CN113926322A

CN113926322A - UPE porous membrane with low specific surface area, and preparation method and application thereof

Info

Publication number: CN113926322A
Application number: CN202111084523.5A
Authority: CN
Inventors: 陈梦泽; 贾建东; 方健
Original assignee: Hangzhou Cobetter Filtration Equipment Co Ltd
Current assignee: Hangzhou Cobetter Filtration Equipment Co Ltd
Priority date: 2021-09-16
Filing date: 2021-09-16
Publication date: 2022-01-14

Abstract

The invention provides a UPE porous membrane with low specific surface area, a preparation method and application thereof, wherein the porous membrane comprises a first porous surface, a second porous surface and a main body positioned between the first porous surface and the second porous surface, and a non-directional tortuous passage is arranged in the main body; the first porous surface is provided with a gully-shaped first hole; the pore area ratio of the first holes on the first porous surface is 20-35%, and the IPA bubble point is 0.15-0.65 MPa; such that the UPE porous membrane has a particle size ofThe interception efficiency of 20-200nm impurity particles is more than 95%, and the interception efficiency is high; meanwhile, the porous membrane has higher filtering speed, the time for the fluid to pass through the porous membrane is shorter, and the time cost is lower; in addition, the UPE porous membrane has small ineffective pore volume and low specific surface which is only 7-24m²The filter material is easy to clean, various impurities are not easy to remain in the UPE porous membrane, and the filter material with high cleanliness is easy to prepare; is particularly suitable for being applied to the field of photoresist filtration; the preparation method provided by the invention can conveniently, quickly and effectively prepare the UPE porous membrane.

Description

UPE porous membrane with low specific surface area, and preparation method and application thereof

Technical Field

The invention relates to the technical field of membrane materials, in particular to a UPE porous membrane with a low specific surface area, and a preparation method and application thereof.

Background

The polymer filter membrane is a kind of membrane made up by using organic high-molecular polymer as raw material and adopting a certain preparation process. With the development of the petroleum industry and science and technology, the application field of the polymer filter membrane is continuously expanded, and the currently applied fields comprise gas separation, seawater desalination, ultrapure water preparation, sewage and waste treatment, artificial organ manufacturing, medicines, foods, agriculture, chemical engineering and the like; the polymer filter membranes may be classified into cellulose-based polymer filter membranes, polyamide-based polymer filter membranes, polysulfone-based polymer filter membranes, polyolefin-based polymer filter membranes, and the like, according to the difference of high molecular polymers.

The polyolefin polymer filter membrane mainly refers to olefin filter membranes such as a polyethylene filter membrane, a polypropylene filter membrane and the like, and has wide application range due to excellent physical and chemical properties; for example, ultra high molecular weight polyethylene (UPE) filters are commonly used in photolithography processing and "wet etch and clean" (WEC) applications; for example, chinese patent application No. 201480026006.4, "substrate for liquid filter", describes a polyethylene filter membrane for use in the field of semiconductor lithography, which has excellent trapping performance for impurity particles of about 10-50nm in size, while having a long service life, and the flux of which can be kept relatively stable at all times during long-term use.

In the field of photoresist filtration, the requirement on the cleanliness of a filter material is extremely strict, so that how to clean the filter material applied to photoresist is very important; the common UPE filter material has an excessively high specific surface area, namely more pore volumes, so that certain impurities are easier to remain and difficult to clean, and the filter material cannot meet the requirements of practical application, so that the development of polyolefin polymer filter membranes is limited to a certain extent.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a UPE porous membrane with low specific surface area, a preparation method and application thereof; the UPE porous membrane has excellent trapping performance on impurity particles and high interception efficiency; meanwhile, the cleaning is convenient, impurities are not easy to remain in the UPE porous membrane, and the filter material with high cleanliness is easy to prepare; is particularly suitable for the field of photoresist filtration.

In order to achieve the purpose, the invention provides the following technical scheme: a low specific surface area UPE porous membrane comprising a first porous surface, a second porous surface, and a body positioned between the first porous surface and the second porous surface, the body having non-directional tortuous pathways therein; the specific surface area of the UPE porous membrane is 7-24m²(ii)/g; the interception efficiency of the UPE porous membrane to impurity particles with the particle size of 20-200nm is more than 95%; the IPA bubble point of the UPE porous membrane is 0.15-0.65 MPa; the first porous surface is provided with a plurality of gully-shaped first holes; the first pores on the first porous surface have a pore area fraction of 20-35%; the polyolefin composition constituting the UPE porous film contains at least an ultra-high molecular weight polyethylene having a mass-average molecular weight of 300 ten thousand or more.

The specific surface area of the UPE porous membrane is surprisingly found to be very low by carrying out a specific surface area test on the UPE porous membrane by a BET method, and the specific surface area of the UPE porous membrane is 7-24m²(the specific surface area of the existing UPE porous membrane is 30 m)²At least one,/g), preferably, the specific surface area thereof is 10 to 20m²The advantages of the UPE porous membrane with low surface area are mainly as follows:

1. the UPE porous membrane with the low surface area has fewer ineffective holes, so that the cleaning of the UPE porous membrane is relatively easier (a UPE filter material meeting the actual requirement can be obtained only by less deionized water and less washing times) while the porous membrane is effectively filtered, impurities (such as metal particles, organic matters and the like) are not easy to remain, the cleaning degree of the membrane and a filter element is ensured, the subsequent photoresist filtering is facilitated, and the photoresist with excellent performance is obtained;

2. photoresist materials generally have a relatively high viscosity for which filtration tends to create various problems associated with bubbles; the filtration of the photoresist is greatly influenced by factors such as the amount of bubbles; the porous membrane has a lower specific surface area and relatively less ineffective pore volume, so that the influence of air in the filter material, which is required to be replaced and eliminated when the photoresist passes through the filter material, can be effectively reduced, the influence of bubbles on the property of the photoresist is reduced, and the photoresist with more excellent property is obtained;

3. in the field of photoresist filtration, the requirement on the cleanliness of a filter material is very strict, the filter material is required to be very clean, certain impurities are introduced in the whole membrane preparation process (including a possibly existing modification process), and although the filter material is cleaned to a certain extent, the content of residual impurities on the filter material is reduced as much as possible, the impurities can not be completely cleaned; the UPE porous membrane has lower specific surface area, even though the impurities have extremely small amount of residues, the probability of the impurities being precipitated is far lower than that of the porous membrane with higher specific surface area due to smaller contact area, so that the properties of the photoresist are not easily influenced; meanwhile, the low specific surface area UPE porous membrane has wider application, and is more suitable for being used as a base membrane to carry out various modifications, such as hydrophilic modification, charge modification (for making the membrane charged), and the like, because the contact area between substances such as a modifier and the like and the low specific surface area UPE is smaller, the substances such as the modifier and the like are not easy to remain in the corresponding modification process, so that the membrane is easier to clean, and the modified filter membrane is cleaner;

in the membrane body structure of the UPE porous membrane provided by the invention, a certain number of first holes with certain pore diameters are clearly seen on the first porous surface of the membrane, and the factors such as the pore diameter size, the number and the shape of the holes of the membrane can have great influence on the filtration precision (interception efficiency) of the membrane; in the invention, the first holes on the first porous surface are in a gully-shaped structure (namely the first holes are in a shape similar to gully), and the gully-shaped first holes are not easy to generate invalid hole capacity, so that the specific surface area of the porous membrane is lower; the pore area ratio (the ratio of the area of the first pores to the area of the membrane) of the first pores is 20-35%, which is beneficial for the porous membrane to have larger flow velocity, facilitates the fluid to rapidly pass through the porous membrane, shortens the filtration time, has larger tensile strength and meets the requirement of practical application;

one of the important performance characteristics of a filter is the bubble point, which is a test method well known in the art. The procedures for these tests are explained in detail, for example, in ASTM F316-70 and ANS/ASTM F316-70 (re-approved in 1976), which are incorporated herein by reference. The size of the bubble point is related to the pore size of the holes on the porous membrane; in general, the larger the pore size of the pores, the lower the bubble point; the smaller the pore diameter of the hole is, the higher the bubble point is; the IPA bubble point of the UPE porous membrane is 0.15-0.65MPa, and the UPE porous membrane passes through a non-directional tortuous passage in the membrane main body, so that the porous membrane can well capture impurity particles with the particle size of 20-200nm, the interception efficiency is more than 95%, the filtration precision is ensured, and a sufficient retention effect on undesired substances is achieved;

the material of each part of the UPE porous membrane is uniform, namely the whole membrane is made of polyethylene material, and no change exists in the material; the ultra-high molecular weight polyethylene (UPE) is thermoplastic engineering plastic with a linear structure and excellent comprehensive performance, and a filter membrane prepared from the ultra-high molecular weight polyethylene has high heat resistance and wear resistance, good mechanical property, high tensile strength, excellent chemical compatibility and wide application range, and is particularly suitable for being applied to the field of photoresist; the polyolefin composition constituting the UPE porous film in the present invention includes at least an ultra high molecular weight polyethylene having a mass average molecular weight of 300 ten thousand or more; the prepared filter membrane is ensured to have higher tensile strength and elongation at break, can meet the requirements of practical application, has wide application range, and is particularly suitable for being applied to the field of photoresist; the mass average molecular weight can be obtained as follows: heating and dissolving a sample of the polyethylene filter membrane in o-dichlorobenzene, and measuring by using a GPC (GPC) liquid chromatograph at a column temperature of 135 ℃ and a flow rate of 1.0 mL/min;

wherein the pore area ratio of the first pores on the first porous surface of the membrane can be characterized by using a scanning electron microscope to characterize the membrane structure, and then using computer software(e.g., Matlab, NIS-Elements, etc.) or manually, and performing corresponding calculations; in the production of the membrane, various characteristics such as the pore size distribution in the direction perpendicular to the thickness of the membrane (the direction is a planar direction if the membrane is in the form of a porous membrane; the direction is perpendicular to the radial direction if the membrane is in the form of a hollow fiber membrane) are substantially uniform and substantially uniform; therefore, the size of the whole hole area rate on the plane can be reflected by the hole area rate of the partial area on the corresponding plane; in practice, the surface of the membrane can be characterized by an electron microscope to obtain a corresponding SEM image, and a certain area, such as 1 μm, can be selected because the pore distribution on the surface of the membrane is approximately uniform²(1 μm by 1 μm) or 25 μm²(5 μm multiplied by 5 μm), the specific area size is determined according to the actual situation, and then the area of all the holes on the area is measured by corresponding computer software or manually, and then calculation is performed to obtain the hole area ratio of the first holes on the first porous surface, although those skilled in the art can obtain the above parameters by other measuring means, and the above measuring means is only used for reference.

As a further improvement of the invention, the thickness of the UPE porous membrane is 30-100 μm, and the porosity is 30-45%; the surface area of the membrane interior per membrane area is 0.058 to 0.267.

When the thickness of the film is too small, the mechanical strength of the film is low; meanwhile, as the filtering time is too short, effective filtering cannot be carried out; when the thickness of the membrane is too large, the filtration time is too long, and the time cost is too large; the thickness of the UPE porous membrane is 30-100 mu m, so that the UPE porous membrane not only has higher mechanical strength, but also can be effectively filtered, has higher filtering efficiency, shorter filtering time and lower time cost, and is suitable for being applied to the field of photoresist;

when the porosity of the membrane is too high, the tensile strength of the membrane is too low, the mechanical property of the membrane is poor, the industrial practical value is low, and the market demand cannot be met; when the porosity of the membrane is too low, on one hand, the flow rate of the membrane is influenced, so that the filtering speed of the membrane is low, the filtering time is long, and the time cost is high; on the other hand, the pollution capacity of the membrane is too low, the service life is too short, the membrane needs to be replaced in a short time, and the economic cost is greatly improved; the porosity of the porous membrane is 30-45%, so that the membrane not only has higher tensile strength, but also has higher filtering speed, high flow rate, higher pollutant carrying capacity, long service life and lower economic cost, and can retain more impurity particles; meanwhile, the porous membrane also has a low specific surface area, impurities are not easy to remain on the porous membrane, and the porous membrane is easier to clean.

When the filtration is carried out, various fluids move along the thickness direction of the filter membrane so as to realize corresponding filtration, and the filtration is disposable, so the characteristic of the surface area inside the membrane per unit membrane area is particularly important; the surface area of the membrane inside of a unit membrane area refers to the surface area of the membrane inside area of a porous membrane with a certain area, the smaller the value of the surface area is, the smaller the ineffective pore volume inside the filter membrane is, the relatively smaller the surface area inside the filter membrane is, the surface area inside the membrane of the unit membrane area is 0.058-0.267, the smaller the value of the surface area inside the membrane is, the less the ineffective pore volume of the porous membrane is, the cleaning is relatively easier (a UPE filter material meeting high cleanliness can be obtained by only needing less deionized water and fewer washing times), and impurities (such as metal particles, organic matters and the like) are not easy to remain inside the membrane, so that the filter material meeting the practical application requirement is facilitated, and the membrane is particularly suitable for being applied to the field of photoresist.

As a further improvement of the invention, the first porous surface comprises a plurality of first lumps, adjacent first lumps are connected with each other or connected through strip fibers, and first holes are formed between the adjacent first lumps.

In the membrane body structure of the UPE porous membrane provided by the invention, a plurality of large and small first agglomerates can be clearly seen on the first porous surface of the membrane, wherein part of adjacent first agglomerates are directly connected with each other, the rest part of adjacent first agglomerates are connected with each other through strip-shaped fibers, and a gully-shaped first hole is formed between the adjacent first agglomerates in a surrounding manner; in addition, the lengths of the adjacent first lumps and the first holes in the longitudinal direction of the film (the film running direction in the film preparation process) are relatively uniform, while the lengths of the adjacent first lumps and the adjacent first holes in the transverse direction of the film (the width direction of the film) are random, have small and large differences and are not uniform enough; the structure is favorable for ensuring the stability of the first hole, and the first hole is not easy to shrink or collapse, so that the membrane is ensured to have stable flow rate, and the flow rate change of the membrane is small in the using process; meanwhile, the tensile strength of the film can be further improved, and the industrial requirement can be met; in addition, the porous membrane has less ineffective pore volume, lower specific surface area, less impurity residue and easier cleaning.

As a further improvement of the invention, the average length of the first agglomerates 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. mu.m.

The film longitudinal direction is the film running direction of the film; the measurement shows that the average length of the first lumps in the longitudinal direction of the membrane is 1-3.5 microns, the average length of the first holes in the longitudinal direction of the membrane is 0.8-2.8 microns, and the average length difference between the first lumps and the first holes is not large, so that the length of the adjacent first lumps and the length of the adjacent first holes in the longitudinal direction of the membrane (the direction of the membrane in the preparation process of the membrane) are relatively uniform, the stability of the first holes is better ensured, the interception efficiency is further ensured, and the membrane has more stable and excellent entrapment capability on impurity particles;

the average length of the first agglomerates and the first holes in the longitudinal direction of the film may reflect the average length of the whole in the plane by the average length of the partial region in the corresponding plane; in practice, the surface of the membrane may be characterized by an electron microscope to obtain a corresponding SEM image, and a certain area is selected, for example, 1 μm²(1 μm by 1 μm) or 25 μm²(5 μm multiplied by 5 μm), the specific area size being determined according to the actual situation, and then measuring the lengths of the first lumps and the first holes in the selected area in the longitudinal direction of the membrane by using corresponding computer software or manually, and obtaining the average value through calculation, namely, the first lumps and the first holes on the first porous surface are considered to be obtainedThe average length in the longitudinal direction of the film, although the person skilled in the art can also obtain the above parameters by other measuring means, which are only given as reference.

As a further improvement of the present invention, the main body comprises two side regions and a middle region, wherein the middle region is a separation layer, one side region of the main body close to the second porous surface is a pre-filter layer, and one 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 that of the pre-filtering layer and the support layer;

the thicknesses of the pre-filtering layer, the separating layer and the supporting layer are 10-40 μm, 5-20 μm and 10-45 μm in sequence.

As a further improvement of the invention, the average pore size of the prefilter layer, the separation layer and the support layer is in the range of 0.06-0.55 μm, 0.02-0.25 μm and 0.05-0.45 μm, respectively.

On the main structure of the membrane, it can be clearly found that the main part of the membrane of the invention is mainly divided into three areas, including two side areas and a middle area, the aperture of the middle area is relatively small, and the aperture of the two side areas is relatively large; the middle area is a separation layer, and the pore diameter of the pores in the separation layer is small (the average pore diameter of the separation layer is 0.02-0.25 mu m) and the thickness of the pores is 5-20 mu m, so that the separation layer can fully retain impurity particles, and the filtering precision of the porous membrane is ensured; in the two side areas, one side area of the main body close to the second porous surface is a pre-filtering layer, and one side area of the main body close to the first porous surface is a supporting layer; the pore diameters of the holes in the pre-filtering layer and the supporting layer are relatively large (the average pore diameter of the pre-filtering layer is 0.06-0.55 mu m, the average pore diameter of the supporting layer is 0.05-0.45 mu m), the thickness of the pre-filtering layer is 10-40 mu m, and the thickness of the supporting layer is 10-45 mu m, so that on one hand, the flow rate and the pollutant carrying capacity of the membrane can be improved, the filtering speed is high, more liquid can be filtered in more time, the time cost is low, the economic benefit is high, and the method is particularly suitable for being applied to the field of photoresist;

on the other hand, the porous membrane has good mechanical strength and meets the requirements of various processing and assembling.

In the context of the present invention, an asymmetric membrane is understood to be a membrane in which the prefiltration layer, the separating layer and the support layer are composed of the same material, the three layers being combined to form a unitary structure and being formed directly during the membrane production process; in the transition from the prefilter layer to the separating layer, the separating layer to the support layer, there is only a change in the membrane structure; in contrast, for example, composite membranes, which have a multilayer structure and in which a dense layer as the separating layer is applied in a separate process step to a porous, frequently microporous, support layer or support membrane, the materials of which the support layer and the separating layer are composed often also being different.

The photoresist generally comprises high molecular resin, a photoacid generator, an inhibitor and the like, and a phenomenon that molecular chains of the high molecular resin in the photoresist form molecular cross-linking by taking impurity metal as a binding point is often generated in the process of dynamic collision in finished product transportation, so that flexible impurities existing in a gel form are finally presented, and the flexible impurities can not be directly intercepted by a porous membrane; in the patent, the asymmetric membrane with the low specific surface further expands the asymmetry of the UPE porous membrane entering and exiting the liquid level, so that the liquid level enters the separation layer (a relatively large and zigzag hole is formed in the middle, and the gel flexible impurities obtain enough kinetic energy in the hole to collide to form gel with an ultra-large physical volume, so that the gel is retained by the separation layer, and meanwhile, the large space of the upper layer (generally a pre-filtering layer) of the separation layer also provides larger capacity for containing large impurities.

As a further improvement of the present invention, the average fiber diameter forming the porous structure in the separation layer is smaller than the average fiber diameter forming the porous structure in the support layer and the pre-filter layer;

the average fiber diameters of the porous structures formed in the pre-filtering layer, the separating layer and the supporting layer are 0.03-0.35 mu m, 0.01-0.14 mu m and 0.035-0.40 mu m in sequence.

In the membrane body structure of the porous membrane provided by the invention, the main body region (the pre-filter layer, the three-layer region of the separation layer and the support layer) between the first porous surface and the second porous surface comprises continuous porous network-shaped fibers, and holes for allowing fluid to pass through when the porous membrane is used for filtering are formed in the network-shaped structure of the fibers, wherein the thickness degree of the cross section of the fibers can be regarded as the average fiber diameter of the fibers, and the inner diameter size of the holes can be regarded as the average pore diameter of the fibers.

Further, it is understood that "continuous" means that substantially all of the fibers are integrally connected to each other, e.g., integrally formed, without the need for additional adhesives or the like to attach them to each other, and the network-like fibers cannot be separated from each other unless torn by an external force. At the same time, the continuous network-like fibers are interconnected with the first porous surface and the second porous surface.

As is clear from the film structure of the porous film, the average diameters of the fibers in the respective regions of the porous film are different; the average diameter of the fibers in the support layer is 0.035-0.40 mu m, the fibers are thick, the porous membrane is guaranteed to have high tensile strength, and the industrial practical value is high; in addition, each area of the porous membrane main body has proper fiber diameter, when the porous membrane main body is acted by external force, the first holes are not easy to deform or shrink, the interception efficiency is not influenced, and the filtration quality is ensured; at the same time, the fibers within each layer of the porous membrane are substantially uniformly distributed, and although the degree of thickness between the fibers in the network is not exactly the same, the fibers are uniform throughout the layers and do not exhibit a significant ascending or descending regularity.

As a further improvement of the present invention, the second porous surface has a plurality of second holes with a gully shape; the pore area fraction of the second pores on the second porous surface is 30-50%; the average pore diameter of the second pores is larger than that of the first pores.

In the membrane body structure of the UPE porous membrane provided by the invention, a certain number of second holes with certain pore diameters are clearly seen on the second porous surface of the membrane, and the factors such as the pore diameter size, the number and the shape of the holes of the membrane can have great influence on the filtration precision (interception efficiency) of the membrane; in the invention, the second holes on the second porous surface are in a gully-shaped structure (namely the second holes are in a gully-like shape), and the gully-shaped second holes are not easy to generate invalid hole capacity, so that the specific surface area of the porous membrane is further lower; the pore area ratio (the ratio of the second pore area to the membrane area) of the second pores is 30-50%, which is beneficial for the porous membrane to have larger flow velocity, is convenient for fluid to rapidly pass through the porous membrane and shortens the filtration time; if the second porous surface is used as the liquid inlet surface, the whole filter material has larger dirt holding capacity, longer service life and high economic benefit; and the average pore diameter of the second pores is larger than that of the first pores, further showing that the UPE porous membrane is an asymmetric membrane, and the porous membrane also has higher retention efficiency and excellent trapping capacity for flexible impurities in the form of gel generated in the photoresist transportation process, so the UPE porous membrane is particularly suitable for being applied to the field of photoresist.

As a further improvement of the invention, the second porous surface comprises a plurality of second agglomerates, adjacent second agglomerates are connected with each other or connected through strip fibers, and second holes are formed between adjacent second agglomerates; the average length of the second agglomerates in the longitudinal direction of the film is 1.2 to 4 μm, and the average length of the second holes in the longitudinal direction of the film is 1 to 3 μm.

In the membrane body structure of the UPE porous membrane provided by the invention, a plurality of large and small second agglomerates can be clearly seen on the second porous surface of the membrane, wherein part of the adjacent second agglomerates are directly connected with each other, the rest part of the adjacent second agglomerates are connected with each other through strip-shaped fibers, and a second gullet-shaped hole is formed between the adjacent second agglomerates in a surrounding manner; in addition, the lengths of the adjacent second lumps and the second holes in the longitudinal direction of the film (the film running direction in the film preparation process) are relatively uniform, while the lengths of the adjacent second lumps and the adjacent second holes in the transverse direction of the film (the width direction of the film) are random, have small and large differences and are not uniform enough; due to the adoption of the structure, the stability of the second hole is favorably ensured, and the second hole is not easy to shrink or collapse, so that the membrane is further ensured to have stable flow rate, and the flow rate change of the membrane is small in the using process; meanwhile, the tensile strength of the film can be further improved, and the industrial requirement can be met; in addition, the ineffective pore volume of the UPE porous membrane is less, the specific surface area is lower, impurities are less prone to remain, and the UPE porous membrane is easier to clean.

The film longitudinal direction is the film running direction of the film; the measurement shows that the average length of the second agglomerates in the longitudinal direction of the membrane is 1.2-4 μm, the average length of the second holes in the longitudinal direction of the membrane is 1-3 μm, and the average length difference between the second agglomerates and the second holes is not large, so that the length of the adjacent second agglomerates and the second holes in the longitudinal direction of the membrane (the direction of the membrane in the preparation process of the membrane) is relatively uniform, the stability of the second holes is better ensured, the interception efficiency is further ensured, and the impurity particles have more stable and more excellent trapping capacity; meanwhile, the UPE porous membrane has larger dirt holding capacity and longer service life.

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

By testing the flow rate of the UPE porous membrane, the time required for 50ml of water to pass through the UPE porous membrane with the diameter of 47mm is 15-350s under the conditions that the pressure is 0.03MPa and the temperature is 20 ℃; the UPE porous membrane has higher flow rate, shorter time for fluid to pass through the porous membrane, lower time cost and higher economic benefit, and simultaneously the UPE porous membrane is suitable for being applied to the field of photoresist;

important indexes for evaluating the mechanical strength of the film are the tensile strength and the elongation at break of the film; under certain conditions, the greater the tensile strength of the film, the better the mechanical strength of the film is said to be; the tensile strength of the UPE porous membrane is 20-100MPa, and the elongation at break is 200-800%; the UPE porous membrane has higher tensile strength and elongation at break, better mechanical property and higher industrial practical value, and can completely meet the market demand;

the heat resistance test is carried out on the UPE porous membrane, after the porous membrane is placed for 1 hour at the temperature of 120 ℃, the shrinkage rate of the porous membrane is not more than 5 percent, which shows that the UPE porous membrane has higher thermal stability, and the membrane pores are not easy to shrink or deform at higher temperature, thereby ensuring that the membrane has higher retention efficiency for a long time, has smaller flow rate change and long service life in the use process, further shows that the application range of the porous membrane is very wide, and is particularly suitable for being applied to the field of photoresist;

when the liquid filter is used for a long time or is processed, the porous membrane needs to be capable of keeping a good porous structure, so that high-efficiency interception efficiency is ensured, and an excellent impurity trapping effect is achieved; the compressibility of the UPE porous membrane is less than 15%, which indicates that the membrane pores of the porous membrane are not easy to deform and the porous structure is stable in various processing treatments or long-term use processes of the porous membrane, further ensures that the porous membrane has stable flow rate, and can ensure the retention efficiency for a long time; the compression ratio in the present invention is obtained in the following manner: the UPE porous membrane was pressurized at 2MPa at 70 ℃ for 30 seconds, then left at 25 ℃ for 30 seconds with the pressure released, and the compressibility was obtained from the ratio of the difference in membrane thickness between before and after pressurization to the membrane thickness before pressurization. In the present invention, if the compressibility of the UPE porous film is 15% or more, the following problems may occur: when the liquid filter is used for a long time or processed, the porous membrane generates pressure change more than necessary, the original porous structure can not be maintained, and the water permeability is unstable; abnormal rise of filtration pressure due to the closing of the hole, and the like.

Furthermore, the pore closing temperature of the UPE porous membrane of the invention is higher than 125 ℃, preferably higher than 140 ℃; when the pore closing temperature of the porous membrane is higher than 125 ℃, the porosity of the UPE porous membrane is not lost near the high-temperature treatment part or near the high-temperature body contact part of the thermal bonding process in the actual processing of the UPE porous membrane, the water permeability is easily maintained, the expected filtration area can be obtained even after the processing, and then the ideal flow rate and the retention efficiency are ensured.

The invention also provides a preparation method of the UPE porous membrane, which comprises the following steps:

s1: adding polyethylene resin into a solvent system consisting of a compound A and a compound B, stirring and mixing, and uniformly mixing to form a mixed material; wherein the polyethylene resin at least comprises an ultrahigh molecular weight polyethylene with the mass-average molecular weight of more than 300 ten thousand; the compound A is a non-solvent of the polyethylene resin; compound B is a solvent for the polyethylene resin; the mixed material comprises the following substances in parts by weight: polyethylene resin: 10-20 parts; a compound A: 50-70 parts; compound B: 45-15 parts of a solvent;

s2: heating, melting and mixing the mixed material at the temperature of 220-250 ℃ to form a membrane casting solution, and then extruding the membrane casting solution through a die head to form a liquid membrane on a carrier; the extrusion temperature of the die head is 180-220 ℃;

s3: the liquid film is extruded from the die head to the state that the liquid film and the carrier are kept relatively static, and the liquid film is longitudinally extended by 5-15 times;

s4: carrying out split-phase curing on the longitudinally extended liquid film at the temperature of 15-120 ℃ to form a raw film; the temperatures of two sides of the liquid film are different when the split-phase solidification is carried out, wherein the temperature of one side is at least 40 ℃ higher than that of the other side, and the split-phase solidification time is 5-60S;

s5: extracting the solvent system with the extract liquid to remove the solvent system from the raw membrane to obtain an original membrane;

s6: and (4) carrying out heat setting on the original membrane to obtain the UPE porous membrane.

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

As a further improvement of the invention, the polyethylene resin consists of 80-90 mass percent of ultrahigh molecular weight polyethylene with the mass-average molecular weight of more than 300 ten thousand and 20-10 mass percent of ultrahigh molecular weight polyethylene with the mass-average molecular weight of 100-200 ten thousand and the density of 0.92-0.98g/cm³High density poly (propylene oxide)Ethylene composition.

As a further improvement of the invention, the viscosity of the casting solution in S2 when the casting solution is extruded through a die head is 80000-120000 CPS;

a space for the liquid supply film to longitudinally extend is arranged between the die head and the carrier, and the distance of the space is 5-20 mm; the traction speed of the carrier to the liquid film is 0.5-2 m/min.

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

The UPE porous membrane is prepared based on a thermally induced phase separation method accompanied with liquid-liquid phase separation, various materials are mixed to form a mixed material during preparation, the mixed material comprises polyethylene resin and a corresponding solvent system, and the ultra-high molecular weight polyethylene is called UPE for short, and is thermoplastic engineering plastic with a linear structure and excellent comprehensive performance; the polyethylene resin used in the invention at least comprises an ultrahigh molecular weight polyethylene with the mass-average molecular weight of more than 300 ten thousand, namely only a UPE with the mass-average molecular weight of more than 300 ten thousand can be used as a film forming raw material in the invention, and the composition can also be carried out, for example, a UPE with the mass-average molecular weight of more than 300 ten thousand and a high density polyethylene with the mass-average molecular weight of less than 300 ten thousand are used as film forming raw materials after the composition; preferably, the polyethylene resin of the present invention comprises 70 to 90 mass% of an ultrahigh molecular weight polyethylene having a mass average molecular weight of 300 ten thousand or more and 10 to 30 mass% of a polyethylene having a mass average molecular weight of 100-200 ten thousand and a density of 0.92 to 0.98g/cm³The high-density polyethylene composition of (a); compared with the method that one ultra-high molecular weight polyethylene is singly selected, the polyethylene resin compounded by the ultra-high molecular weight polyethylene and the high density polyethylene is more favorable for obtaining the UPE porous membrane with relatively small aperture and higher tensile strength;

the solvent system consists of a compound A and a compound B, wherein the compound A is a non-solvent of the polyethylene resin, and the non-solvent means that when the compound is heated to the boiling point of the compound at most, the compound can not dissolve the polyethylene resin to form a homogeneous solution and only can play a certain role in swelling the polyethylene resin; the compound A is at least one of dimethyl phthalate, dioctyl adipate, ethylene glycol diacetate, dimethyl carbonate, palm oil and glycerol triacetate; the compound B is a solvent of the polyethylene resin, and the solvent is that the compound B can completely dissolve the polyethylene resin to form a homogeneous solution when the compound B is heated to the boiling temperature of the compound B at most; the compound B is at least one of paraffin oil, white oil, hydraulic oil, decalin, castor oil extract and castor oil;

compared with the method that a single solvent is selected as a solvent system, the method takes the compounding of the solvent and the non-solvent as a corresponding solvent system, and the solvent system has the following advantages:

1. holes with smaller apertures are easier to appear in the green film formed after the liquid film phase splitting is finished, and more small holes are formed at the same time; this is because the liquid film is subjected to liquid-liquid phase separation and solidification (phase separation and solidification by a thermal method) due to the change of temperature, and simultaneously, the diffusion exchange occurs between the non-solvent and the solvent, so that the phase separation and solidification rate is further improved, and in addition, the content of the compound A in the solvent system is greater than that of the compound B, namely, the content of the non-solvent is greater than that of the non-solvent, so that the phase separation and solidification rate is higher, crystal nuclei are more easily precipitated, small pores are more easily formed, and meanwhile, the number of the formed small pores is larger;

2. the UPE porous membrane is easier to form fibers, so that the UPE porous membrane has higher tensile strength and good mechanical properties, because the crystal nuclei are easier to separate out due to the acceleration of the phase separation rate, and the fibers are produced along the crystal nuclei so as to form fibers more easily; 3. through matching with the temperature during split-phase solidification, gradient holes are more easily formed in the final film forming process, so that an asymmetric film is formed, and a porous film with a film structure required by the invention is formed; of course, if desired, additional substances such as antioxidants, nucleating agents, fillers and the like may be used as additives in the present invention to further enhance certain properties of the UPE porous film; the polyethylene resin and the corresponding solvent system (comprising the compound A and the compound B) can be stirred and mixed for 10 to 24 hours at the temperature of 100 ℃ and 140 ℃ to form the corresponding mixed material;

then the mixed materials are put into an extruder to be heated, melted and mixed under the condition that the temperature is 220-250 ℃, and the heating, melting and mixing is carried out for 10-30min, thereby ensuring that the polyethylene resin is completely melted in a corresponding solvent system and the casting solution has uniform and stable shape; the solid content of the casting solution is preferably 10-20%, and the final film has low tensile strength and poor mechanical strength due to low solid content, so that the requirement of practical application cannot be met; the solid content is too high, so that the viscosity of the casting solution is too high, the requirement on used mechanical equipment is too high, the production cost is too high, and batch production cannot be realized;

then extruding through a die head (die head forming), and forming a flat liquid film on a carrier (the carrier can be a roller or other carriers), wherein the extrusion temperature of the die head is 180-220 ℃; in the process that the liquid film and the carrier are kept relatively static after the film casting solution is extruded from the die head, the temperature is changed to a certain extent due to sudden pressure drop, so that the liquid film is subjected to certain microphase separation in the process, namely, a certain number of particles (crystal nuclei) with certain diameters appear in the liquid film, and the particles collide and fuse and grow in a larger particle form at the same time, so that corresponding holes are formed; meanwhile, in the process, the liquid film is longitudinally extended, and the longitudinal extension has the function of increasing the distance between the particles; the method is favorable for forming a first gully-shaped hole and a second gully-shaped hole on the outer surface of a subsequent membrane, so that the specific surface area of the formed membrane is very low, the extension multiple is controlled to be 5-15, the liquid membrane is longitudinally extended in proper size, the porous membrane is favorable for ensuring proper pore diameter and porosity, and the porous membrane is ensured to have high interception efficiency and high flow rate while the low specific surface area of the porous membrane is ensured; the process of extruding the casting solution through a die head to keep the liquid film and a carrier relatively static mainly comprises 2 steps, wherein in the first step, the liquid film is extruded from the die head to just fall on the carrier, and a certain space exists between the die head and the carrier, and in the space, the liquid film can longitudinally extend to a certain extent under the action of gravity; through continuous research, the proper distance of the space is controlled to be 5-20 mm; the second step is that the liquid film just falls on the carrier (at the moment, the liquid film and the carrier move relatively) until the liquid film and the carrier keep relatively static, because the liquid film needs to be increased from 0 to the same speed as the carrier moves, the carrier inevitably has a traction force on the liquid film and has a proper traction speed on the liquid film, and the traction speed of the carrier on the liquid film is controlled to be 0.5-2 m/min; therefore, the longitudinal stretching of the liquid film by proper times is ensured by adjusting two factors, namely the distance between the die head and the carrier and the traction speed of the carrier to the liquid film; in addition, the viscosity of the liquid film needs to be controlled, because if the viscosity of the liquid film is too high, the liquid film is easy to break; when the viscosity of the liquid film is too low, the mechanical strength of the formed film cannot be ensured, and the viscosity of the casting solution in the invention when the casting solution is extruded through a die head (namely when the liquid film is just formed) is 80000-120000CPS, which is more favorable for obtaining the UPE porous film with an ideal film structure required by the invention;

then the longitudinally extended liquid film is subjected to phase-splitting solidification at the temperature of 15-120 ℃; at a higher temperature, a single homogeneous solution can be formed between a solvent system consisting of the compound A and the compound B and the polyethylene resin, and the homogeneous solution begins to generate liquid-liquid delamination along with the reduction of the system temperature, two liquid phases coexist, namely, one phase with high polymer content and the other phase with low polymer content occur, and then the split-phase solidification phenomenon occurs; in the invention, the solvent system is the combination of the solvent and the non-solvent, so that except for phase separation caused by temperature change, the diffusion exchange between the solvent and the non-solvent can also accelerate the solidification rate of the phase separation, thereby forming a small-pore membrane (the faster the phase separation rate is, the smaller the pore diameter of the formed pores is), namely forming the nano membrane required by the invention; in the invention, in order to ensure that the final film is an asymmetric film, the split-phase curing rates of two sides of the liquid film are different, namely one side is high and the other side is low, and simultaneously, in order to further ensure that the film has higher flow velocity, a certain number of larger holes are formed, and the temperature difference of two sides of the liquid film is at least more than 40 ℃, thereby obtaining the film body structure required by the invention; when the split-phase curing is carried out, the selection of factors such as the split-phase curing temperature, the split-phase curing time and the like is very critical, and the factors determine the speed of the split-phase curing speed and whether the film with an ideal film structure and a film pore size can be finally obtained; the time of phase separation and solidification is 5-60s, and the time is relatively short, so that the UPE porous membrane with an ideal membrane structure required by people can be obtained;

after the liquid films are separated, a raw film is formed, then extraction is carried out, and a solvent system is removed from the raw film through an extraction liquid to obtain a raw film; the extraction liquid is at least one of dichloromethane, acetone, methanol, ethanol, glycerol, tetrafluoroethane and isopropanol, the extraction temperature is 5-25 ℃, and the extraction time is 1-5 h; by selecting proper extraction liquid and extraction conditions, the solvent system is ensured to be completely removed from the raw membrane, meanwhile, the extraction time is short, and the time cost is reduced; after extraction is finished, carrying out heat setting on the original membrane, wherein the heat setting has the functions of eliminating internal stress generated by extraction on one hand, and finally setting the membrane pores of the original membrane on the other hand, so that the membrane pores are ensured not to be changed basically, and the UPE porous membrane with the required membrane pore structure is obtained; the finally obtained UPE porous membrane has a lower specific surface area, is easy to clean, and impurities are not easy to remain; meanwhile, the device has excellent trapping performance on impurity particles and high trapping efficiency; in addition, the porous membrane has higher filtering speed, shorter time for fluid to pass through the porous membrane, lower time cost and wide application range, and is particularly suitable for being applied to the field of photoresist.

As a further improvement of the invention, the use of a UPE porous membrane for filtering photoresist; a cleaning test was carried out on a UPE porous membrane before use with a mixed solvent of 70 mass% of propylene glycol monomethyl ether and 30 mass% of propylene glycol monomethyl ether acetate as a detection agent, and the impurity content was not higher than 0.08 mg/membrane per square meter.

The UPE porous membrane is particularly suitable for being applied to the field of photoresist filtration; after the UPE porous membrane is made into a bag type or cylinder type filter element, cleaning is carried out by using a cleaning solution; before the film is put into use, an organic solvent OK73 (a mixed solvent of 70 mass percent of propylene glycol monomethyl ether and 30 mass percent of propylene glycol monomethyl ether acetate) is used as a detection agent for a cleanliness test, and the content of impurities (including metal ions, organic matters, particles and the like) is not higher than 0.08 mg/film per square meter, so that the film has high cleanliness and meets the requirement of practical application.

As a further improvement of the invention, when the UPE porous membrane is used for filtering photoresist, the second porous surface is used as a liquid inlet surface, and the first porous surface is used as a liquid outlet surface.

When the photoresist is filtered, the large pore surface (second porous surface) of the UPE porous membrane is used as a liquid inlet surface, and the small pore surface (first porous surface) of the porous membrane is used as a liquid outlet surface, so that the porous membrane can be ensured to have excellent trapping performance on various impurity particles in the photoresist, and the filtering precision is high; meanwhile, the device has the advantages of higher pollutant carrying capacity, longer service life and high economic benefit.

As a further improvement of the present invention, a pleated filter element with a UPE porous membrane of low specific surface area comprising a center rod and a UPE porous membrane located at the periphery of the center rod, the UPE porous membrane pleated to form pleats having pleat valleys near the side of the center rod and pleat peaks at the periphery, the UPE porous membrane having an upstream side communicating with the inlet and a downstream side communicating with the outlet, the UPE porous membrane being the UPE porous membrane of any of claims 1-10.

The folding filter element made of the UPE porous membrane is easier to clean, can ensure that the filter material has higher cleanliness and impurities are not easy to remain by only needing less flushing fluid, and can meet the requirements of practical application, thereby obtaining the photoresist with excellent performance.

The invention has the beneficial effects that: the UPE porous membrane provided by the invention is an asymmetric membrane, has a more optimized membrane body structure compared with the existing filter membrane material, and comprises a first porous surface, a second porous surface and a main body positioned between the first porous surface and the second porous surface, wherein a non-directional tortuous passage is arranged in the main body; first plurality of holesA first hole with a gully shape is arranged on the surface; the pore area ratio of the first holes on the first porous surface is 20-35%, and the IPA bubble point is 0.15-0.65 MPa; so that the interception efficiency of the UPE porous membrane to impurity particles with the particle size of 20-200nm is more than 95%, the UPE porous membrane has excellent trapping performance and high interception efficiency; meanwhile, the porous membrane has higher filtering speed, the time for the fluid to pass through the porous membrane is shorter, and the time cost is lower; in addition, the UPE porous membrane has small ineffective pore volume and low specific surface which is only 7-24m²The filter material is easy to clean, various impurities are not easy to remain in the UPE porous membrane, and the filter material with high cleanliness is easy to prepare; is particularly suitable for being applied to the field of photoresist filtration; the preparation method provided by the invention can conveniently, quickly and effectively prepare the UPE porous membrane.

Drawings

FIG. 1 is a Scanning Electron Microscope (SEM) image of a first porous surface on a UPE porous membrane prepared in example 1 at 500 magnification;

FIG. 2 is a further magnified Scanning Electron Microscope (SEM) image of the first porous surface on a UPE porous membrane prepared in example 1 at 2000 magnification;

FIG. 3 is a Scanning Electron Microscope (SEM) image of a second porous surface on a UPE porous membrane prepared according to example 1 at 500 magnification;

FIG. 4 is a further magnified Scanning Electron Microscope (SEM) image of a second porous surface on a UPE porous membrane prepared according to example 1 at 2000 magnification;

FIG. 5 is a Scanning Electron Microscope (SEM) image of the upper cross section of a UPE porous membrane prepared in example 1 at 500 magnification;

FIG. 6 is a Scanning Electron Microscope (SEM) image of a further enlarged cross section of the UPE porous membrane prepared in example 1, wherein the magnification is 2000;

FIG. 7 is a schematic view of the apparatus for measuring the flow rate of the ultra-high molecular weight polyethylene porous membrane according to the present invention;

fig. 8 is a 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

In order to more clearly explain the overall concept of the present application, the following detailed description is given by way of example. Example 1 a method for preparing a UPE porous membrane, comprising the steps of:

s1: adding polyethylene resin into a solvent system consisting of a compound A and a compound B, stirring and mixing, and uniformly mixing to form a mixed material; wherein 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 substances in parts by weight: polyethylene resin: 15 parts of (1); a compound A: 60 parts; compound B: 25 parts of (1); wherein the compound A is dimethyl phthalate, and the compound B is paraffin oil;

the polyethylene resin comprises 80 mass percent of ultra-high molecular weight polyethylene with the mass-average molecular weight of more than 300 ten thousand and 20 mass percent of polyethylene with the mass-average molecular weight of 100-200 ten thousand and the density of 0.92-0.98g/cm³The high-density polyethylene composition of (a);

s2: heating, melting and mixing the mixed material at the temperature of 240 ℃ to form a membrane casting solution, and then extruding the membrane casting solution through a die head to form a liquid membrane on the carrier; the extrusion temperature of the die head is 200 ℃; wherein the viscosity of the casting solution is 100000CPS when the casting solution is extruded by a die head;

s3: the liquid film is extruded from the die head to the state that the liquid film and the carrier are kept relatively static, and the liquid film is longitudinally extended by 10 times; a space for the liquid supply film to longitudinally extend is arranged between the die head and the carrier, and the distance of the space is 13 mm; the traction speed of the carrier to the liquid film is 1.2 m/min;

s4: carrying out split-phase curing on the longitudinally extended liquid film in an environment with the temperature of one side of 25 ℃ and the temperature of the other side of 90 ℃, wherein the split-phase curing time is 30s, and after the split-phase curing is finished, forming a green film;

s5: extracting the solvent system with an extraction liquid, wherein the extraction liquid is isopropanol, the extraction temperature is 15 ℃, and the extraction time is 3h, so that the solvent system is removed from the raw membrane to obtain a raw membrane;

s6: and (3) carrying out heat setting on the original membrane, wherein the heat setting temperature is 120 ℃, and the heat setting time is 300s, so as to obtain the UPE porous membrane.

Example 2 a method of preparing a UPE porous membrane, comprising the steps of:

s1: adding polyethylene resin into a solvent system consisting of a compound A and a compound B, stirring and mixing, and uniformly mixing to form a mixed material; wherein 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 substances in parts by weight: polyethylene resin: 20 parts of (1); a compound A: 70 parts of (B); compound B: 30 parts of (1); wherein compound A is glycerol triacetate, and compound B is castor oil extract; the polyethylene resin comprises 70 mass percent of ultra-high molecular weight polyethylene with the mass-average molecular weight of more than 300 ten thousand and 30 mass percent of polyethylene with the mass-average molecular weight of 100-200 ten thousand and the density of 0.92-0.98g/cm³The high-density polyethylene composition of (a);

s2: heating, melting and mixing the mixed material at the temperature of 250 ℃ to form a membrane casting solution, and then extruding the membrane casting solution through a die head to form a liquid membrane on a carrier; wherein the die extrusion temperature is 215 ℃; the viscosity of the casting solution is 110000CPS when the casting solution is extruded by a die head;

s3: the liquid film is extruded from the die head to the state that the liquid film and the carrier are kept relatively static, and the liquid film is longitudinally extended by 8 times; wherein a space for longitudinal extension of the liquid supply film is provided between the die head and the carrier, and the distance of the space is 11 mm; the traction speed of the carrier to the liquid film is 0.9 m/min;

s4: carrying out split-phase curing on the longitudinally extended liquid film in an environment with the temperature of one side being 25 ℃ and the temperature of the other side being 105 ℃, wherein the split-phase curing time is 45s, and after the split-phase curing is finished, forming a green film;

s5: extracting the solvent system with the extract liquid to remove the solvent system from the raw membrane to obtain an original membrane; wherein the extraction liquid is acetone, the extraction temperature is 20 ℃, and the extraction time is 2 h;

s6: and (3) carrying out heat setting on the original membrane, wherein the temperature during the heat setting is 115 ℃, and the time is 400s, so as to obtain the UPE porous membrane.

Example 3 a method of making a UPE porous membrane comprising the steps of:

s1: adding polyethylene resin into a solvent system consisting of a compound A and a compound B, stirring and mixing,mixing uniformly to form a mixed material; wherein 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 substances in parts by weight: polyethylene resin: 18 parts of a mixture; a compound A: 65 parts of (1); compound B: 25 parts of (1); the compound A is ethylene glycol diacetate and the compound B is white oil; the polyethylene resin comprises 75 mass percent of ultrahigh molecular weight polyethylene with the mass-average molecular weight of more than 300 ten thousand and 25 mass percent of ultrahigh molecular weight polyethylene with the mass-average molecular weight of 100-200 ten thousand and the density of 0.92-0.98g/cm³The high-density polyethylene composition of (a);

s2: heating, melting and mixing the mixed material at the temperature of 245 ℃ to form a membrane casting solution, and then extruding the membrane casting solution through a die head to form a liquid membrane on the carrier; the extrusion temperature of the die head is 210 ℃; the viscosity of the casting solution is 115000CPS when the casting solution is extruded by a die head;

s3: the liquid film is extruded from the die head to the state that the liquid film and the carrier are kept relatively static, and the liquid film is longitudinally extended by 6 times; a space for the liquid supply film to longitudinally extend is arranged between the die head and the carrier, and the distance of the space is 8 mm; the traction speed of the carrier to the liquid film is 0.6 m/min.

S4: carrying out split-phase curing on the longitudinally extended liquid film in an environment with the temperature of one side of 30 ℃ and the temperature of the other side of 120 ℃, wherein the split-phase curing time is 60s, and after the split-phase curing is finished, forming a green film;

s5: extracting the solvent system with the extract liquid to remove the solvent system from the raw membrane to obtain an original membrane; wherein the extraction liquid is dichloromethane, the extraction temperature is 10 ℃, and the extraction time is 4 hours;

s6: and (3) carrying out heat setting on the original membrane, wherein the temperature during the heat setting is 125 ℃, and the time is 250s, so as to obtain the UPE porous membrane.

Example 4 a method of making a UPE porous membrane, comprising the steps of:

s1: adding polyethylene resin into a solvent system consisting of a compound A and a compound B, stirring and mixing, and uniformly mixing to form a mixed material; wherein 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 substances in parts by weight: polyethylene resin: 14 parts of (1); a compound A: 64 parts; compound B: 22 parts of (A); wherein the compound A is palm oil, and the compound B is decalin; the polyethylene resin consists of 85 mass percent of ultrahigh molecular weight polyethylene with the mass-average molecular weight of more than 300 ten thousand and 15 mass percent of high-density polyethylene with the mass-average molecular weight of 100-200 ten thousand and the density of 0.92-0.98g/cm 3; s2: heating, melting and mixing the mixed material at 235 ℃ to form a membrane casting solution, and then extruding the membrane casting solution through a die head to form a liquid membrane on a carrier; the extrusion temperature of the die head is 195 ℃; the viscosity of the casting solution is 95000CPS when the casting solution is extruded through a die head;

s3: the liquid film is extruded from the die head to the state that the liquid film and the carrier are kept relatively static, and the liquid film is longitudinally extended by 11 times; a space for the liquid supply film to longitudinally extend is arranged between the die head and the carrier, and the distance of the space is 15 mm; the traction speed of the carrier to the liquid film is 1.4 m/min;

s4: carrying out split-phase curing on the longitudinally extended liquid film in an environment with the temperature of one side being 20 ℃ and the temperature of the other side being 65 ℃, wherein the split-phase curing time is 12s, and after the split-phase curing is finished, forming a green film;

s5: extracting the solvent system with the extract liquid to remove the solvent system from the raw membrane to obtain an original membrane; wherein the extraction liquid is ethanol, the extraction temperature is 5 ℃, and the extraction time is 5 hours;

s6: and (3) carrying out heat setting on the original membrane, wherein the temperature during the heat setting is 130 ℃, and the time is 200s, so as to obtain the UPE porous membrane.

Example 5 a method of making a UPE porous membrane comprising the steps of:

s1: adding polyethylene resin into a solvent system consisting of a compound A and a compound B, stirring and mixing, and uniformly mixing to form a mixed material; wherein the polyethylene resin is ultra-high molecular weight polyethylene with the mass-average molecular weight of more than 300 ten thousand; the compound A is a non-solvent of the polyethylene resin; compound B is a solvent for the polyethylene resin; the mixed material comprises the following substances in parts by weight: polyethylene resin: 12 parts of (1); a compound A: 58 parts of a mixture; compound B: 27 parts of (1); the compound A is dioctyl adipate, and the compound B is hydraulic oil;

s2: heating, melting and mixing the mixed material at 230 ℃ to form a membrane casting solution, and then extruding the membrane casting solution through a die head to form a liquid membrane on the carrier; the die head extrusion temperature is 190 ℃; the viscosity of the casting solution is 90000CPS when the casting solution is extruded by a die head;

s3: the liquid film is extruded from the die head to the state that the liquid film and the carrier are kept relatively static, and the liquid film is longitudinally extended by 13 times; a space for longitudinal extension of the liquid supply film is arranged between the die head and the carrier, and the distance of the space is 17 mm; the traction speed of the carrier to the liquid film is 1.6 m/min;

s4: carrying out split-phase curing on the longitudinally extended liquid film in an environment with the temperature of one side being 20 ℃ and the temperature of the other side being 75 ℃, wherein the split-phase curing time is 20s, and after the split-phase curing is finished, forming a green film;

s5: extracting the solvent system with the extract liquid to remove the solvent system from the raw membrane to obtain an original membrane; wherein the extraction liquid is glycerol, the extraction temperature is 18 ℃, and the extraction time is 3.5 h;

s6: and (3) carrying out heat setting on the original membrane, wherein the temperature during the heat setting is 105 ℃ and the time is 500s, and obtaining the UPE porous membrane.

Example 6 a method of making a UPE porous membrane comprising the steps of:

s1: adding polyethylene resin into a solvent system consisting of a compound A and a compound B, stirring and mixing, and uniformly mixing to form a mixed material; wherein the polyethylene resin is ultra-high molecular weight polyethylene with the mass-average molecular weight of more than 300 ten thousand; the compound A is a non-solvent of the polyethylene resin; compound B is a solvent for the polyethylene resin; the mixed material comprises the following substances in parts by weight: polyethylene resin: 10 parts of (A); a compound A: 60 parts; compound B: 20 parts of (1); wherein the compound A is dimethyl carbonate, and the compound B is white oil;

s2: heating, melting and mixing the mixed material at 225 ℃ to form a membrane casting solution, and then extruding the membrane casting solution through a die head to form a liquid membrane on the carrier; the extrusion temperature of the die head is 180 ℃; the viscosity of the casting solution is 85000CPS when the casting solution is extruded by a die head;

s3: the liquid film is extruded from the die head to the state that the liquid film and the carrier are kept relatively static, and the liquid film is longitudinally extended by 15 times; a space for the liquid supply film to longitudinally extend is arranged between the die head and the carrier, and the distance of the space is 19 mm; the traction speed of the carrier to the liquid film is 1.9 m/min;

s4: carrying out split-phase curing on the longitudinally extended liquid film in an environment with the temperature of one side of 30 ℃ and the temperature of the other side of 85 ℃, wherein the split-phase curing time is 25s, and after the split-phase curing is finished, forming a green film;

s5: extracting the solvent system with the extract liquid to remove the solvent system from the raw membrane to obtain an original membrane; wherein the extraction liquid is tetrafluoroethane, the extraction temperature is 13 ℃, and the extraction time is 4.5 h;

s6: and (3) carrying out heat setting on the original membrane, wherein the temperature during the heat setting is 110 ℃, and the time is 450s, so as to obtain the UPE porous membrane.

Firstly, the method comprises the following steps: structural characterization

Carrying out morphology characterization on the UPE porous membrane obtained in each embodiment by using a scanning electron microscope, and then obtaining required data; the specific results are as follows:

as can be seen from the above table, in the UPE porous membranes prepared in examples 1-6 of the present invention, the first porous surface has a suitable number of first pores with suitable pore sizes, and the second porous surface has a suitable number of second pores with suitable pore sizes; the structure is favorable for ensuring the stability of the first hole and the second hole, and the membrane is not easy to shrink or collapse, so that the membrane is ensured to have stable flow rate, and the change of the flow rate of the membrane is small in the use process; the porous membrane has high flow velocity, facilitates the fluid to rapidly pass through the porous membrane, shortens the filtering time, has high tensile strength and meets the requirement of practical application; meanwhile, the tensile strength of the film can be further improved, and the industrial requirement can be met; in addition, the porous membrane has less ineffective pore volume, lower specific surface area, less impurity residue and easier cleaning.

The UPE porous membrane prepared in the embodiments 1-6 of the invention has a proper membrane structure, so that on one hand, the full retention effect on impurity particles is ensured, and the filtration precision of the porous membrane is ensured; on the other hand, the flow rate and the pollutant carrying capacity of the membrane can be improved, the filtering speed is high, more liquid can be filtered in more time, the time cost is low, the economic benefit is high, and the membrane is particularly suitable for being applied to the field of photoresist;

the UPE porous membranes prepared in the embodiments 1 to 6 of the present invention have a lower specific surface area and a membrane internal surface area per unit membrane area, which means that the UPE porous membranes have fewer ineffective pores, which can ensure that the cleaning of the UPE porous membranes becomes relatively easier (only less deionized water and less washing times are needed to obtain a UPE filter material meeting actual needs) and impurities (such as metal particles, organic matters and the like) are not easily left while the effective filtration of the porous membranes is performed, thereby ensuring the cleaning degree of the membranes and the filter elements, facilitating the subsequent photoresist filtration, and obtaining a photoresist with excellent performance.

Characteristic features

Water flow rate test (test device as figure 7)

The method comprises the following steps: and (3) mounting the sample to be tested after the IPA is wetted on a support for decompression and filtration, closing a valve 2 on a decompression and filtration frame, opening a valve 1, starting a vacuum pump, adjusting the pressure to 0.03MPa, and closing the valve 1.

Step two: 50ml of test solution (water) is filled into a plastic measuring cylinder of a bracket for reduced pressure filtration, a valve 2 is opened, timing is started from one scale, and timing is stopped from the other scale;

step three: after the test, the value indicated by the stopwatch is recorded, and when all the test solution has passed through the filter, the valve 2 on the holder is closed and the sample is taken out.

Testing the tensile strength and the elongation at break of each sample by using a universal tensile testing machine;

the UPE porous membranes prepared in the embodiments 1-6 of the invention have higher filtering speed and lower time cost; meanwhile, the high-strength high-elongation-at-break cable has high tensile strength and high elongation at break, can meet various requirements on assembly and processing, and really realizes industrialization.

And (3) testing the filtering precision: the membranes obtained in each example were tested for their efficiency of interception.

Experimental equipment: a Tianjin Roots particle counter KB-3; preparation of the experiment: the experimental set-up was assembled as per fig. 8, ensuring the set-up was clean, and the set-up was rinsed with ultra-pure water; a sample with the diameter of 47mm is taken and is arranged in the butterfly filter, and the air tightness of the assembled filter is ensured to be good.

The experimental steps are as follows: pouring the challenge liquid into a storage tank, paying attention to the exhaust of the butterfly filter, pressurizing to 10kPa, and taking the filtrate at the downstream of the butterfly by using a clean bottle; the number of particles in the filtrate and stock solutions was measured using a particle counter.

Intercepting efficiency:

in the formula: eta-type-interception efficiency,%; n 0-number of particles in stock solution, average of 5 groups of counts; n 1-number of particles in filtrate, average of 5 groups of counts.

The interception efficiency test results for each example are as follows:

as can be seen from the above table, the UPE porous membranes prepared in embodiments 1 to 6 of the present invention have a relatively high filtration accuracy, a retention efficiency of 95% or more, a relatively high trapping ability for impurity particles (e.g., standard gold particle impurities), and are particularly suitable for application in the field of photoresists to meet the actual industrial requirements; .

Testing of cleaning efficiency

Comparative example 1: chinese patent No. CN201910132223.6, a method for preparing a porous polyolefin membrane with high porosity and large specific surface area, and a UPE porous membrane (the specific surface of the porous membrane is 82 m) prepared by the method (example 1)²/g)

UPE porous membranes (membrane area 0.4m selected) prepared in examples 1-6 and comparative example 1²) Preparing a corresponding bag type filter element, washing the filter element by using 40L of deionized water, soaking the filter element in a 0K73 detection agent (a mixed solvent of 70 mass percent of propylene glycol monomethyl ether and 30 mass percent of propylene glycol monomethyl ether acetate) for 24 hours after washing is finished, and then measuring the impurity content in the detection agent (the impurities mainly comprise metal ions and organic matters, the metal ions are measured by ICPMS, and the organic matters are measured by GCMS), wherein the test result is as follows;

test specimen	Impurity level (mg/film per square meter)
		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

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 to 6 are easier to clean, and only less deionized water and less washing times are needed to obtain the UPE filter material meeting the actual needs) and impurities (such as metal particles, organic matters and the like) are not easy to remain, so that the cleaning degree of the membrane and the filter element is ensured, and the subsequent photoresist filtration is facilitated, and the photoresist with excellent performance is obtained.

UPE porous membranes (membrane area 0.4m selected) prepared in examples 1-6 and comparative example 1²) The corresponding capsule filter element was prepared, cleaned with a cleaning agent, and then the photoresist was filtered, and at the same time, the amount of gas generated by the UPE porous membrane during the filtration process (the amount of gas generated by the membrane-containing filter element — the amount of gas generated by the membrane-free blank filter element) was collected by a gas detector, as follows:

test specimen	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

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 to 6 generate fewer bubbles during the photoresist filtering process, thereby reducing the influence of the bubbles on the photoresist properties and facilitating the obtaining of a photoresist with more excellent properties;

the above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may occur to those skilled in the art without departing from the principle of the invention, and are considered to be within the scope of the invention.

Claims

1. A low specific surface area UPE porous membrane comprising a first porous surface, a second porous surface, and a body positioned between the first porous surface and the second porous surface, the body having non-directional tortuous pathways therein, characterized in that:

the specific surface area of the UPE porous membrane is 7-24m²/g；

The interception efficiency of the UPE porous membrane to impurity particles with the particle size of 20-200nm is more than 95%;

the IPA bubble point of the UPE porous membrane is 0.15-0.65 MPa;

the first porous surface is provided with a plurality of gully-shaped first holes; the first pores on the first porous surface have a pore area fraction of 20-35%;

the polyolefin composition constituting the UPE porous film contains at least an ultra-high molecular weight polyethylene having a mass-average molecular weight of 300 ten thousand or more.

2. A low specific surface area UPE porous membrane in accordance with claim 1, wherein: the thickness of the UPE porous membrane is 30-100 mu m, and the porosity is 30-45%; the surface area of the membrane interior per membrane area is 0.058 to 0.267.

3. A low specific surface area UPE porous membrane in accordance with claim 1, wherein: the first porous surface comprises a plurality of first lumps, adjacent first lumps are connected with each other or connected through strip-shaped fibers, and first holes are formed between the adjacent first lumps.

4. A low specific surface area UPE porous membrane in accordance with claim 3, wherein: the average length of the first agglomerates 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.

5. A low specific surface area UPE porous membrane in accordance with claim 1, wherein: the main body comprises two side areas and a middle area, wherein the middle area is a separation layer, one side area of the main body close to the second porous surface is a pre-filtering layer, and one side area of the main body close to the first porous surface is a supporting layer; the average pore size of the separation layer is smaller than that of the pre-filtering layer and the support layer;

6. A low specific surface area UPE porous membrane according to claim 5, wherein: the average pore size ranges of the pre-filtering layer, the separating layer and the supporting layer are 0.06-0.55 μm, 0.02-0.25 μm and 0.05-0.45 μm in sequence.

7. A low specific surface area UPE porous membrane according to claim 5, wherein: 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-filter layer;

8. A low specific surface area UPE porous membrane in accordance with claim 1, wherein: the second porous surface is provided with a plurality of second gully-shaped holes; the pore area fraction of the second pores on the second porous surface is 30-50%; the average pore diameter of the second pores is larger than that of the first pores.

9. A low specific surface area UPE porous membrane in accordance with claim 8, wherein: the second porous surface comprises a plurality of second lumps, adjacent second lumps are mutually connected or connected through strip fibers, and second holes are formed between the adjacent second lumps;

the average length of the second agglomerates in the longitudinal direction of the film is 1.2 to 4 μm, and the average length of the second holes in the longitudinal direction of the film is 1 to 3 μm.

10. A low specific surface area UPE porous membrane in accordance with claim 1, wherein:

the time required for 50ml of water to pass through a porous membrane with the diameter of 47mm is 15-350s under the conditions that the pressure is 0.03MPa and the temperature is 20 ℃;

the tensile strength of the porous membrane is 20-100MPa, and the elongation at break is 200% -800%;

after the porous membrane is placed for 1 hour at the temperature of 120 ℃, the shrinkage rate of the porous membrane is not more than 5 percent;

the compressibility of the porous membrane is less than 15%;

the porous membrane has a pore closing temperature greater than 125 ℃.

11. A method of preparing a low specific surface area UPE porous membrane according to any of claims 1 to 10, characterized in that: the method comprises the following steps:

s1: adding polyethylene resin into a solvent system consisting of a compound A and a compound B, stirring and mixing, and uniformly mixing to form a mixed material; wherein the polyethylene resin at least comprises an ultrahigh molecular weight polyethylene with the mass-average molecular weight of more than 300 ten thousand; the compound A is a non-solvent of the polyethylene resin; compound B is a solvent for the polyethylene resin;

the mixed material comprises the following substances in parts by weight:

polyethylene resin: 10-20 parts;

a compound A: 50-70 parts;

compound B: 45-15 parts of a solvent;

12. The method for preparing a low specific surface area UPE porous membrane according to claim 11, wherein: 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, a castor oil extract and castor oil; the mass percent of the compound A in the solvent system is 65-80%, and the mass percent of the compound B is 35-20%.

13. The method for preparing a low specific surface area UPE porous membrane according to claim 11, wherein: the polyethylene resin comprises 70-90 mass% of ultrahigh molecular weight polyethylene with the mass average molecular weight of more than 300 ten thousand and 30-10 mass% of ultrahigh molecular weight polyethylene with the mass average molecular weight of 100-200 ten thousand and the density of 0.92-0.98g/cm³The high-density polyethylene of (1).

14. The method for preparing a low specific surface area UPE porous membrane according to claim 11, wherein: the viscosity of the casting solution in S2 when being extruded through a die head is 80000-120000 CPS;

15. The method for preparing a low specific surface area UPE porous membrane according to claim 11, wherein: the extract is at least one of dichloromethane, acetone, methanol, ethanol, glycerol, tetrafluoroethane and isopropanol; the extraction temperature in S5 is 5-25 ℃; the extraction time is 1-5 h; the temperature in the S6 heat setting is 100-130 ℃, and the time is 200-600S.

16. Use of a low specific surface area UPE porous membrane according to any of claims 1 to 10 wherein: the UPE porous membrane is used for filtering photoresist; a cleaning test was carried out on a UPE porous membrane before use with a mixed solvent of 70 mass% of propylene glycol monomethyl ether and 30 mass% of propylene glycol monomethyl ether acetate as a detection agent, and the impurity content was not higher than 0.08 mg/membrane per square meter.

17. Use of a low specific surface area UPE porous membrane in accordance with claim 16 wherein: when the UPE porous membrane is used for filtering photoresist, the second porous surface is used as a liquid inlet surface, and the first porous surface is used as a liquid outlet surface.

18. A pleated filter insert with a UPE porous membrane having a low specific surface area according to any of claims 1-10 comprising a center rod and a UPE porous membrane located at the periphery of the center rod, the UPE porous membrane being pleated to form pleats having pleat valleys adjacent the side of the center rod and pleat peaks at the periphery, the UPE porous membrane having an upstream side and a downstream side, the upstream side communicating with the inlet and the downstream side communicating with the outlet, wherein: the UPE porous membrane is the UPE porous membrane of any one of claims 1-10.