A diaphragm and a method of making the same

Abstract

This invention relates to a diaphragm and its preparation method. The diaphragm has a three-layer composite structure. The middle layer is made of PP with a medium melt index (MI) of 1.5-2.0, and the two side layers are a mixture of PP with a low melt index (MI) of 0.5-1.0 and PP with a high melt index (MI) of 3.0-4.0. The middle layer material accounts for 30wt%-50wt% of all the raw materials. In the mixture, the low melt index PP accounts for 60wt%-70wt%. The preparation method is as follows: the middle layer material is placed in extruder A, and the two side layer materials are placed in extruder B. After plasticization, a PP melt is obtained. The melts from extruders A and B are combined at the die head and cast by cooling rollers to obtain a PP base film. The PP base film is then processed to obtain the diaphragm. The method of this invention is simple and effectively solves the problem that existing diaphragms cannot simultaneously achieve edge verticality, rib breakage, and needle pull-out film breaking.

Description

Technical Field

[0001] This invention belongs to the field of thin film technology and relates to a diaphragm and its preparation method. Background Technology

[0002] During the production of conventional lithium-ion battery separators, the high friction between the separator and the winding needles inevitably leads to a certain percentage of separator breakage during the needle removal process after winding. Dry-process separators, due to their inherently low lateral strength, experience an even higher rate of breakage, reducing the yield rate and increasing production costs.

[0003] To improve the problem of membrane breakage during dry-process membrane production, existing technologies, besides reducing the friction coefficient of the winding needles, typically use lower melt index (MI) PP raw materials (conventional MI = 2.0-3.0, lower MI = 0.5-1.8) to increase the transverse strength of the membrane and thus mitigate this issue. While this method can improve the breakage situation to some extent, the increased proportion of low melt index raw materials leads to poorer crystallinity of the cast film (reduced crystallinity, poorer uniformity of flake size), worse processability, and consequently, poorer thickness uniformity. After stretching and pore forming, the poorer uniformity of pore forming due to poor crystallinity increases the deformation of the product in later stages, ultimately leading to a higher proportion of sagging edges and cracked veins during membrane production, significantly increasing membrane production costs. The problems of sagging edges, cracked veins, and membrane breakage during needle removal cannot be effectively addressed simultaneously. Summary of the Invention

[0004] The purpose of this invention is to solve the problems existing in the prior art and to provide a diaphragm and its preparation method.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A separator has a three-layer composite structure, wherein the middle layer is made of medium melt index PP, and the two side layers are made of a mixture of low melt index PP and high melt index PP; the middle layer material accounts for 30wt%-50wt% of all raw materials; and the low melt index PP accounts for 60wt%-70wt% of the mixture.

[0007] The melt index (MI) of PP with a medium melt index is 1.5-2.0 under the conditions of 230℃, 2.16kg load, and 2.096mm die inner diameter. The melt index (MI) of PP with a low melt index is 0.5-1.0 under the same conditions. The melt index (MI) of PP with a high melt index is 3.0-4.0 under the same conditions.

[0008] The lower the melt index of the raw material and the larger the molecular weight, the higher the strength of the corresponding product, which will improve the problem of film breakage when needles are pulled out. However, the lower the melt index of the raw material and the larger the molecular weight, the higher the energy required for molecular chain movement and the more stringent the conditions required for crystallization. This results in lower crystallinity of the cast film during the dry-process diaphragm production process, and worse product stability after stretching (crystallization is the ordered arrangement of molecular chains. The principle of pore formation in dry-process diaphragms is: the separation of lamellae, and the stretching and bridging of short tie chains between lamellae to form pores. The lower the crystallinity, the more free short tie chains there are, and the more unstable the product is after stretching, and the easier it is to form defects such as sagging edges and cracked lines).

[0009] When low melt index raw materials are blended with high melt index raw materials for modification, the low melt index raw materials can improve the product strength, while the high melt index raw materials can improve the product crystallinity. The overall effect is different depending on the ratio of the two.

[0010] With the same total thickness, the strength of a three-layer co-extruded product is better than that of a single-layer product because the molecular chain orientations of different layers are different and the different layers have a restraining effect on each other. Through different combination methods, the present invention finally found that the best overall effect is achieved when the above conditions are met, that is, it can take into account the drooping edge, rib breakage and needle pull-out film of the diaphragm.

[0011] Existing diaphragms are mainly divided into two categories: one is a single-layer product (containing one melt index raw material product or two melt index mixed products); the other is a three-layer product (a single melt index raw material product or two melt index mixed products, i.e., the raw materials are the same in all three layers); the structure of the diaphragm of the present invention is different from that of the existing diaphragms, effectively solving the problem that the existing diaphragms cannot simultaneously achieve vertical edges, ribs, and needle-pulling membrane breakage.

[0012] As a preferred technical solution:

[0013] As described above, in a diaphragm, all PP has an isotacticity of ≥96%. Polypropylene is a semi-crystalline material and can be divided into isotactic, syndiotactic, and atactic types. Syndiotactic and atactic polypropylene products have very poor crystallinity, and only isotactic polypropylene can be used in dry diaphragm production. The higher the isotacticity, the smaller the steric hindrance of the molecular chain, and the higher the crystallinity of the product. The higher the crystallinity, the more uniform the pore formation of the product, and the less the proportion of vertical edge defects. When the isotacticity is lower than 96%, the crystallinity is too poor, the pore formation of the product is very poor, and it is impossible to produce diaphragm products that meet the performance requirements.

[0014] As described above, the raw materials for both sides of the membrane are the same. The existing production process in the industry is as follows: the three-layer membrane uses a dual extruder configuration, that is, the middle layer uses one extruder and the two side layers use one extruder, and the material is distributed to the two side layers by a distributor. This configuration determines that the raw materials on both sides are completely consistent. If three extruders are used, it is possible to achieve inconsistent raw materials between the three layers.

[0015] As described above, in a membrane where the raw materials for both sides of the membrane are present in equal proportions of all raw materials.

[0016] The diaphragm described above has a thickness of 10-40 μm.

[0017] As described above, the diaphragm has an air permeability of ≤120s / 100ml, a sagging edge and rib breakage rate of ≤4%, a needle-pulling membrane breakage rate of ≤3.5%, and the sum of the sagging edge rate, rib breakage rate, and needle-pulling membrane breakage rate of ≤6%. Its longitudinal tensile strength is 1200-2200kg / f cm⁻¹. 2 The transverse tensile strength is 120-200 kg / cm². 2 The 2sigma value (used to characterize thickness uniformity) is 0.10–0.16 μm.

[0018] The present invention also provides a method for preparing a diaphragm as described in any of the preceding claims, wherein the intermediate layer material is placed in extruder A and the two side layer materials are placed in extruder B, and after plasticization, a PP melt is obtained. The melts in extruder A and extruder B are combined at the die head, wherein the melt in extruder B enters the two side layers of the die head through a distributor, and the melt in extruder A enters the intermediate layer of the die head. The composite melt is cooled and rolled to obtain a PP base film. The PP base film is then subjected to annealing, cold stretching, hot stretching, natural shrinkage, and high-temperature setting in sequence to obtain the diaphragm.

[0019] As a preferred technical solution:

[0020] As described above, the operating temperature of extruder A or extruder B is 190-255℃; in this invention, the die temperature and cooling roller temperature of extruder A and extruder B are the same; the die temperature of extruder A or extruder B is 200-260℃; and the cooling roller temperature of extruder A or extruder B is 65-95℃.

[0021] As described above, the annealing temperature is 125-155℃, and the annealing time is 5-25 min; the cold stretching temperature is 65-95℃, and the cold stretching ratio is 1.05-1.25; the hot stretching temperature is 125-158℃, and the hot stretching ratio is 1.3-2.7; the shrinkage ratio is 0.8-1.0; and the high-temperature setting temperature is 140-160℃, and the high-temperature setting time is 3-17 min.

[0022] This invention employs a three-layer co-extrusion method for producing cast film. The total thickness of the cast film is between 10-40 μm. The middle layer uses PP raw material with a melt index (MI) of 1.5-2.0, accounting for 30%-50% of the total content. The two side layers use a blend of PP raw material with a melt index (MI) of 0.5-1.0 and PP raw material with a melt index (MI) of 3.0-4.0, accounting for 50%-70% of the total content. Specifically, the melt index PP raw material in the two side layers accounts for 60%-70% of the total content, while the melt index PP raw material in the other two side layers accounts for 40%-70% of the total content. The amount of PP raw material with a melt index of 3.0-4.0 is 30%-40%. Only when the MI (Mean Intake) of the raw material and the proportion of different raw materials are within the range specified in this invention can the final product improve the strength of the dry-process separator, ensure the uniformity of the separator thickness and pore size, and avoid increasing the proportion of vertical edge breakage during separator production due to the increased proportion of low melt index raw materials. This balances the separator production process and the battery pin removal process, improving the overall yield and significantly reducing the total production cost of the industrial chain, bringing substantial benefits to actual production. If multiple combinations are simply used outside the data range specified in this invention, although there may be some improvement within a certain range, the effect is not ideal. Detailed Implementation

[0023] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0024] The test methods for some performance indicators in the following embodiments and comparative examples are as follows:

[0025] The test method for extremely poor air permeability is as follows: Take a diaphragm piece with a width of 350mm and a length of 500mm, take 10 points along the length direction and 3 points along the width direction, for a total of 10*3=30 points, with each point having an area of ​​6.45mm². 2 In the test environment (normal pressure, temperature 25±3℃, humidity 40±3%), using the test instrument (model EG01-55-1MR), the time required for 100mL of air to pass through each point on the diaphragm was measured. The test pressure was 1.21kPa. 30 sets of data were obtained, and the difference between the maximum and minimum values ​​in the data is the air permeability range of the diaphragm.

[0026] The method for testing the vertical edge is as follows: Fix the diaphragm using an air shaft, then flatten the diaphragm in a horizontal roller, and use a standard clamping piece to clamp the falling diaphragm at a specified position. Under the action of gravity, the diaphragm is in a taut and flattened state. Start the automatic scanning device. The automatic scanning device scans 4 times and returns to the starting position. Read the average value of the 4 measurements on the screen as the final wave and vertical edge value, and thus judge the severity of the vertical edge. If the value is within the range allowed by the quality, it is considered that the flatness of the diaphragm is qualified; otherwise, if it exceeds this range, it is considered unqualified. The standard for qualified flatness is that the value ≤ 30mm;

[0027] The proportion of the vertical edge = the number of diaphragms of unqualified vertical edge samples / the total number of sample diaphragms tested × 100%.

[0028] The method for testing the bulging ribs is as follows: After the diaphragm is slit, use a strong flashlight to irradiate the surface of the film roll along the axial direction at an angle of 0 - 15°. If there are concave and convex positions, it is determined that there are bulging ribs at that position. If the width of the bulging rib position ≥ 20mm, it is determined as unqualified;

[0029] The proportion of the bulging ribs = the number of film rolls of unqualified bulging ribs / the total number of measured film rolls × 100%.

[0030] The rate of needle - pulling and film - breaking: During the battery production process (the positive electrode material, negative electrode material, and diaphragm are wound together), when a pre - set winding amount of a battery is reached, that is, the winding is completed, the equipment automatically stops winding and performs needle - pulling, and a single cell is produced. If the film is broken during the needle - pulling process, this single cell is recorded as unqualified. The proportion of the number of unqualified single cells in the total number of single cells is the rate of needle - pulling and film - breaking. Among them, the winding needle is oval, the long axis of the ellipse is 80mm, the short axis is 40mm, the length of the winding needle is 244mm, and the needle - pulling speed is 90mm / s.

[0031] The test method for the tensile strength is as follows:

[0032] a. Use a thickness gauge (model: Mar c1216) to detect the thickness of the diaphragm and record it as A;

[0033] b. Cut the diaphragm into the size of A4 paper, and then place the diaphragm cut into the size of A4 paper on a cutting machine and cut it into strip diaphragms with a width b = 15mm;

[0034] c. Draw marking lines on the strip diaphragms at an interval of 10cm, and then clamp the strip diaphragms on a universal testing machine (manufacturer: Easyt, model: STD50). After inputting the values of parameters A and b, start the measurement. When the strip diaphragm is broken, read the tensile strength. Each strip diaphragm is tested 3 times, and finally take the average value of all test results as the tensile strength of the diaphragm; TD>150kg / f cm 2 , MD>1500kg / f cm 2It is considered excellent.

[0035] The test method for thickness uniformity is as follows: the thickness of the diaphragm is measured using an online thickness gauge (manufacturer: MicroPioneer XRF2000, South Korea) for 10 measurements, and the 2sigma value is calculated. A 2sigma value < 0.2 μm is considered good; 0.2 μm ≤ 2sigma value < 0.25 μm is considered medium; and a 2sigma value ≥ 0.25 μm is considered poor.

[0036] Example 1

[0037] A method for preparing a diaphragm, comprising the following steps:

[0038] (1) Raw material preparation;

[0039] Intermediate layer raw material: medium melt index PP (manufacturer: Daehan Oil & Chemical, grade: S802);

[0040] Upper layer raw materials: a mixture of low melt index PP (manufacturer: Daehan Oil & Chemical, grade: S800) and high melt index PP (manufacturer: Daehan Oil & Chemical, grade: S801), with the proportion of low melt index PP in the mixture being 60 wt%.

[0041] Lower layer raw materials: Same as upper layer raw materials;

[0042] (2) The intermediate layer material is placed in extruder A, and the two side layer materials (i.e., the upper layer material and the lower layer material) are placed in extruder B. After plasticization, PP melt is obtained. The melts in extruder A and extruder B are combined at the die head. The melt in extruder B enters the two side layers of the die head through the distributor, and the melt in extruder A enters the intermediate layer of the die head. The composite melt is cooled and cast into a sheet to obtain a PP base film. The PP base film is then subjected to annealing, cold stretching, hot stretching, natural shrinkage, and high temperature setting to obtain a diaphragm.

[0043] The middle layer raw material accounts for 40 wt% of all raw materials, and the two side layers raw materials account for the same proportion of all raw materials (i.e., the upper and lower layers raw materials account for the same proportion of all raw materials).

[0044] The temperatures of zones 1-7 in extruder A are 55℃, 180℃, 205℃, 235℃, 240℃, 225℃, and 225℃, respectively; the temperatures of zones 1-7 in extruder B are 55℃, 180℃, 210℃, 240℃, 245℃, 230℃, and 230℃, respectively; the die temperature is 225℃, the cooling roller temperature is 80℃; the annealing temperature is 140℃, and the annealing time is 15 min; the cold stretching temperature is 80℃, and the cold stretching ratio is 1.15; the hot stretching temperature is 145℃, and the hot stretching ratio is 2; the shrinkage ratio is 0.9; the high-temperature setting temperature is 150℃, and the high-temperature setting time is 10 min.

[0045] The final membrane thickness was 18 μm, the air permeability was 62 s / 100 ml, the sum of the vertical edge ratio and the rib breakage ratio was 2.9%, the needle pull-out membrane breakage rate was 1.9%, and the longitudinal tensile strength was 2200 kg / f cm. 2 The transverse tensile strength is 140 kg / fcm. 2 The thickness uniformity (expressed as a 2sigma value) is 0.16 μm.

[0046] Comparative Example 1

[0047] A method for preparing a diaphragm is basically the same as in Example 1, except that the proportion of the intermediate layer raw material in all raw materials is 20 wt%.

[0048] The final membrane thickness was the same as in Example 1, with a permeability of 72 s / 100 ml, a combined percentage of vertical edges and ribs of 4.1%, a membrane breakage rate of 2.6%, and a longitudinal tensile strength of 1700 kg / f cm. 2 The transverse tensile strength is 115 kg / f cm. 2 The thickness uniformity (expressed as a 2sigma value) is 0.21 μm.

[0049] Comparing Example 1 with Comparative Example 1, it can be seen that the sum of the vertical edge ratio and the ribbed ratio, as well as the film breakage rate, of Comparative Example 1 are improved to a certain extent. This is because the proportion of medium melt index PP is reduced, while the total proportion of low melt index and high melt index PP is increased. The increase in the proportion of low melt index PP increases the proportion of vertical edge and ribbed ratio, while the high melt index PP reduces the transverse strength and increases the film breakage rate.

[0050] Comparative Example 2

[0051] A method for preparing a diaphragm is basically the same as in Example 1, except that the proportion of the intermediate layer raw material in all raw materials is 60 wt%.

[0052] The final membrane thickness was the same as in Example 1, with an air permeability of 66 s / 100 ml, a combined percentage of vertical edges and exposed ribs of 2.1%, a needle-pulling membrane breakage rate of 3.6%, and a longitudinal tensile strength of 1600 kg / f cm. 2 The transverse tensile strength is 109 kg / f cm. 2 The thickness uniformity (expressed as a 2sigma value) is 0.17 μm.

[0053] Comparing Example 1 with Comparative Example 2, it can be seen that the proportion of vertical edges and exposed ribs in Comparative Example 2 did not change significantly, but the needle-pulling film breakage rate increased. This is because the proportion of low melt index PP decreased, which reduced the molecular weight of the raw material, resulting in smaller intermolecular forces and easier sliding between molecules. Consequently, the tensile strength of the separator decreased, leading to a higher needle-pulling film breakage rate during battery production.

[0054] Comparative Example 3

[0055] A method for preparing a diaphragm is basically the same as in Example 1, except that the proportion of low melt index PP in the upper and lower raw materials is 40 wt%.

[0056] The final membrane thickness was the same as in Example 1, with a permeability of 60 s / 100 ml, a combined percentage of vertical edges and ribs of 1.9%, a membrane breakage rate of 3.7%, and a longitudinal tensile strength of 1600 kg / f cm. 2 The transverse tensile strength is 105 kg / f cm. 2 The thickness uniformity (expressed as a 2sigma value) is 0.16 μm.

[0057] Comparing Example 1 with Comparative Example 3, it can be seen that the vertical edge ridges of Comparative Example 3 are slightly improved, and the needle-pulling film breakage rate is significantly increased. This is because the proportion of low melt index PP is reduced, which makes the molecular weight of the raw material smaller, resulting in smaller intermolecular forces and easier sliding between molecules. The tensile strength of the separator is reduced accordingly, which in turn leads to a larger needle-pulling film breakage rate during battery production.

[0058] Comparative Example 4

[0059] A method for preparing a diaphragm is basically the same as in Example 1, except that the proportion of low melt index PP in the upper and lower raw materials is 80 wt%.

[0060] The final membrane thickness was the same as in Example 1, with a permeability of 86 s / 100 ml, a combined percentage of vertical edges and ribs of 4.4%, a membrane breakage rate of 1.9%, and a longitudinal tensile strength of 2250 kg / f cm. 2 The transverse tensile strength is 155 kg / cm². 2 The thickness uniformity (expressed as a 2sigma value) is 0.22 μm.

[0061] Comparing Example 1 with Comparative Example 4, it can be seen that the film breakage rate of Comparative Example 4 did not change significantly, but the proportion of vertical edges and ridges increased. This is because the increase in the proportion of low melt index PP leads to a decrease in the crystallinity of the cast film (reduced crystallinity and poorer uniformity of flake size), resulting in poorer processability and consequently poorer thickness uniformity. After stretching and forming holes, the poor crystallinity leads to poorer hole uniformity (i.e., a greater air permeability), which increases the deformation of the product in the later stages, ultimately resulting in an increase in the proportion of vertical edges and ridges during the diaphragm production process.

[0062] Comparative Example 5

[0063] A method for preparing a diaphragm is basically the same as in Example 1, except that the intermediate layer material in Example 1 is replaced with an equal mass of low melt index PP from Example 1.

[0064] The final membrane thickness was the same as in Example 1, with a permeability of 105 s / 100 ml, a vertical edge ratio and a rib breakage ratio of 5.8%, a needle pull-out membrane breakage rate of 1.8%, and a longitudinal tensile strength of 2250 kg / f cm. 2 The transverse tensile strength is 158 kg / f cm. 2 The thickness uniformity (expressed as a 2sigma value) is 0.26 μm.

[0065] Comparing Example 1 with Comparative Example 5, it can be seen that the air permeability uniformity of Comparative Example 5 deteriorates (i.e., the air permeability difference increases), and the sum of the vertical edge ratio and the cracked edge ratio increases. This is because the proportion of PP with low melt index increases, resulting in poor crystallinity, poor air permeability uniformity, and exacerbated vertical edge cracking.

[0066] Comparative Example 6

[0067] A method for preparing a diaphragm is basically the same as in Example 1, except that the intermediate layer material in Example 1 is replaced with an equal mass of high melt index PP from Example 1.

[0068] The final membrane thickness was the same as in Example 1, with an air permeability of 49 s / 100 ml, a vertical edge ratio and a rib breakage ratio of 2.1%, a needle pull-out membrane breakage rate of 5.1%, and a longitudinal tensile strength of 1550 kg / f cm. 2 The transverse tensile strength is 98 kg / fcm. 2 The thickness uniformity (expressed as a 2sigma value) is 0.16 μm.

[0069] Comparing Example 1 with Comparative Example 6, it can be seen that Comparative Example 6 has better air permeability uniformity (i.e., smaller air permeability difference) and increased needle pull-out film breakage rate. This is because the proportion of high melt index PP increases, which leads to a decrease in product strength and an increase in film breakage rate.

[0070] Comparative Example 7

[0071] A method for preparing a diaphragm is basically the same as in Example 1, except that the low melt flow index PP in Example 1 is replaced with an equal mass of medium melt flow index PP from Example 1.

[0072] The final membrane thickness was the same as in Example 1, with a permeability of 65 s / 100 ml, a vertical edge ratio and a rib breakage ratio of 2.2%, a needle pull-out membrane breakage rate of 3.7%, and a longitudinal tensile strength of 1700 kg / f cm. 2 The transverse tensile strength is 109 kg / f cm. 2 The thickness uniformity (expressed as a 2sigma value) is 0.19 μm.

[0073] Comparing Example 1 with Comparative Example 7, it can be seen that the needle-pulling film breakage rate of Comparative Example 7 is increased. This is because the proportion of PP with medium melt index is increased, which leads to a decrease in the tensile strength of the product and an increase in the needle-pulling film breakage rate.

[0074] Comparative Example 8

[0075] A method for preparing a diaphragm is basically the same as in Example 1, except that the high melt flow index PP of Example 1 is replaced with an equal mass of medium melt flow index PP of Example 1.

[0076] The final membrane thickness was the same as in Example 1, with a permeability of 79 s / 100 ml, a vertical edge ratio and a rib breakage ratio of 5.7%, a needle pull-out membrane breakage rate of 2.1%, and a longitudinal tensile strength of 2200 kg / f cm. 2 The transverse tensile strength is 140 kg / f cm. 2 The thickness uniformity (expressed as a 2sigma value) is 0.27 μm.

[0077] Comparing Example 1 with Comparative Example 8, it can be seen that the sum of the vertical edge ratio and the rib breakage ratio of Comparative Example 8 increases. This is because the proportion of PP with medium melt index increases, which exacerbates the vertical edge rib breakage of the product.

[0078] Example 2

[0079] A method for preparing a diaphragm, comprising the following steps:

[0080] (1) Raw material preparation;

[0081] Intermediate layer raw material: medium melt index PP (manufacturer: Daehan Oil & Chemical, grade: S802);

[0082] Upper layer raw materials: a mixture of low melt index PP (manufacturer: Singapore TPC, grade: FS1014) and high melt index PP (manufacturer: Daehan Oil & Chemical, grade: S801), with the proportion of low melt index PP in the mixture being 70 wt%.

[0083] Lower layer raw materials: Same as upper layer raw materials;

[0084] (2) The intermediate layer material is placed in extruder A, and the two side layer materials (i.e., the upper layer material and the lower layer material) are placed in extruder B. After plasticization, PP melt is obtained. The melts in extruder A and extruder B are combined at the die head. The melt in extruder B enters the two side layers of the die head through the distributor, and the melt in extruder A enters the intermediate layer of the die head. The composite melt is cooled and cast into a sheet to obtain a PP base film. The PP base film is then subjected to annealing, cold stretching, hot stretching, natural shrinkage, and high temperature setting to obtain a diaphragm.

[0085] The middle layer raw material accounts for 30 wt% of all raw materials, and the two side layers raw materials account for the same proportion of all raw materials (i.e., the upper and lower layers raw materials account for the same proportion of all raw materials).

[0086] The temperatures of zones 1-7 in extruder A are 55℃, 180℃, 200℃, 230℃, 235℃, 220℃, and 220℃, respectively; the temperatures of zones 1-7 in extruder B are 55℃, 180℃, 190℃, 230℃, 235℃, 220℃, and 215℃, respectively; the die temperature is 235℃, the cooling roller temperature is 95℃; the annealing temperature is 125℃, and the annealing time is 25 min; the cold stretching temperature is 65℃, and the cold stretching ratio is 1.05; the hot stretching temperature is 158℃, and the hot stretching ratio is 1.3; the shrinkage ratio is 0.8; the high-temperature setting temperature is 160℃, and the high-temperature setting time is 3 min.

[0087] The final membrane thickness was 18.5 μm, the air permeability was 120 s / 100 ml, the sum of the vertical edge ratio and the rib breakage ratio was 2.8%, the needle pull-out membrane breakage rate was 1.9%, and the longitudinal tensile strength was 1900 kg / f cm. 2 The transverse tensile strength is 175 kg / cm². 2 The thickness uniformity (expressed as a 2sigma value) is 0.14 μm.

[0088] Example 3

[0089] A method for preparing a diaphragm, comprising the following steps:

[0090] (1) Raw material preparation;

[0091] Intermediate layer raw material: medium melt index PP (manufacturer: Singapore TPC, grade: FS2015);

[0092] Upper layer raw materials: a mixture of low melt index PP (manufacturer: Daehan Oil & Chemical, grade: S800) and high melt index PP (manufacturer: Daehan Oil & Chemical, grade: S801), with the proportion of low melt index PP in the mixture being 60 wt%.

[0093] Lower layer raw materials: Same as upper layer raw materials;

[0094] (2) The intermediate layer material is placed in extruder A, and the two side layer materials (i.e., the upper layer material and the lower layer material) are placed in extruder B. After plasticization, PP melt is obtained. The melts in extruder A and extruder B are combined at the die head. The melt in extruder B enters the two side layers of the die head through the distributor, and the melt in extruder A enters the intermediate layer of the die head. The composite melt is cooled and cast into a sheet to obtain a PP base film. The PP base film is then subjected to annealing, cold stretching, hot stretching, natural shrinkage, and high temperature setting to obtain a diaphragm.

[0095] The middle layer raw material accounts for 40 wt% of all raw materials, and the two side layers raw materials account for the same proportion of all raw materials (i.e., the upper and lower layers raw materials account for the same proportion of all raw materials).

[0096] The temperatures of zones 1-7 in extruder A are 55℃, 180℃, 190℃, 215℃, 220℃, 210℃, and 205℃, respectively; the temperatures of zones 1-7 in extruder B are 55℃, 180℃, 210℃, 245℃, 255℃, 230℃, and 230℃, respectively; the die temperature is 200℃, the cooling roller temperature is 80℃; the annealing temperature is 140℃, and the annealing time is 15 min; the cold stretching temperature is 80℃, and the cold stretching ratio is 1.15; the hot stretching temperature is 145℃, and the hot stretching ratio is 2; the shrinkage ratio is 0.9; the high-temperature setting temperature is 150℃, and the high-temperature setting time is 10 min.

[0097] The final membrane thickness was 18 μm, the air permeability was 56 s / 100 ml, the sum of the vertical edge ratio and the rib breakage ratio was 2.4%, the needle pull-out membrane breakage rate was 1.9%, and the longitudinal tensile strength was 2000 kg / f cm. 2 The transverse tensile strength is 200 kg / cm². 2 The thickness uniformity (expressed as a 2sigma value) is 0.11 μm.

[0098] Example 4

[0099] A method for preparing a diaphragm, comprising the following steps:

[0100] (1) Raw material preparation;

[0101] Intermediate layer raw material: medium melt index PP (manufacturer: Singapore TPC, grade: FS2015);

[0102] Upper layer raw materials: a mixture of low melt index PP (manufacturer: Singapore TPC, grade: FS1014) and high melt index PP (manufacturer: Daehan Oil & Chemical, grade: S801), with the proportion of low melt index PP in the mixture being 60 wt%.

[0103] Lower layer raw materials: Same as upper layer raw materials;

[0104] (2) The intermediate layer material is placed in extruder A, and the two side layer materials (i.e., the upper layer material and the lower layer material) are placed in extruder B. After plasticization, PP melt is obtained. The melts in extruder A and extruder B are combined at the die head. The melt in extruder B enters the two side layers of the die head through the distributor, and the melt in extruder A enters the intermediate layer of the die head. The composite melt is cooled and cast into a sheet to obtain a PP base film. The PP base film is then subjected to annealing, cold stretching, hot stretching, natural shrinkage, and high temperature setting to obtain a diaphragm.

[0105] The middle layer raw material accounts for 40 wt% of all raw materials, and the two side layers raw materials account for the same proportion of all raw materials (i.e., the upper and lower layers raw materials account for the same proportion of all raw materials).

[0106] The temperatures of zones 1-7 in extruder A are 55℃, 180℃, 190℃, 225℃, 230℃, 210℃, and 210℃, respectively; the temperatures of zones 1-7 in extruder B are 55℃, 180℃, 200℃, 240℃, 245℃, 225℃, and 225℃, respectively; the die temperature is 250℃, the cooling roller temperature is 80℃; the annealing temperature is 140℃, and the annealing time is 15 min; the cold stretching temperature is 80℃, and the cold stretching ratio is 1.15; the hot stretching temperature is 140℃, and the hot stretching ratio is 2; the shrinkage ratio is 0.9; the high-temperature setting temperature is 150℃, and the high-temperature setting time is 10 min.

[0107] The final membrane thickness was 23 μm, the air permeability was 87 s / 100 ml, the sum of the vertical edge ratio and the rib breakage ratio was 2.2%, the needle pull-out membrane breakage rate was 1.9%, and the longitudinal tensile strength was 1600 kg / f cm. 2 The transverse tensile strength is 140 kg / fcm. 2 The thickness uniformity (expressed as a 2sigma value) is 0.1 μm.

[0108] Example 5

[0109] A method for preparing a diaphragm, comprising the following steps:

[0110] (1) Raw material preparation;

[0111] Intermediate layer raw material: medium melt index PP (manufacturer: Daehan Oil & Chemical, grade: S802);

[0112] Upper layer raw materials: a mixture of low melt index PP (manufacturer: Daehan Oil & Chemical, grade: S800) and high melt index PP (manufacturer: Daehan Oil & Chemical, grade: S801), with the proportion of low melt index PP in the mixture being 60 wt%.

[0113] Lower layer raw materials: Same as upper layer raw materials;

[0114] (2) The intermediate layer material is placed in extruder A, and the two side layer materials (i.e., the upper layer material and the lower layer material) are placed in extruder B. After plasticization, PP melt is obtained. The melts in extruder A and extruder B are combined at the die head. The melt in extruder B enters the two side layers of the die head through the distributor, and the melt in extruder A enters the intermediate layer of the die head. The composite melt is cooled and cast into a sheet to obtain a PP base film. The PP base film is then subjected to annealing, cold stretching, hot stretching, natural shrinkage, and high temperature setting to obtain a diaphragm.

[0115] The middle layer raw material accounts for 40 wt% of all raw materials, and the two side layers raw materials account for the same proportion of all raw materials (i.e., the upper and lower layers raw materials account for the same proportion of all raw materials).

[0116] The temperatures of zones 1-7 in extruder A are 55℃, 180℃, 190℃, 215℃, 220℃, 205℃, and 205℃, respectively; the temperatures of zones 1-7 in extruder B are 55℃, 180℃, 200℃, 240℃, 245℃, 225℃, and 225℃, respectively; the die temperature is 240℃, the cooling roller temperature is 80℃; the annealing temperature is 140℃, and the annealing time is 15 min; the cold stretching temperature is 80℃, and the cold stretching ratio is 1.15; the hot stretching temperature is 140℃, and the hot stretching ratio is 2; the shrinkage ratio is 0.9; the high-temperature setting temperature is 150℃, and the high-temperature setting time is 10 min.

[0117] The final membrane thickness was 10.5 μm, with a permeability poor of 43 s / 100 ml, a combined percentage of vertical edges and ribs of 1.9%, a needle-pulling breakage rate of 3.3%, and a longitudinal tensile strength of 1200 kg / f cm. 2 The transverse tensile strength is 120 kg / fcm. 2 The thickness uniformity (expressed as a 2sigma value) is 0.12 μm.

[0118] Example 6

[0119] A method for preparing a diaphragm, comprising the following steps:

[0120] (1) Raw material preparation;

[0121] Intermediate layer raw material: medium melt index PP (manufacturer: Daehan Oil & Chemical, grade: S802);

[0122] Upper layer raw materials: a mixture of low melt index PP (manufacturer: Daehan Oil & Chemical, grade: S800) and high melt index PP (manufacturer: Daehan Oil & Chemical, grade: S801), with the proportion of low melt index PP in the mixture being 60 wt%.

[0123] Lower layer raw materials: Same as upper layer raw materials;

[0124] (2) The intermediate layer material is placed in extruder A, and the two side layer materials (i.e., the upper layer material and the lower layer material) are placed in extruder B. After plasticization, PP melt is obtained. The melts in extruder A and extruder B are combined at the die head. The melt in extruder B enters the two side layers of the die head through the distributor, and the melt in extruder A enters the intermediate layer of the die head. The composite melt is cooled and cast into a sheet to obtain a PP base film. The PP base film is then subjected to annealing, cold stretching, hot stretching, natural shrinkage, and high temperature setting to obtain a diaphragm.

[0125] The middle layer raw material accounts for 50 wt% of all raw materials, and the two side layers raw materials account for the same proportion of all raw materials (i.e., the upper and lower layers raw materials account for the same proportion of all raw materials).

[0126] The temperatures of zones 1-7 in extruder A are 55℃, 180℃, 190℃, 215℃, 220℃, 205℃, and 205℃, respectively; the temperatures of zones 1-7 in extruder B are 55℃, 180℃, 210℃, 250℃, 255℃, 230℃, and 230℃, respectively; the die temperature is 260℃, the cooling roller temperature is 65℃; the annealing temperature is 155℃, and the annealing time is 5 min; the cold stretching temperature is 95℃, and the cold stretching ratio is 1.25; the hot stretching temperature is 125℃, and the hot stretching ratio is 2.7; the shrinkage ratio is 1; the high-temperature setting temperature is 140℃, and the high-temperature setting time is 17 min.

[0127] The final membrane thickness was 40 μm, the air permeability was 82 s / 100 ml, the sum of the vertical edge ratio and the rib breakage ratio was 2.1%, the needle pull-out membrane breakage rate was 2.4%, and the longitudinal tensile strength was 1900 kg / f cm. 2 The transverse tensile strength is 170 kg / fcm. 2 The thickness uniformity (expressed as a 2sigma value) is 0.11 μm.

Claims

1. A diaphragm, characterized by It has a three-layer composite structure. The middle layer is made of medium melt index PP, and the two side layers are a mixture of low melt index PP and high melt index PP. The middle layer material accounts for 30wt%-50wt% of all raw materials. In the mixture, the low melt index PP accounts for 60wt%-70wt%. The melt index (MI) of PP with a medium melt index is 1.5-2.0 under the conditions of 230℃, 2.16kg load, and 2.096mm die inner diameter. The melt index (MI) of PP with a low melt index is 0.5-1.0 under the same conditions. The melt index (MI) of PP with a high melt index is 3.0-4.0 under the same conditions.

2. A diaphragm according to claim 1, characterised in that All PPs have an isotacticity of ≥96%.

3. A diaphragm according to claim 1, wherein The raw materials for both sides are the same.

4. A diaphragm according to claim 3, wherein The proportion of raw materials in both sides of the layer is the same as that in all raw materials.

5. The separator of claim 1, wherein The thickness of the diaphragm is 10-40 μm.

6. A separator according to any one of claims 1 to 5, characterised in that The diaphragm has an air permeability of ≤120s / 100ml, a combined percentage of sagging edges and ribs of ≤4%, a needle-pulling membrane breakage rate of ≤3.5%, and a combined percentage of sagging edges, ribs of ≤6% and needle-pulling membrane breakage rate of ≤6%. The longitudinal tensile strength is 1200-2200 kg / cm². 2 The transverse tensile strength is 120-200 kg / cm². 2 The 2sigma value is 0.10–0.16 μm.

7. A method of producing a separator as claimed in any one of claims 1 to 6, characterised in that, The intermediate layer material is placed in extruder A, and the two side layer materials are placed in extruder B. After plasticization, PP melt is obtained. The melts from extruder A and extruder B are combined at the die head. The melt from extruder B enters the two side layers of the die head through a distributor, and the melt from extruder A enters the intermediate layer of the die head. The composite melt is cooled and cast into a sheet to obtain a PP base film. The PP base film is then subjected to annealing, cold stretching, hot stretching, natural shrinkage, and high-temperature setting to obtain the separator.

8. The method of claim 7, wherein, The operating temperature of extruder A or extruder B is 190-255℃; the die temperature of extruder A or extruder B is 200-260℃; and the cooling roller temperature of extruder A or extruder B is 65-95℃.

9. The method of claim 7, wherein, The annealing temperature is 125-155℃, and the annealing time is 5-25 min; the cold stretching temperature is 65-95℃, and the cold stretching ratio is 1.05-1.25; the hot stretching temperature is 125-158℃, and the hot stretching ratio is 1.3-2.7; the shrinkage ratio is 0.8-1.0; the high temperature setting temperature is 140-160℃, and the high temperature setting time is 3-17 min.