阅读说明：本技术 一种高比表面积的upe多孔膜及其制备方法与用途 (UPE porous membrane with high specific surface area, and preparation method and application thereof ) 是由 陈梦泽 吕海江 于 2021-09-16 设计创作，主要内容包括：本发明提供了一种高比表面积的UPE多孔膜及其制备方法与用途,该多孔膜包含第一多孔外表面、第二多孔外表面以及位于第一多孔外表面和第二多孔外表面之间的主体,主体内具有非定向曲折通路；该UPE多孔膜的比表面积不低于35m～(2)/g,比表面积高；第一多孔外表面上有若干个枝丫状的连续的第一纤维,相邻的连续的第一纤维之间环绕形成第一孔洞；沿厚度方向的第一纤维相互层叠；第一纤维的平均直径为10-60nm；该UPE多孔膜为对称膜,该高比表面积的UPE多孔膜能够除了通过膜孔进行截留外,还能进行吸附截留,对纳米级细小杂质具有优异的捕集性能,截留效率高；适合应用于光刻胶过滤领域；本发明提供的制备方法能方便、快速、有效地制备获得该UPE多孔膜。(The invention provides a UPE porous membrane with high specific surface area, a preparation method and application thereof, wherein the porous membrane comprises a first porous outer surface, a second porous outer surface and a main body positioned between the first porous outer surface and the second porous outer surface, and a non-directional tortuous passage is arranged in the main body; the specific surface area of the UPE porous membrane is not less than 35m 2 The specific surface area is high; a plurality of branch-shaped continuous first fibers are arranged on the outer surface of the first porous body, and first holes are formed between adjacent continuous first fibers in a surrounding mode; first fibers are stacked on each other in the thickness direction; the first fibers have an average diameter of 10 to 60 nm; the UPE porous membrane is a symmetrical membrane, can carry out adsorption interception besides interception through membrane pores, has excellent trapping performance on nano-scale fine impurities,the interception efficiency is high; the method is suitable for being applied to the field of photoresist filtration; the preparation method provided by the invention can conveniently, quickly and effectively prepare and obtain the UPE porous membrane.)

1. A high surface area UPE porous membrane comprising a first porous outer surface, a second porous outer surface, and a body positioned between the first porous outer surface and the second porous outer surface, the body having a non-directional tortuous path therein characterized by:

the specific surface area of the UPE porous membrane is not less than 35m²/g；

The first porous outer surface comprises a plurality of branch-shaped continuous first fibers, and first holes are formed between adjacent continuous first fibers in a surrounding mode; first fibers are stacked on each other in the thickness direction; the first fibers have an average diameter of 10 to 60 nm;

the UPE porous membrane is a symmetrical membrane, and the polyolefin composition forming the UPE porous membrane at least comprises ultrahigh molecular weight polyethylene with the mass-average molecular weight of more than 300 ten thousand.

2. The UPE porous membrane with high specific surface area according to claim 1, wherein: a plurality of first round hole-shaped holes are formed in the outer surface of the first porous body; the area ratio of the first holes on the outer surface of the first porous body is 30-70%; the average pore diameter of the first pores is 1-150 nm.

3. The UPE porous membrane with high specific surface area according to claim 1, wherein: the thickness of the UPE porous membrane is 1-30 μm; the porosity of the UPE porous membrane is 45-85%; the surface area of the membrane inside per membrane area is 0.4 to 0.8.

4. The UPE porous membrane with high specific surface area according to claim 3, wherein: the specific surface area of the UPE porous membrane is 40-80m²(ii)/g; the porosity of the UPE porous membrane is 50-75%; the thickness of the UPE porous membrane is 5-20 μm.

5. The UPE porous membrane with high specific surface area according to claim 1, wherein: the second porous outer surface comprises a plurality of branch-shaped continuous second fibers, and second holes are formed between adjacent continuous second fibers in a surrounding mode; the second fibers have an average diameter of 10 to 60 nm.

6. The UPE porous membrane with high specific surface area according to claim 5, wherein: the ratio of the average diameter of the second fibers to the average diameter of the first fibers is 0.7 to 1.5; the second hole is in a round hole shape; the area ratio of the second holes on the second porous outer surface is 30-70%.

7. The UPE porous membrane with high specific surface area according to claim 5, wherein: the average pore diameter of the second pores is 1-150 nm; the ratio of the average pore diameter of the second pores to the average pore diameter of the first pores is 0.78-1.35.

8. The UPE porous membrane with high specific surface area according to claim 1, wherein: the ratio of the IPA initial bubble point to the IPA complete bubble point of the UPE porous membrane is not lower than 0.4; the IPA complete foaming point of the UPE porous membrane is not lower than 0.2 MPa.

9. The UPE porous membrane with high specific surface area according to claim 1, wherein: 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 120 ℃.

10. The UPE porous membrane with high specific surface area according to claim 1, wherein:

the interception efficiency of the UPE porous membrane to impurity particles with the particle size of 1-150nm is more than 95%;

the time required for 50ml of water to pass through a porous membrane with a diameter of 47mm is not more than 500s 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%.

11. The preparation method of the UPE porous membrane with high specific surface area as claimed in any one of claims 1 to 10, comprising 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: 10-25 parts; a compound A: 0-20 parts of a solvent; compound B: 70-90 parts;

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;

s2: heating, melting and mixing the mixed material at the temperature of 150-260 ℃ 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 ℃ and 250 ℃;

s3: carrying out phase-splitting curing on the liquid film at the temperature of 15-50 ℃ for 2-50s to form a green film; during split-phase solidification, the temperature difference between the liquid film carrier side and the liquid film air side is 5-20 ℃; and in the phase-splitting curing process, the carrier side and the air side of the liquid film are converted at least once;

s4: then stretching the raw film, and performing primary heat setting after stretching;

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 carrying out secondary heat setting on the original membrane to obtain the UPE porous membrane.

12. The method for preparing a UPE porous membrane with high specific surface area according to claim 11, wherein: the polyethylene resin comprises 65-85 mass% of ultrahigh molecular weight polyethylene with the mass average molecular weight of more than 300 ten thousand and 15-35 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).

13. The method for preparing a UPE porous membrane with high specific surface area according to claim 11, wherein: the stretching treatment of the green film in S4 means that the green film is simultaneously subjected to transverse stretching and longitudinal stretching at a temperature of 60 to 150 ℃, at a transverse stretching ratio of 1 to 10 times, and at a longitudinal stretching ratio of 1 to 10 times.

14. The method for preparing a UPE porous membrane with high specific surface area as claimed in claim 13, wherein: s4, stretching the raw film, wherein the ratio of longitudinal stretching multiple to transverse stretching multiple is 0.8-2; the stretching rate in the transverse direction is 5%/s to 100%/s, and the stretching rate in the longitudinal direction is 5%/s to 100%/s.

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

16. The method for preparing a UPE porous membrane with high specific surface area according to claim 11, wherein: the temperature for the first heat setting is 100-180 ℃, and the time is 20-90 s; the temperature of the second heat setting is 10-40 deg.C higher than that of the first heat setting, and the time is 20-90 s.

17. Use of a high surface area UPE porous membrane according to any of claims 1-10 wherein: the UPE porous membrane is used for filtering photoresist.

18. A folding filter cartridge according to any one of claims 1 to 10 comprising a center stem and a UPE porous membrane positioned about the center stem, the UPE porous membrane folded to form pleats having valleys adjacent the side of the center stem and 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 according to any one of claims 1 to 12, and the membrane area of the UPE porous membrane in the folding filter element is 0.1 to 2m²。

Technical Field

The invention relates to the technical field of membrane materials, in particular to a UPE porous membrane with a high specific surface area, 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, the purity requirement of the photoresist is strict, because a small amount of fine impurities in the photoresist can generate great influence on the photoetching quality, so that the product after photoetching can not meet the requirement of practical application; therefore, it is desirable to intercept various substances (particles, metal ions, etc.) in the photoresist as much as possible when the photoresist is filtered by the filter membrane, so as to meet the requirements of practical application; however, in the current market, the polyolefin filter membrane generally has a high efficiency of intercepting impurity particles in the photoresist, which limits the development of polyolefin polymer filter membranes 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 high specific surface area, a preparation method and application thereof; the UPE porous membrane has high specific surface area, can retain various impurities through the membrane pores, and can also adsorb and retain the impurities, so that various impurities can be captured at high quality, and the retention efficiency is high; is particularly suitable for the field of photoresist filtration.

To achieve the above object, the inventionThe invention provides the following technical scheme: a UPE porous membrane with high specific surface area, comprising a first porous outer surface, a second porous outer surface and a main body positioned between the first porous outer surface and the second porous outer surface, wherein the main body is internally provided with non-directional tortuous passages, and the specific surface area of the UPE porous membrane is not less than 35m²(ii)/g; the first porous outer surface comprises a plurality of branch-shaped continuous first fibers, and first holes are formed between adjacent continuous first fibers in a surrounding mode; first fibers are stacked on each other in the thickness direction; the first fibers have an average diameter of 10 to 60 nm; the UPE porous membrane is a symmetrical membrane, and the polyolefin composition forming the UPE porous membrane at least comprises ultrahigh molecular weight polyethylene with the mass-average molecular weight of more than 300 ten thousand.

After the specific surface area test of the UPE porous membrane of the invention by the BET method, we surprisingly found that the specific surface area of the UPE porous membrane is higher, and the specific surface area is not less than 35m²The specific surface area of the existing UPE porous membrane is generally 25 to 30m²Specific surface area is the total area of unit mass of material (the invention refers to a porous membrane), and the larger the specific surface area is, the larger the total area of a certain mass of UPE porous membrane is; it is demonstrated that the UPE porous membranes of the present invention have the following advantages:

1. besides the impurity substances in the photoresist are intercepted through the membrane pores, the UPE porous membrane can also adsorb various impurity substances through acting forces such as Van der Waals force and the like; thereby improving the efficiency of the filter membrane for intercepting various impurities; meanwhile, according to the experimental results, the UPE porous membrane is slightly negatively charged after being contacted with the feed liquid, and the UPE porous membrane with the negative charge has stronger adsorbability; the UPE film with high specific surface area has the advantages that under the condition that the charge amount of a unit specific surface area is constant, the total charge of the UPE film with high specific surface area is large, so that the adsorption effect is good, and the capability of retaining impurity substances is stronger; besides some metal ions and small particle impurities, the organic resin substances as the effective components in the photoresist are agglomerated in the processes of transportation and the like (for example, PMMA resin as the effective component in KrF photoresist is easily agglomerated, and ketones as the effective components in I line/KrF photoresist are also easily agglomerated), and the agglomerated effective resins have certain influence on the light refractive index, so that the stability of the photoetching process is influenced, and the photoetching process cannot achieve an ideal result; at the moment, the charged UPE film with the high specific surface area has a good adsorption effect on the impurities, so that the stability of the photoetching process is ensured, and an ideal photoetching process is realized; in addition, when the UPE with high specific surface area can also be used as a base membrane material to develop a membrane for purification (removing metal ions), the UPE with high specific surface area has high specific surface area, so that the number of functional groups which can be grafted is relatively more, and the removal rate and the service life of the membrane modified by the UPE with high specific surface area to the metal ions in a solvent are greatly improved; when special applications require functional groups to adsorb or exchange ions in a reagent, the UPE with high surface area can improve higher capacity space, so that the UPE porous membrane is very suitable for various modification uses of a base membrane;

2. when the UPE with high specific surface area is used as a filtering membrane, more contact opportunities of the reagent and the membrane can be provided, so that the possibility of blocking impurities in the reagent by the membrane is improved, the blocking efficiency is further improved, and meanwhile, the UPE porous membrane with high specific surface area can provide more pore volume so that the UPE porous membrane has larger pollutant carrying capacity as a filtering membrane material.

Meanwhile, in the membrane body structure of the UPE porous membrane provided by the invention, a plurality of first fibers are clearly seen on the first porous outer surface of the UPE porous membrane, the first fibers are in a branched structure, and the first fibers are continuous with the first fibers; the adjacent continuous first fibers are mutually encircled to form first holes, so that a porous structure of the membrane is formed, and the membrane formed by the first fiber structure has higher specific surface area; meanwhile, in the thickness direction, the first fibers are mutually laminated and mutually interwoven and superposed near the outer surface of the first porous body, so that the filtering of impurities is facilitated, and the higher interception efficiency of impurity particles is ensured; on the outer surface of the first porous membrane, the average diameter of the first fibers is 10-60nm, so that the thick and thin first fibers ensure that the whole membrane has high tensile strength and can meet the requirements of actual industrial production, and on the other hand, the first holes formed by the first fibers have high stability and are not easy to collapse or shrink, thereby ensuring the stability of the flow rate of the fluid;

in addition, the UPE porous membrane is a symmetrical membrane, and the symmetrical meaning means that the first porous outer surface and the second porous outer surface on the UPE porous membrane have basically similar or even identical structures, and the shapes, the pore sizes and the pore area ratios of the pores on the two outer surfaces are basically similar and have small difference (close to the same); in practical use, any outer surface can be used as a liquid inlet surface (if the membrane is an asymmetric membrane, a specific outer surface is generally required to be used as the liquid inlet surface), so that the relevant processes of assembly of the porous membrane and the like are simpler, and a high-quality filter element is easier to prepare;

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 average diameter of the first fibers on the first porous outer surface of the porous membrane can be measured by computer software (such as Matlab, NIS-Elements, etc.) or manually after the morphology characterization of the membrane structure by using a scanning electron microscope, and corresponding calculation is performed; in the preparation of the film, the film thickness is measured perpendicularly to the film thicknessIn the direction of the degree (if the membrane is in the form of a porous membrane, the direction is a planar direction; if the membrane is in the form of a hollow fiber membrane, the direction is perpendicular to the radial direction), various characteristics such as pore size distribution, fiber thickness are substantially uniform and substantially uniform; therefore, the average diameter of the fibers on the whole plane can be reflected by the average diameter of the fibers in partial areas on the corresponding plane; in practice, the outer surface of the membrane may be characterized by an electron microscope to obtain a corresponding SEM image, and since the fiber thickness on the outer surface of the membrane is substantially uniform, a certain area, such as 1 μm, may be selected²(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, the diameter size of the fibers in the area is measured by corresponding computer software or manually, and then the average value is calculated to obtain the average diameter size of the first fibers on the outer surface of the first porous body, of course, the skilled person can obtain the above parameters by other measuring means, and the above measuring means is only used for reference; the pore area fraction of the first pores on the first porous outer surface, the average pore diameter of the first pores, may also be obtained according to the above-described method.

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 outer surface and the second porous outer surface.

As a further improvement of the invention, a plurality of first round hole-shaped holes are arranged on the outer surface of the first porous body; the area ratio of the first holes on the outer surface of the first porous body is 30-70%; the average pore diameter of the first pores is 1-150 nm.

It is known that factors such as the pore size and number of pores and the shape of the pores of the membrane have great influence on the membrane properties such as filtration precision (interception efficiency) and flow rate of the membrane;

according to the invention, the first holes on the outer surface of the first porous membrane are circular hole-shaped structures, some first holes are circular, some first holes are oval, and the circular hole-shaped first holes can generate higher pore volume, so that the porous membrane has higher specific surface area; the average pore diameter of the first pores is 1-150 nm; through the non-directional tortuous path in the membrane main body, the porous membrane can well capture impurity particles with the particle size of 1-150nm, the interception efficiency is more than 95%, the filtration precision is ensured, enough retention effect on undesirable substances is achieved, and the requirement of practical application is met; and the area ratio of the first holes on the outer surface of the first porous membrane (the ratio of the area of the first holes to the area of the corresponding membrane region) is 30-70%, which is easy to ensure that the whole membrane has higher porosity, thus being beneficial to the porous membrane to have higher flow velocity, facilitating the fluid to rapidly pass through the porous membrane, shortening the filtration time, having higher tensile strength and meeting the requirements of practical application.

As a further improvement of the invention, the thickness of the UPE porous membrane is 1-30 μm; the porosity of the UPE porous membrane is 45-85%; the surface area of the membrane inside per membrane area is 0.4 to 0.8.

In addition, the porosity of the UPE porous membrane is tested, the porosity of the membrane refers to the proportion of the volume of membrane pores of the porous membrane in the total volume, and the membrane pores comprise open pores and closed pores; the commonly used porosity test methods are mercury intrusion method, density method and dry-wet film weighing method; through tests, the porosity of the UPE porous membrane is 45-85%, and the UPE porous membrane has high porosity; i.e., the UPE porous membrane has high porosity while having a high specific surface, it is demonstrated that the UPE porous membrane of the present invention has the following advantages:

1. the photoresist has higher viscosity compared with common chemicals, bubbles are easily generated when the photoresist passes through a filter medium, the subsequent process is greatly influenced by the bubbles, the UPE porous membrane with high specific surface area and high porosity can enable the filtering speed of the photoresist to be higher, and meanwhile, due to the fact that the UPE porous membrane with high porosity exhausts faster (the exhaust rate is higher, the bubbles are exhausted more easily), the content of the bubbles in the filtered photoresist is less, and the quality of the photoresist is guaranteed more favorably;

2. for end-use photoresist cartridges, the housing dimensions are typically small, and therefore the filter area filled inside is typically small (typically no more than 2 m)²) (ii) a With the reduction of membrane pores, and under the condition that the membrane area cannot be greatly increased, the UPE porous membrane with high specific surface area and high porosity can realize lower pressure (smaller pressure loss) under the same flow, so that the UPE membrane with high specific surface area can realize very small pores (filtering nano-level impurity particles) for photoresist with equivalent viscosity and simultaneously meet the flow requirement (the filtering speed is still higher, the time cost is lower, and the economic benefit is high);

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 1-30 μm, 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 filtering, various fluids move along the thickness direction of the membrane so as to realize corresponding filtering, and the filtering is disposable, so that the characteristic of the surface area inside the membrane per unit membrane area is particularly important; the surface area of the membrane inside per membrane area means the surface area of the membrane inside area on a porous membrane having a certain area, and the larger the value, the larger the surface area inside the porous membrane; the surface area of the inner part of the membrane of unit membrane area is 0.4-0.8, and the value is large, so that the UPE porous membrane has the advantages of large dirt holding capacity, long service life and high economic benefit; the area of the fluid passing through the interior of the porous membrane is larger, and impurities are easier to intercept, so that the interception efficiency is improved; thirdly, when the UPE is used as a base membrane for grafting modification, functional groups needing grafting are easier to be grafted on the surface area of the inner part of the membrane, thereby further improving various performances of the UPE porous membrane; is particularly suitable for the field of photoresist.

As a further improvement of the invention, the specific surface area of the UPE porous membrane is 40-80m²(ii)/g; the porosity of the UPE porous membrane is 50-75%; the thickness of the UPE porous membrane is 5-20 μm.

The specific surface area refers to the total area of the materials in unit mass, and the larger the value of the specific surface area is, the larger the total area of the materials in a certain mass is; preferably, the specific surface area of the UPE porous membrane is 40-80m²(ii)/g, indicating that a mass of UPE porous membrane has a large total area; when the fluid is intercepted, the area of the membrane contacted by the fluid is large, so that impurities in the fluid can be intercepted more easily, and the interception efficiency is further improved; meanwhile, when the UPE porous membrane is used as a base membrane and is subjected to various modification treatments, the contact area between a modifier and the membrane is large, the reaction is complete, and various modifications, such as hydrophilic modification of the UPE membrane, can be realized more easily;

the UPE membrane with high specific surface area can be used as a base membrane for charge modification, on the other hand, even if the UPE membrane is not modified, according to experiments, the UPE porous membrane is slightly negatively charged after being contacted with feed liquid, and the UPE porous membrane with the negative charge also has certain adsorbability; the UPE film with high specific surface area has the advantages that under the condition that the charge amount of a unit specific surface area is constant, the total charge of the UPE film with high specific surface area is large, so that the adsorption effect is good, and the capability of retaining impurity substances is stronger;

in addition to some metal ions and particle impurities, the agglomeration of the effective component resin substances in the photoresist (for example, the component PMMA resin in KrF photoresist is easy to agglomerate, and the component ketones in I line/KrF photoresist are easy to agglomerate) has an influence on the refractive index, and further easily influences the stability of the photoetching process; the charged UPE film with a high specific surface area has a good adsorption effect on the impurities.

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; preferably, the porosity of the porous membrane is 50-75%, so that the UPE porous membrane not only has higher tensile strength, but also has higher filtering speed, high flow rate, higher dirt holding capacity, long service life and lower economic cost, and can retain more impurity particles;

preferably, the thickness of the UPE porous membrane is 5-20 μm; the UPE porous membrane is guaranteed to have higher tensile strength, shorter filtering time and higher filtering precision through the mutual synergistic effect of the membrane thickness, the membrane porosity and the membrane specific surface area, and the requirements of practical application are met.

As a further improvement of the invention, the second porous outer surface comprises a plurality of branch-shaped continuous second fibers, and second holes are formed between adjacent continuous second fibers in a surrounding manner; the second fibers have an average diameter of 10 to 60 nm.

In the membrane body structure of the UPE porous membrane provided by the invention, a plurality of second fibers are clearly seen on the second porous outer surface of the UPE porous membrane, the shape of the second fibers is approximately the same as that of the first fibers, and the second fibers are slightly different in thickness, so that the difference is small, which also indicates that the UPE porous membrane is a symmetrical membrane, and the structures of the two outer surfaces of the membrane are very similar; the second fibers also present a branched structure, and the second fibers are continuous with the second fibers; the adjacent continuous second fibers are mutually encircled to form corresponding second holes, so that a porous structure of the membrane is formed, and the membrane formed by the second fiber structure further has higher specific surface area and high porosity; meanwhile, in the thickness direction, the second fibers are mutually laminated and mutually interwoven (staggered) and superposed near the outer surface of the second porous membrane, so that the filtration of impurities is facilitated, and the porous membrane has higher retention efficiency on impurity particles; on the outer surface of the second porous body, the average diameter of the second fibers is 10-60nm, so that the second fibers with the thickness further ensure that the whole membrane has higher tensile strength and can meet the requirements of actual industrial production, and the second holes formed by the second fibers have stronger stability and are not easy to collapse or shrink, thereby ensuring the stability of the flow rate of the fluid.

As a further improvement of the invention, the ratio of the average diameter of the second fibers to the average diameter of the first fibers is 0.7 to 1.5; the second hole is in a round hole shape; the area ratio of the second holes on the second porous outer surface is 30-70%.

As a further improvement of the present invention, the average pore diameter of the second pores is 1 to 150 nm; the ratio of the average pore diameter of the second pores to the average pore diameter of the first pores is 0.78-1.35.

It is known that factors such as the pore size and number of pores and the shape of the pores of the membrane have great influence on the membrane properties such as filtration precision (interception efficiency) and flow rate of the membrane; in the invention, the second holes on the outer surface of the second porous body are of circular hole-shaped structures, the shapes of the second holes are almost the same as those of the first holes, and only the difference of the hole diameters is small; some second holes are circular, some second holes are oval, and the circular second holes are easy to generate higher pore volume, so that the porous membrane has higher specific surface area; the area ratio of the second holes on the outer surface of the second porous film (the ratio of the area of the second holes to the area of the corresponding film area) is 30-70%, so that the porous film has higher flow velocity, the fluid can rapidly pass through the porous film, the filtering time is shortened, the porous film has higher tensile strength, and the requirement of practical application is met; through measurement, the average pore diameter of the second pores is 1-150nm, the average pore diameter of the second pores is approximately equal to the average pore diameter of the first pores, a certain difference exists, and the difference is small, so that the UPE porous membrane is further proved to be a symmetric membrane, each part of the symmetric membrane has approximately the same characteristics, the pore structure and the fiber structure of the membrane cannot change along with the thickness of the membrane, and the membrane can have strong trapping capacity on impurity particles with the particle size of 1-150 nm;

in addition, in the invention, the ratio of the average diameter of the second fibers to the average diameter of the first fibers is 0.7-1.5, and the ratio of the average pore diameter of the second holes to the average pore diameter of the first holes is 0.78-1.35, although the thickness of the second fibers is different from that of the first fibers, the difference between the two is small and relatively uniform; the average pore diameter of the second pores is different from that of the first pores to a certain extent, but the difference is small and relatively uniform; thus further illustrating that the UPE porous membrane is a symmetric membrane, the properties of the two outer surfaces of the membrane being substantially the same; when the filter element is actually used, any outer surface of the porous membrane can be used as a liquid inlet surface, so that the process of manufacturing the filter element by the porous membrane is easier, simpler and more convenient, and the economic benefit is higher.

As a further improvement of the invention, the ratio of the IPA initial bubble point to the IPA complete bubble point of the UPE porous membrane is not lower than 0.4; the IPA complete foaming point of the UPE porous membrane is not lower than 0.2 MPa.

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 bubble point comprises an initial bubble point and a complete bubble point; the IPA complete bubble point of the UPE porous membrane is not lower than 0.2MPa, so that the pore diameter in the UPE porous membrane is relatively small, and the porous membrane can well capture impurity particles with the particle size of 1-150nm through a non-directional tortuous passage in a membrane main body, so that the filtering precision is ensured, and a sufficient retention effect on undesired substances is achieved;

the initial bubble point mainly reflects the maximum pore size inside the membrane, while the complete bubble point mainly reflects the average pore size of the membrane; the ratio between the initial bubble point and the complete bubble point can reflect the symmetry of the film to a certain extent, and the smaller the ratio, the larger the asymmetry of the film to a certain extent, the larger the ratio, and the better the symmetry of the film to a certain extent; the ratio of the IPA initial bubble point and the IPA complete bubble point of the UPE porous membrane is not lower than 0.4, and further shows that the membrane is a symmetrical membrane, the pore size of pores in the membrane main body, the pore distribution and other characteristics are similar to the corresponding characteristics on the two outer surfaces of the membrane, and no pores with extremely large pore sizes exist, so that the filtration precision and the filtration speed are ensured.

As a further improvement of the present invention, the porous film has a shrinkage of not more than 5% after being left at a temperature of 120 ℃ for 1 hour; the compressibility of the porous membrane is less than 15%; the porous membrane has a pore closing temperature greater than 120 ℃.

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.

In addition, the pore closing temperature of the UPE porous membrane is higher than 120 ℃; when the pore closing temperature of the porous membrane is higher than 120 ℃, the porosity of the UPE porous membrane is not lost near a higher temperature treatment part or a higher temperature body contact part in a thermal bonding process during the actual processing of the UPE porous membrane, the water permeability is easy to maintain, a predicted filtration area can be obtained even after the processing, and then the ideal flow rate and the retention efficiency are ensured, the porous performance of the membrane is stable, and the actual industrial requirements are met.

As a further improvement of the invention, the rejection efficiency of the UPE porous membrane to impurity particles with the particle size of 1-150nm is more than 95 percent; the time required for 50ml of water to pass through a porous membrane with a diameter of 47mm is not more than 500s 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%.

Through carrying out retention test on the UPE porous membrane, the porous membrane is found to have good trapping effect on impurity particles with the particle size of 1-150nm, the retention efficiency is more than 95%, the filtering precision is ensured, the enough retention effect on undesired substances is realized, and the UPE porous membrane is suitable for being applied to the field of photoresist;

the flow rate test of the UPE porous membrane shows that the time required for 50ml of water to pass through the UPE porous membrane with the diameter of 47mm is not more than 500s under the conditions of the pressure of 0.03MPa and the temperature of 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 invention also provides a preparation method of the UPE porous membrane with high specific surface area, 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: 10-25 parts; a compound A: 0-20 parts of a solvent; compound B: 70-90 parts; 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;

s2: heating, melting and mixing the mixed material at the temperature of 150-260 ℃ 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 ℃ and 250 ℃;

s3: carrying out phase-splitting curing on the liquid film at the temperature of 15-50 ℃ for 2-50s to form a green film; during split-phase solidification, the temperature difference between the liquid film carrier side and the liquid film air side is 5-20 ℃; and in the phase-splitting curing process, the carrier side and the air side of the liquid film are converted at least once;

s4: then stretching the raw film, and performing primary heat setting after stretching;

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 carrying out secondary heat setting on the original membrane to obtain the UPE porous membrane.

As a further improvement of the invention, the polyethylene resin consists of 65 to 85 mass percent of ultrahigh molecular weight polyethylene with the mass-average molecular weight of more than 300 ten thousand and 15 to 35 mass percent of high density polyethylene with the mass-average molecular weight of 100-200 ten thousand and the density of 0.92 to 0.98g/cm 3.

As a further improvement of the present invention, the stretching treatment of the green film in S4 means that the green film is simultaneously subjected to transverse stretching and longitudinal stretching at a temperature of 60 to 150 ℃, at a transverse stretching ratio of 1 to 10 times, and at a longitudinal stretching ratio of 1 to 10 times.

As a further improvement of the present invention, in S4, the raw film is subjected to stretching treatment, and the ratio of the longitudinal stretching ratio to the transverse stretching ratio is 0.8 to 2; the stretching rate in the transverse direction is 5%/s to 100%/s, and the stretching rate in the longitudinal direction is 5%/s to 100%/s.

As a further improvement of the invention, the extract liquid in S5 is at least one of dichloromethane, acetone, methanol, ethanol, glycerol, tetrafluoroethane and isopropanol; the extraction temperature is 5-25 ℃; the extraction time is 1-5 h.

As a further improvement of the invention, the temperature for the first heat setting is 100-180 ℃, and the time is 20-90 s; the temperature of the second heat setting is 10-40 deg.C higher than that of the first heat setting, and the time is 20-90 s.

The invention forms the casting sheet with hole through thermally induced phase separation method, and then the casting sheet is stretched and formed to prepare the UPE porous membrane with high specific surface area, when the preparation is carried out, various materials are mixed to form a mixed material, the mixed material comprises polyethylene resin and a corresponding solvent system, the ultra-high molecular weight polyethylene is called UPE for short, the UPE porous membrane is thermoplastic engineering plastic with a linear structure and excellent comprehensive performance, and the porous membrane prepared by the UPE can have higher heat resistance and wear resistance, and has good mechanical property, larger tensile strength and wide application range; 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 65 to 85 mass% of ultrahigh molecular weight polyethylene having a mass average molecular weight of 300 ten thousand or more and 15 to 35 mass% of ultrahigh molecular weight 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, high porosity and high tensile strength; the solvent system can be only the compound B, the compound B is a solvent of the polyethylene resin, and the solvent means that when the compound B is heated to the boiling temperature of the compound B at most, the compound B can completely dissolve the polyethylene resin to form a homogeneous solution; the compound B is at least one of paraffin oil, white oil, hydraulic oil, decalin, castor oil extract and castor oil; preferably, the solvent system may be composed 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 swelling role on 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 content of the compound B in the solvent system is far higher than that of the compound A, so that the polyethylene resin can be fully dissolved and dispersed in the solvent system under the action of subsequent higher temperature, and the casting solution has proper solid content;

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 diffusion exchange occurs between the non-solvent and the solvent while liquid-liquid phase separation solidification (phase separation solidification by a thermal method) is performed due to a change in temperature of the liquid film, thereby further increasing the phase separation solidification rate;

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;

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 150-; 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 200 ℃ and 250 ℃; preferably, the highest temperature in the extruder is at least 5 ℃ higher than the temperature extruded by the die head, so that the temperatures of all areas of the liquid film during extrusion are basically the same, subsequent split-phase solidification is facilitated, split phases are more uniform, an ideal film structure is obtained, and a symmetrical film is more facilitated to be formed;

then the liquid film is placed in the temperature environment of 15-50 ℃ for split-phase solidification; at a higher temperature, a single homogeneous solution can be formed between the solvent system and the polyethylene resin, and the homogeneous solution becomes turbid along with the reduction of the temperature of the system, the polyethylene resin is slowly separated out, and then the phenomenon of phase separation and solidification occurs; the phase splitting temperature of both sides of the liquid film is lower (15-50 ℃), the liquid film is easy to split phases quickly, more crystals are formed to form a film (nano holes and small holes are easy to form high specific surface area), more holes are easy to form (high porosity) and fibrosis is more obvious; when the solvent system is a combination of a solvent and a non-solvent, in addition to phase separation caused by temperature change, diffusion exchange between the solvent and the non-solvent can further accelerate the solidification rate of phase separation, so that a porous film is formed (the faster the phase separation rate is, the smaller the pore diameter of the formed pores is), namely the nano film required by the invention is formed; the UPE porous membrane finally formed by the invention is a symmetrical membrane, and in order to form the symmetrical membrane, the phase separation degrees of the two sides of the liquid membrane are required to be basically the same, so that the membrane pore structures of the two outer surfaces of the porous membrane are similar, and the fiber structures are similar; as one of the key points of the invention, the two outer surfaces of the membrane are ensured to be similar in structure through the combined action of two conditions; the first condition is that the temperature difference between the liquid film carrier side (which may be a roller or other carrier) and the air side of the liquid film is 5-20 deg.C, for example, the temperature of the air side is 20 deg.C, then the temperature of the carrier side can be set to 30 deg.C, then the phase separation rate is different at both sides of the liquid film because the temperature is different at both sides of the liquid film and the heat transfer rate is different at both sides; the second condition is that in the process of phase-splitting solidification, the carrier side and the air side of the liquid film are mutually converted at least once, wherein the conversion is that when the liquid film moves on the carrier, when the liquid film is converted from one carrier to another carrier, the two side surfaces of the liquid film are mutually converted, at the moment, the air side of the original liquid film is changed into the carrier side of the liquid film, and the roller side is changed into the air side; the number of transitions is preferably 1 to 3; through the mutual transformation of the two sides of the liquid film between the carrier side and the air side, under the action of proper time, the two sides of the liquid film are ensured to have basically the same phase separation, so that a symmetrical green film can be formed; 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 split-phase curing time is 2-50s, and the time is relatively short, so that the UPE porous membrane with an ideal membrane structure required by people can be obtained;

the method comprises the steps of forming a raw membrane after liquid membranes are combined, wherein a certain number of holes with certain apertures appear on two surfaces of the raw membrane, and the apertures of the holes on the two surfaces are basically the same; however, according to research, if the raw film is treated according to the conventional stretching technology, holes on the raw film are easy to partially collapse or deform, and finally the UPE porous film with the required film structure cannot be obtained, so that the raw film is simultaneously stretched in the transverse direction and the longitudinal direction at the temperature of 60-150 ℃, the transverse stretching multiple is 1-10 times, and the longitudinal stretching multiple is 1-10 times. The stretching has the advantages that the pore diameter of the membrane pores required by the invention is obtained, the tensile strength of the membrane is improved, and meanwhile, the pores are not easy to collapse or deform, so that the UPE filter membrane with the membrane structure required by the invention is obtained; preferably, the ratio of longitudinal stretching multiple to transverse stretching multiple is 0.8-2, the transverse stretching speed is 5%/s-100%/s, and the longitudinal stretching speed is 5%/s-100%/s, so that the uniformity of the pore diameter of the pores in the membrane is further improved, and the symmetry of the membrane is ensured;

carrying out primary heat setting after the synchronous stretching is finished, wherein the primary heat setting has the function of carrying out primary setting on the stretched raw film, ensuring that film holes are basically not changed, and eliminating internal stress generated by stretching; the temperature for the first heat setting is 100-180 ℃, and the time is 20-90 s; then extracting, and removing the solvent system from the raw membrane through an extraction liquid to obtain an original membrane; the extract is at least one of dichloromethane, acetone, methanol, ethanol, glycerol, tetrafluoroethane and isopropanol; the extraction temperature is 5-25 ℃; the extraction time is 1-5 h; by selecting proper extracting agent and extracting conditions, the solvent system is ensured to be completely removed from the raw membrane, and the time required by extraction is short; after extraction, carrying out secondary heat setting on the original membrane, wherein the temperature during the secondary heat setting is 10-40 ℃ higher than that during the primary heat setting, and the secondary 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 basically not changed, and the UPE porous membrane with the required membrane pore structure is obtained; the UPE porous membrane is a symmetrical membrane, the pore size distribution of the pores on the membrane is uniform, the UPE porous membrane has excellent trapping performance on impurity particles, and the interception efficiency is high; meanwhile, the photoresist has high specific surface area and high porosity, has small pressure loss 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;

after the UPE porous membrane is made into a bag-type or cylinder-type filter element, because of the high specific surface area and the high porosity of the UPE porous membrane, gas generated in the photoresist filtering process is easier to discharge, so that the content of bubbles in the filtered photoresist is lower, the adverse effect of the bubbles on the photoresist property is reduced, and the photoresist with excellent property is ensured to be obtained; therefore, the UPE porous membrane is particularly suitable for being applied to the field of photoresist filtration; when the photoresist is filtered, any outer surface of the UPE porous membrane can be used as a liquid inlet surface, and a specific outer surface is not required to be guided to be used as a liquid inlet surface, so that the problem that effective filtration cannot be carried out due to misoperation of a user is avoided; the UPE porous membrane has excellent trapping performance on various impurity particles in the photoresist and high filtering precision; 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 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 and a downstream side, the upstream side communicating with an inlet and the downstream side communicating with an outlet, characterized in that: the UPE porous membrane is the UPE porous membrane according to any one of claims 1 to 12, and the membrane area of the UPE porous membrane in the folding filter element is 0.1 to 2m²。

For end use photoresist cartridges, particularly bladder cartridges, the shell size is generally small and therefore the membrane area packed inside is generally small, and the bladder cartridgesThe membrane area of the UPE porous membrane is 0.1-0.6m²And the membrane area of the UPE porous membrane in the cartridge type filter element does not exceed 2m²(ii) a Compared with the UPE membrane with low specific surface area and low porosity, the UPE membrane with high specific surface area can realize lower pressure under the same flow rate due to high aperture ratio, so that the UPE membrane with high specific surface area can realize very small holes (filtering nano-level particles) for photoresist with equivalent viscosity and simultaneously meet the flow rate requirement, the pressure loss is relatively small, good flow rate can be obtained when filtering nano-level impurity particles, and the economic benefit is higher.

The invention has the beneficial effects that: the UPE porous membrane provided by the invention is a symmetrical membrane, has a more optimized membrane body structure compared with the existing filter membrane material, and comprises a first porous outer surface, a second porous outer surface and a main body positioned between the first porous outer surface and the second porous outer surface, wherein the specific surface area of the UPE porous membrane is not less than 35m²The first porous outer surface comprises a plurality of branch-shaped continuous first fibers, and first holes are formed between adjacent continuous first fibers in a surrounding mode; first fibers are stacked on each other in the thickness direction; the first fibers have an average diameter of 10 to 60 nm; the UPE porous membrane with the high specific surface area has excellent trapping performance on nano-scale fine impurities in the filtering process, can adsorb various fine particulate matters, and has high trapping efficiency; in addition, the UPE porous membrane is particularly suitable for being used as a base membrane for modification, and the modification effect is good; the method is suitable for being applied to the field of photoresist filtration; the preparation method provided by the invention can conveniently, quickly and effectively prepare and obtain the UPE porous membrane.

Drawings

FIG. 1 is a Scanning Electron Microscope (SEM) image of the outer surface of a first pore on a UPE porous membrane prepared in example 6 at 10K ×;

FIG. 2 is a further magnified Scanning Electron Microscope (SEM) image of the outer surface of a first porous on a UPE porous membrane prepared in example 6 at a magnification of 50K ×;

FIG. 3 is a Scanning Electron Microscope (SEM) image of the outer surface of a second porous on a UPE porous membrane prepared in example 6 at a magnification of 10K ×;

FIG. 4 is a further magnified Scanning Electron Microscope (SEM) image of the second porous outer surface of a UPE porous membrane prepared in example 1 at a magnification of 50K ×;

FIG. 5 is a schematic view of the apparatus for flow rate testing of a UPE porous membrane in accordance with the present invention;

fig. 6 is a schematic diagram of the filtration accuracy (retention efficiency) testing device of the UPE 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 with a high specific surface area, 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; the mixed material comprises the following substances in parts by weight: polyethylene resin: 12 parts of (1); a compound A: 5 parts of a mixture; compound B: 72 parts of (1);

the polyethylene resin comprises 83 mass percent of ultrahigh molecular weight polyethylene with the mass-average molecular weight of more than 300 ten thousand and 17 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); the compound A is dioctyl adipate, and the compound B is white oil;

s2: heating, melting and mixing the mixed material at the temperature of 215 ℃ 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 extrusion temperature is 205 ℃;

s3: setting the temperature of the liquid film carrier side to be 25 ℃, setting the temperature of the air side to be 20 ℃, after the liquid film is subjected to phase separation and solidification for 4s, converting two sides of the liquid film, namely changing one side of the liquid film originally close to the carrier to one side close to the air (the phase separation temperature is changed from 25 ℃ to 20 ℃), changing one side of the liquid film originally close to the air to one side close to the carrier (the temperature is changed from 20 to 25 ℃), and continuing to perform the phase separation and solidification for 4 s; after the phase separation solidification is finished, a green film is formed;

s4: then stretching the raw film, and simultaneously performing transverse stretching and longitudinal stretching, wherein the temperature during the transverse stretching and the longitudinal stretching is 80 ℃, the transverse stretching multiple is 3 times, the longitudinal stretching multiple is 3 times, the transverse stretching speed is 20%/s, and the longitudinal stretching speed is 20%/s; carrying out first heat setting after the stretching is finished, wherein the temperature of the first heat setting is 130 ℃ and the time is 65 s;

s5: extracting the solvent system with the extract liquid to remove the solvent system from the raw membrane to obtain an original membrane; the extract in S5 is dichloromethane; the extraction temperature is 15 ℃; the extraction time is 3 h;

s6: and (3) carrying out secondary heat setting on the original membrane, wherein the temperature of the secondary heat setting is 160 ℃ and the time is 45s, and thus obtaining the UPE porous membrane.

Example 2 a method for preparing a UPE porous membrane with a high specific surface area, 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; the mixed material comprises the following substances in parts by weight: polyethylene resin: 14 parts of (1); a compound A: 8 parts of a mixture; compound B: 75 parts of a mixture; 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); the compound A is ethylene glycol diacetate and the compound B is paraffin oil;

s2: heating, melting and mixing the mixed material at 220 ℃ 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 extrusion temperature is 210 ℃;

s3: setting the temperature of the liquid film carrier side to be 30 ℃, setting the temperature of the air side to be 20 ℃, carrying out split-phase solidification for 5s, then carrying out transformation on two sides of the liquid film, namely changing one side of the liquid film, which is originally close to the carrier, to be close to the air (the split-phase temperature is changed from 30 ℃ to 20 ℃), changing one side of the liquid film, which is originally close to the air, to be close to the carrier (the temperature is changed from 20 ℃ to 30 ℃), continuing to carry out split-phase solidification, carrying out split-phase solidification for 10s, then changing two sides of the liquid film again, namely changing one side of the liquid film, which is close to the air, to be close to the carrier again (the split-phase temperature is changed from 20 ℃), changing one side of the liquid film, which is close to the air again (the split-phase temperature is changed from 30 ℃ to 20 ℃), and finally carrying out the split-phase for 5 s; after the phase separation solidification is finished, a green film is formed;

s4: then stretching the raw film, and simultaneously performing transverse stretching and longitudinal stretching, wherein the temperature during the transverse stretching and the longitudinal stretching is 85 ℃, the transverse stretching multiple is 4 times, the longitudinal stretching multiple is 4 times, the transverse stretching speed is 25%/s, and the longitudinal stretching speed is 25%/s; performing first heat setting after the stretching is finished, wherein the temperature during the first heat setting is 135 ℃ and the time is 60 s;

s5: extracting the solvent system with the extract liquid to remove the solvent system from the raw membrane to obtain an original membrane; the extract is acetone; the extraction temperature is 20 ℃; the extraction time is 2.5 h;

s6: and (3) carrying out secondary heat setting on the original membrane, wherein the temperature of the secondary heat setting is 150 ℃ and the time is 75s, and thus obtaining the UPE porous membrane.

Example 3 a method for preparing a UPE porous membrane with high specific surface area, 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; the mixed material comprises the following substances in parts by weight: polyethylene resin: 16 parts of a mixture; a compound A: 12 parts of (1); compound B: 78 parts of (1); 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); the compound A is dimethyl phthalate, and the compound B is hydraulic 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 die head extrusion temperature is 215 ℃;

s3: setting the temperature of the liquid film carrier side to be 32 ℃, setting the temperature of the air side to be 20 ℃, carrying out split-phase solidification for 6s, then carrying out transformation on two sides of the liquid film, namely changing one side of the liquid film, which is originally close to the carrier, to be close to the air (the split-phase temperature is changed from 32 ℃ to 20 ℃), changing one side of the liquid film, which is originally close to the air, to be close to the carrier (the temperature is changed from 20 ℃ to 32 ℃), continuing to carry out split-phase solidification, carrying out split-phase 12s, then carrying out transformation on two sides of the liquid film again, namely changing one side of the liquid film, which is close to the air at this time, to be close to the carrier again (the split-phase temperature is changed from 20 ℃), changing one side of the liquid film, which is close to the air at this time, and finally carrying out split-phase 6 s; after the phase separation solidification is finished, a green film is formed;

s4: then stretching the raw film, and simultaneously performing transverse stretching and longitudinal stretching, wherein the temperature during the transverse stretching and the longitudinal stretching is 90 ℃, the transverse stretching multiple is 4 times, the longitudinal stretching multiple is 5 times, the transverse stretching speed is 40%/s, and the longitudinal stretching speed is 50%/s; carrying out first heat setting after the stretching is finished, wherein the temperature of the first heat setting is 140 ℃ and the time is 55 s;

s5: extracting the solvent system with the extract liquid to remove the solvent system from the raw membrane to obtain an original membrane; the extract is isopropanol; the extraction temperature is 23 ℃; the extraction time was 2 h.

S6: and (3) carrying out secondary heat setting on the original membrane, wherein the temperature of the secondary heat setting is 165 ℃ and the time is 60s, and thus obtaining the UPE porous membrane.

Example 4 a method for preparing a UPE porous membrane with high specific surface area, 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; the mixed material comprises the following substances in parts by weight: polyethylene resin: 18 parts of a mixture; a compound A: 17 parts of (1); compound B: 81 parts;

the polyethylene resin comprises 72 mass percent of ultrahigh molecular weight polyethylene with the mass-average molecular weight of more than 300 ten thousand and 28 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); the compound A is palm oil, and the compound B is castor oil;

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 die head extrusion temperature is 225 ℃;

s3: setting the temperature of the liquid film carrier side to 35 ℃, setting the temperature of the air side to 25 ℃, after phase separation solidification for 15s, converting two sides of the liquid film, namely changing one side of the liquid film originally close to the carrier to one side close to the air (the phase separation temperature is changed from 35 ℃ to 25 ℃), changing one side of the liquid film originally close to the air to one side close to the carrier (the temperature is changed from 25 to 35 ℃), and continuing phase separation solidification for 15 s; after the phase separation solidification is finished, a green film is formed;

s4: then stretching the raw film, and simultaneously performing transverse stretching and longitudinal stretching, wherein the temperature during the transverse stretching and the longitudinal stretching is 80 ℃, the transverse stretching multiple is 6 times, the longitudinal stretching multiple is 5 times, the transverse stretching speed is 60%/s, and the longitudinal stretching speed is 50%/s; carrying out first heat setting after the stretching is finished, wherein the temperature of the first heat setting is 145 ℃, and the time is 50 s;

s5: extracting the solvent system with the extract liquid to remove the solvent system from the raw membrane to obtain an original membrane; the extract in S5 is glycerol; the extraction temperature is 10 ℃; the extraction time was 4 h.

S6: and (5) carrying out secondary heat setting on the original membrane, wherein the temperature of the secondary heat setting is 170 ℃, and the time is 65s, so as to obtain the UPE porous membrane.

Example 5 a method for preparing a UPE porous membrane with high specific surface area, 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; the mixed material comprises the following substances in parts by weight: polyethylene resin: 20 parts of (1); a compound A: 2 parts of (1); compound B: 84 parts of a mixture;

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); the compound A is glycerol triacetate, and the compound B is decalin;

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 die head extrusion temperature is 230 ℃;

s3: setting the temperature of the liquid film carrier side to be 40 ℃, setting the temperature of the air side to be 25 ℃, carrying out split-phase solidification for 9s, then carrying out transformation on two sides of the liquid film, namely changing one side of the liquid film, which is originally close to the carrier, to be close to the air (the split-phase temperature is changed from 40 ℃ to 25 ℃), changing one side of the liquid film, which is originally close to the air, to be close to the carrier (the temperature is changed from 25 ℃ to 40 ℃), continuing to carry out split-phase solidification, carrying out split-phase solidification for 18s, then changing two sides of the liquid film again, namely changing one side of the liquid film, which is close to the air at this time, to be close to the carrier again (the split-phase temperature is changed from 25 ℃), changing one side of the liquid film, which is close to the air at this time, and finally carrying out split-phase for 9 s; after the phase separation solidification is finished, a green film is formed;

s4: then stretching the raw film, and simultaneously performing transverse stretching and longitudinal stretching, wherein the temperature during the transverse stretching and the longitudinal stretching is 100 ℃, the transverse stretching multiple is 6 times, the longitudinal stretching multiple is 6 times, the transverse stretching speed is 60%/s, and the longitudinal stretching speed is 60%/s; performing first heat setting after the stretching is finished, wherein the temperature during the first heat setting is 150 ℃ and the time is 45 s;

s5: extracting the solvent system with the extract liquid to remove the solvent system from the raw membrane to obtain an original membrane; the extract is ethanol; the extraction temperature is 8 ℃; the extraction time was 4.5 h.

S6: and (3) carrying out secondary heat setting on the original membrane, wherein the temperature of the secondary heat setting is 180 ℃ and the time is 50s, and thus obtaining the UPE porous membrane.

Example 6 a method for preparing a UPE porous membrane with high specific surface area, 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; the mixed material comprises the following substances in parts by weight: polyethylene resin: 22 parts of (A); compound B: 89 parts of; compound B is castor oil extract;

the polyethylene resin comprises 65 mass percent of ultrahigh molecular weight polyethylene with the mass-average molecular weight of more than 300 ten thousand and 35 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 255 ℃ 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 extrusion temperature is 245 ℃;

s3: setting the temperature of the liquid film carrier side to be 50 ℃, setting the temperature of the air side to be 30 ℃, after the liquid film is subjected to phase separation solidification for 24s, converting two sides of the liquid film, namely changing one side of the liquid film originally close to the carrier to one side close to the air (the phase separation temperature is changed from 50 ℃ to 30 ℃), changing one side of the liquid film originally close to the air to one side close to the carrier (the temperature is changed from 30 ℃ to 50 ℃), and continuing to perform the phase separation solidification for 24 s; after the phase separation solidification is finished, a green film is formed;

s4: then stretching the raw film, and simultaneously performing transverse stretching and longitudinal stretching, wherein the temperature during the transverse stretching and the longitudinal stretching is 120 ℃, the transverse stretching multiple is 9 times, the longitudinal stretching multiple is 9 times, the transverse stretching speed is 80%/s, and the longitudinal stretching speed is 80%/s; carrying out first heat setting after the stretching is finished, wherein the temperature of the first heat setting is 160 ℃ and the time is 40 s;

s5: extracting the solvent system with the extract liquid to remove the solvent system from the raw membrane to obtain an original membrane; the extract is isopropanol; the extraction temperature is 13 ℃; the extraction time was 3.5 h.

S6: and (5) carrying out secondary heat setting on the original membrane, wherein the temperature of the secondary heat setting is 170 ℃, and the time is 80s, 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 outer surface has a suitable number of first pores with suitable pore sizes, and the second porous outer 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; the distribution of pores on the first porous outer surface is relatively similar to the distribution of pores on the second porous outer surface, also indicating that the UPE porous membrane is a symmetric membrane.

The UPE porous membranes prepared in the embodiments 1-6 of the invention have higher specific surface area and surface area inside the membrane per unit membrane area, high porosity and proper thickness, which are beneficial to subsequent photoresist filtration and obtain photoresist with excellent performance.

Characteristic features

Water flow rate test (test device as figure 5)

Experimental procedure

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;

test specimen	Flow rate/s	Tensile strength/MPa	Elongation at break/%
				Example 1	406	60	400
Example 2	300	45	550
				Example 3	217	65	350
Example 4	148	55	450
				Example 5	80	50	500
Example 6	30	40	600

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. 6, 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 for meeting the actual industrial requirements.

After the samples prepared in examples 1 to 6 were used as a filter element (membrane area 1.3m2), the membrane was wetted with IPA, and then deionized water was passed through the filter element at a flow rate of 20 ℃ to measure the pressure before and after the deionized water passed through the filter element, thereby obtaining the pressure loss corresponding to the filter element.

Test specimen	Pressure loss
		Example 1	[email protected]/min
Example 2	[email protected]/min
		Example 3	[email protected]/min
Example 4	[email protected]/min
		Example 5	[email protected]/min
Example 6	[email protected]/min

The above table shows that after the filter element is prepared by the UPE porous membrane, the pressure loss is small during filtering, so that the filter element still has high filtering speed and high economic benefit when filtering nano-scale impurity particles; is particularly suitable for filtering high-viscosity photoresist.

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.