Polypropylene film and aluminum plastic film

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to a polypropylene film and an aluminum-plastic film. The polypropylene film comprises: a bonding layer comprising maleic anhydride grafted polypropylene resin and a first elastomer; wherein the grafting rate of maleic anhydride in the maleic anhydride grafted polypropylene resin is 0.5-2.5%, the mass percent of ethylene in the maleic anhydride grafted polypropylene resin is less than or equal to 30%, and the mass percent of ethylene is less than or equal to 25% based on the total mass of the bonding layer; the core layer is arranged on at least part of the surface of the bonding layer, and the core layer comprises polypropylene random copolymer and a second elastomer; the heat sealing layer is arranged on at least part of the surface, far away from the bonding layer, of the core layer. According to the polypropylene film, the phenomenon of deep punching stress whitening is effectively reduced, the interlayer strength of the core layer and the bonding layer is improved, and the packaging reliability is improved.

Description

Technical Field

[0001] This application belongs to the field of polymer materials technology, specifically relating to polypropylene film and aluminum-plastic film. Background Technology

[0002] Polypropylene film used in aluminum-plastic composite films for soft-pack lithium batteries requires heat treatment to strengthen its adhesion to aluminum foil. However, heat treatment can cause the polypropylene crystal structure to restructure, leading to stress whitening defects in the aluminum-plastic film during stamping and packaging. Existing technologies often improve the whitening problem by adding polyolefin elastomers to the polypropylene film, but this damages the polypropylene crystal structure, causing a decrease in the barrier properties and elastic modulus of the polypropylene film, leading to potential problems such as electrolyte penetration, aluminum foil corrosion, and stamping curling. Adjusting the heat treatment process requires stringent equipment and is difficult to scale up. Therefore, polypropylene film still needs further improvement. Summary of the Invention

[0003] This application aims to at least partially address one of the technical problems in the related art. To this end, this application proposes a polypropylene film and an aluminum-plastic film, wherein the polypropylene film effectively reduces the whitening phenomenon caused by deep drawing stress and improves the interlayer strength between the core layer and the adhesive layer, thereby enhancing packaging reliability.

[0004] A first aspect of this application provides a polypropylene film comprising: The adhesive layer comprises maleic anhydride-grafted polypropylene resin and a first elastomer; wherein the grafting rate of maleic anhydride in the maleic anhydride-grafted polypropylene resin is 0.5% to 2.5%, the mass percentage of ethylene in the maleic anhydride-grafted polypropylene resin is ≤30%, and the mass percentage of ethylene based on the total mass of the adhesive layer is ≤25%. A core layer is disposed on at least a portion of the surface of the adhesive layer, the core layer comprising random copolymer polypropylene and a second elastomer; A heat-sealing layer is disposed on at least a portion of the surface of the core layer away from the adhesive layer.

[0005] This application optimizes the composition and interfacial compatibility of the core layer and adhesive layer through the synergistic design of their structure and composition. This effectively reduces the whitening phenomenon caused by deep drawing stress and improves the interlayer strength between the core layer and adhesive layer, thereby enhancing the reliability of the packaging.

[0006] According to embodiments of this application, the above-described polypropylene film satisfies at least one of the following conditions: The random copolymer polypropylene has a melting point of 135.0℃~155.0℃; At 230℃ and 2.16kg load, the melt index of the random copolymer polypropylene is 1.5g / 10min~10.0g / 10min; At 230℃ and 2.16kg load, the melt index of the maleic anhydride-grafted polypropylene resin is 2g / 10min to 9g / 10min.

[0007] According to embodiments of this application, the above-described polypropylene film satisfies at least one of the following conditions: The first elastomer includes at least one of propylene-based elastomers, ethylene-acrylic acid copolymers, ethylene-octene copolymers, styrene-based elastomers, and olefin block copolymers; The second elastomer includes at least one of propylene-based elastomers, vinyl elastomers, ethylene-acrylic acid copolymers, and styrene-based elastomers.

[0008] According to embodiments of this application, the above-described polypropylene film satisfies at least one of the following conditions: The density of the second elastomer is ≥0.870 g / cm³. 3 ; At 230℃ and 2.16kg load, the melt index of the second elastomer is ≤8.0g / 10min.

[0009] According to an embodiment of this application, the adhesive layer further includes a first additive, which includes at least one of a polymer processing agent, an antioxidant, an antistatic agent, and a slip-opening agent.

[0010] According to an embodiment of this application, the adhesive layer includes: 70-95 parts by weight of the maleic anhydride-grafted polypropylene resin; 5 to 25 parts by weight of the first elastomer; 0.1 to 5 parts by weight of the first additive.

[0011] According to an embodiment of this application, the core layer further includes a second additive, which includes at least one of a polymer processing agent, an antioxidant, and a slip-forming agent.

[0012] According to an embodiment of this application, the core layer includes: 70-90 parts by weight of the random copolymer polypropylene; 10 to 25 parts by weight of the second elastomer; 0.1 to 5 parts by weight of the second adjuvant.

[0013] According to embodiments of this application, the above-described polypropylene film satisfies at least one of the following conditions: The thickness of the adhesive layer is 2μm to 10μm; The thickness of the heat-sealing layer is 4μm to 10μm.

[0014] A second aspect of this application provides an aluminum-plastic film comprising the polypropylene film described in the first aspect. This aluminum-plastic film includes all the features and advantages of the aforementioned polypropylene film, which will not be elaborated upon here. Detailed Implementation

[0015] The embodiments of this application are described in detail below and are intended to explain this application, but should not be construed as limiting this application.

[0016] The main production processes of thermal aluminum-plastic film include sandwich coating process, co-extrusion coating process, and hot-applied process. All three processes involve heat treatment, which can be used to improve the adhesion between polypropylene film and aluminum foil. However, the heat treatment process will cause the core layer crystal morphology to be reconstructed, making thermal aluminum-plastic film more prone to deep-drawing whitening. This will cause the aluminum-plastic film to curl easily during subsequent processing, affecting the processing efficiency of soft-pack lithium batteries. At the same time, it will also cause electrolyte penetration, aluminum foil corrosion and other hidden dangers affecting battery safety. To solve the above problems, the main solutions of related technologies to solve the deep-drawing whitening problem are: (1) using block polypropylene as the main resin of the core layer, adding polyolefin and other elastomers to the core layer and adhesive layer, reducing the deep-drawing whitening problem by reducing the degree of crystallinity of polypropylene film; (2) optimizing the relevant process parameters of the heat treatment process, using the enhanced heat treatment and cooling capacity of the equipment to accurately control the degree of crystallinity of the PP layer, and reducing the occurrence of deep-drawing whitening from the source of the process.

[0017] However, the above solutions still have some problems: Block polypropylene consists of propylene homopolymer segments and ethylene-propylene rubber (EPR) segments, forming a heterogeneous system of "hard segment (propylene) - soft segment (ethylene propylene rubber)". Due to the presence of the rubber phase in the heterogeneous structure, stress whitening is more likely to occur, which is a concomitant defect of its high impact resistance. Moreover, the larger the particle size of the rubber phase (e.g., >2μm), the more significant the stress whitening. As a dispersed phase (particle size usually 0.1μm-5μm), the rubber phase becomes a stress concentration point under stress, inducing microcracks, streaks, or voids. These defects lead to a decrease in local refractive index, and light scattering forms visible white spots. In addition, optimizing the heat treatment process parameters places high demands on the equipment's processing capabilities, requiring the equipment to have strong heat treatment and cooling capabilities.

[0018] Based on the above, the first aspect of this application provides a polypropylene film, comprising: The adhesive layer comprises maleic anhydride-grafted polypropylene resin and a first elastomer; wherein the grafting rate of maleic anhydride in the maleic anhydride-grafted polypropylene resin is 0.5% to 2.5%, the mass percentage of ethylene in the maleic anhydride-grafted polypropylene resin is ≤30%, and the mass percentage of ethylene based on the total mass of the adhesive layer is ≤25%. A core layer is disposed on at least a portion of the surface of the adhesive layer, the core layer comprising random copolymer polypropylene and a second elastomer; A heat-sealing layer is disposed on at least a portion of the surface of the core layer away from the adhesive layer.

[0019] In random copolymer polypropylene, ethylene units are randomly and uniformly distributed within propylene segments. The low molecular chain regularity and crystallinity (typically <50%) result in a homogeneous structure. Under stress, the molecular chains have weak slippage ability, making it difficult to generate microcrack aggregation zones. Therefore, the stress whitening phenomenon during deep drawing is slight. Furthermore, its crystallinity and grain size remain low before and after heat treatment, further mitigating stress whitening. The core layer of this application uses random copolymer polypropylene and a second elastomer. While retaining the aforementioned advantages in resisting stress whitening, it further improves the toughness of the core layer. However, the low proportion of ethylene segments in random copolymer polypropylene can easily lead to interlayer adhesion stability issues between the core layer and the adhesive layer. Therefore, this application further synergistically controls the ethylene content of maleic anhydride-grafted polypropylene resin in the adhesive layer, the total ethylene content in the adhesive layer, and the grafting rate of maleic anhydride. By utilizing the hydrogen bonds or chemical coupling between the maleic anhydride groups and the polypropylene in the core layer, the interfacial bonding force is enhanced, reducing or avoiding the problem of decreased interlayer adhesion strength due to excessive ethylene content. Furthermore, the first elastomer can enhance the flexibility of the adhesive layer, ensure the homogeneity of the interface between the adhesive layer and the core layer, and simultaneously work with the bonding effect of maleic anhydride-grafted polypropylene to maintain interlayer strength, thereby reducing the risk of microcracks and delamination. In summary, through the synergistic design of the structure and composition of the core layer and adhesive layer, and by optimizing the composition and interfacial compatibility of the core layer and adhesive layer, the phenomenon of whitening due to deep drawing stress is effectively reduced, and the interlayer strength between the core layer and adhesive layer is improved, thus enhancing the reliability of the encapsulation.

[0020] According to embodiments of this application, the maleic anhydride-grafted polypropylene resin includes at least one of Mitsui QF551, Dow Chemical BYNEL 50e739, and SK OREVAC® 18722.

[0021] According to embodiments of this application, at 230°C and a load of 2.16 kg, the melt index of the maleic anhydride-grafted polypropylene resin is 2 g / 10 min to 9 g / 10 min, specifically within the ranges of 2 g / 10 min, 3 g / 10 min, 4 g / 10 min, 5 g / 10 min, 6 g / 10 min, 7 g / 10 min, 8 g / 10 min, 9 g / 10 min, or any two of these ranges. Within this range, the interlayer bonding performance of the adhesive layer and the core layer can be balanced, ensuring sufficient diffusion and entanglement of molecular chains between the adhesive layer and the atactic polypropylene core layer during casting, resulting in more complete interfacial bonding.

[0022] Melt flow index (MFR), also known as melt flow rate, is a core indicator characterizing the melt flowability of polymer materials under specific temperatures and pressures. A higher MFR value indicates better melt flowability, and vice versa. For polypropylene (PP) materials, the physical meaning of MFR is: the mass of melt passing through a standard capillary every 10 minutes under specified temperature and load, expressed in g / 10min. It can be tested according to the national standard GB / T 3682.1-2018.

[0023] According to embodiments of this application, the first elastomer includes at least one selected from propylene-based elastomers, ethylene-acrylic acid copolymers, ethylene-octene copolymers, styrene-based elastomers, and olefin block copolymers (OBCs). The aforementioned first elastomer can achieve uniform dispersion with maleic anhydride-grafted polypropylene in the adhesive layer, avoiding the formation of coarse phase separation structures, ensuring the homogeneity of the interface between the adhesive layer and the core layer, thereby promoting molecular chain entanglement and maintaining interlayer bonding strength.

[0024] According to embodiments of this application, the propylene-based elastomer includes at least one of VERSIFY™ 3980FL, VERSIFY™ 2000, and VERSIFY™ 3000.

[0025] According to embodiments of this application, styrene-based elastomers include SEBS, SEPS, Kraton MD6951, and Kraton G1765.

[0026] According to embodiments of this application, the OBC includes at least one of INFUSE™ OBC 9000, INFUSE™ OBC 9007, TAFMER™ DF605, and TAFMER™ PN-20300.

[0027] According to embodiments of this application, the adhesive layer further includes a first additive, which includes at least one of a polymer processing agent, an antioxidant, an antistatic agent, and a slip-opening agent. Therefore, the aforementioned first additive helps improve the processing flowability of the adhesive layer, inhibit high-temperature degradation of the material, reduce static electricity during film processing, and enhance the slip properties between layers.

[0028] According to embodiments of this application, polymer processing agents include Constance PA0833PPR, Meilian A2738, etc.

[0029] According to embodiments of this application, the antioxidant includes Constance AP3020PP.

[0030] According to embodiments of this application, the antistatic agent includes Constance SL5004PPR.

[0031] According to embodiments of this application, the slippery opening agent includes Meilian A2617 and Constance SAB6527PPR.

[0032] According to an embodiment of this application, the adhesive layer comprises: 70-95 parts by weight of the maleic anhydride-grafted polypropylene resin; 5-25 parts by weight of the first elastomer; and 0.1-5 parts by weight of the first additive. The above proportions achieve a balance of performance among the components. A high proportion of maleic anhydride-grafted polypropylene resin improves interlayer adhesion, an appropriate amount of the first elastomer enhances the flexibility of the adhesive layer, and a small amount of the first additive optimizes processing and performance.

[0033] According to embodiments of this application, the thickness of the adhesive layer is 2μm to 10μm, specifically within the range of 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, or any two of these ranges. Within this range, it can be ensured that the adhesive layer has sufficient maleic anhydride-grafted polypropylene to form a sufficient interfacial bond with the core layer, thus stabilizing the interlayer bond strength.

[0034] It is understood that random copolymer polypropylene is a copolymer formed by the random distribution of propylene monomers and a small amount of ethylene (or other α-olefin) monomers along the propylene molecular chain during polymerization, mainly including propylene-ethylene random copolymers. This application does not limit the specific types of random copolymers; specific choices can be made flexibly according to needs.

[0035] According to embodiments of this application, the propylene-ethylene random copolymer includes at least one of LyondellBasell (such as RP215M, RC5056, RC6142, RC112L, RP210G, RP220M, RP310M, etc.), BOREALS (such as RD204CF, RD208CF, RB707, etc.), and SABIC (such as PP621P, etc.).

[0036] According to embodiments of this application, the melting point of the random copolymer polypropylene is 135.0℃~155.0℃, specifically 135.0℃, 140℃, 145℃, 150℃, 155℃, or any range between two of these. Within this range, the processing temperature can be reduced, the risk of high-temperature degradation can be decreased, and the uniformity of the polypropylene film thickness and the surface finish can be ensured.

[0037] According to embodiments of this application, at 230°C and a load of 2.16 kg, the melt index of the random copolymer polypropylene is 1.5 g / 10 min to 10.0 g / 10 min, specifically within the ranges of 1.5 g / 10 min, 2 g / 10 min, 3 g / 10 min, 4 g / 10 min, 5 g / 10 min, 6 g / 10 min, 7 g / 10 min, 8 g / 10 min, 9 g / 10 min, 10 g / 10 min, or any two of these ranges. Within these ranges, the core melt can be uniformly formed during casting, and the elastomer can be used to achieve uniform dispersion, thereby maintaining the homogeneous structure advantage of the low crystallinity of the core layer, ensuring resistance to stress whitening, and providing a good foundation for subsequent interfacial molecular entanglement with the adhesive layer.

[0038] According to embodiments of this application, the second elastomer includes at least one selected from propylene-based elastomers, vinyl elastomers, ethylene-acrylic acid copolymers, and styrene-based elastomers. The molecular chain structure of the aforementioned second elastomer is similar to that of random copolymer polypropylene, allowing for uniform dispersion in the core layer, further enhancing its structural uniformity and maintaining its stress-resistant whitening properties.

[0039] According to an embodiment of this application, the density of the second elastomer is ≥0.870 g / cm³. 3 A suitable density can maintain the uniform dispersion of the second elastomer, while ensuring the overall compactness of the core layer structure and improving the stress whitening resistance of the polypropylene film.

[0040] According to an embodiment of this application, at 230°C and a load of 2.16 kg, the melt index of the second elastomer is ≤8.0 g / 10 min. A suitable melt index can improve the dispersion of the first elastomer, ensure that the molecular chains of the elastomer and the random copolymer polypropylene are fully entangled, strengthen the core layer toughness, and at the same time reduce or avoid the phenomenon of excessive plasticization and agglomeration of the second elastomer due to an excessively high melt index.

[0041] According to embodiments of this application, the core layer further includes a second additive, which includes at least one of a polymer processing agent, an antioxidant, and a slip-opening agent. Therefore, the aforementioned second additive helps improve the processing stability of the upper core layer, inhibit the aging and degradation of the core layer material, and enhance interlayer slip properties.

[0042] The types of polymer processing agents and antioxidants are the same as those mentioned above, and will not be repeated here.

[0043] According to embodiments of this application, the slippery opening agent includes at least one of Meilian A2602 and Constance SL5091PPR.

[0044] According to an embodiment of this application, the core layer comprises: 70-90 parts by weight of the random copolymer polypropylene; 10-25 parts by weight of the second elastomer; and 0.1-5 parts by weight of the second additive. The above proportions achieve a balance in the performance of each component. The high proportion of random copolymer polypropylene allows it to exert its advantage in resisting stress whitening, an appropriate amount of the second elastomer can improve the toughness of the core layer, and a small amount of the second additive can optimize processing and performance.

[0045] According to embodiments of this application, the thickness of the core layer is not specifically limited. As an example, the thickness of the core layer can be 20μm to 70μm, specifically 20μm, 25μm, 30μm, 36μm, 40μm, 50μm, 60μm, 70μm, or any range between two of these. Within the above range, the stress-whitening resistance of random copolymer polypropylene can be fully utilized, while matching the thickness ratio of the adhesive layer and the heat-sealing layer, ensuring the overall flexibility and structural stability of the polypropylene film, and supporting subsequent processing and usage requirements.

[0046] According to embodiments of this application, the main components of the heat-sealing layer include at least one of binary random copolymer polypropylene and ternary random copolymer polypropylene, as well as a third elastomer and a third additive. In this application, the composition and proportion of the heat-sealing layer are not specifically limited. Specifically, they can be selected based on the initial sealing temperature and processing stability of the polypropylene film, as long as the initial sealing temperature of the heat-sealing layer is between 130°C and 140°C and the processing performance is good.

[0047] According to embodiments of this application, the thickness of the heat-sealing layer is 4μm-10μm, specifically 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, or any combination thereof. Within this range, the heat-sealing layer can fully exert its protective function on the core layer and adhesive layer, effectively improving the performance of the polypropylene film, such as its durability and barrier properties. Simultaneously, by matching the thickness of the core layer and adhesive layer, it maintains the overall flexibility and balance of the polypropylene film, balancing performance and practical cost.

[0048] A second aspect of this application provides an aluminum-plastic film comprising the polypropylene film described in the first aspect. This aluminum-plastic film includes all the features and advantages of the aforementioned polypropylene film, which will not be elaborated upon here.

[0049] It should be noted that the aluminum-plastic film of this application can be used as a packaging material for soft-pack lithium-ion batteries, improving the lifespan and safety of soft-pack lithium-ion batteries.

[0050] The embodiments of this application are described in detail below.

[0051] Example 1 (1) Preparation of adhesive layer: 75 parts by weight of maleic anhydride-grafted polypropylene 18722 (melt index of 5.2 g / 10min, ethylene content of 15%, maleic anhydride grafting rate of 2.0%), 20 parts by weight of propylene-based elastomer VIDAM™ 3980FL and 5 parts by weight of antioxidant Constance AP3020PP additive are mixed evenly to obtain the first mixture; (2) Preparation of the core layer: 75 parts by weight of random copolymer polypropylene resin RD204 (melt index 8.0 g / 10min, melting point 150℃) and 20 parts by weight of VERSIFY™ 3000 elastomer (density 0.891 g / cm³) were mixed. 3 The mixture (with a melt index of 8.0 g / 10 min) and 2 parts by weight of slip opening agent Meilian A2602 and 3 parts by weight of antioxidant Constance AP3020PP were mixed evenly to obtain a second mixture; (3) Preparation of heat-sealing layer: 60 parts by weight of random copolymer polypropylene RD208, 30 parts by weight of ternary copolymer polypropylene RC221L, and 5 parts by weight of linear low-density polyethylene SP0510 (density 0.904 g / cm³) are mixed. 3 ) and 5 parts by weight of the opening agent, Smooth & Smooth A2617 additive, are mixed evenly to obtain a third mixture; The above mixture was fed into the hoppers of the three-layer co-extrusion casting machine, and the thickness ratio of the three layers was set to approximately 1:5:1 (wherein, the core layer thickness is 36μm, the adhesive layer thickness is 7μm, and the heat-sealing layer thickness is 7μm). A 50μm polypropylene film was produced by the co-extrusion casting process, and the adhesive layer was corona-treated.

[0052] The specific parameters for Examples 2-8 and Comparative Examples 1-3 are shown in Table 1. All other parameters are the same as those for Example 1.

[0053] Performance testing (1) Coat the polypropylene film obtained above with a thin layer of adhesive (thickness 0.01 g / m). 2 Aluminum-plastic film is obtained by laminating PA / Al (nylon / Al) aluminum foil. It is then heat-treated using a heat treatment testing machine. The heat treatment conditions are as follows: heat treatment is carried out in an infrared lamp chain furnace to ensure that the film surface temperature is greater than 160℃ and the machine speed is 40m / min. The stress whitening of the aluminum-plastic film is tested at a drawing depth of 7mm (using a 57mm×98mm die). The whitening is manifested in the appearance as local or large areas of white haze. (2) Delamination between layers: The above aluminum-plastic film was heat-sealed at 185℃, 0.3Mpa and 3s. The appearance of the peel was tested by hand tearing at 25℃ and the peeling appearance was observed. The delamination was judged by the appearance of the peel after sealing. If the interlayer strength is good, the two sides are uniformly white after hand tearing and the thickness difference between the two sides is <10μm when tested alone. If the interlayer bonding strength is low, there is a delamination problem between the composite layer and the core layer. The two sides cannot be uniformly white after hand tearing. The peeled interface shows a non-uniform double white state, that is, one side is thicker and white, and the other side is thinner and non-white. Only the thickness of the composite layer remains on the surface of the aluminum foil, and the thickness difference between the two sides is >30μm. (3) Maleic anhydride grafting rate: Weigh about 2.0g of the sample to be tested, dissolve it in 80 mL of xylene, and reflux it in an oil bath at 120℃. After the sample is fully dissolved, raise the reflux device to cool to room temperature, add an excess of alkaline solution KOH-ethanol solution (about 15ml), and add 2 drops of phenolphthalein. Seal the device and maintain a micro-reflux state at 75℃ for 5h (observe that the solution is light red, which proves that the alkali is in excess) to ensure that the alkali and maleic anhydride (MAH) react fully. To facilitate the observation of the titration phenomenon, raise the reflux device and add one drop of phenolphthalein. The solution turns purple-red. Start adding acid solution (HCl-isopropanol). Observe that the solution suddenly becomes colorless and remains unchanged for 5min. Record the amount of acid used and calculate the grafting rate. Acid-base titration was performed using potassium hydroxide isopropanol solution (KOH-isopropanol) to react fully with the MAH in the sample. An acid solution (HCl-isopropanol) was added dropwise, and the amount of alkali consumed was recorded. The content of acid anhydride consumed was calculated. The grafting rate formula is:

[0054] In the formula, G MAH —Grafting rate; 98.06 g / mol — Molecular weight of MAH; V1 and C1 represent the volume (mL) and concentration (mol / L) of the excess potassium hydroxide isopropanol solution, respectively. V2 and C2 represent the volume (mL) and concentration (mol / L) of the isopropanol hydrochloride solution in the back titration, respectively. m — the mass of the sample being measured, in grams.

[0055] Table 1

[0056] In Table 1, "no whitening on the stamped surface" means that after the aluminum-plastic film is stamped, there is no obvious white haze or streaky whitening phenomenon in the stress concentration areas such as the sidewalls and bottom of the groove. This indicator directly reflects the stamping performance and stress whitening resistance of the aluminum-plastic film. As can be seen from Table 1, there is no whitening phenomenon on the stamped surface of all embodiments, which indicates that the polypropylene film of this application has excellent stress whitening resistance.

[0057] "Uniform whitening on the surface after tearing" refers to the uniform whitening of the torn surface and surrounding area after the edge of the aluminum-plastic film is torn, with the torn surface exhibiting a uniform tough fracture morphology. As shown in Table 1, all embodiments exhibit uniform whitening on both sides after tearing, separating evenly from the packaging location, indicating that the polypropylene film of this application has packaging reliability.

[0058] In Comparative Examples 1-3, both Comparative Examples 1 and 3 showed whitening on the surface of the punched shells, indicating that the addition of block polypropylene under existing heat treatment conditions leads to whitening due to drawing stress. In Comparative Example 2, the high polyethylene (PE) content in the adhesive layer resulted in decreased interlayer adhesion strength between the adhesive layer and the core layer, leading to delamination. In summary, the polypropylene film of this application effectively reduces whitening due to drawing stress by optimizing the composition and interfacial compatibility of the core layer and adhesive layer, while also improving the interlayer strength between the core layer and the adhesive layer, thus enhancing packaging reliability.

[0059] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0060] 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 this application. In this specification, the illustrative expressions of the above terms do not necessarily refer 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. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0061] Although embodiments of this application have been shown and described above, it is to be understood that the above embodiments... These are exemplary embodiments and should not be construed as limiting the scope of this application. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of this application.

Claims

1. A polypropylene film, characterized in that, include: The adhesive layer comprises maleic anhydride-grafted polypropylene resin and a first elastomer; wherein the grafting rate of maleic anhydride in the maleic anhydride-grafted polypropylene resin is 0.5% to 2.5%, the mass percentage of ethylene in the maleic anhydride-grafted polypropylene resin is ≤30%, and the mass percentage of ethylene based on the total mass of the adhesive layer is ≤25%. A core layer is disposed on at least a portion of the surface of the adhesive layer, the core layer comprising random copolymer polypropylene and a second elastomer; A heat-sealing layer is disposed on at least a portion of the surface of the core layer away from the adhesive layer.

2. The polypropylene film according to claim 1, characterized in that, At least one of the following conditions must be met: The random copolymer polypropylene has a melting point of 135.0℃~155.0℃; At 230℃ and 2.16kg load, the melt index of the random copolymer polypropylene is 1.5g / 10min~10.0g / 10min; At 230℃ and 2.16kg load, the melt index of the maleic anhydride-grafted polypropylene resin is 2g / 10min to 9g / 10min.

3. The polypropylene film according to claim 1, characterized in that, At least one of the following conditions must be met: The first elastomer includes at least one of propylene-based elastomers, ethylene-acrylic acid copolymers, ethylene-octene copolymers, styrene-based elastomers, and olefin block copolymers; The second elastomer includes at least one of propylene-based elastomers, vinyl elastomers, ethylene-acrylic acid copolymers, and styrene-based elastomers.

4. The polypropylene film according to claim 3, characterized in that, At least one of the following conditions must be met: The density of the second elastomer is ≥0.870 g / cm³. 3 ; At 230℃ and 2.16kg load, the melt index of the second elastomer is ≤8.0g / 10min.

5. The polypropylene film according to claim 1, characterized in that, The adhesive layer further includes a first additive, which includes at least one of a polymer processing agent, an antioxidant, an antistatic agent, and a slip-forming agent.

6. The polypropylene film according to claim 5, characterized in that, The adhesive layer includes: 70-95 parts by weight of the maleic anhydride-grafted polypropylene resin; 5 to 25 parts by weight of the first elastomer; 0.1 to 5 parts by weight of the first additive.

7. The polypropylene film according to claim 1, characterized in that, The core layer further includes a second additive, which includes at least one of a polymer processing agent, an antioxidant, and a slip-forming agent.

8. The polypropylene film according to claim 7, characterized in that, The core layer includes: 70-90 parts by weight of the random copolymer polypropylene; 10 to 25 parts by weight of the second elastomer; 0.1 to 5 parts by weight of the second adjuvant.

9. The polypropylene film according to claim 1, characterized in that, At least one of the following conditions must be met: The thickness of the adhesive layer is 2μm-10μm; The thickness of the heat-sealing layer is 4μm-10μm.

10. An aluminum-plastic film, characterized in that, The polypropylene film included in any one of claims 1 to 9.

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