A UPE porous membrane with low specific surface area and its preparation method and use

Abstract

The present invention provides a UPE porous membrane with a low specific surface area and a preparation method and use thereof. The porous membrane comprises a first porous surface, a second porous surface and a main body located between the first porous surface and the second porous surface, wherein a non-directional tortuous passage is provided in the main body; the first porous surface is provided with a gully-shaped first hole; the pore area ratio of the first hole on the first porous surface is 20-35%, and the IPA bubble point is 0.15-0.65MPa; thus, the UPE porous membrane has a retention efficiency of greater than 95% for impurity particles with a particle size of 20-200nm, and has a high retention efficiency; at the same time, the membrane also has a large filtration speed, and the time required for a fluid to pass through the porous membrane is short, and the time cost is low; in addition, the UPE porous membrane has a small ineffective pore volume and a very low specific surface area of ​​only 7-24m 2 / g, easy to clean, various impurities are not easy to remain in the UPE porous membrane, and high-cleanliness filter material is easy to prepare; it is particularly suitable for application in the field of photoresist filtration; the preparation method provided by the present invention can prepare the UPE porous membrane conveniently, quickly and effectively.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane materials, and more particularly to a UPE porous membrane with a low specific surface area and a preparation method and application thereof. Background Art

[0002] Polymer membrane is a kind of membrane made of organic high molecular polymer as raw material according to a certain process. The membrane mainly plays the role of filtration and separation. With the development of petroleum industry and science and technology, the application field of polymer membrane is constantly expanding. At present, it has been applied in gas separation, seawater desalination, ultrapure water preparation, waste treatment, artificial organ manufacturing, medicine, food, agriculture, chemical industry and other fields. According to the different high molecular polymers, polymer membrane can be divided into cellulose polymer membrane, polyamide polymer membrane, polysulfone polymer membrane, polyolefin polymer membrane and so on.

[0003] Polyolefin polymer filter membranes mainly refer to olefin filter membranes such as polyethylene filter membranes and polypropylene filter membranes. Due to their excellent physical and chemical properties, they have a wide range of applications. For example, ultra-high molecular weight polyethylene (UPE) filter membranes are usually used in fields such as lithography processing and "wet etching and cleaning" (WEC) applications. For example, the Chinese patent "Substrate for Liquid Filter" with application number 201480026006.4 introduces a polyethylene filter membrane used in the field of semiconductor lithography, which has excellent capture performance for impurity particles of about 10-50nm in size, and has a long service life. In addition, its flux can remain relatively stable during long-term use.

[0004] In the field of photoresist filtration, the cleanliness requirements for the filter material itself are extremely strict, so it is very important to clean the filter material used for photoresist. Ordinary UPE filter materials have too high specific surface area, that is, more pore volume, which makes it easier for certain impurities to remain and difficult to clean, resulting in the filter material being unable to meet the needs of actual applications. This also limits the development of polyolefin polymer filter membranes to a certain extent. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a UPE porous membrane with a low specific surface area and a preparation method and use thereof; the UPE porous membrane not only has excellent capture performance for impurity particles and high interception efficiency; it is also easy to clean, impurities are not easily retained in the UPE porous membrane, and a filter material with high cleanliness is easily prepared; it is particularly suitable for application in the field of photoresist filtration.

[0006] To achieve the above object, the present invention provides the following technical solution: a UPE porous membrane with a low specific surface area, comprising a first porous surface, a second porous surface and a main body located between the first porous surface and the second porous surface, wherein the main body has a non-directional tortuous path; the specific surface area of ​​the UPE porous membrane is 7-24m 2 / g; the UPE porous membrane has a retention efficiency of greater than 95% for impurity particles with a particle size of 20-200nm; the IPA bubble point of the UPE porous membrane is 0.15-0.65MPa; the first porous surface is provided with a plurality of groove-shaped first holes; the pore area ratio of the first holes on the first porous surface is 20-35%; the polyolefin composition constituting the UPE porous membrane includes at least ultra-high molecular weight polyethylene with a mass average molecular weight of more than 3 million.

[0007] The specific surface area of ​​the UPE porous membrane of the present invention was tested by the BET method. We were surprised to find that the specific surface area of ​​the UPE porous membrane was very low, with a specific surface area of ​​7-24 m 2 / g (the specific surface area of ​​existing UPE porous membrane is 30m 2 / g or more), preferably, its specific surface area is 10-20m 2 / g, and the advantages of low surface area UPE porous membrane are mainly in the following aspects:

[0008] 1. The UPE porous membrane with low surface area has fewer invalid pores, which can ensure that the porous membrane can filter effectively and at the same time, it can also ensure that the cleaning of the UPE porous membrane will become relatively easier (only less deionized water and fewer rinse times are needed to obtain the UPE filter material that meets the actual needs) and impurities (such as metal particles, organic matter and other impurities) are not easy to remain, ensuring the cleanliness of the membrane and the filter element, which is beneficial to the subsequent photoresist filtration and obtaining photoresist with excellent performance;

[0009] 2. Photoresist materials generally have relatively high viscosity, and their filtration often causes various problems related to bubbles. Among them, factors such as the number of bubbles will have a great impact on the filtration of photoresist. The porous membrane of the present invention has a relatively small ineffective pore volume due to its low specific surface area, which can effectively reduce the need to replace and eliminate the air in the filter material when the photoresist passes through the filter material, thereby reducing the influence of bubbles on the properties of the photoresist, and then obtaining a photoresist with better properties.

[0010] 3. In the field of photoresist filtration, the cleanliness requirement for the filter material itself is extremely strict, requiring the filter material itself to be very clean. In the entire membrane preparation process (including the possible modification process), certain impurities will be introduced. Although the filter material will be cleaned to a certain extent to reduce the impurity content remaining on the filter material as much as possible, the impurities can never be completely cleaned; and the UPE porous membrane of the present invention has a low specific surface area, even if there are very small amounts of residual impurities, due to its small contact area, the probability of these impurities being precipitated is also much lower than that of the porous membrane with a high specific surface area, so it is less likely to affect the properties of the photoresist; At the same time, the UPE porous membrane with a low specific surface area has a wider range of uses and is more suitable as a base membrane for various modifications, such as hydrophilic modification, charge modification (making the membrane charged), etc. This is because in the corresponding modification process, the contact area between the modifier and the UPE with a low specific surface area is smaller, and the modifier and the like are not easy to remain, so it is easier to clean, and the modified filter membrane is also cleaner;

[0011] In the membrane structure of the UPE porous membrane provided by the present invention, it can be clearly seen that there are a certain number of first holes with a certain pore size on the first porous surface of the membrane. It is well known that factors such as the pore size, number and shape of the membrane holes will have a great influence on the filtration accuracy (retention efficiency) of the membrane; the first holes on the first porous surface of the present invention are gully-shaped structures (that is, the first holes are gully-like in shape), and the gully-shaped first holes are not easy to produce invalid pore volume, thereby making the specific surface area of ​​the porous membrane lower; and the pore area ratio of the first holes (the ratio of the area of ​​the first holes to the area of ​​the membrane) is 20-35%, which is conducive to the porous membrane having a larger flow rate, facilitating the rapid passage of the fluid through the porous membrane, shortening the filtration time, and also having a larger tensile strength, meeting the needs of practical applications;

[0012] One of the important performance characteristics of the filter membrane is the bubble point, and the test method of the bubble point is well known in the art. For example, the procedures of these tests are explained in detail in ASTM F316-70 and ANS / ASTM F316-70 (reapproved in 1976), and these documents are incorporated herein by reference. The size of the bubble point is related to the pore size of the holes on the porous membrane; generally speaking, the larger the pore size of the hole, the lower the bubble point; the smaller the pore size of the hole, the higher the bubble point; the IPA bubble point of the UPE porous membrane in the present invention is 0.15-0.65MPa, and through the non-directional tortuous path in the membrane body, the porous membrane can play a good capture effect on impurity particles with a particle size of 20-200nm, and its interception efficiency is greater than 95%, which ensures the accuracy of filtration and plays a sufficient role in retaining undesirable substances;

[0013] The material of the UPE porous membrane in the present invention is uniform everywhere, that is, the entire membrane is made of polyethylene material, and there is no change in the material; ultra-high molecular weight polyethylene is referred to as UPE, which is a thermoplastic engineering plastic with a linear structure and excellent comprehensive performance. The filter membrane made of ultra-high molecular weight polyethylene has high heat resistance and wear resistance, good mechanical properties, large tensile strength, excellent chemical compatibility, wide application range, and is particularly suitable for application in the field of photoresists; the polyolefin composition constituting the UPE porous membrane in the present invention at least includes ultra-high molecular weight polyethylene with a mass average molecular weight of more than 3 million; this ultimately ensures that the prepared filter membrane has a large tensile strength and elongation at break, can meet the needs of practical applications, has a wide application range, and is particularly suitable for application in the field of photoresists; it should be noted that the mass average molecular weight can be obtained as follows: a sample of the polyethylene filter membrane is heated and dissolved in o-dichlorobenzene, and measured using a GPC liquid chromatograph at a column temperature of 135° C. and a flow rate of 1.0 mL / min;

[0014] The pore area ratio of the first hole on the first porous surface of the membrane can be measured by computer software (such as Matlab, NIS-Elements, etc.) or manually after the membrane structure is characterized by a scanning electron microscope, and then the measurement is performed and the corresponding calculation is performed; in the preparation process of the membrane, in the direction perpendicular to the membrane thickness (if the membrane is in the form of a porous membrane, the direction is the plane direction; if the membrane is in the form of a hollow fiber membrane, the direction is perpendicular to the radius direction), its various characteristics such as pore size distribution are roughly uniform and basically consistent; therefore, the pore area ratio of a part of the area on the corresponding plane can be used to reflect the size of the overall pore area ratio on the plane; when actually measuring, the membrane surface can be characterized by an electron microscope to obtain a corresponding SEM image, and since the pore distribution on the membrane surface is roughly uniform, a certain area can be selected, such as 1μm 2 (1μm times 1μm) or 25μm 2 (5μm multiplied by 5μm), the specific area size depends on the actual situation, and then the area of ​​all holes on the area is measured by corresponding computer software or manually, and then calculated to obtain the pore area rate of the first hole on the first porous surface. Of course, technical personnel in this field can also obtain the above parameters by other measurement methods. The above measurement methods are for reference only.

[0015] As a further improvement of the present invention, the thickness of the UPE porous membrane is 30-100 μm, the porosity is 30-45%, and the surface area of ​​the membrane inside per unit membrane area is 0.058-0.267.

[0016] When the thickness of the membrane is too small, the mechanical strength of the membrane will be low; at the same time, due to the short filtration time, effective filtration cannot be performed; when the thickness of the membrane is too large, the filtration time will be too long and the time cost will be too high; the thickness of the UPE porous membrane of the present invention is 30-100 μm, which ensures that the UPE porous membrane not only has high mechanical strength, but also can perform effective filtration with high filtration efficiency, short filtration time, low time cost, and is suitable for application in the field of photoresist;

[0017] When the porosity of the membrane is too high, the tensile strength of the membrane will be too low, its mechanical properties will be poor, its industrial practical value will be low, and it will be unable to meet market demand; and when the porosity of the membrane is too low, on the one hand, it will affect the flow rate of the membrane, resulting in a slower filtration speed, a longer filtration time, and a higher time cost; on the other hand, it will result in the membrane's dirt holding capacity being too low and its service life being too short, and the membrane will need to be replaced in a shorter period of time, greatly increasing the economic cost; the porosity of the porous membrane in the present invention is 30-45%, so that the membrane not only has a higher tensile strength, but also has a faster filtration speed, a large flow rate, a higher dirt holding capacity, can intercept more impurity particles, has a long service life, and has a lower economic cost; at the same time, the porous membrane also has a lower specific surface area, impurities are not easily retained on the porous membrane, and it is easier to clean.

[0018] When filtering, various fluids move along the thickness direction of the filter membrane to achieve corresponding filtration and the filtration is disposable, so the feature of the surface area of ​​the membrane inside per unit membrane area is particularly important; the surface area of ​​the membrane inside per unit membrane area refers to the surface area of ​​the membrane inside area on a porous membrane of a certain area, and the smaller its value is, the less the invalid pore volume inside the filter membrane is, and the surface area inside the filter membrane is also relatively small. The surface area of ​​the membrane inside per unit membrane area in the present invention is 0.058-0.267, and its value is very small, which shows that the invalid pore volume of the porous membrane is very small, and cleaning is relatively easier (only less deionized water and less flushing times are needed to obtain UPE filter material that meets high cleanliness), and impurities (such as metal particles, organic impurities, etc.) are not easy to remain inside the membrane, which is then conducive to obtaining a filter material with high cleanliness, meeting the needs of practical applications, and is particularly suitable for application in the field of photoresists.

[0019] As a further improvement of the present invention, the first porous surface includes a plurality of first clusters, adjacent first clusters are connected to each other or connected by strip fibers, and first holes are formed between adjacent first clusters.

[0020] In the membrane structure of the UPE porous membrane provided by the present invention, it can be clearly seen that there are a number of large and small first clusters on the first porous surface of the membrane, wherein some adjacent first clusters are directly connected to each other, while the remaining adjacent first clusters are connected by strip fibers, and the adjacent first clusters are surrounded by gully-shaped first holes; in addition, we also found that the lengths of adjacent first clusters and first holes in the longitudinal direction of the membrane (the membrane running direction during the membrane preparation process) are relatively uniform, while the lengths of adjacent first clusters and first holes in the transverse direction of the membrane (the width direction of the membrane) are relatively random, some large and some small, with a large difference, and are not uniform enough; the existence of such a structure is conducive to ensuring the stability of the first holes, and it is not easy to shrink or collapse, thereby ensuring that the membrane has a stable flow rate, and the membrane flow rate changes less during use; at the same time, it can further improve the tensile strength of the membrane to meet the needs of industrialization; in addition, the porous membrane also has less ineffective pore volume, lower specific surface area, less impurities, and is easier to clean.

[0021] As a further improvement of the present invention, the average length of the first clusters in the longitudinal direction of the membrane is 1-3.5 μm, and the average length of the first holes in the longitudinal direction of the membrane is 0.8-2.8 μm.

[0022] The longitudinal direction of the membrane is the membrane running direction; after measurement, it was found that the average length of the first cluster in the longitudinal direction of the membrane was 1-3.5μm, while the average length of the first hole in the longitudinal direction of the membrane was 0.8-2.8μm. The average length difference between the two is not large, which further explains that the lengths of adjacent first clusters and first holes in the longitudinal direction of the membrane (the membrane running direction during the membrane preparation process) are relatively uniform, which is more conducive to ensuring the stability of the first hole, and then ensuring the interception efficiency, and having a more stable and excellent capture ability for impurity particles;

[0023] The average length of the first clusters and the first holes in the longitudinal direction of the membrane can be reflected by the average length of a portion of the corresponding plane to reflect the average length of the entire plane. When actually measuring, the membrane surface can be characterized by an electron microscope to obtain a corresponding SEM image. By selecting a certain area, such as 1 μm 2 (1μm times 1μm) or 25μm 2 (5μm multiplied by 5μm), the specific area size depends on the actual situation, and then the length of the first clusters and the first holes in the selected area in the longitudinal direction of the membrane is measured by corresponding computer software or manually, and the average value is obtained by calculation, which is considered to be the average length of the first clusters and the first holes on the first porous surface in the longitudinal direction of the membrane. Of course, technical personnel in this field can also obtain the above parameters by other measurement methods. The above measurement methods are for reference only.

[0024] As a further improvement of the present invention, the main body includes two side regions and a middle region, wherein the middle region is a separation layer, a side region of the main body close to the second porous surface is a pre-filtration layer, and a side region of the main body close to the first porous surface is a support layer; the average pore size of the separation layer is smaller than the average pore size of the pre-filtration layer and the support layer;

[0025] The thicknesses of the pre-filter layer, the separation layer and the support layer are 10-40 μm, 5-20 μm and 10-45 μm respectively.

[0026] As a further improvement of the present invention, the average pore sizes of the pre-filtration layer, the separation layer and the support layer are in the range of 0.06-0.55 μm, 0.02-0.25 μm and 0.05-0.45 μm respectively.

[0027] In the main structure of the membrane, it can be clearly found that the main part of the membrane of the present invention is mainly divided into three regions, including two side regions and a middle region. The pore size of the middle region is relatively small, while the pore size of the two side regions is relatively large; the middle region is a separation layer. Since the pore size of the holes in the separation layer is small (the average pore size of the separation layer is 0.02-0.25 μm) and the thickness is 5-20 μm, the separation layer can fully intercept the impurity particles and ensure the filtration accuracy of the porous membrane; and in the two side regions, the area on one side of the main body close to the second porous surface is The pre-filter layer, the area on one side of the main body close to the first porous surface is the support layer; the pores in the pre-filter layer and the support layer are relatively large (the average pore size of the pre-filter layer is 0.06-0.55μm, and the average pore size of the support layer is 0.05-0.45μm), the thickness of the pre-filter layer is 10-40μm, and the thickness of the support layer is 10-45μm, which can improve the flow rate and dirt holding capacity of the membrane, the filtration speed is fast, more liquid can be filtered in a longer time, the time cost is low, and the economic benefit is high, which is particularly suitable for application in the field of photoresist;

[0028] On the other hand, it ensures that the porous membrane has good mechanical strength to meet various processing and assembly requirements.

[0029] In the present invention, an asymmetric membrane should be understood as a membrane in which the pre-filtration layer, the separation layer and the support layer are all composed of the same material, the three layers are combined into an integral structure, and are directly formed during the membrane preparation process; in the transition from the pre-filtration layer to the separation layer and the separation layer to the support layer, there is only a change in the membrane structure; in contrast, for example, a composite membrane has a multi-layer structure, in which a dense layer serving as a separation layer is applied in a separate process step to a porous, often microporous, support layer or support membrane, and the materials constituting the support layer and the separation layer in the composite membrane are often different.

[0030] The composition of photoresist generally includes polymer resin, photoacid generator, inhibitor, etc. During the dynamic collision process of finished product transportation, the polymer resin molecular chain in the photoresist often forms molecular cross-links with impurity metal as the bonding point, and finally presents flexible impurities in the form of gel. Such flexible impurities usually cannot be directly intercepted by the porous membrane; while in this patent, the asymmetric membrane with low specific surface area further expands the asymmetry of the inlet and outlet liquid surfaces of the UPE porous membrane, so that the liquid inlet surface to the separation layer (relatively large and tortuous holes are presented in the middle, so that such gel flexible impurities obtain sufficient kinetic energy in such holes to collide and form a gel of ultra-large physical volume, thereby being retained by the separation layer, and at the same time, the large space of the upper layer of the separation layer (generally the pre-filtration layer) also provides a greater ability to accommodate large impurities.

[0031] As a further improvement of the present invention, the average fiber diameter of the porous structure formed in the separation layer is smaller than the average fiber diameter of the porous structure formed in the support layer and the pre-filtration layer;

[0032] The average fiber diameters of the porous structures formed in the pre-filtration layer, the separation layer and the support layer are 0.03-0.35 μm, 0.01-0.14 μm and 0.035-0.40 μm respectively.

[0033] In the membrane body structure of the porous membrane provided by the present invention, the main area (three-layer area of ​​pre-filtration layer, separation layer and support layer) located between the first porous surface and the second porous surface includes continuous porous network fibers, and the holes for allowing fluid to pass through the porous membrane when used for filtration are formed in the network structure of the fibers, wherein the coarseness of the fiber cross-section can be considered as its average fiber diameter, and the inner diameter of the hole can be considered as its average pore size.

[0034] In addition, it is understood that "continuous" means that substantially all fibers are integrally connected to each other, such as being formed in one piece, without the need to use additional adhesives to connect them to each other, and the network of fibers cannot be separated from each other unless torn by external force. At the same time, the continuous network of fibers is also connected to the first porous surface and the second porous surface.

[0035] It can be seen from the membrane structure of the above-mentioned porous membrane that the average diameter of the fibers in each area of ​​the porous membrane is different; the average diameter of the fibers in the support layer is 0.035-0.40μm, and the fibers are relatively coarse, which ensures that the porous membrane has a large tensile strength and a high industrial practical value; in addition, each area of ​​the porous membrane body has a suitable fiber diameter, and when subjected to external force, the first hole is not easy to deform or shrink, and will not affect the interception efficiency, and the filtration quality is guaranteed; at the same time, the fibers inside each layer of the porous membrane are roughly evenly distributed. Although the thickness of the network-like fibers is not exactly the same, they are still uniform from the overall perspective of each layer, and do not show an obvious increasing or decreasing pattern.

[0036] As a further improvement of the present invention, the second porous surface is provided with a plurality of second groove-shaped holes; the pore area ratio of the second holes on the second porous surface is 30-50%; and the average pore diameter of the second holes is greater than the average pore diameter of the first holes.

[0037] In the membrane structure of the UPE porous membrane provided by the present invention, it can be clearly seen that there are a certain number of second holes with a certain pore size on the second porous surface of the membrane. It is well known that factors such as the pore size, number and shape of the membrane holes will have a great influence on the filtration accuracy (retention efficiency) of the membrane; the second holes on the second porous surface of the present invention are gully-shaped structures (i.e., the second holes are gully-like in shape), and the gully-shaped second holes are not easy to produce invalid pore volume, which further makes the specific surface area of ​​the porous membrane lower; and the pore area ratio of the second holes (the second pore area ratio) is The ratio of the surface area to the membrane area) is 30-50%, which is conducive to the porous membrane having a larger flow rate, facilitating the rapid passage of the fluid through the porous membrane and shortening the filtration time; if the second porous surface is used as the liquid inlet surface, the entire filter material can have a larger dirt holding capacity, a longer service life and high economic benefits; and the average pore size of the second holes is greater than that of the first holes, further illustrating that the UPE porous membrane is an asymmetric membrane, and the porous membrane also has a larger retention efficiency and excellent capture ability for flexible impurities in the form of gel generated during the transportation of the photoresist, and is therefore particularly suitable for application in the field of photoresists.

[0038] As a further improvement of the present invention, the second porous surface includes a plurality of second clusters, adjacent second clusters are connected to each other or connected by strip fibers, and second holes are formed between adjacent second clusters; the average length of the second clusters in the longitudinal direction of the membrane is 1.2-4μm, and the average length of the second holes in the longitudinal direction of the membrane is 1-3μm.

[0039] In the membrane structure of the UPE porous membrane provided by the present invention, it can be clearly seen that there are a number of large and small second clusters on the second porous surface of the membrane, wherein some adjacent second clusters are directly connected to each other, while the remaining adjacent second clusters are connected by strip fibers, and gully-shaped second holes are formed around the adjacent second clusters; in addition, we also found that the lengths of adjacent second clusters and second holes in the longitudinal direction of the membrane (the membrane running direction during the membrane preparation process) are relatively uniform, while the lengths of adjacent second clusters and second holes in the transverse direction of the membrane (the width direction of the membrane) are relatively random, some large and some small, with a large difference, and are not uniform enough; the existence of such a structure is conducive to ensuring the stability of the second holes, and it is not easy to shrink or collapse, thereby further ensuring that the membrane has a stable flow rate, and the membrane flow rate changes less during use; at the same time, it can further improve the tensile strength of the membrane to meet the needs of industrialization; in addition, the UPE porous membrane also has less ineffective pore volume, lower specific surface area, less impurities, and is easier to clean.

[0040] The longitudinal direction of the membrane is the direction in which the membrane runs. After measurement, it was found that the average length of the second clusters in the longitudinal direction of the membrane was 1.2-4μm, while the average length of the second holes in the longitudinal direction of the membrane was 1-3μm. The difference between the average lengths of the two is not large, which further illustrates that the lengths of adjacent second clusters and second holes in the longitudinal direction of the membrane (the direction in which the membrane is prepared) are relatively uniform, which is more conducive to ensuring the stability of the second holes, and then ensuring the interception efficiency, and having a more stable and better capture ability for impurity particles; at the same time, the UPE porous membrane has a larger dirt holding capacity and a longer service life.

[0041] As a further improvement of the present invention, under the conditions of a pressure of 0.03MPa and a temperature of 20°C, the time required for 50ml of water to pass through a porous membrane with a diameter of 47mm is 15-350s; the tensile strength of the porous membrane is 20-100MPa, and the elongation at break is 200%-800%; after the porous membrane is placed at a temperature of 120°C for 1 hour, its shrinkage rate is not more than 5%; the compression rate of the porous membrane is less than 15%; the pore closing temperature of the porous membrane is higher than 125°C.

[0042] By testing the flow rate of the UPE porous membrane, it is found that under the conditions of a pressure of 0.03 MPa and a temperature of 20°C, the time required for 50 ml of water to pass through the UPE porous membrane with a diameter of 47 mm is 15-350 seconds; this indicates that the UPE porous membrane has a large flow rate, the time required for the fluid to pass through the porous membrane is short, the time cost is low, and the economic benefit is high; it also indicates that the UPE porous membrane of the present invention is suitable for application in the field of photoresist;

[0043] The important indexes for evaluating the mechanical strength of a membrane are the tensile strength and elongation at break of the membrane; under certain conditions, the greater the tensile strength of the membrane, the better the mechanical strength of the membrane; the tensile strength of the UPE porous membrane of the present invention is 20-100MPa, and the elongation at break is 200%-800%, which indicates that the UPE porous membrane of the present invention has a large tensile strength and elongation at break, has good mechanical properties, has a high industrial practical value, and can fully meet market demand;

[0044] The UPE porous membrane was subjected to a heat resistance test. After the porous membrane of the present invention was placed at a temperature of 120° C. for 1 hour, it was found that its shrinkage rate was no more than 5%, indicating that the UPE porous membrane had high thermal stability. At a high temperature, the membrane pores were not easy to shrink or deform, thereby ensuring that the membrane had a high retention efficiency for a long time, the flow rate changed little during use, and the service life was long, further indicating that the membrane had a wide range of applications, and was particularly suitable for application in the field of photoresists.

[0045] During long-term use or processing of the liquid filter, the porous membrane needs to be able to maintain a good porous structure to ensure efficient interception efficiency and excellent capture of impurities; and the compression rate of the UPE porous membrane of the present invention is less than 15%, indicating that during various processing or long-term use of the porous membrane, the membrane pores of the porous membrane are not easily deformed, the porous structure remains stable, and the porous membrane is further guaranteed to have a stable flow rate, and the interception efficiency can be guaranteed for a long time; the compression rate in the present invention is obtained in the following manner: the UPE porous membrane is pressurized at 2MPa for 30 seconds at a temperature of 70°C, and then the pressure is released at 25°C for 30 seconds, and the compression rate is obtained from the ratio of the membrane thickness difference before and after pressurization to the membrane thickness before pressurization. In the present invention, if the compression rate of the UPE porous membrane is more than 15%, the following problems may arise: during long-term use or processing of the liquid filter, the porous membrane undergoes a pressure change above the necessary level, cannot maintain the original porous structure, and the water permeability becomes unstable; the filtration pressure abnormally rises due to the closure of the pores, and other problems.

[0046] In addition, the pore closing temperature of the UPE porous membrane of the present invention is higher than 125°C, preferably higher than 140°C; when the pore closing temperature of the porous membrane is higher than 125°C, the porosity of the UPE porous membrane will not be lost near the high-temperature treatment part or the high-temperature body contact part of the thermal bonding process during the actual processing of the UPE porous membrane, and the water permeability is easily maintained. Even after processing, the expected filtration area can be obtained, thereby ensuring the ideal flow rate and retention efficiency.

[0047] The present invention also provides a method for preparing a UPE porous membrane, comprising the following steps:

[0048] S1: adding polyethylene resin to a solvent system consisting of compound A and compound B, stirring and mixing, and forming a mixed material after uniform mixing; wherein the polyethylene resin comprises at least one ultra-high molecular weight polyethylene with a mass average molecular weight of more than 3 million; compound A is a non-solvent for the polyethylene resin; compound B is a solvent for the polyethylene resin; the mixed material comprises the following material compositions in parts by weight: polyethylene resin: 10-20 parts; compound A: 50-70 parts; compound B: 45-15 parts;

[0049] S2: heating the mixed material to melt and knead at a temperature of 220-250° C. to form a casting liquid, and then extruding it through a die head to form a liquid film on a carrier; the die head extrusion temperature is 180-220° C.;

[0050] S3: During the process from the liquid film being extruded from the die head to the liquid film and the carrier being relatively still, the liquid film is longitudinally stretched by 5-15 times;

[0051] S4: performing phase separation curing on the longitudinally stretched liquid film in a temperature environment of 15-120° C. to form a raw film; during the phase separation curing, the temperatures on both sides of the liquid film are different, and the temperature on one side is at least 40° C. higher than the temperature on the other side, and the phase separation curing time is 5-60S;

[0052] S5: extracting the solvent system with an extraction liquid, so that the solvent system is removed from the raw membrane to obtain an original membrane;

[0053] S6: heat-setting the original membrane to obtain a UPE porous membrane.

[0054] As a further improvement of the present invention, the compound A is at least one of dimethyl phthalate, dioctyl adipate, ethylene glycol diacetate, dimethyl carbonate, palm oil, and triacetin, and the compound B is at least one of paraffin oil, white oil, hydraulic oil, decalin, castor oil extract, and castor oil; the mass percentage of compound A in the solvent system is 65-80%, and the mass percentage of compound B is 35-20%.

[0055] As a further improvement of the present invention, the polyethylene resin is composed of 80-90% by mass of ultra-high molecular weight polyethylene with a mass average molecular weight of more than 3 million and 20-10% by mass of polyethylene with a mass average molecular weight of 1 million to 2 million and a density of 0.92-0.98 g / cm 3 Composition of high-density polyethylene.

[0056] As a further improvement of the present invention, the viscosity of the casting liquid in S2 when extruded through the die head is 80000-120000 CPS;

[0057] There is a space between the die head and the carrier for the liquid film to extend longitudinally, and the distance of the space is 5-20 mm; the pulling speed of the carrier on the liquid film is 0.5-2 m / min.

[0058] As a further improvement of the present invention, the extracting liquid is at least one of dichloromethane, acetone, methanol, ethanol, glycerol, tetrafluoroethane and isopropanol; the extraction temperature in S5 is 5-25°C; the extraction time is 1-5h; the temperature during heat setting in S6 is 100-130°C and the time is 200-600s.

[0059] The present invention prepares the UPE porous membrane based on the thermally induced phase separation method accompanied by liquid-liquid phase separation. When preparing, various materials are first mixed to form a mixed material, and the mixed material includes polyethylene resin and a corresponding solvent system. Ultra-high molecular weight polyethylene is referred to as UPE, which is a thermoplastic engineering plastic with a linear structure and excellent comprehensive performance. The porous membrane prepared by UPE can have high heat resistance and wear resistance, good mechanical properties, large tensile strength, and a wide range of applications; the polyethylene resin used in the present invention includes at least one with a mass average molecular weight of 3 million or more. The ultra-high molecular weight polyethylene of the present invention, that is, only one UPE with a mass average molecular weight of more than 3 million can be used as the film-forming raw material, or a compound can be used, for example, a UPE with a mass average molecular weight of more than 3 million and a high-density polyethylene with a mass average molecular weight of less than 3 million are compounded as the film-forming raw material; preferably, the polyethylene resin of the present invention is composed of 70-90% by mass of an ultra-high molecular weight polyethylene with a mass average molecular weight of more than 3 million and 10-30% by mass of a high-density polyethylene with a mass average molecular weight of 1 million to 2 million and a density of 0.92-0.98 g / cm 3 Compared with the use of only one ultra-high molecular weight polyethylene, the polyethylene resin compounded by ultra-high molecular weight polyethylene and high-density polyethylene is more conducive to obtaining a UPE porous membrane with relatively small pore size and high tensile strength;

[0060] The solvent system is composed of compound A and compound B, wherein compound A is a non-solvent for polyethylene resin, and non-solvent means that when heated to the boiling point of the compound at most, the compound cannot dissolve the polyethylene resin to form a homogeneous solution, and can only have a certain swelling effect on the polyethylene resin; compound A is at least one of dimethyl phthalate, dioctyl adipate, ethylene glycol diacetate, dimethyl carbonate, palm oil, and triacetin; compound B is a solvent for polyethylene resin, and solvent means that when heated to the boiling point of compound B at most, compound B can completely dissolve the polyethylene resin to form a homogeneous solution; compound B is at least one of paraffin oil, white oil, hydraulic oil, decalin, castor oil extract, and castor oil;

[0061] Compared with the use of a single solvent as the solvent system, the present invention uses a compound of a solvent and a non-solvent as the corresponding solvent system. Such a solvent system has the following advantages:

[0062] 1. The raw film formed after the phase separation of the liquid film is more likely to have holes with smaller pores, and more small holes are formed at the same time; this is because when the liquid film undergoes liquid-liquid phase separation and solidification (phase separation and solidification by thermal method) due to the change in temperature, diffusion exchange occurs between the non-solvent and the solvent, thereby further improving the phase separation and solidification rate. In addition, the content of compound A in the solvent system is greater than the content of compound B, that is, the non-solvent content is greater than the non-solvent content, which is conducive to a faster phase separation and solidification rate in the present invention, and crystal nuclei are more likely to precipitate, thereby forming more small holes, and more small holes are formed at the same time;

[0063] 2. It is easier to form fibers, and the fibers are easier to form, thereby ensuring that the UPE porous membrane has higher tensile strength and good mechanical properties. This is because due to the accelerated phase separation rate, the crystal nucleus is easier to precipitate, and the fibers are produced along the crystal nucleus, which makes it easier to form fibers; 3. By matching the temperature during phase separation and solidification, the final film formation is more likely to have gradient pores, thereby forming an asymmetric membrane, forming a porous membrane with the membrane structure required by the present invention; of course, if necessary, other substances such as antioxidants, nucleating agents, fillers and similar substances can be used as additives of the present invention to further improve a certain performance of the UPE porous membrane; the polyethylene resin and the corresponding solvent system (including compound A and compound B) can be stirred and mixed at a temperature of 100-140° C. for 10-24 hours to form a corresponding mixed material;

[0064] Next, the mixed material is put into an extruder and heated and melted and kneaded at a temperature of 220-250° C. for 10-30 minutes, thereby ensuring that the polyethylene resin is completely melted in the corresponding solvent system, and the shape is uniform and the casting liquid is stable; the solid content of the casting liquid of the present invention is preferably 10-20%. If the solid content is too low, the tensile strength of the final film will be too low, the mechanical strength will be poor, and the requirements of practical applications cannot be met; if the solid content is too high, the viscosity of the casting liquid will be too high, the requirements for the mechanical equipment used will be too high, the production cost will be too high, and mass production cannot be achieved;

[0065] Then, it is extruded through a die (die forming) to form a flat liquid film on a carrier (the carrier can be a roller or other carrier). In the present invention, the extrusion temperature of the die is 180-220°C. During the process from the extrusion of the casting liquid through the die to the relative stillness of the liquid film and the carrier, the temperature also changes to a certain extent due to the sudden drop in pressure, which leads to a certain microphase separation of the liquid film in this process, that is, a certain number of particles (crystal nuclei) with a certain diameter appear in the liquid film. These particles will collide and fuse while growing in the form of larger particles, thereby forming corresponding holes. At the same time, in this process, In the first process, the liquid film is longitudinally extended, and the role of the longitudinal extension is to increase the distance between the particles; then it is conducive to the subsequent formation of the first and second gully-shaped holes on the outer surface of the membrane, so that the specific surface area of ​​the membrane is very low, and the extension multiple is controlled to be 5-15. The liquid film is longitudinally extended to a suitable size, which is conducive to ensuring that the porous membrane has a suitable pore size and porosity. While ensuring that the porous membrane has a low specific surface area, it also ensures that the porous membrane has a large retention efficiency and a high flow rate; the process from the casting liquid being extruded through the die head to the liquid film and the carrier being relatively still mainly includes two steps. The first step is to extrude the casting liquid from the die head. In the step from the first step to the step when the liquid film just falls on the carrier, there is a certain space between the die head and the carrier, and in this space, the liquid film will undergo a certain longitudinal extension due to the effect of gravity; after continuous research, it is found that the appropriate distance of the space is controlled at 5-20mm; the second step is from the step when the liquid film just falls on the carrier (at this time, the liquid film and the carrier are in relative motion) to the step when the liquid film and the carrier remain relatively still. Since the liquid film needs to be increased from a speed of 0 to the same speed as the carrier movement, the carrier must have a traction force on the liquid film and a suitable traction speed for the liquid film. In the present invention, the carrier has a traction force on the liquid film. The pulling speed is controlled at 0.5-2m / min; therefore, in the present invention, the distance between the die head and the carrier and the pulling speed of the carrier on the liquid film are adjusted to ensure that the liquid film is longitudinally stretched by an appropriate multiple; in addition, the viscosity of the liquid film needs to be controlled, because if the viscosity of the liquid film is too large, it is easy to be broken; and if the viscosity of the liquid film is too small, the mechanical strength of the film cannot be guaranteed. In the present invention, the viscosity of the casting liquid when it is extruded through the die head (that is, when the liquid film is just formed) is 80000-120000 CPS, which is more conducive to obtaining the UPE porous membrane with the ideal membrane structure required by the present invention;

[0066] Then, the longitudinally stretched liquid film is subjected to phase separation and solidification at a temperature of 15-120°C. At a relatively high temperature, a single homogeneous solution can be formed between the solvent system composed of compound A and compound B and the polyethylene resin. As the temperature of the system decreases, the homogeneous solution begins to undergo liquid-liquid stratification, and two liquid phases coexist, i.e., one phase with a high polymer content and another phase with a low polymer content appear, followed by phase separation and solidification. In the present invention, the solvent system is a combination of a solvent and a non-solvent. In addition to the phase separation caused by the change in temperature, the diffusion exchange between the solvent and the non-solvent will also accelerate the phase separation and solidification rate, thereby forming a small-pore membrane (the faster the phase separation rate, the smaller the pore size of the formed hole), i.e., forming the nanostructured membrane required by the present invention. Membrane; in order to ensure that the final film is an asymmetric membrane in the present invention, the phase solidification rates on both sides of the liquid membrane are required to be different, that is, one side is high and the other side is low. At the same time, in order to further ensure that the membrane has a higher flow rate and form a certain number of larger pores, the temperature difference on both sides of the liquid membrane is at least 40°C, so as to obtain the membrane structure required by the present invention; when performing phase solidification, the selection of factors such as the phase solidification temperature and the phase solidification time is extremely critical. These factors determine the speed of the phase solidification and whether a membrane with an ideal membrane structure and membrane pore size can be obtained in the end; the phase solidification time in the present invention is 5-60s, which is relatively short, so as to facilitate the UPE porous membrane with the ideal membrane structure we need;

[0067] After the liquid film phase separation is completed, a raw film is formed, and then extraction is performed. The solvent system is removed from the raw film by an extracting liquid to obtain an original film; the extracting liquid is at least one of dichloromethane, acetone, methanol, ethanol, propylene glycol, tetrafluoroethane and isopropanol, the extraction temperature is 5-25°C, and the extraction time is 1-5h; by selecting a suitable extracting liquid and extraction conditions, the solvent system is ensured to be completely removed from the raw film, and the time required for extraction is short, thereby reducing the time cost; after the extraction is completed, the original film is heat-set, and the role of heat-setting is to eliminate the internal stress generated by the extraction on the one hand, and to finally set the membrane pores of the original film on the other hand, thereby ensuring that the membrane pores will not basically change, thereby obtaining a UPE porous membrane with the required membrane pore structure; the UPE porous membrane finally obtained has a lower specific surface area, is easy to clean, and impurities are not easy to remain; at the same time, it has excellent capture performance for impurity particles and high interception efficiency; in addition, it also has a large filtration speed, the time required for the fluid to pass through the porous membrane is short, the time cost is low, and the application range is wide, and it is particularly suitable for application in the field of photoresists.

[0068] As a further improvement of the present invention, a use of a UPE porous membrane, wherein the UPE porous membrane is used to filter photoresist; a mixed solvent of 70 mass% propylene glycol monomethyl ether and 30 mass% propylene glycol monomethyl ether acetate is used as a detection agent to perform a cleaning test on the UPE porous membrane before use, and the impurity content is not higher than 0.08 mg / membrane per square meter.

[0069] The UPE porous membrane of the present invention is particularly suitable for application in the field of photoresist filtration; after the UPE porous membrane is made into a capsule or a cartridge filter element, it is cleaned with a cleaning solution; before being put into use, an organic solvent OK73 (a mixed solvent of 70% by mass of propylene glycol monomethyl ether and 30% by mass of propylene glycol monomethyl ether acetate) is used as a detection agent to perform a cleanliness test, and it is found that the impurity content (impurities include metal ions, organic matter, particles, etc.) is not higher than 0.08 mg / membrane per square meter, the cleanliness is high, and the needs of practical applications are met.

[0070] As a further improvement of the present invention, when the UPE porous membrane is used to filter photoresist, the second porous surface is the liquid inlet surface and the first porous surface is the liquid outlet surface.

[0071] When filtering photoresist, the large-pore surface (second porous surface) of the UPE porous membrane is used as the liquid inlet surface, and the small-pore surface (first porous surface) of the porous membrane is used as the liquid outlet surface. This not only ensures that the porous membrane has excellent capture performance for various impurity particles in the photoresist and has high filtration accuracy; it also has a higher dirt holding capacity, a longer service life, and high economic benefits.

[0072] As a further improvement of the present invention, a pleated filter element with a UPE porous membrane with a low specific surface area includes a center rod and a UPE porous membrane located on the periphery of the center rod, the UPE porous membrane is folded to form pleats, the pleats have pleat valleys close to the center rod side and pleat peaks on the periphery, the UPE porous membrane has an upstream side and a downstream side, the upstream side is connected to an inlet, and the downstream side is connected to an outlet, and the UPE porous membrane is the UPE porous membrane described in any one of claims 1-10.

[0073] The folded filter element made of the UPE porous membrane of the present invention is easier to clean and only requires less flushing liquid to make the filter material have a higher cleanliness, impurities are not easily left, and it can better meet the needs of practical applications, thereby obtaining a photoresist with excellent performance.

[0074] Beneficial effects of the present invention: The UPE porous membrane provided by the present invention is an asymmetric membrane, which has a more optimized membrane structure than the existing filter membrane materials, comprising a first porous surface, a second porous surface and a main body located between the first porous surface and the second porous surface, wherein the main body has a non-directional tortuous passage; the first porous surface has a first gully-shaped hole; the pore area ratio of the first hole on the first porous surface is 20-35%, and the IPA bubble point is 0.15-0.65MPa; so that the UPE porous membrane has a retention efficiency of more than 95% for impurity particles with a particle size of 20-200nm, has excellent capture performance, and has a high retention efficiency; at the same time, it also has a large filtration speed, and the time required for the fluid to pass through the porous membrane is short, and the time cost is low; in addition, the UPE porous membrane has a small ineffective pore volume and a very low specific surface area, which is only 7-24m 2 / g, easy to clean, various impurities are not easy to remain in the UPE porous membrane, and high-cleanliness filter material is easy to prepare; it is particularly suitable for application in the field of photoresist filtration; the preparation method provided by the present invention can prepare the UPE porous membrane conveniently, quickly and effectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 This is a scanning electron microscope (SEM) image of the first porous surface of the UPE porous membrane prepared in Example 1, wherein the magnification is 500×;

[0076] Figure 2 This is a further magnified scanning electron microscope (SEM) image of the first porous surface of the UPE porous membrane prepared in Example 1, wherein the magnification is 2000×;

[0077] Figure 3 This is a scanning electron microscope (SEM) image of the second porous surface on the UPE porous membrane prepared in Example 1, wherein the magnification is 500×;

[0078] Figure 4 This is a further magnified scanning electron microscope (SEM) image of the second porous surface on the UPE porous membrane prepared in Example 1, wherein the magnification is 2000×;

[0079] Figure 5 This is a scanning electron microscope (SEM) image of the cross section of the UPE porous membrane prepared in Example 1, wherein the magnification is 500×;

[0080] Figure 6 This is a further enlarged scanning electron microscope (SEM) image of the cross section of the UPE porous membrane prepared in Example 1, wherein the magnification is 2000×;

[0081] Figure 7 Schematic diagram of the device for testing the flow rate of the ultra-high molecular weight polyethylene porous membrane of the present invention;

[0082] Figure 8 Schematic diagram of the device for testing the filtration accuracy (retention efficiency) of the ultra-high molecular weight polyethylene porous membrane of the present invention. DETAILED DESCRIPTION

[0083] In order to more clearly explain the overall concept of the present application, the following is a detailed description by way of examples. Example 1 A method for preparing a UPE porous membrane comprises the following steps:

[0084] S1: adding polyethylene resin to a solvent system consisting of compound A and compound B, stirring and mixing, and forming a mixed material after uniform mixing; wherein compound A is a non-solvent for polyethylene resin; compound B is a solvent for polyethylene resin; the mixed material comprises the following material compositions by weight: polyethylene resin: 15 parts; compound A: 60 parts; compound B: 25 parts; wherein compound A is dimethyl phthalate, and compound B is paraffin oil;

[0085] The polyethylene resin is composed of 80% by mass of ultra-high molecular weight polyethylene with a mass average molecular weight of more than 3 million and 20% by mass of polyethylene with a mass average molecular weight of 1-2 million and a density of 0.92-0.98 g / cm 3 Composition of high-density polyethylene;

[0086] S2: The mixed material is heated and melted at a temperature of 240° C. to form a casting liquid, and then extruded through a die to form a liquid film on the carrier; the die extrusion temperature is 200° C. The viscosity of the casting liquid when extruded through the die is 100,000 CPS;

[0087] S3: During the process from the extrusion of the liquid film from the die head to the relative stillness of the liquid film and the carrier, the liquid film is longitudinally extended by 10 times; there is a space between the die head and the carrier for the liquid film to longitudinally extend, and the distance of the space is 13 mm; the pulling speed of the carrier on the liquid film is 1.2 m / min;

[0088] S4: the liquid film after longitudinal stretching is subjected to phase-separation curing in an environment where the temperature on one side is 25° C. and the temperature on the other side is 90° C. The phase-separation curing time is 30 seconds. After the phase-separation curing is completed, a green film is formed;

[0089] S5: extracting the solvent system with an extraction liquid, wherein the extraction liquid is isopropanol, the extraction temperature is 15° C., and the extraction time is 3 h, so that the solvent system is removed from the raw membrane to obtain the original membrane;

[0090] S6: heat setting the original membrane at a temperature of 120° C. for 300 seconds to obtain a UPE porous membrane.

[0091] Embodiment 2 A method for preparing a UPE porous membrane comprises the following steps:

[0092] S1: Add polyethylene resin to a solvent system consisting of compound A and compound B, stir and mix, and form a mixed material after uniform mixing; wherein compound A is a non-solvent for polyethylene resin; compound B is a solvent for polyethylene resin; the mixed material comprises the following substances in parts by weight: polyethylene resin: 20 parts; compound A: 70 parts; compound B: 30 parts; wherein compound A is triacetin, and compound B is castor oil extract; the polyethylene resin is composed of 70% by mass of ultra-high molecular weight polyethylene with a mass average molecular weight of more than 3 million and 30% by mass of a polyethylene with a mass average molecular weight of 1-2 million and a density of 0.92-0.98 g / cm 3 Composition of high-density polyethylene;

[0093] S2: The mixed material is heated and melted at a temperature of 250° C. to form a casting liquid, which is then extruded through a die to form a liquid film on a carrier; wherein the die extrusion temperature is 215° C.; and the viscosity of the casting liquid when extruded through the die is 110,000 CPS;

[0094] S3: During the process from the extrusion of the liquid film from the die head to the relative stillness of the liquid film and the carrier, the liquid film is longitudinally extended by 8 times; there is a space between the die head and the carrier for the liquid film to longitudinally extend, and the distance of the space is 11 mm; the pulling speed of the carrier on the liquid film is 0.9 m / min;

[0095] S4: the liquid film after longitudinal stretching is subjected to phase-separation curing in an environment where the temperature on one side is 25° C. and the temperature on the other side is 105° C. The phase-separation curing time is 45 seconds. After the phase-separation curing is completed, a green film is formed;

[0096] S5: extracting the solvent system with an extraction liquid, so that the solvent system is removed from the raw membrane to obtain an original membrane; wherein the extraction liquid is acetone, the extraction temperature is 20° C., and the extraction time is 2 h;

[0097] S6: heat setting the original membrane at a temperature of 115° C. for 400 seconds to obtain a UPE porous membrane.

[0098] Embodiment 3 A method for preparing a UPE porous membrane comprises the following steps:

[0099] S1: Add polyethylene resin to a solvent system consisting of compound A and compound B, stir and mix, and form a mixed material after uniform mixing; wherein compound A is a non-solvent for polyethylene resin; compound B is a solvent for polyethylene resin; the mixed material comprises the following substances in parts by weight: polyethylene resin: 18 parts; compound A: 65 parts; compound B: 25 parts; compound A is ethylene glycol diacetate, and compound B is white oil; the polyethylene resin is composed of 75% by mass of ultra-high molecular weight polyethylene with a mass average molecular weight of more than 3 million and 25% by mass of a mass average molecular weight of 1-2 million and a density of 0.92-0.98 g / cm 3 Composition of high-density polyethylene;

[0100] S2: The mixed material is heated and melted at a temperature of 245°C to form a casting liquid, which is then extruded through a die to form a liquid film on the carrier; the die extrusion temperature is 210°C; the viscosity of the casting liquid when extruded through the die is 115000 CPS;

[0101] S3: During the process from the extrusion of the liquid film from the die head to the relative stillness of the liquid film and the carrier, the liquid film is longitudinally extended by 6 times; there is a space between the die head and the carrier for the liquid film to undergo longitudinal extension, and the distance of the space is 8 mm; the pulling speed of the carrier on the liquid film is 0.6 m / min.

[0102] S4: the liquid film after longitudinal stretching is subjected to phase-separation curing in an environment where the temperature on one side is 30° C. and the temperature on the other side is 120° C. The phase-separation curing time is 60 seconds. After the phase-separation curing is completed, a green film is formed;

[0103] S5: extracting the solvent system with an extraction liquid, so that the solvent system is removed from the raw membrane to obtain an original membrane; wherein the extraction liquid is dichloromethane, the extraction temperature is 10° C., and the extraction time is 4 hours;

[0104] S6: heat setting the original film at a temperature of 125° C. for 250 seconds to obtain a UPE porous film.

[0105] Embodiment 4 A method for preparing a UPE porous membrane comprises the following steps:

[0106] S1: Add polyethylene resin to a solvent system consisting of compound A and compound B, stir and mix, and form a mixture after uniform mixing; wherein compound A is a non-solvent for polyethylene resin; compound B is a solvent for polyethylene resin; the mixture comprises the following substances in parts by weight: polyethylene resin: 14 parts; compound A: 64 parts; compound B: 22 parts; wherein compound A is palm oil, and compound B is decalin; the polyethylene resin is composed of 85% by mass of ultra-high molecular weight polyethylene with a mass average molecular weight of more than 3 million and 15% by mass of high-density polyethylene with a mass average molecular weight of 1-2 million and a density of 0.92-0.98 g / cm3; S2: Heat the mixture at a temperature of 235°C to melt and knead to form a casting liquid, and then extrude it through a die to form a liquid film on a carrier; the die extrusion temperature is 195°C; the viscosity of the casting liquid when extruded through the die is 95000 CPS;

[0107] S3: During the process from the extrusion of the liquid film from the die head to the relative stillness of the liquid film and the carrier, the liquid film is longitudinally extended by 11 times; there is a space between the die head and the carrier for the liquid film to longitudinally extend, and the distance of the space is 15 mm; the pulling speed of the carrier on the liquid film is 1.4 m / min;

[0108] S4: the liquid film after longitudinal stretching is subjected to phase-separation curing in an environment where the temperature on one side is 20° C. and the temperature on the other side is 65° C. The phase-separation curing time is 12 seconds. After the phase-separation curing is completed, a green film is formed;

[0109] S5: extracting the solvent system with an extraction liquid, so that the solvent system is removed from the raw membrane to obtain an original membrane; wherein the extraction liquid is ethanol, the extraction temperature is 5° C., and the extraction time is 5 h;

[0110] S6: heat setting the original membrane at a temperature of 130° C. for 200 seconds to obtain a UPE porous membrane.

[0111] Embodiment 5 A method for preparing a UPE porous membrane comprises the following steps:

[0112] S1: adding polyethylene resin to a solvent system consisting of compound A and compound B, stirring and mixing, and forming a mixed material after uniform mixing; wherein the polyethylene resin is an ultra-high molecular weight polyethylene with a mass average molecular weight of more than 3 million; compound A is a non-solvent for the polyethylene resin; compound B is a solvent for the polyethylene resin; the mixed material comprises the following material compositions in parts by weight: polyethylene resin: 12 parts; compound A: 58 parts; compound B: 27 parts; compound A is dioctyl adipate, and compound B is hydraulic oil;

[0113] S2: The mixed material is heated and melted at a temperature of 230°C to form a casting liquid, which is then extruded through a die to form a liquid film on a carrier; the die extrusion temperature is 190°C; the viscosity of the casting liquid when extruded through the die is 90000CPS;

[0114] S3: During the process from the extrusion of the liquid film from the die head to the relative stillness of the liquid film and the carrier, the liquid film is longitudinally extended by 13 times; there is a space between the die head and the carrier for the liquid film to longitudinally extend, and the distance of the space is 17 mm; the pulling speed of the carrier on the liquid film is 1.6 m / min;

[0115] S4: the liquid film after longitudinal stretching is subjected to phase-separation curing in an environment where the temperature on one side is 20° C. and the temperature on the other side is 75° C. The phase-separation curing time is 20 seconds. After the phase-separation curing is completed, a green film is formed;

[0116] S5: extracting the solvent system with an extraction liquid, so that the solvent system is removed from the raw membrane to obtain an original membrane; wherein the extraction liquid is glycerol, the extraction temperature is 18° C., and the extraction time is 3.5 h;

[0117] S6: heat setting the original membrane at a temperature of 105° C. for 500 seconds to obtain a UPE porous membrane.

[0118] Embodiment 6 A method for preparing a UPE porous membrane comprises the following steps:

[0119] S1: adding polyethylene resin to a solvent system consisting of compound A and compound B, stirring and mixing, and forming a mixed material after uniform mixing; wherein the polyethylene resin is an ultra-high molecular weight polyethylene with a mass average molecular weight of more than 3 million; compound A is a non-solvent for the polyethylene resin; compound B is a solvent for the polyethylene resin; the mixed material comprises the following material compositions in parts by weight: polyethylene resin: 10 parts; compound A: 60 parts; compound B: 20 ​​parts; wherein compound A is dimethyl carbonate, and compound B is white oil;

[0120] S2: The mixed material is heated and melted at a temperature of 225°C to form a casting liquid, which is then extruded through a die to form a liquid film on a carrier; the die extrusion temperature is 180°C; the viscosity of the casting liquid when extruded through the die is 85000CPS;

[0121] S3: During the process from the extrusion of the liquid film from the die head to the relative stillness of the liquid film and the carrier, the liquid film is longitudinally extended by 15 times; there is a space between the die head and the carrier for the liquid film to longitudinally extend, and the distance of the space is 19 mm; the pulling speed of the carrier on the liquid film is 1.9 m / min;

[0122] S4: the liquid film after longitudinal stretching is subjected to phase-separation curing in an environment where the temperature on one side is 30° C. and the temperature on the other side is 85° C. The phase-separation curing time is 25 seconds. After the phase-separation curing is completed, a green film is formed;

[0123] S5: extracting the solvent system with an extraction liquid, so that the solvent system is removed from the raw membrane to obtain an original membrane; wherein the extraction liquid is tetrafluoroethane, the extraction temperature is 13° C., and the extraction time is 4.5 h;

[0124] S6: heat setting the original membrane at a temperature of 110° C. for 450 seconds to obtain a UPE porous membrane.

[0125] I. Structural Characterization

[0126] The morphology of the UPE porous membrane obtained in each embodiment was characterized by scanning electron microscopy, and then the required data was obtained; the specific results are shown in the following table:

[0127]

[0128]

[0129]

[0130] As can be seen from the above table, in the UPE porous membranes prepared in Examples 1-6 of the present invention, there are a suitable number of first holes with a suitable pore size on the first porous surface, and a suitable number of second holes with a suitable pore size on the second porous surface; the existence of such a structure is conducive to ensuring the stability of the first holes and the second holes, and it is not easy to shrink or collapse, thereby ensuring that the membrane has a stable flow rate. During use, the membrane flow rate changes less; and it has a large flow rate, which is convenient for the fluid to pass through the porous membrane quickly, shortening the filtration time, and also has a large tensile strength to meet the needs of practical applications; at the same time, it can further improve the tensile strength of the membrane to meet the needs of industrialization; in addition, the porous membrane also has less ineffective pore volume, a lower specific surface area, less impurities, and is easier to clean.

[0131]

[0132] The UPE porous membranes prepared in Examples 1-6 of the present invention have a suitable membrane structure, which, on the one hand, ensures that the impurity particles are fully intercepted and the filtering accuracy of the porous membrane is ensured; on the other hand, the flow rate and the dirt holding capacity of the membrane can be increased, the filtering speed is fast, and more liquid can be filtered in a longer time, the time cost is low, and the economic benefit is high, and it is particularly suitable for application in the field of photoresist;

[0133]

[0134] The UPE porous membranes prepared in Examples 1-6 of the present invention all have a lower specific surface area and a surface area inside the membrane per unit membrane area, which means that the UPE porous membrane has fewer invalid pores, which can ensure that the porous membrane can perform effective filtration while also ensuring that the cleaning of the UPE porous membrane becomes relatively easier (only less deionized water and fewer rinses are required to obtain a UPE filter material that meets actual needs) and impurities (such as metal particles, organic matter and other impurities) are not easy to remain, thereby ensuring the cleanliness of the membrane and the filter element, which is then beneficial to subsequent photoresist filtration and obtaining a photoresist with excellent performance.

[0135] Performance characteristics

[0136] Water flow rate test (test device such as Figure 7 )

[0137] Experimental steps Step 1: Place the sample to be tested moistened with IPA on the vacuum filtration support, close valve 2 on the vacuum filtration support, open valve 1, start the vacuum pump, adjust the pressure to the test pressure of 0.03 MPa, and then close valve 1.

[0138] Step 2: Put 50 ml of test liquid (water) into the plastic measuring cylinder of the vacuum filtration support, open valve 2, start timing from a certain scale and stop timing at another scale;

[0139] Step 3: After the test is completed, record the value displayed on the stopwatch. When all the test liquid has passed through the filter membrane, close valve 2 on the bracket and take out the sample.

[0140] The tensile strength and elongation at break of each sample were tested using a universal tensile testing machine;

[0141]

[0142]

[0143] The UPE porous membranes prepared in Examples 1-6 of the present invention all have a relatively high filtration speed and a relatively low time cost; at the same time, they have a relatively high tensile strength and elongation at break, and can meet various assembly and processing requirements, thus truly realizing industrialization.

[0144] Filtration accuracy test: The interception efficiency of the filter membrane obtained in each example was tested.

[0145] Experimental equipment: Tianjin Logan particle counter KB-3; Experimental preparation: press Figure 8 Assemble the experimental device, ensure that the device is clean, and rinse the device with ultrapure water; take a sample with a diameter of 47 mm, install it in a butterfly filter, and ensure that the assembled filter has good airtightness.

[0146] Experimental steps: Pour the challenge solution into the storage tank, pay attention to the exhaust of the butterfly filter, pressurize to 10kPa, use a clean bottle to collect the filtrate downstream of the butterfly; use a particle counter to test the number of particles in the filtrate and the original solution.

[0147] Interception efficiency:

[0148] In the formula: η───interception efficiency, %; n0───number of particles in the original solution, the average value of 5 groups of counts, pieces; n1───number of particles in the filtrate, the average value of 5 groups of counts, pieces.

[0149] The interception efficiency test results of each example are as follows:

[0150]

[0151] It can be seen from the above table that the UPE porous membranes prepared in Examples 1-6 of the present invention have a large filtration accuracy, and their interception efficiency is above 95%. They have a strong capture ability for impurity particles (such as standard gold particle impurities), meet actual industrial needs, and are particularly suitable for application in the field of photoresists.

[0152] Cleaning efficiency test

[0153] Comparative Example 1: A method for preparing a polyolefin porous membrane with high porosity and large specific surface area according to a Chinese patent application number CN201910132223.6. The UPE porous membrane prepared by the preparation method (Example 1) (the specific surface area of ​​the porous membrane is 82 m 2 / g)

[0154] The UPE porous membranes (membrane area of ​​0.4 m 2 ) was made into a corresponding capsule filter element, and then rinsed with 40L of deionized water. After the rinsing was completed, the filter element was immersed in an OK73 detection agent (a mixed solvent of 70% by mass of propylene glycol monomethyl ether and 30% by mass of propylene glycol monomethyl ether acetate) for 24 hours, and then the impurity content in the detection agent was measured (impurities mainly included metal ions and organic matter, metal ions were measured by ICPMS, and organic matter was measured by GCMS), and the test results were as follows;

[0155] Sample Impurity content (mg / m2 of membrane) Example 1 0.42 Example 2 0.47 Example 3 0.51 Example 4 0.34 Example 5 0.35 Example 6 0.38 Comparative Example 1 0.96

[0156] It can be seen from the above table that compared with the UPE porous membrane of Comparative Example 1, the UPE porous membranes prepared in Examples 1-6 are easier to clean, and only require less deionized water and fewer rinses to obtain UPE filter materials that meet actual needs. Impurities (such as metal particles, organic matter and other impurities) are not easy to remain, ensuring the cleanliness of the membrane and the filter element, which is beneficial to subsequent photoresist filtration and obtaining photoresist with excellent performance.

[0157] The UPE porous membranes (membrane area of ​​0.4 m 2 ) was made into a corresponding capsule filter element, which was cleaned with a cleaning agent and then filtered for photoresist. At the same time, a gas detector was used to collect the amount of gas generated by the UPE porous membrane during the filtration process (the amount of gas = the amount of gas generated by the filter element with the membrane - the amount of gas generated by the blank filter element without the membrane). The results are as follows:

[0158] Sample Gas volume / ml Example 1 0.22 Example 2 0.24 Example 3 0.27 Example 4 0.17 Example 5 0.19 Example 6 0.21 Comparative Example 1 0.45

[0159] As can be seen from the above table, compared with the UPE porous membrane of Comparative Example 1, the UPE porous membranes prepared in Examples 1-6 will produce fewer bubbles during the photoresist filtration process, reducing the impact of bubbles on the properties of the photoresist, which is conducive to obtaining a photoresist with better properties;

[0160] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A UPE porous membrane with a low specific surface area, comprising a first porous surface, a second porous surface and a body located between the first porous surface and the second porous surface, wherein the body has a non-directional tortuous path, characterized in that: The specific surface area of ​​the UPE porous membrane is 7-24m 2 / g; The UPE porous membrane has a retention efficiency of greater than 95% for impurity particles with a particle size of 20-200 nm; The IPA bubble point of the UPE porous membrane is 0.15-0.65 MPa; The first porous surface has a plurality of groove-shaped first holes, and the first porous surface includes a plurality of first clusters, and adjacent first clusters are connected to each other or connected by strip fibers, and first holes are formed between adjacent first clusters; the pore area ratio of the first holes on the first porous surface is 20-35%; The polyolefin composition constituting the UPE porous membrane includes at least ultra-high molecular weight polyethylene having a mass average molecular weight of more than 3 million; The UPE porous membrane is an asymmetric membrane; the second porous surface has a plurality of second holes; the average pore size of the second holes is greater than the average pore size of the first holes.

2. A UPE porous membrane with low specific surface area according to claim 1, characterized in that: The thickness of the UPE porous membrane is 30-100 μm, the porosity is 30-45%, and the surface area of ​​the membrane inside the unit membrane area is 0.058-0.

267.

3. A UPE porous membrane with low specific surface area according to claim 1, characterized in that: The average length of the first clusters in the longitudinal direction of the membrane is 1-3.5 μm, and the average length of the first holes in the longitudinal direction of the membrane is 0.8-2.8 μm.

4. A UPE porous membrane with low specific surface area according to claim 1, characterized in that: The main body comprises two side regions and a middle region, wherein the middle region is a separation layer, a side region of the main body close to the second porous surface is a pre-filtration layer, and a side region of the main body close to the first porous surface is a support layer; the average pore size of the separation layer is smaller than the average pore size of the pre-filtration layer and the support layer; The thicknesses of the pre-filtration layer, the separation layer and the support layer are 10-40 μm, 5-20 μm and 10-45 μm respectively.

5. A UPE porous membrane with low specific surface area according to claim 4, characterized in that: The average pore sizes of the pre-filtration layer, the separation layer and the support layer are in the range of 0.06-0.55 μm, 0.02-0.25 μm and 0.05-0.45 μm respectively.

6. A UPE porous membrane with low specific surface area according to claim 4, characterized in that: The average fiber diameter of the porous structure formed in the separation layer is smaller than the average fiber diameter of the porous structure formed in the support layer and the pre-filtration layer; The average fiber diameters of the porous structures formed in the pre-filtration layer, the separation layer and the support layer are 0.03-0.35 μm, 0.01-0.14 μm and 0.035-0.40 μm respectively.

7. A UPE porous membrane with low specific surface area according to claim 1, characterized in that: The second porous surface is provided with a plurality of second gully-shaped holes; the pore area ratio of the second holes on the second porous surface is 30-50%.

8. A UPE porous membrane with low specific surface area according to claim 7, characterized in that: The second porous surface includes a plurality of second clusters, adjacent second clusters are connected to each other or connected by strip fibers, and second holes are formed between adjacent second clusters; The average length of the second clusters in the longitudinal direction of the membrane is 1.2-4 μm, and the average length of the second holes in the longitudinal direction of the membrane is 1-3 μm.

9. A UPE porous membrane with low specific surface area according to claim 1, characterized in that: Under the conditions of pressure of 0.03MPa and temperature of 20℃, the time required for 50ml of water to pass through a porous membrane with a diameter of 47mm is 15-350s; The tensile strength of the porous membrane is 20-100 MPa, and the elongation at break is 200%-800%; After the porous film is placed at a temperature of 120° C. for 1 hour, its shrinkage rate is no more than 5%; The compression rate of the porous membrane is less than 15%; The pore closing temperature of the porous membrane is higher than 125°C.

10. The method for preparing a UPE porous membrane with a low specific surface area according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1: adding polyethylene resin to a solvent system consisting of compound A and compound B, stirring and mixing, and forming a mixed material after uniform mixing; wherein the polyethylene resin includes at least one ultra-high molecular weight polyethylene with a mass average molecular weight of more than 3 million; compound A is a non-solvent for the polyethylene resin; and compound B is a solvent for the polyethylene resin; The mixture comprises the following components by weight: Polyethylene resin: 10-20 parts; Compound A: 50-70 parts; Compound B: 45-15 parts; S2: heating the mixed material to melt and knead at a temperature of 220-250° C. to form a casting liquid, and then extruding it through a die head to form a liquid film on a carrier; the die head extrusion temperature is 180-220° C.; S3: During the process from the liquid film being extruded from the die head to the liquid film and the carrier being relatively still, the liquid film is longitudinally stretched by 5-15 times; S4: performing phase separation curing on the longitudinally stretched liquid film in a temperature environment of 15-120° C. to form a raw film; during the phase separation curing, the temperatures on both sides of the liquid film are different, and the temperature on one side is at least 40° C. higher than the temperature on the other side, and the phase separation curing time is 5-60S; S5: extracting the solvent system with an extraction liquid, so that the solvent system is removed from the raw membrane to obtain an original membrane; S6: heat-setting the original membrane to obtain a UPE porous membrane.

11. The method for preparing a UPE porous membrane with a low specific surface area according to claim 10, characterized in that: The compound A is at least one of dimethyl phthalate, dioctyl adipate, ethylene glycol diacetate, dimethyl carbonate, palm oil, and triacetin; the compound B is at least one of paraffin oil, white oil, hydraulic oil, decalin, castor oil extract, and castor oil; the mass percentage of compound A in the solvent system is 65-80%, and the mass percentage of compound B is 35-20%.

12. The method for preparing a UPE porous membrane with a low specific surface area according to claim 10, characterized in that: The polyethylene resin is composed of 70-90% by mass of ultra-high molecular weight polyethylene with a mass average molecular weight of more than 3 million and 30-10% by mass of polyethylene with a mass average molecular weight of 1 million to 2 million and a density of 0.92-0.98 g / cm 3 Composition of high-density polyethylene.

13. The method for preparing a UPE porous membrane with a low specific surface area according to claim 10, characterized in that: The viscosity of the casting liquid in S2 when extruded through the die head is 80000-120000 CPS; There is a space between the die head and the carrier for the liquid film to extend longitudinally, and the distance of the space is 5-20 mm; The pulling speed of the carrier on the liquid film is 0.5-2m / min.

14. The method for preparing a UPE porous membrane with a low specific surface area according to claim 10, characterized in that: The extracting liquid is at least one of dichloromethane, acetone, methanol, ethanol, glycerol, tetrafluoroethane and isopropanol; the extraction temperature in S5 is 5-25°C; the extraction time is 1-5h; the temperature during heat setting in S6 is 100-130°C, and the time is 200-600s.

15. Use of a UPE porous membrane with a low specific surface area according to any one of claims 1 to 9, characterized in that: The UPE porous membrane is used to filter photoresist; a mixed solvent of 70 mass % propylene glycol monomethyl ether and 30 mass % propylene glycol monomethyl ether acetate is used as a detection agent to perform a cleaning test on the UPE porous membrane before use, and the impurity content is not higher than 0.08 mg / membrane per square meter.

16. The use of a UPE porous membrane with a low specific surface area according to claim 15, characterized in that: When the UPE porous membrane is used to filter photoresist, the second porous surface is the liquid inlet surface and the first porous surface is the liquid outlet surface.

17. A pleated filter element with a UPE porous membrane with a low specific surface area as claimed in any one of claims 1 to 9, comprising a central rod and a UPE porous membrane located at the periphery of the central rod, wherein the UPE porous membrane is folded to form pleats, wherein the pleats have pleat valleys close to the central rod side and pleat peaks at the periphery, wherein the UPE porous membrane has an upstream side and a downstream side, wherein the upstream side is connected to an inlet, and the downstream side is connected to an outlet, wherein: The UPE porous membrane is a UPE porous membrane with a low specific surface area as described in any one of claims 1 to 9.

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