Method for improving edge collapse deformation of base film after slitting

Abstract

The invention relates to the technical field of preparation of lithium battery diaphragms, in particular to a method for improving edge collapse deformation of a base membrane after slitting, and the method comprises the following steps: S1, mixing a polyethylene raw material, a plasticizer and a stabilizer to obtain a mixed raw material, and performing melt extrusion on the mixed raw material to obtain a substrate; s2, the substrate is subjected to two-way stretching treatment including transverse stretching and longitudinal stretching, and an initial base film is prepared; s3, performing extraction treatment on the initial base membrane by adopting a continuous counter-current extraction technology to obtain an extracted base membrane; s4, the extracted base membrane is subjected to hot air circulation shaping treatment, and a shaped base membrane is obtained; and S5, high-precision slitting equipment is adopted for slitting the shaped base film, and the finished base film is obtained. According to the method, a systematic solution is constructed from three dimensions of a material formula, process parameters and an equipment structure, and the problems of edge collapse and deformation after the base film is slit are remarkably improved through the synergistic effect of all technical elements.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery separator preparation, and particularly to a method for improving the edge collapse and deformation after slitting of a base film. Background Art

[0002] As a highly efficient energy storage device that can be repeatedly charged and discharged, lithium batteries are widely used in fields such as new energy vehicles and 3C products. The separator is an important component of a lithium battery, playing the role of electrolyte isolation and battery protection. The quality of the separator has a crucial impact on the processing and performance of lithium batteries. Wet separators are widely used in the field of power batteries due to their advantages such as thinness, high porosity, and good pore size uniformity. The impact of the edge collapse and deformation problem: (1) Battery production process: Edge collapse and deformation of the wet separator base film after slitting can lead to problems such as equipment failures and poor product winding during battery winding. (2) Battery performance aspect: It may affect the insulation, porosity and other properties of the separator, thereby changing the interface structure, internal resistance, etc. of the battery, and ultimately affecting the energy density, cycle life, and safety of the battery.

[0003] Currently, the problem of edge collapse and deformation generally exists in the slitting process of wet separator base films, which is mainly due to the uneven distribution of internal stress in the base film. In the prior art, the factors affecting the stress distribution of the base film are mainly reflected in the following aspects: First, the quality and performance fluctuations of raw materials, such as unreasonable molecular weight distribution of polyethylene raw materials and improper control of the content of additives, will cause uneven internal stress to be formed in the base film during production; second, in processes such as stretching, extraction, and shaping, insufficient control accuracy of process parameters will further exacerbate this uneven stress distribution; finally, the accuracy and stability problems of slitting equipment, especially the operating states of components such as unwind reels, tension rollers, and rewind reels, as well as the wear condition of slitting tools, will apply additional stress to the base film with existing stress unevenness during the slitting process, ultimately resulting in edge collapse and deformation of the slitted base film. In addition, due to the characteristics of the wet process itself, such as long process flow and high equipment accuracy requirements, these problems often interact and superimpose on each other in actual production, making it difficult to effectively guarantee the slitting quality of the base film. Summary of the Invention

[0004] In view of this, the present invention proposes a method for improving the edge collapse and deformation after slitting of a base film to solve the problem that the separator will cause edge collapse and deformation after slitting during the preparation process of the wet process of existing lithium battery separators.

[0005] The technical solution of the present invention is realized as follows: The present invention provides a method for improving the edge collapse and deformation after slitting of a base film, including the following steps:

[0006] S1. Mix the polyethylene raw material, plasticizer and stabilizer to obtain a mixed raw material, and subject the mixed raw material to melt extrusion to produce a substrate;

[0007] S2. Perform biaxial stretching treatment on the substrate, including transverse stretching and longitudinal stretching, to produce an initial base film; [[ID=X]]

[0008] S3. Use the continuous countercurrent extraction technology to extract the initial base film to obtain an extracted base film;

[0009] S4. Perform hot air circulation shaping treatment on the extracted base film to obtain a shaped base film;

[0010] S5. Use a high-precision slitting device to slit the shaped base film to obtain a finished base film.

[0011] Based on the above technical solutions, preferably, in step S1, the molecular weight distribution index of the polyethylene raw material is 2.0 - 2.5; the plasticizer is dioctyl phthalate; the stabilizer is a hindered phenol stabilizer.

[0012] Based on the above technical solutions, preferably, in step S1, the addition amount of the plasticizer is 3% - 5% of the mass of the polyethylene raw material, and the addition amount of the stabilizer is 0.5% - 1% of the mass of the polyethylene raw material.

[0013] Based on the above technical solutions, preferably, in step S2, the transverse stretching ratio is 3 - 6 times, and the longitudinal stretching ratio is 5 - 8 times.

[0014] Based on the above technical solutions, preferably, in step S3, during the continuous countercurrent extraction process, the extractant concentration is 90% - 95%, the extraction temperature is 40 - 50 °C, and the extraction time is 30 - 45 min.

[0015] Based on the above technical solutions, preferably, in step S4, during the hot air circulation shaping treatment, the hot air temperature is 130 - 150 °C, the hot air velocity is 2 - 3 m / s, and the shaping time is 10 - 15 min.

[0016] Based on the above technical solutions, preferably, the high-precision slitting device includes a slitting machine body, a tension control system and an auxiliary support device. The tension control system includes a tension sensor and an automatic tension adjustment device. The auxiliary support device is arranged in the slitting area. The tension sensor is used to monitor the tension of the shaped base film during the slitting process in real time, and the automatic tension adjustment device is used to adjust the tension of the shaped base film during the slitting process in real time. The change range of the tension of the shaped base film during the slitting process ≤ 0.5 N.

[0017] Based on the above technical solutions, preferably, the slitting machine body includes slitting tools, and the surface roughness of the slitting tools is 0.05 - 0.1 μm.

[0018] On the basis of the above technical solutions, preferably, the rake angle of the slitting tool is 15 - 20°, the clearance angle is 8 - 12°, and the cutting angle is 30 - 35°.

[0019] On the basis of the above technical solutions, preferably, a plurality of auxiliary support devices are arranged in the slitting area along the width direction of the shaped base film, and the auxiliary support devices are in contact with the surface of the shaped base film to support the shaped base film during the slitting process.

[0020] The method for improving the edge collapse and deformation of the base film after slitting of the present invention has the following beneficial effects compared with the prior art:

[0021] (1) The present invention constructs a systematic solution from three dimensions of material formula, process parameters and equipment structure. Through the synergistic effect of various technical elements, the stress distribution in the whole process of base film production is effectively controlled, the edge collapse and deformation problem after base film slitting is significantly improved, and the stability and qualification rate of product quality are improved;

[0022] (2) By using polyethylene raw materials with a narrow molecular weight distribution and optimizing the ratio of plasticizer and stabilizer, a uniform orientation structure is formed at the molecular chain level of the base film, the internal structure uniformity of the base film is improved, and the stress non-uniformity caused by the material itself is reduced, laying a good foundation for the subsequent processing process;

[0023] (3) By establishing a coordinated control system for process parameters of biaxial stretching, continuous countercurrent extraction and hot air circulation shaping, uniform orientation during the stretching process of the base film, uniform desolvation during the extraction process, and uniform stress release during the shaping process are realized, effectively avoiding the stress accumulation and superposition effects in each process, and ensuring the overall mechanical property uniformity of the base film;

[0024] (4) By equipping with a precise tension control system, optimizing the geometric parameters of the slitting tool, and setting multiple-point auxiliary support devices, precise tension control and stable support during the slitting process are realized, reducing the stress fluctuation and disturbance during the slitting process, ensuring the stability of the base film during the slitting process, and effectively preventing the occurrence of edge collapse and deformation. Description of the Drawings

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 It is a flowchart of the method for improving the edge collapse and deformation of the base film after slitting of the present invention;

[0027] Figure 2 Schematic three - dimensional structure diagram of the slitting tool of the present invention;

[0028] Figure 3 Side view of the slitting tool of the present invention. Detailed implementation manners

[0029] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0030] As Figure 1 shown, the present invention provides a method for improving the edge collapse and deformation after the slitting of the base film, including the following steps:

[0031] S1. Mix polyethylene raw material, plasticizer and stabilizer to obtain a mixed raw material, and subject the mixed raw material to melt extrusion to obtain a base sheet;

[0032] S2. Perform biaxial stretching treatment on the base sheet, including transverse stretching and longitudinal stretching, to obtain an initial base film;

[0033] S3. Use continuous counter - current extraction technology to extract the initial base film to obtain an extracted base film;

[0034] S4. Perform hot - air circulation shaping treatment on the extracted base film to obtain a shaped base film;

[0035] S5. Use a slitting device to slit the shaped base film to obtain a finished base film.

[0036] Preferably, in step S1, the molecular weight distribution index (Mw / Mn) of the polyethylene raw material is 2.0 - 2.5; the plasticizer is dioctyl phthalate; the stabilizer is a hindered phenol stabilizer; the addition amount of the plasticizer is 3% - 5% of the mass of the polyethylene raw material, and the addition amount of the stabilizer is 0.5% - 1% of the mass of the polyethylene raw material.

[0037] Furthermore, the temperature of the melt extrusion is 110 - 220 °C. The extrusion time depends on the specific extruder model and screw speed. Usually, the screw speed can be set between 50 - 100 rpm, and the extrusion time can be adjusted according to the production requirements and material characteristics. The present invention does not make further limitations here.

[0038] In the present invention, a polyethylene raw material with a narrower molecular weight distribution is selected. The raw material with a narrow molecular weight distribution can enable the base film to form a more uniform molecular structure during the processing, improve the mechanical properties and dimensional stability of the base film, and reduce the possibility of edge collapse and deformation after slitting. At the same time, the polyethylene raw material is mixed with dioctyl phthalate and a hindered phenol stabilizer. Dioctyl phthalate can effectively reduce the glass transition temperature of the base film, improve the flexibility and processing performance of the base film, and the hindered phenol stabilizer can enhance the antioxidant performance and thermal stability of the base film, reducing the deterioration of the base film performance caused by environmental factors. The synergistic effect of the two can further improve the problem of edge collapse and deformation after slitting.

[0039] Preferably, in step S2, the transverse draw ratio is 4.5 - 5.5 times, and the longitudinal draw ratio is 5 - 6.5 times. Further, the temperature of transverse stretching is 110 - 135 °C, and the temperature of longitudinal stretching is 90 - 120 °C. In the stretching process stage of the wet-process separator base film, according to the material characteristics, thickness and expected mechanical properties of the base film, using high-precision stretching equipment and an automated control system, the longitudinal draw ratio is accurately adjusted to 5 - 8 times, and the transverse draw ratio is set at 3 - 6 times. By controlling the transverse and longitudinal draw ratios, the internal stress distribution of the base film can be made uniform, and the probability of edge collapse and deformation after slitting can be effectively reduced. Further, for a conventional 9UM polyethylene base film, when the longitudinal draw ratio is 6.5 and the transverse draw ratio is 4.5, the probability of edge collapse and deformation after slitting can be reduced more effectively.

[0040] Further, before stretching, it is necessary to measure the thickness of the substrate, and adjust the stretching parameters according to the substrate thickness, as follows:

[0041] Longitudinal stretching

[0042] Stretching temperature: Generally, the temperature of the preheating section can be controlled at 90 - 100 °C, and the temperature of the stretching section is 110 - 120 °C. If the base film is too thick > 1500 μm, the temperature can be appropriately increased to 95 - 100 °C in the preheating section and 115 - 120 °C in the stretching section; if it is too thin < 1400 μm, the temperature is reduced to 90 - 95 °C in the preheating section and 110 - 115 °C in the stretching section. Draw ratio: Generally set at 5 - 6.5 times. If the base film is too thick > 1500 μm, the draw ratio can be increased to 6 - 6.5 times; if the base film is too thin < 1400 μm, the draw ratio is controlled at 5 - 5.5 times. Stretching rate: Generally 3 - 5 m / min. When the base film is thick, it can be appropriately increased to 4 - 5 m / min; when it is thin, it is reduced to 3 - 4 m / min.

[0043] Transverse stretching

[0044] Stretching temperature: The temperature in the preheating section is generally 110 - 120°C, and the temperature in the stretching section is 125 - 135°C. If the base film is relatively thick, >1500μm, the preheating section temperature can be increased to 115 - 120°C, and the stretching section temperature to 130 - 135°C; if it is relatively thin, <1400μm, then the preheating section temperature is 110 - 115°C, and the stretching section temperature is 125 - 130°C. Stretching ratio: Usually 4.5 - 5.5 times. If the base film is relatively thick, >1500μm, the stretching ratio can be adjusted to 5 - 5.5 times; if the base film is thin, <1400μm, then it is 4.5 - 5 times. Stretching rate: Generally 2 - 3m / min. If the base film is thick, >1500μm, it can be increased to 2.5 - 3m / min; if the base film is thin, <1400μm, then it is slowed down to 2 - 2.5m / min.

[0045] During stretching, thickness and stress data are collected at regular intervals. If unevenness is found, the equipment parameters are adjusted in a timely manner. By dynamically adjusting the process parameters of longitudinal and transverse stretching (including temperature, stretching ratio, and rate), combined with the differential control strategy of the base film thickness, the orientation uniformity of molecular chains is effectively optimized, and local stress concentration is avoided. During longitudinal stretching, through the temperature gradient control of the preheating section and the stretching section, the progressive orientation arrangement of polymer chains is ensured, enhancing the mechanical properties; during transverse stretching, the transverse structural density of the base film is improved through the coordinated adjustment of temperature and stretching rate. At the same time, based on the feedback mechanism of real-time thickness and stress data, the uniformity and stability of material deformation during stretching are ensured, significantly reducing the risk of edge collapse deformation caused by the release of residual stress after slitting, and the overall process adaptability is stronger.

[0046] Preferably, in step S3, during the continuous countercurrent extraction process, the extractant is dichloromethane, its concentration is 90% - 95%, the extraction temperature is 40 - 50°C, and the extraction time is 30 - 45min. The present invention adopts the continuous countercurrent extraction technology to improve the extraction efficiency and uniformity, reasonably control the concentration, temperature, and extraction time of the extractant, maintain the extractant concentration at 90% - 95%, control the temperature at 40 - 50°C, and set the extraction time to 30 - 45min, which can ensure that the solvent (i.e., dichloromethane) in the base film is fully and evenly extracted, avoiding internal stress concentration caused by solvent residue, thereby reducing edge collapse deformation. Further, during continuous countercurrent extraction, the concentration and temperature of the extractant are monitored in real time. When the concentration is low, it is automatically added, and when the temperature deviates, it is adjusted in a timely manner. The solvent residue amount in the base film is regularly detected. If it exceeds the standard (<99.9%), the extraction time or stage number is adjusted.

[0047] Preferably, in step S4, during the hot air circulation setting process, the hot air temperature is 130 - 150 °C, the hot air velocity is 2 - 3 m / s, and the setting time is 10 - 15 min. In the setting stage, the hot air circulation setting technology is used to precisely control the hot air temperature, velocity, and setting time. The hot air temperature is set at 130 - 150 °C, the velocity is controlled at 2 - 3 m / s, and the setting time is 10 - 15 min, so that the base film is fully set in a stable thermal environment, the internal residual stress is eliminated, and the dimensional stability of the base film is enhanced. Further, an intelligent control system is used to precisely control the hot air temperature and velocity. During setting, the base film is monitored by an on-line flatness detection device, and the setting time or hot air distribution is adjusted in a timely manner when unevenness occurs.

[0048] The slitting of the present invention can be achieved by a high-precision slitting device as follows. The high-precision slitting device includes a slitting machine body, a tension control system, and an auxiliary support device. The slitting machine body includes a servo control system and a slitting tool. The servo control system is used to intelligently control the slitting position of the slitting tool. Through intelligent control, the position accuracy of the slitting tool can be ensured to reach ±0.01 mm, and the straightness error during the operation of the cutting tool is controlled within ±0.005 mm. The slitting tool is made of tungsten-cobalt alloy material, and the tool edge has been processed by ultra-precision grinding, and the surface roughness reaches 0.05 - 0.1 μm. The tool edge is sharp and wear-resistant. As Figures 2-3 shown, Figure 2 shows a three-dimensional structure diagram of the slitting tool, Figure 3 shows a side view in the thickness direction of the slitting tool. The rake angle of the slitting tool is 15 - 20°, the clearance angle is 8 - 12°, and the cutting angle is 30 - 35°. By using the above slitting tool, the impact force and friction force of the tool on the base film during slitting can be reduced, and the risk of edge collapse and deformation of the base film caused by uneven stress can be lowered.

[0049] Further, the tension control system includes a tension sensor and an automatic tension adjustment device. The auxiliary support device is arranged in the slitting area. The tension sensor is signal-connected to the unwinding, winding, and traction systems of the slitting machine, and is used to monitor the tension of the set base film during slitting in real time. The automatic tension adjustment device is used to adjust the tension of the set base film during slitting in real time according to the tension value monitored by the tension sensor, so as to ensure that the change range of the tension of the set base film during slitting ≤ 0.5 N, and ensure uniform stress on the base film during slitting.

[0050] Further, the auxiliary support device is arranged in the slitting area of the slitter. A plurality of auxiliary support rollers with adjustable heights are arranged along the width direction of the shaped base film. The surface of the support roller is made of a rubber material with high elasticity and low friction coefficient, and its hardness is Shore A60 - 70. During the slitting process, according to the thickness and material characteristics of the base film, the height of the auxiliary support roller is precisely adjusted to make it in close contact with the surface of the base film, providing uniform support force for the base film and preventing the base film from collapsing and deforming due to local suspension during slitting.

[0051] To further illustrate the present invention, the following is a detailed description of a method for improving the edge collapse deformation of the base film provided by the present invention in combination with embodiments.

[0052] All reagents used in the following embodiments are commercially available. Among them, the polyethylene raw material is from Daelim Petrochemical and is of the 9UM model.

[0053] Example 1

[0054] This embodiment provides a method for improving the edge collapse deformation of the base film, including the following steps:

[0055] S1. Mix 40 kg of polyethylene raw material with a molecular weight distribution index of 2.3, 1.6 kg of dioctyl phthalate, and 0.3 kg of antioxidant 1010 to obtain a mixed raw material. The mixed raw material is melt-extruded at a temperature of 110 - 220 °C to produce a base film with a thickness of 1450 μm.

[0056] S2. Perform biaxial stretching treatment on the base film, including transverse stretching and longitudinal stretching. Among them, the preheating section temperature of the transverse stretching is set at 115 °C, the stretching section temperature is 130 °C, the stretching ratio is 4.5 times, and the stretching rate is 2.5 m / min; the preheating section temperature of the longitudinal stretching can be controlled at 95 °C, the stretching section temperature is 115 °C, the stretching ratio is 6.5 times, and the stretching rate is 4 m / min to produce an initial base film. During stretching, thickness and stress data are collected every 10 - 15 s. If unevenness is found, the equipment parameters are adjusted in a timely manner.

[0057] S3. Use the continuous countercurrent extraction technology to extract the initial base film. During the extraction process, the extractant is [extractant name], the extractant concentration is 93%, the extraction temperature is 45 °C, and the extraction time is 38 min to obtain the extracted base film. During extraction, the extractant concentration and temperature are monitored in real time, and the deviation of the extractant temperature is controlled not to exceed ±2 °C, and the deviation of the extraction concentration is not to exceed ±2%.

[0058] S4. Perform hot air circulation shaping treatment on the extracted base film, where the hot air temperature is 140 °C, the hot air velocity is 2.5 m / s, and the shaping time is 13 min to obtain the shaped base film.

[0059] S5. Use a high-precision slitting device to slit the shaped base film to obtain the finished base film.

[0060] Example 2

[0061] This example provides a method for improving the edge collapse and deformation after slitting of a base film, including the following steps:

[0062] S1. Mix 40 kg of polyethylene raw material with a molecular weight distribution index of 2.0, 1.2 kg of dioctyl phthalate, and 0.2 kg of antioxidant 1010 to obtain a mixed raw material. Extrude the mixed raw material through melting, and the melting extrusion temperature is 110 - 220 °C to produce a base film with a thickness of 1300 μm.

[0063] S2. Perform biaxial stretching on the base film, including transverse stretching and longitudinal stretching. Set the preheating section of transverse stretching at 110 °C, the stretching section at 125 °C, the stretching ratio at 4.5 times, and the stretching rate at 2 m / min; set the preheating section of longitudinal stretching at 90 °C, the stretching section at 110 °C, the stretching ratio at 5 times, and the stretching rate at 3 m / min to produce an initial base film. During stretching, collect thickness and stress data every 10 - 15 s. If unevenness is found, adjust the equipment parameters in a timely manner.

[0064] S3. Use the continuous countercurrent extraction technology to extract the initial base film. During the extraction process, the extractant is [extractant name], the extractant concentration is 90%, the extraction temperature is 40 °C, and the extraction time is 45 min to obtain the extracted base film. During extraction, monitor the extractant concentration and temperature in real time, and control the deviation of the extractant temperature not to exceed ±2 °C and the deviation of the extraction concentration not to exceed ±2%.

[0065] S4. Perform hot air circulation shaping on the extracted base film, where the hot air temperature is 130 °C, the hot air velocity is 2 m / s, and the shaping time is 15 min to obtain the shaped base film.

[0066] S5. Use a high-precision slitting device to slit the shaped base film to obtain the finished base film.

[0067] Example 3

[0068] This example provides a method for improving the edge collapse and deformation after slitting of a base film, including the following steps:

[0069] S1. Mix 40 kg of polyethylene raw material with a molecular weight distribution index of 2.5, 2 kg of dioctyl phthalate, and 0.4 kg of antioxidant 1010 to obtain a mixed raw material. Extrude the mixed raw material through melting, and the melting extrusion temperature is 110 - 220 °C to produce a base film with a thickness of 1600 μm.

[0070] S2. Perform biaxial stretching on the substrate, including transverse stretching and longitudinal stretching. Set the preheating section temperature for transverse stretching at 120°C, the stretching section temperature at 135°C, the stretching ratio at 5.5 times, and the stretching rate at 3 m / min. For longitudinal stretching, set the preheating section temperature at 100°C, the stretching section temperature at 120°C, the stretching ratio at 6.5 times, and the stretching rate at 5 m / min to obtain the initial base film. During stretching, collect thickness and stress data every 10 - 15 s. If unevenness is found, adjust the equipment parameters in a timely manner;

[0071] S3. Use the continuous countercurrent extraction technique to extract the initial base film. During the extraction process, the extractant is [extractant name], the extractant concentration is 95%, the extraction temperature is 50°C, and the extraction time is 30 min to obtain the extracted base film. During extraction, monitor the extractant concentration and temperature in real time, and control the extractant temperature deviation not to exceed ±2°C and the extraction concentration deviation not to exceed ±2%;

[0072] S4. Perform hot air circulation shaping on the extracted base film, where the hot air temperature is 150°C, the hot air velocity is 3 m / s, and the shaping time is 10 min to obtain the shaped base film;

[0073] S5. Use a high-precision slitting equipment to slit the shaped base film to obtain the finished base film.

[0074] Comparative Example 1

[0075] This comparative example provides a method for improving the edge collapse and deformation after slitting of the base film. The difference from Example 1 is that polyethylene raw materials with a relatively wide molecular weight distribution are used, including the following steps:

[0076] S1. Mix 40 kg of polyethylene raw materials with a molecular weight distribution index of 3, 1.6 kg of dioctyl phthalate, and 0.3 kg of antioxidant 1010 to obtain a mixed raw material. Extrude the mixed raw material through melting to obtain a substrate;

[0077] Steps S2 - S5 are the same as those in Example 1.

[0078] Comparative Example 2

[0079] This comparative example provides a method for improving the edge collapse and deformation after slitting of the base film. The difference from Example 1 is that continuous countercurrent extraction is not used, including the following steps:

[0080] S1 - S2 are the same as those in Example 1;

[0081] S3. Use the conventional extraction technique: Extract the initial base film. During the extraction process, the extractant is dichloromethane, the extractant concentration is 85%, the extraction temperature is 35°C, and the extraction time is 50 min to obtain the extracted base film. During extraction, monitor the extractant concentration and temperature in real time, and control the extractant temperature deviation not to exceed ±2°C and the extraction concentration deviation not to exceed ±2%;

[0082] S4. Perform hot air circulation setting on the extracted base film, where the hot air temperature is 140 °C, the hot air velocity is 2.5 m / s, and the setting time is 13 min to obtain the set base film;

[0083] S5. Use a high-precision slitting equipment to slit the set base film to obtain the finished base film.

[0084] Comparative Example 3

[0085] This comparative example provides a method for improving the edge collapse and deformation after slitting of the base film. The difference from Example 1 is that a high-precision slitting equipment is not used, and it includes the following steps:

[0086] S1 - S4 are the same as those in Example 1;

[0087] S5. Use a conventional slitting equipment to slit the set base film to obtain the finished base film.

[0088] Comparative Example 4

[0089] This comparative example provides a method for improving the edge collapse and deformation after slitting of the base film. The difference from Example 1 is that conventional slitting tools are used, and it includes the following steps:

[0090] S1 - S4 are the same as those in Example 1;

[0091] S5. Use a high-precision slitting equipment to slit the set base film, but the slitting tool in the high-precision slitting equipment is a conventional slitting tool to obtain the finished base film. The length of the conventional slitting tool is generally 50 mm - 150 mm, the width is 9 mm - 18 mm, and the thickness is 0.4 - 0.6 mm. The material is high-carbon steel or stainless steel. The hardness of the high-carbon steel blade is usually between HRC58 - 62, and the hardness of the stainless steel blade is generally about HRC52 - 56.

[0092] Performance Detection

[0093] Take the finished base films of the examples and comparative examples, and detect the edge warpage degree of the base film (i.e., the maximum deviation distance between the edge of the base film and the standard plane) and the thickness uniformity (use a precision thickness gauge to measure at multiple points in the edge area and calculate the average value of the thickness deviation at the edge). Measure the edge collapse and deformation of the base film through the edge warpage degree and thickness uniformity. The detection results are shown in Table 1.

[0094] Table 1 Edge Collapse and Deformation of the Base Film

[0095] Edge warpage degree (μm) Thickness uniformity (μm) Example 1 3 1.2 Example 2 5 1.8 Example 3 4 1.5 Comparative Example 1 15 2.0 Comparative Example 2 13 3.0 Comparative Example 3 18 3.5 Comparative Example 4 12 4.0

[0096] As can be seen from Table 1, the technical solution of the example of the present invention can greatly reduce the edge collapse and deformation after slitting of the base film.

[0097] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for improving the edge collapse and deformation after slitting of a base film, characterized in that: It includes the following steps: S1. Mix the polyethylene raw material, plasticizer and stabilizer to obtain a mixed raw material, and subject the mixed raw material to melt extrusion to prepare a substrate; S2. Perform biaxial stretching treatment on the substrate, including transverse stretching and longitudinal stretching, to prepare an initial base film; S3. Use the continuous countercurrent extraction technology to extract the initial base film to obtain an extracted base film; S4. Perform hot air circulation shaping treatment on the extracted base film to obtain a shaped base film; S5. Use a high-precision slitting device to slit the shaped base film to obtain a finished base film.

2. The method for improving the edge collapse and deformation after slitting of the base film according to claim 1, wherein: In step S1, the molecular weight distribution index of the polyethylene raw material is 2.0 - 2.5; the plasticizer is dioctyl phthalate; the stabilizer is a hindered phenol stabilizer.

3. A method for improving the edge collapse and deformation after slitting of a base film as claimed in claim 1, characterized in that: In step S1, the addition amount of the plasticizer is 3% - 5% of the mass of the polyethylene raw material, and the addition amount of the stabilizer is 0.5% - 1% of the mass of the polyethylene raw material.

4. A method for improving the edge collapse and deformation after slitting of the base film according to claim 1, characterized in that: In step S2, the transverse stretching ratio is 4.5 - 5.5 times, and the longitudinal stretching ratio is 5 - 6.5 times.

5. A method for improving the edge collapse and deformation after slitting of the base film according to claim 1, characterized in that: In step S3, during the continuous countercurrent extraction process, the extractant concentration is 90% - 95%, the extraction temperature is 40 - 50 °C, and the extraction time is 30 - 45 min.

6. A method for improving the edge collapse and deformation after slitting of a base film according to claim 1, characterized in that: In step S4, during the hot air circulation shaping treatment, the hot air temperature is 130 - 150 °C, the hot air velocity is 2 - 3 m / s, and the shaping time is 10 - 15 min.

7. A method for improving the edge collapse and deformation after slitting of the base film according to claim 1, characterized in that: In step S5, the high-precision slitting device includes a slitting machine body, a tension control system and an auxiliary support device. The tension control system includes a tension sensor and an automatic tension adjustment device. The auxiliary support device is arranged in the slitting area. The tension sensor is used to monitor the tension of the shaped base film during the slitting process in real time, and the automatic tension adjustment device is used to adjust the tension of the shaped base film during the slitting process in real time. The change range of the tension of the shaped base film during the slitting process ≤ 0.5 N.

8. A method for improving the edge collapse and deformation after slitting of the base film according to claim 7, characterized in that: The slitting machine body includes slitting tools, and the surface roughness of the slitting tools is 0.05 - 0.1 μm.

9. A method for improving the edge collapse and deformation after slitting of the base film according to claim 8, characterized in that: The rake angle of the slitting tool is 15 - 20 °, the clearance angle is 8 - 12 °, and the cutting angle is 30 - 35 °.

10. A method for improving the edge collapse and deformation after slitting of a base film according to claim 7, characterized in that: A plurality of the auxiliary support devices are arranged in the slitting area along the width direction of the shaped base film. The auxiliary support device is in contact with the surface of the shaped base film and is used to support the shaped base film during the slitting process.

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