CN112717728B

CN112717728B - PTFE macroporous membrane and preparation method and application thereof

Info

Publication number: CN112717728B
Application number: CN202011579751.5A
Authority: CN
Inventors: 吕海江; 张佳欢; 庞铁生
Original assignee: Individual
Current assignee: Zhang Chunyan
Priority date: 2020-12-28
Filing date: 2020-12-28
Publication date: 2023-03-17
Anticipated expiration: 2040-12-28
Also published as: CN112717728A

Abstract

The invention discloses a PTFE macroporous membrane and a preparation method and application thereof.A node and a fibril are included on the outer surface of the membrane, and the adjacent nodes are connected by the fibril; on a section cut along the length direction of the original fiber of the macroporous membrane, the length of the node in the first direction is greater than that in the second direction; the first direction is parallel to the thickness direction of the macroporous film, and the second direction is vertical to the thickness direction of the macroporous film, so that the macroporous film has high tensile strength, good mechanical property, low pressure loss, high energy conversion rate and high economic value; also has higher air permeability; the filter is particularly suitable for filtering stripping liquid and etching liquid in the semiconductor manufacturing process, and is used as a breathable film in electronic equipment and medical equipment; in addition, the invention also provides a preparation method of the macroporous membrane, and the preparation method is convenient, quick and effective, simple to operate, green and environment-friendly, and suitable for large-scale popularization.

Description

PTFE macroporous membrane and preparation method and application thereof

Technical Field

The invention relates to the technical field of membrane materials, in particular to a PTFE (polytetrafluoroethylene) macroporous membrane and a preparation method and application thereof.

Background

Polytetrafluoroethylene, abbreviated as PTFE, is a high molecular polymer polymerized from tetrafluoroethylene as a monomer. The PTFE material has excellent thermal stability, insulativity, weather resistance, incombustibility and chemical corrosion resistance, and plays a significant role in the national economic fields of petroleum, chemical engineering, textile and the like. Membrane materials prepared from PTFE resins are also widely used in the fields of filter materials, biomedical materials, textile garment materials, and the like; particularly in the field of filtration, the PTFE filter membrane plays an important role in the fields of electronics, semiconductors and the like because of the characteristics of high temperature resistance, strong acid and alkali resistance, no toxicity and the like, and has larger demand gaps at home and abroad.

At present, PTFE filtration membranes are generally prepared by the preparation methods disclosed in U.S. Pat. nos. US 3953566 and US 4187390, which mainly comprise the following steps: mixing PTFE dispersion resin with lubricant such as kerosene, extruding to obtain paste, and removing lubricant; and then performing unidirectional or bidirectional stretching below the melting point of the PTFE to obtain the PTFE filtering membrane.

Most of PTFE filter membranes sold in the market at present have the average pore diameter of 0.2-0.6 mu m and the tensile strength of more than 2.5MPa, and basically meet the requirements of practical application; however, certain disadvantages exist, such as excessive pressure loss (pressure loss is also called pressure drop and pressure loss, which is a technical index representing the energy consumption), that is, excessive energy consumption in the practical application process of filtration and the like, which greatly improves the economic cost and also influences the development of the PTFE filter membrane to a certain extent, and researches show that an important factor influencing the pressure loss of the PTFE filter membrane is that the porosity of the membrane is low; the pressure loss of the membrane can be reduced by improving the porosity of the membrane, but the tensile strength of the membrane is greatly reduced along with the improvement of the porosity of the membrane, and the mechanical property is deteriorated, so that the requirement of actual industrial application cannot be met; how to reduce the pressure loss of the PTFE membrane and ensure that the tensile strength of the membrane is higher simultaneously troubles researchers researching the PTFE membrane all the time, and limits the development of the PTFE membrane to a certain extent.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a PTFE (polytetrafluoroethylene) macroporous membrane, a preparation method and application thereof.

In order to realize the purpose, the invention provides the following technical scheme: a PTFE macroporous membrane, comprising nodes and fibrils on the outer surface thereof, adjacent nodes being connected by the fibrils, the nodes extending in a uniform direction, the nodes having a length in a first direction greater than a length in a second direction in a cross section taken along the length of the fibrils of the macroporous membrane; wherein the first direction is parallel to the thickness direction of the macroporous film, and the second direction is perpendicular to the thickness direction of the macroporous film.

In the main membrane structure of the PTFE macroporous membrane provided by the invention, a plurality of nodes and fibrils can be clearly seen on the outer surface of the macroporous membrane, and compared with the fibrils, the nodes have larger width and longer length; the extending directions of a plurality of nodes are kept consistent (the extending direction of the nodes is the width direction of the film and the transverse stretching direction), the nodes are almost arranged in parallel, and adjacent nodes are connected through fibrils, namely, both ends of the fibrils are connected with the nodes; the presence of these nodes and fibrils greatly affects the pressure loss and tensile strength of the macroporous membrane; on a section (the section is cut along the length direction of the protofibrils, namely, a node is cut, the length direction of the protofibrils is the film running direction, and is also the longitudinal stretching direction) of the macroporous film, through research, the node is in a long strip structure, can also be considered as an approximate ellipse structure, and the length of the node in a first direction is larger, and the first direction is parallel to the thickness direction of the macroporous film (namely, on the section, the length direction of the node is basically parallel to the thickness of the film); as is known, the filtration process is mainly performed in the thickness direction of the membrane, the filtration medium passing through the thickness of the membrane from one surface of the membrane and then coming out from the other surface of the membrane; the orientation direction with longer node length is basically parallel to the film thickness direction, so that the resistance during filtration is reduced, and the pressure difference during filtration is reduced, thereby ensuring that the macroporous film has smaller pressure loss; since the nodes can be regarded as relatively dense block regions with low porosity and the fibrils as regions with high porosity, if the orientation of the longer length direction of the nodes is perpendicular to the film thickness direction, the filtration resistance is high, so that the pressure loss of the macroporous film is high, the energy consumption is high, and the economic cost is high.

Meanwhile, the length direction and the thickness direction of the nodes are basically parallel, so that the nodes can play a skeleton supporting role in the thickness direction, and the macroporous film is ensured to have higher tensile strength; the nodes have a certain length in the direction vertical to the thickness, so that the tensile strength of the macroporous film can be further improved; in addition, we also found that the long axis direction (length orientation) of some nodes is parallel to the thickness direction of the membrane, that is, the included angle between the long axis direction of the nodes and the thickness direction of the membrane is 0 degree, so that the node structure is beneficial to the membrane to have small pressure loss; the long axis direction (length orientation) of part of the nodes is not completely parallel to the thickness direction of the membrane, certain inclination exists, a certain included angle exists between the long axis direction and the thickness direction of the membrane, and the acute angle included angle is not more than 45 degrees, so that the node structure is beneficial to obtaining higher rejection rate of the membrane and has smaller influence on high flow rate; it can therefore be considered that the angle between the long axis direction (length orientation) of the nodes and the thickness direction of the film is 0 ° to 45 °; the node structure and the fibril structure of the membrane are beneficial to the finally obtained macroporous membrane not only having higher tensile strength, but also having smaller pressure loss, and when the membrane is actually used in an industrialized way, the energy conversion rate is high, the economic value is high, and the membrane is more green and environment-friendly; the filter is particularly suitable for filtering stripping liquid and etching liquid in semiconductor manufacturing process, and can be used as a breathable film in electronic equipment and medical equipment.

As a further development of the invention, the length of the junction in the first direction is 8-45 μm and the length in the second direction is 0.5-7 μm.

Preferably, the length of the junction in the first direction is 10-40 μm and the length in the second direction is 1-6 μm; the length of the nodes is beneficial to the ideal performance of the membrane, so that the membrane has low pressure loss, high energy conversion rate, high tensile strength and good mechanical property, meets various industrial requirements, and has a wide application range.

On the section cut along the length direction of the original fiber of the macroporous membrane, the length of the node in the first direction and the length of the node in the second direction can be obtained by performing shape characterization on a membrane structure by using a scanning electron microscope, then measuring by using computer software (such as Matlab, NIS-Elements and the like) or manually, and performing corresponding calculation; of course, the skilled person can obtain the above parameters by other measuring means, and the above measuring means is only used for reference.

As a further improvement of the invention, the ratio of the length of the knot in the first direction to the length in the second direction is 3-15.

When the ratio of the length of the node in the first direction to the length of the node in the second direction is too large, the film is not favorable for obtaining larger tensile strength; when the ratio of the length of the node in the first direction to the length in the second direction is too small, it is not favorable for the membrane to obtain a low pressure loss; therefore, in order to make the film have a large tensile strength and a low pressure loss, it is necessary to ensure that the ratio of the length of the nodes in the first direction to the length in the second direction is within a reasonable range; the ratio of the length of the nodes in the first direction to the length in the second direction in the present invention is 3 to 15, thereby allowing the film to have a large tensile strength and a low pressure loss.

As a further improvement of the invention, on the section taken along the length direction of the original fiber of the macroporous membrane, the length of the node in the first direction accounts for 25-75% of the thickness of the membrane.

The first direction is a direction parallel to the thickness direction of the membrane, the filtering process is mainly completed in the thickness direction of the membrane, and when the length of the node in the first direction accounts for too large percentage of the thickness of the membrane, the filtering pores are close to a straight line shape, so that the traveling path of the filtering medium in the filtering membrane is too short, impurity particles in the filtering medium are not easy to be intercepted, the filtering efficiency is too low, and the filtering quality cannot be ensured; because the nodes play a role of framework support in the thickness direction, when the length of the nodes in the first direction accounts for the film thickness in an excessively small percentage, the nodes cannot play a role of framework support, so that the tensile strength of the film is excessively low, and the film has no practical value; it also causes a collapse of the structure of the membrane in the thickness direction, resulting in too low porosity and low filtration rate; the length of the node in the first direction accounts for 25% -75% of the thickness of the membrane, so that the node can play a role of framework support, the membrane has high tensile strength, and high interception efficiency and high filtration quality of the membrane are guaranteed.

As a further improvement of the invention, the distance between adjacent nodes along the length of the second direction on the section which is cut along the length direction of the raw fiber of the macroporous membrane is 4-30 μm.

The second direction is a direction perpendicular to the thickness direction of the membrane, and since the cross section is obtained by cutting along the length direction of the raw fiber of the macroporous membrane, the second direction is actually the membrane running direction, namely the longitudinal stretching direction; because the nodes are all in a long strip structure, the distance between the adjacent nodes refers to the distance of the center points of the adjacent nodes in the second direction, and the center points of the nodes refer to a long axis (a line segment of the maximum length of the nodes in the first direction) and a short axis (a line segment of the maximum length of the nodes in the second direction); the nodes are block-shaped areas with relatively compact porosity, and if the distance between adjacent nodes is too small, the porosity of the whole membrane is too low, and the pressure loss of the membrane is large; if the distance between adjacent nodes is too large, the tensile strength of the film is too low, and the mechanical properties are poor; the distance between adjacent nodes in the invention is 4-30 μm along the length of the second direction, which not only can lead the film to have lower pressure loss, but also has higher tensile strength, has wide application range, and is particularly suitable for filtering stripping liquid and etching liquid in semiconductor manufacturing process, and being used as a breathable film in electronic equipment and medical equipment.

As a further improvement of the invention, on a section taken along the length direction of the original fiber of the macroporous membrane, the projections of two adjacent nodes along the thickness direction of the membrane partially overlap, and the length of the overlapping area is 0.5-10 μm.

On a section cut along the length direction of the original fiber of the macroporous membrane, the research finds that the projections of two adjacent nodes along the thickness direction of the membrane are partially overlapped, namely the distribution of the nodes is basically in an alternative arrangement (staggered arrangement) form, so that the filtration pores are in an S-shaped distribution form, and the staggered arrangement makes the filtration channel become tortuous under the condition that the distance between the nodes is kept unchanged, thereby increasing the traveling path of the filtration medium in the filtration membrane, leading the impurities to be easier to be intercepted and captured, and improving the filtration efficiency; the length of the overlapping area is 0.5-10 μm, which not only ensures the high interception efficiency of the membrane, but also does not influence the filtration speed, the membrane still has high flow speed, the filtration speed is high, and the filtration time is short.

As a further improvement of the present invention, on the outer surface of the macroporous membrane, the average width of the nodes is 1.3 to 4.3 μm; the fibrils have an average width of 0.15-0.85 μm.

The widths of the nodes and the widths of the fibrils have great influence on the tensile strength of the macroporous film; the average width of the nodes is 1.3-4.3 μm, and the average width of the fibrils is 0.15-0.85 μm, so that the macroporous film has the advantages of high tensile strength, good mechanical property, capability of meeting industrial requirements and wide application range.

In the production of the membrane, in the direction perpendicular to the thickness of the membrane (the direction is a planar direction if the membrane is in a flat-plate membrane form; the direction is perpendicular to the radial direction if the membrane is in a hollow fiber membrane form), its characteristics such as node width, fibril width distribution are substantially uniform and substantially uniform; therefore, the node width and fibril width of the whole plane can be reflected by the node width and fibril width of partial area 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 node width and fibril width distributions on the outer surface of the membrane are substantially uniform, a certain area, such as 1000 μm, may be selected ² (40 μm by 25 μm) or 10000 μm ² (100 μm multiplied by 100 μm), the specific area size is determined according to actual conditions, the node width and the fibril width on the area are measured by corresponding computer software or manually, and then the average value is obtained, thereby obtaining the node average width and the fibril average width of the surface; of course, the skilled person can obtain the above parameters by other measuring means, and the above measuring means is only used for reference.

As a further development of the invention, the fibrils have an average length of 5-30 μm; the difference between the maximum length and the minimum length of said fibrils is 4-35 μm.

Besides the characteristics of node width and fibril width, fibril length is an important factor influencing the characteristic properties of the macroporous membrane such as pore size, tensile strength and the like, and the fibril length is essentially the distance between two adjacent nodes; the distance between adjacent fibrils and the fibril length jointly determine the pore size of the pores of the macroporous membrane, so that under certain conditions, the larger the fibril length is, the larger the pore size of the pores of the macroporous membrane is, the largest fibril length is easy to form pores with the largest pore size, the smallest fibril length is easy to form pores with the smallest pore size, and the difference between the largest fibril length and the smallest fibril length also influences the difference between the pore sizes of the largest pores and the smallest pores on the outer surface of the membrane to a certain extent; in the invention, on the outer surface of the membrane, the average length of the fibril is 5-30 μm, preferably 8-26 μm, so that the fibril with the length not only has larger tensile strength and good mechanical property, but also has proper pore diameter and small pressure loss; the difference between the maximum length and the minimum length of the fibril is 4-35 μm, which indicates that the aperture difference of the membrane pores is not large and is relatively uniform, namely the macroporous membrane of the invention has better pore uniformity, ensures the interception efficiency, is suitable for being used as a filter membrane, and is particularly suitable for filtering stripping liquid and etching liquid in the semiconductor manufacturing process.

On the outer surface of the macroporous membrane, the average length of the fibrils can be selected over an area, for example 1000 μm, after the morphological characterization of the membrane structure using scanning electron microscopy ² (40 μm by 25 μm) or 10000 μm ² (100 μm multiplied by 100 μm), the specific area size is determined according to actual conditions; then measuring by using computer software (such as Matlab, NIS-Elements, etc.) or manually, and performing corresponding calculation to obtain the product; of course, the skilled person can also obtain the above parameters by other measuring means, which are only used as reference.

As a further improvement of the invention, the thickness of the macroporous film is 10-100 μm, and the IPA bubble point is 5-70kPa; the average pore diameter of the macroporous membrane is 1-20 mu m, and the porosity is 60-90%.

The thickness of the film can be measured by using a scanning electron microscope to perform morphology characterization on the film structure, and then using computer software (such as Matlab, NIS-Elements and the like) or manually measuring and then calculating; one of the important performance characteristics of the filter membrane is the bubble point, the height of the bubble point reflects the size of the membrane aperture, and the height of the bubble point also greatly influences the application range of the filter membrane; the methods of bubble point testing are well known in the art, and the procedures for such testing 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; of course, the skilled person can also obtain the above parameters by other measuring means, which are only used as reference.

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 filter membrane is too large, the filtering time is too long, and the time cost is too large. The thickness of the macroporous film is 10-100 mu m, so that the macroporous film has high mechanical strength, can effectively filter, and has high filtering efficiency, short filtering time and low time cost.

The test liquid used for measuring the bubble point size of the macroporous film in the invention is IPA (isopropyl alcohol); the IPA bubble point of the macroporous film is 5-70kPa, which shows that the macroporous film has larger pore diameter, so that the macroporous film has smaller pressure loss, larger flow rate and high filtering speed; meanwhile, the gas permeable membrane has higher gas permeability, so the gas permeable membrane is particularly suitable for being applied to the filtration of stripping liquid and etching liquid in the semiconductor manufacturing process and being used as a gas permeable membrane in electronic equipment and medical equipment.

The average pore diameter of the macroporous film can be measured by a PMI pore diameter distribution instrument, and also can be measured by a bubble point method, a mercury intrusion method or other measuring methods; the porosity of the membrane is the proportion of the volume of membrane pores of the filter membrane to 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; of course, the skilled person can also obtain the above parameters by other measuring means, which are only used as reference.

The average pore diameter of the PTFE macroporous membrane is 1-20 mu m, and the pore diameter is larger, so that the macroporous membrane has larger flow velocity, high transition speed and short filtration time; the porosity of the macroporous membrane is 60-90%, so that the filter membrane has higher dirt holding capacity, can retain more impurity particles and has longer service life; in addition, the combination of large aperture and high porosity ensures that the macroporous film has lower pressure loss, less energy waste, reduced resource waste and more environmental protection.

As a further improvement of the invention, the transverse tensile strength of the macroporous film is 5-40MPa, and the longitudinal tensile strength is 5-40MPa; the transverse elongation at break is 30-200%, and the longitudinal elongation at break is 30-150%;

the time required for 50ml of water to pass through a macroporous membrane with the diameter of 47mm is 1-8s under the conditions that the pressure is 0.03MPa and the temperature is 20 ℃;

the pressure loss when air passed through the large pore membrane at a flow rate of 5.3 cm/sec was 98-980Pa.

Important indexes for evaluating the mechanical strength of the filter membrane are the tensile strength and the elongation at break of the filter membrane; under certain conditions, the greater the tensile strength of the film, the better the mechanical strength of the film is said to be; tensile strength refers to the ability of a film to withstand parallel stretching; when the film is tested under a certain condition, the film sample is acted by a tensile load until the film sample is damaged, and the tensile strength and the elongation at break of the film can be calculated according to the maximum tensile load corresponding to the damage of the film sample, the change of the size (length) of the film sample and the like; tensile strength, elongation at break can be measured by a universal tensile tester, tensile strength testing methods are well known in the art, for example, tensile strength testing procedures are explained in detail in ASTM D790 or ISO 178; the transverse tensile strength of the polytetrafluoroethylene macroporous film is 5-40MPa, and the longitudinal tensile strength is 5-40MPa; the longitudinal elongation at break is 30-150%, and the transverse elongation at break is 30-200%; the macroporous film has higher tensile strength and elongation at break, better mechanical property and higher industrial practical value, and can completely meet the market demand.

Through a pressure loss test of the macroporous membrane, when air passes through the macroporous membrane at a flow speed of 5.3 cm/sec, the pressure loss is only 98-980Pa, which shows that the macroporous membrane has the advantages of extremely low pressure loss, high energy utilization rate, low filtration cost and environmental protection.

By testing the flow rate of the macroporous membrane, the time required for 50ml of water to pass through a filter membrane with the diameter of 47mm is only 1-8s under the conditions that the pressure is 0.03MPa and the temperature is 20 ℃; the large-pore membrane has the advantages of large flow rate, short filtration time and low time cost; further illustrates that the macroporous film is suitable for being applied to the filtration of stripping liquid and etching liquid in the semiconductor manufacturing process and used as a breathable film in electronic equipment and medical equipment. In addition, the invention also provides a preparation method of the polytetrafluoroethylene macroporous membrane, which comprises the following steps:

A. mixing materials: mixing and stirring PTFE dispersion resin and a lubricant, and uniformly mixing to obtain paste;

B. blank preparation: prepressing the paste into a cylindrical blank;

C. extruding: b, extruding the blank obtained in the step B to form a flat banded matrix;

D. and then pressing: the banded matrix is rolled again, so that the thickness of the banded matrix after rolling is 20 to 80 percent of that of the banded matrix before rolling

E. And (3) drying: drying the belt-shaped matrix to volatilize the lubricant;

F. longitudinal stretching: longitudinally stretching the dried banded matrix, wherein the longitudinal stretching temperature is 100-250 ℃, the longitudinal stretching multiple is 4-20 times, and the longitudinal stretching speed is 1-20%/s, so as to obtain a first banded matrix;

G. heat setting for the first time: placing the first strip-shaped substrate in an environment with the temperature of 330-360 ℃ for primary heat setting, wherein the heat setting time is 5-20min; calendering the first strip-shaped substrate while performing primary heat setting, so that the thickness of the calendered first strip-shaped substrate is 20-80% of the thickness of the first strip-shaped substrate before calendering;

H. and (3) transverse stretching: transversely stretching the first strip-shaped substrate at the transverse stretching temperature of 330-380 ℃ and the transverse stretching multiple of 8-30 times to obtain a second strip-shaped substrate;

I. and (3) heat setting for the second time: and placing the second banded matrix in an environment with the temperature of 350-380 ℃ for second heat setting for 3-10min to obtain the PTFE macroporous film.

As a further improvement of the present invention, the PTFE dispersion resin includes at least a PTFE dispersion resin having a number-average molecular weight of 100 to 1200 ten thousand;

the lubricant is at least one of lubricating oil, palm oil, naphthenic oil, white oil, aviation kerosene, degreased kerosene and paraffin.

In a further improvement of the present invention, the crystallinity of the PTFE dispersion resin is 90% or more, and the crystallinity of the macroporous film is 18% to 30%.

As a further improvement of the invention, the step A mixing specifically means that the PTFE dispersion resin and the lubricant are mixed and stirred at the temperature of 5-25 ℃, then the mixture is put into the environment at the temperature of 25-50 ℃ for curing, and the standing time is 8-48h, so that the paste is obtained.

As a further improvement of the invention, the step B of prepressing the paste into a cylindrical blank specifically means prepressing the paste into a cylindrical blank under the condition of the pressure of 1-3MPa, and the pressure maintaining time is 10-20min.

As a further improvement of the invention, the stretching rate in the transverse direction in step G is 5 to 25%/s and the ratio of the stretching ratio in the transverse direction to the stretching ratio in the longitudinal direction is 2 to 10 times.

When preparing the PTFE macroporous film, firstly, mixing and stirring raw material PTFE dispersion resin and a lubricant, wherein the PTFE dispersion resin at least comprises polytetrafluoroethylene dispersion resin with the number average molecular weight of 100-1200 ten thousand, namely the used PTFE dispersion resin can be one, and the number average molecular weight of the PTFE dispersion resin is 100-1200 ten thousand; the polytetrafluoroethylene dispersion resin used may be plural (2 or more), for example, a mixed dispersion resin composed of one kind of PTFE dispersion resin having a number average molecular weight of 100 ten thousand and one kind of PTFE dispersion resin having a number average molecular weight of 1200 ten thousand; the PTFE dispersion resin with a certain number average molecular weight is selected, so that the prepared PTFE macroporous membrane has enough mechanical strength, the crystallinity of the used raw material PTFE dispersion resin is over 90 percent, and the PTFE dispersion resin with high crystallinity is beneficial to generating fibrils and nodes required by the invention, so that the PTFE macroporous membrane with high tensile strength and low pressure loss is beneficial to obtaining the PTFE macroporous membrane; the lubricant is at least one of lubricating oil, palm oil, naphthenic oil, white oil, aviation kerosene, degreased kerosene and paraffin; the lubricant can be only one substance or a mixture of the substances, and the PTFE fractional resin can be conveniently processed by selecting a proper lubricant to obtain a macroporous film with a required film structure; in the present invention, 15 to 35 parts by weight of a lubricant is required per 100 parts by weight of the PTFE dispersion resin; the activation energy of the PTFE dispersion resin used in the invention is very low, and the fibrillation is very easy to occur, so the environmental temperature required by the PTFE dispersion resin and the lubricant is lower and is not suitable to be too high when stirring and mixing are carried out, and the PTFE dispersion resin and the lubricant are mixed and stirred under the condition that the temperature is 5-25 ℃, thereby ensuring that the PTFE dispersion resin can not be fibrillated too early, being beneficial to the subsequent stretching and shaping treatments, and further obtaining a macroporous film with ideal nodes and fibril structures; uniformly mixing PTFE dispersion resin and a lubricant, putting the mixture into an oven at the temperature of 25-50 ℃ for curing for 8-48h to obtain paste, wherein the curing aims to ensure that the PTFE dispersion resin and the lubricant are uniformly mixed, and the lubricant can be uniformly dispersed in the PTFE dispersion resin, so that the subsequent blank-making extrusion is facilitated;

then, blank making is carried out, the paste is pre-pressed, under the condition that the pressure is 1-3MPa, the paste is pre-pressed into a cylindrical blank, and the pressure maintaining time is 10-20min; in the process of prepressing and forming the blank, the pressure and the pressure maintaining time are important factors influencing the quality of the blank. If the pressure is insufficient and the pressure maintaining time is short, the lubricant is unevenly distributed in the resin, and air gaps still exist in the resin, so that the extrusion is unstable, and various properties of the film are influenced; if the pressure is too high or the pressure maintaining time is too long, the lubricant is extruded from the resin, so that insufficient lubrication is caused, the surface of an extruded product is rough, and the extruded product is easy to crack in the calendering process; in the invention, prepressing is carried out under the condition that the pressure is 1-3MPa, and meanwhile, the pressure maintaining time is 10-20min, thus being beneficial to obtaining a green body with better quality; then extruding, and putting the blank into a pushing machine for extrusion to form a flat banded matrix; the reason that the film with an ideal film structure (the joints are long in section) is finally obtained is that in the process of stretching and shaping, the joints are partially fused in the thickness direction, and the fusion cannot be realized only by stretching and shaping, in the invention, the extruded banded matrix is calendered, and after the calendering treatment, the thickness of the banded matrix is 20-80% of that of the banded matrix before calendering, so that certain acting force is generated among resin particles, and the subsequent fusion is facilitated; and drying after the repressing, putting the banded matrix into an oven for drying to volatilize the lubricant, wherein the drying temperature is 100-250 ℃.

After drying is finished, longitudinal stretching is carried out, the dried banded base body is longitudinally stretched, the longitudinal stretching temperature is 100-250 ℃, the longitudinal stretching multiple is 4-20 times, and the longitudinal stretching speed is 1-20%/s, so that a first banded base body is obtained; the stretching rates (including the longitudinal stretching rate and the transverse stretching rate) in the present invention are embodied by the distance between the rolls and the difference in the rotation speed between the rolls; the longitudinal stretching temperature is below the melting point of polytetrafluoroethylene, and cannot be too high, so that the splitting of nodes is facilitated, and the structural characteristics of high node density and small fiber length are obtained; the longitudinal stretching temperature is controlled between 100 ℃ and 250 ℃, which is favorable for forming long fibers and high-density nodes, the longitudinal stretching multiple is 4-20 times, the longitudinal stretching speed is 1-20%/s, and the elongation of the fibers is favorable; after the previous recompression treatment, fibers are tangled among the resin particles in the thickness direction and have strong acting force, so that the nodes in the thickness direction become longer and larger after longitudinal stretching; then carrying out primary heat setting, namely placing the first strip-shaped substrate in an environment with the temperature of 330-360 ℃ for primary heat setting for 5-20min; calendering the first strip-shaped base body while performing primary heat setting, so that the thickness of the calendered first strip-shaped base body is 20% -80% of the thickness of the first strip-shaped base body before calendering; therefore, a plurality of nodes in the thickness direction are mutually entangled, and the nodes have larger interaction and are not easy to separate; the purpose of carrying out reheating shaping and simultaneously carrying out calendaring is to carry out further compaction, reduce the slippage and even separation between nodes in the thickness direction in the subsequent stretching process and obtain an ideal node structure more easily; then stretching in the transverse direction: transversely stretching the first banded matrix at the transverse stretching temperature of 330-380 ℃ by 8-30 times to obtain a second banded matrix; the transverse stretching speed is 5-25%/s, and the ratio of the transverse stretching multiple to the longitudinal stretching multiple is 2-10 times; namely, the temperature of transverse stretching is higher than the melting point of PTFE, and the transverse stretching multiple is larger than that of longitudinal stretching, so that on one hand, the joint is partially fused and fixed in the thickness direction, and the joint structure required by the invention can be obtained; on the other hand, the proper membrane pore diameter is obtained, and the membrane is ensured to have lower pressure loss, higher air permeability and excellent tensile strength. Finally, the second banded matrix is placed in an environment with the temperature of 350-380 ℃ for second heat setting, and the heat setting time is 3-10min, so that the PTFE macroporous film can be obtained; the second heat setting temperature needs to be higher than the first heat setting temperature, and the film cannot be further set, because the first heat setting has already performed the function of partially setting the film, the second heat setting temperature needs to be higher than the first heat setting temperature to completely set the film, and thus a product with good dimensional stability and high strength is obtained.

The PTFE macroporous film finally prepared has high tensile strength and low pressure loss, and also has higher air permeability and wide application range.

As a further improvement of the invention, the PTFE macroporous membrane is used for filtering stripping liquid and etching liquid in a semiconductor manufacturing process, and is used as a breathable membrane in electronic equipment and medical equipment.

The PTFE macroporous membrane is used for filtering stripping liquid and etching liquid in a semiconductor manufacturing process, in particular to filtering stripping liquid and etching liquid in a panel manufacturing process (such as a liquid crystal panel); and as breathable films in electronic and medical devices, for example, as waterproof breathable films in cell phones.

The invention has the beneficial effects that: the outer surface of the PTFE macroporous membrane comprises nodes and fibrils, adjacent nodes are connected through the fibrils, and the extending directions of the nodes are consistent; on a section cut along the length direction of the original fiber of the macroporous membrane, the length of the node in the first direction is greater than that in the second direction; the first direction is parallel to the thickness direction of the macroporous film, and the second direction is perpendicular to the thickness direction of the macroporous film, so that the macroporous film has high tensile strength, good mechanical property and low pressure loss, and has high energy conversion rate and economic value and is more environment-friendly when being used in actual industrialization; also has higher air permeability; the filter is particularly suitable for filtering stripping liquid and etching liquid in the semiconductor manufacturing process, and is used as a breathable film in electronic equipment and medical equipment; in addition, the invention also provides a preparation method of the macroporous membrane, and the preparation method is convenient, quick and effective, simple to operate, green and environment-friendly, and suitable for large-scale popularization.

Drawings

FIG. 1 is a Scanning Electron Microscope (SEM) image of a longitudinal section of a PTFE macroporous membrane obtained in example 1, at a magnification of 500;

FIG. 2 is a further enlarged Scanning Electron Microscope (SEM) photograph of a longitudinal section of the macroporous PTFE membrane prepared in example 1, at 1000 magnification;

FIG. 3 is a Scanning Electron Microscope (SEM) image of the outer surface of a PTFE macroporous membrane prepared in example 2, at a magnification of 300 ×;

FIG. 4 is a further enlarged Scanning Electron Microscope (SEM) image of the outer surface of the macroporous PTFE membrane prepared in example 2, at 1000 magnification;

FIG. 5 is a schematic view of an IPA bubble point testing device of a PTFE macroporous membrane of the present invention;

fig. 6 is a schematic view of a PTFE macroporous membrane flow rate testing device 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. In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present application. It will be apparent, however, to one skilled in the art, that the present application may be practiced without one or more of these specific details. In other instances, well-known features of the art have not been described in order to avoid obscuring the present application.

In the following examples, the raw materials and equipment for producing the PTFE macroporous membranes were all commercially available, unless otherwise specified. The structural morphology of the PTFE macroporous membrane is characterized by adopting a scanning electron microscope with the model number of S-5500 provided by Hitachi company.

Example 1

A preparation method of a PTFE macroporous membrane comprises the following steps:

A. mixing materials: mixing and stirring 100 parts by weight of PTFE dispersion resin and 19 parts by weight of lubricating oil at the temperature of 22 ℃, and then putting into an oven at the temperature of 46 ℃ for curing for 14 hours to obtain paste; the number average molecular weight of the PTFE dispersion resin is 300 ten thousand, and the crystallinity is 91%;

B. blank preparation: prepressing the paste under the pressure of 1MPa to form a cylindrical blank, and keeping the pressure for 18min;

C. extruding: b, extruding the blank obtained in the step B to form a flat strip-shaped matrix;

D. and then pressing: rolling the banded matrix again to ensure that the thickness of the rolled banded matrix is 35% of that of the banded matrix before rolling;

E. and (3) drying: putting the strip-shaped matrix into an oven for drying so as to volatilize the lubricating oil;

F. longitudinal stretching: longitudinally stretching the dried banded base body on a film drawing machine, wherein the longitudinal stretching temperature is 130 ℃, the longitudinal stretching multiple is 4 times, and the longitudinal stretching speed is 2%/s, so as to obtain a first banded base body;

G. heat setting for the first time: placing the first strip-shaped substrate in an environment with the temperature of 330 ℃ for primary heat setting, wherein the heat setting time is 8min; calendering the first strip-shaped base body while performing primary heat setting, so that the thickness of the calendered first strip-shaped base body is 40% of the thickness of the first strip-shaped base body before calendering;

H. transverse stretching: transversely stretching the first banded base body on a film drawing machine, wherein the transverse stretching temperature is 335 ℃, the transverse stretching multiple is 9 times, and the transverse stretching speed is 7%/s, so as to obtain a second banded base body;

I. and (3) heat setting for the second time: placing the second banded matrix in an environment with the temperature of 350 ℃ for second heat setting for 8min to obtain a PTFE macroporous film; the crystallinity of the PTFE macroporous membrane was 20%.

Example 2

A. mixing materials: mixing and stirring 100 parts by weight of PTFE dispersion resin and 26 parts by weight of paraffin at the temperature of 17 ℃, and then putting the mixture into a drying oven at the temperature of 40 ℃ for curing for 24 hours to obtain paste; the PTFE dispersion resin has a number average molecular weight of 600 ten thousand and a crystallinity of 94%;

B. blank preparation: prepressing the paste under the pressure of 2MPa to form a cylindrical blank, and keeping the pressure for 15min;

D. and then, pressing: rolling the banded matrix again to ensure that the thickness of the rolled banded matrix is 50% of that of the banded matrix before rolling;

E. and (3) drying: putting the strip-shaped matrix into an oven for drying so as to volatilize paraffin;

F. longitudinal stretching: longitudinally stretching the dried banded base body on a film drawing machine, wherein the longitudinal stretching temperature is 180 ℃, the longitudinal stretching multiple is 8 times, and the longitudinal stretching speed is 8%/s, so as to obtain a first banded base body;

G. heat setting for the first time: placing the first strip-shaped substrate in an environment with the temperature of 345 ℃ for primary heat setting, wherein the heat setting time is 14min; rolling the first strip-shaped base body while performing primary heat setting, so that the thickness of the first strip-shaped base body after rolling is 50% of the thickness of the first strip-shaped base body before rolling;

H. and (3) transverse stretching: transversely stretching the first strip-shaped substrate on a film drawing machine at the transverse stretching temperature of 355 ℃, the transverse stretching multiple of 20 times and the transverse stretching speed of 16%/s to obtain a second strip-shaped substrate;

I. and (3) heat setting for the second time: placing the second banded matrix in an environment with the temperature of 365 ℃ for second heat setting, wherein the heat setting time is 7min, and obtaining a PTFE macroporous film; the crystallinity of the PTFE macroporous membrane was 25%.

Example 3

A. mixing materials: mixing and stirring 100 parts by weight of PTFE dispersion resin and 22 parts by weight of palm oil at the temperature of 20 ℃, and then putting into an oven at the temperature of 43 ℃ for curing for 20 hours to obtain paste; the number average molecular weight of the PTFE dispersion resin is 500 ten thousand, and the crystallinity is 92%;

B. blank preparation: prepressing the paste under the pressure of 2MPa to form a cylindrical blank, and keeping the pressure for 13min;

D. and then, pressing: rolling the banded matrix again to ensure that the thickness of the rolled banded matrix is 45 percent of that of the banded matrix before rolling;

E. and (3) drying: putting the banded matrix into an oven for drying so as to volatilize the palm oil;

F. longitudinal stretching: longitudinally stretching the dried banded matrix on a film drawing machine, wherein the longitudinal stretching temperature is 150 ℃, the longitudinal stretching multiple is 6 times, and the longitudinal stretching speed is 5%/s, so as to obtain a first banded matrix;

G. heat setting for the first time: placing the first strip-shaped substrate in an environment with the temperature of 335 ℃ for primary heat setting, wherein the heat setting time is 10min; calendering the first strip-shaped base body while performing primary heat setting, so that the thickness of the calendered first strip-shaped base body is 45% of the thickness of the first strip-shaped base body before calendering;

H. and (3) transverse stretching: transversely stretching the first banded base body on a film drawing machine, wherein the transverse stretching temperature is 345 ℃, the transverse stretching multiple is 15 times, and the transverse stretching speed is 12%/s, so as to obtain a second banded base body;

I. and (3) heat setting for the second time: placing the second banded matrix in an environment with the temperature of 355 ℃ for second heat setting for 6min to obtain a PTFE macroporous membrane; the crystallinity of the PTFE macroporous membrane was 21%.

Example 4

A. mixing materials: mixing and stirring 100 parts by weight of PTFE dispersion resin and 32 parts by weight of naphthenic oil at the temperature of 8 ℃, and then putting the mixture into a drying oven at the temperature of 30 ℃ for curing for 40 hours to obtain paste; the PTFE dispersion resin has the number average molecular weight of 1000 ten thousand and the crystallinity of 97 percent;

B. blank preparation: prepressing the paste under the pressure of 3MPa to form a cylindrical blank, and keeping the pressure for 12min;

D. and then, pressing: rolling the banded matrix again to ensure that the thickness of the rolled banded matrix is 70% of that of the banded matrix before rolling;

E. and (3) drying: putting the strip-shaped matrix into an oven for drying so as to volatilize naphthenic oil;

F. longitudinal stretching: longitudinally stretching the dried banded base body on a film drawing machine, wherein the longitudinal stretching temperature is 240 ℃, the longitudinal stretching multiple is 13 times, and the longitudinal stretching speed is 10%/s, so as to obtain a first banded base body;

G. heat setting for the first time: placing the first strip-shaped substrate in an environment with the temperature of 358 ℃ for first heat setting, wherein the heat setting time is 16min; rolling the first strip-shaped base body while performing primary heat setting, so that the thickness of the first strip-shaped base body after rolling is 65% of the thickness of the first strip-shaped base body before rolling;

H. and (3) transverse stretching: transversely stretching the first banded base body on a film drawing machine, wherein the transverse stretching temperature is 365 ℃, the transverse stretching multiple is 27 times, and the transverse stretching speed is 23%/s, so as to obtain a second banded base body;

I. and (3) second heat setting: placing the second banded matrix in an environment with the temperature of 375 ℃ for second heat setting for 4min to obtain a PTFE macroporous film; the crystallinity of the PTFE macroporous membrane was 28%.

Example 5

A. mixing materials: mixing and stirring 100 parts by weight of PTFE dispersion resin and 28 parts by weight of white oil at the temperature of 12 ℃, and then putting into an oven at the temperature of 35 ℃ for curing for 34 hours to obtain paste; the number average molecular weight of the PTFE dispersion resin is 900 ten thousand, and the crystallinity is 95%;

B. blank preparation: prepressing the paste under the pressure of 3MPa to form a cylindrical blank, and keeping the pressure for 14min;

D. and then, pressing: rolling the banded matrix again to ensure that the thickness of the rolled banded matrix is 65% of that of the banded matrix before rolling;

E. and (3) drying: putting the banded matrix into an oven for drying so as to volatilize the white oil;

F. longitudinal stretching: longitudinally stretching the dried banded base body on a film drawing machine, wherein the longitudinal stretching temperature is 220 ℃, the longitudinal stretching multiple is 11 times, and the longitudinal stretching speed is 10%/s, so as to obtain a first banded base body;

G. heat setting for the first time: placing the first strip-shaped substrate in an environment with the temperature of 352 ℃ for primary heat setting, wherein the heat setting time is 12min; rolling the first strip-shaped base body while performing primary heat setting, so that the thickness of the first strip-shaped base body after rolling is 60% of the thickness of the first strip-shaped base body before rolling;

H. and (3) transverse stretching: transversely stretching the first strip-shaped substrate on a film drawing machine, wherein the transverse stretching temperature is 360 ℃, the transverse stretching multiple is 24 times, and the transverse stretching speed is 17%/s, so as to obtain a second strip-shaped substrate;

I. and (3) heat setting for the second time: placing the second banded matrix in an environment with the temperature of 370 ℃ for second heat setting for 5min to obtain a PTFE macroporous membrane; the crystallinity of the PTFE macroporous membrane was 26%.

Example 6

A. mixing materials: mixing and stirring 40 parts by weight of PTFE resin with the molecular weight of 400 ten thousand and the crystallinity of 92, 60 parts by weight of PTFE dispersion resin with the molecular weight of 800 ten thousand and the crystallinity of 94 percent and 24 parts by weight of aviation kerosene at the temperature of 15 ℃, then putting the mixture into an oven with the temperature of 35 ℃ for curing, and standing for 28 hours to obtain paste;

B. blank preparation: prepressing the paste under the pressure of 2MPa to form a cylindrical blank, and keeping the pressure for 19min;

D. and then pressing: rolling the banded matrix again to enable the thickness of the rolled banded matrix to be 60% of that of the banded matrix before rolling;

E. and (3) drying: putting the strip-shaped matrix into an oven for drying so as to volatilize the aviation kerosene;

F. longitudinal stretching: longitudinally stretching the dried banded base body on a film drawing machine, wherein the longitudinal stretching temperature is 200 ℃, the longitudinal stretching multiple is 7 times, and the longitudinal stretching speed is 11%/s, so as to obtain a first banded base body;

G. heat setting for the first time: placing the first strip-shaped substrate in an environment with the temperature of 348 ℃ for first heat setting, wherein the heat setting time is 18min; calendering the first strip-shaped substrate while performing primary heat setting, so that the thickness of the calendered first strip-shaped substrate is 55% of the thickness of the first strip-shaped substrate before calendering;

H. and (3) transverse stretching: transversely stretching the first strip-shaped substrate on a film drawing machine, wherein the transverse stretching temperature is 352 ℃, the transverse stretching multiple is 26 times, and the transverse stretching speed is 19%/s, so as to obtain a second strip-shaped substrate;

I. and (3) heat setting for the second time: placing the second banded matrix in an environment with the temperature of 368 ℃ for second heat setting for 9min to obtain a PTFE macroporous membrane; the crystallinity of the PTFE macroporous membrane was 24%.

Firstly, the method comprises the following steps: structural characterization

And (3) performing morphology characterization on the polytetrafluoroethylene macroporous film obtained in each embodiment by using a scanning electron microscope, so as to obtain corresponding required data.

Table 1:

table 2:

table 3:

TABLE 4

As can be seen from tables 1-4, the PTFE macroporous film of the invention has reasonable node and fibril structure, is beneficial to the high tensile strength and low pressure loss of the polytetrafluoroethylene macroporous film and has wide application range.

Table 5:

test specimen	IPA bubble point/KPa	Average pore diameter/. Mu.m	Porosity/%
				Example 1	60	1.7	86.1
Example 2	21	7.1	80.7
				Example 3	32	4.3	75.4
Example 4	8	18.4	65.9
				Example 5	13	13.6	69.2
Example 6	17	10.2	72.6

Table 6:

as can be seen from the above table, the PTFE macroporous film has the advantages of higher tensile strength and elongation at break, good mechanical properties, wide application range and capability of meeting various industrial requirements

Table 7:

and (3) pressure loss test: air was passed through a surface area of 100cm at a flow rate of 32L/min ² (e.g., 10 cm: 10 cm) and the pressure before and after the air flow through the membrane was tested to obtain a pressure loss corresponding to the membrane.

Water flow rate test (the testing device is as shown in figure 6)

Experimental procedure

The method comprises the following steps: and (3) mounting the filter membrane to be tested on a support for reduced pressure filtration, closing a valve 2 on the reduced pressure filtration support, 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 displayed by the stopwatch is recorded, when all the test liquid passes through the filter membrane, the valve 2 on the bracket is closed, and the filter membrane is taken out.

Test specimen	Pressure loss/Pa	Flow rate/s
			Example 1	432	4.5
Example 2	513	6.2
			Example 3	284	3.1
Example 4	446	4.7
			Example 5	371	4.0
Example 6	478	5.6

As can be seen from the table above, the PTFE macroporous film has the advantages of less pressure loss, high energy utilization rate and greenness and environmental protection; meanwhile, the filter has the advantages of high flow rate, high filtering speed and low filtering time cost.

Table 8:

and (3) testing the air permeability:

gurley air permeability test of the obtained PTFE macroporous film was carried out according to standard JIS P8117-2009 (paper and board, measurement of air permeability and air resistance (middle range) -Gurley (GURLEY) method)

Unit: s (300 mL/1 inch) ² )

Test specimen	Gurley air permeability
		Example 1	7.8
Example 2	9.6
		Example 3	5.2
Example 4	6.7
		Example 5	7.2
Example 6	6.1

From the above table, the PTFE macroporous membrane prepared by the present invention has high air permeability, and is particularly suitable for filtration of stripping solutions and etching solutions in semiconductor processes, and for use as an air permeable membrane in electronic devices and medical devices.

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 adaptations to those skilled in the art without departing from the principles of the present invention should also be considered as within the scope of the present invention.

Claims

1. A PTFE macroporous membrane comprising nodes and fibrils on the outer surface thereof, adjacent ones of said nodes being connected by fibrils, said nodes extending in a uniform direction, characterized in that: on a section cut along the length direction of the original fiber of the macroporous membrane, the length of the node in the first direction is greater than that in the second direction; wherein the first direction is parallel to the thickness direction of the macroporous film, and the second direction is perpendicular to the thickness direction of the macroporous film;

the ratio of the length of the node in the first direction to the length of the node in the second direction is 3-15;

on a section cut along the length direction of the original fiber of the macroporous membrane, the length of the node in the first direction accounts for 25-75% of the thickness of the membrane.

2. A PTFE macroporous membrane according to claim 1, wherein: the nodes have a length in the first direction of 8-45 μm and a length in the second direction of 0.5-7 μm.

3. A PTFE macroporous membrane according to claim 1, wherein: and on the section cut along the length direction of the raw fiber of the macroporous membrane, the distance between adjacent nodes along the length of the second direction is 4-30 μm.

4. A PTFE macroporous membrane according to claim 1, wherein: on a section cut along the length direction of the original fiber of the macroporous film, projections of two adjacent nodes along the thickness direction of the film are partially overlapped, and the length of an overlapped area is 0.5-10 mu m.

5. A PTFE macroporous membrane according to claim 1, wherein: on the outer surface of the macroporous membrane, the average width of the nodes is 1.3-4.3 μm; the fibrils have an average width of 0.15-0.85 μm.

6. A PTFE macroporous membrane as in claim 5, wherein: the fibrils have an average length of 5-30 μm; the difference between the maximum length and the minimum length of said fibrils is 4-35 μm.

7. A PTFE macroporous membrane according to claim 1, wherein: the thickness of the macroporous film is 10-100 mu m, and the IPA bubble point is 5-70kPa; the average pore diameter of the macroporous membrane is 1-20 mu m, and the porosity is 60-90%.

8. A PTFE macroporous membrane according to claim 1, wherein: the transverse tensile strength of the macroporous film is 5-40MPa, and the longitudinal tensile strength of the macroporous film is 5-40MPa;

the transverse elongation at break is 30-200%, and the longitudinal elongation at break is 30-150%;

the pressure loss when air passed through the macroporous membrane at a flow rate of 5.3 cm/sec was 98-980Pa.

9. The method for preparing a PTFE macroporous membrane of any one of claims 1 to 8, wherein: the method comprises the following steps:

B. blank preparation: prepressing the paste into a cylindrical blank;

D. and then pressing: rolling the banded matrix again to enable the thickness of the rolled banded matrix to be 20% -80% of that of the banded matrix before rolling;

E. and (3) drying: drying the belt-shaped matrix to volatilize the lubricant;

G. heat setting for the first time: placing the first strip-shaped substrate in an environment with the temperature of 330-360 ℃ for primary heat setting, wherein the heat setting time is 5-20min; calendering the first strip-shaped base body while performing primary heat setting, so that the thickness of the calendered first strip-shaped base body is 20% -80% of the thickness of the first strip-shaped base body before calendering;

H. transverse stretching: transversely stretching the first banded matrix at the transverse stretching temperature of 330-380 ℃ by 8-30 times to obtain a second banded matrix;

I. and (3) heat setting for the second time: and (3) placing the second banded matrix in an environment with the temperature of 350-380 ℃ for second heat setting for 3-10min to obtain the PTFE macroporous membrane.

10. The method for preparing a PTFE macroporous membrane according to claim 9, wherein: the PTFE dispersion resin at least comprises PTFE dispersion resin with a number average molecular weight of 100-1200 ten thousand;

11. The method for preparing a PTFE macroporous membrane of claim 9, wherein: the crystallinity of the PTFE dispersion resin is more than 90%, and the crystallinity of the macroporous film is 18% -30%.

12. The method for preparing a PTFE macroporous membrane according to claim 9, wherein: the step A mixing material specifically refers to mixing and stirring the PTFE dispersion resin and the lubricant at the temperature of 5-25 ℃, then putting into the environment at the temperature of 25-50 ℃ for curing, and standing for 8-48h to obtain paste.

13. The method for preparing a PTFE macroporous membrane of claim 9, wherein: and B, prepressing the paste into a cylindrical blank, namely prepressing the paste into the cylindrical blank under the condition that the pressure is 1-3MPa, and keeping the pressure for 10-20min.

14. The method for preparing a PTFE macroporous membrane of claim 9, wherein: the transverse stretching rate in step H is 5 to 25%/s, and the ratio of the transverse stretching magnification to the longitudinal stretching magnification is 2 to 10 times.

15. Use of a PTFE macroporous membrane according to any one of claims 1 to 8, wherein: the PTFE macroporous membrane is used for filtering stripping liquid and etching liquid in a semiconductor manufacturing process, and is used as a breathable membrane in electronic equipment and medical equipment.