CN116571103A

CN116571103A - UPE porous filter membrane and preparation method and application thereof

Info

Publication number: CN116571103A
Application number: CN202310446023.4A
Authority: CN
Inventors: 陈梦泽; 贾建东
Original assignee: Hangzhou Cobetter Filtration Equipment Co Ltd
Current assignee: Hangzhou Cobetter Filtration Equipment Co Ltd
Priority date: 2023-04-24
Filing date: 2023-04-24
Publication date: 2023-08-11
Also published as: WO2024222404A1; CN118416704A

Abstract

The application relates to the technical field of membrane materials, and discloses a UPE porous filtering membrane, a preparation method and application thereof, wherein the UPE porous filtering membrane comprises a main body, a first outer surface and a second outer surface are respectively formed on two sides of the main body, a non-directional tortuous path is formed in the main body, and the PMI average pore diameter of the porous membrane is 2-100nm; the first outer surface is provided with first micropores, the second outer surface is provided with second micropores, the first micropores are in a lace hole shape and are formed by surrounding a plurality of block structures, the second micropores are in a round hole shape, the SEM average pore diameter of the first micropores is larger than that of the second micropores, and the SEM average pore diameters from the first micropores to the second micropores are in gradient change; the first outer surface and the second outer surface are formed by continuous fibers. The UPE porous filter membrane prepared by the application has the characteristics of both permeation flux and interception efficiency.

Description

UPE porous filter membrane and preparation method and application thereof

Technical Field

The application relates to the technical field of membrane materials, in particular to a UPE porous filter membrane, a preparation method and application thereof.

Background

The porous polymer film is one film prepared with organic polymer as material and has the functions of filtering and separating impurity. Depending on the polymer, the polymer porous membrane may be classified into a cellulose-based polymer porous membrane, a polyamide-based polymer porous membrane, a polysulfone-based polymer porous membrane, a polyester-based polymer porous membrane, a polyolefin-based polymer porous membrane, and the like.

Among these porous polyolefin polymer films, there are mainly porous polyethylene films, porous polypropylene films, etc., and polyethylene is classified into Low Density Polyethylene (LDPE) (high pressure polymerization), high Density Polyethylene (HDPE) (low pressure Ziegler catalytic polymerization), linear Low Density Polyethylene (LLDPE), ultra high molecular weight polyethylene (UHMPE), etc., depending on the polymerization method and catalyst. In recent years, ultra-high molecular weight polyethylene (UPE) porous membranes have been widely used in various fields such as battery separator members and filtration.

When the ultra-high molecular weight polyethylene is applied to a battery separator, the ultra-high molecular weight polyethylene porous membrane needs to consider more performances such as air permeability, mechanical properties, heat shrinkage, heat shutdown and the like due to factors such as characteristics of a battery, safety and the like.

The polyethylene microporous membrane of the patent CN101253232B is a polyethylene microporous membrane comprising a polyethylene resin having a mass average molecular weight of 7×105 or more and a ratio of 5 to 300, wherein the polyethylene microporous membrane comprises a coarse structure layer having an average pore diameter exceeding 0.04 μm and a dense structure layer having an average pore diameter of 0.04 μm or less, the coarse structure layer being formed on at least one surface. The polyethylene microporous membrane is used for a separator for a battery, and the coarse structural layer is mainly used for increasing the permeation amount of a battery separator to electrolyte by utilizing the matching of the coarse structural layer and the dense structural layer, and the dense structural layer is used for maintaining the structural strength of the battery separator, so that the change of air permeability of the battery separator when the battery separator is pressurized is small, the electrolyte is absorbed fast, and the safety of the battery can be improved.

The polyethylene microporous membrane of CN101233176a is a microporous membrane comprising a polyethylene resin having a mass average molecular weight of not less than 1×106 and a proportion of ultra-high molecular weight polyethylene of not more than 15%, and has a dense structural layer having an average pore diameter of 0.01 to 0.05 μm and a coarse structural layer having an average pore diameter 1.2 to 5.0 times that of the dense structural layer formed on at least one surface, and the thickness ratio of the coarse structural layer to the dense structural layer is 5/1 to 1/10. The preparation method comprises the following steps: extruding a melt-kneaded product of a polyethylene resin and a film-forming solvent from a die, cooling to obtain an extrusion molded body, quenching the extrusion molded body while cooling the extrusion molded body slowly to form a gel-like sheet, uniaxially stretching the gel-like sheet at a crystal dispersion temperature of the polyethylene resin of +10 ℃ to a crystal dispersion temperature of +30 ℃, removing the solvent, and uniaxially stretching the gel-like sheet again to obtain a polyethylene microporous film.

Therefore, when the ultra-high molecular weight polyethylene filter membrane is applied to a battery diaphragm member, more consideration is required to be given to the performance such as the absorption speed of electrolyte, and meanwhile, due to the working requirement of the battery diaphragm member, the battery diaphragm is required to have the functions of high-temperature closing and blocking the anode and the cathode, and the battery diaphragm is required to provide a passage through which lithium ions and the like pass so as to charge and discharge the anode and the cathode. However, when the membrane is applied to the field of membrane filtration, more performances such as flux and interception efficiency of the filtration membrane are required to be considered, and the performances are not considered and are ignored in the application environment of the battery membrane.

As disclosed in chinese patent application No. CN101107063B, a multi-layer microporous polymer membrane and a method for preparing the same are disclosed, wherein the multi-layer microporous polymer membrane has at least two porous layers, at least two layers have different average pore diameters, the layers with different pore diameters are separated by porous interfaces, the pore diameters of the layers are uniform or form a gradient, the porous layers form an integral porous main body matrix, the polymer material of each layer is ultra-high molecular weight polyethylene, the multi-layer microporous polymer membrane has a lace-like open structure, and the membrane thickness is 20-70 microns. The multi-layer microporous polymer film is prepared by heating the mixture of each layer independently to obtain solutions, extruding each solution through a forming die under shearing to form a double-layer sheet, cooling the double-layer sheet to separate phases, and finally selectively removing a microporous structure formed by a pore-forming agent. Because the filtering membrane has a porous interface, materials on two sides of the porous interface can be different, and the attenuation or loss of flow at the porous interface can be avoided in the process of filtering and separating, thereby affecting the interception efficiency of the porous filtering membrane to a certain extent.

The applicant found in the experimental investigation that the polyethylene microporous membrane prepared by using the ultra-high molecular weight polyethylene also has good effect in terms of photoresist filtration treatment, therefore, the inventor provides an application patent with publication number of CN113926322A, and discloses a UPE porous membrane with low specific surface area, the UPE porous membrane comprises a main body, and a first porous surface and a second porous surface positioned at two sides of the main body, wherein the first porous surface and the second porous surface are respectively provided with a plurality of gully-shaped first holes and second holes, the main body is provided with a three-layer structure, namely a pre-filtering layer, a separating layer and a supporting layer, the average pore diameter of the separating layer is smaller than that of the pre-filtering layer and the supporting layer, the ineffective pore volume is reduced by using the gully-shaped first holes and the second holes, so that the porous membrane is easier to clean, and meanwhile, the porous membrane has a large flow rate. Meanwhile, the pre-filtering layer provides a space for accommodating large impurities, and the separating layer plays a role of intercepting gel, so that the porous membrane has good dirt receiving amount and filtering speed. In the application process, the separation layer is actually used for stopping, the stopping efficiency of the porous membrane is not too high in the process of realizing the filtration, and although the porous membrane has a large flow rate, the stopping efficiency of the porous membrane is not too high due to the thickness of the separation layer and the limitation of the thickness of the whole porous membrane, so that the stopping efficiency of the UPE porous membrane in the aspect of being applied to the photoresist filtration treatment still has a space for improvement.

Disclosure of Invention

The invention aims to provide a UPE porous filter membrane, a preparation method and application thereof.

In order to achieve the above purpose, the invention adopts the following technical scheme:

a UPE porous filtering membrane comprises a main body, wherein a first outer surface and a second outer surface are respectively formed on two sides of the main body, a non-directional tortuous passage is formed in the main body, and the PMI average pore diameter of the porous membrane is 2-100nm;

the first outer surface is provided with first micropores, the second outer surface is provided with second micropores, the first micropores are in a lace hole shape and are formed by surrounding a plurality of block structures, the second micropores are in a round hole shape, the SEM average pore diameter of the first micropores is larger than that of the second micropores, and the SEM average pore diameters from the first micropores to the second micropores are in gradient change;

the first outer surface and the second outer surface are formed by continuous fibers.

The first outer surface and the second outer surface are respectively used as a liquid inlet surface and a liquid outlet surface, the first micropore is formed by surrounding a plurality of block structures and is in a lace hole shape, and compared with a sheet-shaped or strip-shaped structure, the thickness of the hole wall of the first micropore formed by the block structures is relatively larger, and the first micropore has relatively larger pressure when being subjected to external stress, so that the first micropore structure formed by the block structures is more stable, is not easy to collapse, and can improve the strength of the holes of the UPE porous filtering membrane;

Meanwhile, the first micropores formed by surrounding the block-shaped structures are in a lace hole shape, and due to the irregular shape of the block-shaped structures, the adjacent first micropores cannot avoid forming a complete closed loop, so that a plurality of tiny openings exist, namely the openings possibly exist between the adjacent first micropores and are mutually communicated through the tiny openings, and the holes formed by surrounding the sheet-shaped or strip-shaped structures are usually closed holes;

when the conditions such as the number of holes, the average hole diameter and the area ratio of the holes are kept basically consistent, the first micropores formed by surrounding the first micropores with the block-shaped structure are found to have a relatively larger infiltration flow than the first micropores formed by surrounding the first micropores with the sheet-shaped or strip-shaped structure. The analysis may be that when the first micropores are in a closed state, the fluid to be filtered permeates the first micropores of the first outer surface, and due to the existence of surface tension, the fluid to be filtered inevitably forms bubbles on the surface of the first micropores, and the first micropores are blocked in a short time, and under the action of the fluid to be filtered which continuously flows, the bubbles are broken, so that the first micropores are unblocked and continuously permeate the fluid to be filtered. Due to the irregularity of the block structure, the invention inevitably has mutually communicated openings between the first micropores formed by surrounding the block structure, so that the membrane bubble can be pulled to the adjacent first micropores along the openings in the process of receiving the acting force, thereby promoting the rupture of the membrane bubble, reducing the blocking time of the first micropores caused by forming the membrane bubble to a certain extent, and further improving the permeation rate of the first micropores to the fluid to be filtered in unit time.

According to the invention, the SEM average pore diameter of the first micropores is changed in a gradient manner to the SEM average pore diameter of the second micropores, the SEM average pore diameter of the first micropores is larger than the SEM average pore diameter of the second micropores, the first micropores are in a lace pore shape to play a role in increasing flow, and the second micropores are in a round hole shape to play a role in intercepting impurity particles, so that the permeation flux of the porous filter membrane is ensured, and meanwhile, the interception efficiency of the impurity particles is improved. The SEM average pore diameter along the thickness direction of the porous filtering membrane gradually decreases, and usually, a certain error fluctuation range exists in the SEM average pore diameter, and in general, a part of pores larger than the SEM average pore diameter exist in the measured SEM pore diameter, namely, a part of macropores inevitably exist in each section along the thickness direction of the porous filtering membrane, and impurity particles possibly pass through the macropores; however, because the process and other factors have a substantially stable error fluctuation range of the SEM average pore diameter, although a part of macropores exists in each section, the SEM average pore diameter of the next section along the thickness direction of the porous filtering membrane is reduced, so that the SEM pore diameter of the next section is generally smaller than that of the previous section even though the next section exists, and thus the interception effect on particles passing through the previous section is realized. SEM average pore diameter in first micropore to second micropore direction is gradient change and can play "macropore" district to the effect of filtration that dams to impurity particle's multistage to a certain extent, and then further improves porous filtration membrane's efficiency of stopping.

The present invention differs from conventional composite membranes which typically have a multi-layer structure in that a dense layer is applied as a separate process step to a microporous support layer or membrane, the materials comprising the support layer and skin layer often being different, and the fluid to be filtered may have some flow attenuation at the transition separating surface due to the different materials on both sides. According to the invention, the porous filtering membrane formed by continuous fibers is specific to the composite membrane, and a transition separation surface does not exist, so that flow attenuation caused by the transition separation surface of the traditional composite membrane is avoided, and the interception filtering rate of the porous filtering membrane is improved to a certain extent.

Further, a plurality of fine protruding thorns are formed on the surface of each block structure, the fine protruding thorns are mutually hooked, ravines are formed between the block structures, a plurality of sub-holes communicated with the ravines are formed on the block structures, and the non-directional tortuous paths are formed between the ravines in a surrounding mode.

In the porous filtering membrane structure provided by the invention, a plurality of fine spines can be clearly observed to be formed on the surface of the block structure, and the fine spines are mutually hooked on the first outer surface, and as the fine spines are smaller in volume and length compared with the block structure, the fine spines usually do not influence the fluid to be filtered to permeate the first micropores when filtering is performed, namely, although the fine spines exist on the surface of the block structure, the fine spines do not influence the flux of the fluid to be filtered to permeate the first micropores.

When the porous filtering membrane is applied to the photoresist filtration, due to the existence of the fine-shaped spurs, macromolecules in the photoresist can be blocked and pulled by the fine-shaped spurs when entering the first micropores, and meanwhile, the fine-shaped spurs between the ravines can also block and pull macromolecular impurities entering the porous filtering membrane, so that the prefiltering effect on the macromolecular impurities in the photoresist is achieved to a certain extent.

According to the invention, the sub-holes of the block structure are arranged, so that the fluid to be filtered can move to the gully position in the porous filtering membrane through the sub-holes of the block structure, and compared with the solid block structure, the flux of the fluid to be filtered penetrating into the porous filtering membrane in unit time is improved to a certain extent while the integral strength of the block structure is ensured; meanwhile, the sub-holes of the block structure generally have smaller apertures, so that the block structure can play a role in blocking macromolecular impurities in photoresist to a certain extent, and a certain pre-filtering effect is achieved.

Further, the thickness ratio of the block structure along the thickness direction of the porous filtering membrane is more than 30%, and the area ratio of the sub-holes along the surface of the block structure is not less than 5%.

In the porous filtering membrane structure provided by the invention, the thickness ratio of the block structures is controlled to be more than 30%, and the gaps formed between the block structures can guide the fluid to be filtered to move along the thickness direction of the porous filtering membrane, so that the porous filtering membrane has better permeation rate; however, the thickness ratio of the block structure along the thickness direction of the porous filtering membrane is not preferably greater than 60%, if the thickness ratio of the block structure is too large, the thickness of the effective pore layer actually playing a role in intercepting is reduced, and although the increase of the thickness ratio of the block structure is favorable for improving the permeation rate of fluid to be filtered into the porous filtering membrane, the reduction of the thickness of the effective pore layer in intercepting can lead to the reduction of the actual intercepting efficiency of the porous filtering membrane.

Since the sub-pores are in communication with the corrugations within the porous filter membrane, the area ratio of the sub-pores to the surface of the block structure (i.e., on the first outer surface) can be used to some extent to characterize the distribution ratio of the sub-pores within the block structure. The area ratio of the sub-holes is controlled to be not less than 5%, so that the first hole strength is ensured, and meanwhile, a space for permeation of fluid to be filtered/photoresist molecules is provided, so that most of fluid to be filtered enters the porous filtering membrane through the first micropores, and a small part of fluid to be filtered can enter ravines in the porous filtering membrane through the sub-holes, so that the effect of improving the permeation quantity of the fluid to be filtered in unit time is achieved to a certain extent, and meanwhile, the sub-hole structure can also play a certain pre-filtering role, so that macromolecules in the fluid to be filtered such as photoresist are blocked at the sub-hole structure. However, the ratio of the area of the sub-holes is not preferably larger than 30%, and if the ratio of the area of the sub-holes is too large, the structural strength of the block structure is affected, when the block structure is pressed or pulled, the spacing between adjacent sub-holes is too close, and the ratio of the sub-holes is too large, so that the sub-holes may collapse.

Further, the SEM average pore size of the first micropores/the SEM average pore size of the second micropores is not less than 10.

In the porous filtering membrane structure provided by the invention, the SEM average pore diameter of the first micropore influences the permeation rate of fluid to be filtered into the porous filtering membrane to a greater extent, and the SEM average pore diameter of the second micropore influences the interception efficiency of the porous filtering membrane to a greater extent, so that the ratio of the SEM average pore diameter of the first micropore to the SEM average pore diameter of the second micropore is controlled to be not less than 10, and the porous filtering membrane has better permeation rate and better interception efficiency; if the ratio between the two is too small, it indicates that the SEM average pore size of the first microwell is not much different from the SEM average pore size of the second microwell. If the SEM average pore diameter of the first micropore is too small, the SEM average pore diameter of the second micropore is smaller, and although the fluid to be filtered can be well shut off, the porous filtering membrane cannot obtain a good permeation rate; on the contrary, if the SEM average pore diameter of the first micropore is too large, the SEM average pore diameter of the second micropore is larger, so that the porous filtering membrane cannot sufficiently shut off the fluid to be filtered, and further flux and shut off efficiency cannot be simultaneously considered.

The SEM average pore size of the first micropores/the SEM average pore size of the second micropores is not greater than 30.

Considering the overall structural strength of the porous filtering membrane, the ratio of the SEM average pore diameter of the first micropore to the SEM average pore diameter of the second micropore should not be too large, if the ratio of the SEM average pore diameter of the first micropore to the SEM average pore diameter of the second micropore exceeds 30, the pore diameter of the first micropore is too large, and the strength of the lace pore surface is reduced, and even the first micropore is likely to collapse due to fluid pressure during filtering. Therefore, adjusting the ratio of the SEM average pore size of the first micropores to the SEM average pore size of the second micropores to a proper value can ensure the permeation rate and simultaneously have the interception efficiency.

The SEM average pore diameters of the first micropores on the first outer surface and the second micropores on the second outer surface of the membrane can be measured by computer software (such as Matlab, NIS-Elements, etc.) or manually after the morphology of the membrane structure is characterized by using a scanning electron microscope, and corresponding calculation is performed; during the preparation of the membrane, its various characteristics, such as pore size distribution, are substantially uniform, substantially consistent, in the direction perpendicular to the membrane thickness; the average pore size of the whole on the corresponding plane can be reflected by the average pore size of the partial region on the plane. In the actual measurement, the surface of the film may be first subjected to electron microscopy Characterization, a corresponding SEM image is obtained, and since the film surface holes are substantially uniform, a certain area, e.g., 1 μm, can be selected ² (1 μm by 1 μm) or 25 μm ² (5 μm by 5 μm), measuring the pore diameters of all the pores on the specific area by corresponding computer software or manually according to the actual condition, and calculating to obtain the average pore diameter of the pores on the surface; of course, the person skilled in the art can also obtain the above parameters by other measuring means, which are only used as reference.

Further, the SEM average pore diameter of the second micropores is 15-80nm, and the dispersion coefficient of the SEM average pore diameter of the second micropores is not greater than 0.5.

According to the invention, the PMI interception pore diameter of the porous filtering membrane is 2-100nm, the SEM average pore diameter of the second micropore is 15-80nm, and the dispersion coefficient of the SEM average pore diameter of the second micropore is not more than 0.5, so that even though the SEM average pore diameter of the second micropore is controlled to be 15-80nm, the distribution uniformity of the SEM average pore diameter of the second micropore on the second outer surface is controlled to be maintained to a certain degree, and the porous filtering membrane can filter impurities with smaller particle diameters than the SEM average pore diameter. The smaller the dispersion coefficient of the SEM average pore diameter of the second micropores, the more uniform the SEM average pore diameter distribution of the second micropores on the second outer surface is proved, so that the effective PMI cutoff pore diameter range of the porous filtering membrane is adjusted by the cooperation between the SEM average pore diameter of the second micropores and the dispersion coefficient of the SEM average pore diameter of the second micropores. For example, when the porous filtration membrane of the model UPE-598-1 is tested, the SEM average pore diameter of the second micropore is measured to be about 56.4nm, the SEM average pore diameter of the second micropore is measured to be about 0.307, and the effective PMI interception pore diameter range of the porous filtration membrane of the model UPE-598-1 is tested to be 20nm.

The discrete coefficient of the second micropore can be obtained by measuring the SEM aperture and the SEM average aperture of the second micropore in the selected area by the method, calculating to obtain the average number and standard deviation, and finally obtaining the discrete coefficient of the second micropore by the standard deviation/average number obtained by calculation.

Further, the hole area ratio of the first outer surface is A1, the hole area ratio of the second outer surface is A2, and the value interval of A1/A2 is 1.1-1.4.

Further, A1 is 15-25%, A2 is 12-18%.

In the invention, the area ratio of the holes on the first outer surface and the second outer surface can be measured by computer software (such as Matlab, NIS-Elements and the like) or manually after the morphology of the film structure is characterized by using a scanning electron microscope, and corresponding calculation is performed; during the preparation of the membrane, its various characteristics, such as pore size distribution, are substantially uniform, substantially consistent, in the direction perpendicular to the membrane thickness; the overall hole area rate on the corresponding plane can be reflected by the hole area rate of a partial area on the plane; in practice, the surface of the film can be characterized by electron microscopy to obtain corresponding SEM image, and a certain area, such as 1 μm, can be selected due to the approximately uniform distribution of the holes on the surface of the film ² (1 μm by 1 μm) or 25 μm ² The hole area ratio of the first outer surface and the second outer surface can be obtained by other measuring means, and the measuring means is used for reference.

The area ratio of the holes on the first outer surface and the area ratio of the holes on the second outer surface of the porous filtering membrane are 1.1-1.4, so that the area ratio of the holes on the liquid inlet surface side is larger than the area ratio of the holes on the liquid outlet surface side, and on one hand, the area of a single first micropore in the shape of a flower edge hole is far larger than that of a single second micropore in the shape of a round hole; on the other hand, the first micropores of the first outer surface mainly play a role in increasing the permeation flow, and the control of the pore area rate of the first outer surface is maintained to a certain extent, so that the fluid to be filtered can enter the porous filtering membrane quickly, wherein the pore area rate is controlled to be 15-25% preferably, and the porous filtering membrane has a better permeation rate. If the area ratio of the holes is too high, the wall of the first micropores on the first outer surface of the porous filtering membrane may be thinner, and the first micropores may deform or even collapse when continuously subjected to external force, so that the area ratio of the holes is not too high.

The porous filtering membrane has the advantages that the hole area rate of the first outer surface of the porous filtering membrane is larger than that of the second outer surface, so that the permeation rate of one side (the liquid inlet side) of the first outer surface for fluid to be filtered is larger than that of the second outer surface (the liquid outlet side) to a certain extent; therefore, when filtering, the liquid inlet amount of the porous filtering membrane is slightly larger than the liquid outlet amount to a certain extent, and the liquid in the porous filtering membrane is subjected to the pressure of the liquid at one side of the liquid inlet, so that a certain pressure difference exists between the liquid inlet side and the liquid outlet side of the porous filtering membrane, and the movement of the fluid to be filtered in the porous filtering membrane to the liquid outlet side is promoted.

Further, the first outer surface has a pore density of 0.2 to 6 pores/μm ² The second outer surface has a pore density of 120-260 pores/μm ² 。

The pore density refers to the number of pores per unit area, and the pore density of the first outer surface and the second outer surface can be determined by, for example, observing a scanning electron microscope image of a given square surface area of the first outer surface and the second outer surface of the porous filtration membrane and calculating the number of pores within the given area. The number of holes in a given square area calculated can be normalized to a particular reference area by a simple scale; it will be appreciated that the above parameters may also be obtained by other measurement means by a person skilled in the art.

According to the porous filtering membrane, the SEM average pore diameter of the first micropores is far larger than that of the second micropores, the pore density of the first outer surface is far lower than that of the second outer surface, on one hand, the SEM average pore diameter of the first micropores is matched with the pore density, the characteristic of large pore diameter and sparse distribution is reflected, the effect of increasing the permeation flow is achieved, the liquid inlet surface of the porous filtering membrane has good permeation rate, meanwhile, the distribution of the first micropores is not excessively dense, and therefore the strength and the stability of the holes at one side of the liquid inlet surface of the porous filtering membrane are improved, and the probability of collapse of the holes is reduced; the SEM average pore diameter and the pore density of the second micropores are combined, so that the characteristics of thin pore diameter and dense distribution are reflected, the fine interception function of fluid to be filtered is achieved, and the porous filtering membrane has better interception efficiency.

Further, the SEM average pore size gradient from the first outer surface to the second outer surface is 10-80nm/μm.

Further, under the condition that the positive pressure is 0.03MPa and the temperature is 20 ℃, the time required for 50ml of water to pass through the porous filtering membrane with the diameter of 47mm is 60-3000s;

the transverse tensile strength of the porous filtering membrane is 3.4-14.18MPa; the longitudinal tensile strength of the porous filtering membrane is 4.4-14.83MPa.

In the application, the flow rate test is carried out on the polyethylene flat membrane, and the time required for 50ml of water to pass through the polyethylene flat membrane with the diameter of 47mm is 300-3000s under the conditions of the pressure of 0.03MPa and the temperature of 20 ℃, wherein the polyethylene flat membrane can be divided into the models of 2nm, 5nm, 10nm, 20nm, 50nm, 100nm and the like according to the difference of PMI interception pore diameters, and the time required for fluid to pass through a UPE porous filter membrane with the PMI interception pore diameter of 2nm is longest; the flow rate test experiment shows that the porous filtering membrane has larger flow rate, the time required by fluid passing through the porous filtering membrane is shorter, the time cost during filtering is lower, and higher economic benefit can be generated, and meanwhile, the porous filtering membrane is suitable for being applied to the field of photoresist.

The time of water passing through the porous filtering membrane reflects the flux of the porous filtering membrane to a certain extent, and on the premise of carrying out multiple experiments, based on the structure of the UPE porous filtering membrane in the application, the time of water passing through the porous filtering membrane can be influenced by the combined action of the thickness of the membrane, the pore diameters of the first outer surface and the second outer surface, the proportion of the block structure in the membrane thickness direction and the pore area ratio of the first outer surface and the second outer surface.

Further, the preparation method of the UPE porous filtering membrane 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 with the solid content of 8-14%; wherein the polyethylene resin is ultra-high molecular weight polyethylene with mass average molecular weight of 200 ten thousand to 500 ten thousand, the compound A is a non-solvent of the polyethylene resin, the compound B is a solvent of the polyethylene resin, and the content of the compound A is higher than that of the compound B;

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

s3: carrying out split-phase solidification on the liquid film at 15-120 ℃ to form a raw film; wherein the ratio of the cooling rate of the second outer surface side to the cooling rate of the first outer surface side is more than or equal to 2, the cooling rate of the second outer surface side is controlled to be 20-100 ℃/s, and the cooling rate of the first outer surface side is controlled to be 8.5-50 ℃/s;

s4: performing primary heat setting on the original film, and controlling the temperature of the primary heat setting to be 40-100 ℃ to obtain a green film;

S5: extracting the solvent system with an extraction liquid, so that the solvent system is removed from the green film to obtain a formed film;

s6: and (3) performing secondary heat setting on the original film, and controlling the temperature of the secondary heat setting to be 60-120 ℃ to prepare the ultra-high molecular weight polyethylene porous film.

In the application, the aim of low solid content in the casting film liquid is fulfilled by controlling the molecular weight of the polyethylene resin to be 200-500 ten thousand, and simultaneously, a UPE porous filter film with a flower-edge hole on one side and a round hole on the other side is formed by utilizing different phase separation speeds on two sides of the liquid film. The solid content refers to the content of the ultra-high molecular weight polyethylene molecules in the casting solution, and the solid content is controlled by controlling the addition amount and the mass average molecular weight of the ultra-high molecular weight polyethylene. Under the condition that other conditions such as phase separation conditions and the like are basically the same, the casting solution with low solid content is easier to form macropores, and the casting solution with high solid content is easier to form pinholes; at the moment, the cooling rate of the second outer surface side is controlled to be higher than that of the first outer surface side; the second outer surface is formed into dense small holes due to the sudden drop of temperature and the influence of the solid content of the second outer surface side, and the first outer surface side is also formed into flower edge holes, namely large holes due to the influence of the cooling rate and the solid content of the first outer surface side.

Through multiple experiments, the aperture of the first micropore on the first outer surface and the aperture of the second micropore on the second outer surface can be influenced by the solid content, the cooling rate and other factors in the casting film liquid.

In the invention, heat setting is carried out before extraction, and the stress in the original film is eliminated as much as possible by heat setting before extraction under the condition that the original film has stress and possibly contracts due to the stress in the extraction process; the first heat setting temperature is controlled to be 40-100 ℃, and because the porous filtering membrane contains oily substances, potential safety hazards can be caused by the excessive heat setting temperature, and the first heat setting temperature is preferably 60-80 ℃. The second heat setting is used for stabilizing the structure with the flower edge holes on one side and the round holes on the other side of the porous filtering membrane, the control temperature is 60-120 ℃, and the condition that the fibers in the porous filtering membrane are combined and shrinkage holes are generated due to the fact that the temperature is too high, and the second heat setting temperature is preferably 70-100 ℃.

In the course of multiple experiments, controlling the temperature of the first heat setting and the second heat setting in a proper range may be one of factors affecting the uniformity of dispersion of the first micropores on the first outer surface and the second micropores on the second outer surface.

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

polyethylene resin: 10-18 parts of a lubricant;

compound a:50-70 parts;

compound B:15-45 parts;

the compound A is at least one of dimethyl phthalate, dioctyl adipate, glycol diacetate, triphenyl phosphate, dicyclohexyl phthalate, glyceryl triacetate and dipropyl carbonate, and the compound B is at least one of paraffin oil, white oil, hydraulic oil, decalin, castor oil extract, castor oil and acetyl tributyl citrate.

Further, one side of the liquid film is provided with a liquid cooling roller, the temperature of the liquid cooling roller is set to be 5-40 ℃, the other side of the liquid film is provided with air, and the temperature of the air side is set to be 20-25 ℃.

According to the invention, the compound A is a volatile component, the component B is a non-volatile component, the volatilization speed of the compound A is controlled to a certain extent by controlling the volatilization environments on two sides of the liquid film, so that the adjustment of the solid content on two sides of the liquid film is realized, when the liquid inlet side (namely the macroporous side) of the liquid film is set to be the air side, the film casting liquid is exposed in the air environment, the film casting liquid can volatilize to a certain extent, the proportion of the compound A in the film casting liquid is gradually reduced, and the proportion of the compound B and the polyethylene resin in the film casting liquid is gradually increased; the liquid film liquid outlet side (small hole side) is set as a carrier side, the volatilization environment of the casting film liquid is not as good as that of the liquid film liquid inlet side, and further, the liquid inlet side and the liquid outlet side are different in solid content due to the fact that the liquid inlet side and the liquid outlet side are different in volatilization environment, and the phase separation speed difference of the liquid inlet side and the liquid outlet side is added, so that UPE porous asymmetric filtering films with a flower side hole on one side and a round hole on the other side are finally formed under the influence of various process parameters, generally speaking, the phase separation speed on one side with relatively high solid content is controlled relatively fast, and the round holes are formed; the phase separation speed of one side with relatively low solid content is controlled slowly, and the flower edge holes are formed.

In the invention, different influencing factors influencing the phase separation speed of the liquid inlet side and the liquid outlet side are medium and temperature gradient difference, the medium at the liquid inlet side adopts air, the cooling rate is lower than that at the liquid outlet side, the cooling rate is adaptively adjusted according to the difference of the thickness of the porous filtering film, for example, the time required for reducing the temperature from 200 ℃ to 30 ℃ is 3-20s, and the lace-shaped pore morphology at the liquid inlet side is further formed; the liquid-cooled roller is adopted as the liquid-outlet side medium, for example, the time required for reducing the temperature from 200 ℃ to 100 ℃ is 1-5s, and the quenching mode is adopted, and the solid content of the liquid-outlet side is set, so that the appearance of a compact round hole on the liquid-outlet side is formed.

Further, the UPE porous filter membrane is used for filtering photoresist and solvent filtration.

In the invention, the macroporous surface (first outer surface) of the porous filtering membrane is used as a liquid inlet surface, and the small pore surface (first outer surface) of the porous filtering membrane is used as a liquid outlet surface, so that the porous filtering membrane has excellent trapping performance, permeation speed and filtering precision on impurity particles in the photoresist field; meanwhile, the porous filtering membrane has higher sewage containing amount, longer service life and higher economic benefit. For example UPE is used in developer and ultrapure water, mainly Solvent, and mainly OK73, PGMEA, PGME, IPA and so on.

Drawings

The application is further described below with reference to the accompanying drawings:

FIG. 1 is a scanning electron microscope image of a second outer surface of the ultra high molecular weight polyethylene porous filtration membrane prepared in example 1, wherein the magnification is 50K×;

FIG. 2 is a scanning electron microscope image of a first outer surface of the ultra high molecular weight polyethylene porous filtration membrane prepared in example 1, wherein the magnification is 5K×;

FIG. 3 is a scanning electron microscope image of the second outer surface of the ultra high molecular weight polyethylene porous filtration membrane prepared in example 6, wherein the magnification is 20K×;

FIG. 4 is a scanning electron microscope image of the first outer surface of the ultra high molecular weight polyethylene porous filtration membrane prepared in example 6, wherein the magnification is 5K×;

FIG. 5 is a further scanning electron microscope image of the first outer surface of the ultra high molecular weight polyethylene porous filtration membrane prepared in example 6, at 20K× magnification;

FIG. 6 is a scanning electron microscope image of a cross section of an ultra high molecular weight polyethylene porous filtration membrane prepared in example 1, wherein the magnification is 10K×;

FIG. 7 is a schematic diagram of an apparatus for flow rate testing of ultra-high molecular weight polyethylene flat sheet membranes according to the present application;

FIG. 8 is a schematic diagram of an apparatus for testing the filtration accuracy (rejection efficiency) of an ultra-high molecular weight polyethylene flat membrane according to the present application.

Detailed Description

The present invention will be described in further detail with reference to the following examples, in which raw materials and equipment for producing a porous filtration membrane are commercially available, unless otherwise specified.

Example 1

A preparation method of a UPE porous filter membrane comprises the following steps:

s1: adding polyethylene resin into a solvent system consisting of a compound A and a compound B, stirring and mixing the polyethylene resin and the solvent system to form a mixed material after uniform mixing; the compound A is a non-solvent of polyethylene resin; the compound B is a solvent for the polyethylene resin;

the mixed material comprises the following raw materials in parts by weight: polyethylene resin: 12 parts; compound a:62 parts; compound B:28 parts;

wherein the polyethylene resin is ultra-high molecular weight polyethylene with mass average molecular weight of 300 ten thousand; the compound A is dimethyl phthalate, and the compound B is paraffin oil;

s2: heating, melting and mixing the mixed material in an extruder at 220-250 ℃ for 20min to form a casting solution, and extruding the casting solution through a die head to form a liquid film; wherein the die extrusion temperature is 235 ℃;

s3: the liquid film is placed in different environments for split-phase solidification, one side of the liquid film is placed in an air environment, the temperature of the air side is set to 25 ℃, the liquid cooling roller is arranged on the other side of the liquid film, the carrier temperature is set to 30 ℃, the cooling rate of the air side is 20 ℃/s, the cooling rate of the carrier side is 60 ℃/s, and after the split-phase solidification is finished, a raw film is formed;

S4: performing primary heat setting on the original film, and controlling the primary heat setting temperature to be 60 ℃ to form a green film;

s5: extracting the solvent system with extracting solution dichloromethane to remove the solvent system from the green film and obtain a formed film;

s6: and (3) performing secondary heat setting on the formed film, and controlling the temperature of the secondary heat setting to be 80 ℃ to obtain the UPE porous filtering film.

Wherein the UPE porous filter membrane prepared by the example 1 is shown in figures 1-2 and 6.

Examples 2 to 26

Examples 2 to 26 are different from example 1 in the composition ratio of the casting solution and the process parameters, and are shown in tables 1 to 1, 1 to 2, 1 to 3, and 1 to 4.

Wherein the UPE porous filtration membrane prepared by example 6 is shown in FIGS. 3-5.

Comparative example 1

Comparative example 1 differs from example 5 in that an equivalent amount of paraffin oil was used instead of dimethyl phthalate, and the remaining process parameters are shown in tables 1-5.

Comparative examples 2 to 3

Comparative examples 2-3 differ from example 5 in that both sides of the liquid film were cooled in the same environment, and the remaining process parameters are shown in tables 1-5.

Comparative example 4

Comparative example 4 differs from example 1 in that the polyethylene resin has a mass average molecular weight of 150 ten thousand, and the remaining process parameters are specified in tables 1 to 5.

TABLE 1-1

TABLE 1-2

Tables 1 to 3

Tables 1 to 4

Tables 1 to 5

Membrane structure parameter detection

The ultra-high molecular weight polyethylene porous filtering membranes prepared in examples 1-26 and comparative examples 1-4 were subjected to morphology characterization by using a scanning electron microscope, and the first outer surface, the second outer surface and the cross section of the ultra-high molecular weight polyethylene porous filtering membrane were selected as observation objects, and specific detection and measurement results are shown in tables 2-1, 2-2, 2-3 and 2-4.

TABLE 2-1

TABLE 2-2

Tables 2 to 3

Tables 2 to 4

Membrane performance parameter detection

The surfaces and the sections of the UPE porous filtering membranes prepared in examples 1-26 and comparative examples 1-4 are observed through a scanning electron microscope, wherein the UPE porous filtering membrane prepared in examples 1-26 comprises a main body, a first outer surface and a second outer surface are respectively formed on two sides of the main body, a first micropore in a lace hole shape is formed on the first outer surface, a second micropore in a round hole shape is formed on the second outer surface, the SEM average pore diameter of the first micropore is far greater than that of the second micropore, the SEM average pore diameters of the first micropore and the second micropore are in gradient change in the section, the first outer surface and the second outer surface serve as a liquid inlet surface and a liquid outlet surface respectively, and a non-directional tortuous path is formed between the first outer surface and the second outer surface.

The liquid inlet surface side can clearly see that a plurality of block structures are arranged, the first micropores are formed by surrounding the block structures, a plurality of fine openings are inevitably arranged between the adjacent first micropores due to the diversity of the block structures, so that the adjacent first micropores are mutually communicated, a plurality of fine spurs extend out of the surfaces of the block structures, and compared with the block structures, the fine spurs are small in volume and length, and the fine spurs are mutually hooked on the first outer surface and the section of the UPE porous filtering membrane. The block structure is provided with a plurality of grooves, a plurality of groups of grooves are longitudinally communicated to form a non-directional tortuous path, the block structure is also provided with a plurality of sub-holes communicated with the grooves, and the sub-holes are communicated with the internal non-directional tortuous path.

The UPE porous filtering membrane obtained in comparative examples 1 to 4 could not obtain the morphology described above, so that the mass average molecular weight of the polyethylene resin, the difference between the solid contents of both sides of the liquid membrane, and the phase separation speed difference could be decisive factors for forming the UPE porous filtering membrane, and when the mass average molecular weight of the ultra-high molecular weight polyethylene is less than 200 ten thousand, the formed UPE porous filtering membrane could not have a structure with one side of "flower-edge hole" and one side of round hole.

1.1 Water flow Rate test (test device As shown in FIG. 7)

Experimental procedure

Step one: the IPA wet test sample (the ultra-high molecular weight polyethylene porous filter membrane prepared in examples 1-26 and comparative examples 1-4) was mounted on a support for reduced pressure filtration, the valve 2 on the reduced pressure filtration support was closed, the valve 1 was opened, the vacuum pump was started, the pressure was adjusted to 0.03MPa, and the valve 1 was closed.

Step two: filling 50ml of test liquid (water) into a plastic measuring cylinder of a support for decompression filtration, opening a valve 2, starting timing from one scale to the other scale, and stopping timing;

step three: after the test is completed, the value displayed by the stopwatch is recorded, when all the test liquid passes through the filter membrane, the valve 2 on the bracket is closed, and the sample is taken out.

The test results are shown in Table 3.

TABLE 3 Table 3

1.2 filtration accuracy test: the ultra high molecular weight polyethylene porous filtration membranes prepared in examples 1 to 26 and comparative examples 1 to 4 were subjected to a test for interception efficiency.

Experimental facilities: tianjin root particle counter KB-3; experiment preparation: the experimental device was assembled according to fig. 8, ensuring the device was clean, and rinsed with ultrapure water; a sample with a diameter of 47mm is taken and placed in the butterfly filter, so that the air tightness of the assembled filter is ensured to be good.

The experimental steps are as follows:

The challenge fluid was poured into a tank, the butterfly filter was carefully vented, pressurized to 10kPa, and the butterfly downstream filtrate was taken using a clean bottle.

The number of particles in the filtrate and stock solutions was measured with a particle counter.

Interception efficiency:

wherein: η -interception efficiency,%; n 0-number of particles in stock solution, average of 5 counts, one; n 1-number of particles in filtrate, average of 5 counts.

The interception efficiency test results of each example and comparative example are shown in table 4:

TABLE 4 Table 4

1.3 tensile Strength test: the ultra-high molecular weight polyethylene porous filtration membranes prepared in examples 1 to 26 and comparative examples 1 to 4 were tested for transverse tensile strength and longitudinal tensile strength by a universal tensile tester, wherein the tensile tester had a width of 10mm and a pitch of 30mm, and tensile strength mpa=breaking force cN/102/(thickness mean mm×width mm), (1n=102 cN,1 mm=1000 μm), wherein the longitudinal tensile strength was tensile strength in the film winding direction and the transverse tensile strength was tensile strength perpendicular to the film winding direction, and the test results are shown in table 5.

TABLE 5

As can be seen from Table 3, the UPE porous filtration membranes prepared in examples 1 to 26 of the present application have a wide filtration accuracy, the UPE porous filtration membranes of different types are each capable of substantially exhibiting a trapping efficiency of more than 95% for impurity particles of 2 to 100nm, and a strong trapping ability for impurity particles, whereas in the UPE porous filtration membranes prepared in comparative examples 1 to 3, the UPE porous membranes of comparative example 3 exhibit a reduction in the trapping accuracy for impurity particles as compared to the comparative example (example 5).

As can be seen from Table 4, the UPE porous filter membranes prepared in examples 1-26 of the application have good flow rates according to different filter accuracies, namely, the UPE porous filter membranes ensure the interception efficiency of impurity particles and simultaneously have good flow rates, and are particularly suitable for being applied to the field of photoresist; in the UPE porous filtration membranes produced in comparative examples 1 to 3, however, the UPE porous membranes of comparative examples 1 to 2 exhibited a decrease in flow rate as compared to the control example (example 5).

As can be seen from Table 5, the UPE porous filtration membranes prepared in examples 1 to 26 of the present application had better tensile strength, whereas the UPE porous filtration membranes prepared in comparative examples 1 to 4 showed a decrease in tensile strength as compared to the comparative example (example 5) and an increase in tensile strength as compared to the comparative example (example 5) in comparative examples 2 to 3; the analysis may be that the tensile strength may be affected by factors such as the solid content of the casting film liquid and the film thickness, and comparative examples 2 to 3 make the volatile environment on both sides of the liquid film better, and to some extent, the volatile component compound a is reduced, and the contents of the compound B and the polyethylene resin are increased, thereby amplifying the solid content to some extent, thus making the tensile strength of comparative examples 2 to 3 slightly larger than that of the comparative example (example 5).

The UPE porous filtering membranes prepared in comparative examples 1-4 are difficult to simultaneously have membrane flux and interception efficiency, while the UPE porous filtering membranes prepared in examples 1-26 have better membrane flux and better tensile strength under the division of interception precision, so that the UPE porous filtering membranes are suitable for being applied to the field of photoresist.

While the preferred embodiments of the present application have been described in detail, it will be appreciated that those skilled in the art, upon reading the above teachings, may make various changes and modifications to the application. Such equivalents are also intended to fall within the scope of the application as defined by the following claims.

Claims

1. The utility model provides a UPE porous filter membrane, includes the main part, the both sides of main part are formed with first surface and second external surface respectively, be formed with non-directional tortuous passageway in the main part, its characterized in that: the PMI average pore diameter of the porous membrane is 2-100nm; the first outer surface is provided with first micropores, the second outer surface is provided with second micropores, the first micropores are in a lace hole shape and are formed by surrounding a plurality of block structures, the second micropores are in a round hole shape, the SEM average pore diameter of the first micropores is larger than that of the second micropores, and the SEM average pore diameters from the first micropores to the second micropores are in gradient change;

2. A UPE porous filtration membrane according to claim 1, characterized in that: the surface of each block structure is provided with a plurality of fine spurs, the fine spurs are mutually hooked, grooves are formed between the block structures, the block structures are provided with a plurality of sub-holes communicated with the grooves, and the non-directional tortuous passages are formed between the grooves in a surrounding mode.

3. A UPE porous filtration membrane according to claim 1, characterized in that: the thickness ratio of the block structure along the thickness direction of the porous filtering membrane is more than 30%.

4. A UPE porous filtration membrane according to claim 2, characterized in that: the area of the sub-holes along the surface of the block structure is not less than 5%.

5. A UPE porous filtration membrane according to claim 1, characterized in that: the SEM average pore size of the first micropores/the SEM average pore size of the second micropores is not less than 10.

6. A UPE porous filtration membrane according to claim 1, characterized in that: the SEM average pore diameter of the second micropores is 15-80nm, and the dispersion coefficient of the SEM average pore diameter of the second micropores is not more than 0.5.

7. A UPE porous filtration membrane according to claim 1, characterized in that: the hole area ratio of the first outer surface is A1, the hole area ratio of the second outer surface is A2, the value interval of A1/A2 is 1.1-1.4, and A1 is 15-25%.

8. A UPE porous filtration membrane according to claim 7, wherein: the first outer surface has a pore density of 0.2-6 pores/μm ² The second outer surface has a pore density of 120-260 pores/μm ² 。

9. A UPE porous filtration membrane according to claim 1, characterized in that: the SEM average pore size gradient from the first outer surface to the second outer surface is 4-30nm/μm.

10. A UPE porous filtration membrane according to claim 1, characterized in that: under the conditions of positive pressure of 0.03MPa and temperature of 20 ℃, the time required for 50ml of water to pass through the porous filtering membrane with the diameter of 47mm is 60-3000s;

11. A method for preparing a UPE porous filtration membrane according to any one of claims 1-10, comprising the steps of:

S2: heating, melting and mixing the mixed materials at 220-250 ℃ to form a casting solution, and extruding the casting solution through a die head to form a liquid film;

s3: carrying out split-phase solidification on the liquid film at 15-120 ℃ to form a raw film; the phase separation speeds at two sides of the film are different, wherein the ratio of the cooling rate at one side of the second outer surface to the cooling rate at one side of the first outer surface is more than or equal to 2, the cooling rate at one side of the second outer surface is controlled to be 20-100 ℃/s, and the cooling rate at one side of the first outer surface is controlled to be 8.5-50 ℃/s;

s4: performing primary heat setting on the original film, and controlling the temperature of the primary heat setting to be 40-100 ℃ to form a green film;

s6: and (3) performing secondary heat setting on the formed film, and controlling the temperature of the secondary heat setting to be 60-120 ℃ to prepare the ultra-high molecular weight polyethylene porous film.

12. The method for preparing a UPE porous filtering membrane according to claim 11, wherein the method comprises the following steps: the mixed material comprises the following substances in parts by weight:

polyethylene resin: 10-18 parts of a lubricant;

compound a:50-70 parts;

compound B:15-45 parts;

13. The method for preparing a UPE porous filtering membrane according to claim 12, wherein the method comprises the following steps: one side of the liquid film is provided with a liquid cooling roller, the temperature of the liquid cooling roller is set to be 5-40 ℃, the other side of the liquid film is provided with air, and the temperature of the air side is set to be 20-25 ℃.

14. Use of a UPE porous filtration membrane according to any one of claims 1-10, characterized in that: the UPE porous filter membrane is used for filtering photoresist and solvent.