Polypropylene-based ultrathin special film and preparation method thereof

Abstract

The invention relates to the field of special films, in particular to a polypropylene-based ultrathin special film and a preparation method thereof. The film is prepared from the following components in parts by weight: 80 to 90 parts of isotactic polypropylene resin, 10 to 20 parts of syndiotactic polypropylene resin, 5 to 10 parts of a composite modifier, 5 to 10 parts of a compatilizer, 3 to 8 parts of amino modified nano silicon dioxide, 0.1 to 0.5 part of an antioxidant, 0.3 to 0.7 part of a lubricant, 0.1 to 0.3 part of an anti-hydrolysis agent, 0.1 to 0.3 part of a nucleating agent and 0.05 to 0.3 part of a light stabilizer. The special film prepared by the preparation method disclosed by the invention can still keep excellent mechanical bearing capacity under the ultrathin specification with the thickness of less than or equal to 20 microns, and the mechanical property, the flame retardant property, the weather resistance, the processability and the interfacial compatibility are synergistically improved.

Description

Technical Field

[0001] This invention relates to the field of special films, specifically to a polypropylene-based ultrathin special film and its preparation method. Background Technology

[0002] With the rapid development of flexible electronics, wearable devices, biomedical sensing, and high-end display packaging, the demand for high-performance, ultra-thin, and lightweight polymer films is becoming increasingly urgent. Polypropylene (PP), as a thermoplastic resin with excellent comprehensive properties, has advantages such as low density, good chemical stability, excellent dielectric properties, and strong processing adaptability, making it one of the ideal substrates for preparing ultra-thin functional films.

[0003] However, conventional polypropylene faces a series of technical bottlenecks in the process of ultrathinning (thickness ≤20μm): (1) Ultrathinning leads to a sharp decrease in mechanical strength: When the film thickness is reduced to below 20μm, the orientation and crystallization behavior of polypropylene molecular chains change significantly, the film layer load-bearing capacity is weakened, and it is difficult to meet the mechanical requirements of flexible devices under tension or external impact; (2) Surface functionalization is difficult: Polypropylene molecular chains are non-polar structures with low surface energy, making it difficult to directly perform chemical modification, patterning processing or form a stable bond with functional layers, which limits its application in multifunctional integrated films; (3) Insufficient environmental stability: Ultrathin PP films are prone to aging, embrittlement or dimensional deformation in humid and hot environments, affecting the long-term reliability of devices in complex environments.

[0004] Currently, there are some polypropylene films on the market modified through blending, filling, or surface treatment, but they often struggle to balance ultrathinness and high performance: adding traditional inorganic fillers can improve mechanical properties, but it leads to decreased film transparency and loss of flexibility; introducing small molecule additives can easily migrate and precipitate, affecting the long-term stability of the film. In addition, existing modification methods mostly focus on improving a single property, such as reinforcement, toughening, or flame retardancy, lacking a systematic functional design for ultrathin films in various scenarios such as flexible electronics and environmental resistance.

[0005] Therefore, there is an urgent need to develop a new type of polypropylene-based ultrathin special film that, while achieving ultrathin thickness, also possesses functional properties such as high mechanical strength, excellent surface modifiability, and environmental stability, in order to promote its innovative application in high-end flexible electronics and integrated devices. Summary of the Invention

[0006] To address the problems existing in the prior art, the purpose of this invention is to provide a polypropylene-based ultrathin special film and its preparation method.

[0007] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides a polypropylene-based ultrathin special film, comprising, by weight parts: 80-90 parts isotactic polypropylene resin, 10-20 parts syndiotactic polypropylene resin, 5-10 parts composite modifier, 5-10 parts compatibilizer, 3-8 parts amino-modified nano silica, 0.1-0.5 parts antioxidant, 0.3-0.7 parts lubricant, 0.1-0.3 parts anti-hydrolysis agent, 0.1-0.3 parts nucleating agent, and 0.05-0.3 parts light stabilizer.

[0008] Preferably, the density of the isotactic polypropylene resin is 0.908-0.912 g / cm³. 3 Melting point ≥165℃, melt index (230℃, 2.16kg) is 1-6g / 10min.

[0009] Preferably, the density of the syndiotactic polypropylene resin is 0.889-0.895 g / cm³. 3 Melting point ≥145℃, melt index (230℃, 2.16kg) is 2-8g / 10min.

[0010] Preferably, the preparation method of the composite modifier includes: S1. Nitrogen gas is introduced into the reaction vessel, and N,N'-di(3-isocyanate-4-methylphenyl)urea and N,N-dimethylformamide are added. After stirring and heating to 65-75℃ to dissolve, the catalyst is added and stirred evenly. 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is dissolved in N,N-dimethylformamide and slowly added dropwise to the reaction vessel. After the addition is complete, the temperature is raised to 80-90℃, and the reaction is stirred and kept at this temperature for 3-5 hours to obtain the DMMU-DOPO reaction solution. S2. Dissolve aminopropylheptaisobutylsilsesquioxane in N,N-dimethylformamide and slowly add it dropwise to the DMMU-DOPO reaction solution. Maintain the temperature at 80-90°C during the dropwise addition process. After the dropwise addition is completed, raise the temperature to 100-110°C and keep the temperature for 4-6 hours. After the reaction is completed, the mixture is subjected to precipitation, filtration, washing, vacuum drying, pulverization and sieving to obtain the composite modifier.

[0011] Preferably, the mass ratio of N,N'-bis(3-isocyanate-4-methylphenyl)urea, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and aminopropylheptaisobutylsilsesquioxane is 8-12:5.5-7.5:8-12.

[0012] Preferably, the mass ratio of N,N'-bis(3-isocyanate-4-methylphenyl)urea, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and aminopropylheptaisobutylsilsesquioxane is 10:6.7:10.1.

[0013] Preferably, the compatibilizer is maleic anhydride-grafted polypropylene (PP-g-MAH) with a grafting rate of 0.8-1.2% and a melt index of 3-8 g / 10 min at 230°C and 2.16 kg.

[0014] Preferably, the preparation method of the amino-modified nano-silica includes: Nano-silica was added to a mixture of anhydrous ethanol and deionized water and dispersed evenly at room temperature to obtain a dispersion. γ-aminopropyltriethoxysilane was mixed with anhydrous ethanol and added dropwise to the dispersion. The reaction system was heated to reflux and reacted. After the reaction was completed, it was naturally cooled to room temperature, and the precipitate was collected by centrifugation. After washing and drying, amino-modified nano-silica was obtained.

[0015] Preferably, the antioxidant is a compound of a primary antioxidant and a secondary antioxidant in a mass ratio of 3:1; wherein the primary antioxidant is antioxidant 1010 and the secondary antioxidant is antioxidant DLTP.

[0016] Preferably, the lubricant is a mixture of zinc stearate and polyethylene wax in a mass ratio of 2:1.

[0017] Preferably, the anti-hydrolysis agent is polycarbodiimide.

[0018] Preferably, the nucleating agent is sodium benzoate.

[0019] Preferably, the light stabilizer is one or a mixture of light stabilizers TH-944, HS-770, and HS-292.

[0020] More preferably, the light stabilizer is a mixture of high molecular weight TH-944 and low molecular weight HS-770 in a mass ratio of 2:1.

[0021] Secondly, the present invention provides a method for preparing a polypropylene-based ultrathin special film, comprising the following steps: Step 1: After drying the raw materials, weigh and mix isotactic polypropylene resin, syndiotactic polypropylene resin, and compatibilizer to obtain the matrix mixture; mix antioxidant, lubricant, light stabilizer, anti-hydrolysis agent, and nucleating agent to obtain the additive mixture. Step 2: Add composite modifier and amino-modified nano-silica to the matrix mixture, mix evenly, then add auxiliary agent mixture and continue mixing to obtain a uniform premix. Step 3: The premixed material is fed into a twin-screw extruder and extruded and granulated to obtain modified polypropylene masterbatch. Step 4: The modified polypropylene masterbatch is processed by a single-screw extrusion casting film machine. After melting, casting, and shaping, a polypropylene-based ultrathin special film is prepared.

[0022] The beneficial effects of this invention are as follows: 1. The polypropylene-based ultrathin special film of the present invention uses isotactic polypropylene and syndiotactic polypropylene as a composite matrix, relying on the high crystallinity rigidity of isotactic polypropylene and the flexibility of syndiotactic polypropylene to form a synergistic effect; the composite modifier, combined with the interfacial strengthening effect of amino-modified nano-silica, significantly improves the stability of the film. The special film prepared by the present invention can still maintain excellent mechanical load-bearing capacity at ultrathin specifications with a thickness ≤20μm, and achieves a synergistic improvement in mechanical properties, flame retardancy, weather resistance, processing performance and interfacial compatibility.

[0023] 2. This invention uses amino-modified nano-silica as a filler, which is uniformly dispersed around the matrix and modifier. The surface amino groups form hydrogen bonds and chemical bonds with the matrix or modifier, which enhances the interfacial interaction and structural density. The overall structure is dense and the interfacial bonding is strong, ensuring the performance stability of the film in the ultra-thin state.

[0024] 3. The composite modifier of this invention is prepared through a two-step reaction. First, the PH bond of DOPO undergoes an addition reaction with the -NCO group of DMMU to generate an intermediate containing a phosphorus-urea group. Second, the -NH2 in POSS undergoes a condensation reaction with the unreacted -NCO group in the intermediate to generate a urea bond. This achieves covalent bonding between N,N'-bis(3-isocyano-4-methylphenyl)urea (DMMU), DOPO, and POSS, forming an organic-inorganic hybrid structure. The framework of this hybrid structure is the cage-like siloxane of POSS, with aromatic groups and phosphorus-phenanthroline rings connected by urea bonds, possessing both the rigidity of the inorganic phase and the compatibility of the organic phase.

[0025] 4. The composite modifier of this invention integrates the nano-reinforcing function of POSS, the high-efficiency flame-retardant function of DOPO, and the urea-based interface-modifying function of DMMU into one, which reduces the amount of additives used and avoids the antagonistic effects between different modifiers. Among them, cage-like POSS improves mechanical strength, DOPO provides flame retardant properties, and urea groups improve compatibility with polypropylene matrix and nanofillers, achieving synergistic optimization of multiple functions and significantly improving the overall performance of the film.

[0026] 5. The special film of the present invention has multiple advantages such as ultra-thinness, high strength, flame retardancy, and weather resistance, overcoming the limitation of the single function of traditional polypropylene film. It can be widely used in special fields such as electronic component packaging, new energy battery separator substrate, high-end product packaging, and outdoor advertising substrate. Compared with polypropylene film in the prior art, it has stronger market competitiveness and application value. Detailed Implementation

[0027] The technical solution of the present invention is illustrated below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or defining the scope of the present invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the present invention.

[0028] To better understand the above technical solutions, exemplary embodiments of the present invention are described in more detail below. While exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0029] The present invention will be further described below with reference to the following embodiments.

[0030] A polypropylene-based ultrathin special film, comprising, by weight parts: 85 parts isotactic polypropylene resin, 15 parts syndiotactic polypropylene resin, 8 parts composite modifier, 7 parts compatibilizer, 5 parts amino-modified nano silica, 0.3 parts antioxidant, 0.5 parts lubricant, 0.2 parts anti-hydrolysis agent, 0.2 parts nucleating agent and 0.15 parts light stabilizer.

[0031] The density of isotactic polypropylene resin is 0.910 g / cm³. 3 Melting point ≥165℃, melt index (230℃, 2.16kg) 3.5g / 10min; density of syndiotactic polypropylene resin 0.891g / cm³ 3 Melting point ≥145℃, melt index (230℃, 2.16kg) is 5g / 10min; maleic anhydride grafted polypropylene (PP-g-MAH), grafting rate 1.0%, melt index (230℃, 2.16kg) 5.5g / 10min; antioxidant is antioxidant 1010 and DLTP compounded in a mass ratio of 3:1; lubricant is zinc stearate and polyethylene wax compounded in a mass ratio of 2:1; anti-hydrolysis agent is polycarbodiimide; nucleating agent is sodium benzoate; light stabilizer is TH-944 and HS-770 compounded in a mass ratio of 2:1.

[0032] The preparation methods of the composite modifier include: S1. Take a 100mL three-necked flask, assemble a condenser, nitrogen delivery tube, constant pressure dropping funnel, and thermometer. Purge high-purity nitrogen into the flask, add 10.00g N,N'-bis(3-isocyanate-4-methylphenyl)urea (DMMU) and 50mL N,N-dimethylformamide, and heat to 70℃ with stirring. After complete dissolution, add 0.08g of catalyst dibutyltin dilaurate (0.8% of the mass of DMMU) and stir evenly. Dissolve 6.70g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) in 20mL N,N-dimethylformamide, and slowly add it dropwise to the flask through the constant pressure dropping funnel at a rate of 1-2 drops / second. After the addition is complete, heat to 85℃, stir vigorously at a speed of 600r / min, and maintain the temperature for 4h to obtain the DMMU-DOPO reaction solution. S2. Dissolve 10.10 g of aminopropyl heptaisobutylsilsesquioxane (APTES-POSS) in 30 mL of N,N-dimethylformamide and sonicate for 15 min. Slowly add the dispersion dropwise to the DMMU-DOPO reaction solution at a rate of 1 drop / second. Maintain the temperature at 85°C and increase the stirring speed to 800 r / min during the addition process. After the addition is complete, raise the temperature to 105°C and maintain the temperature for 5 h. S3. After the reaction is complete, slowly pour the reaction solution into 4 times the volume of ice-cold ethanol and stir vigorously for 30 minutes to precipitate a light yellow solid precipitate. Filter the precipitate using a Buchner funnel, collect the precipitate, wash it 3 times with anhydrous ethanol, place the precipitate in a vacuum drying oven, and dry it at 100°C under vacuum for 12 hours. After drying, the product is pulverized by a high-speed pulverizer and passed through a 600-mesh sieve to obtain a white powdery composite modifier.

[0033] The preparation methods for amino-modified nano-silica include: 5g of nano-silica (particle size 20-30nm) was added to a three-necked flask containing 200mL of anhydrous ethanol and 20mL of deionized water and dispersed evenly at room temperature to obtain a SiO2 dispersion. 1.2g of γ-aminopropyltriethoxysilane (APTES) was mixed with 20mL of anhydrous ethanol and added dropwise to the SiO2 dispersion. The reaction system was heated to 70℃ and refluxed for 8h. After the reaction was completed, heating was stopped, and the mixture was allowed to cool naturally to room temperature. The precipitate was collected by centrifugation, washed with water 3-4 times, and dried at 70℃ for 12h to obtain amino-modified nano-silica.

[0034] The preparation method of the above-mentioned polypropylene-based ultrathin special film includes the following steps: Step 1: Place all raw materials in an 80℃ vacuum drying oven and dry for 4 hours (moisture content controlled ≤0.04%). Weigh isotactic polypropylene resin, syndiotactic polypropylene resin, and compatibilizer and add them to the first high-speed mixer. Set the speed to 500 r / min and mix at room temperature for 5 minutes to obtain a uniform matrix mixture. Add antioxidant, lubricant, light stabilizer, anti-hydrolysis agent, and nucleating agent to the second high-speed mixer. Mix at 500 r / min and room temperature for 5 minutes to obtain an additive mixture. Step 2: Add composite modifier and amino-modified nano-silica to the matrix mixture, increase the mixer speed to 800 r / min, mix at room temperature for 10 min, then add the additive mixture, reduce the speed to 300 r / min, and continue mixing for 3 min. During this period, observe that there is no obvious agglomeration, and a uniformly dispersed premix is ​​obtained. Step 3: Feed the premixed material into a twin-screw extruder (screw length-to-diameter ratio L / D=44), set the temperatures of each zone as follows: Zone 1 170℃, Zone 2 185℃, Zone 3 195℃, Zone 4 205℃, Zone 5 210℃, Zone 6 210℃, die temperature 215℃, screw speed 280r / min, feed rate 35kg / h. After extrusion, water cooling, and pelletizing, modified polypropylene masterbatch is obtained. The masterbatch particle size is controlled at 2-3mm, and the moisture content is ≤0.04%. Step 4: The modified polypropylene masterbatch was dried again in an 80℃ vacuum drying oven for 3 hours, and then fed into a single-screw extrusion casting film machine (screw length-to-diameter ratio L / D=32). The temperatures of each zone were set as follows: zone 1 180℃, zone 2 195℃, zone 3 205℃, zone 4 210℃, and the die temperature was 215℃; the cooling roller temperature was 38℃, the screw speed was 100r / min, the traction rate was 35m / min, and the traction ratio was 1.8. After melting, casting, shaping, and winding, a polypropylene-based ultrathin current collector film was prepared with a final film thickness of 10.2μm.

[0035] Example 2 A polypropylene-based ultrathin special film, comprising, by weight parts: 80 parts isotactic polypropylene resin, 10 parts syndiotactic polypropylene resin, 5 parts composite modifier, 5 parts compatibilizer, 3 parts amino-modified nano silica, 0.1 parts antioxidant, 0.3 parts lubricant, 0.1 parts anti-hydrolysis agent, 0.1 parts nucleating agent and 0.05 parts light stabilizer.

[0036] The density of isotactic polypropylene resin is 0.910 g / cm³. 3 Melting point ≥165℃, melt index (230℃, 2.16kg) 3.5g / 10min; density of syndiotactic polypropylene resin 0.891g / cm³ 3Melting point ≥145℃, melt index (230℃, 2.16kg) is 5g / 10min; maleic anhydride grafted polypropylene (PP-g-MAH), grafting rate 1.0%, melt index (230℃, 2.16kg) 5.5g / 10min; antioxidant is antioxidant 1010 and DLTP compounded in a mass ratio of 3:1; lubricant is zinc stearate and polyethylene wax compounded in a mass ratio of 2:1; anti-hydrolysis agent is polycarbodiimide; nucleating agent is sodium benzoate; light stabilizer is TH-944.

[0037] The preparation methods of the composite modifier and amino-modified nano-silica are the same as in Example 1.

[0038] The preparation method of the above-mentioned polypropylene-based ultrathin special film includes the following steps: Step 1: Place all raw materials in a 75℃ vacuum drying oven and dry for 5 hours. Weigh isotactic polypropylene resin, syndiotactic polypropylene resin, and compatibilizer and add them to the first high-speed mixer. Set the speed to 500 r / min and mix at room temperature for 5 minutes to obtain a uniform matrix mixture. Add antioxidant, lubricant, light stabilizer, anti-hydrolysis agent, and nucleating agent to the second high-speed mixer. Mix at 500 r / min and room temperature for 5 minutes to obtain an additive mixture. Step 2: Add composite modifier and amino-modified nano-silica to the matrix mixture, increase the mixer speed to 800 r / min, mix at room temperature for 10 min, then add the additive mixture, reduce the speed to 300 r / min, and continue mixing for 3 min to obtain a premix that is free of agglomeration and uniformly dispersed; Step 3: Feed the premixed material into a twin-screw extruder (screw length-to-diameter ratio L / D=44), set the temperature of each zone as follows: zone 1 165℃, zone 2 180℃, zone 3 190℃, zone 4 200℃, zone 5 205℃, zone 6 205℃, die temperature 210℃, screw speed 250r / min, feed rate 30kg / h, and after extrusion, water cooling, and pelleting, obtain modified polypropylene masterbatch. The masterbatch particle size is controlled at 2-3mm. Step 4: The modified polypropylene masterbatch is dried again in a vacuum drying oven at 75℃ for 3 hours, and then fed into a single-screw extrusion casting film machine (screw length-to-diameter ratio L / D=32). The temperatures of each zone are set as follows: zone 1 175℃, zone 2 190℃, zone 3 200℃, zone 4 205℃, die temperature 210℃, cooling roller temperature 35℃, screw speed 90r / min, traction speed 30m / min, traction ratio 1.6. After melting, casting, shaping, and winding, a polypropylene-based ultrathin current collector film is prepared.

[0039] Example 3 A polypropylene-based ultrathin special film, comprising, by weight parts: 90 parts isotactic polypropylene resin, 20 parts syndiotactic polypropylene resin, 10 parts composite modifier, 10 parts compatibilizer, 8 parts amino-modified nano silica, 0.5 parts antioxidant, 0.7 parts lubricant, 0.3 parts anti-hydrolysis agent, 0.3 parts nucleating agent and 0.3 parts light stabilizer.

[0040] The density of isotactic polypropylene resin is 0.910 g / cm³. 3 Melting point ≥165℃, melt index (230℃, 2.16kg) 3.5g / 10min; density of syndiotactic polypropylene resin 0.891g / cm³ 3 Melting point ≥145℃, melt index (230℃, 2.16kg) is 5g / 10min; maleic anhydride grafted polypropylene (PP-g-MAH), grafting rate 1.0%, melt index (230℃, 2.16kg) 5.5g / 10min; antioxidant is antioxidant 1010 and DLTP compounded in a mass ratio of 3:1; lubricant is zinc stearate and polyethylene wax compounded in a mass ratio of 2:1; anti-hydrolysis agent is polycarbodiimide; nucleating agent is sodium benzoate; light stabilizer is TH-944, HS-770 and HS-292 compounded in a mass ratio of 2:1:1.

[0041] The preparation methods of the composite modifier and amino-modified nano-silica are the same as in Example 1.

[0042] The preparation method of the above-mentioned polypropylene-based ultrathin special film includes the following steps: Step 1: Place all raw materials in an 85℃ vacuum drying oven and dry for 4 hours (moisture content controlled ≤0.03%). Weigh isotactic polypropylene resin, syndiotactic polypropylene resin, and compatibilizer and add them to the first high-speed mixer. Set the speed to 500 r / min and mix at room temperature for 5 minutes to obtain a uniform matrix mixture. Add antioxidant, lubricant, light stabilizer, anti-hydrolysis agent, and nucleating agent to the second high-speed mixer. Mix at 500 r / min and room temperature for 5 minutes to obtain an additive mixture. Step 2: Add composite modifier and amino-modified nano-silica to the matrix mixture, increase the mixer speed to 800 r / min, mix at room temperature for 10 min, then add the additives and mix, reduce the speed to 300 r / min, and continue mixing for 3 min. During this period, use an online dispersion monitor to confirm that there is no agglomeration, and obtain a uniformly dispersed premix. Step 3: Feed the premixed material into a twin-screw extruder (screw length-to-diameter ratio L / D=44), set the temperatures of each zone as follows: Zone 1 175℃, Zone 2 190℃, Zone 3 200℃, Zone 4 210℃, Zone 5 215℃, Zone 6 215℃, die temperature 220℃, screw speed 300r / min, feed rate 40kg / h. After extrusion, water cooling, and pelletizing, modified polypropylene masterbatch is obtained. The masterbatch particle size is controlled at 2-3mm, and the moisture content is ≤0.03%. Step 4: Place the modified polypropylene masterbatch in an 85℃ vacuum drying oven for 3 hours, then put it into a single-screw extrusion casting film machine (screw length-to-diameter ratio L / D=32). Set the temperatures of each zone as follows: Zone 1 185℃, Zone 2 200℃, Zone 3 210℃, Zone 4 215℃, and the die temperature 220℃; the cooling roller temperature 40℃, the screw speed 110r / min, the traction rate 40m / min, and the traction ratio 2.0. After melting, casting, shaping, and winding, a polypropylene-based ultrathin current collector film is prepared.

[0043] Comparative Example 1 A polypropylene-based film differs from Example 1 in that the composite modifier in the formulation is removed, while the remaining raw materials, dosages, and preparation processes are the same as in Example 1, resulting in a final film thickness of 10.6 μm.

[0044] Comparative Example 2 A polypropylene-based film differs from Example 1 in that the preparation method of the composite modifier is different (i.e., the S1 product prepared using the composite modifier of Example 1 is not subjected to the S2 reaction), while the rest is the same as Example 1, and the final film thickness is 10.3 μm.

[0045] The preparation process of this comparative composite modifier includes: S1. High-purity nitrogen gas is introduced into the reaction vessel, followed by the addition of 10g of N,N'-bis(3-isocyanate-4-methylphenyl)urea (DMMU) and 100mL of N,N-dimethylformamide. The mixture is mechanically stirred (350r / min) and heated to 70℃. The mixture is then stirred at a constant temperature until DMMU is completely dissolved. 0.2g of dibutyltin dilaurate catalyst is added, and stirring is continued until the catalyst is evenly dispersed. 6.7g of DOPO is dissolved in 50mL of N,N-dimethylformamide and slowly added dropwise to the reaction vessel at a rate of 2 drops / second. After the addition is complete, the temperature is raised to 85℃, and the mixture is stirred and kept at this temperature for 4 hours to obtain the DMMU-DOPO reaction solution. S2. After the reaction is complete, the DMMU-DOPO reaction solution is slowly poured into 250 mL of anhydrous ethanol to precipitate. The precipitate is collected by filtration, washed 3 times with deionized water and 2 times with anhydrous ethanol, dried under vacuum at 80°C for 12 h, pulverized and passed through a 600-mesh sieve to obtain the composite modifier.

[0046] Comparative Example 3 A polypropylene-based film differs from Example 1 in that the preparation method of the composite modifier is different (using N,N'-bis(3-isocyanate-4-methylphenyl)urea and aminopropylheptaisobutylsilsesquioxane to react), while the rest is the same as Example 1, and the final film thickness is 10.4 μm.

[0047] The preparation process of this comparative composite modifier includes: S1. High-purity nitrogen gas is introduced into the reaction vessel, 10g of N,N'-bis(3-isocyanate-4-methylphenyl)urea (DMMU) and 100mL of N,N-dimethylformamide are added, and the mixture is mechanically stirred (350r / min) and heated to 70℃. The mixture is stirred at a constant temperature until DMMU is completely dissolved. 0.2g of dibutyltin dilaurate catalyst is added, and stirring is continued until the catalyst is evenly dispersed to obtain the DMMU reaction solution. S2. Dissolve 10.1g of aminopropylheptaisobutylsilsesquioxane in 60mL of N,N-dimethylformamide, maintain the reaction system temperature at 70℃, and slowly add the above DMMU reaction solution at a rate of 2 drops / second. After the addition is complete, raise the temperature to 105℃ and keep the temperature and stir for 5h. S3: After the reaction is complete, the reaction solution is slowly poured into 250 mL of anhydrous ethanol to precipitate. The precipitate is collected by filtration, washed 3 times with deionized water and 2 times with anhydrous ethanol, dried under vacuum at 80°C for 12 h, pulverized and passed through a 600-mesh sieve to obtain the composite modifier.

[0048] Comparative Example 4 A polypropylene-based film differs from Example 1 in that the preparation method of the composite modifier is different (DOPO is reacted with aminopropylheptaisobutylsilsesquioxane), while the rest is the same as Example 1, and the final film thickness is 10.1 μm.

[0049] The preparation process of this comparative composite modifier includes: S1. High-purity nitrogen gas (purity ≥99.99%) is introduced into the reaction vessel. 6.7g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 80mL of N,N-dimethylformamide are added. The mixture is mechanically stirred (350r / min) and heated to 70℃. The mixture is stirred at a constant temperature until DOPO is completely dissolved. 0.2g of dibutyltin dilaurate catalyst is added, and stirring is continued until the catalyst is evenly dispersed to obtain the DOPO reaction solution. S2. Dissolve 10.1g of aminopropylheptaisobutylsilsesquioxane in 60mL of N,N-dimethylformamide, maintain the reaction system temperature at 70℃, and slowly add the above DOPO reaction solution at a rate of 2 drops / second. After the addition is complete, raise the temperature to 105℃ and keep the temperature and stir for 5h. S3. After the reaction is complete, the reaction solution is slowly poured into 250 mL of anhydrous ethanol to precipitate. The precipitate is collected by filtration, washed 3 times with deionized water and 2 times with anhydrous ethanol, dried under vacuum at 80°C for 12 h, pulverized and passed through a 600-mesh sieve to obtain the composite modifier.

[0050] Experimental Example The properties of the films prepared in Example 1 and Comparative Examples 1-4 were tested, and the test items included: (1) Mechanical properties: tensile strength and elongation at break were tested according to GB / T 1040.3-2006, with a tensile rate of 50 mm / min; (2) Surface modification performance: Surface roughness (Ra) was tested by atomic force microscopy, ranging from 0.08 to 0.15 μm (which is beneficial for the adhesion of material coating); surface tension was tested by dyne pen, referring to GB / T 14216-2008; (3) Electrochemical stability: damp heat aging test (placed in an environment of 85℃ and 85%RH for 500h), tensile strength retention rate was tested; electrolyte stability: immersed in ethylene carbonate / dimethyl carbonate (v:v=1:1, containing 1mol / L LiPF6) electrolyte, placed at 25℃ for 300h, tensile strength retention rate was tested. (4) Flame retardant performance: The oxygen index (LOI) was tested according to ASTM D2863-19 standard. The sample size was 100mm×10mm×10μm, and the test environment was 25℃ and 50%RH.

[0051] The test results are shown in Table 1: Table 1 Performance test results of different films As shown in Table 1, the film thickness of Example 1 is 10.1 μm, and the tensile strength reaches 82.1 MPa, which is 18.6% higher than that of Comparative Example 1 without the composite modifier, meeting the high-strength mechanical requirements of the device. The oxygen index (LOI) of the film of Example 1 reaches 30.2%, which is 34.2% higher than that of Comparative Example 1, indicating that the composite modifier plays an efficient flame-retardant role. After 500 hours of damp heat aging, the tensile strength retention rate of the film of Example 1 is 87.2%, and after 300 hours of electrolyte immersion, the retention rate is 86.5%, both of which are more than 20% higher than that of Comparative Example 1, demonstrating the synergistic weather resistance effect of antioxidants, light stabilizers, and composite modifiers. The surface roughness Ra of the film of Example 1 is 0.11 μm, which is within the optimal adhesion range of 0.08-0.15 μm, and the surface tension reaches 43 mN / m, which is 19.4% higher than that of Comparative Example 1, providing good interfacial compatibility for subsequent chemical modification and functional layer coating.

[0052] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. The illustrative expressions of the above terms in this specification should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0053] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A polypropylene-based ultrathin special film, characterized in that, Calculated by weight, including: 80-90 parts isotactic polypropylene resin, 10-20 parts syndiotactic polypropylene resin, 5-10 parts composite modifier, 5-10 parts compatibilizer, 3-8 parts amino-modified nano silica, 0.1-0.5 parts antioxidant, 0.3-0.7 parts lubricant, 0.1-0.3 parts anti-hydrolysis agent, 0.1-0.3 parts nucleating agent, and 0.05-0.3 parts light stabilizer.

2. The polypropylene-based ultrathin special film according to claim 1, characterized in that, The density of the isotactic polypropylene resin is 0.908-0.912 g / cm³. 3 The resin has a melting point ≥165℃ and a melt index of 1-6 g / 10 min at 230℃ and 2.16 kg; the density of the syndiotactic polypropylene resin is 0.889-0.895 g / cm³. 3 Melting point ≥145℃, melt index is 2-8g / 10min at 230℃ and 2.16kg.

3. The polypropylene-based ultrathin special film according to claim 1, characterized in that... The preparation method of the composite modifier includes: S1. Nitrogen gas is introduced into the reaction vessel, and N,N'-di(3-isocyanate-4-methylphenyl)urea and N,N-dimethylformamide are added. After stirring and heating to 65-75℃ to dissolve, the catalyst is added and stirred evenly. 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is dissolved in N,N-dimethylformamide and slowly added dropwise to the reaction vessel. After the addition is complete, the temperature is raised to 80-90℃, and the reaction is stirred and kept at this temperature for 3-5 hours to obtain the DMMU-DOPO reaction solution. S2. Dissolve aminopropylheptaisobutylsilsesquioxane in N,N-dimethylformamide and slowly add it dropwise to the DMMU-DOPO reaction solution. Maintain the temperature at 80-90°C during the dropwise addition process. After the dropwise addition is completed, raise the temperature to 100-110°C and keep the temperature for 4-6 hours. After the reaction is completed, the mixture is subjected to precipitation, filtration, washing, vacuum drying, pulverization and sieving to obtain the composite modifier.

4. The polypropylene-based ultrathin special film according to claim 3, characterized in that... The mass ratio of N,N'-bis(3-isocyanate-4-methylphenyl)urea, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and aminopropylheptaisobutylsilsesquioxane is 8-12:5.5-7.5:8-12.

5. The polypropylene-based ultrathin special film according to claim 1, characterized in that... The compatibilizer is maleic anhydride-grafted polypropylene with a grafting rate of 0.8-1.2% and a melt index of 3-8 g / 10 min at 230℃ and 2.16 kg.

6. The polypropylene-based ultrathin special film according to claim 1, characterized in that... The preparation method of the amino-modified nano-silica includes: Nano-silica was added to a mixture of anhydrous ethanol and deionized water and dispersed evenly at room temperature to obtain a dispersion. γ-aminopropyltriethoxysilane was mixed with anhydrous ethanol and added dropwise to the dispersion. The reaction system was heated to reflux and reacted. After the reaction was completed, it was naturally cooled to room temperature, and the precipitate was collected by centrifugation. After washing and drying, amino-modified nano-silica was obtained.

7. The polypropylene-based ultrathin special film according to claim 1, characterized in that... The antioxidant is a compound of a primary antioxidant and a secondary antioxidant in a mass ratio of 3:1; wherein the primary antioxidant is antioxidant 1010 and the secondary antioxidant is antioxidant DLTP.

8. The polypropylene-based ultrathin special film according to claim 1, characterized in that... The lubricant is a compound of zinc stearate and polyethylene wax in a mass ratio of 2:

1.

9. The polypropylene-based ultrathin special film according to claim 1, characterized in that... The anti-hydrolysis agent is polycarbodiimide; the nucleating agent is sodium benzoate; and the light stabilizer is one or more of the light stabilizers TH-944, HS-770, and HS-292.

10. A method for preparing a polypropylene-based ultrathin special film according to claim 1, characterized in that, Includes the following steps: Step 1: After drying the raw materials, weigh and mix isotactic polypropylene resin, syndiotactic polypropylene resin, and compatibilizer to obtain the matrix mixture; mix antioxidant, lubricant, light stabilizer, anti-hydrolysis agent, and nucleating agent to obtain the additive mixture. Step 2: Add composite modifier and amino-modified nano-silica to the matrix mixture, mix evenly, then add auxiliary agent mixture and continue mixing to obtain a uniform premix. Step 3: The premixed material is fed into a twin-screw extruder and extruded and granulated to obtain modified polypropylene masterbatch. Step 4: The modified polypropylene masterbatch is processed by a single-screw extrusion casting film machine. After melting, casting, and shaping, a polypropylene-based ultrathin special film is prepared.

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