A cast polypropylene film, composite packaging film

Abstract

The application relates to the technical field of materials, in particular to a cast polypropylene film and a composite packaging film. The cast polypropylene film comprises a corona layer, a core layer and an encapsulation layer which are sequentially arranged; wherein the material forming the core layer comprises 65-95 parts by weight of block copolymerized polypropylene, 5-20 parts by weight of a first elastomer and 0-5 parts by weight of a first additive; the block copolymerized polypropylene comprises a rubber phase, the average size of the rubber phase is 0-0.2 microns, and the average size is not 0. The cast polypropylene film has good interlayer stability, so that the cast polypropylene film does not produce self-layering when being peeled from a base material, and the reliability of the corresponding composite film is improved.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to a cast polypropylene film and a composite packaging film. Background Technology

[0002] Cast polypropylene film (CPP film) features high transparency, good stiffness, low heat-sealing temperature, heat resistance, moisture resistance, good barrier properties, strong adaptability to printing and lamination, and a smooth surface. It also boasts uniform thickness and balanced performance. Due to its excellent comprehensive properties and broad application prospects, it occupies an important position in the packaging materials field.

[0003] In recent years, with the rapid development of pre-packaged food packaging materials, high-end barrier packaging materials, soft-pack lithium-ion batteries, and solid-state battery packaging materials, the demand for related packaging materials has increased significantly, and the requirements for the packaging materials themselves have also become increasingly stringent. Common composite packaging materials typically consist of an outer protective layer (made of nylon or polyethylene terephthalate PET), a barrier layer (made of aluminum foil, high-barrier PET, or other films or sheets with barrier effects), and an encapsulation layer (made of polypropylene (PP) film or polyethylene (PE) film). These layers are usually bonded together using appropriate adhesives. The encapsulation layer may use PP or PE film depending on the specific packaging requirements. For composite materials requiring high packaging strength and operating in harsh environments, CPP film is generally used as the inner encapsulation material.

[0004] While PP film plays a crucial role in packaging materials, its performance variations can lead to numerous problems. CPP exhibits excellent heat resistance; with a softening point of approximately 140℃, it can be used in hot-fill, retort pouches, and aseptic packaging. It also boasts excellent acid, alkali, and oil resistance, high transparency, good flexibility, high barrier properties, high strength and tear resistance, and ease of processing. For example, retortable CPP film is typically laminated with pre-printed biaxially oriented polypropylene (BOPP) or biaxially oriented polyester (BOPET) film to create two- or multi-layer retort films. This requires the CPP film to possess good lamination properties, high heat-sealing and peel strength, impact resistance, and tear strength.

[0005] However, CPP films with poor interlayer stability can indeed lead to delamination problems during use. In aluminum-plastic films used as encapsulation materials for lithium-ion batteries, if the interlayer stability of the CPP film is poor, electrolyte may seep through the gaps between the layers, potentially causing safety issues such as fires. Traditional aluminum-plastic films generally have a layered structure, typically either polyamide (PA) / aluminum (Al) / CPP or PET / PA / aluminum (Al) / CPP, with each layer bonded together with adhesives. However, the most critical weakness of multilayer composite aluminum-plastic films in application is the delamination problem, namely, separation between CPP layers, between CPP and Al layers, and between the aluminum-plastic film and the tab layer.

[0006] Delamination of CPP film can also occur during peel strength testing of CPP film and substrate. For example, in solvent-free BOPP / CPP lamination, low peel strength sometimes occurs. One common cause is interlayer delamination of the CPP film during peeling. When the adhesive strength between the BOPP and CPP layers is greater than the interlayer bonding strength of the CPP film itself, the film separates at the weaker points. Furthermore, delamination at the seal after heat sealing of composite film packaging may also be related to the CPP film.

[0007] Existing literature suggests that improving the interlayer stability of CPP membranes can be achieved primarily through raw material selection and formulation optimization, as well as improvements in the production process, as detailed below:

[0008] (1) Selecting suitable polymer materials: In the production of CPP membranes, selecting polypropylene resins with good compatibility is crucial. For example, homopolymer polypropylene and copolymer polypropylene with different melt indices can be combined. Homopolymer polypropylene provides better rigidity and barrier properties, while copolymer polypropylene increases toughness and flexibility. By mixing them in a reasonable ratio, such as mixing homopolymer polypropylene and copolymer polypropylene in a 7:3 ratio, the overall performance of the membrane can be improved, making the bonding between layers tighter, thereby improving interlayer stability;

[0009] (2) Adding compatibilizers: Compatibilizers can enhance the affinity between different polymers. For example, in a multilayer CPP film structure, when polypropylene layers with different properties are present, maleic anhydride-grafted polypropylene is added as a compatibilizer. This compatibilizer's molecular chain contains active groups that can react with polypropylene, allowing it to form chemical bonds or physical entanglements between different polypropylene layers, effectively improving interlayer adhesion. Generally, the amount of compatibilizer added can be controlled at around 3-5% depending on the actual situation.

[0010] (3) Optimize the extrusion process: In the casting extrusion process, controlling parameters such as extrusion temperature, screw speed, and traction speed is crucial for interlayer stability. Excessive extrusion temperature can lead to excessive degradation of polypropylene resin, affecting its performance; excessively low temperature can result in incomplete plasticization of the resin. For example, for commonly used CPP film extrusion equipment, controlling the extrusion temperature between 200-230℃, maintaining the screw speed at 50-80 r / min, and the traction speed at 10-15 m / min can ensure uniform resin extrusion and the formation of a continuous and stable film layer, reducing interlayer stress and improving interlayer stability.

[0011] (4) Optimization of Multilayer Co-extrusion Technology: When producing CPP film using multilayer co-extrusion technology, it is essential to ensure tight adhesion between each layer. Adjusting the extrusion thickness and speed of each layer during co-extrusion is crucial. For example, in a three-layer CPP film structure, the middle layer is a barrier layer, and the outer layer is a heat-sealing layer. During extrusion, the barrier layer should be extruded at a slightly slower speed than the heat-sealing layer. This allows the barrier layer to be better encapsulated by the heat-sealing layer after extrusion, enhancing the interlayer bonding. Simultaneously, the ratio of extruded thickness of each layer should be adjusted according to the specific requirements of the product; for example, a 1:2:1 ratio of heat-sealing layer:barrier layer:heat-sealing layer thickness can be used.

[0012] The above technical methods can be applied to conventional CPP film products. For applications requiring high impact strength, the core layer is generally made of impact-resistant polypropylene, and homopolymer polypropylene cannot be used. The addition of compatibilizer will increase costs. Process technology improvement is a basic process optimization, which cannot fundamentally solve the problem. Summary of the Invention

[0013] The present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides a cast polypropylene film and a composite packaging film, wherein the cast polypropylene film has good interlayer stability, so that it does not delaminate itself when peeled from the substrate, thereby improving the reliability of the corresponding composite film.

[0014] Therefore, the first aspect of the present invention provides a cast polypropylene film, the cast polypropylene film comprising a corona layer, a core layer and an encapsulation layer stacked sequentially;

[0015] The material forming the core layer includes 65-95 parts by weight of block copolymer polypropylene, 5-20 parts by weight of a first elastomer, and 0-5 parts by weight of a first additive.

[0016] The block copolymer polypropylene includes a rubber phase, wherein the average size of the rubber phase in the block copolymer polypropylene is 0-0.2 μm and is not 0.

[0017] To address the issue of poor encapsulation performance caused by low interlayer stability in cast polypropylene films used as encapsulation materials, this invention limits the size of the rubber phase of block copolymer polypropylene in the core layer of the cast polypropylene film, thereby increasing the bonding sites at the internal interfaces between the layers and creating a "micro-crosslinking" effect. This enhances the interlayer stability of the cast polypropylene film and solves the problem of delamination in cast polypropylene film encapsulation. Simultaneously, it prevents the cast polypropylene film from delaminating during peeling from the substrate, improving the reliability of the corresponding composite film.

[0018] According to an embodiment of the present invention, the content of the rubber phase in the block copolymer polypropylene is 20wt%-30wt%.

[0019] According to an embodiment of the present invention, the average size of the rubber phase in the block copolymer polypropylene is 0-0.15 μm, and is not 0.

[0020] According to an embodiment of the present invention, the material constituting the core layer further includes random copolymer polypropylene.

[0021] According to an embodiment of the present invention, the block copolymer polypropylene is ethylene propylene block polypropylene with a melting point of 160℃-170℃ and a melt index of 1-4g / 10min.

[0022] According to an embodiment of the present invention, the first elastomer includes at least one of a propylene-based elastomer, a vinyl elastomer, an ethylene-acrylic acid copolymer, or a styrene-based elastomer.

[0023] According to an embodiment of the present invention, the first additive includes at least one of a polymer processing aid, an antioxidant, an antistatic agent, or a slip-forming agent.

[0024] According to an embodiment of the present invention, the material forming the corona layer comprises 70-98 parts by weight of random copolymer polypropylene, 10-20 parts by weight of a second elastomer, and 0-2 parts by weight of a second additive.

[0025] According to an embodiment of the present invention, the second elastomer includes at least one of a propylene-based elastomer, a vinyl elastomer, an ethylene-acrylic acid copolymer, or a styrene-based elastomer.

[0026] According to an embodiment of the present invention, the second additive includes at least one of a polymer processing aid, an antioxidant, an antistatic agent, or a slip-forming agent.

[0027] According to an embodiment of the present invention, the material forming the heat-sealing layer comprises 70-98 parts by weight of random copolymer polypropylene, 10-20 parts by weight of a third elastomer, and 0-2 parts by weight of a third additive.

[0028] According to embodiments of the present invention, the third elastomer includes at least one of a propylene-based elastomer, a vinyl elastomer, an ethylene-acrylic acid copolymer, or a styrene-based elastomer.

[0029] According to an embodiment of the present invention, the third auxiliary agent includes at least one of a polymer processing aid, an antioxidant, an antistatic agent, or a slip-forming agent.

[0030] According to an embodiment of the present invention, the initial sealing temperature of the encapsulation layer is 120-135°C.

[0031] According to an embodiment of the present invention, the thickness ratio of the corona layer, the core layer and the encapsulation layer is 1:(3-9):1.

[0032] A second aspect of the present invention provides a composite packaging film comprising the cast polypropylene film described in the first aspect. This composite packaging film thus exhibits good interlayer stability and reliability.

[0033] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0034] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0035] It should be noted that 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 indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0036] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0037] To facilitate understanding of the invention, certain technical and scientific terms are specifically defined below. Unless otherwise expressly defined elsewhere in this document, all other technical and scientific terms used herein have the meanings commonly understood by one of ordinary skill in the art to which this invention pertains.

[0038] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this invention, but do not exclude other aspects.

[0039] In this document, the terms “optionally,” “optionally,” or “optionally” generally refer to an event or condition that may, but may not, occur, and the description includes both cases in which the event or condition occurs and cases in which the event or condition does not occur.

[0040] According to an embodiment of the present invention, a first aspect of the present invention provides a cast polypropylene film, the cast polypropylene film comprising a corona layer, a core layer and an encapsulation layer stacked sequentially;

[0041] The material forming the core layer includes 65-95 parts by weight of block copolymer polypropylene, 5-20 parts by weight of a first elastomer, and 0-5 parts by weight of a first additive.

[0042] The block copolymer polypropylene includes a rubber phase, wherein the average size of the rubber phase in the block copolymer polypropylene is 0-0.2 μm and is not 0.

[0043] To address the issue of poor encapsulation performance caused by low interlayer stability in cast polypropylene films used as encapsulation materials, this invention limits the size of the rubber phase of block copolymer polypropylene in the core layer of the cast polypropylene film, thereby increasing the bonding sites at the internal interfaces between the layers and creating a "micro-crosslinking" effect. This enhances the interlayer stability of the cast polypropylene film and solves the problem of delamination in cast polypropylene film encapsulation. Simultaneously, it prevents the cast polypropylene film from delaminating during peeling from the substrate, improving the reliability of the corresponding composite film.

[0044] Specifically, there is a close relationship between the size of the rubber phase in block copolymer polypropylene and its interlayer stability. Smaller rubber phase sizes have a positive impact on interlayer stability. When the rubber phase is small and uniformly dispersed in the polypropylene matrix, it acts as a kind of "micro-crosslinking point," enhancing the connection and interaction between polymer molecular chains. In this case, the interlayer structure of the film is more compact, and the interlayer bonding force is stronger. Under external forces or complex environmental conditions, separation or delamination is less likely to occur, thus giving the cast polypropylene film better interlayer stability. For example, in applications where the interlayer stability of packaging materials is critical, such as pharmaceutical and food packaging, smaller rubber phase sizes better ensure the integrity and safety of the packaging. Conversely, larger rubber phase sizes have a negative impact on interlayer stability, forming larger aggregates or phase separation regions in the polypropylene matrix. These larger rubber phase regions have weaker interfacial bonding with the polypropylene matrix. Under the influence of external forces, temperature changes, or chemical corrosion, stress concentration easily occurs at the interface, leading to interlayer separation or delamination, thereby reducing the interlayer stability of the cast polypropylene film. For example, in high-temperature or high-humidity environments, cast polypropylene films with large-sized rubber phases may experience interlayer delamination, affecting their performance. Therefore, limiting the size of the block copolymer polypropylene rubber phase in the cast polypropylene film is necessary to obtain a cast polypropylene film with good interlayer stability and overall performance.

[0045] The "size of the rubber phase" can be determined by injection molding block copolymer polypropylene into a sample, first brittle-breaking it in liquid nitrogen, then immersing it in m-xylene at room temperature for 72 hours. During this process, the non-crystallizable rubber phase will dissolve in the m-xylene, leaving only crystalline polypropylene in the casting. Since the rubber phase is removed, leaving pores, the pore locations in the figure represent the original rubber phase. The mass percentage of the rubber phase can be calculated using the mass difference, and the size of the rubber phase can be determined using IPP software.

[0046] According to a specific embodiment of the present invention, the content of the rubber phase in the block copolymer polypropylene is 20wt%-30wt%, thereby giving the cast polypropylene film sufficient toughness.

[0047] According to a specific embodiment of the present invention, the average size of the rubber phase in the block copolymer polypropylene is 0-0.15 μm and is not 0, thereby further achieving better interlayer stability.

[0048] According to a specific embodiment of the present invention, the material constituting the core layer further includes random copolymer polypropylene. This can adjust the flowability of the core layer and further improve interlayer stability, while replacing some of the impact-resistant polypropylene to reduce the probability of crystal point formation.

[0049] According to a specific embodiment of the present invention, the block copolymer polypropylene is ethylene-propylene block copolymer polypropylene with a melting point of 160℃-170℃ and a melt index of 1-4 g / 10 min. Here, "melt index" should be understood as the melt flow rate of the block copolymer polypropylene at a temperature of 230℃ and a load of 2.16 kg being 1-4 g / 10 min.

[0050] According to specific embodiments of the present invention, the types of the first elastomer and the first additive are not particularly limited. The first elastomer includes, but is not limited to, propylene-based elastomers, vinyl elastomers, ethylene-acrylic acid copolymers, and styrene-based elastomers. The first additive includes, but is not limited to, polymer processing aids, antioxidants, antistatic agents, and slip-forming agents. The first additive may be added as needed during the formation of the core layer.

[0051] According to a specific embodiment of the present invention, the material forming the corona layer comprises 70-98 parts by weight of random copolymer polypropylene, 10-20 parts by weight of a second elastomer, and 0-2 parts by weight of a second additive.

[0052] The types of the random copolymer polypropylene, the second elastomer, and the second additive are not particularly limited. The second elastomer includes, but is not limited to, propylene-based elastomers, vinyl elastomers, ethylene-acrylic acid copolymers, and styrene-based elastomers. The second additive includes, but is not limited to, polymer processing aids, antioxidants, antistatic agents, and slip-forming agents. The second additive may be added as needed during the formation of the corona layer.

[0053] According to a specific embodiment of the present invention, the material forming the encapsulation layer includes 70-98 parts by weight of random copolymer polypropylene, 10-20 parts by weight of a third elastomer, and 0-2 parts by weight of a third additive.

[0054] The types of the random copolymer polypropylene, the third elastomer, and the third auxiliary agent are not particularly limited. The third elastomer includes, but is not limited to, propylene-based elastomers, vinyl elastomers, ethylene-acrylic acid copolymers, and styrene-based elastomers. The third auxiliary agent includes, but is not limited to, polymer processing aids, antioxidants, antistatic agents, and slip-forming agents. The third auxiliary agent may be added as needed during the formation of the encapsulation layer.

[0055] According to a specific embodiment of the present invention, the initial sealing temperature of the encapsulation layer is 120-135°C. As some examples, the initial sealing temperature of the encapsulation layer may be 120°C, 125°C, 130°C, 135°C, etc.

[0056] According to a specific embodiment of the present invention, the thickness ratio of the corona layer, the core layer and the encapsulation layer is 1:(3-9):1.

[0057] According to a specific embodiment of the present invention, the preparation method of the cast polypropylene film is not particularly limited. It can be obtained by mixing the raw materials of each layer separately, forming a film by casting process, and corona-electrode the corona layer to obtain the final product.

[0058] According to an embodiment of the present invention, a second aspect of the present invention provides a composite packaging film comprising the cast polypropylene film described in the first aspect.

[0059] Specifically, the composite packaging film may further include a PA / Al composite film, wherein the corona layer of the cast polypropylene film is laminated with the aluminum foil side of the composite film.

[0060] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0061] Example 1

[0062] The material forming the core layer is:

[0063] Block copolymer polypropylene (rubber phase average size 0.15 μm, content 25 wt%; melting point 165℃, melt index 1.8 g / 10 min) 89.5 parts by weight

[0064] 10 parts by weight of propylene-based elastomer 3980FL

[0065] Antioxidant 168, 0.5 parts by weight.

[0066] The material forming the corona layer is:

[0067] Random copolymer polypropylene 84.5 parts by weight

[0068] 15 parts by weight of styrene-based elastomer TAIPOL 6014

[0069] Antioxidant 168, 0.5 parts by weight.

[0070] The material forming the encapsulation layer is:

[0071] Random copolymer polypropylene 84.5 parts by weight

[0072] Vinyl elastomer LC175 15 parts by weight

[0073] Antioxidant 168, 0.5 parts by weight.

[0074] Example 2

[0075] The material forming the core layer is:

[0076] Block copolymer polypropylene (rubber phase average size 0.2 μm, content 28 wt%; melting point 163℃, melt index 2.0 g / 10 min) 89.5 parts by weight

[0077] 10 parts by weight of propylene-based elastomer 3980FL

[0078] Antioxidant 168, 0.5 parts by weight.

[0079] The material forming the corona layer is:

[0080] Random copolymer polypropylene 84.5 parts by weight

[0081] Acrylic-based elastomer 3980FL 15 parts by weight

[0082] Antioxidant 168, 0.5 parts by weight.

[0083] The material forming the encapsulation layer is:

[0084] Random copolymer polypropylene 84.5 parts by weight

[0085] Acrylic-based elastomer 3980FL 15 parts by weight

[0086] Antioxidant 168, 0.5 parts by weight.

[0087] Example 3

[0088] The material forming the core layer is:

[0089] Block copolymer polypropylene (rubber phase average size 0.1 μm, content 20 wt%; melting point 167℃, melt index 1.0 g / 10 min) 89.5 parts by weight

[0090] 10 parts by weight of styrene-based elastomer TAIPOL 6014

[0091] Antioxidant 168, 0.5 parts by weight.

[0092] The material forming the corona layer is:

[0093] Random copolymer polypropylene 84.5 parts by weight

[0094] 15 parts by weight of styrene-based elastomer TAIPOL 6014

[0095] Antioxidant 168, 0.5 parts by weight.

[0096] The material forming the encapsulation layer is:

[0097] Random copolymer polypropylene 84.5 parts by weight

[0098] Acrylic-based elastomer 3980FL 15 parts by weight

[0099] Antioxidant 168, 0.5 parts by weight.

[0100] Comparative Example 1

[0101] The material forming the core layer is:

[0102] Block copolymer polypropylene (rubber phase average size 0.3 μm, content 20 wt%; melting point 167℃, melt index 1.5 g / 10 min) 89.5 parts by weight

[0103] 10 parts by weight of propylene-based elastomer 3980FL

[0104] Antioxidant 168, 0.5 parts by weight.

[0105] The material forming the corona layer is:

[0106] Random copolymer polypropylene 84.5 parts by weight

[0107] Acrylic-based elastomer 3980FL 15 parts by weight

[0108] Antioxidant 168, 0.5 parts by weight.

[0109] The material forming the encapsulation layer is:

[0110] Random copolymer polypropylene 84.5 parts by weight

[0111] Acrylic-based elastomer 3980FL 15 parts by weight

[0112] Antioxidant 168, 0.5 parts by weight.

[0113] Comparative Example 2

[0114] The material forming the core layer is:

[0115] Block copolymer polypropylene (rubber phase average size 0.4 μm, content 28 wt%; melting point 165℃, melt index 3.0 g / 10 min) 89.5 parts by weight

[0116] 10 parts by weight of styrene-based elastomer TAIPOL 6014

[0117] Antioxidant 168, 0.5 parts by weight.

[0118] The material forming the corona layer is:

[0119] Random copolymer polypropylene 84.5 parts by weight

[0120] Acrylic-based elastomer 3980FL 15 parts by weight

[0121] Antioxidant 168, 0.5 parts by weight.

[0122] The material forming the encapsulation layer is:

[0123] Random copolymer polypropylene 84.5 parts by weight

[0124] Vinyl elastomer LC175 15 parts by weight

[0125] Antioxidant 168, 0.5 parts by weight.

[0126] Test case

[0127] In Examples 1-3 and Comparative Examples 1-2, the raw materials for forming the corona layer, core layer and encapsulation layer were mixed and fed into the hoppers of the three-layer co-extrusion casting machine according to the above weight ratio. The thickness ratio of the three layers was set to 1:4:1. A 50μm cast polypropylene film was produced by co-extrusion casting process, and the corona layer was corona-treated.

[0128] The cast polypropylene films of Examples 1-3 and Comparative Examples 1-2 were laminated onto the aluminum foil surface of PA / Al. After the adhesive was cured, the peel force between the cast polypropylene film and the aluminum foil (tested at a speed of 100 mm / min) and the peel appearance were tested at 25°C and 85°C, respectively. The results are shown in Table 1.

[0129] The results show that, compared with Comparative Examples 1-2, Examples 1-3, by limiting the size of the rubber phase in the block copolymer polypropylene used in the core layer, can play a role similar to "micro-crosslinking points," enhancing the connection and interaction between polymer molecular chains and forming hydrogen bonds with other molecular chains to produce effective bonding. This can improve the interlayer bonding strength between the core layer and the corona layer and the encapsulation layer. Therefore, the prepared cast polypropylene film has better interlayer stability, preventing it from delaminating when peeled from the substrate.

[0130] Table 1

[0131]

[0132] 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 present invention. 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.

[0133] 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 cast polypropylene film, characterized in that, It includes a corona layer, a core layer, and an encapsulation layer stacked sequentially; The material forming the core layer includes 65-95 parts by weight of block copolymer polypropylene, 5-20 parts by weight of a first elastomer, and 0-5 parts by weight of a first additive. The block copolymer polypropylene includes a rubber phase, wherein the average size of the rubber phase in the block copolymer polypropylene is 0-0.2 μm and is not 0; The content of the rubber phase in the block copolymer polypropylene is 20wt%-30wt%.

2. The cast polypropylene film according to claim 1, characterized in that, The average size of the rubber phase in the block copolymer polypropylene is 0-0.15 μm, and is not 0.

3. The cast polypropylene film according to claim 1, characterized in that, The materials that make up the core layer also include random copolymer polypropylene.

4. The cast polypropylene film according to claim 1, characterized in that, The block copolymer polypropylene is ethylene propylene block polypropylene with a melting point of 160℃-170℃ and a melt index of 1-4g / 10min.

5. The cast polypropylene film according to claim 1, characterized in that, The first elastomer includes at least one of a propylene-based elastomer, a vinyl elastomer, an ethylene-acrylic acid copolymer, or a styrene-based elastomer; Optionally, the first additive includes at least one of a polymer processing aid, an antioxidant, an antistatic agent, or a slip-forming agent.

6. The cast polypropylene film according to claim 1, characterized in that, The material forming the corona layer includes 70-98 parts by weight of random copolymer polypropylene, 10-20 parts by weight of the second elastomer, and 0-2 parts by weight of the second additive; Optionally, the second elastomer includes at least one of a propylene-based elastomer, a vinyl elastomer, an ethylene-acrylic acid copolymer, or a styrene-based elastomer; Optionally, the second additive includes at least one of a polymer processing aid, an antioxidant, an antistatic agent, or a slip-forming agent.

7. The cast polypropylene film according to claim 1, characterized in that, The material forming the encapsulation layer includes 70-98 parts by weight of random copolymer polypropylene, 10-20 parts by weight of a third elastomer, and 0-2 parts by weight of a third additive. Optionally, the third elastomer includes at least one of a propylene-based elastomer, a vinyl elastomer, an ethylene-acrylic acid copolymer, or a styrene-based elastomer; Optionally, the third additive includes at least one of a polymer processing aid, an antioxidant, an antistatic agent, or a slip-forming agent.

8. The cast polypropylene film according to claim 1, characterized in that, The initial sealing temperature of the encapsulation layer is 120-135℃.

9. The cast polypropylene film according to claim 1, characterized in that, The thickness ratio of the corona layer, core layer and encapsulation layer is 1:(3-9):

1.

10. A composite packaging film, characterized in that, Includes the cast polypropylene film according to any one of claims 1-9.

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