Polyolefin filtration membrane and method for producing the same

Abstract

The application relates to a polyolefin filter membrane and a preparation method thereof, and the polyolefin filter membrane comprises a main body, the main body has a first outer surface and a second outer surface on two sides, non-oriented zigzag channels are formed in the main body, the first outer surface to the second outer surface is composed of continuous fibers, the PMI average pore diameter of the filter membrane is 2-100 nm, and the oxygen-carbon ratio of the filter membrane is in the range of 0.01-0.10. Through the interception effect of the PMI pore diameter on metal particles and the adsorption effect of the oxygen-containing functional groups on the modified polyolefin molecular chain on metal particles, high-precision interception removal of metal particles and microcolloid particles related to the metal particles in the organic solvent and the photoresist to be filtered is realized, and then a filter membrane with better adsorption performance on metal particles and microcolloid particles, faster flow rate and higher cleanliness is obtained.

Description

Technical Field

[0001] This invention relates to the technical field of membrane materials, and in particular to a polyolefin filter membrane and its preparation method. Background Technology

[0002] Polymer filter membranes are thin films made from organic polymers, primarily used for filtering and separating impurities. Based on the type of polymer, polymer filter membranes can be classified into cellulose-based polymer filter membranes, polyamide-based polymer filter membranes, polysulfone-based polymer filter membranes, polyester-based polymer filter membranes, and polyolefin-based polymer filter membranes, specifically including PP membranes, PVDF membranes, PTFE membranes, CA membranes, and UPE membranes.

[0003] Liquid filtration or purification typically involves passing the fluid to be filtered through a membrane filter, commonly used in the pharmaceutical, chemical, and food industries. The fluid to be filtered is usually chemically active, including ultrapure water, liquids containing peroxides, and liquids containing organic solvents. Considering the recycling of organic solvents, how to further remove impurity particles from organic solvents has become an important criterion for the recycling of organic solvents.

[0004] Chinese invention patent CN110860213B discloses a thin porous membrane, which is prepared by composite material of porous metal matrix support sheet and porous ceramic membrane layer. The porous metal matrix support sheet improves the strength of the composite material. The patent reveals in the background art that the composite membrane layer of porous metal material and ceramic material is prone to membrane defects when heated or cooled, resulting in cracks and deformation. When the above membrane is used to filter organic solvents, while removing impurities from the solvent, impurities such as metal particles that have fallen off due to cracks on the membrane layer may be introduced, which will affect the cleanliness of the organic solvent. At the same time, organic solvents are usually chemically corrosive, which also poses a certain challenge to the corrosion resistance and durability of the filter membrane.

[0005] Nanofiltration membranes for organic solvents are widely used in water purification (e.g., pesticide filtration) and industrial applications (e.g., ultrapure water filtration, organic solvent filtration) due to their excellent corrosion resistance. Patent CN116194195A discloses a nanofiltration membrane that exhibits excellent resistance to various organic solvents. Even when in contact with various types of industrially used organic solvents, it can stably maintain its properties and demonstrate good adsorption and rejection efficiency for solutes and particles in organic solvents. However, the objects filtered in the aforementioned patent are typically non-metallic particles such as plastic particles. For metallic particles, due to factors such as metallic bonds, the filtration efficiency of the aforementioned nanofiltration membrane for metallic particles is not high.

[0006] Meanwhile, in the semiconductor field, semiconductor materials mainly include wafer manufacturing materials, which mainly include silicon wafers, photoresists, wet electronic chemicals, sputtering targets, etc. In the wafer manufacturing process, wet electronic chemicals are mainly used to clean contaminants such as particles, organic residues, metal ions, and natural oxide layers. Semiconductors have strict requirements on the content of trace metal impurities (such as K, Ca, Al, Ti, Mn, Co, Ni, Cu, Mo, Au, etc.), particle size, and quantity of wet electronic chemicals.

[0007] Microcolloidal particles are commonly generated during photoresist filtration. These particles typically refer to small molecules within the photoresist itself, as well as micro-impurities introduced during the manufacturing process. The formation of these microcolloidal particles may be due to the inevitable introduction of metal particles or ions during photoresist production. The presence of small molecules and micro-impurities in the photoresist, combined with the potential for aging during transportation and storage, can cause these small molecules and impurities to aggregate around the metal particles or ions, forming localized "agglomerates" of gel centered around the metal particles or ions.

[0008] Therefore, there is an urgent need for a filter membrane that can effectively filter metal particles. Summary of the Invention

[0009] The objective of this invention is to provide a polyolefin filter membrane and its preparation method.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: a polyolefin filter membrane, comprising a main body, wherein the main body has a first outer surface and a second outer surface on both sides, and a non-directional tortuous passage is formed within the main body, wherein the first outer surface and the second outer surface are connected by continuous fibers.

[0011] The average pore size of the filter membrane is 2-100 nm.

[0012] The filter membrane has an oxygen-to-carbon ratio in the range of 0.01-0.10.

[0013] The average pore size (PMI) of the polyolefin filter membrane of this invention is 2-100 nm, reflecting the overall pore size of the membrane. This also indicates that the polyolefin filter membrane of this invention is a nanoscale filter membrane, capable of intercepting and filtering impurities at the nanoscale, such as metal particles like K, Ca, Al, Ti, Mn, Co, Ni, Cu, Mo, and Au. This allows the polyolefin filter membrane of this invention to meet the high-precision filtration requirements of solvent filtration, semiconductors, and other fields.

[0014] This invention introduces oxygen-containing functional groups into the molecular chain of a polyolefin filter membrane through graft modification to meet the filtration requirements for metal particles. Graft modification can be achieved through irradiation, such as gamma-ray irradiation or UV irradiation. Furthermore, the oxygen-to-carbon ratio of the polyolefin filter membrane is limited to 0.01-0.10. The applicant has found that when the oxygen-to-carbon ratio of the polyolefin filter membrane is 0.01-0.10, the polyolefin filter membrane can effectively adsorb metal particles and exhibit high removal efficiency. The reason for this may be that after modification, oxygen-containing functional groups may be further grafted onto the molecular chain of polyolefins. The grafting of oxygen-containing functional groups gives this part of the polyolefin molecular chain a certain electronegativity, thus making it easy to gain electrons and form lone electron pairs at the oxygen-containing functional groups. Metal particles usually have empty electron orbitals, so the metal particles and oxygen-containing functional groups form "coordinate bonds" through the cooperation of empty electron orbitals and lone electron pairs, thereby achieving further adsorption of metal particles. At the same time, the research found that the polyolefin filter membrane of the present invention also has a good adsorption effect on microcolloid particles, especially metal-related microcolloid particles. Ultimately, this is reflected in the significant improvement of the adsorption and removal efficiency of the modified filter membrane for metal particles and microcolloid particles. When the oxygen-to-carbon ratio of the polyolefin filter membrane is below 0.01, the adsorption and removal efficiency of the filter membrane with a larger average pore size of PMI decreases to a certain extent. This may be because there are not enough oxygen-containing functional groups grafted on the surface of the filter membrane (outer surface and internal pore surface), which cannot effectively improve the electronegativity of the polyolefin molecular chain, thus resulting in a relatively weak adsorption effect of oxygen-containing functional groups on metal particles.

[0015] On the other hand, a further increase in the oxygen-to-carbon ratio implies an increase in oxygen-containing functional groups, giving the filter membrane a better ability to adsorb metal particles. After grafting oxygen-containing functional groups onto the polyolefin molecular chain, this may manifest as adhesion to the pore surface, potentially leading to a reduction in the pore size at the grafting site. This increases the time it takes for the feed liquid to flow through the polyolefin filter membrane, thus affecting its flow rate performance. Therefore, the higher the oxygen-to-carbon ratio, the more oxygen-containing functional groups are grafted onto the polyolefin molecular chain, the greater the impact of these grafted oxygen-containing functional groups on the pore size, and the more significant the reduction in the filter membrane's flow rate performance.

[0016] At the same time, it is inevitable that as the number and degree of grafting of oxygen-containing functional groups increase, the problem of dissolution of oxygen-containing functional groups will often follow. The applicant found that when the oxygen-to-carbon ratio of the polyolefin filter membrane is higher than 0.1, the risk of dissolution of the polyolefin filter membrane will increase.

[0017] In summary, the polyolefin filter membrane of this invention has an average PMI pore size of 2-100 nm. Utilizing an oxygen-to-carbon ratio of 0.01-0.1, the polyolefin filter membrane with an average PMI pore size of 2-100 nm exhibits good adsorption performance for metal particles, reducing the probability of dissolution of oxygen-containing functional groups due to excessively high oxygen-to-carbon ratios, while also avoiding excessive flow rate attenuation caused by excessively high oxygen-to-carbon ratios. Furthermore, the filter membrane with an average PMI pore size of 2-100 nm can, to a certain extent, intercept metal particles. This invention achieves high-precision interception and removal of metal particles from the fluid to be filtered, such as organic solvents, by combining the interception effect of the PMI pore size with the adsorption effect of oxygen-containing functional groups on the modified polyolefin molecular chain. Additionally, the polyolefin filter membrane of this invention can also remove microcolloidal impurities in photoresist filtration by adsorbing "aggregate" gels centered on metal particles or metal ions.

[0018] The polyolefin filter membrane of the present invention has non-directional tortuous pathways in its main body. These non-directional tortuous pathways refer to randomly oriented groove structures and / or discretely distributed pore structures, and each non-directional tortuous pathway is interconnected. Furthermore, the fibers forming the porous structure of the membrane are continuous. It is understood that "continuous" means that essentially all the fibers are interconnected as a whole, as if formed integrally, without the need for additional adhesives or the like to connect them. Unless torn by external force, the network of fibers cannot be separated from each other. That is, the polyolefin filter membrane of the present invention is a single-layer membrane structure, rather than a composite membrane structure.

[0019] The raw material of the filter membrane of the present invention is polyolefin, which is composed of carbon and oxygen elements. The oxygen-carbon ratio is determined by X-ray photoelectron spectroscopy (XPS) analysis, which can better characterize the number and degree of oxygen-containing functional groups grafted by irradiation modification. The oxygen-carbon ratio is obtained by calculating the relative proportion of C and O elements in C1s and O1s by analyzing the carbon spectrum and oxygen spectrum respectively. Then, the overall oxygen-carbon ratio of the polyolefin filter membrane is obtained by calculating the relative proportion of C and O elements.

[0020] The XPS instrument used was the Thermo Scientific K-Alpha from the USA, with an Al target, a spot size of approximately 400 μm, a testing depth not exceeding 10 nm, and a sample chamber pressure of less than 2.0 × 10⁻⁶. -7 Approximately mbar, operating voltage 12kV, filament current 6mA; full spectrum scanning power is 150eV, step size 1eV; narrow spectrum scanning power is 50eV, step size 0.1eV.

[0021] The average pore size of the PMI in this invention is obtained by measuring with a PMI pore size meter.

[0022] The oxygen-to-carbon ratio of the present invention is further preferably 0.01-0.06. When the oxygen-to-carbon ratio of the polyolefin filter membrane is controlled at 0.01-0.06, the applicant found that with the increase of the oxygen-to-carbon ratio, the flow rate performance of the polyolefin filter membrane only decreases slightly, and even in polyolefin filter membranes with larger PMI pore sizes, the flow rate performance does not change. However, when the oxygen-to-carbon ratio is higher than 0.06, the degree of decrease in the flow rate performance of the polyolefin filter membrane tends to increase gradually. When the oxygen-to-carbon ratio is higher than 0.1, the flow rate performance of the polyolefin filter membrane decreases to a relatively large extent, which may affect the filtration efficiency.

[0023] Furthermore, the XPS analysis spectrum of the filter membrane includes "CO" and "C=O", wherein the content of "CO" is 0.6-5%, the content of "C=O" is 0.5-4.5%, and the ratio of the content of "CO" to "C=O" is 0.5-2.

[0024] When the present invention modifies the polyolefin filter membrane by grafting, it is often accompanied by the grafting and presence of "CO" and "C=O". The above results can be obtained based on the XPS analysis spectrum results and combined with oxygen spectrum analysis.

[0025] The relative content of "CO" and "C=O" is related to the overall oxygen-carbon ratio of the filter membrane. When the relative content of "CO" and "C=O" is low, the number of "CO" and "C=O" groups grafted onto the polyolefin molecular chain is less. To a certain extent, this represents a reduction in the number of lone pairs formed by the electronegativity of "CO" and "C=O" groups. Consequently, the number of "coordinate bonds" formed by lone pairs cooperating with the empty electron orbitals of metal particles also decreases. Ultimately, this results in low adsorption and removal efficiency for metal particles and related microcolloidal particles.

[0026] At the same time, it is not always better to have a higher relative content of "CO" and "C=O". The more "CO" and "C=O" grafted, the more "coordinate bonds" they can form with metal particles, meaning that the modified filter membrane will have a stronger adsorption capacity for metal particles. However, as the number of "CO" and "C=O" grafted increases, the degree to which "CO" and "C=O" adhere to the pore surface increases, resulting in a significant decrease in the flow rate of the filter membrane. On the other hand, the increased number of "CO" and "C=O" grafted also greatly increases the probability of "CO" and "C=O" leaching, thus affecting the cleanliness of the final filtrate and making it difficult to meet the cleanliness requirements of solvent filtration, semiconductors, and other fields.

[0027] Given a fixed overall oxygen-to-carbon ratio, the filter membrane inevitably contains CO and C=O. In C=O, oxygen and carbon share two pairs of electrons, resulting in an octet stability of the electrons around the oxygen element. This makes the electron-attracting ability of C=O more biased towards carbon. In CO, oxygen and carbon share one pair of electrons, allowing oxygen to further attract electrons. Since oxygen is more electronegative than carbon, CO is considered more electronegative than C=O. Experimental studies have shown that the higher the CO content, the better the adsorption performance of the filter membrane for metal particles. Because CO is relatively more electronegative than C=O, it more easily gains electrons and forms lone pairs. Metal particles have empty electron orbitals. The lone pairs of CO and C=O may coordinate with the empty electron orbitals of the metal particles to form "coordinate bonds," thereby achieving the adsorption of metal particles.

[0028] Therefore, this invention limits the ratio of the two groups "CO" and "C=O" to 0.6-5% and 0.5-4.5%, respectively, with the content of "CO" being higher than that of "C=O". Since the electronegativity of "CO" is relatively stronger than that of "C=O", controlling the relative content of "CO" to be higher than that of "C=O" allows the filter membrane to have good adsorption capacity and removal efficiency for metal particles even when the overall oxygen-carbon ratio is 0.01-0.1.

[0029] Compared to C=O, CO can impart better electronegativity and metal particle adsorption and removal efficiency to the modified filter membrane. However, during the modification process, C=O is inevitably grafted onto the filter membrane. When the CO content is too low, the electronegativity imparted by the C=O group to the filter membrane may be insufficient, thus reducing the filter membrane's adsorption and removal efficiency for metal particles.

[0030] Furthermore, the polyolefin is a crystalline polyolefin, and the crystallinity of the filter membrane, as measured by XRD, is 45-85%.

[0031] When the polyolefin is a crystalline polyolefin, such as UPE (ultra-high molecular weight polyethylene), the crystalline polyolefin, as a crystalline substance, causes the internal structure of the crystalline polyolefin filter membrane to be oriented to form crystalline and amorphous regions. The polyolefin filter membrane of the present invention further limits the crystallinity to 45-85%. The higher the crystallinity of the crystalline polyolefin filter membrane, the more stable the crystal structure and the better the low dissolution performance of the crystal. The applicant found that when the crystallinity of the crystalline polyolefin filter membrane is 45-85%, the TOC dissolution test of the crystalline polyolefin filter membrane can meet the cleanliness standards of solvent filtration, semiconductor fields, etc.

[0032] It is generally believed that the higher the crystallinity of a crystalline polyolefin filter membrane, the better its low-dissolution performance, thus maximizing the crystallinity of the crystalline polyolefin filter membrane. This invention modifies the polyolefin filter membrane through irradiation grafting modification, such as using irradiation (gamma rays, UV light, etc.). For example, gamma ray irradiation causes the crystalline polyolefin molecular chains to break, forming short-chain molecules. These short-chain molecules are more mobile and further promote crystallization, resulting in a further increase in crystallinity. Therefore, the increased crystallinity leads to a higher oxygen-to-carbon ratio, which increases the adhesion to the pore surface, resulting in a decrease in the overall flow rate of the filter membrane. This may make the filter membrane unsuitable for high-flow-rate filtration applications. Therefore, the upper limit of crystallinity in this invention is 85%, and it is not necessarily true that the higher the crystallinity, the better.

[0033] Meanwhile, the applicant found that when the crystallinity is 45-85%, the higher the crystallinity of the crystalline polyolefin filter membrane, the better its low-dissolution performance and strength. The reason for this may be that the higher the crystallinity of the crystalline polyolefin filter membrane, the better its low-dissolution performance and the better its heat resistance. This further reduces the probability of grafted oxygen-containing functional groups falling off or dissolving after heating, which is beneficial to improving the overall low-dissolution performance of the crystalline polyolefin filter membrane.

[0034] The crystallinity claimed in this invention, obtained by XRD, refers to the peak fitting of the original X-ray diffraction data using Jade software to obtain the fitting peaks for the crystalline and amorphous regions. The fitting peaks for the crystalline region are approximately 2θ = 19.6°, 2θ = 21.6°, and 2θ = 23.7°, while the remaining fitting peaks represent the amorphous region. The area of ​​the fitting peaks for the crystalline and amorphous regions is then calculated by integration. The crystallinity claimed in this invention is calculated as: Crystallinity = Integrated fitting peak area of ​​the crystalline region / (Integrated fitting peak area of ​​the crystalline region + Integrated fitting peak area of ​​the amorphous region). The XRD instrument used is a Rigaku Ultima IV (Japan); step size 0.02, tube voltage 40kV, and tube current 40mA.

[0035] The crystallinity of the crystalline polyolefin filter membrane of the present invention is further preferably 55-70%. When the crystallinity of the crystalline polyolefin filter membrane is 55-70%, it is found that the decrease in flow rate performance of the filter membrane is relatively small when the crystallinity is increased. When the crystallinity of the polyolefin filter membrane of the present invention is further increased, the flow rate performance of the filter membrane will decrease to a certain extent, and the flow rate performance of the filter membrane will decrease to a greater extent when the crystallinity is higher than 85%.

[0036] Furthermore, the filter membrane satisfies I 正交晶型 :I 单斜晶相 50 or greater;

[0037] Where I 正交晶型 The scattering intensity of the UPE filter membrane near 2θ angles of 21.6° and 23.7°;

[0038] I 单斜晶相 The scattering intensity of the UPE filter membrane is located near a 2θ angle of 19.6°.

[0039] When the polyolefin used in this invention is UPE (ultra-high molecular weight polyethylene), both monoclinic and orthorhombic crystal forms are common crystal types of UPE. The orthorhombic crystal form, being the most prevalent, exhibits better thermal stability, thus imparting good thermal stability to the filter membrane and improving the grafting stability of the irradiated graft groups to a certain extent, thereby helping to reduce the probability of leaching of the irradiated graft groups. Compared to the orthorhombic crystal form, the monoclinic crystal form has a larger angle between adjacent crystal planes, resulting in greater surface tension. An appropriate proportion of monoclinic crystal form can improve the surface tension of the filter membrane; however, the monoclinic crystal form has poor thermal stability and will transform into the orthorhombic crystal form under thermal effects. A higher proportion of orthorhombic crystal form results in better thermal stability of the filter membrane and better grafting stability of the irradiated graft groups, thereby reducing the probability of leaching of the irradiated graft groups. Simultaneously, better grafting stability of the irradiated graft groups leads to better continuous adsorption capacity of the irradiated graft groups for metal particles, thereby improving the interception efficiency of metal particles.

[0040] Furthermore, the half-maximum width of the characteristic peak of the filter membrane located near a 2θ angle of 21.6° is 0.4°-1.5°; the half-maximum width of the characteristic peak of the filter membrane located near a 2θ angle of 23.7° is 0.4°-1.5°.

[0041] Generally, the narrower the half-width at half-maximum (WHM) of a crystallization characteristic peak, the lower the crystallinity, the larger the grains, and the more complete the crystal structure. Conversely, an excessively wide WHM indicates that the crystalline region is not clearly defined. The UPE filter membrane of this invention exhibits a relatively suitable WHM at the absorption characteristic peak of the orthorhombic crystal form, reflecting that the UPE filter membrane of this invention has a relatively complete orthorhombic crystallization region and good crystallinity. At the same time, the grains in the crystalline region are relatively large, and the crystal structure is relatively complete, thereby endowing the filter membrane with relatively good low-dissolution performance.

[0042] Furthermore, the average SEM pore size of the first outer surface is not less than the average SEM pore size of the second outer surface, the average SEM pore size of the second outer surface is 15-100 nm, and the thickness of the filter membrane is 20-120 μm.

[0043] The second outer surface of the filter membrane of the present invention can usually be used as the liquid outlet surface. The oxygen-carbon ratio of the second outer surface is of greater concern because the feed liquid becomes the filtrate after flowing through the second outer surface. If leaching occurs near the second outer surface or the adsorption capacity for metal particles is insufficient, the cleanliness of the filtrate will be significantly affected. Even if leaching occurs on the first outer surface or the adsorption capacity for metal particles is insufficient, the filter membrane has a certain thickness. Therefore, the filter membrane can still further adsorb the leached molecules or metal particles in the feed liquid in the thickness direction. The leaching or insufficient adsorption capacity for metal particles on the first outer surface has a smaller impact on the cleanliness of the filtrate.

[0044] The area near the second outer surface plays a major adsorption role in the filtration process. The average pore size of the second outer surface, as measured by SEM, is 15-100 nm. Combined with the average pore size of the filter membrane (PMI), which is 2-100 nm, the small pore size of the second outer surface reflects its large specific surface area. This, along with the oxygen-carbon ratio distribution near the second outer surface, gives it a good adsorption capacity for metal particles. In addition, the PMI pore size of the filter membrane allows for the effective interception of nanoscale particles, thus enabling a certain degree of interception and removal of metal particles in the feed solution.

[0045] The average pore size of the first and second outer surfaces of the membrane, the average diameter of the cross-sectional fibers, and the surface fiber diameters of the first and second outer surfaces can be characterized by scanning electron microscopy (SEM) of the membrane structure, followed by measurement and calculation using computer software (such as Matlab, NIS-Elements, etc.) or manually. During membrane fabrication, the pore size distribution is generally uniform and consistent along the direction perpendicular to the membrane thickness. Therefore, the average pore size of a portion of the corresponding plane can reflect the overall average pore size of that plane. In actual measurement, the membrane surface can be characterized using an electron microscope to obtain the corresponding SEM image. Since the pores on the membrane surface are generally uniform, a certain area, such as 1 μm, can be selected. 2 (1μm x 1μm) or 25μm 2 (5μm by 5μm), the specific area size depends on the actual situation. Then, use appropriate computer software or manual measurement to determine the diameter of all holes on the area, and then calculate to obtain the average diameter of the holes on the surface. Of course, those skilled in the art can also obtain the above parameters through other measurement methods. The above measurement methods are for reference only.

[0046] Furthermore, the porosity of the second outer surface is 10-30%, and the pore density of the second outer surface is 120-300 pores / μm.2 .

[0047] The porosity of the second outer surface of the present invention is controlled to be 10-30%, and the pore density of the second outer surface is controlled to be 120-300 pores / μm. 2 This results in a more uniform distribution of the solid portion of the second outer surface, thereby giving the second outer surface a more stable flow rate and an adsorption effect on metal particles; if the porosity and pore density of the second outer surface are too high, it reflects that the proportion of the solid portion of the second outer surface is small, which may lead to a lower strength of the porosity of the second outer surface; if the porosity and pore density of the second outer surface are too low, it reflects that the proportion of the solid portion of the second outer surface is large, which may lead to a lower flow rate performance of the second outer surface.

[0048] The crystallinity of the filter membrane of the present invention is limited to the range of 45-85%, thereby making the solid part on the second outer surface have good low dissolution performance. In addition, the solid part has high crystallinity, which also has good impact resistance, strength and thermal stability, thereby reducing the probability of leaching of the irradiated graft groups after impact and heating by the feed liquid, so that the filtrate has high cleanliness.

[0049] In this invention, the pore area ratio and pore density of the first and second outer surfaces can be characterized by scanning electron microscopy (SEM) of the membrane structure, followed by measurement and calculation using computer software (such as Matlab, NIS-Elements, etc.) or manually. During the membrane preparation process, in the direction perpendicular to the membrane thickness, its various characteristics, such as pore size distribution, are approximately uniform and consistent. Therefore, the overall pore area ratio and pore density on the corresponding plane can be reflected by the pore area ratio and pore density of a portion of the plane. In actual measurement, the membrane surface can be characterized first using an electron microscope to obtain the corresponding SEM image. Since the pore distribution on the membrane surface is approximately uniform, a certain area, such as 1 μm, can be selected. 2 (1μm x 1μm) or 25μm 2 (5μm x 5μm), the specific area size depends on the actual situation. Then, use appropriate computer software or manual measurement to determine the area and number of all holes on this area, and then calculate to obtain the pore area ratio and pore density of the first and second outer surfaces. Of course, those skilled in the art can also obtain the above parameters through other measurement methods. The above measurement methods are for reference only.

[0050] Furthermore, the overall porosity of the filter membrane is 20-70%, and the filter membrane has a second cross-sectional fiber near the second outer surface along the thickness direction, the SEM average diameter of the second cross-sectional fiber being 30-100 nm.

[0051] When the overall porosity of the filter membrane is kept constant, the finer the diameter of the cross-sectional fibers, the larger the specific surface area of ​​the cross-sectional fibers, and the stronger the adsorption capacity of the cross-sectional fibers. When the porosity of the filter membrane is maintained at 20-70%, and the second cross-sectional fibers are controlled at 30-100nm, the second cross-sectional fibers have a strong adsorption capacity and can further adsorb molecules dissolved near the first outer surface, thereby reducing the impact of dissolution near the first outer surface on the cleanliness of the filtrate. In addition, the better the adsorption capacity of the second cross-sectional fibers, the higher the adsorption and removal rate of metal particles in the feed solution will be.

[0052] Meanwhile, it is generally understood that the finer the diameter of the cross-sectional fiber, the weaker its strength, and the more likely the cross-sectional fiber will dissolve. However, the filter membrane of the present invention has a high degree of crystallinity, which further enhances the strength of the second cross-sectional fiber and avoids the problems of insufficient strength and dissolution caused by the small diameter of the second cross-sectional fiber as much as possible.

[0053] Membrane porosity refers to the proportion of the membrane pore volume to the total volume of the filter membrane. Membrane pores include open pores and closed pores. Commonly used porosity testing methods include mercury intrusion porosimetry, density method, and wet-dry membrane weighing method. Of course, those skilled in the art can also obtain the above parameters through other measurement methods. The above measurement methods are for reference only.

[0054] Furthermore, the mass-average molecular weight of the filter membrane is 2 million to 5 million, and the first water contact angle of the second outer surface is 40° to 120°.

[0055] Generally, substances with higher mass-average molecular weight (MAM) tend to have better low-dissolution performance compared to those with lower MAM. Based on the porosity of the filter membrane and the diameter of the second cross-section fiber, this invention utilizes a larger MAM to ensure that even with a smaller diameter second cross-section fiber, the low-dissolution performance of the second cross-section fiber can still be maintained at a good level due to the larger MAM and higher crystallinity. Thus, while the second cross-section fiber adsorbs dissolution molecules and metal particles in the feed solution, it also possesses good low-dissolution performance, thereby improving the cleanliness of the filtrate.

[0056] Since polyolefin molecular chains are composed entirely of hydrophobic groups, and XPS testing reveals the grafting of oxygen-containing functional groups onto the irradiated polyolefin molecular chains, comparing the first water contact angle of the polyolefin filter membrane before and after irradiation modification can, to some extent, characterize the degree of grafting of oxygen-containing functional groups after irradiation modification. The water contact angle of the second outer surface is 40°-120°, which to some extent reflects the number of oxygen-containing functional groups grafted onto the second outer surface, thus ensuring the adsorption of metal particles. Furthermore, combined with the mass-average molecular weight and crystallinity of the filter membrane, the membrane ensures efficient filtration of metal particles while reducing the impact of leaching on the cleanliness of the filtrate.

[0057] The mass-average molecular weight can be obtained as follows: the sample of polyolefin filter membrane is heated and dissolved in o-dichlorobenzene, and the mass-average molecular weight is determined by GPC liquid chromatography at a column temperature of 135℃ and a flow rate of 1.0 mL / min.

[0058] The first water contact angle refers to the regular contact angle formed when 10-100 microliters of water droplets are uniformly applied to the material surface for an instant (within 0.4s) using a contact angle tester with water as the test liquid.

[0059] Furthermore, the filter membrane has a first cross-sectional fiber along the thickness direction near the first outer surface, the SEM average diameter of the first cross-sectional fiber is 30-110 nm, and the first water contact angle of the first outer surface is 40°-120°.

[0060] The first outer surface can usually be used as the liquid inlet surface. The first water contact angle of the first outer surface is 40°-120°. The first water contact angle reflects the degree of grafting of oxygen-containing functional groups on the first outer surface, thus giving the first outer surface a good adsorption effect on metal particles. On the other hand, the diameter of the first cross-section fiber is 30-100nm, which has a large specific surface area and a better adsorption capacity. To a certain extent, it can adsorb the dissolved molecules and metal particles in the feed solution. Under the influence of a large mass-average molecular weight and high crystallinity, the low dissolution performance of the first cross-section fiber can also be maintained at a good level, thereby reducing the impact on the cleanliness of the filtrate.

[0061] When the diameter of the first cross-section fiber is too large, the specific surface area of ​​the first cross-section fiber is relatively small, and its adsorption capacity will be poor, which is not conducive to adsorbing impurities such as metal particles in the liquid. When the diameter of the first cross-section fiber is too small, the strength of the first cross-section fiber is poor, which will make the cross-section fiber more prone to dissolution.

[0062] Furthermore, the average SEM pore size of the first outer surface is greater than that of the second outer surface, and the average SEM pore size of the first outer surface to the second outer surface exhibits a gradient change, with the average SEM pore size of the first outer surface being 500-2000 nm and the average SEM pore size of the second outer surface being 15-100 nm.

[0063] When the filter membrane of the present invention is an asymmetric membrane, the larger pore size near the first outer surface enables pre-filtration of the feed liquid and increases the dirt-holding capacity of the filter membrane. Simultaneously, the flow rate of the feed liquid through the filter membrane is relatively fast. The feed liquid has a greater impact on the pores near the first outer surface, and the increased number of irradiated grafted oxygen-containing functional groups easily leads to the dissolution of these irradiated grafted groups. The smaller pore size near the second outer surface allows for a certain degree of interception of impurities such as metal particles in the feed liquid. The second outer surface also has a relatively larger number of irradiated grafted oxygen-containing functional groups. This gives the area near the second outer surface a good adsorption capacity for metal particles, ensuring sufficient adsorption of metal particles. At the same time, even if dissolution occurs near the first outer surface, the area near the second outer surface can still adsorb the dissolved molecules to a certain extent. Through the irradiation of grafted groups on the first and second outer surfaces and the asymmetry of pore size, the filter membrane can ensure the adsorption efficiency of metal particles in the feed liquid under the premise of an oxygen-carbon ratio of 0.01-0.1, while having a small impact on the flow rate. It is suitable for filtration applications that require high flow rates and high dirt holding capacity.

[0064] Furthermore, the pore density of the first outer surface is 0.5-80 pores / μm. 2 The porosity of the first outer surface is 10-25%.

[0065] The pore density and pore area ratio of the first outer surface are controlled within the range of 0.5-80 pores / μm. 2 Within the range of 10-25%, the pore area ratio of the first outer surface is calculated from the number and size of the pores on the first outer surface. This reflects both the relatively large pore diameter and the relatively uniform distribution of the pores on the first outer surface, resulting in a better flow rate when the liquid flows through the first outer surface. At the same time, because the filter membrane has a certain porosity and high crystallinity (which to some extent reflects the proportion of solid parts in the filter membrane), the solid parts of the first outer surface have better compressive and impact resistance, which can reduce the probability of leaching of irradiated graft groups to some extent. In addition, the high crystallinity also gives the first outer surface better low leaching performance.

[0066] Furthermore, the SEM average apertures of the first outer surface to the second outer surface are symmetrically arranged, and the SEM average apertures of the first outer surface and the second outer surface are 15-100nm.

[0067] When the filter membrane of the present invention is a symmetrical membrane, the overall pore size distribution of the membrane is relatively uniform. The symmetrical membrane has a better interception effect on impurities such as metal particles in the feed solution. Since the overall pore size distribution of the symmetrical membrane is relatively uniform, the grafting uniformity of oxygen-containing functional groups after irradiation is also relatively better, thereby making the filter membrane have better adsorption performance for metal particles. To a certain extent, the stability of oxygen-containing functional groups after irradiation grafting is also relatively better, which can reduce the probability of dissolution of irradiated grafted groups while ensuring continuous adsorption of metal particles in the feed solution and improving the cleanliness of the final filtrate. It is suitable for filtration fields with high filtration accuracy requirements and few filtration impurities.

[0068] Furthermore, the pore density of the first outer surface is 150-300 pores / μm. 2 The porosity of the first outer surface is 10-30%.

[0069] When the filter membrane of the present invention is a symmetrical membrane, the pore size of the first outer surface is small, which mainly plays the role of removing particles. The pore density of the first outer surface is higher, and the number of oxygen-containing functional groups grafted on the pores of the first outer surface is greater, thereby giving the pores near the first outer surface a better adsorption capacity for metal particles. At the same time, the setting of a larger pore density and pore area ratio reflects that the pore size distribution of the first outer surface is more uniform and smaller. Combined with the setting of higher crystallinity, the pores near the first outer surface have better low dissolution performance and compressive strength, thereby enabling the filter membrane to continuously adsorb metal particles in the feed solution.

[0070] Furthermore, the average diameter of the fibers on the first outer surface is 50-150 nm, and the average diameter of the fibers on the second outer surface is 50-100 nm.

[0071] Compared to the fibers on the second outer surface, the fibers on the first outer surface of this invention are subject to continuous impact from the liquid as the inlet surface, making them more prone to dissolution. The average diameter of the fibers on the first outer surface is 50-150 nm, resulting in better strength and self-dissolution performance. Meanwhile, the liquid flowing through the second outer surface becomes filtrate, so the diameter of the fibers on the second outer surface is controlled to be 50-100 nm. Furthermore, the high crystallinity setting results in better low dissolution performance of the fibers on the second outer surface, reducing the impact on the cleanliness of the filtrate.

[0072] Furthermore, the longitudinal tensile strength of the filter membrane is 6-18 MPa, and the transverse tensile strength is 4-16 MPa; the TOC leaching amount of the filter membrane does not exceed 0.5 ppb; under the conditions of a positive pressure of 0.03 MPa and a temperature of 20°C, the time required for 50 ml of water to pass through a porous filter membrane with a diameter of 47 mm is 100-3000 s.

[0073] The present invention has good longitudinal tensile strength and transverse tensile strength values, thereby giving the filter membrane good impact resistance and reducing the probability of leaching to a certain extent. At the same time, through TOC leaching test, it can be found that the filter membrane of the present invention has a low leaching amount, so it can be applied to solvent filtration, semiconductor, ultrapure water and other filtration fields. Secondly, the filter membrane of the present invention has little impact on the flow rate after irradiation modification.

[0074] Furthermore, the polyolefin is any one of PE, PP, and UPE.

[0075] Furthermore, this invention discloses a process for preparing a polyolefin filter membrane, comprising the following steps:

[0076] S1, Prepare a modified solution by adding 2.5-10% sulfite and 1-5% surfactant by mass to water to prepare a modified solution;

[0077] S2, the filter membrane is soaked in an alcohol solution, and after the filter membrane is wetted, it is soaked and rinsed in pure water. The filter membrane is then immersed in a modified solution for material-liquid replacement.

[0078] S3. The filter membrane impregnated with the modified solution is irradiated with X-rays. The X-ray irradiation is controlled so that the oxygen-carbon ratio of the filter membrane is controlled within 0.01-0.1. After the filter membrane is removed from the modified solution, it is soaked in pure water and dried to obtain a polyolefin filter membrane.

[0079] The polyolefin filter membrane of the present invention is grafted with oxygen-containing functional groups through irradiation modification. In the present invention, the polyolefin filter membrane can be grafted and modified by both gamma-ray irradiation and UV irradiation, and the oxygen-carbon ratio of the polyolefin filter membrane is controlled within 0.01-0.1, thereby endowing the polyolefin filter membrane with adsorption properties for metal particles and related gels.

[0080] The purpose of soaking in alcohol solvent is that the original polyolefin filter membrane contains hydrophobic groups, giving it a certain degree of hydrophobicity. Direct contact between the original polyolefin filter membrane and the modification solution may result in the modification solution not being able to wet the original polyolefin filter membrane well. However, wetting with alcohol solvent allows the modification solution to penetrate and wet the original polyolefin filter membrane better. Secondly, rinsing with pure water after soaking in alcohol solvent is to remove the influence of alcohol solvent during the irradiation modification process.

[0081] Furthermore, in step S3, the filter membrane impregnated with the modified solution is irradiated with UV radiation, with the feed solution temperature controlled at 30-50℃ and the irradiance controlled at 10-200mW / cm². 2The wavelength of UV irradiation is 100-320nm, and the irradiation time is 10-30min.

[0082] This invention utilizes UV irradiation to graft and modify polyolefin filter membranes. Compared to long-wave UV light, short-wave and medium-wave UV light contain higher energy to initiate the reaction, thus effectively grafting and modifying the polyolefin filter membrane and giving it better adsorption capacity for metal particles and metal-related microcolloidal particles.

[0083] Furthermore, in step S3, the filter membrane is immersed in a container containing the modified solution, sealed, and evacuated for 1-3 hours. The container containing the modified solution and the filter membrane is then irradiated with gamma rays at a radiation intensity of 2-4 Mrad / h for 13-25 hours, with the solution temperature controlled at 30-50°C and the total radiation dose at 25-50 Mrad. After the filter membrane is removed from the solution, it is soaked in pure water and dried to obtain a polyolefin filter membrane.

[0084] This invention utilizes gamma rays to graft and modify polyolefin filter membranes. By using relatively high feed temperature and relatively high total irradiation dose, the grafting reaction of the polyolefin filter membrane is more intense, resulting in a better degree of grafting of oxygen-containing functional groups on the polyolefin filter membrane, thus endowing the polyolefin filter membrane with better adsorption capacity for metal particles.

[0085] Furthermore, the filter membrane has undergone pretreatment.

[0086] The pretreatment steps include gamma-ray pretreatment:

[0087] 1) Prepare a pre-modified solution by adding 1-5% sulfite and 0.5-2.5% surfactant to water to prepare a pre-modified solution, wherein the mass fractions of sulfite and surfactant in the pre-modified solution are lower than those in the modified solution.

[0088] 2) Soak the filter membrane in an alcohol solution. After the filter membrane is wetted, soak and rinse it in pure water. Immerse the filter membrane in a container with a pre-modified solution for material-liquid replacement and introduce an oxygen environment.

[0089] 3) Irradiate the container containing the pre-modified solution and the filter membrane with gamma rays at a radiation intensity of 0.2-0.5 Mrad / h for 16-40 hours, wherein the irradiation time of the pre-modification process is longer than that of the modification process. Control the temperature of the feed solution at 10-25℃ and the total radiation dose at 4-8 Mrad. After removing the filter membrane from the pre-modified solution, soak it in pure water.

[0090] Alternatively, the pretreatment steps may include UV pretreatment:

[0091] 1) Prepare a pre-modified solution by adding 1-5% sulfite and 0.5-2.5% surfactant to water to prepare a pre-modified solution, wherein the mass fractions of sulfite and surfactant in the pre-modified solution are lower than those in the modified solution.

[0092] 2) Soak the filter membrane in an alcohol solution. After the filter membrane is wetted, soak and rinse it in pure water. Then immerse the filter membrane in a pre-modified solution for material-liquid replacement.

[0093] 3) Irradiate the filter membrane impregnated with the pre-modified solution using UV irradiation, controlling the feed solution temperature at 10-25℃ and the irradiance at 1000-2000 mW / cm². 2 The UV irradiation wavelength is 100-320nm, the irradiation time is 1-3h, and the filter membrane is removed from the pre-modified solution and soaked in pure water.

[0094] This invention employs a two-stage irradiation modification method to modify polyolefin filter membranes. The first irradiation modification is a pre-modification process, which can be carried out using either gamma-ray irradiation or UV irradiation. When using gamma-ray irradiation, a low pre-modification solution concentration, a low radiation dose (4-8 Mard), a low temperature (10-25°C), and an oxygen-filled environment are used. The main purpose of the first irradiation modification is to increase the crystallinity of the polyolefin filter membrane while simultaneously pre-grafting it. When exposed to low-dose gamma rays (4-8 Mard), the molecular chains of polyolefin filter membranes break down under gamma ray irradiation. The broken chains are more mobile, rearrange themselves, and recrystallize, resulting in a significant increase in crystallinity during the first irradiation modification stage, further enhancing the low-dissolution performance of the polyolefin filter membrane. At low-dose (4-8 Mard), however, the cross-linking effect in the molecular chains is not significant, and the resulting three-dimensional network structure is detrimental to crystallinity improvement. Simultaneously, in an oxygen environment, the molecular chains of polyolefin filter membranes undergo oxidative breakage at low-dose (4-8 Mard). This oxidative breakage reduces the crystallite size and generates a fine-grained phase in the amorphous region, thus contributing to increased crystallinity. Furthermore, a low pre-modification solution concentration allows for better material exchange within the polyolefin filter membrane compared to a high-concentration modification solution. The low-temperature modification environment and low pre-modification solution concentration facilitate pre-graft modification of the polyolefin filter membrane and impart a certain degree of hydrophilicity.

[0095] The second irradiation modification employs a high concentration of modifying solution, a high radiation dose (25-50 Mard), a high temperature (30-50℃), and a vacuum environment. The primary purpose of this second irradiation modification is to further enhance the degree of irradiation modification of the polyolefin filter membrane. The high concentration of the modifying solution and the vacuum environment allow the modifying solution to penetrate the polyolefin filter membrane effectively under vacuum. Furthermore, since the solution modified in the first irradiation has a certain degree of hydrophilicity, it is unnecessary to wet it again with an alcohol solution during the second irradiation modification. The high concentration of the modifying solution also allows for better material exchange within the polyolefin filter membrane. The relatively high temperature environment intensifies the activity of the polyolefin molecular chains, and combined with the high concentration of the modifying solution, it facilitates graft modification of the polyolefin filter membrane, thereby increasing the degree of irradiation modification. Additionally, the two irradiation modifications can, to some extent, improve the uniformity of grafting of the irradiated graft groups. The applicant discovered that under high radiation doses (25-50 Mard) of gamma rays, the crystallinity of the polyolefin filter membrane modified by the second irradiation increased to a certain extent compared with that of the polyolefin filter membrane modified by the first irradiation. The reason for this may be that under high radiation doses (25-50 Mard), the crystalline regions begin to melt, and the polymer molecular chains undergo complex processes such as cracking and reconstruction. There are still a certain number of short-chain free radicals in the polyolefin filter membrane, which have strong mobility and rearrangement ability. At this time, the effects of crystal rearrangement and other behaviors are greater than the cross-linking effects of molecular chains, thus manifesting as an increase in crystallinity, which in turn further improves the low dissolution performance of the polyolefin filter membrane.

[0096] The irradiation modification of this invention is carried out in two steps. The first irradiation modification uses a lower irradiation intensity and a longer irradiation time, while the second irradiation modification uses a higher irradiation intensity and a shorter irradiation time. Firstly, those skilled in the art have found that when using gamma rays to irradiate and modify polyolefin filter membranes, since the polyolefin filter membrane is in a closed container and the environment for gamma ray irradiation is also relatively enclosed, maintaining a constant temperature of the feed solution has become a problem for those skilled in the art, as the temperature of the feed solution affects the intensity of the grafting reaction. The applicant discovered that during gamma ray irradiation, heat loss occurs within the system along with the grafting reaction. When the first irradiation intensity is low and prolonged, the applicant found that the feed solution temperature is relatively constant, fluctuating only within a small range. The reason for this is likely that gamma ray irradiation generates heat within the system, and the heat generated by using low-intensity (4-8 Mard) gamma rays is equivalent to the heat lost within the system, thus unexpectedly solving the problem of maintaining a constant feed solution temperature. Simultaneously, the combination of low irradiation intensity and long irradiation time in the first irradiation modification allows the polyolefin filter membrane more time to crystallize and improve. At the same time, the use of low-concentration modification solution allows the interior of the polyolefin filter membrane to also have sufficient time for pre-graft modification.

[0097] The second irradiation modification uses a higher irradiation intensity, which means that the gamma rays have higher energy. When the polyolefin filter membrane is irradiated with high-intensity gamma rays, the heat generated in the system will increase. When the temperature of the feed liquid is controlled at 30-50℃, the heat exchange rate between the feed liquid and the closed system will also change. This may be because the heat generated by the high-intensity gamma rays and the heat lost by the feed liquid system have reached a dynamic balance. Therefore, the temperature of the feed liquid is relatively constant under an irradiation intensity of 25-50 Mard. On the other hand, due to the greater intensity of the second irradiation modification, the reaction between the high-concentration modification solution and the polyolefin filter membrane is also more intense and faster, making it easier for the irradiation modification process of the polyolefin filter membrane to reach the expected level. Therefore, the irradiation time should be controlled to be relatively low. Further increasing the irradiation time will not further increase the degree of irradiation modification of the polyolefin filter membrane (the effective components in the modification solution are almost depleted due to the intensity and speed of the reaction), and may even cause further irradiation by gamma rays to break the grafted molecular chains, thus affecting the number of irradiated graft groups. Therefore, the time for the second irradiation modification should not be too long.

[0098] Secondly, the applicant found that when the irradiation intensity was 0.2-0.5 Mrad / h, the content of "CO" and "C=O" was lower than that when the irradiation intensity was 2-4 Mrad / h, and the ratio of the content of "CO" and "C=O" was lower when the irradiation intensity was 0.2-0.5 Mrad / h than that when the irradiation intensity was 2-4 Mrad / h. In other words, as the irradiation intensity increased, the rate of increase of "CO" bonds was greater than the rate of increase of "C=O" bonds. The reason for this may be that at low irradiation intensities (0.2-0.5 Mrad / h), the energy generated by gamma-ray irradiation for modification and grafting is relatively small. At this time, because the bond energy of "CO" is lower than that of "C=O", the content of "CO" is higher than that of "C=O", and the ratio of the two contents is not high. However, at irradiation intensities (2-4 Mrad / h), the energy generated by gamma-ray irradiation for modification and grafting is relatively abundant. Since the bond energy of "CO" is low, more of the abundant energy is used to generate "CO", which is reflected in the increased ratio of "CO" to "C=O" contents.

[0099] Meanwhile, the applicant discovered that UV irradiation could achieve the same effect as gamma ray irradiation during the pre-modification process, when the irradiance was controlled at 1000-2000 mW / cm². 2 When UV irradiation is applied at wavelengths of 100-320 nm for 1-3 hours, the molecular chains of the polyolefin filter membrane can undergo certain pre-grafting modification, which can also improve the crystallinity of the polyolefin filter membrane to a certain extent.

[0100] Furthermore, the sulfite is sodium sulfite or potassium sulfite, and the surfactant is sodium dodecyl sulfate or sodium dodecylbenzene sulfonate.

[0101] In summary, the present invention has at least one of the following beneficial technical effects:

[0102] 1. The polyolefin filter membrane of the present invention has an average PMI pore size of 2-100 nm and an oxygen-to-carbon ratio of 0.01-0.1. The present invention achieves the adsorption and removal of metal particles in organic solvents by combining the interception effect of the average PMI pore size with the adsorption effect of oxygen-containing functional groups on the polyolefin molecular chain after irradiation modification on metal particles. It can also remove microcolloidal impurities in photoresist filtration by adsorbing "aggregate" gels centered on metal particles or metal ions. At the same time, it reduces the probability of dissolution of oxygen-containing functional groups due to excessively high oxygen-to-carbon ratio, and reduces the impact of irradiation modification and grafting on the flow rate of the filter membrane.

[0103] 2. The filter membrane of the present invention has a crystallinity of 45-85%, which gives the polyolefin filter membrane good low dissolution performance, further reducing the impact of dissolution caused by the leaching of more grafted groups due to irradiation modification on the cleanliness of the filtrate. At the same time, it gives the polyolefin filter membrane good heat resistance, thereby reducing the probability of grafted oxygen-containing functional groups falling off or dissolving after heating, which is beneficial to improving the cleanliness of the filtrate.

[0104] 3. The irradiation modification of this invention is carried out in two steps. The first irradiation modification uses a lower irradiation intensity and a longer irradiation time, while the second irradiation modification uses a higher irradiation intensity and a shorter irradiation time, which further improves the uniformity of the irradiated graft groups. At the same time, the first irradiation modification gives the filter membrane a higher crystallinity and better low dissolution performance, and the pre-grafting of the filter membrane imparts a certain degree of hydrophilicity to the filter membrane. This eliminates the need for rewetting with alcohol solvents during the second irradiation modification. The second irradiation modification is mainly used to further improve the grafting degree of the irradiated graft groups and give the filter membrane a better metal particle adsorption capacity. Attached Figure Description

[0105] The present invention will be further described below with reference to the accompanying drawings:

[0106] Figure 1 The image shown is a scanning electron microscope (SEM) image of the first outer surface of the ultra-high molecular weight polyethylene (UHMWPE) filter membrane prepared in Example 2, with a magnification of 20K×.

[0107] Figure 2 The image shown is a scanning electron microscope (SEM) image of the second outer surface of the ultra-high molecular weight polyethylene (UHMWPE) filter membrane prepared in Example 2, with a magnification of 10K×.

[0108] Figure 3 The image shown is a scanning electron microscope (SEM) image of the cross-section of the ultra-high molecular weight polyethylene (UHMWPE) filter membrane prepared in Example 2, with a magnification of 1K×.

[0109] Figure 4 The image shown is a scanning electron microscope (SEM) image of the first outer surface of the ultra-high molecular weight polyethylene (UHMWPE) filter membrane prepared in Example 3, with a magnification of 50K×.

[0110] Figure 5 The image shown is a scanning electron microscope (SEM) image of the second outer surface of the ultra-high molecular weight polyethylene (UHMWPE) filter membrane prepared in Example 3, with a magnification of 50K×.

[0111] Figure 6 This is a schematic diagram of the device for testing the flow rate of the ultra-high molecular weight polyethylene filter membrane according to the present invention. Detailed Implementation

[0112] The present invention will be further described in detail below with reference to the embodiments. Unless otherwise specified, the raw materials and equipment used to prepare polyolefin filter membranes in the following embodiments can be purchased commercially.

[0113] Example 1

[0114] A method for preparing a polyolefin filter membrane includes the following steps:

[0115] S1, Prepare the first modified solution by adding sulfite and surfactant to water to prepare the first modified solution. The mass fraction of sulfite in the first modified solution is 5%, and the mass fraction of surfactant in the first modified solution is 2.5%.

[0116] Sodium sulfite is selected as the sulfite and sodium dodecyl sulfate is selected as the surfactant.

[0117] S2, immerse the filter membrane in a 60% methanol solution. After the filter membrane is wetted, soak and rinse it twice in pure water. Place the filter membrane in a container containing the first modification solution and ensure that the filter membrane is completely wetted by the first modification solution. Then, introduce an oxygen environment.

[0118] The filter membrane used is a UPE filter membrane.

[0119] S3, the container containing the filter membrane and the first modified solution is placed under γ-ray irradiation and irradiated for 20 hours at an irradiation intensity of 0.4Mrad / h, the temperature of the feed solution is controlled at 15℃, and the total radiation dose is 8Mrad. After the filter membrane is removed from the first modified solution, it is soaked in pure water.

[0120] S4, Prepare the second modified solution by adding sulfite and surfactant to water to prepare the second modified solution. The mass fraction of sulfite in the second modified solution is 10%, and the mass fraction of surfactant in the second modified solution is 5%.

[0121] Sodium sulfite is selected as the sulfite and sodium dodecyl sulfate is selected as the surfactant.

[0122] S5, place the filter membrane into a container containing the second modified solution and ensure that the filter membrane is completely wetted by the second modified solution, seal it and evacuate for 1 hour.

[0123] S6. The container containing the filter membrane and the second modified solution is placed under γ-rays for 12.5 hours with an irradiation intensity of 4Mrad / h. The temperature of the feed solution is controlled at 45℃ and the total radiation dose is 50Mrad. After the filter membrane is removed from the second modified solution, it is soaked in pure water and dried to obtain the irradiated modified polyolefin filter membrane.

[0124] The polyolefin filter membrane selected is the UPE filter membrane.

[0125] Example 2-11

[0126] The difference between Examples 2-11 and Example 1 lies in the different process parameters, as shown in Tables 1-1, 1-2, and 1-3. In Examples 2 and 4, the sulfite and surfactant are different from those in Example 1. In Example 2, the sulfite is potassium sulfite and the surfactant is sodium dodecylbenzenesulfonate; in Example 4, the sulfite is potassium sulfite and the surfactant is potassium dodecyl sulfate. In Example 6, the crystalline polyolefin used is polypropylene.

[0127] Example 12

[0128] The difference between Example 12 and Example 11 is that the filter membrane is pretreated by UV and then modified by γ-ray irradiation. The concentration of the modifying solution and process parameters in the irradiation modification process are shown in Tables 1-4.

[0129] Example 13

[0130] The difference between Example 13 and Example 2 is that the filter membrane did not undergo a pretreatment step, but was modified by gamma ray irradiation. The concentration of the modifying solution and process parameters during the irradiation modification process are shown in Tables 1-3.

[0131] Example 14

[0132] The difference between Example 14 and Example 2 is that the filter membrane did not undergo a pretreatment step, but was modified by UV irradiation. The concentration of the modifying solution and process parameters during the UV irradiation modification process are shown in Tables 1-4.

[0133] Comparative Example 1

[0134] The difference between Comparative Example 1 and Example 2 is that only one γ-irradiation modification was performed, and the concentration of the modifying solution and process parameters during the irradiation modification process were different, as shown in Tables 1-3.

[0135] Comparative Example 2

[0136] The difference between Comparative Example 2 and Example 2 is that only one UV irradiation modification was performed, and the concentration of the modifying solution and process parameters during the irradiation modification process were different, as shown in Tables 1-4.

[0137] Table 1-1

[0138]

[0139]

[0140] Table 1-2

[0141]

[0142] Table 1-3

[0143]

[0144]

[0145] Table 1-4

[0146]

[0147] Membrane structure parameter detection

[0148] The morphology of the polyolefin filter membranes prepared in Examples 1-14 and Comparative Examples 1-2 was characterized by scanning electron microscopy. The first outer surface, the second outer surface, and the cross-section of the polyolefin filter membrane were selected as the observation objects. The specific detection and measurement results are shown in Tables 2-1, 2-2, 2-3, and 2-4. It should be noted that ultra-high molecular weight polyethylene was used as the polyolefin.

[0149] When measuring the first cross-section fiber and the second cross-section fiber, the first cross-section fiber and the second cross-section fiber have two morphologies depending on the polyolefin filter membrane. The first type is a polyolefin filter membrane with a lace-like pore pattern on the outer surface, which is formed by the aggregation of multiple first cross-section fibers or second cross-section fibers. When measuring the diameter of the first cross-section fiber and the second cross-section fiber, it is characterized by the smallest aggregation unit. The second type is a strip-shaped fiber. When measuring the diameter of the first cross-section fiber and the second cross-section fiber, it is characterized by the diameter of the strip.

[0150] The oxygen-to-carbon ratio of the filter membrane was characterized by X-ray photoelectron spectroscopy (XPS) after irradiation with X-rays. The oxygen-to-carbon ratio was determined by analyzing the carbon and oxygen spectra separately and calculating the relative contents of carbon (C) and oxygen (O) elements in the C1s and O1s spectra, respectively. The overall oxygen-to-carbon ratio of the polyolefin filter membrane was then calculated from these relative contents. (Note that the XPS spot width is approximately 100 μm, and the penetration thickness is approximately 10 nm. The relative contents of C and O elements obtained from testing the inlet and outlet surfaces of the filter membrane are not significantly different; therefore, the relative contents of C and O elements obtained from either the inlet or outlet surface are approximated as the overall oxygen-to-carbon ratio of the filter membrane.)

[0151] The original image data obtained by X-ray diffraction of the filter membrane was used to perform peak fitting using Jade software to obtain the fitting peaks of the crystalline and amorphous regions of UPE. The fitting peaks of the crystalline region are approximately 2θ = 19.6°, 2θ = 21.6°, and 2θ = 23.7°. The remaining fitting peaks are representative of the amorphous region. The fitting peak areas of the crystalline and amorphous regions were then calculated by integration. The crystallinity claimed in this invention is calculated as: integral fitting peak area of ​​the crystalline region / (integral fitting peak area of ​​the crystalline region + integral fitting peak area of ​​the amorphous region).

[0152] Half-width at half-maximum (HWHM) refers to the distance between the intersection points of the parallel line drawn at half the peak height and the diffraction peak after correcting the diffraction peaks on the original XRD pattern and processing the corresponding diffraction peak base with a tangent.

[0153] Table 2-1

[0154]

[0155]

[0156] Table 2-2

[0157]

[0158]

[0159] Table 2-3

[0160]

[0161] Table 2-4

[0162] Test parameters Comparative Example 2 Average pore size of the first outer surface (SEM) / nm 628 Average pore size of the second outer surface (SEM) / nm 30.2 Thickness / μm 53.8 First outer surface hole area ratio / % 18.4 Second outer surface hole area ratio / % 14.2 <![CDATA[First outer surface hole density / (holes / μm 2 )]]> 3.2 <![CDATA[Second outer surface hole density / (holes / μm 2 )]]> 254 Porosity / % 42.7 Average fiber diameter in the first cross section (nm) 69.5 Average fiber diameter in the second cross section (nm) 45.4 Quality average molecular weight 4 million Average diameter of fibers on the first outer surface (nm) / Average diameter of fibers on the second outer surface (nm) / PMI average pore size / nm 5 Oxygen-to-carbon ratio 0.008 CO content / % 0.42 C=O content / % 0.33 Crystallinity / % 31.3 <![CDATA[I 正交晶型 :I 单斜晶相 ]]> 50.5 Half-peak width 2θ = approximately 21.6° 0.63 Half-peak width 2θ = approximately 23.7° 0.6 First water contact angle of the first outer surface / ° 111.5 Second outer surface first water contact angle / ° 111.6

[0163] Membrane performance parameter testing

[0164] 1.1 Water flow velocity test (testing device such as...) Figure 6 )

[0165] Experimental steps

[0166] Step 1: Place the IPA-wetted test sample (polyolefin filter membranes prepared in Examples 1-14 and Comparative Examples 1-2) on the vacuum filter holder, close valve 2 on the vacuum filter holder, open valve 1, start the vacuum pump, adjust the pressure to the test pressure of 0.03 MPa, and then close valve 1.

[0167] Step 2: Pour 50ml of test solution (water) into the plastic graduated cylinder of the pressure-reducing filter holder, open valve 2, start timing from one scale mark, and stop timing when the other scale mark is reached;

[0168] Step 3: After the test is completed, record the value displayed by the stopwatch. When all the test solution has passed through the filter membrane, close valve 2 on the support and remove the sample.

[0169] The test results are shown in Table 3.

[0170] Table 3

[0171] Sample Flow rate / s Example 1 2839 Example 2 1268 Example 3 1248 Example 4 354 Example 5 122 Example 6 104 Example 7 1269 Example 8 1243 Example 9 1290 Example 10 1246 Example 11 1268 Example 12 1265 Example 13 1270 Example 14 1266 Comparative Example 1 1240 Comparative Example 2 1238

[0172] 1.2 Tensile Strength Test: The transverse and longitudinal tensile strengths of the polyolefin filter membranes prepared in Examples 1-14 and Comparative Examples 1-2 were tested using a universal tensile testing machine. The width of the tensile testing machine was 10 mm and the spacing was 30 mm. The tensile strength (MPa) was calculated as: breaking force (cN) / 10² / (average thickness (mm) * width (mm)) (1N = 10²cN, 1mm = 1000μm). The longitudinal tensile strength was the tensile strength along the membrane winding direction, and the transverse tensile strength was the tensile strength perpendicular to the membrane winding direction. The test results are shown in Table 4.

[0173] Table 4

[0174]

[0175]

[0176] 1.3 TOC dissolution test

[0177] The polyolefin filter membranes prepared in Examples 1-14 and Comparative Examples 1-2 were used to fabricate an effective filtration area of ​​0.55 m². 2 The filter element was sterilized by high-pressure steam at 130℃ for 30 minutes. The filter was then connected to an ultrapure water source that meets the TOC standard for water for injection for rinsing. The rinsing volume was controlled at 20L and the rinsing speed at 500ml / min. The downstream filtrate was subjected to a total organic carbon (TOC) test (testing instrument: total organic carbon analyzer). The test results are shown in Table 5.

[0178] Table 5

[0179]

[0180]

[0181] 1.4 Metal particle interception efficiency

[0182] The interception efficiency of metal particles of the polyolefin filter membranes prepared in Examples 1-14 and Comparative Examples 1-2 was tested.

[0183] Experimental steps:

[0184] A sample solution was prepared by adding an appropriate amount of Au particles to a propylene glycol methyl ether acetate solution. The Au particles were divided into four groups, numbered 1-4, based on their particle size. The Au particle sizes of samples 1-4 were 2-5 nm, 15-20 nm, 40-50 nm, and 90-100 nm, respectively. The initial Au particle concentration in samples 1-4 was determined using ICP-MS, with the initial Au particle concentration controlled at approximately 1-3 ppb. Samples 1-4 were then passed through PMI membranes with average pore sizes of 5 nm, 20 nm, 50 nm, and 100 nm, respectively. The filtrates were then analyzed using ICP-MS to determine the Au particle concentration in the filtrate. (Note that in this invention, a filter membrane with an average PMI pore size of 2 nm was used for testing sample solution 1.)

[0185] Interception efficiency for Au particles:

[0186] Where: η─── interception efficiency, %; n0──── Au particle concentration in the sample solution, the average of 5 counts; n1──── Au particle concentration in the filtrate, the average of 5 counts. (Note that Au particles are used here to characterize the interception efficiency for metal particles.)

[0187] The interception efficiency test results of metal particles in Examples 1-14 and Comparative Examples 1-2 are shown in Table 6. The above-mentioned interception efficiency test was also performed on the original film in Example 2 that had not undergone any modification treatment.

[0188] Table 6

[0189] Sample Interception efficiency / % Example 1 99.24 Example 2 98.65 Example 3 97.58 Example 4 96.62 Example 5 95.18 Example 6 97.22 Example 7 97.77 Example 8 93.58 Example 9 99.36 Example 10 96.38 Example 11 98.32 Example 12 98.36 Example 13 98.52 Example 14 98.58 Comparative Example 1 42.35 Comparative Example 2 41.02 Original membrane in Example 2 12.31

[0190] As can be seen from Tables 2-1, 2-2, and 2-3, combined with Table 4-6, the filter membrane of the present invention has a wide PMI average pore size distribution, which can meet the filtration requirements of different filter particles. Furthermore, the filter membrane has good longitudinal and transverse tensile strength and good low-dissolution performance, resulting in high purity of the filtered filtrate, thus meeting the high purity requirements of semiconductor, solvent filtration, and photoresist filtration. In addition, the filter membrane of the present invention has high interception efficiency for metal particles, effectively removing metal particles from organic solvents, and also effectively removing microcolloidal particles from photoresist filtration.

[0191] As can be seen from Tables 2-1 and 2-2, combined with Table 4-6, when the ratio of "CO" to "C=O" content is low in Example 7, the overall oxygen-carbon ratio of the filter membrane does not change significantly. However, it may lead to a certain degree of reduction in the crystallinity of the filter membrane and its interception efficiency for metal particles. The reason for this may be that at low irradiation intensities of 0.2-0.5 Mrad / h, the energy generated by γ-ray irradiation for modification and grafting is relatively small. At this time, since the bond energy of "CO" is lower than that of "C=O", the ratio of "CO" to "C=O" decreases. At the same time, since the electronegativity of "CO" is greater than that of "C=O", the adsorption capacity of the polyolefin filter membrane for metal particles imparted by "CO" and "C=O" is weakened.

[0192] As can be seen from Tables 2-2, 2-3, 5, and 6, and in conjunction with Example 3, when the crystallinity of the filter membrane of the present invention does not fall within the range of 45-85% defined in the dependent claims, such as in Example 8 (crystallinity below 45%), although the flow rate performance of the filter membrane is improved to a certain extent, the adsorption efficiency of the filter membrane for metal particles is reduced to a certain extent. At the same time, the longitudinal tensile strength, transverse tensile strength, and low-dissolution performance of the filter membrane are relatively significantly reduced. As in Example 9 (crystallinity above 85%), although the adsorption efficiency of the filter membrane for metal particles and low-dissolution performance are improved to a certain extent, and the longitudinal tensile strength and transverse tensile strength of the filter membrane are significantly enhanced, the flow rate of the filter membrane is reduced to a certain extent, thus affecting the application of the filter membrane in high-flow-rate applications. The reason for this may be that when the crystallinity is too high, although the low dissolution performance of the filter membrane will be better, the higher the crystallinity of the filter membrane, the higher the oxygen-carbon ratio of the filter membrane will be. A higher oxygen-carbon ratio means that more oxygen-containing functional groups act on the surface of the pores, which in turn has a greater impact on the flow rate, making the filter membrane unable to meet the requirements of high flow rate filtration applications.

[0193] As can be seen from Tables 2-1 and 2-2, and in conjunction with Examples 5 and 10, when the ratio of orthorhombic crystal form to monoclinic crystal phase is lower than the lower limit specified in the dependent claims, the low dissolution performance of the filter membrane decreases to a certain extent. The reason for this may be that the higher the ratio of orthorhombic crystal form, the better the thermal stability of the filter membrane, and the better the grafting stability of the irradiated grafting group, thereby reducing the probability of dissolution of the irradiated grafting group; at the same time, the better the grafting stability of the irradiated grafting group, the better the continuous adsorption capacity of the irradiated grafting group for metal particles, thereby improving the interception efficiency of metal particles.

[0194] As can be seen from Tables 2-1, 2-3, and 6, and in conjunction with Examples 4 and 11-12, when the diameters of the first and second cross-section fibers are too fine, the low-dissolution performance of the filter membrane decreases to some extent. Conversely, when the diameters of the first and second cross-section fibers are too large, the low-dissolution performance of the filter membrane is improved to some extent. The reason for this may be that while finer fibers result in a larger specific surface area and better adsorption performance, they are also more prone to dissolution. Conversely, coarser fibers, while having a smaller specific surface area, exhibit relatively better low-dissolution performance.

[0195] As can be seen from Tables 2-1, 2-3, 2-4, and 6, and in conjunction with Examples 2, 13, 14, and Comparative Examples 1-2, the two-stage irradiation modification method of the present invention enables the filter membrane to have good crystallinity and good low dissolution performance, while also giving the filter membrane a high interception efficiency for metal particles. When γ-ray irradiation is used, when the total irradiation dose is low, the crystallinity, longitudinal tensile strength, and transverse tensile strength of the filter membrane are significantly reduced, and the adsorption efficiency of the filter membrane for metal particles is significantly affected and decreases. Secondly, the flow rate of the filter membrane increases to a certain extent due to the decrease in the oxygen-carbon ratio. When the total irradiation dose is high, the crystallinity, longitudinal tensile strength, and transverse tensile strength of the filter membrane increase to a certain extent, but the flow rate of the filter membrane decreases to a certain extent.

[0196] The preferred embodiments of the present invention have been described in detail above. However, it should be understood that after reading the above teachings, those skilled in the art can make various alterations or modifications to the present invention. These equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A polyolefin filter membrane, comprising a body, wherein the body has a first outer surface and a second outer surface on both sides, and a non-directional tortuous pathway is formed within the body, wherein the first outer surface to the second outer surface is composed of continuous fibers, characterized in that: The average pore size of the filter membrane is 2-100 nm. The filter membrane has an oxygen-to-carbon ratio in the range of 0.01-0.

10.

2. The polyolefin filter membrane according to claim 1, characterized in that: The XPS analysis spectrum of the filter membrane includes "CO" and "C=O", wherein the content of "CO" is 0.6-8%, the content of "C=O" is 0.5-6%, and the ratio of the content of "CO" to "C=O" is 0.5-2.

3. The polyolefin filter membrane according to claim 1, characterized in that: The polyolefin is a crystalline polyolefin, and the crystallinity of the filter membrane, as measured by XRD, is 45-85%.

4. A polyolefin filter membrane according to claim 3, characterized in that: The filter membrane satisfies I 正交晶型 :I 单斜晶相 50 or greater; Where I 正交晶型 The scattering intensity of the UPE filter membrane near 2θ angles of 21.6° and 23.7°; I 单斜晶相 The scattering intensity of the UPE filter membrane is located near a 2θ angle of 19.6°.

5. A polyolefin filter membrane according to claim 4, characterized in that: The half-peak width (WHM) of the characteristic peak of the filter membrane located near a 2θ angle of 21.6° is 0.4°-1.5°; the half-peak width (WHM) of the characteristic peak of the filter membrane located near a 2θ angle of 23.7° is 0.4°-1.5°.

6. A polyolefin filter membrane according to claim 3, characterized in that: The average SEM pore size of the first outer surface is not less than the average SEM pore size of the second outer surface, the average SEM pore size of the second outer surface is 15-100 nm, and the thickness of the filter membrane is 20-120 μm.

7. A polyolefin filter membrane according to claim 3, characterized in that: The porosity of the second outer surface is 10-30%, and the pore density of the second outer surface is 120-300 pores / μm. 2 .

8. A polyolefin filter membrane according to claim 3, characterized in that: The overall porosity of the filter membrane is 20-70%, and the filter membrane has a second cross-sectional fiber near the second outer surface along the thickness direction. The SEM average diameter of the second cross-sectional fiber is 30-100 nm.

9. A polyolefin filter membrane according to claim 8, characterized in that: The relative molecular mass of the filter membrane is 2 million to 5 million, and the first water contact angle of the second outer surface is 40° to 120°.

10. A polyolefin filter membrane according to claim 8, characterized in that: The filter membrane has a first cross-sectional fiber near the first outer surface along the thickness direction. The SEM average diameter of the first cross-sectional fiber is 30-110 nm, and the first water contact angle of the first outer surface is 40°-120°.

11. A polyolefin filter membrane according to claim 6, characterized in that: The average SEM pore size of the first outer surface is greater than that of the second outer surface, and the average SEM pore size of the first outer surface to the second outer surface shows a gradient change. The average SEM pore size of the first outer surface is 500-2000 nm, and the average SEM pore size of the second outer surface is 15-100 nm.

12. A polyolefin filter membrane according to claim 11, characterized in that: The pore density of the first outer surface is 0.5-80 pores / μm. 2 The porosity of the first outer surface is 10-25%.

13. A polyolefin filter membrane according to claim 6, characterized in that: The average SEM aperture of the first outer surface to the second outer surface is symmetrically arranged, and the average SEM aperture of the first outer surface and the second outer surface is 15-100nm.

14. A polyolefin filter membrane according to claim 13, characterized in that: The pore density of the first outer surface is 150-300 pores / μm. 2 The porosity of the first outer surface is 10-30%.

15. A polyolefin filter membrane according to claim 13, characterized in that: The average diameter of the fibers on the first outer surface is 50-150 nm, and the average diameter of the fibers on the second outer surface is 50-100 nm.

16. A polyolefin filter membrane according to claim 1, characterized in that: The longitudinal tensile strength of the filter membrane is 6-18 MPa, and the transverse tensile strength is 4-16 MPa. The TOC leaching amount of the filter membrane does not exceed 0.5 ppb; Under a positive pressure of 0.03 MPa and a temperature of 20°C, it takes 100-3000 seconds for 50 ml of water to pass through a porous filter membrane with a diameter of 47 mm.

17. A polyolefin filter membrane according to claim 1, characterized in that: The polyolefin is any one of PE, PP and UPE.

18. A process for preparing a polyolefin filter membrane according to any one of claims 1-17, characterized in that, The process includes the following steps: S1, Prepare a modified solution by adding 2.5-10% sulfite and 1-5% surfactant by mass to water to prepare a modified solution; S2, the filter membrane is soaked in an alcohol solution, and after the filter membrane is wetted, it is soaked and rinsed in pure water. The filter membrane is then immersed in a modified solution for material-liquid replacement. S3. The filter membrane impregnated with the modified solution is irradiated with X-rays. The X-ray irradiation is controlled so that the oxygen-carbon ratio of the filter membrane is controlled within 0.01-0.

1. After the filter membrane is removed from the modified solution, it is soaked in pure water and dried to obtain a polyolefin filter membrane.

19. The preparation process of a polyolefin filter membrane according to claim 18, characterized in that, Step S3 involves irradiating the filter membrane impregnated with the modified solution using UV light, controlling the feed solution temperature at 30-50℃ and the irradiance at 10-200 mW / cm². 2 The wavelength of UV irradiation is 100-320nm, and the irradiation time is 10-30min.

20. The preparation process of a polyolefin filter membrane according to claim 18, characterized in that, In step S3, the filter membrane is immersed in a container containing the modified solution, sealed, and evacuated for 1-3 hours. The container containing the modified solution and the filter membrane is then irradiated with gamma rays at a radiation intensity of 2-4 Mrad / h for 13-25 hours, with the temperature of the solution controlled at 30-50℃ and the total radiation dose at 25-50 Mrad. After the filter membrane is removed from the solution, it is soaked in pure water and dried to obtain a polyolefin filter membrane.

21. The preparation process of a polyolefin filter membrane according to claim 20, characterized in that, The filter membrane has also undergone pretreatment. The pretreatment steps include gamma-ray pretreatment: 1) Prepare a pre-modified solution by adding 1-5% sulfite and 0.5-2.5% surfactant to water to prepare a pre-modified solution, wherein the mass fractions of sulfite and surfactant in the pre-modified solution are lower than those in the modified solution. 2) Soak the filter membrane in an alcohol solution. After the filter membrane is wetted, soak and rinse it in pure water. Immerse the filter membrane in a container with a pre-modified solution for material-liquid replacement and introduce an oxygen environment. 3) Irradiate the container containing the pre-modified solution and the filter membrane with gamma rays at a radiation intensity of 0.2-0.5 Mrad / h for 16-40 hours, wherein the irradiation time of the pre-modification process is longer than that of the modification process. Control the temperature of the feed solution at 10-25℃ and the total radiation dose at 4-8 Mrad. After removing the filter membrane from the pre-modified solution, soak it in pure water. Alternatively, the pretreatment steps may include UV pretreatment: 1) Prepare a pre-modified solution by adding 1-5% sulfite and 0.5-2.5% surfactant to water to prepare a pre-modified solution, wherein the mass fractions of sulfite and surfactant in the pre-modified solution are lower than those in the modified solution. 2) Soak the filter membrane in an alcohol solution. After the filter membrane is wetted, soak and rinse it in pure water. Then immerse the filter membrane in a pre-modified solution for material-liquid replacement. 3) Irradiate the filter membrane impregnated with the pre-modified solution using UV irradiation, controlling the feed solution temperature at 10-25℃ and the irradiance at 1000-2000 mW / cm². 2 The UV irradiation wavelength is 100-320nm, the irradiation time is 1-3h, and the filter membrane is removed from the pre-modified solution and soaked in pure water.

22. The preparation process of a polyolefin filter membrane according to any one of claims 18-21, characterized in that, The sulfite is sodium sulfite or potassium sulfite, and the surfactant is sodium dodecyl sulfate or sodium dodecylbenzene sulfonate.

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