondary heat setting. The primary heat setting is kept at 80℃-100℃ for 15min-30min. At a relatively low temperature, it can activate the "micro Brownian motion" of molecular chains, causing the molecular chains in the stress concentration area to slowly relax and rearrange, eliminating internal stress. Moreover, the relatively low temperature heat setting can promote the diffusion and entanglement of molecular chains at the interface of casting solution A and casting solution B, resulting in better interfacial compatibility. The secondary heat setting is kept at 100℃-120℃ for 5min-10min. The secondary heat setting is closer to the lower limit of the crystallization melting temperature of polyethylene and belongs to the "high temperature setting process". It can promote the perfection and growth of subcrystalline grains, and together with the draw ratio and HDPE, it can enhance the crystallization zone and fix the pore size of the original membrane.

[0084] A third aspect of the present invention provides an application of a polyethylene filter membrane for filtering semiconductor photolithography process materials.

[0085] For example, semiconductor photolithography process materials include, but are not limited to, primer, wafer cleaning solution, photoresist, anti-reflective coating, top protective layer, developer, rinsing solution, photoresist stripping solution, edge trimming agent, photoresist diluent, and leveling agent. The filter membrane of the present invention can effectively remove nanoscale impurities (including impurities as small as 2 nm) from semiconductor process materials.

[0086] Compared with the prior art, the present invention has the following beneficial technical effects:

[0087] 1. This invention scientifically regulates the main body of the polyethylene filter membrane, which includes a flow guiding zone, an adsorption zone, a retention zone, and a non-directional tortuous path. The thickness of the adsorption zone, the ratio of the thickness of the adsorption zone to the thickness of the retention zone, the complete bubble point of HFE, and the specific surface area of ​​the filter membrane are all within a reasonable range. Furthermore, the average SEM diameter of the flow guiding zone is greater than that of the adsorption zone, and the average SEM diameter of the adsorption zone is greater than that of the retention zone. This achieves a weakening of resistance in the flow guiding zone and a layered enhancement of retention (including size exclusion, adsorption, and retention) in the adsorption and retention zones. In other words, the flow guiding zone ensures the initial flux, the adsorption zone balances the flux and retention, and the retention zone ensures the retention accuracy, achieving a balance between high flux and high retention efficiency. This makes it highly efficient for filtering photoresist process materials.

[0088] 2. In the preparation process of the polyethylene filter membrane of the present invention, through scientific control of the composition of casting solution A and casting solution B, the phase separation conditions on both sides of the molded product, and the gas quenching optimization treatment after phase separation, the filter membrane body prepared contains a flow guiding zone, an adsorption zone, a retention zone, and a non-directional tortuous path. The thickness of the adsorption zone, the ratio of the thickness of the adsorption zone to the thickness of the retention zone, the complete bubble point of HFE, and the specific surface area of ​​the filter membrane are within a reasonable range. Furthermore, the average SEM diameter of the flow guiding zone is greater than that of the adsorption zone, and the average SEM diameter of the adsorption zone is greater than that of the retention zone.

[0089] 3. The polyethylene filter membrane of the present invention is integrally formed using two different casting solutions, which has the advantages of simple preparation method, lower cost, green and environmentally friendly, and suitable for industrial production. Attached Figure Description

[0090] Figure 1 This is a scanning electron microscope (SEM) schematic diagram of the cross-section of the polyethylene filter membrane prepared in Example 2, with a magnification of 1000×.

[0091] Figure 2 This is a scanning electron microscope (SEM) schematic diagram of the cross-section of the adsorption region of the polyethylene filter membrane prepared in Example 2, with a magnification of 20000×.

[0092] Figure 3 This is a scanning electron microscope (SEM) schematic diagram of the cross-section of the polyethylene filter membrane prepared in Example 6, with a magnification of 1000×. Detailed Implementation

[0093] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0094] Example 1

[0095] A method for preparing a polyethylene filter membrane includes the following steps:

[0096] Step 1: Preparation of casting solution:

[0097] Casting solution A consists of 15 parts by mass of polyethylene resin with a weight-average molecular weight of 900,000 and a molecular weight distribution of 3, 28 parts by mass of decahydronaphthalene, and 60 parts by mass of dimethyl phthalate. The solid content of casting solution A is 14.6%, and the temperature of casting solution A is 245℃. Casting solution B consists of 9 parts by mass of UPE with a weight-average molecular weight of 2.1 million and a molecular weight distribution of 2.2, and a weight-average molecular weight of 900,000 with a density of 0.93 g / cm³. 3 It consists of 6 parts by weight of HDPE, 15 parts by weight of decahydronaphthalene, and 60 parts by weight of dimethyl phthalate. The solid content of casting solution B is 16.7%, and the temperature of casting solution B is 245℃.

[0098] Step 2: Extrusion

[0099] Casting solution A and casting solution B are combined into a two-layer solution structure by flowing through a co-extrusion feed head with two inlets. Then, they are extruded through a flat die to form a molded product with an inlet surface and an outlet surface. The inlet surface is formed by casting solution A and the outlet surface is formed by casting solution B. The die extrusion temperature is 230℃.

[0100] Step 3: Phase separation process:

[0101] The liquid inlet side of the molded product obtained in step two is subjected to air blowing pretreatment. The air blowing pretreatment time is 1 second, the temperature is 120℃, the air blowing pretreatment rate is 15m / min, and the air blowing pretreatment direction is perpendicular to the liquid inlet side.

[0102] Next, a phase separation process is performed. The liquid outlet side of the pretreated molded product is contacted with a cooling roller at 10°C, and the liquid inlet side is subjected to air blowing to obtain film I. The air blowing speed is 50m / min, the air blowing temperature is 110°C, the air blowing direction is parallel to the liquid inlet side of the film, the phase separation time is 10s, and the draw ratio is 4.5 times.

[0103] Step 4: Gas quenching optimization treatment:

[0104] Nitrogen gas at 70°C was introduced into the liquid inlet side of the biofilm I obtained in step 3 for 15 seconds to optimize the biofilm II. The nitrogen gas introduction rate was 120 m / min, and the flow direction of the nitrogen gas was parallel to the film thickness direction.

[0105] Step 5: Extraction:

[0106] The original membrane was obtained by extracting the membrane-forming II obtained in step four with dichloromethane for 10 hours.

[0107] Step Six: Heat Setting

[0108] The original membrane obtained in step 5 was kept at 100℃ for 20 minutes and then at 110℃ for 8 minutes to obtain a polyethylene filter membrane containing a flow guiding zone, an adsorption zone, and a retention zone.

[0109] Example 2

[0110] A method for preparing a polyethylene filter membrane includes the following steps:

[0111] Step 1: Preparation of casting solution:

[0112] Casting solution A consists of 16 parts by mass of polyethylene resin with a weight-average molecular weight of 600,000 and a molecular weight distribution of 1.8, 32 parts by mass of hydraulic oil, and 65 parts by mass of dioctyl adipate. The solid content of casting solution A is 14.2%, and the temperature of casting solution A is 240℃. Casting solution B consists of 8 parts by mass of UPE with a weight-average molecular weight of 1.8 million and a molecular weight distribution of 2.8, and 600,000 parts by mass of a liquid with a weight-average molecular weight of 600,000 and a density of 0.92 g / cm³. 3 It consists of 6 parts by weight of HDPE, 16 parts by weight of hydraulic oil, and 55 parts by weight of dioctyl adipate. The solid content of casting solution B is 16.5%, and the temperature of casting solution B is 240℃.

[0113] Step 2: Extrusion

[0114] Casting solution A and casting solution B are combined into a two-layer solution structure by flowing through a co-extrusion feed head with two inlets. Then, they are extruded through a flat die to form a molded product with an inlet surface and an outlet surface. The inlet surface is formed by casting solution A and the outlet surface is formed by casting solution B. The die extrusion temperature is 220℃.

[0115] Step 3: Phase separation process:

[0116] The liquid inlet side of the molded product obtained in step two is subjected to air blowing pretreatment. The air blowing pretreatment time is 1 second, the temperature is 130℃, the air blowing pretreatment rate is 10m / min, and the air blowing pretreatment direction is perpendicular to the liquid inlet side.

[0117] Next, a phase separation process is performed. The liquid outlet side of the pretreated molded product is contacted with a cooling roller at 10°C, and the liquid inlet side is subjected to air blowing to obtain film I. The air blowing speed is 40m / min, the air blowing temperature is 110°C, the air blowing direction is parallel to the liquid inlet side of the film, the phase separation time is 12s, and the draw ratio is 3.5 times.

[0118] Step 4: Gas quenching optimization treatment:

[0119] Nitrogen gas at 60°C was introduced into the liquid inlet side of the biofilm I obtained in step 3 for 14s to optimize the biofilm II. The nitrogen gas introduction rate was 100m / min, and the flow direction of the nitrogen gas was parallel to the film thickness direction.

[0120] Step 5: Extraction:

[0121] The original membrane was obtained by extracting the membrane-forming II membrane obtained in step four with acetone for 12 hours.

[0122] Step Six: Heat Setting

[0123] The original membrane obtained in step 5 was kept at 90℃ for 25 minutes and then at 105℃ for 10 minutes to obtain a polyethylene filter membrane containing a flow guiding zone, an adsorption zone, and a retention zone.

[0124] Example 3

[0125] A method for preparing a polyethylene filter membrane includes the following steps:

[0126] Step 1: Preparation of casting solution:

[0127] Casting solution A consists of 14 parts by mass of polyethylene resin with a weight-average molecular weight of 350,000 and a molecular weight distribution of 1.6, 40 parts by mass of white oil, and 70 parts by mass of ethylene glycol diacetate. The solid content of casting solution A is 11.3%, and the temperature of casting solution A is 220℃. Casting solution B consists of 7 parts by mass of UPE with a weight-average molecular weight of 1.6 million and a molecular weight distribution of 3.6, and ethylene glycol diacetate with a weight-average molecular weight of 350,000 and a density of 0.96 g / cm³. 3 It consists of 7 parts by weight of HDPE, 22 parts by weight of white oil, and 60 parts by weight of ethylene glycol diacetate. The solid content of casting solution B is 14.6%, and the temperature of casting solution B is 220℃.

[0128] Step 2: Extrusion

[0129] Casting solution A and casting solution B are combined into a two-layer solution structure by flowing through a co-extrusion feed head with two inlets. Then, they are extruded through a flat die to form a molded product with an inlet surface and an outlet surface. The inlet surface is formed by casting solution A and the outlet surface is formed by casting solution B. The die extrusion temperature is 210℃.

[0130] Step 3: Phase separation process:

[0131] The liquid inlet side of the molded product obtained in step two is subjected to air blowing pretreatment. The air blowing pretreatment time is 2s, the temperature is 140℃, the air blowing pretreatment rate is 30m / min, and the air blowing pretreatment direction is perpendicular to the liquid inlet side.

[0132] Next, a phase separation process is performed. The liquid outlet side of the pretreated molded product is contacted with a cooling roller at 15°C, and the liquid inlet side is subjected to air blowing to obtain film I. The air blowing speed is 60m / min, the air blowing temperature is 90°C, the air blowing direction is parallel to the liquid inlet side of the film, the phase separation time is 16s, and the draw ratio is 3 times.

[0133] Step 4: Gas quenching optimization treatment:

[0134] Nitrogen gas at 50°C was introduced into the liquid inlet side of the biofilm I obtained in step 3 for 10 seconds to optimize the biofilm II. The nitrogen gas introduction rate was 85 m / min, and the flow direction of the nitrogen gas was parallel to the film thickness direction.

[0135] Step 5: Extraction:

[0136] The original membrane was obtained by extracting the membrane-forming II membrane obtained in step four with acetone for 10 hours.

[0137] Step Six: Heat Setting

[0138] The original membrane obtained in step 5 is kept at 80°C for 30 minutes and then at 100°C for 10 minutes to obtain a polyethylene filter membrane containing a flow guiding zone, an adsorption zone, and a retention zone.

[0139] Example 4

[0140] A method for preparing a polyethylene filter membrane includes the following steps:

[0141] Step 1: Preparation of casting solution:

[0142] Casting solution A consists of 12 parts by mass of polyethylene resin with a weight-average molecular weight of 1.45 million and a molecular weight distribution of 3.3, 50 parts by mass of paraffin oil, and 75 parts by mass of dimethyl carbonate. The solid content of casting solution A is 8.8%, and the temperature of casting solution A is 220℃. Casting solution B consists of 8.5 parts by mass of UPE with a weight-average molecular weight of 2.6 million and a molecular weight distribution of 2.7, and a weight-average molecular weight of 1.45 million with a density of 0.95 g / cm³. 3 It consists of 4.5 parts by weight of HDPE, 20 parts by weight of paraffin oil, and 70 parts by weight of dimethyl carbonate. The solid content of casting solution B is 12.6%, and the temperature of casting solution B is 220℃.

[0143] Step 2: Extrusion

[0144] Casting solution A and casting solution B are combined into a two-layer solution structure by flowing through a co-extrusion feed head with two inlets. Then, they are extruded through a flat die to form a molded product with an inlet surface and an outlet surface. The inlet surface is formed by casting solution A and the outlet surface is formed by casting solution B. The die extrusion temperature is 200℃.

[0145] Step 3: Phase separation process:

[0146] The liquid inlet side of the molded product obtained in step two is subjected to air blowing pretreatment. The air blowing pretreatment time is 3s, the temperature is 150℃, the air blowing pretreatment rate is 20m / min, and the air blowing pretreatment direction is perpendicular to the liquid inlet side.

[0147] Next, a phase separation process is performed. The liquid outlet side of the pretreated molded product is contacted with a cooling roller at 20°C, and the liquid inlet side is subjected to air blowing to obtain film I. The air blowing speed is 70 m / min, the air blowing temperature is 80°C, the air blowing direction is parallel to the liquid inlet side of the film, the phase separation time is 20 s, and the draw ratio is 6 times.

[0148] Step 4: Gas quenching optimization treatment:

[0149] Nitrogen gas at 50°C was introduced into the liquid inlet side of the biofilm I obtained in step 3 for 12 seconds to optimize the biofilm II. The nitrogen gas introduction rate was 105 m / min, and the flow direction of the nitrogen gas was parallel to the film thickness direction.

[0150] Step 5: Extraction:

[0151] The original membrane was obtained by extracting the membrane II obtained in step four with ethanol for 10 hours.

[0152] Step Six: Heat Setting

[0153] The original membrane obtained in step 5 was kept at 85°C for 30 minutes and then at 120°C for 6 minutes to obtain a polyethylene filter membrane containing a flow guiding zone, an adsorption zone, and a retention zone.

[0154] Example 5

[0155] A method for preparing a polyethylene filter membrane includes the following steps:

[0156] Step 1: Preparation of casting solution:

[0157] Casting solution A consists of 17 parts by mass of polyethylene resin with a weight-average molecular weight of 1.1 million and a molecular weight distribution of 2.1, 30 parts by mass of castor oil extract, and 68 parts by mass of palm oil. The solid content of casting solution A is 14.8%, and the temperature of casting solution A is 230℃. Casting solution B consists of 9 parts by mass of UPE with a weight-average molecular weight of 2.8 million and a molecular weight distribution of 1.9, and a weight-average molecular weight of 1.1 million with a density of 0.94 g / cm³. 3 It consists of 7 parts by weight of HDPE, 9 parts by weight of castor oil, and 64 parts by weight of triacetin. The solid content of casting solution B is 18.0%, and the temperature of casting solution B is 230℃.

[0158] Step 2: Extrusion

[0159] Casting solution A and casting solution B are combined into a two-layer solution structure by flowing through a co-extrusion feed head with two inlets. Then, they are extruded through a flat die to form a molded product with an inlet surface and an outlet surface. The inlet surface is formed by casting solution A and the outlet surface is formed by casting solution B. The die extrusion temperature is 220℃.

[0160] Step 3: Phase separation process:

[0161] The liquid inlet side of the molded product obtained in step two is subjected to air blowing pretreatment. The air blowing pretreatment time is 1 second, the temperature is 130℃, the air blowing pretreatment rate is 25m / min, and the air blowing pretreatment direction is perpendicular to the liquid inlet side.

[0162] Next, a phase separation process is performed. The liquid outlet side of the pretreated molded product is contacted with a cooling roller at 15°C, and the liquid inlet side is subjected to air blowing to obtain film I. The air blowing speed is 80m / min, the air blowing temperature is 100°C, the air blowing direction is parallel to the liquid inlet side of the film, the phase separation time is 22s, and the draw ratio is 5 times.

[0163] Step 4: Gas quenching optimization treatment:

[0164] Nitrogen gas at 80°C was introduced into the liquid inlet side of the biofilm I obtained in step 3 for 20 seconds to optimize the biofilm II. The nitrogen gas introduction rate was 110 m / min, and the flow direction of the nitrogen gas was parallel to the film thickness direction.

[0165] Step 5: Extraction:

[0166] The membrane obtained in step four was extracted with dichloromethane for 15 hours to obtain the original membrane.

[0167] Step Six: Heat Setting

[0168] The original membrane obtained in step 5 was kept at 95℃ for 25 minutes and then at 115℃ for 8 minutes to obtain a polyethylene filter membrane containing a flow guiding zone, an adsorption zone, a flow guiding enhancement zone, and a retention zone.

[0169] Example 6

[0170] A method for preparing a polyethylene filter membrane includes the following steps:

[0171] Step 1: Preparation of casting solution:

[0172] Casting solution A consists of 10 parts by mass of polyethylene resin with a weight-average molecular weight of 680,000 and a molecular weight distribution of 2.7, 42 parts by mass of castor oil, and 72 parts by mass of triacetin. The solid content of casting solution A is 8.1%, and the temperature of casting solution A is 210℃. Casting solution B consists of 8 parts by mass of UPE with a weight-average molecular weight of 1.9 million and a molecular weight distribution of 3.4, and 680,000 parts by mass of caster oil with a weight-average molecular weight of 680,000 and a density of 0.95 g / cm³. 3 It consists of 7 parts by weight of HDPE, 16 parts by weight of castor oil extract, and 90 parts by weight of palm oil. The solid content of casting solution B is 12.4%, and the temperature of casting solution B is 210℃.

[0173] Step 2: Extrusion

[0174] Casting solution A and casting solution B are combined into a two-layer solution structure by flowing through a co-extrusion feed head with two inlets. Then, they are extruded through a flat die to form a molded product with an inlet surface and an outlet surface. The inlet surface is formed by casting solution A and the outlet surface is formed by casting solution B. The die extrusion temperature is 190℃.

[0175] Step 3: Phase separation process:

[0176] The liquid inlet side of the molded product obtained in step two is subjected to air blowing pretreatment. The air blowing pretreatment time is 2s, the temperature is 140℃, the air blowing pretreatment rate is 15m / min, and the air blowing pretreatment direction is perpendicular to the liquid inlet side.

[0177] Next, a phase separation process is performed. The liquid outlet side of the pretreated molded product is contacted with a cooling roller at 10°C, and the liquid inlet side is subjected to air blowing to obtain film I. The air blowing speed is 60m / min, the air blowing temperature is 80°C, the air blowing direction is parallel to the liquid inlet side of the film, the phase separation time is 25s, and the draw ratio is 4 times.

[0178] Step 4: Gas quenching optimization treatment:

[0179] Nitrogen gas at 70°C was introduced into the liquid inlet side of the biofilm I obtained in step 3 for 18s to optimize the process and obtain biofilm II. The nitrogen gas introduction rate was 100 m / min, and the flow direction of the nitrogen gas was parallel to the film thickness direction.

[0180] Step 5: Extraction:

[0181] The membrane obtained in step four was extracted with dichloromethane for 15 hours to obtain the original membrane.

[0182] Step Six: Heat Setting

[0183] The original membrane obtained in step 5 is kept at 100℃ for 15 minutes and then at 120℃ for 5 minutes to obtain a polyethylene filter membrane containing a flow guiding zone, an adsorption zone, a flow guiding enhancement zone, and a retention zone.

[0184] The structure, porosity, HFE complete bubble point, specific surface area, XRD crystallinity, grain size, basis weight, retention efficiency, water flow rate, longitudinal tensile strength, and transverse tensile strength of the polyethylene filter membranes prepared in Examples 1-6 were characterized. The specific results are shown in Tables 1-3.

[0185] Table 1 - Overall characteristics of polyethylene filter membranes in Examples 1-6

[0186]

[0187]

[0188] Table 2 - Characteristics of the cross-section of polyethylene filter membranes in Examples 1-6

[0189]

[0190]

[0191] Table 3 - Other characteristics of polyethylene filter membranes in Examples 1-6

[0192]

[0193] The results above show that the polyethylene filter membranes prepared in Examples 1-4 have a three-layer structure consisting of a flow-guiding zone, an adsorption zone, and a retention zone, while the polyethylene filter membranes prepared in Examples 5-6 have a four-layer structure consisting of a flow-guiding zone, an adsorption zone, a flow-guiding enhancement zone, and a retention zone. The water flow rate of the polyethylene membranes obtained in Examples 1-4 and Examples 5-6 is within 2000 s / @50 mL@20℃@φ47 mm@0.03 MPa, exhibiting high flux. The retention efficiency for 5 nm colloidal gold is above 95%, demonstrating excellent retention efficiency. It can remove nano-impurities with particle sizes of 2 nm and smaller. The longitudinal tensile strength is greater than 5 MPa, and the transverse tensile strength is greater than 3.5 MPa, indicating good tensile strength, i.e., good compressive strength.

[0194] Example 7

[0195] A polyethylene filter membrane was prepared according to the preparation method of Example 2, except that in step one, the casting solution B contained 7 parts by mass of UPE with a weight-average molecular weight of 2 million and 6 parts by mass of HDPE, and the solid content of casting solution B was 15.5%; in step three, the temperature of the cooling roller was 50°C and the blowing temperature for phase separation was 90°C. The SEM average pore size of the adsorption region of the finally obtained polyethylene filter membrane was 312.4 nm. Compared with Example 2, the polyethylene filter membrane obtained in Example 7 had a 90%-95% retention efficiency for 5 nm colloidal gold, which was slightly lower.

[0196] Example 8

[0197] A polyethylene filter membrane was prepared according to the preparation method of Example 2, except that in step one, the hydraulic oil in casting solution B was 7 parts by mass, the dioctyl adipate was 57 parts by mass, and the solid content of casting solution B was 17.9%; in step three, the temperature of the cooling roller was 5°C, and the blowing temperature for phase separation was 120°C. The SEM average pore size of the adsorption region of the finally obtained polyethylene filter membrane was 95.1 nm. Compared with Example 2, the water flow rate of the polyethylene filter membrane obtained in Example 8 was 2487 s / @50 mL@20°C@φ

[0198] 47mm@0.03MPa, its flux is slightly lower.

[0199] Example 9

[0200] A polyethylene filter membrane was prepared according to the preparation method in Example 2, except that the thickness of the molded product during extrusion with the flat die was changed, the temperature of the cooling roller in step three was 30°C, the blowing temperature for phase separation was 80°C, the blowing rate for phase separation was 30 m / min, and the phase separation time was 5 s. The final polyethylene filter membrane had a thickness of 58.1 μm, a thickness of 22.2 μm in the adsorption zone, and a basis weight of 18.7 g / m³. 2 The specific surface area is 8.27 m². 2 / g, compared to Example 2, the polyethylene filter membrane obtained in Example 9 has a retention efficiency of 90%-95% for 5nm colloidal gold, which is slightly lower.

[0201] Example 10

[0202] A polyethylene filter membrane was prepared according to the preparation method in Example 2, except that the thickness of the molded product during extrusion with the flat die was changed, the extrusion temperature was 200°C, the pre-phase separation time in step three was 3 seconds, the blowing temperature for pre-phase separation was 180°C, the blowing temperature for phase separation was 115°C, and the phase separation time was 30 seconds. The final polyethylene filter membrane had a thickness of 153.2 μm, an adsorption zone thickness of 83.4 μm, and a basis weight of 47.1 g / m³. 2 The specific surface area is 19.74 m². 2 / g, compared to Example 2, the water flow rate of the polyethylene filter membrane obtained in Example 10 was 2412s / @50mL@20℃@φ47mm@0.03MPa, and its flux was slightly lower.

[0203] Example 11

[0204] A polyethylene filter membrane was prepared according to the preparation method of Example 2, except that in step one, the casting solution B contained 6.5 parts by mass of UPE with a weight-average molecular weight of 1.9 million, 6 parts by mass of HDPE with a weight-average molecular weight of 800,000, 6 parts by mass of hydraulic oil, and 54 parts by mass of dioctyl adipate. The solid content of casting solution B was 17.2%. The extrusion temperature in step two was 240°C. The temperature of the cooling roller in step three was 5°C. The final polyethylene filter membrane had a SEM average pore size ratio of 2.8 to the SEM average diameter of the fibers in the adsorption zone, and a porosity of 33.8%. Compared with Example 2, the polyethylene filter membrane obtained in Example 11 had a water flow rate of 2154 s / @50 mL@20°C@φ47 mm@0.03 MPa, and its flux was slightly lower.

[0205] Example 12

[0206] A polyethylene filter membrane was prepared according to the preparation method of Example 2, except that in step one, the casting solution B contained 7 parts by mass of UPE, 5 parts by mass of HDPE, and 52 parts by mass of dioctyl adipate, and the solid content of casting solution B was 15.0%; in step three, the temperature of the cooling roller was 40°C, the blowing temperature for phase separation was 80°C, and the phase separation time was 20s. The final polyethylene filter membrane had a SEM average pore size ratio of 12.5 to the SEM average diameter of the fiber in the adsorption region and a porosity of 77.2% in the adsorption region. Compared with Example 2, the polyethylene filter membrane obtained in Example 12 had a 90%-95% retention efficiency for 5nm colloidal gold, which was slightly lower.

[0207] Example 13

[0208] A polyethylene filter membrane was prepared according to the preparation method in Example 2, except that in step one, the amount of polyethylene resin in casting solution A was 14.5 parts by weight, and the amount of UPE in casting solution B was 10 parts by weight, and the amount of HDPE was 5.5 parts by weight. The density of HDPE was 0.97 g / cm³. 3 The solid content of casting solution A was 13.0%, and the solid content of casting solution B was 17.9%. The pre-phase separation time in step three was 0.5 s, and the temperature of the cooling roller was 6 °C. The ratio of the average SEM pore size of the adsorption zone to the average SEM pore size of the retention zone of the final polyethylene filter membrane was 2.7, and the average SEM pore size of the outlet pores was 13.7 nm. Compared with Example 2, the water flow rate of the polyethylene filter membrane obtained in Example 13 was 2357 s / @50 mL@20 °C@φ47 mm@0.03 MPa, and its flux was slightly lower.

[0209] Example 14

[0210] A polyethylene filter membrane was prepared according to the preparation method of Example 2, except that in step one, the polyethylene resin in casting solution A was 12 parts by mass, the weight average molecular weight of the polyethylene resin was 800,000, and the molecular weight distribution was 3.7; in casting solution B, UPE was 6 parts by mass and HDPE was 4 parts by mass; the solid content of casting solution A was 11.0% and the solid content of casting solution B was 12.3%; in step three, the pre-phase separation time was 3s, and the temperature of the cooling roller was 45°C. The final polyethylene filter membrane had a SEM average pore size ratio of 10.2 for the adsorption zone to 10.2 for the retention zone, and an SEM average pore size of 53.1 nm for the outlet pores. Compared with Example 2, the polyethylene filter membrane obtained in Example 14 had a retention efficiency of 90%-95% for 5 nm colloidal gold, which was slightly lower.

[0211] Example 15

[0212] A polyethylene filter membrane was prepared according to the preparation method of Example 2, except that in step one, the casting solution B contained 9 parts by mass of UPE and 5 parts by mass of HDPE; in step three, the draw ratio was 2 times; and in step six, the secondary heat setting was replaced with a single heat setting at a temperature of 100°C for 30 minutes. The final polyethylene filter membrane had an XRD crystallinity of 14.1% and an average grain size of 32.1 nm. Compared with Example 2, the polyethylene filter membrane obtained in Example 15 had a 90%-95% retention efficiency for 5 nm colloidal gold, which was slightly lower.

[0213] Example 16

[0214] A polyethylene filter membrane was prepared according to the preparation method of Example 2, except that in step one, the casting solution B contained 7 parts by mass of UPE and 7 parts by mass of HDPE; in step three, the draw ratio was 8 times; and in step six, the secondary heat setting was replaced with a single heat setting at a temperature of 110°C for 40 minutes. The final polyethylene filter membrane had an XRD crystallinity of 42.3% and a grain size of 13.7 nm. Compared with Example 2, the polyethylene filter membrane obtained in Example 16 had a retention efficiency of 90%-95% for 5 nm colloidal gold, which was slightly lower.

[0215] Example 17

[0216] A polyethylene filter membrane was prepared according to the preparation method of Example 2, except that in step one, the hydraulic oil in casting solution A was 30 parts by mass and the dioctyl adipate was 67 parts by mass; in casting solution B, the hydraulic oil was 21 parts by mass and the dioctyl adipate was 50 parts by mass; and in step three, the temperature of the cooling roller was 60°C. The final polyethylene filter membrane had a thickness ratio of 0.7 between the adsorption zone and the flow guiding zone, and a SEM average pore size ratio of 1.8 between the flow guiding zone and the adsorption zone. Compared to Example 2, the polyethylene filter membrane obtained in Example 17 had a retention efficiency of 90%-95% for 5nm colloidal gold, which was slightly lower.

[0217] Example 18

[0218] A polyethylene filter membrane was prepared according to the preparation method of Example 2, except that in step one, the hydraulic oil in casting solution A was 38 parts by mass and the dioctyl adipate was 59 parts by mass, and in casting solution B, the hydraulic oil was 8 parts by mass and the dioctyl adipate was 63 parts by mass; in step three, the temperature of the cooling roller was 8°C and the blowing temperature for phase separation was 120°C. The final polyethylene filter membrane had a thickness ratio of 2.7 between the adsorption zone and the flow guiding zone, and a SEM average pore size ratio of 5.3 between the flow guiding zone and the adsorption zone. Compared to Example 2, the polyethylene filter membrane obtained in Example 18 had a water flow rate of 2178 s / @50 mL@20°C@φ47 mm@0.03 MPa, and its flux was slightly lower.

[0219] Example 19

[0220] A polyethylene filter membrane was prepared according to the preparation method of Example 2, except that the pre-phase separation in step 3 was omitted and the blowing temperature for phase separation was 70°C. The pore area ratio of the liquid inlet surface of the final polyethylene filter membrane was 28.6%, and the fibers in the flow guiding zone did not form a block structure. Compared with Example 2, the water flow rate of the polyethylene filter membrane obtained in Example 19 was 2103s / @50mL@20°C@φ47mm@0.03MPa, and its flux was slightly lower.

[0221] Example 20

[0222] The polyethylene filter membrane was prepared according to the preparation method of Example 2, except that the extrusion temperature in step two was 200°C, the pre-phase separation time in step three was 5s, the pre-phase separation temperature was 170°C, and the phase separation temperature was 120°C. The pore area ratio of the liquid inlet surface of the final polyethylene filter membrane was 74.1%. Compared with Example 2, the polyethylene filter membrane obtained in Example 20 had a retention efficiency of 90%-95% for 5nm colloidal gold, which was slightly lower.

[0223] The results from Examples 7-20 show that the following parameters are considered in relation to the SEM average pore size of the polyethylene filter membrane: pore size of the adsorption zone, thickness of the adsorption zone, membrane thickness, basis weight, ratio of the SEM average pore size of the adsorption zone to the SEM average diameter of the fibers in the adsorption zone, porosity of the adsorption zone, ratio of the SEM average pore size of the adsorption zone to the SEM average pore size of the retention zone, SEM average pore size of the effluent pores, XRD crystallinity of the filter membrane, average grain size of the filter membrane, and the thickness of the adsorption zone relative to the flow conductivity. The ratio of the thickness of the zone, or the ratio of the average SEM pore size of the flow guiding zone to the average SEM pore size of the adsorption zone, or the pore area ratio of the liquid inlet surface are not within the preferred range, or the fibers of the flow guiding zone are not composed of a block structure. The water flow rate of the resulting polyethylene filter membrane is between 2000-2500s / @50mL@20℃@φ47mm@0.03MPa, which has good flux. The partial polyethylene filter membrane has a retention efficiency of 90%-95% for 5nm colloidal gold, which has good retention efficiency.

[0224] Comparative Example 1

[0225] A polyethylene filter membrane was prepared according to the preparation method of Example 2, except that in step one, the polyethylene resin in casting solution A was 8 parts by mass and the solid content of casting solution A was 7.6%, while in casting solution B, UPE was 5 parts by mass, HDPE was 4 parts by mass and the solid content of casting solution B was 11.3%. The final polyethylene filter membrane had a complete bubble point of 0.46 MPa. Compared with Example 2, the polyethylene filter membrane obtained in Comparative Example 1 had a retention efficiency of <90% for 5 nm colloidal gold.

[0226] Comparative Example 2

[0227] A polyethylene filter membrane was prepared according to the preparation method of Example 2, except that in step one, the polyethylene resin in casting solution A was 18 parts by mass, and the solid content of casting solution A was 15.7%; in casting solution B, UPE and HDPE were 9 parts by mass, and the solid content of casting solution B was 20.2%. The final polyethylene filter membrane had a complete HFE bubble point of 1.57 MPa. Compared with Example 2, the water flow rate of the polyethylene filter membrane obtained in Comparative Example 2 was 2847 s / @50 mL@20℃@φ

[0228] 47mm@0.03MPa.

[0229] Comparative Example 3

[0230] A polyethylene filter membrane was prepared according to the preparation method in Example 2, except that in step one, the hydraulic oil in casting solution A was 48 parts by mass and the dioctyl adipate was 49 parts by mass; in casting solution B, the hydraulic oil was 25 parts by mass and the dioctyl adipate was 46 parts by mass; in step three, the cooling roller temperature was 50°C and the blowing temperature for phase separation was 80°C; the specific surface area of ​​the finally obtained polyethylene filter membrane was 7.25 m². 2 / g, the thickness of the adsorption zone is 18.7μm, and the ratio of the thickness of the adsorption zone to the thickness of the retention zone is 2.7. Compared with Example 2, the polyethylene filter membrane obtained in Comparative Example 3 has a retention efficiency of <90% for 5nm colloidal gold.

[0231] Comparative Example 4

[0232] A polyethylene filter membrane was prepared according to the preparation method in Example 2, except that in step one, the hydraulic oil in casting solution A was 27 parts by mass and the dioctyl adipate was 70 parts by mass, while in casting solution B, the hydraulic oil was 5 parts by mass and the dioctyl adipate was 66 parts by mass; in step three, the temperature of the cooling roller was 0°C and the blowing temperature was 130°C. The specific surface area of ​​the final polyethylene filter membrane was 23.75 m². 2 / g, compared to Example 2, the water flow rate of the polyethylene filter membrane obtained in Comparative Example 4 was 3017s / @50mL@20℃@φ47mm@0.03MPa.

[0233] Comparative Example 5

[0234] A polyethylene filter membrane was prepared according to the preparation method of Example 2, except that the gas quenching optimization treatment in step four was omitted. The final polyethylene filter membrane had a complete HFE bubble point of 1.64 MPa. Compared with Example 2, the water flow rate of the polyethylene filter membrane obtained in Comparative Example 5 was 3147 s / @50 mL@20℃@φ47 mm@0.03 MPa.

[0235] Comparative Example 6

[0236] The polyethylene filter membrane was prepared according to the preparation method of Example 2, except that the inlet side was composed of casting solution B and the outlet side was composed of casting solution A. Both the inlet and outlet sides were cooled by cooling rollers during phase separation, with the temperature of the cooling rollers being 30°C. The final polyethylene filter membrane had a smaller SEM average pore size in the flow guiding zone than in the adsorption zone. Compared to Example 2, the water flow rate of the polyethylene filter membrane obtained in Comparative Example 6 was 3474 s / @50 mL@20°C@φ

[0237] 47mm@0.03MPa.

[0238] Comparative Example 7

[0239] Polyethylene filter membranes were prepared according to the preparation method of Example 2, except that the casting solution B contained 14 parts by mass of UPE and did not contain HDPE. The weight-average molecular weight of UPE was 5 million. The resulting polyethylene filter membrane was prone to delamination and could not be used for filtering photoresist process materials.

[0240] The results of Comparative Examples 1-6 show that when the HFA bubble point of the polyethylene filter membrane is too low or too high, or the specific surface area is too large or too small, or the thickness of the adsorption zone is less than 20 μm, or the ratio of the thickness of the adsorption zone to the thickness of the retention zone is less than 3, or the average SEM pore size of the flow guiding zone is smaller than the average SEM pore size of the adsorption zone, the polyethylene filter membrane will either have too high a water flow rate or too low a retention efficiency for 5 nm colloidal gold. Therefore, it cannot be effectively used for filtering semiconductor photolithography process materials, and its industrial practical value is low.

[0241] 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 polyethylene filter membrane, comprising a main body, one side of which is a liquid inlet surface and the other side of which is a liquid outlet surface, wherein the main body has a non-directional tortuous passage, characterized in that: The complete bubble point of the HFE of the filter membrane is 0.5 MPa-1.5 MPa; The main body comprises, in the thickness direction from the inlet surface to the outlet surface, a guiding zone, an adsorption zone, and a retention zone in sequence. The average SEM pore size of the flow guiding zone is greater than that of the adsorption zone, and the average SEM pore size of the adsorption zone is greater than that of the retention zone. The specific surface area of ​​the filter membrane is 8m². 2 / g-20m 2 / g; The thickness of the adsorption region is not less than 20 μm; The ratio of the thickness of the adsorption zone to the thickness of the retention zone is greater than 3.

2. The polyethylene filter membrane according to claim 1, characterized in that: The average pore size of the adsorption region, as measured by SEM, is 100 nm to 300 nm. The thickness of the adsorption region is 25μm-80μm; And / or, the thickness of the filter membrane is 60μm-150μm.

3. The polyethylene filter membrane according to claim 1, characterized in that: The adsorption zone has adsorption zone fibers that form a porous structure, and the ratio of the average SEM pore size of the adsorption zone to the average SEM diameter of the adsorption zone fibers is 3-12. The porosity of the adsorption zone is 35%-75%.

4. The polyethylene filter membrane according to claim 1, characterized in that: The thickness of the retention zone is 3μm-15μm; The ratio of the average SEM pore size of the adsorption zone to the average SEM pore size of the retention zone is 3-10. And / or, the liquid outlet surface includes a plurality of liquid outlet holes, and the SEM average pore size of the liquid outlet holes is 15nm-50nm.

5. The polyethylene filter membrane according to claim 1, characterized in that: The pore area of ​​the mesopores in the filter membrane accounts for 50%-80% of the total pore area in the filter membrane, wherein the pore diameter is greater than 2nm and less than or equal to 50nm. The pore area of ​​the micropores in the filter membrane accounts for 1%-10% of the total pore area in the filter membrane, wherein the pore size of the micropores is less than or equal to 2nm; The porosity of the filter membrane is 40%-80%.

6. The polyethylene filter membrane according to claim 1, characterized in that: The XRD crystallinity of the filter membrane is 15%-40%; the average grain size of the filter membrane is 15nm-30nm. And / or, the basis weight of the filter membrane is 20 g / m³. 2 -45g / m 2 .

7. The polyethylene filter membrane according to claim 1, characterized in that: The ratio of the thickness of the adsorption zone to the thickness of the flow guiding zone is 0.8-2.5; The ratio of the average SEM pore size of the flow guiding zone to the average SEM pore size of the adsorption zone is 2-5. And / or, the inlet surface includes a plurality of inlet holes, wherein the hole area ratio of the inlet surface is 30%-70%.

8. The polyethylene filter membrane according to claim 1, characterized in that: The flow guiding region has flow guiding region fibers that form a porous structure. Each flow guiding region fiber agglomerates with each other to form a block structure. The diameter of the block structure is 500nm-900nm. The ratio of the average SEM diameter of the block structure to the average SEM aperture of the flow guiding area is 1.0-1.

5.

9. The polyethylene filter membrane according to claim 1, characterized in that: The filter membrane further includes a flow-enhancing zone, which is located between the adsorption zone and the retention zone. The retention zone has retention zone fibers forming a porous structure, and the flow-enhancing zone has flow-enhancing zone fibers forming a porous structure. The flow-enhancing zone fibers and the adsorption zone fibers are continuous, and the flow-enhancing zone fibers and the retention zone fibers are continuous. The ratio of the average SEM pore size of the flow-enhancing zone to the average SEM pore size of the flow-guiding zone is 0.3-0.

7. The average SEM pore size of the flow-enhancing zone is greater than that of the adsorption zone.

10. The polyethylene filter membrane according to claim 9, characterized in that: The ratio of the thickness of the adsorption region to the thickness of the flow-enhancing region is 1.2-4; The thickness of the flow-guiding enhancement zone is greater than the thickness of the interception zone.

11. The polyethylene filter membrane according to claim 1, characterized in that: The filter membrane has a retention efficiency of over 90% for 5nm colloidal gold; The water flow rate of the filter membrane is less than 2500 s / @50 mL@20 ℃@φ47 mm@0.03 MPa; The longitudinal tensile strength of the filter membrane is greater than 5 MPa, and the transverse tensile strength of the filter membrane is greater than 3.5 MPa.

12. A method for preparing a polyethylene filter membrane as described in any one of claims 1-11, characterized in that: Includes the following steps: Step 1: Preparation of casting solution: Casting solution A is composed of polyethylene resin A1, solvent A2 and non-solvent A3. The solid content of casting solution A is 8%-15%, the weight average molecular weight of polyethylene resin A1 is 300,000-1,500,000, and the mass of solvent A2 accounts for 30%-40% of the total mass of solvent A2 and non-solvent A3. Casting solution B is composed of polyethylene resin B1, polyethylene resin B2, solvent B3 and non-solvent B4. The solid content of casting solution B is 12%-18%. Polyethylene resin B1 is UPE with a weight average molecular weight of 1.5 million to 3 million. Polyethylene resin B2 is HDPE with a weight average molecular weight of 300,000 to 1.5 million. The mass of polyethylene resin B1 is 50%-70% of the total mass of polyethylene resin B1 and polyethylene resin B2. The mass of solvent B3 accounts for 10%-30% of the total mass of solvent B3 and non-solvent B4. The solid content of the casting solution B is greater than that of the casting solution A; Step 2: Extrusion: Casting solution A and casting solution B are combined into a two-layer solution structure by flowing through a co-extrusion feed head with two inlets. Then, they are extruded through a flat die to form a molded product with an inlet surface and an outlet surface. The inlet surface is formed by casting solution A and the outlet surface is formed by casting solution B. The die extrusion temperature is 190℃-240℃. Step 3: Phase separation process: The molded product obtained in step 2 is subjected to phase separation at 5℃-120℃ for 5s-30s to obtain film I; the temperature on both sides of the liquid film is different during phase separation, and the temperature on the liquid inlet side is at least 40℃ higher than the temperature on the liquid outlet side. Step 4: Gas quenching optimization treatment: The inlet side of the biofilm I obtained in step 3 is circulated with gas for optimization treatment to obtain biofilm II. The gas flow temperature is 50℃-80℃, the gas flow rate is 85m / min-120m / min, and the gas flow direction is parallel to the film thickness direction. The optimization treatment time is 10s-20s. Step 5: Extraction; The membrane II obtained in step four is extracted with the extraction solution, thereby removing solvent A2, solvent B3, non-solvent A3 and non-solvent B4 from membrane II to obtain the original membrane; Step Six: Heat Setting The original membrane obtained in step 5 is kept at 80℃-120℃ for 20min-40min to obtain a polyethylene filter membrane.

13. The method for preparing a polyethylene filter membrane according to claim 12, characterized in that: The solvent in step one is at least one of paraffin oil, white oil, hydraulic oil, decahydronaphthalene, castor oil extract, and castor oil. The non-solvent in step one is at least one of dimethyl phthalate, dioctyl adipate, ethylene glycol diacetate, dimethyl carbonate, palm oil, and triacetin. The extraction solution in step five is at least one of dichloromethane, acetone, methanol, ethanol, glycerol, tetrafluoroethane, and isopropanol.

14. The method for preparing a polyethylene filter membrane according to claim 12, characterized in that: The molecular weight distribution of polyethylene resin A1 in step one is 1.5-3.5; The density of polyethylene resin B2 in step one is 0.92 g / cm³. 3 -0.96g / cm 3 ; The difference between the solid content of casting solution B and the solid content of casting solution A is 1.5%-4.5%.

15. The method for preparing a polyethylene filter membrane according to claim 12, characterized in that: In step two, the casting solution A and casting solution B have the same temperature, and both are 10°C-20°C higher than the die extrusion temperature. Before the phase separation process in step three, the molded product obtained in step two is also pretreated. The pretreatment is a blowing pretreatment on the liquid inlet side. The blowing pretreatment time is 1s-3s, the temperature is 120℃-150℃, the blowing pretreatment rate is 10m / min-30m / min, and the blowing pretreatment direction is perpendicular to the liquid inlet side.

16. The method for preparing a polyethylene filter membrane according to claim 12, characterized in that: During the phase separation process, the liquid outlet side contacts the cooling roller for phase separation, while the liquid inlet side undergoes phase separation through air blowing. The temperature of the cooling roller is 10℃-20℃; the air blowing speed is 40m / min-80m / min, the air blowing direction is parallel to the liquid inlet surface of the membrane, and the temperature is 80℃-110℃.

17. The method for preparing a polyethylene filter membrane according to claim 12, characterized in that: The heat setting step six includes a primary heat setting and a secondary heat setting, wherein the primary heat setting is held at 80℃-100℃ for 15min-30min; and the secondary heat setting is held at 100℃-120℃ for 5min-10min. And / or, the stretch ratio of the filter membrane is 3 to 6 times.

18. An application of a polyethylene filter membrane as described in any one of claims 1-11, characterized in that: The filter membrane is used for filtering materials in semiconductor photolithography processes.

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