Polytetrafluoroethylene composite microporous membrane for air purification and preparation method thereof

Abstract

The invention discloses a polytetrafluoroethylene composite microporous membrane for air purification and a preparation method thereof, and the polytetrafluoroethylene composite microporous membrane comprises: a porous base membrane comprising a fiber material; the polytetrafluoroethylene membranes are arranged on the two sides of the porous base membrane, the thickness ratio of the porous base membrane to the polytetrafluoroethylene membrane on any side is 1: (1-1.5), and the average pore size of the polytetrafluoroethylene membranes is 280-450 nm. The polytetrafluoroethylene composite microporous membrane has good thickness uniformity, the filtering effect of the polytetrafluoroethylene composite microporous membrane can be exerted, and the problem that the service life is short due to the fact that the proportion of the transverse tensile strength to the longitudinal tensile strength is too large is solved.

Description

Technical Field

[0001] The present application relates to the technical field of air purification, and in particular to a polytetrafluoroethylene composite microporous membrane for air purification and a preparation method thereof. Background Art

[0002] Polytetrafluoroethylene composite microporous membrane is a semi-finished product made of polytetrafluoroethylene extruded rods and strips, which is calendered into a film, and then stretched and heat-set at a temperature below the melting point to obtain a porous membrane product. Polytetrafluoroethylene composite microporous membrane is a flexible and elastic microporous material with high porosity and uniform pore size distribution. It has the characteristics of being breathable and impermeable to water. It can be used as a sterilizing filter membrane, an ultra-clean filter membrane for various solvents, etc. It has a wide range of applications.

[0003] Air purification is of great significance in high-tech fields such as biology, pharmaceuticals, chemicals, electronics, environmental protection, and scientific experiments. Traditional air purification filter membranes include microporous membranes such as polypropylene, polyester, and polytetrafluoroethylene. The obtained filter membranes have low filtration efficiency during air filtration, and are accompanied by the penetration of filter retentate, which affects the mechanical properties of the filter membrane and results in a low service life of the filter membrane. Summary of the invention

[0004] The embodiment of the present application provides a polytetrafluoroethylene composite microporous membrane for air purification and a preparation method thereof. The polytetrafluoroethylene composite microporous membrane has good transverse tensile strength and longitudinal tensile strength, small thickness deviation, and can also improve the air permeability, filtration effect and service life of the polytetrafluoroethylene composite microporous membrane.

[0005] In a first aspect, the present application provides a polytetrafluoroethylene composite microporous membrane for air purification, comprising:

[0006] A porous base membrane including a fibrous material;

[0007] A polytetrafluoroethylene membrane, wherein the polytetrafluoroethylene membrane is arranged on both sides of the porous base membrane, wherein the thickness ratio of the porous base membrane to the polytetrafluoroethylene membrane on either side is 1:(1-1.5)), and the average pore size of the polytetrafluoroethylene membrane is 280nm to 450nm.

[0008] In some optional embodiments, the fiber material includes at least one of a polyester fiber material and a polyamide material.

[0009] In some optional embodiments, the porosity of the porous base membrane is 40%-60%;

[0010] In some optional embodiments, the porosity of the polytetrafluoroethylene membrane is 80%-90%;

[0011] In some optional embodiments, the average thickness of the polytetrafluoroethylene film is 3 to 4.5 μm;

[0012] In some optional embodiments, the average pore size of the polytetrafluoroethylene membrane is 300nm to 400nm;

[0013] In some optional embodiments, the average thickness of the porous base membrane is 2-3 μm.

[0014] In some optional embodiments, in the polytetrafluoroethylene composite microporous membrane, the weight average molecular weight of polytetrafluoroethylene is 700,000-900,000.

[0015] In some optional embodiments, the transverse tensile strength of the polytetrafluoroethylene composite microporous membrane is 130 MPa to 160 MPa;

[0016] In some optional embodiments, the longitudinal tensile strength of the polytetrafluoroethylene composite microporous membrane is 100 MPa to 150 MPa;

[0017] In some optional embodiments, the porosity of the polytetrafluoroethylene composite microporous membrane is 70%-85%;

[0018] In some optional embodiments, the ratio of the transverse tensile strength to the longitudinal tensile strength of the polytetrafluoroethylene composite microporous membrane is 1:(0.8 to 1).

[0019] In a second aspect, the present application embodiment provides a method for preparing the polytetrafluoroethylene composite microporous membrane of the first aspect, comprising:

[0020] Providing a porous base membrane and a polytetrafluoroethylene membrane, wherein the porous base membrane comprises a fiber material;

[0021] The polytetrafluoroethylene membranes are arranged on both sides of the porous base membrane and subjected to heat pressing treatment to obtain the polytetrafluoroethylene composite microporous membrane.

[0022] In some optional embodiments, the temperature of the hot pressing treatment is controlled at 90-110° C., the line pressure of the hot pressing treatment is 0.5-0.8 MPa, and the speed of the hot pressing treatment is 0.8-1.5 m / min.

[0023] In some optional embodiments, the method for preparing the polytetrafluoroethylene membrane comprises:

[0024] The polytetrafluoroethylene dispersion resin is heat-treated at a temperature of 300° C. to 600° C. to obtain a melt;

[0025] The melt and the auxiliary are mixed and extruded at 40°C to 150°C to obtain a paste;

[0026] The paste is heat-shrunk, cooled, extruded, stretched and heat-set at a temperature of 600°C to 900°C to obtain a polytetrafluoroethylene film, wherein the cooling terminal temperature is 60°C to 100°C; the extrusion and stretching sequentially include longitudinal stretching and transverse stretching, and the ratio of the longitudinal stretching to the transverse stretching is (2 to 5):1.

[0027] In some optional embodiments, the multiple of longitudinal stretching is 100 to 160 times, and the multiple of transverse stretching is 20 to 50 times. The porosity is high, the filtration efficiency is good, and the embodiments of the present application have at least the following beneficial effects:

[0028] The embodiments of the present application use a porous base membrane and a polytetrafluoroethylene membrane. The porous base membrane is used as a supporting material, which has good stability and is conducive to providing good mechanical properties for the polytetrafluoroethylene composite microporous membrane. The average pore size of the polytetrafluoroethylene membrane is 280nm to 450nm, which can better balance the transverse tensile strength and longitudinal tensile strength of the polytetrafluoroethylene membrane. The polytetrafluoroethylene membrane is arranged on both sides of the porous base membrane, and the thickness ratio of the porous base membrane to the polytetrafluoroethylene membrane on either side is 1:(1 to 1.5), which can better perform hot pressing treatment, improve the bonding effect between the layers, and improve the thickness uniformity of the polytetrafluoroethylene composite microporous membrane. The filtering effect of the polytetrafluoroethylene composite microporous membrane can be further exerted, the thickness deviation of the polytetrafluoroethylene composite microporous membrane can be reduced, and the ratio of the transverse tensile strength to the longitudinal tensile strength can be reduced, thereby avoiding the short life due to the transverse and longitudinal tensile strengths. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The features, advantages and technical effects of exemplary embodiments of the present application will be described below with reference to the accompanying drawings.

[0030] Figure 1 This is an electron microscope image of the surface of the polytetrafluoroethylene composite microporous membrane of Example 1 of the present application. DETAILED DESCRIPTION

[0031] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In the detailed description below, many specific details are proposed to provide a comprehensive understanding of the present application. However, it is obvious to those skilled in the art that the present application can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present application by illustrating examples of the present application. In the accompanying drawings and the following description, at least some of the known structures and technologies are not shown to avoid unnecessary ambiguity in the present application; and, for clarity, the size of some structures may be exaggerated. In addition, the features, structures or characteristics described below may be combined in one or more embodiments in any suitable manner.

[0032] It should be noted that, in this application, the terms "first", "second", etc. are used to distinguish similar objects, and are not used to describe a specific order or sequence. Moreover, the term "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprising..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0033] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be measured by various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application). Unless otherwise specified, the test temperature of the parameters mentioned in this application is 25° C. and the test pressure is standard atmospheric pressure.

[0034] A list of items connected by the term "one or more of" may mean any combination of the listed items. The term "plurality" means more than two. Similarly, a list of items connected by "one or more of" may mean any combination of the listed items.

[0035] The embodiment of the present application selects the adhesive and the polyvinylidene fluoride based polymer and limits the mass ratio, so that the polytetrafluoroethylene composite microporous membrane prepared has good bonding strength and good peel strength, and also takes into account the improvement of the internal resistance and air permeability value-added of the polytetrafluoroethylene composite microporous membrane.

[0036] The term "permeability value" reflects the permeability of the polytetrafluoroethylene composite microporous membrane. That is, the time required for a certain volume of gas, usually 100cc, to pass through a polytetrafluoroethylene composite microporous membrane with an area of ​​1 square inch under certain pressure conditions, for example, the pressure is quickly increased to 10kPa within 2s.

[0037] like Figure 1 As shown, the embodiment of the present application proposes a polytetrafluoroethylene composite microporous membrane for air purification, comprising:

[0038] A porous base membrane including a fibrous material;

[0039] A polytetrafluoroethylene membrane is provided on both sides of the porous base membrane, wherein the thickness ratio of the porous base membrane to the polytetrafluoroethylene membrane on either side is 1:(1-1.5), and the average pore size of the polytetrafluoroethylene membrane is 280nm to 450nm.

[0040] A porous base membrane and a polytetrafluoroethylene membrane are used. The porous base membrane is used as a supporting material, and has good stability, which is conducive to providing good mechanical properties for the polytetrafluoroethylene composite microporous membrane. The average pore size of the polytetrafluoroethylene membrane is 280nm to 450nm, which can better balance the transverse tensile strength and longitudinal tensile strength of the polytetrafluoroethylene membrane. The polytetrafluoroethylene membrane is arranged on both sides of the porous base membrane, and the thickness ratio of the porous base membrane to the polytetrafluoroethylene membrane on either side is 1: (1 to 1.5), which can better perform hot pressing treatment, improve the bonding effect between the layers, and improve the thickness uniformity of the polytetrafluoroethylene composite microporous membrane, which can further exert the filtering effect of the polytetrafluoroethylene composite microporous membrane and avoid the short life due to the large ratio of transverse and longitudinal tensile strengths.

[0041] Optionally, the thickness ratio of the porous base membrane to the polytetrafluoroethylene membrane on any one side is any one of 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, and 1:1.5.

[0042] In some optional embodiments, the fiber material includes at least one of a polyester fiber material and a polyamide material. Further, the average diameter of the fiber material is 0.3 to 0.8 microns. The melting point of the polyester fiber material is 130°C to 160°C.

[0043] In some optional embodiments, the porosity of the porous base membrane is 40%-60%, which is beneficial to increase the air flow rate in the polytetrafluoroethylene composite microporous membrane and improve the filtration efficiency in the polytetrafluoroethylene composite microporous membrane.

[0044] In some optional embodiments, the porosity of the polytetrafluoroethylene membrane is 80%-90%, which is beneficial to increase the air flow rate in the polytetrafluoroethylene composite microporous membrane and improve the filtration efficiency in the polytetrafluoroethylene composite microporous membrane.

[0045] In some optional embodiments, the average thickness of the polytetrafluoroethylene film is 3-4.5 μm. Optionally, the average thickness of the polytetrafluoroethylene film can be any one of 3 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, and 4 μm.

[0046] In some optional embodiments, the average pore size of the polytetrafluoroethylene membrane is 300nm to 400nm; optionally, the average pore size of the polytetrafluoroethylene membrane can be any one of 300nm, 310nm, 320nm, 330nm, 340nm, 350nm, 360nm, 370nm, 380nm, 390nm, and 400nm.

[0047] In some optional embodiments, the average thickness of the porous base film is 2-3 μm. The average thickness of the porous base film can be any one of 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, and 3 μm.

[0048] In some optional embodiments, in the polytetrafluoroethylene composite microporous membrane, the weight average molecular weight of polytetrafluoroethylene is 700,000-900,000, optionally 750,000-850,000, and further optionally 800,000.

[0049] In some optional embodiments, the transverse tensile strength of the polytetrafluoroethylene composite microporous membrane is 130 MPa to 160 MPa; optionally 140 MPa to 155 MPa.

[0050] In some optional embodiments, the longitudinal tensile strength of the polytetrafluoroethylene composite microporous membrane is 100 MPa to 150 MPa; optionally 110 MPa to 140 MPa.

[0051] In some optional embodiments, the porosity of the polytetrafluoroethylene composite microporous membrane is 70%-85%; optionally 75% to 80%.

[0052] In some optional embodiments, the maximum value of the thickness deviation of the polytetrafluoroethylene composite microporous membrane is 0.4 μm to 1.0 μm, and optionally 0.48 μm to 0.96 μm.

[0053] In some optional embodiments, the peel strength of the polytetrafluoroethylene composite microporous membrane is 148 N / m to 170 N / m.

[0054] In some optional embodiments, the toluene diffusion rate of the polytetrafluoroethylene composite microporous membrane is 1.25 to 1.5 ug / min.

[0055] In some optional embodiments, the ratio of the transverse tensile strength to the longitudinal tensile strength of the polytetrafluoroethylene composite microporous membrane is 1:(0.8 to 1).

[0056] In a second aspect, the present application embodiment provides a method for preparing the polytetrafluoroethylene composite microporous membrane of the first aspect, comprising:

[0057] Providing a porous base membrane and a polytetrafluoroethylene membrane, wherein the porous base membrane comprises a fiber material;

[0058] The polytetrafluoroethylene membrane is arranged on both sides of the porous base membrane and subjected to heat pressing treatment to obtain the polytetrafluoroethylene composite microporous membrane, the thickness ratio of the porous base membrane to the polytetrafluoroethylene membrane on either side is 1:(1-1.5); the average pore size of the polytetrafluoroethylene membrane is 280nm to 450nm.

[0059] According to the embodiments of the present application, a polytetrafluoroethylene membrane with a thickness ratio of 1: (1 to 1.5) is arranged on both sides of the porous base membrane, which can provide a good support effect for the polytetrafluoroethylene composite microporous membrane, which is beneficial to control the hot pressing treatment, improve the bonding effect between layers, and thus improve the stability of the polytetrafluoroethylene composite microporous membrane; the average pore size of the polytetrafluoroethylene membrane is 280nm to 450nm, which is beneficial to fine-tune the performance of the polytetrafluoroethylene membrane by hot pressing treatment, thereby better balancing the transverse tensile strength and longitudinal tensile strength of the polytetrafluoroethylene membrane; improving the thickness uniformity of the polytetrafluoroethylene composite microporous membrane can further exert the filtering effect of the polytetrafluoroethylene composite microporous membrane, and avoid the short life due to the large ratio of transverse and longitudinal tensile strengths.

[0060] In some optional embodiments, the temperature of the hot pressing treatment is controlled at 90-110° C., the line pressure of the hot pressing treatment is 0.5-0.8 MPa, and the speed of the hot pressing treatment is 0.8-1.5 m / min.

[0061] In some optional embodiments, the method for preparing the polytetrafluoroethylene membrane comprises:

[0062] The polytetrafluoroethylene dispersion resin is heat-treated at a temperature of 300° C. to 600° C. to obtain a melt;

[0063] The melt and the additive are mixed and extruded at 40°C to 150°C to obtain a paste;

[0064] The paste is heat-shrunk, cooled, extruded, stretched and heat-set at a temperature of 600°C to 900°C to obtain a polytetrafluoroethylene film, wherein the cooling terminal temperature is 60°C to 100°C; the extrusion and stretching sequentially include longitudinal stretching and transverse stretching, and the ratio of the longitudinal stretching to the transverse stretching is (2 to 5):1.

[0065] According to the embodiments of the present application, by controlling the multiples of longitudinal stretching and transverse stretching, the average pore size of the polytetrafluoroethylene membrane can be further adjusted, which is beneficial to balancing the transverse tensile strength and longitudinal tensile strength of the polytetrafluoroethylene membrane, reducing the ratio of transverse tensile strength to longitudinal tensile strength, and increasing the service life of the membrane.

[0066] In some optional embodiments, the multiple of longitudinal stretching is 100 to 160 times, and the multiple of transverse stretching is 20 to 50 times. Thus, the average pore size can be further adjusted to balance the transverse tensile strength and longitudinal tensile strength of the polytetrafluoroethylene membrane.

[0067] Example

[0068] The following examples describe the disclosure of the present application in more detail, and these examples are for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present application are apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the examples are commercially available.

[0069] Example 1

[0070] Preparation of polytetrafluoroethylene film: heat-treating polytetrafluoroethylene dispersion resin with a weight average molecular weight of 760,000 at a temperature of 510° C. to obtain a melt;

[0071] The melt and extrusion aids liquid paraffin and dibutyl phthalate are mixed in a mass ratio of 99:0.2:0.8, and extruded at 125° C. to obtain a paste;

[0072] The paste is heat-shrunk, cooled, extruded, stretched and heat-set at a temperature of 820° C. to obtain a polytetrafluoroethylene film, wherein the cooling end temperature is 100° C.; the longitudinal stretching multiple is 140 times, and the transverse stretching multiple is 30 times.

[0073] Preparation of polytetrafluoroethylene composite microporous membrane for air purification: polytetrafluoroethylene membranes are arranged on both sides of a porous base membrane and subjected to hot pressing treatment to obtain the polytetrafluoroethylene composite microporous membrane, wherein the porous base membrane has an average thickness of 3 μm and a porosity of 55%, the porosity of the polytetrafluoroethylene membrane is 86%, the average thickness of the polytetrafluoroethylene membrane is 3.4 μm, and the average pore size is 310 nm; the hot pressing treatment temperature is 108°C, the line pressure is 0.75 MPa, and the hot pressing treatment speed is 0.9 m / min, so that the average thickness of the obtained polytetrafluoroethylene composite microporous membrane is 9.5 microns and the porosity is 74.6%.

[0074] Example 2

[0075] The difference between this embodiment and embodiment 1 is that the average pore size of the polytetrafluoroethylene membrane is 450 nm.

[0076] Example 3

[0077] The difference between this embodiment and embodiment 1 is that the average pore size of the polytetrafluoroethylene membrane is 380 nm.

[0078] Example 4

[0079] The difference between this embodiment and embodiment 1 is that the average thickness of the polytetrafluoroethylene film is 3 μm.

[0080] Example 5

[0081] The difference between this embodiment and embodiment 1 is that the average thickness of the polytetrafluoroethylene film is 4.5 μm.

[0082] Example 6

[0083] The difference between this embodiment and embodiment 1 is that the weight average molecular weight of polytetrafluoroethylene is 850,000.

[0084] Example 7

[0085] The difference between this embodiment and embodiment 1 is that the weight average molecular weight of polytetrafluoroethylene is 700,000.

[0086] Example 8

[0087] The difference between this embodiment and embodiment 1 is that the longitudinal stretching multiple is 90 times, the transverse stretching multiple is 45 times, the temperature of the hot pressing treatment is controlled at 107°C, the line pressure of the hot pressing treatment is 0.6MPa, and the speed of the hot pressing treatment is 0.8m / min.

[0088] Example 9

[0089] The difference between this embodiment and embodiment 1 is that the longitudinal stretching multiple is 160 times, the transverse stretching multiple is 32 times, the temperature of the hot pressing treatment is controlled at 107°C, the line pressure of the hot pressing treatment is 0.5MPa, and the speed of the hot pressing treatment is 0.8m / min.

[0090] Comparative Example 1

[0091] The difference between this comparative example and Example 1 is that two layers of polytetrafluoroethylene membranes are sequentially arranged on one side of the porous base membrane and subjected to heat pressing treatment.

[0092] Test Method

[0093] (1) Gas diffusion rate: 5 mL of toluene was added to a sample bottle, and the bottle mouth was sealed with a polytetrafluoroethylene composite microporous membrane prepared in the embodiment or the comparative example, and the sealing diameter was 8 mm. The sample bottle was placed in a constant temperature diffusion cell. High-purity nitrogen was passed into the diffusion cell at a temperature of 25° C. and a humidity of less than 80%. The nitrogen flow rate was 0.8 L / min. The diffusion rate of toluene gas through the polytetrafluoroethylene composite microporous membrane was tested for a certain period of time. The test time was 1 month and 3 months. The results are shown in Table 1.

[0094] The toluene diffusion rate is (test end sample bottle weight - test initial sample bottle weight) / test time

[0095] (3) Peel strength test: Use a film cutter to cut a 2.5 cm × 30 cm long sample along the longitudinal direction (MD) of the polytetrafluoroethylene composite microporous membrane, stick 3M (200MP) double-sided tape evenly on the peeling board, and stick the whole sample on the peeling board with the double-sided tape, with the coated surface on the double-sided tape. The hand cannot touch the sample area. And use the pressure roller (2kg) configured by the equipment to roll back and forth 2 times (roll 4 times alone). Finally, test it on a tensile test machine at a speed of 50 mm / min, and take the average value of three tests. The peel strength of comparative example 1 also measures the strength between the porous base membrane and the polytetrafluoroethylene microporous membrane.

[0096] (4) The test method for tensile strength shall refer to GB / T 1040.3-2006.

[0097] (5) Maximum thickness deviation: Take a sample of polytetrafluoroethylene composite microporous membrane, measure multiple thicknesses, sort the measured thicknesses by size, take the first 5 largest thickness values, and the last 5 smallest thickness values; subtract the sum of the 5 smallest thickness values ​​from the sum of the 5 largest thickness values, and divide by 5 to obtain the maximum thickness deviation value.

[0098] The air permeability values ​​of the polytetrafluoroethylene composite microporous membranes of Examples 1-9 and Comparative Example are shown in Table 1.

[0099] Table 1

[0100]

[0101] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A polytetrafluoroethylene composite microporous membrane for air purification, characterized in that: include: A porous base membrane including a fibrous material; A polytetrafluoroethylene membrane, wherein the polytetrafluoroethylene membrane is arranged on both sides of the porous base membrane, wherein the thickness ratio of the porous base membrane to the polytetrafluoroethylene membrane on either side is 1:(1-1.5), and the average pore size of the polytetrafluoroethylene membrane is 280nm to 450nm.

2. The polytetrafluoroethylene composite microporous membrane according to claim 1, characterized in that: The fiber material includes at least one of a polyester fiber material and a polyamide material.

3. The polytetrafluoroethylene composite microporous membrane according to claim 1, characterized in that: The polytetrafluoroethylene composite microporous membrane meets one or more of the following conditions: (1) The porosity of the porous base film is 40% to 60%; (2) The porosity of the polytetrafluoroethylene membrane is 80% to 90%; (3) The average thickness of the polytetrafluoroethylene film is 3 to 4.5 μm; (4) The average pore size of the polytetrafluoroethylene membrane is 300 nm to 400 nm; (5) The average thickness of the porous base film is 2 to 3 μm.

4. The polytetrafluoroethylene composite microporous membrane according to claim 1, characterized in that: In the polytetrafluoroethylene composite microporous membrane, the weight average molecular weight of polytetrafluoroethylene is 700,000-900,000.

5. The polytetrafluoroethylene composite microporous membrane according to claim 1, characterized in that: The polytetrafluoroethylene composite microporous membrane meets one or more of the following conditions: (1) The transverse tensile strength of the polytetrafluoroethylene composite microporous membrane is 130 MPa to 160 MPa; (2) The longitudinal tensile strength of the polytetrafluoroethylene composite microporous membrane is 100 MPa to 150 MPa; (3) The porosity of the polytetrafluoroethylene composite microporous membrane is 70% to 85%; (4) The ratio of the transverse tensile strength to the longitudinal tensile strength of the polytetrafluoroethylene composite microporous membrane is 1:(0.8 to 1).

6. A method for preparing a polytetrafluoroethylene composite microporous membrane according to any one of claims 1 to 5, characterized in that: include: Providing a porous base membrane and a polytetrafluoroethylene membrane, wherein the porous base membrane comprises a fiber material; The polytetrafluoroethylene membranes are arranged on both sides of the porous base membrane and subjected to heat pressing treatment to obtain the polytetrafluoroethylene composite microporous membrane.

7. The preparation method according to claim 6, characterized in that: The temperature of the hot pressing treatment is controlled at 90-110° C., the line pressure of the hot pressing treatment is 0.5-0.8 MPa, and the speed of the hot pressing treatment is 0.8-1.5 m / min.

8. The preparation method according to claim 6, characterized in that: The method for preparing the polytetrafluoroethylene film comprises: The polytetrafluoroethylene dispersion resin is heat-treated at a temperature of 300° C. to 600° C. to obtain a melt; The melt and the additive are mixed and extruded at 40°C to 150°C to obtain a paste; The paste is heat-shrunk, cooled, extruded, stretched and heat-set at a temperature of 600°C to 900°C to obtain a polytetrafluoroethylene film, wherein the cooling terminal temperature is 60°C to 100°C; the extrusion and stretching sequentially include longitudinal stretching and transverse stretching, and the ratio of the longitudinal stretching to the transverse stretching is (2 to 5):

1.

9. The preparation method according to claim 8, characterized in that: The multiple of the longitudinal stretching is 100 to 160 times, and the multiple of the transverse stretching is 20 to 50 times.

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