A method for preparing a crystallization-induced polyolefin microporous membrane

Abstract

A method for preparing a crystallization-induced polyolefin microporous membrane comprises the following steps: alkylation of a powder surface, grafting a polymer onto particles, preparing a prefabricated membrane, heat treatment, post-stretching, and heat setting. The present invention couples and modifies the powder surface to improve the compatibility between the powder and an organic matrix, generating uniform micropores and high porosity under stretching. The powder can serve as a toughening unit, imparting good toughness to the polyolefin. The material of the present invention can form a highly crystalline polymer with a regular surface-coupled grafting configuration. The powder particle size and distribution width are increased, thereby enhancing porosity. The molecular chains of the polyolefin membrane are easily incorporated into the crystal lattice, improving crystallinity. Under high-stress conditions during stretching, the polyolefin can form a lamellar structure, improving the mechanical properties of the microporous membrane. The preparation process of the present invention is environmentally friendly and easy to operate industrially.

Description

Technical Field

[0001] The invention relates to the field of microporous films, in particular to a method for preparing a crystallization-induced polyolefin microporous film. Background Art

[0002] Microporous membranes are thin plastic films with numerous interconnected micropores, with pore sizes ranging from approximately 0.1 to 10 μm. Polyolefin resins offer excellent mechanical properties, corrosion resistance, and electrical insulation, along with low density and low cost. Therefore, porous membranes made from polyolefin resins offer advantages such as lightweight, low cost, excellent mechanical properties, solvent resistance, and chemical stability. Industrialized products are widely used in medical protective clothing, sanitary products, battery separators, bipolar membrane substrates, food safety films, and composite paper.

[0003] Powdered reinforcing agents such as calcium carbonate and silica are readily available, low in toxicity, minimally polluting, and possess high whiteness. They are used as porogens to fill polyolefins to create specialized materials for breathable membranes. Under stretching, these powders separate the polymer matrix from the filler particle surface and develop interconnected micropores between the filler particles, forming a microporous breathable membrane. However, unmodified powders have poor compatibility with the organic polymer matrix, resulting in poor reinforcing and filling effects. The resulting porous membranes have low porosity and poor dimensional stability.

[0004] The most widely used method is thermally induced phase separation, which is relatively easy to prepare microporous membranes. However, the high cost of the solvents used, the toxicity of some, solvent contamination, and the expensive process have severely limited its application in polyolefin microporous membranes. (Patent No.: CN202010351529.3 for "A Method for Preparing a High-Flux Virus-Removing Polyvinylidene Fluoride Hollow Fiber Microporous Membrane.") Patent No.: CN202010539621.2 for "A Method and System for Preparing a Waterproof Breathable Membrane for Protective Clothing." This method utilizes a melt-stretching method, using calcium carbonate as a pore-enhancing agent. The membrane is then extruded and then directionally stretched to a specific ratio. The pore size and moisture permeability of polyolefin breathable membranes are closely related to the properties of the calcium carbonate pore-enhancing agent. The membrane requires calcium carbonate to achieve relatively high moisture permeability. However, the addition of large amounts of inorganic fillers results in poor mechanical properties of polyolefins, limiting their application as mid- to high-end protective materials. Summary of the Invention

[0005] The object of the present invention is to overcome the above-mentioned shortcomings and provide a method for preparing a crystallization-induced polyolefin microporous membrane with higher pore density, stronger tensile strength and dimensional stability.

[0006] To achieve the above object, the technical solution of the present invention is: a method for preparing a crystallization-induced polyolefin microporous membrane, comprising the following steps:

[0007] Alkylation of the powder surface: adding a coupling agent dropwise into a powder ethanol solution to alkylate the powder surface; the powder ethanol solution is an anhydrous ethanol solution of the powder containing a certain solid content; and drying the powder ethanol solution to obtain an alkylated powder;

[0008] Grafting polymer particles: alkylated powder is mixed with polymer, extruded, and granulated to obtain grafted modified powder particles;

[0009] To prepare a prefabricated film, the modified powder, polyolefin, antioxidant, antistatic agent, and plasticizer are melt-blended and then extruded through a die. The melt is stretched under the dual action of temperature field and stress field to form a prefabricated film with an orderly arranged crystal structure.

[0010] Heat treatment, annealing the prefabricated membrane;

[0011] Post-stretching, through the combination of cold stretching and hot stretching processes, a microporous membrane with large porosity and high pore density is obtained;

[0012] Heat setting: After the microporous membrane is subjected to heat setting treatment after post-stretching, a finished product is obtained.

[0013] This invention utilizes coupling modification on the powder surface to improve its compatibility with the organic matrix (polyolefin). The powder typically uses nanometer-sized particles. Due to surface effects, small size effects, and macroscopic quantum tunneling effects, nanometer-sized powders can act as toughening units, imparting excellent toughness to the polyolefin. Furthermore, coupling modification of the powder surface enhances its compatibility with the matrix, preventing the formation of bumps or even film breakage during film formation. Under tension, uniform micropores and high porosity are generated.

[0014] Nanosized powder particles are less likely to cause cavitation damage, and even if silver streaks are induced, the particles are far apart, preventing effective crystallization and the efficient stretching-induced pore formation. The present invention graft-modifies the coupled-modified powder to form a highly crystalline polymer with a well-regarded surface coupled grafting configuration. This can achieve the following effects:

[0015] 1. Increasing the powder particle size and distribution width is beneficial to increasing the porosity of the breathable membrane.

[0016] Second, due to the lubricating effect of the coupling agent, the molecular chains of the polyolefin film are easily introduced into the crystal lattice. During the heating process, they tend to absorb heat and disentangle at a lower temperature. The width of the polyolefin absorption peak becomes wider, and the crystallinity is improved.

[0017] 3. Polyolefins can form lamellar structures under high stress fields during stretching. Highly crystalline polymers act like macroscopic fibers in the polyolefin matrix. When heat-set under stretching, they tend to form lamellar structures that are perpendicular to the extrusion direction and arranged in parallel. In addition, highly crystalline polymers act like macroscopic fibers in the resin matrix, branching cracks, terminating cracks, and enhancing toughness, thereby improving the mechanical properties of the microporous membrane.

[0018] Preferably, the powder is one or more of calcium carbonate, silicon dioxide, kaolin, and montmorillonite; the particle size of the powder is 10 to 500 nm. The inorganic calcium carbonate phase can serve as a toughening unit, imparting good toughness to the polyolefin.

[0019] Preferably, the coupling agent is one or more of silane coupling agent KH550, coupling agent 201, titanate GR-101, titanate GR-300, and aluminate GR-AL18; and the polymer is one or more of linear polyethylene, isotactic polypropylene, polyethylene terephthalate, polyurethane, polyvinylidene chloride, polytetrafluoroethylene, poly-1-butene, and poly-4-methyl-1-pentene. Silane coupling agent KH550, coupling agent 201, titanate GR-101, titanate GR-300, and aluminate GR-AL18 have excellent lubrication effects.

[0020] Preferably, the antioxidant is one or more of antioxidant 1010, antioxidant 1076, antioxidant 168, antioxidant TNP, and antioxidant CA; the antistatic agent is one or more of dithiocarbamate, phosphate, quaternary ammonium salt, and alkyl amino acid salt; and the plasticizer is one or more of dioctyl sebacate, dioctyl oxalate, dibutyl phthalate, and dioctyl phthalate.

[0021] Preferably, the solid content of the powder in the powder ethanol solution is 5-50%; the mass of the coupling agent is 1-8% of the mass of the powder; the reaction temperature of the coupling agent and the powder ethanol solution is 50-150°C, and the reaction time is 0.5-2h; the powder ethanol solution is dried at 50-150°C.

[0022] Preferably, the alkylated powder and the polymer are mixed and then extruded, and the extrusion molding temperature is 120-250°C.

[0023] Preferably, in the step of preparing the pre-film, the modified powder, polyolefin, antioxidant, antistatic agent and plasticizer are first dispersed and mixed in a high-speed mixer to form a blended pellet; the blended pellet is melted at high temperature by an extruder to form a flowing melt, and the flowing melt temperature is 150-250°C; the flowing melt is attached to a casting roller to form a melt film, and the melt film is cooled by winding around a cooling roller, the rotation speed of the casting roller is 10-70r / min, the temperature of the cooling roller is 50-150°C, and the melt film is stretched into a film-shaped pre-film with a draw ratio of 10-250.

[0024] Preferably, the annealing treatment is performed at a temperature of 100° C. to 250° C. and for a time of 0.5 to 3 hours.

[0025] Preferably, the stretching ratio of the cold stretching is 1.1 to 2; the stretching temperature of the hot stretching is 80 to 250° C., and the stretching ratio is 1.1 to 3.5.

[0026] Preferably, the temperature of the heat setting treatment is 100-200° C., and the time is 5-20 minutes.

[0027] By adopting the above technical solution, the beneficial effects of the present invention are as follows: the present invention couples and modifies the surface of the powder, thereby improving the compatibility with the matrix, avoiding the generation of lumps or even film breakage during film formation, and generating uniform micropores and high porosity under stretching.

[0028] The present invention graft-modifies the coupled-modified powder to form a highly crystalline polymer with a regular surface coupled-graft configuration. This increases the powder particle size and distribution width, enhancing the porosity of the breathable membrane and improving the crystallinity of the polyolefin. When heat-set under tension, the highly crystalline polymer tends to form a lamellar structure with parallel alignment perpendicular to the extrusion direction. The highly crystalline polymer acts like a macroscopic fiber in the resin matrix, branching and terminating cracks, strengthening and toughening the membrane, and improving the mechanical properties of the microporous membrane.

[0029] The preparation process of the present invention is environmentally friendly and easy to operate industrially. It does not involve toxic or hazardous organic solvents, uses a wide range of raw materials, and is easy to operate, including porogen modification, hot and cold stretching, and heat treatment. The process is particularly suitable for industrial production and has good operability and applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The pore size distribution of the microporous membranes of Example 3 and Comparative Example 8 of the present invention;

[0031] Figure 2 The porosity of the microporous membranes of Example 3 of the present invention and Comparative Examples 2-4 and Comparative Example 7;

[0032] Figure 3is the tensile strength of the microporous membranes of Example 3 of the present invention and Comparative Examples 1-5 and Comparative Example 9;

[0033] Figure 4 The scanning electron microscope images of the microporous membranes of Example 3, Comparative Example 6, and Comparative Example 10 of the present invention are shown;

[0034] Figure 5 The air permeability values ​​of the microporous membranes of Example 3 of the present invention and Comparative Examples 1-10;

[0035] Figure 6 These are the comprehensive performance data of the microporous membranes of Examples 1-4 and Comparative Examples 1-10 of the present invention. DETAILED DESCRIPTION

[0036] The present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0037] Example 1:

[0038] like Figure 1 As shown, the present invention

[0039] A method for preparing a crystallization-induced polyolefin microporous membrane comprises the following steps:

[0040] S1. Surface alkylation of the powder: Prepare a 20% solids nano-calcium carbonate (particle size 20 nm) anhydrous ethanol solution to form a powder-ethanol solution. Add 4% (based on the weight of the powder) of silane coupling agent KH550 dropwise to the powder-ethanol solution. Control the reaction temperature to 100°C and allow the reaction to proceed for 1 hour. After the reaction, the powder-ethanol solution is dried at 80°C to obtain an alkylated powder containing alkylated nano-calcium carbonate.

[0041] S2. Granular grafted polymer: An alkylated powder of alkylated nano-calcium carbonate and a polymer of nylon 6 are melt-extruded and granulated at a mass ratio of 1:5 to obtain nano-calcium carbonate grafted modified nylon 6. The extrusion molding temperature is 170-230°C.

[0042] S3. Prepare a prefabricated film. Take 100 parts of polypropylene, 70 parts of nano-calcium carbonate grafted modified nylon 6, 1 part of antioxidant 1010, 1.2 parts of dithiocarbamate, and 10 parts of dibutyl phthalate respectively by mass, mix them, and stir them in a high-speed stirrer at 80r / min for 30 minutes. Use an extruder to melt the blended pellets at a high temperature of 180-210°C, and extrude the melt through a die at 210°C; the flowing melt quickly sticks to the casting roller, the roller speed of the casting roller is 30r / min, the temperature of the cooling roller is 80°C, the flowing melt forms a melt film, and the melt film is stretched, and the draw ratio is controlled to be 80 to obtain a prefabricated film.

[0043] S4. Heat treatment: annealing the prefabricated membrane at a temperature of 140° C. for 1.5 h.

[0044] S5. Post-stretching: cold stretching the annealed pre-film at a stretching ratio of 1.4; hot stretching the cold-stretched pre-film at a temperature of 120° C. at a stretching ratio of 1.6 to obtain a microporous membrane with large porosity and high pore density.

[0045] S6. Heat setting: heat setting the microporous membrane at a temperature of 140° C. for 10 minutes to obtain a finished product.

[0046] Example 2:

[0047] A method for preparing a crystallization-induced polyolefin microporous membrane comprises the following steps:

[0048] S1. Surface alkylation of the powder: Prepare a 20% solids nano-calcium carbonate (50 nm particle size) solution in anhydrous ethanol to form an ethanol solution of the powder. Add 5% of the powder's mass to the ethanol solution with GR-101 titanate dropwise. Control the reaction temperature at 100°C and allow the reaction to proceed for 1 hour. After the reaction, dry the ethanol solution at 80°C to obtain an alkylated powder containing alkylated nano-calcium carbonate.

[0049] S2. Particle grafted polymer: The alkylated powder of alkylated nano-calcium carbonate and the polymer of isotactic polypropylene are melt-extruded and granulated in a mass ratio of 1:5 to obtain nano-calcium carbonate grafted modified polypropylene. The extrusion molding temperature is 180-220°C.

[0050] S3. Prepare a prefabricated film. Take 100 parts of polyethylene, 70 parts of nano-calcium carbonate grafted modified polypropylene, 1 part of antioxidant 168, 1.2 parts of dithiocarbamate, and 10 parts of dibutyl phthalate respectively by mass, mix them, and stir them in a high-speed stirrer at 80r / min for 30 minutes. Use an extruder to melt the blended pellets at a high temperature of 180-210°C, and extrude the melt through a die at 210°C; the flowing melt quickly sticks to the casting roller, the roller speed of the casting roller is 30r / min, the temperature of the cooling roller is 80°C, the flowing melt forms a melt film, and the melt film is stretched, and the draw ratio is controlled to be 100 to obtain a prefabricated film.

[0051] S4. Heat treatment: annealing the prefabricated membrane at a temperature of 140° C. for 1.5 h.

[0052] S5. Post-stretching: cold stretching the annealed pre-film at a stretching ratio of 1.4; hot stretching the cold-stretched pre-film at a temperature of 120° C. at a stretching ratio of 2 to obtain a microporous membrane with large porosity and high pore density.

[0053] S6. Heat setting: heat setting the microporous membrane at a temperature of 140° C. for 10 minutes to obtain a finished product.

[0054] Example 3:

[0055] A method for preparing a crystallization-induced polyolefin microporous membrane comprises the following steps:

[0056] Step 1, powder grafting modification: ① Alkylation of the powder surface, preparation of an anhydrous ethanol solution of nano-calcium carbonate (50nm) containing 20% ​​solid content, control of the system reaction temperature at 100°C, dropwise addition of 5% titanate GR-101 by weight of the powder, reaction for 1 hour, and drying at 80°C to obtain alkylated nano-calcium carbonate; ② Particle grafting polymer: melt-extrude and granulate alkylated nano-calcium carbonate and nylon 6 (mass ratio of 1:5) to obtain nano-calcium carbonate grafted modified nylon 6, and the extrusion molding temperature is 190-240°C.

[0057] Step 2, preparation of prefabricated membrane: take 100 parts by mass of polypropylene, 60 parts by mass of nano-calcium carbonate grafted modified nylon 6, 1 part by mass of antioxidant 168, 1 part by mass of alkyl amino acid salt, and 10 parts by mass of dibutyl phthalate, respectively, and stir in a high-speed stirrer at 80r / min for 30min, use an extruder to high-temperature melt the blended pellets at 180-220°C, and extrude through a die at 210°C; the flowing melt is quickly applied to the roller, the temperature of the casting cooling roller is 80°C, the speed of the casting roller is 30r / min, and the draft ratio is controlled to be 100 to obtain a prefabricated membrane.

[0058] Step 3: Heat treatment process: the prefabricated film annealing temperature is 140° C., and the annealing time is 1.5 h.

[0059] Step 4, post-stretching process: cold stretching ratio is 1.4; hot stretching ratio is 1.8, temperature is 120°C.

[0060] Step 5: Heat setting process: the heat setting temperature is 140°C and the heat setting time is 10 minutes.

[0061] Example 4

[0062] A method for preparing a crystallization-induced polyolefin microporous membrane comprises the following steps:

[0063] Step 1, powder grafting modification: ① Alkylation of the powder surface, preparation of nano-silica (50nm) anhydrous ethanol solution containing 20% ​​solid content, control the system reaction temperature to 100°C, add 5% titanate GR-300 by weight of the powder, react for 1 hour, and then dry at 80°C to obtain alkylated nano-silica; ② Particle grafting polymer: Alkylated nano-silica and polyethylene terephthalate (mass ratio of 1:5) are melt-extruded and granulated to obtain nano-silica grafted modified polyester, and the extrusion molding temperature is 190-240°C.

[0064] Step 2, preparation of prefabricated film: take 100 parts by mass of polypropylene, 60 parts by mass of nano-silica grafted modified polyester, 1 part by mass of antioxidant 168, 1 part by mass of alkyl amino acid salt, and 10 parts by mass of dibutyl phthalate, respectively, and stir in a high-speed stirrer at 80r / min for 30min, use an extruder to high-temperature melt the blended pellets at 180-230°C, and extrude through a die at 220°C; the flowing melt is quickly applied to the roller, the temperature of the casting cooling roller is 80°C, the speed of the casting roller is 30r / min, and the draft ratio is controlled to be 130 to obtain a prefabricated film.

[0065] Step 3: Heat treatment process: the prefabricated film annealing temperature is 140° C., and the annealing time is 1.5 h.

[0066] Step 4, post-stretching process: cold stretching ratio is 1.3; hot stretching ratio is 2, temperature is 120°C.

[0067] Step 5: Heat setting process: the heat setting temperature is 140°C and the heat setting time is 10 minutes.

[0068] The present invention provides comparative examples for comparison with the embodiments.

[0069] Comparative Example 1

[0070] The polyolefin melt-stretched breathable membrane is substantially the same as that in Example 3, except that no silane coupling agent is added in step 1, and the other steps remain unchanged.

[0071] Comparative Example 2

[0072] The polyolefin melt-stretched breathable membrane is substantially the same as that in Example 3, except that alkylated nano-calcium carbonate is prepared in step 1 and nylon 6 is no longer grafted.

[0073] Comparative Example 3

[0074] The polyolefin melt-stretched breathable membrane is substantially the same as that in Example 3, except that: in step 1, alkylated nano-calcium carbonate is prepared and grafted with acrylonitrile-butadiene-styrene copolymer (mass ratio is 1:5).

[0075] Comparative Example 4

[0076] The polyolefin melt-stretched breathable membrane is substantially the same as that of Example 3, except that 60 parts by mass of nano-calcium carbonate graft-modified nylon 6 is replaced with 60 parts by mass of nano-calcium carbonate (unmodified).

[0077] Comparative Example 5

[0078] The polyolefin melt-stretched breathable film is substantially the same as that in Example 3, except that the draw ratio in step 2 is controlled to be 200, and the other steps remain unchanged.

[0079] Comparative Example 6

[0080] The polyolefin melt-stretched breathable film is substantially the same as that in Example 3, except that no heat treatment is performed.

[0081] Comparative Example 7

[0082] The polyolefin melt-stretched breathable film is substantially the same as that in Example 3, except that the post-stretching process in step 4 is not performed.

[0083] Comparative Example 8

[0084] The polyolefin melt-stretched breathable film is substantially the same as that in Example 3, except that no cold stretching is performed.

[0085] Comparative Example 9

[0086] The polyolefin melt-stretched breathable film is substantially the same as that in Example 3, except that no heat setting process is performed.

[0087] Comparative Example 10

[0088] The polyolefin melt-stretched breathable membrane is substantially the same as that in Example 3, except that no powder grafting modification is performed and calcium carbonate with a particle size of 20 μm is directly used.

[0089] from Figure 6 It can be seen from the graph that the porosity and tensile strength of the microporous membranes of Examples 1-4 are both higher than those of the microporous membranes of Comparative Examples 1-10.

[0090] from Figure 1 It can be seen that when Example 3 adopts a cold stretching ratio of 1.4, the degree of separation of the lamellae is greater, thereby producing more and larger pores. Compared with the comparative example 8, the pore size distribution of the microporous membrane is more concentrated. At this time, the pore structure stability and regularity of the microporous membrane are better.

[0091] from Figure 2 and Figure 5It can be seen that compared with Example 3, the alkylated nano-calcium carbonate in Comparative Example 2 is not grafted with an easily crystallized polymer, and the porosity and air permeability of the prepared microporous membrane are lower than those of Example 3; in Comparative Example 3, the alkylated nano-calcium carbonate is grafted with a non-crystallized acrylonitrile-butadiene-styrene copolymer, and the modified nano-calcium carbonate grafted with acrylonitrile-butadiene-styrene copolymer cannot form an effective crystallization system. Affected by the crystal size, the prefabricated membrane is separated under the action of stretching to produce an effective porosity reduction; in Comparative Example 4, the unmodified nano-calcium carbonate is an inorganic material, and its high specific surface area makes it poorly compatible with the matrix, and it is easy to form a team, resulting in the particles being unable to be evenly dispersed in the system, and the porosity is reduced. Comparative Example 7 lacks a post-stretching process. The post-stretching step is an important measure to form and expand the pore structure. Cold drawing induces the separation of the lamellae to form the initial pore structure and a small amount of bridging structure, and hot drawing expands the pore structure and forms a large number of pore structures.

[0092] Figure 3 Compared with Example 3, Comparative Example 1 lacks the modifying effect of the silane coupling agent, and the nano-calcium carbonate agglomerates in the system, resulting in a decrease in its mechanical properties. In Comparative Example 5, the draw ratio is reduced to 20, and the tensile properties of the resulting microporous membrane decrease. Because the increase in the draw ratio increases the number of oriented lamellae formed and the orderliness of the crystalline region increases, when the draw ratio is low, the external force is small and insufficient to maintain the ordered orientation state, resulting in a lower orientation of the amorphous region. Comparative Example 6 does not undergo heat treatment, and the tensile properties of the microporous membrane decrease. The crystal structure of the polymer partially melts at high temperatures, the molecular chains rearrange, and in addition to the initial crystal structure, new crystals are recrystallized to form, thereby improving the crystal structure.

[0093] Figure 4 In Example 3, compared to Comparative Example 6, an additional annealing process was added. The annealed prefabricated membrane had increased sheet thickness, improved sheet structure, and uniform bridge and pore sizes in the resulting microporous membrane. Comparative Example 10, which directly replaced nano-modified calcium carbonate with large-particle calcium carbonate, showed significant fractures in the microporous membrane bridges. The unmodified surface powder easily agglomerated within the matrix, resulting in uneven pore size during melt stretching. The grafted polymer toughened and reinforced the melt, making it less susceptible to breakage during stretching.

[0094] The above embodiments do not limit the product form and style of the present invention. Any appropriate changes or modifications made by ordinary technicians in the relevant technical field should be deemed to be within the patent scope of the present invention.

Claims

1. A method for preparing a crystallization-induced polyolefin microporous membrane, characterized in that: The following steps are involved: Alkylation of the powder surface: adding a coupling agent dropwise into a powder ethanol solution to alkylate the powder surface; the powder ethanol solution is an anhydrous ethanol solution of the powder containing a certain solid content; and drying the powder ethanol solution to obtain an alkylated powder; The powder is one or more of calcium carbonate, silicon dioxide, kaolin, and montmorillonite; the particle size of the powder is 10 to 500 nm; The solid content of the powder in the powder ethanol solution is 5-50%; the mass of the coupling agent is 1-8% of the mass of the powder; the reaction temperature of the coupling agent and the powder ethanol solution is 50-150° C., and the reaction time is 0.5-2 hours; The powder ethanol solution is dried at 50-150°C; Grafting polymer particles: alkylated powder is mixed with polymer, extruded, and granulated to obtain grafted modified powder particles; To prepare a prefabricated film, the modified powder, polyolefin, antioxidant, antistatic agent, and plasticizer are melt-blended and then extruded through a die. The melt is stretched under the dual action of temperature field and stress field to form a prefabricated film with an orderly arranged crystal structure. Heat treatment, annealing the prefabricated membrane; Post-stretching, through the combination of cold stretching and hot stretching processes, a microporous membrane with large porosity and high pore density is obtained; Heat setting: After the microporous membrane is subjected to heat setting treatment after post-stretching, a finished product is obtained.

2. The method for preparing a crystallization-induced polyolefin microporous membrane according to claim 1, wherein: The coupling agent is one or more of silane coupling agent KH550, coupling agent 201, titanate GR-101, titanate GR-300, and aluminate GR-AL18; the polymer is one or more of linear polyethylene, isotactic polypropylene, polyethylene terephthalate, polyurethane, polyvinylidene chloride, polytetrafluoroethylene, poly-1-butene, and poly-4-methyl-1-pentene.

3. The method for preparing a crystallization-induced polyolefin microporous membrane according to claim 1, wherein: The antioxidant is one or more of antioxidant 1010, antioxidant 1076, antioxidant 168, antioxidant TNP, and antioxidant CA; the antistatic agent is one or more of dithiocarbamate, phosphate, quaternary ammonium salt, and alkyl amino acid salt; and the plasticizer is one or more of dioctyl sebacate, dioctyl oxalate, dibutyl phthalate, and dioctyl phthalate.

4. The method for preparing a crystallization-induced polyolefin microporous membrane according to claim 1, wherein: The alkylated powder and the polymer are mixed and then extruded at an extrusion molding temperature of 120 to 250°C.

5. The method for preparing a crystallization-induced polyolefin microporous membrane according to claim 1, wherein: In the step of preparing the prefabricated film, the modified powder, polyolefin, antioxidant, antistatic agent and plasticizer are first dispersed and mixed in a high-speed mixer to form a blended pellet; the blended pellet is melted at high temperature in an extruder to form a flowing melt, and the flowing melt temperature is 150-250°C; the flowing melt is attached to a casting roller to form a melt film, and the melt film is cooled by winding on a cooling roller, the casting roller rotates at a speed of 10-70 r / min, and the cooling roller temperature is 50-150°C, and the melt film is stretched into a film-shaped prefabricated film, and the draw ratio is 10-250.

6. The method for preparing a crystallization-induced polyolefin microporous membrane according to claim 1, wherein: The annealing treatment is performed at a temperature of 100° C. to 250° C. and for a time of 0.5 to 3 hours.

7. The method for preparing a crystallization-induced polyolefin microporous membrane according to claim 1, characterized in that: The cold stretching ratio is 1.1 to 2; the stretching temperature of the hot stretching is 80 to 250° C., and the hot stretching ratio is 1.1 to 3.

5.

8. The method for preparing a crystallization-induced polyolefin microporous membrane according to claim 1, characterized in that: The temperature of the heat setting treatment is 100-200° C., and the time is 5-20 minutes.

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