UPE filter membrane and preparation method thereof

Abstract

The invention discloses a UPE filter membrane and a preparation method thereof, and belongs to the technical field of membrane materials, and the preparation method comprises the following steps: preparing two layers of non-uniform raw membranes with asymmetric pore structures in a heat dissipation plate assisted split-phase curing mode, and then preparing a pre-membrane by adopting specific pressure hot-pressing lamination; after subsequent stretching and heat setting treatment, the interception precision of the obtained product can be guaranteed based on compact pores, close to the buffer space, in the center of the film layer; meanwhile, ideal membrane structure stability can be maintained under the condition of realizing a high-throughput working mode by virtue of a macropore structure on the surface of the membrane layer and a deep buffer space, and smooth photoresist filtering can be ensured; the preparation method is simple to operate, and industrial production scale can be realized.

Description

Technical Field

[0001] This application relates to the field of membrane technology, specifically to a UPE filter membrane and its preparation method. Background Technology

[0002] Photoresist is a key material used in the electronics industry for micro-patterning, especially indispensable in the manufacture of semiconductor chips, display panels, and printed circuit boards. Due to the extremely high purity requirements of photoresist, it must undergo rigorous high-precision purification before both production and use. Filter membranes are a preferred filtration medium for high-precision photoresist purification. Therefore, in the purification process, in addition to ensuring sufficient retention accuracy to achieve high purification results, a high throughput is also required to increase the purification rate and ensure the overall process capacity. Furthermore, under high throughput conditions, the structural strength of the purification medium cannot be too low to avoid damage due to insufficient strength during application, which would affect photoresist filtration.

[0003] To meet the specific technical requirements of this field, various process and material improvements have been attempted to prepare matching filter membrane products. However, these products or technical indicators cannot be met, or are difficult to mass-produce industrially, and can only be prepared on a small scale under laboratory conditions. Therefore, there is an urgent need to develop a method for preparing filter membranes with high retention accuracy, high flux, high strength, and industrial mass production capability. Summary of the Invention

[0004] The purpose of this application is to overcome the shortcomings of existing technologies and provide a method for preparing a UPE filter membrane. A two-layer non-uniform membrane with an asymmetric pore structure is prepared by a heat sink-assisted phase separation curing method. A pre-film is then prepared by hot-pressing under specific pressure, creating an interlocking buffer space with microscopic pores in the center of the membrane layer. After subsequent stretching and heat setting, the resulting product not only ensures retention accuracy based on the dense pores near the buffer space in the center of the membrane layer, but also maintains ideal membrane structure stability under high-throughput operating conditions thanks to the large pore structure on the membrane surface and the deep buffer space, ensuring smooth photoresist filtration. The preparation method is simple to operate and can be scaled up for industrial production.

[0005] To achieve the above objectives, in a first aspect of this application, a method for preparing a UPE thin film is provided, comprising the following steps:

[0006] (1) A casting solution is prepared by compounding and melting polyethylene resin, organic S and organic N; wherein the polyethylene resin is ultra-high molecular weight polyethylene resin, the organic S is a solvent for polyethylene resin, and the organic N is a non-solvent for polyethylene resin; the temperature of the casting solution is 220-250℃.

[0007] (2) The casting liquid is extruded through a die to form a liquid film, which is then placed on a heat sink plate with a rough surface and cooled to a temperature of 15-120°C for phase separation and solidification to form a green film I; the two sides of the liquid film have different temperatures during phase separation and solidification, and satisfy T2≥T1, where T1 is the temperature on the side in contact with the heat sink plate and T2 is the temperature on the side not in contact with the heat sink plate; the cooling rate of the liquid film on the side in contact with the heat sink plate is 10-20°C / s; the cooling rate of the liquid film on the side not in contact with the heat sink plate is ≤6°C / s; the heat sink plate includes micron-sized copper particles with a roughness Ra of 8-15μm;

[0008] (3) Prepare another film II in the same manner as steps (1) and (2). After film I and film II are completely cured, separate the heat dissipation plate and attach the two films on the side in contact with the heat dissipation plate. Hot press to obtain a pre-film. The hot pressing satisfies A / B = 1 to 5, where A is the hot pressing pressure in MPa and B is the total thickness of film I and film II before hot pressing in mm.

[0009] (4) The pre-film is subjected to stretching, first heat setting, extraction, and second heat setting in sequence to obtain the UPE filter membrane.

[0010] To overcome the limitations of existing filter membrane products in achieving both high retention accuracy and high strength for high-precision purification of photoresists, thus failing to meet the demands of high-throughput applications or enabling industrial-scale production, this application's technical solution employs a traditional die-extrusion phase-separation curing method to first prepare an asymmetric membrane. This method involves mixing ultra-high molecular weight polyethylene with solvents and non-solvents, then melting and compounding to form a casting liquid. This liquid is subsequently extruded into a liquid film and cured under conditions where the curing temperatures and cooling rates differ on both sides. In this process, the liquid film cools faster and at a lower temperature on the side in contact with the heat sink, while it cools slower and at a higher temperature on the side not in contact with the heat sink. This means the phase separation rate of the liquid film is faster on the side in contact with the heat sink and slower on the side not in contact with the heat sink. Combined with the solvent-non-solvent combination in the liquid film and the temperature of the casting solution, the overall phase separation rate on the side in contact with the heat sink is faster than on the side not in contact with the heat sink, resulting in a relatively smaller pore size. Simultaneously, the ultra-high molecular weight polyethylene melt is at a high temperature before phase separation, and under this high temperature state, the polyethylene... The molecular chains of polyethylene move violently and randomly. When the cooling rate is slow, the molecular chains have ample time to arrange themselves in a regular pattern. These molecular chains gradually move towards the crystal nucleus, which not only promotes the formation of more crystal nuclei but also allows the crystal to grow and mature fully, ultimately resulting in a more complete crystal structure and increased crystallinity. If the cooling rate is too fast, the molecular chains will be quickly "frozen." At this time, the movement of the molecular chains is suddenly greatly restricted, and there is not enough time to complete the regular arrangement to form a crystal structure. Even if there are a few crystal nuclei, the crystal cannot grow fully, and a large number of amorphous regions will form in the fiber, significantly reducing the crystallinity. Therefore, the polyethylene fibers on both sides of the film have different thicknesses and pore sizes. The polyethylene fibers on the side in contact with the heat sink are thinner and have smaller pore sizes, while the polyethylene fibers on the side not in contact with the heat sink are thicker and have larger pore sizes. That is, the resulting film is an asymmetric film layer with a gradient size distribution. The structural part with a large pore size can improve the product throughput, while the structural part with a small pore size can improve the retention accuracy during product operation, providing a basis for achieving both high throughput and high retention accuracy. Meanwhile, a heat dissipation plate with micron-sized copper metal particles with high heat dissipation is also provided on one side of the liquid film to further accelerate heat dissipation. This makes the pores on this side smaller and the fibers finer, making it easier to shape into a good dense structure. With the synergistic effect of the differential cooling rate, it can achieve both good concave morphology and pore structure effect.During this process, if the cooling rate on the side in contact with the heat sink is less than 10℃ / s, the phase separation speed is too slow, resulting in excessively large pore sizes, poor product retention efficiency, and excessively high crystallinity of the formed filter membrane, which can lead to brittle fracture and affect subsequent processing. If the rate is higher than 20℃ / s, due to the auxiliary heat dissipation of the heat sink, the fiber crystallinity formed in the part close to the heat sink will be very low or even non-formed, making it difficult to achieve the desired effect. Organic compound S is the solvent for polyethylene resin. A solvent is one that, when heated to at most its boiling point, can completely dissolve the polyethylene resin to form a homogeneous solution. A non-solvent is one that, when heated to at most its boiling point, cannot dissolve the polyethylene resin to form a homogeneous solution, but only has a certain swelling effect on the polyethylene resin.

[0011] During the film curing process, due to the template effect of the heat sink, a concave morphology corresponding to the contact surface of the heat sink will be formed on the side of the liquid film in contact with the heat sink. Subsequently, the present application proposes to attach two identical films with concave morphologies on their sides and perform hot pressing, and set the pressure according to the thickness of the pressing, so that after pressing, the two film layers can not only fit together exactly based on the morphology of the concave morphology, but also leave a buffer space with a certain concave morphology in the middle (this space can be semi-closed or fully closed, and the pore size range is uncertain). After this space is prepared, on the one hand, it can ensure the normal operation of the dense pores of the filter membrane itself, that is, based on the pressure setting, the dense pores will not be damaged. These buffer spaces can provide a certain flow channel for the fluid, increase the membrane flux, and at the same time, at high flux, the buffer space can also store a certain amount of hydraulic pressure, ensuring that there is a certain pressure reserve inside, avoiding expansion or rupture due to excessive local pressure. This further improves the structural strength and flux range that the product can withstand while ensuring the interception accuracy. If the pressure control during hot pressing is improper, such as if the ratio of pressure to thickness is too high, the pores on the surfaces of the two biofilms will be locally crushed and damaged in the later stages of pressing, resulting in insufficient flux and reduced filtration efficiency. If the ratio of pressure to thickness is too low, the biofilms will not adhere tightly enough, the buffer space will be too large, and the proportion of liquid flowing into the buffer space will increase. When the proportion of liquid is high, the biofilms may separate, making effective filtration impossible.

[0012] Meanwhile, the surface roughness of the heat sink directly affects the morphology of the film formation depressions. The greater the roughness, the more obvious the depression morphology. However, if the roughness is too high, the film will stick to the heat sink and cannot be separated. Forced separation will lead to the destruction of the depression morphology, resulting in a significant decrease in the effect during subsequent pressing. At the same time, the interception accuracy will also be affected. Therefore, it is necessary to accurately control it within the range of Ra = 8 to 15 μm.

[0013] In some embodiments, the roughness Ra of the heat sink can be at least one of 8μm, 9μm, 10μm, 10.5μm, 11μm, 12μm, 13μm, 14μm, 15μm or any value between two adjacent values.

[0014] As mentioned above, the roughness of the heat sink is related to the surface profile of the side in contact with the film formation. By adjusting the size or distribution of the micron-sized copper particles, the surface roughness of the heat sink can be changed. Since the surface of the heat sink is similar to a template for the depression morphology formed by the film formation, the change in roughness can effectively control the uniformity of the depression morphology distribution and the depression size. Within the above range, the uniformity of the depression morphology is good and the depression size is moderate. Combined with subsequent hot pressing, a buffer space with high buffering efficiency can be formed without affecting the throughput and retention accuracy.

[0015] The pre-film after hot pressing is subjected to stretching, first heat setting, extraction, and second heat setting in sequence to obtain UPE filter membrane.

[0016] In summary, by controlling the temperature and cooling rate on both sides during liquid film solidification, the heat dissipation plate containing micron-sized copper particles on one side during liquid film solidification, the roughness of the heat dissipation plate, and the ratio of pressure to the sum of the thicknesses of film I and film II, the prepared UPE filter membrane has high retention accuracy, high flux, and good structural stability, and can be mass-produced on an industrial scale.

[0017] It should be noted that the roughness Ra of the heat sink described in this application is the arithmetic mean deviation of the heat sink, which is confirmed by a roughness measuring instrument (Malvin PS10) in accordance with GB / T 1031-2009.

[0018] In some embodiments, in step (1), the polyethylene resin includes at least one ultra-high molecular weight polyethylene with a weight-average molecular weight ≥ 1 million, and the ultra-high molecular weight polyethylene has a molecular weight distribution of 6 to 10.

[0019] The type of ultra-high molecular weight polyethylene (UHMWPE) resin used in the film-forming process described in this application is not specifically limited. Preferably, at least one type of UHMWPE with a weight-average molecular weight ≥ 1 million is used. The weight-average molecular weight of the UHMWPE can be one of 1 million, 1.5 million, 2 million, 3 million, or 4 million, or any value between two adjacent values. The molecular weight distribution of the UHMWPE can be one of 6, 7, 8, 9, or 10, or any value between two adjacent values ​​(e.g., 6.1, 6.2). Of course, the polyethylene resin can also include polyethylene with a weight-average molecular weight of less than 1 million. There are no specific limitations on this, as long as the type used can ensure that the mechanical strength and retention efficiency of the obtained product meet the standards.

[0020] In some embodiments, the organic compound S includes at least one of paraffin oil, white oil, hydraulic oil, castor oil, or extracts thereof.

[0021] In some embodiments, the organic compound N includes at least one of dimethyl phthalate, dioctyl adipate, ethylene glycol diacetate, dimethyl carbonate, palm oil, and triacetin.

[0022] In this application, the specific type of organic compound S selected as the solvent is not specifically limited. Any solvent commonly used in the art is acceptable, provided that its solvent properties and low impurity content are guaranteed, and it is not limited to the scope described above. Similarly, the specific type of organic compound N selected as the non-solvent is not specifically limited. Any non-solvent commonly used in the art is acceptable, and it is not limited to the scope described above.

[0023] In some embodiments, T2-T1 ≥ 30°C, and the ratio of the cooling rate of the liquid film on the side in contact with the heat sink to the cooling rate of the liquid film on the side not in contact with the heat sink is (2-10):1.

[0024] In some embodiments, the ratio of the cooling rate of the liquid film on the side in contact with the heat sink to the cooling rate of the liquid film on the side not in contact with the heat sink is one of 2:1, 3:1, 4:1, 6:1, 8:1, 10:1 or any value between the two adjacent ratios.

[0025] More preferably, when T2-T1 ≥ 50℃, the ratio of the cooling rate of the liquid film on the side in contact with the heat sink to the cooling rate of the liquid film on the side not in contact with the heat sink is (4-8):1.

[0026] As mentioned above, during phase separation curing, setting different cooling conditions on both sides of the liquid film can result in different crystallinity and phase separation rates of the ultra-high molecular weight polyethylene resin on both sides, thereby forming fiber structures of different thicknesses and pores of different sizes. Setting a certain temperature difference between the two regions and controlling the ratio of the cooling rates on both sides of the liquid film within a certain range can make the differences in fiber structures on both sides greater, and the gradient effect formed from one side to the other side more obvious. Especially when the temperature difference on both sides is controlled above 30°C, preferably above 50°C, and the ratio of the cooling rates on both sides is controlled at (2-10):1, preferably (4-8):1, the resulting gradient structure of the product can not only further improve the stability of the structure and be applied to higher throughput, but also ensure that the filtrate can enter the product sequentially. The flow rate of the filtrate first slows down and then increases, and the retention efficiency is better, thus improving the retention effect of the product.

[0027] In some embodiments, during the phase separation curing process, the target temperatures on both sides of the film are controlled by a temperature controller to be T1 and T2, respectively, and different cooling rates are set. After the actual temperatures on both sides reach the target temperatures, they are maintained for 10 to 20 seconds to complete the phase separation curing.

[0028] In some embodiments, T1 is 15–50°C and T2 is 45–120°C.

[0029] It should be noted that the solution described in this application can be based on the requirements of the interception accuracy in the actual application scenario, and different cooling temperatures can be used to make the size span and size range of the pores in the final product different, without making specific restrictions.

[0030] In some embodiments, in step (2), the average particle size of the micron-sized copper particles is 5 to 50 μm.

[0031] In some embodiments, the average particle size of the micron-sized copper particles is one of 5μm, 8μm, 10μm, 12μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm or any value between two adjacent values.

[0032] In this application, the roughness of the heat sink is related to the size of the copper particles. On the one hand, if the particle size is too large, the density of the depression morphology formed by the film layer will decrease, resulting in fewer and less uniform buffer spaces formed after subsequent hot pressing. Some spaces may be too large in volume and have too many channels. If too much liquid flows into the buffer space, it may squeeze the two hot-pressed single layers, increasing the interlayer porosity and ultimately leading to layer separation. On the other hand, if the micron-sized copper particles of the heat sink are too small, the heat sink will actually adhere to the green film, requiring a certain space to maintain pressure. This prevents the heat sink from being unable to separate or from damaging the green film during separation, ultimately failing to achieve the desired depression morphology effect and even damaging the pore structure.

[0033] It should be noted that the heat sink described in this application can be a commercially available product or a self-made product, and there is no specific limitation in this regard. The preparation method of the heat sink may include the following steps:

[0034] Micron-sized copper particles are dispersed and mixed with binder and then placed in a mold and pressed at 50-150 MPa. After pressing, they are preheated and degreased, then heated to 350-450℃ for calcination, and cooled to obtain green blanks.

[0035] The green billet is preheated to 600-700℃ and held for 60-90 minutes, followed by multiple hot rolling processes and annealing at 400-450℃ for 120-180 minutes to obtain the rough billet.

[0036] The blank is sanded and then fixed onto the substrate to obtain the heat sink.

[0037] In the preparation method described above, those skilled in the art can adjust the roughness based on the number of sand milling processes (e.g., sand milling with an 800-mesh grinding wheel 1 to 6 times, 2s-5s each time). They can also adjust it in combination with other variables. For example, the larger the particle size of the micron-sized copper particles, the lower the density of the green blank after pressing. After the same sand milling process, the smoothness is smaller, the roughness is larger, and the distribution density of the formed depression morphology will also be smaller. Those skilled in the art can also use other methods to control it, and there are no specific limitations on this.

[0038] In some embodiments, the mass ratio of the micron-sized copper particles to the binder is 99:1 to 95:5.

[0039] More preferably, the adhesive includes at least one of polyvinyl alcohol and stearic acid.

[0040] More preferably, the micron-sized copper particles and the binder are mixed in an organic solvent, which includes at least one of alcohol, copper, and ether.

[0041] In some embodiments, the temperature of the heating degreasing treatment is 250–350°C, and the time is 100–200 min.

[0042] In some embodiments, the calcination treatment time is 40 to 60 minutes.

[0043] In some embodiments, the deformation per pass of the hot rolling is 8-15%, the rolling speed is 0.5-1m / min, and the deformation of the product obtained after hot rolling is controlled to be 8-10%.

[0044] In some embodiments, the temperature of the hot pressing in step (3) is 60-90°C.

[0045] In some embodiments, the hot pressing time is 0.5 to 1 minute.

[0046] In some implementations, A = 1 to 5 MPa.

[0047] In some implementations, A is one of 1 MPa, 2 MPa, 3 MPa, 5 MPa, or any value between two adjacent values.

[0048] In some embodiments, B = 0.5–2 mm.

[0049] In some implementations, B is one of 0.5mm, 1mm, 1.5mm, 2mm or any value between two adjacent values.

[0050] In the technical solution of this application, based on the requirements of actual application scenarios, the total thickness of the biofilm can be designed to be in different ranges. Based on the thickness of the biofilm, the solution of this application needs to simultaneously control the pressure of hot pressing to ensure the basic integrity of the pore structure and the formation effect of the buffer space. If the pressure is simply controlled according to the conventional hot pressing range, it will be impossible to effectively adapt the pressure to the thickness of the biofilm, which will lead to poor final product performance.

[0051] After matching, the temperature, pressure, and membrane layer of the hot pressing can be further optimized to the above range: On the one hand, as mentioned above, if the temperature is too low and the pressure is too small, the adhesion between layers cannot be guaranteed, and the buffer space is too large. On the other hand, if the temperature is too high and the pressure is too large, in addition to crushing the pore structure mentioned above, the fibers will also become excessively adhered, affecting the flux. After further optimizing the temperature and pressure, in addition to ensuring the retention accuracy, the upper limit of the product in high flux can also be further improved. Similarly, if the membrane layer is too thick, it will also affect the flux of the product. Under the condition that the membrane layer is not too small and affects the total amount of retention (if it is too thin, the effective retention area is very thin, and the membrane layer is easy to reach retention saturation. At the same time, if the membrane is too thin, it will also reduce the strength of the membrane), a smaller thickness can further improve the upper limit of flux.

[0052] In some embodiments, in step (3), the two films are pre-stretched before being bonded, and the temperature of the pre-stretching treatment is 80 to 110°C, and the pre-stretching ratio is 1.2 to 5 times.

[0053] In the scheme described in this application, the raw film can be further pre-stretched before thermal bonding. While ensuring the retention accuracy, pre-stretching the raw film before bonding can improve the porosity between fibers to a certain extent, especially on the side bonding to the heat sink. This results in a richer and more uniform distribution of buffer spaces formed after bonding, which is more conducive to improving its buffering effect in high-throughput processing and enhancing the overall structural stability of the product. At the same time, the pore size on the other side will also be increased to a certain extent, further increasing the upper limit of throughput. Furthermore, by controlling the stretching ratio and temperature of the pre-stretching, the polyethylene fibers in the raw film can be prevented from sticking together before hot pressing and excessive crystallization can be avoided, which would affect the overall structural integrity and porosity accuracy.

[0054] More preferably, the pre-stretching treatment includes simultaneous transverse pre-stretching and longitudinal pre-stretching treatments, wherein the transverse pre-stretching multiple is 1.2 to 5 times and the stretching rate is 5 to 100% / s, and the longitudinal pre-stretching multiple is 1.2 to 5 times and the stretching rate is 5 to 100% / s.

[0055] Pre-stretching treatment involves simultaneous pre-stretching in both the transverse and longitudinal directions, with controlled pre-stretching rates. This results in more uniform pore size and further enhances the product's durability.

[0056] In some embodiments, step (4) includes a stretching process that is performed simultaneously in the transverse direction and in the longitudinal direction. The temperature of the stretching process is 70 to 140°C, the transverse stretching process is 2 to 10 times, and the longitudinal stretching process is 2 to 10 times.

[0057] In some embodiments, in step (4), the temperature of the first heat setting is 120-140°C and the time is 5-120 seconds.

[0058] In some embodiments, in step (4), the temperature of the second heat setting is 145-160°C and the time is 5-120 seconds.

[0059] In some embodiments, in step (4), the extraction uses at least one of dichloromethane, tetrafluoroethane, alcohol, and ketone as a solvent, and the extraction time is 10 to 24 hours.

[0060] After casting, curing, and pressing, those skilled in the art can use appropriate parameter settings to perform stretching, heat setting, and extraction processes on the product based on actual needs to obtain suitable size and purity. However, they are not limited to this. Those skilled in the art can also use other adaptability parameters to adjust during stretching, heat setting, and extraction processes based on actual needs.

[0061] In a second aspect of this application, this application also provides a UPE filter membrane prepared by the method for preparing the UPE filter membrane.

[0062] Preferably, the average pore size of the PMI of the UPE filter membrane is 10–30 nm.

[0063] Preferably, the thickness of the UPE filter membrane is 45–100 μm.

[0064] Preferably, the tensile strength of the UPE filter membrane is greater than 4 MPa.

[0065] The tensile strength of the UPE filter membrane mentioned in this invention refers to the longitudinal tensile strength of the UPE filter membrane.

[0066] The UPE film prepared by the method described in this application has high mechanical strength, can be adapted to high-throughput working liquids, can achieve high retention accuracy based on actual requirements during operation, has a wide retention range, strong applicability and long service life. At the same time, the preparation method of the product has simple operation steps, involves few instruments, and uses widely available raw materials, which can realize industrial mass production.

[0067] The beneficial effects of this invention are as follows: This invention provides a method for preparing a UPE filter membrane, which uses a heat sink-assisted phase separation curing method to prepare two non-uniform biofilms with asymmetric pore structures. Subsequently, a pre-film is prepared by hot-pressing under specific pressure, which creates an interlocking buffer space with microscopic pores on the surface of the membrane layer. After subsequent stretching and heat setting treatments, the resulting product not only ensures the interception accuracy based on the dense pores near the buffer space in the center of the membrane layer, but also maintains ideal membrane structure stability under high-throughput working mode by relying on the large pore structure on the surface of the membrane layer and the deep buffer space, thus ensuring the smooth operation of photoresist filtration. The preparation method is simple to operate and can be industrialized. Detailed Implementation

[0068] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0069] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0070] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0071] A method for preparing a UPE thin film includes the following steps:

[0072] (1) A casting solution is prepared by compounding and melting polyethylene resin, organic S and organic N; wherein the polyethylene resin is ultra-high molecular weight polyethylene resin, the organic S is a solvent for polyethylene resin, and the organic N is a non-solvent for polyethylene resin; the temperature of the casting solution is 220-250℃.

[0073] (2) The casting liquid is extruded through a die to form a liquid film, which is then placed on a heat sink plate with a rough surface and cooled to a temperature of 15-120°C for phase separation and solidification to form a green film I; the two sides of the liquid film have different temperatures during phase separation and solidification, and satisfy T2≥T1, where T1 is the temperature on the side in contact with the heat sink plate and T2 is the temperature on the side not in contact with the heat sink plate; the cooling rate of the liquid film on the side in contact with the heat sink plate is 10-20°C / s; the cooling rate of the liquid film on the side not in contact with the heat sink plate is ≤6°C / s; the heat sink plate includes micron-sized copper particles with a roughness Ra of 8-15μm;

[0074] (3) Prepare another film II in the same manner as steps (1) and (2). After film I and film II are completely cured, separate the heat dissipation plate and attach the two films on the side in contact with the heat dissipation plate. Hot press to obtain a pre-film. The hot pressing satisfies A / B = 1 to 5, where A is the hot pressing pressure in MPa and B is the total thickness of film I and film II before hot pressing in mm.

[0075] (4) The pre-film is subjected to stretching, first heat setting, extraction, and second heat setting in sequence to obtain the UPE filter membrane.

[0076] In some embodiments, the temperature of the casting solution can be one of 220°C, 225°C, 230°C, 235°C, 240°C, 245°C, 250°C, or any value between two adjacent values.

[0077] In some embodiments, in step (2), the cooling rate of the liquid film on the side in contact with the heat sink can be one of 10℃ / s, 12℃ / s, 15℃ / s, 18℃ / s, 20℃ / s or any value between two adjacent values.

[0078] In some embodiments, the cooling rate of the liquid film on the non-contact heat sink side can be one of 6℃ / s, 5℃ / s, 4℃ / s, 3℃ / s, 2℃ / s, or any value between two adjacent values.

[0079] In some embodiments, in step (3), the hot pressing satisfies A / B = one of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or any value between any two of the above.

[0080] In some embodiments, during the phase separation curing process, the target temperatures on both sides of the film are controlled by a temperature controller to be T1 and T2, respectively, and different cooling rates are set. After the actual temperatures on both sides reach the target temperatures, they are maintained for 10 to 20 seconds to complete the phase separation curing.

[0081] In some embodiments, T1 is 15–50°C and T2 is 45–120°C.

[0082] In some implementations, T1 can be one of 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 50°C, or any value between two adjacent values.

[0083] In some implementations, T2 can be one of 45°C, 60°C, 85°C, 100°C, 105°C, 110°C, 120°C, or any value between two adjacent values.

[0084] In some embodiments, in step (2), the average particle size of the micron-sized copper particles is 5 to 50 μm.

[0085] In some embodiments, the average particle size of the micron-sized copper particles is one of 5μm, 8μm, 10μm, 12μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm or any value between two adjacent values.

[0086] In some embodiments, the method for preparing the heat sink includes the following steps:

[0087] Micron-sized copper particles are dispersed and mixed with binder and then placed in a mold and pressed at 50-150 MPa. After pressing, they are preheated and degreased, then heated to 350-450℃ for calcination, and cooled to obtain green blanks.

[0088] The green billet is preheated to 600-700℃ and held for 60-90 minutes, followed by multiple hot rolling processes and annealing at 400-450℃ for 120-180 minutes to obtain the rough billet.

[0089] The blank is sanded and then fixed onto the substrate to obtain the heat sink.

[0090] In some embodiments, the mass ratio of the micron-sized copper particles to the binder is 99:1 to 95:5.

[0091] In some embodiments, the adhesive includes at least one of polyvinyl alcohol and stearic acid.

[0092] In some embodiments, the micron-sized copper particles and the binder are mixed in an organic solvent, including ethanol.

[0093] In some embodiments, the temperature of the heating degreasing treatment is 250–350°C, and the time is 100–200 min.

[0094] In some embodiments, the calcination treatment time is 40 to 60 minutes.

[0095] In some embodiments, the deformation per pass of the hot rolling is 8-15%, the rolling speed is 0.5-1m / min, and the deformation of the product obtained after hot rolling is controlled to be 8-10%.

[0096] In some embodiments, the sanding process is performed using an 800-mesh grinding wheel, with 1 to 6 sanding passes, each lasting 2 to 5 seconds.

[0097] In some embodiments, in step (3), the temperature of the hot pressing is 60 to 90°C, specifically one of 60°C, 70°C, 80°C, and 90°C, or any value between two adjacent values.

[0098] In some embodiments, the hot pressing time is 0.5 to 1 minute.

[0099] In some implementations, A = 1 to 5 MPa.

[0100] In some implementations, A is one of 1 MPa, 2 MPa, 3 MPa, 5 MPa, or any value between two adjacent values.

[0101] In some embodiments, B = 0.5–2 mm.

[0102] In some implementations, B is one of 0.5mm, 1mm, 1.5mm, 2mm or any value between two adjacent values.

[0103] In some embodiments, in step (3), the two films are pre-stretched before being bonded, and the temperature of the pre-stretching treatment is 80 to 110°C, and the pre-stretching ratio is 1.2 to 5 times.

[0104] In some embodiments, the temperature of the pre-stretching treatment can be one of 80°C, 85°C, 90°C, 95°C, 100°C, 110°C or any value between two adjacent values, and the pre-stretching multiple can be one of 1.2 times, 1.5 times, 2 times, 2.5 times, 3 times, 4 times, 5 times or any value between two adjacent values.

[0105] In some embodiments, the pre-stretching treatment includes simultaneous transverse pre-stretching and longitudinal pre-stretching treatments, wherein the transverse pre-stretching multiple is 1.2 to 5 times and the stretching rate is 5 to 100% / s, and the longitudinal pre-stretching multiple is 1.2 to 5 times and the stretching rate is 5 to 100% / s.

[0106] In some embodiments, step (4) includes a stretching process that is performed simultaneously in the transverse direction and in the longitudinal direction. The temperature of the stretching process is 70 to 140°C, the transverse stretching process is 2 to 10 times, and the longitudinal stretching process is 2 to 10 times.

[0107] In some embodiments, in step (4), the temperature of the first heat setting is 120-140°C and the time is 5-120 seconds.

[0108] In some embodiments, in step (4), the temperature of the second heat setting is 145-160°C and the time is 5-120 seconds.

[0109] In some embodiments, in step (4), the extraction uses at least one of dichloromethane, tetrafluoroethane, alcohol, and ketone as a solvent, and the extraction time is 10 to 24 hours.

[0110] In some embodiments, the average pore size (PMI) of the UPE filter membrane is 10–30 nm.

[0111] In some embodiments, the thickness of the UPE filter membrane is 45–100 μm.

[0112] In some embodiments, the tensile strength of the UPE filter membrane is greater than 4 MPa.

[0113] The present application is further illustrated below with specific embodiments:

[0114] Example 1

[0115] An embodiment of a UPE filter membrane and its preparation method, wherein the preparation method includes the following steps:

[0116] (1) A casting solution is prepared by compounding and melting polyethylene resin, organic matter S, and organic matter N; the polyethylene resin is polyethylene resin 1 with a molecular weight distribution of 9 and a weight average molecular weight of 3 million and polyethylene resin 2 with a molecular weight distribution of 8 and a weight average molecular weight of 1.5 million, which are mixed at a mass ratio of 8:2; the organic matter S is paraffin oil and the organic matter N is dimethyl phthalate; the temperature of the casting solution is 230°C.

[0117] (2) The casting liquid is extruded through a die to form a liquid film, which is then placed on a heat sink plate with a rough surface and cooled for phase separation and solidification to form a 1.7 mm green film I. During the phase separation and solidification, the target temperatures on both sides of the green film are controlled by a temperature controller to be T1 and T2, respectively, and different cooling rates are set. After the actual temperatures on both sides reach the target temperatures, they are held for 10 seconds to complete the phase separation and solidification. T1 is the temperature on the side in contact with the heat sink plate, T1 = 25℃, and T2 is the temperature on the side not in contact with the heat sink plate, T2 = 80℃. The cooling rate of the liquid film on the side in contact with the heat sink plate is 15℃ / s. The cooling rate of the liquid film on the side not in contact with the heat sink plate is 3℃ / s. The heat sink plate includes micron-sized copper particles with a roughness Ra of 10 μm.

[0118] The heat sink is a self-made product, and its preparation method is as follows:

[0119] Micron-sized copper particles with an average particle size of 20 μm were dispersed and mixed with binder polyvinyl alcohol at a mass ratio of 98:2 in ethanol and then placed in a mold and pressed at 100 MPa. After pressing, the mixture was preheated at 300℃ for 150 min under a nitrogen atmosphere to remove the fat, and then calcined at 400℃ for 60 min. After cooling, the green body was obtained.

[0120] The billet is preheated to 650℃ and held for 80 minutes, followed by multiple hot rolling and annealing at 420℃ for 150 minutes to obtain a rough billet; the deformation amount of each hot rolling pass is controlled at 8% except for the first pass which is controlled at 15%, and the rolling speed is 0.5 m / min, so that the deformation amount of the product obtained after hot rolling is controlled at 8%.

[0121] The blank is sanded four times with an 800-grit grinding wheel for 3 seconds each time, and then fixed on the substrate to obtain the heat sink.

[0122] (3) Prepare another film II in the same manner as steps (1) and (2). After film I and film II are completely cured, separate the heat dissipation plate and perform a pre-stretching treatment at the same time. The temperature of the pre-stretching treatment is 90°C, including a transverse pre-stretching treatment and a longitudinal pre-stretching treatment performed simultaneously. The transverse pre-stretching treatment is twice the length and the stretching rate is 50% / s. The longitudinal pre-stretching treatment is twice the length and the stretching rate is 50% / s. The thickness of film I and film II after pre-stretching is 0.4 mm.

[0123] The two film-forming plates are then bonded together on one side in contact with the heat sink, and hot-pressed at 80°C for 30 seconds to obtain a pre-film. During the hot-pressing, A / B = 1.9 is satisfied, where A is the hot-pressing pressure of 1.5 MPa and B is the total thickness of film-forming plates I and II before hot-pressing, which is 0.8 mm.

[0124] (4) The pre-film is subjected to stretching treatment, first heat setting at 130℃ for 60s, extraction, and second heat setting at 150℃ for 60s in sequence to obtain the UPE filter membrane; the stretching treatment includes simultaneous transverse stretching treatment and longitudinal stretching treatment, the temperature of the stretching treatment is 100℃, the transverse stretching treatment ratio is 3.5 times and the stretching rate is 30% / s, the longitudinal stretching treatment ratio is 3.5 times and the stretching rate is 30% / s; the extraction uses dichloromethane as solvent and the extraction time is 18h.

[0125] The final thickness of the UPE filter membrane was 64 μm. The pore size of the UPE filter membrane was tested using a PMI pore size analyzer, and the tensile strength was tested using a universal tensile testing machine. The tensile strength and PMI average pore size are shown in Table 1.

[0126] Example 2

[0127] An embodiment of a UPE filter membrane and its preparation method differs from Example 1 only in that:

[0128] The heat sink comprises micron-sized copper particles with a roughness Ra of 8μm.

[0129] The heat sink is a self-made product, and its preparation method is as follows:

[0130] Micron-sized copper particles with an average particle size of 6 μm and binder polyvinyl alcohol were dispersed and mixed in ethanol at a mass ratio of 98:2 and then placed in a mold and pressed at 100 MPa. After pressing, the mixture was preheated at 300℃ for 150 min under a nitrogen atmosphere to remove the fat, and then calcined at 400℃ for 60 min. After cooling, the green body was obtained.

[0131] The billet is preheated to 650℃ and held for 80 minutes, followed by multiple hot rolling and annealing at 420℃ for 150 minutes to obtain a rough billet; the deformation amount of each hot rolling pass is controlled at 8% except for the first pass which is controlled at 15%, and the rolling speed is 0.5 m / min, so that the deformation amount of the product obtained after hot rolling is controlled at 8%.

[0132] The blank is surface-grinding three times with an 800-grit grinding wheel, each time for 4 seconds, and then fixed on the substrate to obtain the heat sink.

[0133] Example 3

[0134] An embodiment of a UPE filter membrane and its preparation method differs from Example 1 only in that:

[0135] The heat sink comprises micron-sized copper particles with a roughness Ra of 14μm.

[0136] The heat sink is a self-made product, and its preparation method is as follows:

[0137] Micron-sized copper particles with an average particle size of 45 μm were dispersed and mixed with binder polyvinyl alcohol at a mass ratio of 98:2 in ethanol and then placed in a mold and pressed at 100 MPa. After pressing, the mixture was preheated at 300℃ for 150 min under a nitrogen atmosphere to remove the fat, and then calcined at 400℃ for 60 min. After cooling, the green body was obtained.

[0138] The billet is preheated to 650℃ and held for 80 minutes, followed by multiple hot rolling and annealing at 420℃ for 150 minutes to obtain a rough billet; the deformation amount of each hot rolling pass is controlled at 8% except for the first pass which is controlled at 15%, and the rolling speed is 0.5 m / min, so that the deformation amount of the product obtained after hot rolling is controlled at 8%.

[0139] The blank is surface-grinding treated 6 times with an 800-grit grinding wheel, each time for 5 seconds, and then fixed on the substrate to obtain the heat sink.

[0140] Example 4

[0141] An embodiment of a UPE filter membrane and its preparation method differs from Example 1 only in that:

[0142] During the phase separation curing process, the target temperatures on both sides of the film are controlled by a temperature controller to be T1 and T2, respectively, and different cooling rates are set. After the actual temperatures on both sides reach the target temperatures, they are maintained for 10 seconds to complete the phase separation curing. T1 is the temperature on the side in contact with the heat sink, T1 = 50℃, and T2 is the temperature on the side not in contact with the heat sink, T2 = 120℃. The cooling rate of the liquid film on the side in contact with the heat sink is 20℃ / s, and the cooling rate of the liquid film on the side not in contact with the heat sink is 5℃ / s.

[0143] Example 5

[0144] An embodiment of a UPE filter membrane and its preparation method differs from Example 1 only in that:

[0145] During the phase separation curing process, the target temperatures on both sides of the film are controlled by a temperature controller to be T1 and T2, respectively, and different cooling rates are set. After the actual temperatures on both sides reach the target temperatures, they are maintained for 10 seconds to complete the phase separation curing. T1 is the temperature on the side in contact with the heat sink, T1 = 15℃, and T2 is the temperature on the side not in contact with the heat sink, T2 = 65℃. The cooling rate of the liquid film on the side in contact with the heat sink is 12℃ / s, and the cooling rate of the liquid film on the side not in contact with the heat sink is 2℃ / s.

[0146] Example 6

[0147] An embodiment of a UPE filter membrane and its preparation method differs from Example 1 only in that:

[0148] During the phase separation curing process, the target temperatures on both sides of the film are controlled by a temperature controller to be T1 and T2, respectively, and different cooling rates are set. After the actual temperatures on both sides reach the target temperatures, they are maintained for 10 seconds to complete the phase separation curing. T1 is the temperature on the side in contact with the heat sink, T1 = 45℃, and T2 is the temperature on the side not in contact with the heat sink, T2 = 75℃. The cooling rate of the liquid film on the side in contact with the heat sink is 10℃ / s, and the cooling rate of the liquid film on the side not in contact with the heat sink is 3℃ / s.

[0149] Example 7

[0150] An embodiment of a UPE filter membrane and its preparation method differs from Embodiment 1 only in that the thickness of the resulting formed membrane I is 0.8 mm. In the steps described:

[0151] (3) Prepare another film II in the same manner as steps (1) and (2). After film I and film II are completely cured, separate the heat dissipation plate and perform a pre-stretching treatment at the same time. The temperature of the pre-stretching treatment is 90°C, including a transverse pre-stretching treatment and a longitudinal pre-stretching treatment performed simultaneously. The transverse pre-stretching treatment is 1.2 times and the stretching rate is 50% / s. The longitudinal pre-stretching treatment is 1.2 times and the stretching rate is 50% / s. The thickness of film I and film II after stretching is 0.5 mm.

[0152] The two film-forming plates are then bonded together on one side in contact with the heat sink, and hot-pressed at 80°C for 30 seconds to obtain a pre-film. During the hot-pressing, A / B = 1 is satisfied, where A is the hot-pressing pressure of 1 MPa and B is the total thickness of film-forming I and film-forming II before hot-pressing of 1 mm.

[0153] Example 8

[0154] An embodiment of a UPE filter membrane and its preparation method differs from Embodiment 1 only in that the thickness of the resulting formed membrane I is 7.8 mm. In the steps described:

[0155] (3) Prepare another film II in the same manner as steps (1) and (2). After film I and film II are completely cured, separate the heat dissipation plate and perform a pre-stretching treatment. The temperature of the pre-stretching treatment is 90°C, including a transverse pre-stretching treatment and a longitudinal pre-stretching treatment performed simultaneously. The transverse pre-stretching treatment is performed by a factor of 5 and the stretching rate is 50% / s. The longitudinal pre-stretching treatment is performed by a factor of 5 and the stretching rate is 50% / s. The thickness of film I and film II after stretching is 0.3 mm.

[0156] The two film-forming plates are then bonded together on one side in contact with the heat sink, and hot-pressed at 80°C for 30 seconds to obtain a pre-film; the hot-pressing process satisfies A / B = 5, where A is the hot-pressing pressure of 3MPa and B is the total thickness of film-forming I and film-forming II before hot-pressing, 0.6mm;

[0157] Example 9

[0158] An embodiment of a UPE filter membrane and its preparation method differs from Embodiment 1 only in that the thickness of the resulting formed membrane I is 2.5 mm. In the steps described:

[0159] (3) Prepare another film II in the same manner as steps (1) and (2). After film I and film II are completely cured, separate the heat dissipation plate and perform pre-stretching treatment at the same time. The temperature of the pre-stretching treatment is 90°C, including simultaneous transverse pre-stretching treatment and longitudinal pre-stretching treatment. The transverse pre-stretching treatment is twice the length and the stretching rate is 50% / s. The longitudinal pre-stretching treatment is twice the length and the stretching rate is 50% / s. The thickness of film I and film II after pre-stretching is 0.6 mm.

[0160] The two film-forming plates are then bonded together on one side in contact with the heat sink, and hot-pressed at 90°C for 30 seconds to obtain a pre-film. During the hot pressing, A / B = 2.1 is satisfied, where A is the hot pressing pressure of 2.5 MPa and B is the total thickness of film-forming I and film-forming II before hot pressing, which is 1.2 mm.

[0161] Example 10

[0162] An embodiment of a UPE filter membrane and its preparation method differs from Embodiment 1 only in that the thickness of the resulting formed membrane I is 0.5 mm, and the steps described are as follows:

[0163] (3) Prepare another film II in the same way as steps (1) and (2), without pre-stretching treatment. After film I and film II are completely cured, separate the heat dissipation plate.

[0164] The two film-forming plates are then bonded together on one side in contact with the heat sink, and hot-pressed at 80°C for 30 seconds to obtain a pre-film. During the hot-pressing, A / B = 2 is satisfied, where A is the hot-pressing pressure of 2MPa and B is the total thickness of film-forming I and film-forming II before hot-pressing, which is 1mm.

[0165] Example 11

[0166] An embodiment of a UPE filter membrane and its preparation method, wherein the preparation method includes the following steps:

[0167] (1) A casting solution is prepared by compounding and melting polyethylene resin, organic matter S, and organic matter N; the polyethylene resin is polyethylene resin 1 with a molecular weight distribution of 6 and a weight average molecular weight of 3.5 million and polyethylene resin 2 with a molecular weight distribution of 7 and a weight average molecular weight of 800,000, mixed at a mass ratio of 7:3; the organic matter S is white oil and the organic matter N is dioctyl adipate; the temperature of the casting solution is 220°C.

[0168] (2) The casting liquid is extruded through a die to form a liquid film, which is then placed on a heat sink plate with a rough surface and cooled for phase separation and solidification to form a 3.1 mm green film I. During the phase separation and solidification, the target temperatures on both sides of the green film are controlled by a temperature controller to be T1 and T2, respectively, and different cooling rates are set. After the actual temperatures on both sides reach the target temperatures, they are held for 10 seconds to complete the phase separation and solidification. T1 is the temperature on the side in contact with the heat sink plate, T1 = 25℃, and T2 is the temperature on the side not in contact with the heat sink plate, T2 = 80℃. The cooling rate of the liquid film on the side in contact with the heat sink plate is 15℃ / s. The cooling rate of the liquid film on the side not in contact with the heat sink plate is 3℃ / s. The heat sink plate includes micron-sized copper particles with a roughness Ra of 10 μm.

[0169] The heat sink is a self-made product, and its preparation method is as follows:

[0170] Micron-sized copper particles with an average particle size of 20 μm were dispersed and mixed with binder polyvinyl alcohol at a mass ratio of 98:2 in ethanol and then placed in a mold and pressed at 100 MPa. After pressing, the mixture was preheated at 300℃ for 150 min under a nitrogen atmosphere to remove the fat, and then calcined at 400℃ for 60 min. After cooling, the green body was obtained.

[0171] The billet is preheated to 650℃ and held for 80 minutes, followed by multiple hot rolling and annealing at 420℃ for 150 minutes to obtain a rough billet; the deformation amount of each hot rolling pass is controlled at 8% except for the first pass which is controlled at 15%, and the rolling speed is 0.5 m / min, so that the deformation amount of the product obtained after hot rolling is controlled at 8%.

[0172] The blank is sanded four times with an 800-grit grinding wheel for 3 seconds each time, and then fixed on the substrate to obtain the heat sink.

[0173] (3) Prepare another film II in the same manner as steps (1) and (2). After film I and film II are completely cured, separate the heat dissipation plate and perform a pre-stretching treatment at the same time. The temperature of the pre-stretching treatment is 90°C, including a transverse pre-stretching treatment and a longitudinal pre-stretching treatment performed simultaneously. The transverse pre-stretching treatment is twice the length and the stretching rate is 50% / s. The longitudinal pre-stretching treatment is twice the length and the stretching rate is 50% / s. The thickness of film I and film II after pre-stretching is 0.7 mm.

[0174] The two film-forming plates are then bonded together on one side in contact with the heat sink, and hot-pressed at 80°C for 30 seconds to obtain a pre-film. During the hot-pressing, A / B = 1.9 is satisfied, where A is the hot-pressing pressure of 2.7 MPa and B is the total thickness of film-forming plates I and II before hot-pressing, which is 1.4 mm.

[0175] (4) The pre-film is subjected to stretching treatment, first heat setting at 120℃ for 80s, extraction, and second heat setting at 155℃ for 50s in sequence to obtain the UPE filter membrane; the stretching treatment includes simultaneous transverse stretching treatment and longitudinal stretching treatment, the temperature of the stretching treatment is 100℃, the transverse stretching treatment ratio is 4 times and the stretching rate is 30% / s, the longitudinal stretching treatment ratio is 4 times and the stretching rate is 30% / s; the extraction uses dichloromethane as solvent and the extraction time is 24h.

[0176] Comparative Example 1

[0177] A UPE filter membrane and its preparation method differ from Example 1 only in that, in the phase separation and solidification process in step (2), no heat dissipation plate is set up, and a glass plate with a surface roughness Ra < 1 μm is used to place the liquid membrane, and the thickness of the resulting raw membrane is 3.4 mm. In step (3), the preparation of raw membrane II and subsequent hot pressing are not carried out, and pre-stretching and subsequent step (4) are carried out directly.

[0178] Comparative Example 2

[0179] A UPE filter membrane and its preparation method differ from Example 1 only in that:

[0180] The heat sink comprises micron-sized copper particles with a roughness Ra of 4μm.

[0181] The heat sink is a self-made product, and its preparation method is as follows:

[0182] Micron-sized copper particles with an average particle size of 4 μm were dispersed and mixed with binder polyvinyl alcohol at a mass ratio of 98:2 in ethanol and then placed in a mold and pressed at 100 MPa. After pressing, the mixture was preheated at 300℃ for 150 min under a nitrogen atmosphere to remove the fat, and then calcined at 400℃ for 60 min. After cooling, the green body was obtained.

[0183] The billet is preheated to 650℃ and held for 80 minutes, followed by multiple hot rolling and annealing at 420℃ for 150 minutes to obtain a rough billet; the deformation amount of each hot rolling pass is controlled at 8% except for the first pass which is controlled at 15%, and the rolling speed is 0.5 m / min, so that the deformation amount of the product obtained after hot rolling is controlled at 8%.

[0184] The blank is sanded twice with an 800-grit grinding wheel for 4 seconds each time, and then fixed on the substrate to obtain the heat sink.

[0185] Comparative Example 3

[0186] A UPE filter membrane and its preparation method differ from Example 1 only in that...

[0187] The heat sink comprises micron-sized copper particles with a roughness Ra of 18 μm.

[0188] The heat sink is a self-made product, and its preparation method is as follows:

[0189] Micron-sized copper particles with an average particle size of 60 μm were dispersed and mixed with binder polyvinyl alcohol at a mass ratio of 98:2 in ethanol and then placed in a mold and pressed at 100 MPa. After pressing, the mixture was preheated at 300°C for 150 min under a nitrogen atmosphere to remove the fat, and then calcined at 400°C for 60 min. After cooling, the green body was obtained.

[0190] The billet is preheated to 650℃ and held for 80 minutes, followed by multiple hot rolling and annealing at 420℃ for 150 minutes to obtain a rough billet; the deformation amount of each hot rolling pass is controlled at 8% except for the first pass which is controlled at 15%, and the rolling speed is 0.5 m / min, so that the deformation amount of the product obtained after hot rolling is controlled at 8%.

[0191] The rough blank is sanded eight times with an 800-grit grinding wheel, each time for 6 seconds, and then fixed on the substrate to obtain the heat sink.

[0192] Comparative Example 4

[0193] An embodiment of a UPE filter membrane and its preparation method differs from Example 1 only in that:

[0194] During the phase separation curing process, the target temperatures on both sides of the film are controlled by a temperature controller, namely T1 and T2, and different cooling rates are set. After the actual temperatures on both sides reach the target temperatures, they are maintained for 10 seconds to complete the phase separation curing. T1 is the temperature on the side in contact with the heat sink, T1 = 25℃, and T2 is the temperature on the side not in contact with the heat sink, T2 = 80℃. The cooling rate of the liquid film on the side in contact with the heat sink is 25℃ / s, and the cooling rate of the liquid film on the side not in contact with the heat sink is 10℃ / s.

[0195] Comparative Example 5

[0196] An embodiment of a UPE filter membrane and its preparation method differs from Example 1 only in that:

[0197] During the phase separation curing process, the target temperatures on both sides of the film are controlled by a temperature controller, namely T1 and T2, and different cooling rates are set. After the actual temperatures on both sides reach the target temperatures, they are maintained for 10 seconds to complete the phase separation curing. T1 is the temperature on the side in contact with the heat sink, T1 = 25℃, and T2 is the temperature on the side not in contact with the heat sink, T2 = 80℃. The cooling rate of the liquid film on the side in contact with the heat sink is 5℃ / s, and the cooling rate of the liquid film on the side not in contact with the heat sink is 5℃ / s.

[0198] Comparative Example 6

[0199] A UPE filter membrane and its preparation method differ from Example 1 only in that the thickness of the resulting formed membrane I is 6.5 mm. In the steps described:

[0200] (3) Prepare another film II in the same manner as steps (1) and (2). After film I and film II are completely cured, separate the heat dissipation plate and perform a pre-stretching treatment at the same time. The temperature of the pre-stretching treatment is 90°C, including a transverse pre-stretching treatment and a longitudinal pre-stretching treatment performed simultaneously. The transverse pre-stretching treatment is twice the length and the stretching rate is 50% / s. The longitudinal pre-stretching treatment is twice the length and the stretching rate is 50% / s. The thickness of film I and film II after stretching is 1.5 mm.

[0201] The two film-forming plates are then bonded together on one side in contact with the heat sink, and hot-pressed at 80°C for 30 seconds to obtain a pre-film. During the hot-pressing, A / B = 0.7 is satisfied, where A is the hot-pressing pressure of 2MPa and B is the total thickness of film-forming I and film-forming II before hot-pressing of 3mm.

[0202] Comparative Example 7

[0203] A UPE filter membrane and its preparation method differ from Example 1 only in that the thickness of the resulting formed membrane I is 4.5 mm. In the steps described:

[0204] (3) Prepare another film II in the same way as steps (1) and (2). After film I and film II are completely cured, separate the heat dissipation plate and perform pre-stretching treatment at the same time. The temperature of the pre-stretching treatment is 90°C, including the simultaneous transverse pre-stretching treatment and longitudinal pre-stretching treatment. The transverse pre-stretching treatment is twice the length and the stretching rate is 50% / s. The longitudinal pre-stretching treatment is twice the length and the stretching rate is 50% / s. The thickness of film I and film II after pre-stretching is 1 mm.

[0205] The two film-forming plates are then bonded together on one side in contact with the heat sink, and hot-pressed at 80°C for 30 seconds to obtain a pre-film. During the hot-pressing, A / B = 6 is satisfied, where A is the hot-pressing pressure of 12MPa and B is the total thickness of film-forming I and film-forming II before hot-pressing, which is 2mm.

[0206] Example of effect 1

[0207] To verify the performance of the UPE film described in this application, the following tests were conducted on the various embodiments and comparative products:

[0208] (1) Refer to the test method in section

[0137] of CN113351033B manual and use the same device to test the water flow rate;

[0209] (2) Referring to the instruction manual

[0148] of CN113351033B, the retention accuracy of Examples 1-11 and Comparative Examples 1-7 was tested using a particle counter and a rinsing test device. The particle size of the test medium was 2nm and 5nm. When the 2nm retention efficiency was >95%, the 5nm retention efficiency was no longer tested. If it was ≤95%, the 5nm retention efficiency was further tested. If it was still ≤95%, it indicated that the sample retention accuracy was insufficient.

[0210] The test results are shown in Table 1.

[0211] Table 1

[0212]

[0213] The test results show that the UPE filter membrane prepared by the method described in this application has ideal performance. The fluid passage time through the UPE filter membrane is no more than 3200s, which is short, the throughput is high, and the tensile strength is high. All embodiments can ensure a retention efficiency of at least 95% for impurities with a particle size of 5nm. This is mainly due to the preparation of two non-uniform membranes with asymmetric pore structures by a heat sink-assisted phase separation curing method, followed by hot-pressing with specific pressure to prepare a pre-film, which forms an interlocking buffer space with micro-pores on the surface of the membrane layer. After subsequent stretching and heat setting treatment, the resulting product can not only ensure retention accuracy based on the dense pores near the buffer space in the center of the membrane layer, but also maintain ideal membrane structure stability in high-throughput working mode by relying on the large pore structure on the surface of the membrane layer and the deep buffer space. In contrast, the comparative example Example 1 uses a traditional non-rough heat sink as the support structure for the liquid film. This type of product lacks an obvious buffer structure, resulting in low throughput. Example 2 uses a heat sink with too small a roughness, leading to insufficient buffer space and inadequate throughput gain. Example 3, due to excessive roughness, not only has too many depressions and an excessively large buffer space, but also causes damage to the pore structure of the film layer during separation from the heat sink, resulting in low retention accuracy. Examples 4 and 5 were cured at the same temperatures T1 and T2 as Example 1, but with inappropriate cooling rates. Example 4 had too small pores, resulting in low throughput, while Example 5 had too large pores, leading to low tensile strength and retention accuracy. Examples 6 and 7, due to mismatch between the pressing pressure and film thickness, failed to achieve both tensile strength and retention accuracy requirements. Example 7 also had very low throughput.

[0214] As can be seen from Examples 1, 4 to 6, when the temperature difference of phase separation and solidification is set at 50°C or above during the film preparation process, and the cooling rates on both sides are in the range of (4 to 8): 1, the product can achieve higher retention accuracy while taking into account high throughput.

[0215] As can be seen from Examples 1, 7-8, and 10, pre-stretching the film before pressing can further improve the throughput.

[0216] As can be seen from Examples 1-11, when the UPE filter membrane obtained by the present invention is used for photoresist filtration, it can remove nano-impurities in the photoresist. In particular, it has a rejection efficiency of more than 95% for 5nm impurities and even 2nm impurities.

Claims

1. A method for preparing a UPE filter membrane, characterized by, The method comprises the following steps: (1) preparing a casting solution by compounding polyethylene resin, organic substance S and organic substance N; the polyethylene resin is ultra-high molecular weight polyethylene resin, the organic substance S is a solvent of the polyethylene resin, and the organic substance N is a non-solvent of the polyethylene resin; the temperature of the casting solution is 220-250 ℃; (2) extruding the casting solution through a die to form a liquid film, then placing the liquid film on a rough-surfaced heat sink and cooling to a temperature of 15-120 ℃ to perform phase separation solidification to form a green film I; the temperature of the liquid film on both sides is different during the phase separation solidification, and T2≥T1 is satisfied, wherein T1 is the temperature on the side in contact with the heat sink, and T2 is the temperature on the side not in contact with the heat sink; the cooling rate of the liquid film on the side in contact with the heat sink is 10-20 ℃ / s; the cooling rate of the liquid film on the side not in contact with the heat sink is ≤6 ℃ / s; the heat sink comprises micron copper particles, and the roughness Ra is 8-15 μm; (3) preparing another green film II in the same way as steps (1) and (2); after the green films I and II are completely solidified, separating the heat sink and bonding the two green films on the side in contact with the heat sink to perform hot pressing to obtain a pre-membrane; during the hot pressing, A / B=1-5 is satisfied, wherein A is the pressure of the hot pressing, in MPa, and B is the total thickness of the green films I and II before hot pressing, in mm; (4) sequentially performing stretching treatment, first heat setting, extraction and second heat setting on the pre-membrane to obtain the UPE filter membrane.

2. The method of claim 1, wherein the UPE filter membrane is prepared by the steps of: In step (1), the polyethylene resin comprises at least one kind of ultra-high molecular weight polyethylene with a weight average molecular weight ≥1 million, and the molecular weight distribution of the ultra-high molecular weight polyethylene is 6-10; and / or; In step (1), the organic substance S comprises at least one of paraffin oil, white oil, hydraulic oil, castor oil or an extract thereof, and / or the organic substance N comprises at least one of dimethyl phthalate, dioctyl adipate, ethylene glycol diacetate, dimethyl carbonate, palm oil or triacetin.

3. The method of claim 1, wherein the UPE filter membrane is prepared by the steps of: T2-T1≥30 ℃, and the ratio of the cooling rate of the liquid film on the side in contact with the heat sink to the cooling rate of the liquid film on the side not in contact with the heat sink is (2-10):1; preferably, T2-T1≥50 ℃, and the ratio of the cooling rate of the liquid film on the side in contact with the heat sink to the cooling rate of the liquid film on the side not in contact with the heat sink is (4-8):

1.

4. The method for preparing the UPE filter membrane as described in claim 1, characterized in that, In step (2), the average particle size of the micron copper particles is 5-50 μm.

5. The method for preparing the UPE filter membrane as described in claim 1, characterized in that, In step (3), the temperature of the hot pressing is 60-90 ℃, and / or A=1-5 MPa, and / or B=0.5-2 mm.

6. The method of claim 1, wherein the UPE filter membrane is prepared by the steps of: In step (3), the two green films are also subjected to pre-stretching treatment before bonding, the temperature of the pre-stretching treatment is 80-110 ℃, and the pre-stretching treatment multiple is 1.2-5 times.

7. The method for preparing the UPE filter membrane as described in claim 6, characterized in that, The pre-stretching treatment includes simultaneously conducted transverse pre-stretching treatment and longitudinal pre-stretching treatment, the transverse pre-stretching treatment has a multiple of 1.2-5 and a stretching rate of 5-100% / s, and the longitudinal pre-stretching treatment has a multiple of 1.2-5 and a stretching rate of 5-100% / s.

8. The method for preparing the UPE filter membrane as described in claim 1, characterized in that, The method comprises at least one of the following: (a) in the step (4), the stretching treatment includes simultaneously conducted transverse stretching treatment and longitudinal stretching treatment, the stretching treatment has a temperature of 70-140℃, the transverse stretching treatment has a multiple of 2-10, and the longitudinal stretching treatment has a multiple of 2-10; (b) in the step (4), the first heat setting has a temperature of 120-140℃ and a time of 5-120s; (c) in the step (4), the second heat setting has a temperature of 145-160℃ and a time of 5-120s; (d) in the step (4), the extraction uses at least one of dichloromethane, tetrafluoroethane, alcohol and ketone as a solvent, and the extraction has a time of 10-24h.

9. The UPE filter membrane prepared by the method of any one of claims 1-8.

10. The UPE filter membrane of claim 9, wherein the UPE filter membrane has a PMI average pore size of 10-30nm, a thickness of 45-100μm, and a tensile strength greater than 4MPa.

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