Membrane base membrane and preparation method thereof

Abstract

The invention provides a diaphragm base membrane and a preparation method thereof, and belongs to the technical field of batteries. The preparation method of the diaphragm base membrane comprises the steps that raw materials are sequentially extruded and stretched, the raw materials comprise a dry material and a pore forming agent, the dry material comprises ultra-high molecular weight polyethylene and a toughening agent, the mass ratio of the toughening agent in the dry material is 1-8 wt%, the toughening agent is a graft copolymer, the main chain of the graft copolymer is polypropylene, and the graft is polyethylene. According to the preparation method of the diaphragm base membrane, the flexibilizer and the ultra-high molecular weight polyethylene are used as dry materials, the graft copolymer used as the flexibilizer can reinforce the ultra-high molecular weight polyethylene, and the needling strength of the diaphragm base membrane can be improved on the premise that other properties of the prepared diaphragm base membrane are not affected basically.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery, in particular to a separator base film and a preparation method thereof. BACKGROUND

[0002] With the development of the times, new energy electric vehicles have gradually become a part of people's life, and the safety and endurance of lithium ion batteries as the power source of electric vehicles are the focus of scientific research. The separator base film of lithium battery plays an important role in lithium ion battery.

[0003] The endurance of electric vehicles has become the focus of more attention. To extend the endurance of electric vehicles, on the one hand, the capacity of lithium battery should be improved, and on the other hand, the safety problem of lithium battery pole spur puncturing the separator base film to cause short circuit during the running of electric vehicles should be solved. The problem of pole spur puncturing the separator base film can be solved by improving the puncture strength of the separator base film and reducing the thickness of the separator base film. The conventional lithium battery separator base film is polypropylene or polyethylene, which has general puncture strength performance and cannot meet the above requirements. SUMMARY

[0004] The present application provides a separator base film and a preparation method thereof, which can improve the puncture strength of the separator base film.

[0005] The embodiments of the present application are implemented as follows: In a first aspect, the present application provides a preparation method of a separator base film, comprising: extruding and stretching raw materials in sequence, the raw materials comprising dry materials and pore-forming agents, the dry materials comprising ultra-high molecular weight polyethylene and toughening agents, and the mass fraction of the toughening agents in the dry materials being 1wt%-8wt%, the toughening agents being graft copolymers, the main chain of the graft copolymers being polypropylene, and the grafting substances being polyethylene.

[0006] In the above technical solution, the preparation method of the separator base film of the present application uses the graft copolymers as the toughening agents and the ultra-high molecular weight polyethylene as the dry materials, which can strengthen the ultra-high molecular weight polyethylene, and is conducive to improving the puncture strength of the separator base film without affecting other properties of the prepared separator base film.

[0007] In some possible embodiments, the main chain of the graft copolymers is homopolymer polypropylene.

[0008] In the above technical solution, by making the main chain of the graft copolymers be homopolymer polypropylene, the puncture strength of the prepared separator base film can be further improved.

[0009] In some possible embodiments, the mass fraction of the toughening agents in the dry materials is 3wt%-5wt%.

[0010] In the technical solution, the mass percentage of the toughening agent in the dry material is in the range, which is beneficial to further improve the needle puncture strength of the prepared diaphragm base film.

[0011] In some possible embodiments, the viscosity average molecular weight of the ultra-high molecular weight polyethylene is 1.5 million to 2.5 million.

[0012] In the technical solution, the ultra-high molecular weight polyethylene with a viscosity average molecular weight of 1.5 million to 2.5 million can be well matched with the graft copolymer, and the ultra-high molecular weight polyethylene with a viscosity average molecular weight of 1.5 million to 2.5 million not only has high strength, but also can be uniformly processed and plasticized, thereby further improving the needle puncture strength of the prepared diaphragm base film.

[0013] In some possible embodiments, the melt temperature is 225℃ to 235℃ when the raw material is extruded.

[0014] In the technical solution, the melt temperature during extrusion is in the range, which is beneficial to the uniform mixing of the raw material including the ultra-high molecular weight polyethylene and the toughening agent during extrusion, avoids or improves the layered condition, and improves the uniformity of the prepared diaphragm base film.

[0015] In some possible embodiments, the extrusion temperature is 195℃ to 205℃ when the raw material is extruded.

[0016] In some possible embodiments, the extrusion speed is 70r / min to 200r / min when the raw material is extruded.

[0017] In the technical solution, the extrusion speed during extrusion is in the range, which is beneficial to the uniform plasticization of the raw material including the ultra-high molecular weight polyethylene and the toughening agent during extrusion, avoids or improves the layered condition, and improves the uniformity of the prepared diaphragm base film.

[0018] In some possible embodiments, the feeding amount of the raw material is 250kg / h to 500kg / h.

[0019] In the second aspect, the diaphragm base film is prepared according to the preparation method of the diaphragm base film in the above embodiments.

[0020] In the technical solution, the diaphragm base film has high needle puncture strength and low MD and TD heat shrinkage.

[0021] In some possible embodiments, the thickness of the diaphragm base film is ≤5.5μm, and the needle puncture strength of the diaphragm base film is ≥400gf. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0023] Figure 1 Flow chart of the preparation method of the separator base film of the present application; Figure 2 Structural diagram of the toughening agent of the present application. DETAILED DESCRIPTION

[0024] The embodiments of the present application will be described in detail below with reference to the embodiments, but those skilled in the art will understand that the following embodiments are only for illustration of the present application and should not be regarded as limiting the scope of the present application. The specific conditions are not specified in the embodiments, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be obtained by market purchase.

[0025] The following will specifically describe a separator base film and a preparation method thereof according to an embodiment of the present application: Please refer to Figure 1 The present application provides a preparation method of a separator base film, which comprises the following steps: S1, preparing raw materials The raw materials include dry materials and pore-forming agents, wherein the dry materials include ultra-high molecular weight polyethylene and a toughening agent.

[0026] The viscosity average molecular weight of the ultra-high molecular weight polyethylene is 1.5 million to 2.5 million.

[0027] For example, the viscosity average molecular weight of the ultra-high molecular weight polyethylene can be 1.5 million, 1.6 million, 1.7 million, 1.8 million, 1.9 million, 2.0 million, 2.1 million, 2.2 million, 2.3 million, 2.4 million or 2.5 million.

[0028] Optionally, the viscosity average molecular weight of the ultra-high molecular weight polyethylene is 1.8 million to 2.0 million.

[0029] The ultra-high molecular weight polyethylene with a viscosity average molecular weight of 1.5 million to 2.5 million can better match the graft copolymer, and the ultra-high molecular weight polyethylene with a viscosity average molecular weight of 1.5 million to 2.5 million not only has high strength, but also can be uniformly processed and plasticized, thereby further improving the needle puncture strength of the prepared separator base film.

[0030] Please refer to Figure 2 The toughening agent is a graft copolymer, the main chain of the graft copolymer is polypropylene, and the graft is polyethylene.

[0031] Optionally, the main chain of the graft copolymer is homopolymer polypropylene, and the homopolymer polypropylene includes isotactic polypropylene, syndiotactic polypropylene and random polypropylene.

[0032] wherein the methyl groups (-CH3) of the isotactic polypropylene are arranged alternately on the same side of the main chain of the molecule, and when the main chain of the graft copolymer is isotactic polypropylene, the graft copolymer includes the following structure: .

[0033] when the main chain of the graft copolymer is syndiotactic polypropylene, the graft copolymer includes the following structure: .

[0034] when the main chain of the graft copolymer is random polypropylene, the graft copolymer includes the following structure: .

[0035] By making the main chain of the graft copolymer be homopolymer polypropylene, it is beneficial to further improve the needle puncture strength of the prepared diaphragm base film.

[0036] The mass percentage of the toughening agent in the dry material is 1wt%-8wt%.

[0037] For example, the mass percentage of the toughening agent in the dry material can be 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt% or 8wt%.

[0038] Optionally, the mass percentage of the toughening agent in the dry material is 3wt%-5wt%.

[0039] By making the mass percentage of the toughening agent in the dry material be in the above range, it is beneficial to further improve the needle puncture strength of the prepared diaphragm base film.

[0040] The pore-forming agent includes white oil.

[0041] S2, extrusion The raw materials are put into the double screw extruder, the feeding amount of the raw materials is set to 250kg / h-500kg / h, the extrusion speed is 70r / min-200r / min, the melt temperature in the double screw extruder is 225℃-235℃, and the extrusion temperature of the double screw extruder is 195℃-205℃, to obtain a cast film piece.

[0042] As an example, the feedstock can be fed at a rate of 250 kg / h, 280 kg / h, 300 kg / h, 320 kg / h, 350 kg / h, 380 kg / h, 400 kg / h, 420 kg / h, 450 kg / h, 480 kg / h, or 500 kg / h; and the extruder can be rotated at a speed of 70 r / min, 80 r / min, 100 r / min, 120 r / min, 150 r / min, 180 r / min, or 200 r / min.

[0043] The present application is advantageous in that the feedstock including the ultra-high molecular weight polyethylene and the toughening agent is uniformly plasticized during the extrusion, and the occurrence of delamination is avoided or improved, thereby improving the uniformity of the prepared separator base film.

[0044] As an example, the melt temperature in the twin-screw extruder can be 225℃, 226℃, 227℃, 228℃, 229℃, 230℃, 231℃, 232℃, 233℃, 234℃, or 235℃.

[0045] The present application is advantageous in that the feedstock including the ultra-high molecular weight polyethylene and the toughening agent is uniformly mixed during the extrusion, and the occurrence of delamination is avoided or improved, thereby improving the uniformity of the prepared separator base film.

[0046] As an example, the extrusion temperature of the twin-screw extruder can be 195℃, 200℃, or 205℃.

[0047] S3, stretching and setting The prepared cast film is sequentially subjected to longitudinal stretching, first transverse stretching, extraction, and second transverse stretching.

[0048] The longitudinal stretching is performed at a ratio of 9 times to 12 times, and is preceded by preheating at a temperature lower than the temperature of the longitudinal stretching.

[0049] Optionally, the preheating temperature of the longitudinal stretching is 80℃ to 90℃, and the stretching temperature is 90℃ to 100℃.

[0050] It should be noted that, in order to obtain a higher crystal orientation, the stretching should be performed at the lowest stretching temperature that can be stretched.

[0051] The first transverse stretching is performed at a ratio of 7 times to 16 times, and is preceded by preheating at a temperature higher than the temperature of the first transverse stretching.

[0052] Optionally, the preheating temperature of the first transverse stretching is 105℃ to 125℃, and the temperature of the first transverse stretching is 95℃ to 120℃.

[0053] Optionally, the cast film is longitudinally stretched to obtain a first film, the first film is in motion along the longitudinal direction, and the first transverse stretching rate is 0.7 times to 1.4 times / m, that is, when the first film moves 1 m along the longitudinal direction, the first film is transversely stretched by 0.7 times to 1.4 times.

[0054] Before the first transverse stretching, when the diaphragm has a transverse length of 400 mm and the diaphragm base film moves at a rate of 40 m / min to 60 m / min along the longitudinal direction, the first transverse stretching rate is 186 mm / s to 568 mm / s.

[0055] Optionally, the first transverse stretching further includes shrinkage, the first film is transversely stretched to obtain a second film, and the second film is shrunk, the shrinkage rate is 5% to 8%, and the shrinkage distance is 3 m to 6 m.

[0056] The extraction includes washing away the pore-forming agent in the diaphragm base film by using an extraction agent.

[0057] The second transverse stretching rate is 1.2 times to 1.8 times.

[0058] The heat setting temperature is 120°C to 135°C, and the heat setting time is 20 s to 30 s.

[0059] The preparation method of the diaphragm base film provided in the application uses dry materials including a toughening agent and ultra-high molecular weight polyethylene, and the graft copolymer as the toughening agent can strengthen the ultra-high molecular weight polyethylene, which is conducive to improving the needle puncture strength of the diaphragm base film without affecting other properties of the diaphragm base film.

[0060] The application further provides a diaphragm base film prepared according to the preparation method of the diaphragm base film in the above embodiment.

[0061] The diaphragm base film has a thickness of ≤5.5 μm and a needle puncture strength of ≥400 gf.

[0062] Optionally, the diaphragm base film has a thickness of 4.5 μm to 5.5 μm and a needle puncture strength of 400 gf to 580 gf.

[0063] The diaphragm base film provided in the application has both high needle puncture strength and low MD and TD heat shrinkage rates.

[0064] The diaphragm base film and the preparation method thereof provided in the application are described in further detail below in combination with embodiments.

[0065] Embodiment 1 The embodiments provided in the application provide a diaphragm base film and a preparation method thereof, which include the following steps: S1, preparing raw materials The raw material includes 19wt% dry material and 81wt% white oil, the dry material includes 97wt% ultra-high molecular weight polyethylene and 1wt% toughening agent, the ultra-high molecular weight polyethylene has a viscosity average molecular weight of 2 million, and the toughening agent is a graft copolymer, the main chain of the graft copolymer is isotactic polypropylene, and the graft is polyethylene.

[0066] S2, extrusion The raw material is put into a double screw extruder, the feeding amount of the raw material is set to 420kg / h, the extrusion speed is 125r / min, the melt temperature in the double screw extruder is 231℃, the extrusion temperature of the double screw extruder is 200℃, and a cast film piece is obtained.

[0067] S3, stretching and setting The prepared cast film piece is sequentially subjected to longitudinal stretching, first transverse stretching, extraction, and second transverse stretching. The longitudinal stretching ratio is 10 times, the preheating temperature of the longitudinal stretching is 86℃, and the stretching temperature is 92℃; the first transverse stretching ratio is 14 times, the preheating temperature of the first transverse stretching is 110℃, the temperature of the first transverse stretching is 105℃, the cast film piece is obtained after the longitudinal stretching, the first film is in a moving state along the longitudinal direction, the first transverse stretching rate is 1.1 times / m, that is, when the first film moves 1m along the longitudinal direction, the first film is transversely stretched by 1.1 times, the second film is obtained after the first film is transversely stretched, the second film is retracted, the retraction rate is 5%, and the retraction distance is 3m; the second transverse stretching ratio is 1.5 times; the heat setting temperature is 130℃, and the heat setting time is 25s.

[0068] Example 2 The embodiment of the application provides a diaphragm base film and a preparation method thereof, which changes the raw material to include 19wt% dry material and 81wt% white oil on the basis of example 1, the dry material includes 97wt% ultra-high molecular weight polyethylene and 3wt% toughening agent, the ultra-high molecular weight polyethylene has a viscosity average molecular weight of 2 million, and the toughening agent is a graft copolymer, the main chain of the graft copolymer is isotactic polypropylene, and the graft is polyethylene.

[0069] Example 3 The embodiment of the application provides a diaphragm base film and a preparation method thereof, which changes the raw material to include 19wt% dry material and 81wt% white oil on the basis of example 1, the dry material includes 97wt% ultra-high molecular weight polyethylene and 5wt% toughening agent, the ultra-high molecular weight polyethylene has a viscosity average molecular weight of 2 million, and the toughening agent is a graft copolymer, the main chain of the graft copolymer is isotactic polypropylene, and the graft is polyethylene.

[0070] Example 4 The embodiment of the present application provides a diaphragm base film and a preparation method thereof, which changes raw materials including 19wt% dry materials and 81wt% white oil on the basis of the embodiment 1, the dry materials including 97wt% ultra-high molecular weight polyethylene and 8wt% toughening agent, the ultra-high molecular weight polyethylene having a viscosity average molecular weight of 2 million, and the toughening agent being a graft copolymer, the main chain of the graft copolymer being isotactic polypropylene, and the graft being polyethylene.

[0071] Embodiment 5 The embodiment of the present application provides a diaphragm base film and a preparation method thereof, which changes raw materials including 19wt% dry materials and 81wt% white oil on the basis of the embodiment 1, the dry materials including 97wt% ultra-high molecular weight polyethylene and 1wt% toughening agent, the ultra-high molecular weight polyethylene having a viscosity average molecular weight of 1.8 million, and the toughening agent being a graft copolymer, the main chain of the graft copolymer being isotactic polypropylene, and the graft being polyethylene.

[0072] Embodiment 6 The embodiment of the present application provides a diaphragm base film and a preparation method thereof, which changes raw materials including 19wt% dry materials and 81wt% white oil on the basis of the embodiment 1, the dry materials including 97wt% ultra-high molecular weight polyethylene and 3wt% toughening agent, the ultra-high molecular weight polyethylene having a viscosity average molecular weight of 1.8 million, and the toughening agent being a graft copolymer, the main chain of the graft copolymer being isotactic polypropylene, and the graft being polyethylene.

[0073] Embodiment 7 The embodiment of the present application provides a diaphragm base film and a preparation method thereof, which changes raw materials including 19wt% dry materials and 81wt% white oil on the basis of the embodiment 1, the dry materials including 97wt% ultra-high molecular weight polyethylene and 5wt% toughening agent, the ultra-high molecular weight polyethylene having a viscosity average molecular weight of 1.8 million, and the toughening agent being a graft copolymer, the main chain of the graft copolymer being isotactic polypropylene, and the graft being polyethylene.

[0074] Embodiment 8 The embodiment of the present application provides a diaphragm base film and a preparation method thereof, which changes raw materials including 19wt% dry materials and 81wt% white oil on the basis of the embodiment 1, the dry materials including 97wt% ultra-high molecular weight polyethylene and 8wt% toughening agent, the ultra-high molecular weight polyethylene having a viscosity average molecular weight of 1.8 million, and the toughening agent being a graft copolymer, the main chain of the graft copolymer being isotactic polypropylene, and the graft being polyethylene.

[0075] Embodiment 9 The embodiment of the present application provides a diaphragm base film and a preparation method thereof, which changes raw materials on the basis of the embodiment 1 to include 19wt% dry materials and 81wt% white oil, the dry materials include 97wt% ultra-high molecular weight polyethylene and 3wt% toughening agent, the viscosity average molecular weight of the ultra-high molecular weight polyethylene is 2 million, the main chain of the graft copolymer is atactic polypropylene, and the grafting material is polyethylene.

[0076] Example 10 The embodiment of the present application provides a diaphragm base film and a preparation method thereof, which changes raw materials on the basis of the embodiment 1 to include 19wt% dry materials and 81wt% white oil, the dry materials include 97wt% ultra-high molecular weight polyethylene and 3wt% toughening agent, the viscosity average molecular weight of the ultra-high molecular weight polyethylene is 2 million, the main chain of the graft copolymer is atactic polypropylene, and the grafting material is polyethylene.

[0077] Comparative Example 1 The comparative example of the present application provides a diaphragm base film and a preparation method thereof, which changes raw materials on the basis of the embodiment 1 to include 19wt% dry materials and 81wt% white oil, the dry materials include 100wt% ultra-high molecular weight polyethylene, and the viscosity average molecular weight of the ultra-high molecular weight polyethylene is 2 million.

[0078] Comparative Example 2 The comparative example of the present application provides a diaphragm base film and a preparation method thereof, which changes raw materials on the basis of the embodiment 1 to include 19wt% dry materials and 81wt% white oil, the dry materials include 100wt% ultra-high molecular weight polyethylene, and the viscosity average molecular weight of the ultra-high molecular weight polyethylene is 1.8 million.

[0079] Comparative Example 3 The comparative example of the present application provides a diaphragm base film and a preparation method thereof, which changes raw materials on the basis of the embodiment 1 to include 19wt% dry materials and 81wt% white oil, the dry materials include 90wt% ultra-high molecular weight polyethylene and 10wt% toughening agent, the viscosity average molecular weight of the ultra-high molecular weight polyethylene is 2 million, the main chain of the graft copolymer is isotactic polypropylene, and the grafting material is polyethylene.

[0080] Comparative Example 4 The comparative example of the present application provides a diaphragm base film and a preparation method thereof, which changes raw materials on the basis of the embodiment 1 to include 19wt% dry materials and 81wt% white oil, the dry materials include 97wt% ultra-high molecular weight polyethylene and 3wt% toughening agent, the viscosity average molecular weight of the ultra-high molecular weight polyethylene is 2 million, the main chain of the graft copolymer is isotactic polypropylene, and the grafting material is polyethylene. ; Wherein, m and n are both greater than or equal to 10.

[0081] Comparative Example 5 The comparative example of the present application provides a diaphragm base film and a preparation method thereof. Based on Example 1, the raw materials are changed to include 19 wt% dry material and 81 wt% white oil. The dry material includes 97 wt% ultra-high molecular weight polyethylene and 3 wt% toughening agent. The viscosity-average molecular weight of the ultra-high molecular weight polyethylene is 2 million. The toughening agent is ethylene-propylene copolymer. The structural formula of the ethylene-propylene copolymer is as follows: ; Among them, p≥10.

[0082] The preparation parameters of the diaphragm base films of Examples 1 to 10 and Comparative Examples 1 to 5 are shown in Table 1.

[0083] Table 1 Parameters of the preparation method of the diaphragm base film of Examples 1 to 10 and Comparative Examples 1 to 5

[0084] Among them, tougheners A, B and C are all graft copolymers, and the main chain of graft copolymer A is isotactic polypropylene, the main chain of graft copolymer B is syndiotactic polypropylene, the main chain of graft copolymer C is atactic polypropylene, tougheners D and E are both ethylene-propylene copolymers, and the structural formula of toughener D is , m and n are both ≥ 10, the structural formula of toughening agent E is , p≥10.

[0085] Test Example 1 The thickness, needle punch strength, porosity, air permeability, MD heat shrinkage rate and TD heat shrinkage rate of the diaphragm base films prepared in Examples 1 to 10 and Comparative Examples 1 to 5 were measured. The results are shown in Table 2.

[0086] The test method is as follows: 1. Thickness Use a digital thickness gauge to measure. First, use an ion blower to remove static electricity from the sample surface, calibrate the instrument, reset it to zero, and then perform the thickness test.

[0087] 2. Acupuncture intensity Cut a sample no smaller than 5cm x 5cm and secure it to a sample stand. Measure the strength using an electronic puncture strength tester. After the test is complete, average the values ​​from three samples. The puncture needle diameter is 1mm, and the test speed is 250mm / min.

[0088] 3. Porosity Raw material density: 0.955 g / cm³, sample size: 4 cm x 6 cm. Weigh the sample, measure the thickness with a thickness gauge, and then calculate the porosity.

[0089] Porosity calculation method: porosity = (1 - 10 * film weight / 0.955 / (6 * 4 * film thickness)) * 100%.

[0090] 4, Air permeability The average time t required to pass 100 ml of gas is measured.

[0091] 5, MD and TD heat shrinkage Five 40*60mm samples were cut from the 1m wide separator base film, respectively placed flat between two papers, placed in an oven, and after cooling, the length and width were measured using an image instrument to calculate the MD and TD heat shrinkage.

[0092] Table 2 Parameters of the separator base films prepared in Examples 1-10 and Comparative Examples 1-5

[0093] From Examples 1-4, it can be seen that the average molecular weight of polyethylene is 2 million, and as the proportion of toughening agent increases, the needle penetration strength of the separator base film first increases and then decreases; From Examples 5-8, it can be seen that the average molecular weight of polyethylene is 1.8 million, and as the proportion of toughening agent increases, the needle penetration strength of the separator base film first increases and then decreases; From Examples 1, 9-10, it can be seen that the toughening agent A of Example 1 is a graft copolymer, the toughening agent B of Example 9 is a graft copolymer, and the toughening agent C of Example 10 is a graft copolymer. The main chain of toughening agent A is isotactic polypropylene, the main chain of toughening agent B is syndiotactic polypropylene, and the main chain of toughening agent C is atactic polypropylene. The needle penetration strength of the separator base films prepared in Examples 1, 9-10 remains at a high level; From the comparison of Comparative Example 1 and Example 1, it can be seen that Comparative Example 1 has no toughening agent, and the needle penetration strength of the separator base film of Comparative Example 1 is much lower than that of the separator base film of Example 1; From the comparison of Comparative Example 2 and Example 5, it can be seen that Comparative Example 2 has no toughening agent, and the needle penetration strength of the separator base film of Comparative Example 2 is much lower than that of the separator base film of Example 5; From the comparison of Comparative Example 3 and Example 1, it can be seen that the proportion of toughening agent in Comparative Example 3 is 10wt%, and the needle penetration strength of the separator base film of Comparative Example 3 is much lower than that of the separator base film of Example 1; From the comparison of Comparative Examples 4-5 and Example 1, it can be seen that the toughening agent D of Comparative Example 4 and the toughening agent E of Comparative Example 5 are both ethylene-propylene copolymers, the structural formula of the toughening agent D is , and the structural formula of the toughening agent E of Comparative Example 5 is The needle penetration strength of the separator base films of Comparative Examples 4-5 is much lower than that of the separator base film of Example 1.

[0094] The above descriptions are only specific embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a diaphragm base film, characterized in that: The preparation method of the diaphragm base film includes: sequentially extruding and stretching raw materials, the raw materials including dry material and a pore-forming agent, the dry material including ultra-high molecular weight polyethylene and a toughening agent, and the mass proportion of the toughening agent in the dry material is 1wt%~8wt%, the toughening agent is a graft copolymer, the main chain of the graft copolymer is polypropylene, and the graft is polyethylene.

2. The method for preparing a diaphragm base film according to claim 1, wherein: The main chain of the graft copolymer is homopolypropylene.

3. The method for preparing a diaphragm base film according to claim 1, wherein: The mass proportion of the toughening agent in the dry material is 3wt%~5wt%.

4. The method for preparing a diaphragm base film according to claim 1, wherein: The viscosity average molecular weight of the ultra-high molecular weight polyethylene is 1.5 million to 2.5 million.

5. The method for preparing a diaphragm base film according to claim 1, wherein: When the raw material is extruded, the melt temperature is 225° C. to 235° C.

6. The method for preparing a diaphragm base film according to claim 1, wherein: When the raw material is extruded, the extrusion temperature is 195° C. to 205° C.

7. The method for preparing a diaphragm base film according to claim 1, wherein: When the raw material is extruded, the extrusion speed is 70 r / min to 200 r / min.

8. The method for preparing a diaphragm base film according to claim 1, wherein: The feed rate of the raw material is 250kg / h~500kg / h.

9. A diaphragm base film, characterized in that: The diaphragm base film is prepared according to the method for preparing the diaphragm base film according to any one of claims 1 to 8.

10. The diaphragm base film according to claim 9, characterized in that The thickness of the diaphragm base film is ≤5.5 μm, and the needle puncture strength of the diaphragm base film is ≥400 gf.

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