Polypropylene film for aluminum plastic film, aluminum plastic film and battery

Abstract

The invention discloses a polypropylene film for an aluminum-plastic film, the aluminum-plastic film and a battery, and relates to the technical field of battery packaging materials. The polypropylene film comprises a heat sealing layer, a core layer and a corona layer which are sequentially arranged in a stacked mode. Wherein the materials for forming the core layer comprise first polypropylene and a first polyolefin elastomer, the mass content of a rubber phase in the first polypropylene is 15-25%, and the melting point of the first polyolefin elastomer is 100-160 DEG C. The aluminum plastic film formed by the polypropylene film has excellent deep punching forming performance, high temperature resistance and electrolyte resistance.

Description

Technical Field

[0001] The invention relates to the technical field of battery packaging materials, and in particular to a polypropylene film used for an aluminum-plastic film, the aluminum-plastic film and a battery. Background Art

[0002] The battery cell is mainly soft-packaged by aluminum-plastic film, and the electrolyte is injected to form a soft-pack battery. By improving the deep-drawing and forming performance of the aluminum-plastic film, the energy density of the battery can be increased. The aluminum-plastic film includes an inner layer, an aluminum foil layer and an outer layer stacked in sequence. In order to make the aluminum-plastic film have excellent deep-drawing and forming performance, it is mainly achieved by adjusting the layer structure at this stage, such as increasing the thickness of the aluminum foil layer, the thickness of the outer layer, etc. These methods have limited improvement in the deep-drawing and forming performance. At present, there are few studies on the influence of the physical and chemical properties of the inner layer (polypropylene cast film) itself on the deep-drawing and forming performance. Secondly, the inner layer is directly in contact with the battery cell and the electrolyte, and its high temperature resistance and electrolyte resistance will directly affect the safety and packaging of the battery. However, at present, it is mainly through the additional addition of a passivation layer in the aluminum-plastic film to make the aluminum-plastic film have good high temperature resistance and electrolyte resistance, and the improvement is limited. Therefore, how to provide a polypropylene film that can improve the deep-drawing and forming performance and has good high temperature resistance and electrolyte resistance is a technical problem to be solved in this field. Summary of the invention

[0003] The main purpose of the present invention is to provide a polypropylene film for aluminum-plastic film, an aluminum-plastic film and a battery, so as to solve the problem that there is no polypropylene film with improved deep drawing and forming performance and good high temperature resistance and electrolyte resistance in the prior art.

[0004] In order to achieve the above object, according to a first aspect of the present invention, a polypropylene film for aluminum-plastic film is provided, the polypropylene film comprising a heat-sealing layer, a core layer and a corona layer stacked in sequence;

[0005] The material forming the core layer includes a first polypropylene and a first polyolefin elastomer, the mass content of the rubber phase in the first polypropylene is 15% to 25%, and the melting point of the first polyolefin elastomer is 100 to 160°C.

[0006] Furthermore, taking the thickness of the polypropylene film as 100%, the thickness of the heat sealing layer accounts for 5% to 20%, the thickness of the core layer accounts for 60% to 90%, and the thickness of the corona layer accounts for 5% to 20%.

[0007] Furthermore, the mass content of ethylene in the rubber phase of the first polypropylene is 20% to 40%.

[0008] Furthermore, the mass content of the first polyolefin elastomer in the material forming the core layer is ≤30%;

[0009] Preferably, the mass content of the first polypropylene in the material forming the core layer is 70-95%, and the mass content of the first polyolefin elastomer is 5-30%.

[0010] Further, the material forming the heat-sealing layer includes a second polypropylene and a second polyolefin elastomer;

[0011] The mass content of the second polypropylene in the material forming the heat-sealing layer is 90-97%, and the mass content of the second polyolefin elastomer is 3%-10%;

[0012] Preferably, the melting point of the second polyolefin elastomer is less than the melting point of the first polyolefin elastomer.

[0013] Furthermore, the melting point of the second polyolefin elastomer is 50-80°C.

[0014] Further, the first polyolefin elastomer and the second polyolefin elastomer are each independently selected from at least one of ethylene-α-olefin elastomer and propylene-α-olefin elastomer;

[0015] Preferably, the first polyolefin elastomer is copolymerized from propylene monomer and ethylene monomer, or the first polyolefin elastomer is copolymerized from propylene monomer and 1-butene monomer;

[0016] Preferably, the second polyolefin elastomer is copolymerized from ethylene monomer and 1-butene monomer, or the first polyolefin elastomer is copolymerized from ethylene monomer and 1-octene monomer;

[0017] Preferably, the weight average molecular weight of the first polyolefin elastomer is 150,000 to 250,000, and the weight average molecular weight of the second polyolefin elastomer is 120,000 to 200,000.

[0018] Further, the first polypropylene is a block copolymer polypropylene, and the second polypropylene is a binary random copolymer polypropylene or a ternary random copolymer polypropylene;

[0019] Preferably, the first polypropylene is a block copolymer formed by polymerizing propylene monomers and ethylene monomers; the second polypropylene is a random copolymer formed by polymerizing propylene monomers and ethylene monomers; or, the second polypropylene is a random copolymer formed by polymerizing propylene monomers and butene monomers; or, the second polypropylene is a random copolymer formed by polymerizing ethylene monomers, propylene monomers and butene monomers;

[0020] Preferably, the weight average molecular weight of the first polypropylene is 200,000 to 500,000, and the weight average molecular weight of the second polypropylene is 200,000 to 400,000.

[0021] Further, the material forming the corona layer includes a third polypropylene, and the third polypropylene is a binary random copolymer polypropylene;

[0022] Preferably, the third polypropylene is a binary random copolymer formed by polymerizing propylene monomer and ethylene monomer; or, the third polypropylene is a binary random copolymer formed by polymerizing propylene monomer and butene monomer;

[0023] Preferably, the weight average molecular weight of the third polypropylene is 200,000 to 400,000.

[0024] The second aspect of the present invention provides an aluminum-plastic film, which includes an inner layer, an aluminum foil layer and an outer layer stacked in sequence, wherein the inner layer is the polypropylene film for the aluminum-plastic film provided in the first aspect, the corona layer of the polypropylene film is bonded to one surface of the aluminum foil layer, and the other surface of the aluminum foil layer is bonded to the outer layer.

[0025] A third aspect of the present invention provides a battery, comprising a battery cell and the aluminum-plastic film provided in the second aspect, wherein the aluminum-plastic film is used to encapsulate the battery cell.

[0026] By applying the technical scheme of the present invention, the impact strength and toughness of the polypropylene film can be improved by limiting the composition of the polypropylene film and the physical parameters such as the rubber phase content of the first polypropylene and the melting point of the first polyolefin elastomer, and the yield elongation can be improved, so that the generation of silver streaks and microcracks can be reduced during the cold stamping forming process when preparing the aluminum-plastic film, and the aluminum foil layer can be effectively protected from being over-stretched and generating pinholes during the stamping process, thereby improving the deep stamping forming performance of the aluminum-plastic film formed by the polypropylene film. In addition, the ability of the polypropylene film to resist the penetration of polar solvents in the electrolyte can be enhanced, so that the aluminum-plastic film prepared has good electrolyte resistance, and the polypropylene film has good thermal stability, ensuring the bonding strength between the layers of the aluminum-plastic film, so that the aluminum-plastic film prepared has good high temperature resistance, and the aluminum-plastic film made of the polypropylene film is applied to the battery, which is helpful to improve the energy density and safety performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the structure of a polypropylene film used for an aluminum-plastic film in one embodiment of the present invention;

[0028] Figure 2 Schematic diagram of the structure of an aluminum-plastic film in one embodiment of the present invention.

[0029] Description of reference numerals:

[0030] 1-polypropylene film; 11-core layer; 12-corona layer; 13-heat sealing layer; 2-aluminum foil layer; 3-outer layer. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0032] As described in the background of the present invention, the prior art has the problem that there is no polypropylene film with improved deep drawing performance and good electrolyte resistance. In order to solve the above problems, Figure 1 As shown, in the first aspect of the present invention, a polypropylene film 1 for aluminum-plastic film is provided, the polypropylene film 1 comprises a heat-sealing layer 13, a core layer 11 and a corona layer 12 which are stacked in sequence, the material forming the core layer 11 comprises a first polypropylene and a first polyolefin elastomer, the mass content of the rubber phase in the first polypropylene is 15% to 25%, and the melting point of the first polyolefin elastomer is 100 to 160°C.

[0033] In the specific implementation process of the present invention, the polypropylene film 1 for aluminum-plastic film can be used as the inner layer of the aluminum-plastic film. At this time, the heat sealing layer 13 plays a packaging role, the core layer 11 plays an overall supporting role, and the corona layer 12 is attached to the aluminum foil layer 2 to play a bonding role.

[0034] In the polypropylene film 1 used for the aluminum-plastic film of the present invention, the core layer 11 is an important component of the aluminum-plastic film, and the quality of its performance directly affects the performance and quality of the aluminum-plastic film. The material forming the core layer 11 includes a first polypropylene and a first polyolefin elastomer, that is, the core layer 11 is obtained by film-forming a slurry formed by the first polypropylene and the first polyolefin elastomer.

[0035] Specifically, the first polypropylene is a thermoplastic, which includes a polypropylene matrix formed by polymerization of propylene monomers. The first polypropylene also includes a rubber phase, which can be a copolymer (such as ethylene-propylene rubber) formed by polymerization of ethylene monomers and propylene monomers. The rubber phase can form a dispersed phase in the polypropylene matrix, and the rubber phase content directly affects the physical properties of the first polypropylene, such as elasticity, impact resistance, etc., thereby improving the overall performance of the material.

[0036] The mass content of the rubber phase in the first polypropylene is 15% to 25%, for example, 15%, 18%, 20%, 22%, 25% or any two of them. By limiting the rubber phase content in the first polypropylene, the polypropylene film 1 has better toughness and impact resistance, and the deep-drawing forming performance of the aluminum-plastic film formed by the polypropylene film 1 can be improved.

[0037] It should be noted that the first polypropylene sample can be analyzed by infrared spectroscopy (FTIR) to identify the characteristic absorption peaks of the rubber phase therein, and the content of the rubber phase can be calculated by quantitatively analyzing the intensity of these peaks.

[0038] The first polyolefin elastomer can be a polymer copolymerized by propylene and α-olefin (such as ethylene, 1-butene, 1-hexene, etc.), and this type of polymer has good elasticity, heat resistance and chemical resistance. Adding the first polyolefin elastomer to the polypropylene film 1 can improve its performance, such as improving high temperature resistance, chemical resistance, etc., so that the polypropylene film 1 has good high temperature resistance and electrolyte resistance.

[0039] The melting point of the polyolefin elastomer will directly affect its thermal stability. Polyolefin elastomers with higher melting points usually have better thermal stability and can maintain their performance at higher temperatures. In addition, the regularity, crystallinity and molecular weight of the molecular chain will affect the melting point. The higher the regularity of the molecular chain and the greater the crystallinity, the higher the melting point; the larger the molecular weight, the stronger the interaction between the molecular chains and the higher the melting point. The melting point of the first polyolefin elastomer is 100-160°C, for example, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C or a range composed of any two of them. By limiting the melting point of the first polyolefin elastomer to 100-160°C, the thermal stability of the polypropylene film 1 can be improved, and the bonding strength between the polypropylene film 1 and the aluminum foil layer 2 can be ensured under high temperature conditions, so that the aluminum-plastic film prepared has better high temperature resistance. When the melting point of the first polyolefin elastomer is 100-160° C., it indicates that the first polyolefin elastomer of the present invention has high molecular chain regularity, high crystallinity, high molecular weight, and strong interaction between molecular chains, which can further improve the high temperature resistance and electrolyte resistance of the formed polypropylene film 1.

[0040] It should be noted that the melting point of the first polyolefin elastomer can be measured by differential scanning calorimetry (DSC), and the thermal performance parameters such as the melting point of the sample can be obtained by measuring the heat change of the sample during the heating or cooling process. Specifically, the first polyolefin elastomer sample to be tested is ground into fine powder to ensure that the contact area between the sample and the heat is large enough; the weighed sample is placed in a crucible to ensure that the sample is evenly distributed; the crucible containing the sample is placed in a differential scanning calorimeter, and appropriate parameters such as heating or cooling rate and temperature range are set, and heating or cooling is performed according to the set experimental conditions, and the heat change between the sample and the reference is recorded in real time; on the formed differential scanning calorimetry curve, the melting point is usually manifested as an obvious endothermic peak, and the melting point of the first polyolefin can be obtained by analyzing the position of this endothermic peak.

[0041] The polypropylene film 1 used for the aluminum-plastic film of the present invention can improve the impact strength and toughness of the polypropylene film 1 and improve the yield elongation by limiting the composition of the polypropylene film 1 and the physical parameters such as the rubber phase content of the first polypropylene and the melting point of the first polyolefin elastomer, so as to reduce the generation of silver streaks and microcracks during the cold stamping forming process when preparing the aluminum-plastic film, and effectively protect the aluminum foil layer 2 from being over-stretched and generating pinholes during the stamping process, thereby improving the deep stamping forming performance of the aluminum-plastic film formed by the polypropylene film 1. In addition, the ability of the polypropylene film 1 to resist the penetration of polar solvents in the electrolyte can be enhanced, so that the aluminum-plastic film prepared by the polypropylene film has good electrolyte resistance. The polypropylene film 1 has good thermal stability, ensures the bonding strength between the layers of the aluminum-plastic film, and has good high temperature resistance. The aluminum-plastic film made of the polypropylene film 1 is applied to a battery, which is helpful to improve the energy density and safety performance of the battery.

[0042] The present invention does not limit the specific thickness ratio of each layer in the polypropylene film 1, and can be adjusted and obtained according to actual needs. For example, in some embodiments, the thickness of the polypropylene film 1 is 100%, the thickness of the heat sealing layer 13 accounts for 5% to 20%, such as 5%, 8%, 10%, 12%, 15%, 20% or any two of them, the thickness of the core layer 11 accounts for 60% to 90%, such as 60%, 70%, 75%, 80%, 85%, 90% or any two of them, and the thickness of the corona layer 12 accounts for 5% to 20%, such as 5%, 8%, 10%, 12%, 15%, 20% or any two of them. Among them, the thickness of the core layer 11 accounts for 60% to 90% of the thickness of the entire polypropylene film 1, which is an important component of the aluminum-plastic film, and the quality of its performance directly affects the performance and quality of the aluminum-plastic film. By limiting the thickness ratio of each layer, the yield strength and tensile strength of the polypropylene film 1 can be improved.

[0043] The mass content of the rubber phase in the first polypropylene is 15% to 25%. In some embodiments, the mass content of ethylene in the rubber phase of the first polypropylene is 20% to 40%, that is, in this rubber phase, the mass of ethylene accounts for 20% to 40% of the total mass of the rubber phase, for example, 20%, 25%, 30%, 35%, 40% or a range composed of any two of them. By limiting the mass proportion of ethylene, the comprehensive performance of the polypropylene film 1 can be further improved.

[0044] It should be noted that the first polypropylene sample can be analyzed by infrared spectroscopy (FTIR) to identify the characteristic absorption peaks of the rubber phase and the characteristic absorption peaks of the vinyl group. By quantitatively analyzing the intensities of these peaks, the content of the rubber phase and the content of ethylene in the rubber phase can be calculated.

[0045] The present invention does not limit the specific mass content of each component in the material forming the core layer 11, and can be adjusted and obtained according to actual needs. In some embodiments, the mass content of the first polyolefin elastomer in the material forming the core layer 11 is ≤30%. In some preferred embodiments, the mass content of the first polypropylene in the material forming the core layer 11 is 70% to 95%, such as 70%, 75%, 80%, 85%, 90%, 95% or the range of any two thereof, and the mass content of the first polyolefin elastomer is 5% to 30%, such as 5%, 10%, 15%, 20%, 25%, 30% or the range of any two thereof.

[0046] In the specific implementation process of the present invention, the heat-sealing layer 13 is in direct contact with the battery core to ensure that the aluminum-plastic film can be tightly bonded to the battery core during the heat-sealing process to form a sealed package.

[0047] In some embodiments, the material forming the heat seal layer 13 includes a second polypropylene and a second polyolefin elastomer, wherein the mass content of the second polypropylene is 90% to 97%, such as 90%, 92%, 95%, 97% or a range consisting of any two thereof, and the mass content of the second polyolefin elastomer is 3% to 10%, such as 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range consisting of any two thereof, and the melting point of the second polyolefin elastomer is less than the melting point of the first polyolefin elastomer, which can significantly reduce the heat seal temperature, improve the heat seal strength, and meet the packaging requirements of the battery. Introducing the second polyolefin elastomer into the heat seal layer 13 helps to further improve the deep forming performance and reduce the heat seal temperature to improve the heat seal strength.

[0048] The second polypropylene is a thermoplastic plastic, which includes a polypropylene matrix polymerized from propylene monomers. The second polyolefin elastomer can be a polymer copolymerized from ethylene and α-olefins (such as 1-butene, 1-hexene, etc.). In some preferred embodiments, the melting point of the second polyolefin elastomer is 50-80°C, such as 50°C, 60°C, 70°C, 80°C or any two thereof. By limiting the melting point of the second polyolefin elastomer to 50-80°C, the packaging temperature can be further reduced and the packaging strength can be improved.

[0049] It should be noted that the specific material types of the first polyolefin elastomer and the second polyolefin elastomer can be the same or different, as long as the above melting point requirements are met. For example, in some embodiments, the first polyolefin elastomer and the second polyolefin elastomer are each independently selected from at least one of ethylene-α-olefin elastomer and propylene-α-olefin elastomer.

[0050] In some preferred embodiments, the first polyolefin elastomer is formed by copolymerization of propylene monomer and ethylene monomer, or the first polyolefin elastomer is formed by copolymerization of propylene monomer and 1-butene monomer, and the second polyolefin elastomer is formed by copolymerization of ethylene monomer and 1-butene monomer, or the second polyolefin elastomer is formed by polymerization of ethylene monomer and 1-octene monomer.

[0051] In some preferred embodiments, the weight average molecular weight of the first polyolefin elastomer is 150,000 to 250,000, and the weight average molecular weight of the second polyolefin elastomer is 120,000 to 200,000.

[0052] The present invention does not limit the specific type of polypropylene, as long as the rubber phase and ethylene content in the first polypropylene are guaranteed. In some embodiments, the first polypropylene is a block copolymer polypropylene, and the second polypropylene is a binary random copolymer polypropylene or a ternary random copolymer polypropylene. Specifically, when the first polypropylene is a block copolymer polypropylene, the first polypropylene is a block copolymer formed by polymerization of propylene monomer and ethylene monomer. At this time, the first polypropylene includes propylene homopolymer and ethylene-propylene rubber, wherein the propylene homopolymer is a homopolymer (i.e., a polypropylene matrix) formed by polymerization of propylene monomer, and the ethylene-propylene rubber is a rubber phase formed by copolymerization of ethylene and propylene monomers, which constitutes the total amount of rubber phase in the first polypropylene. When the second polypropylene is a binary random copolymer polypropylene, the second polypropylene can be a random copolymer formed by polymerization of propylene monomer and other olefin monomers (such as ethylene monomer or butene monomer); when the second polypropylene is a ternary random copolymer polypropylene, the second polypropylene can be a random copolymer formed by polymerization of ethylene monomer, propylene monomer and butene monomer. By limiting the specific types of the first polypropylene and the second polypropylene, the comprehensive performance of the polypropylene film 1 can be further improved.

[0053] In some preferred embodiments, the weight average molecular weight of the first polypropylene is 200,000 to 500,000, for example, 200,000, 250,000, 300,000, 350,000, 400,000, 450,000, 500,000 or any two thereof, and the weight average molecular weight of the second polypropylene is 200,000 to 400,000, for example, 200,000, 250,000, 300,000, 350,000, 400,000 or any two thereof.

[0054] The present invention does not limit the material forming the corona layer 12, and it can be a conventional polypropylene material in the art. For example, in some embodiments, the material forming the corona layer 12 includes a third polypropylene, and the third polypropylene includes a binary random copolymer polypropylene, that is, the third polypropylene is a random copolymer formed by polymerization of propylene monomers and other olefin monomers (such as ethylene monomers or butene monomers).

[0055] In some preferred embodiments, the weight average molecular weight of the third polypropylene is 200,000 to 400,000, for example, 200,000, 250,000, 300,000, 350,000, 400,000 or any two thereof.

[0056] like Figure 2 As shown, in the second aspect of the present invention, an aluminum-plastic film is provided, which includes an inner layer, an aluminum foil layer 2 and an outer layer 3 stacked in sequence, the inner layer is the polypropylene film 1 for the aluminum-plastic film provided in the first aspect, the corona layer 12 of the polypropylene film 1 is bonded to one surface of the aluminum foil layer 2, and the other surface of the aluminum foil layer 2 is bonded to the outer layer 3.

[0057] Specifically, the polypropylene film 1 for the aluminum-plastic film comprises a heat-sealing layer 13, a core layer 11 and a corona layer 12 which are stacked in sequence, and in the aluminum-plastic film, the corona layer 12 is attached to the aluminum foil layer 2 to play a bonding effect. It can also be understood that the aluminum-plastic film comprises a corona layer 12, a core layer 11, a heat-sealing layer 13, an aluminum foil layer 2 and an outer layer 3 which are stacked in sequence.

[0058] The polypropylene film 1 can be arranged on one surface of the aluminum foil layer 2 by heat bonding or gluing. The polypropylene film 1 serves as the inner surface of the aluminum-plastic film and will come into contact with the electrolyte and the battery cell after packaging. The outer layer 3 can be arranged on the other surface of the aluminum foil layer 2 by heat bonding or gluing, and serves as the outer surface of the aluminum-plastic film and will come into contact with the outside air after packaging. Due to the inclusion of the above-mentioned excellent polypropylene film 1, the aluminum-plastic film of the present invention has excellent deep-drawing forming performance, high temperature resistance and electrolyte resistance, and can be used as a soft packaging material for the battery cell. In some embodiments, the peeling force of the inner layer of the aluminum-plastic film is greater than 3N / 15mm at 120°C.

[0059] In some embodiments, the thickness ratio of the polypropylene film 1 , the aluminum foil layer 2 , and the outer layer 3 is (10-40):(20-80):(10-40).

[0060] A third aspect of the present invention provides a battery, comprising a battery cell and the aluminum-plastic film provided in the second aspect, wherein the aluminum-plastic film is used to encapsulate the battery cell.

[0061] The aluminum-plastic film of the present invention is mainly used in lithium batteries. Specifically, the battery cell of the present invention can be a lithium battery cell. After the aluminum-plastic film is packaged, the inner layer of the aluminum-plastic film is closely attached to the battery cell, and the polypropylene film 1 is actually in contact with the electrolyte. It can be understood that the corona layer 12 is closely attached to the battery cell. Due to the inclusion of the aluminum-plastic film with excellent performance, the battery of the present invention has both excellent energy density and safety performance, and good packaging performance.

[0062] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0063] Example 1

[0064] 1. Preparation of polypropylene film 1

[0065] S1, melt-mixing a first polypropylene (block copolymer polypropylene) and a first polyolefin elastomer (propylene-ethylene polyolefin elastomer) at a mass ratio of 80:20 at a temperature of 260° C. to obtain a core layer slurry;

[0066] The second polypropylene (binary random copolymer polypropylene) and the second polyolefin elastomer (ethylene-butene polyolefin elastomer) are melt-mixed at a mass ratio of 90:10 at a temperature of 250° C. to obtain a heat sealing layer slurry;

[0067] The third polypropylene (binary random copolymer polypropylene) is melted at a temperature of 250° C. to obtain a corona layer slurry;

[0068] S2, co-extrude the heat sealing layer slurry, the core layer slurry and the corona layer slurry at a temperature of 270°C to form a polypropylene film 1 consisting of a heat sealing layer 13, a core layer 11 and a corona layer 12, wherein the thicknesses of the heat sealing layer 13, the core layer 11 and the corona layer 12 are 6μm, 28μm and 6μm respectively.

[0069] The first polypropylene is a block copolymer polypropylene, wherein the mass content of the rubber phase is 15%, the mass content of ethylene in the rubber phase is 20%, and the weight average molecular weight of the first polypropylene is 350,000;

[0070] The second polypropylene is a binary random copolymer polypropylene with a weight average molecular weight of 230,000;

[0071] The third polypropylene is a binary random copolymer polypropylene with a weight average molecular weight of 230,000;

[0072] The first polyolefin elastomer is a propylene-ethylene elastomer having a melting point of 100° C. and a weight average molecular weight of 150,000;

[0073] The second polyolefin elastomer is vinyl-1-butene elastomer, having a melting point of 60° C. and a weight average molecular weight of 120,000.

[0074] 2. Preparation of aluminum-plastic film

[0075] Aluminum foil with a thickness of 40 μm is selected as the aluminum foil layer 2;

[0076] The corona layer 12 of the polypropylene film 1 is arranged opposite to the aluminum foil layer 2, and the polypropylene film 1 is thermally bonded to one surface of the aluminum foil layer 2 at a temperature of 110°C; a composite biaxially oriented nylon film is coated on the other surface of the aluminum foil layer 2 as an outer layer film, and after aging at a temperature of 60°C for 5 days, an outer layer 3 with a thickness of 25 μm is formed to obtain the aluminum-plastic film of this embodiment.

[0077] Example 2

[0078] Compared with Example 1, the mass content of the rubber phase in the first polypropylene is 20%, the mass content of ethylene in the rubber phase is 30%, and the weight average molecular weight of the first polypropylene is 300,000.

[0079] Example 3

[0080] Compared with Example 1, the mass content of the rubber phase in the first polypropylene is 25%, the mass content of ethylene in the rubber phase is 40%, and the weight average molecular weight of the first polypropylene is 250,000.

[0081] Example 4

[0082] Compared with Example 1, the melting point of the first polyolefin elastomer is 120° C. and the weight average molecular weight is 160,000.

[0083] Example 5

[0084] Compared with Example 1, the melting point of the first polyolefin elastomer is 160° C. and the weight average molecular weight is 180,000.

[0085] Example 6

[0086] Compared with Example 1, the thicknesses of the heat sealing layer 13, the core layer 11 and the corona layer 12 are 8 μm, 24 μm and 8 μm respectively.

[0087] Example 7

[0088] Compared with Example 1, the thicknesses of the heat sealing layer 13, the core layer 11 and the corona layer 12 are 2 μm, 36 μm and 2 μm respectively.

[0089] Example 8

[0090] Compared with Example 1, the mass ratio of the first polypropylene to the first polyolefin elastomer is 70:30.

[0091] Example 9

[0092] Compared with Example 1, the mass ratio of the first polypropylene to the first polyolefin elastomer is 95:5.

[0093] Example 10

[0094] Compared with Example 1, the melting point of the second polyolefin elastomer is 50° C. and the weight average molecular weight is 100,000.

[0095] Embodiment 11

[0096] Compared with Example 1, the melting point of the second polyolefin elastomer is 80° C. and the weight average molecular weight is 150,000.

[0097] Example 12

[0098] Compared with Example 1, the melting point of the second polyolefin elastomer is 100° C. and the weight average molecular weight is 180,000.

[0099] Comparative Example 1

[0100] The difference from Example 1 is that the core layer 11 does not contain the first polyolefin elastomer.

[0101] Comparative Example 2

[0102] The difference from Example 1 is that the mass content of the rubber phase in the first polypropylene is 10%, the melting point of the first polyolefin elastomer is 80° C., and the weight average molecular weight of the first polypropylene is 480,000.

[0103] Comparative Example 3

[0104] The difference from Example 1 is that the mass content of the rubber phase in the first polypropylene is 10%, the mass content of ethylene in the rubber phase is 15%, and the weight average molecular weight of the first polypropylene is 420,000.

[0105] Comparative Example 4

[0106] The difference from Example 1 is that the mass content of the rubber phase in the first polypropylene is 30%, the mass content of ethylene in the rubber phase is 20%, and the weight average molecular weight of the first polypropylene is 280,000.

[0107] Comparative Example 5

[0108] The difference from Example 1 is that the melting point of the first polyolefin elastomer is 80° C. and the weight average molecular weight is 120,000.

[0109] Comparative Example 6

[0110] The difference from Example 1 is that the melting point of the first polyolefin elastomer is 170° C. and the weight average molecular weight is 230,000.

[0111] Test example

[0112] 1. Deep drawing performance

[0113] The aluminum-plastic film was cut into 110mm (TD) * 130mm (MD) samples, and cold stamped using a 60mm (TD) * 75mm (MD) mold with a molding depth of 5.0mm. The whitening degree of the inner layer side of the edge of the corner was observed. Slight whitening was marked as √, severe whitening was marked as ×, and the presence of microcracks was marked as ××.

[0114] 2. High temperature resistance

[0115] The aluminum-plastic film was cut into 15mm (TD)*100mm (MD) specimens, and the peel strength between the inner CPP layer and the aluminum foil layer at 120°C was tested using a universal testing machine. The test method was T-type peeling, and the tensile rate was 100mm / min.

[0116] 3. Electrolyte resistance

[0117] The aluminum-plastic film was cut into 15mm (TD) * 100mm (MD) strips, placed in a PP bottle filled with electrolyte, and 1000ppm of water was added. The PP bottle containing the strips was placed in a 60℃ oven and left to stand for 14 days. The peel strength between the inner CPP layer and the aluminum foil layer at room temperature was tested using a universal testing machine. The test method was T-type peeling and the tensile rate was 100mm / min.

[0118] The test results are shown in Table 1.

[0119] Table 1

[0120] serial number Deep drawing performance High temperature resistance N / 15mm Electrolyte resistance N / 15mm Example 1 √ 4.0 8.5 Example 2 √ 3.9 8.6 Example 3 √ 3.8 8.8 Example 4 √ 4.5 8.2 Example 5 √ 5.0 8.3 Example 6 √ 4.8 8.0 Example 7 √ 5.2 7.8 Example 8 √ 4.5 9 Example 9 √ 3.4 7.5 Example 10 √ 3.1 8 Embodiment 11 √ 4.2 8.1 Example 12 √ 3 7 Comparative Example 1 ×× 0.5 2.8 Comparative Example 2 ×× 1.5 4.7 Comparative Example 3 × 3.5 6.1 Comparative Example 4 √ 2.5 4.8 Comparative Example 5 × 2.5 3.5 Comparative Example 6 × 3.8 6.8

[0121] According to Table 1, the material of the polypropylene film forming the core layer in the embodiment satisfies: the mass content of the rubber phase in the first polypropylene is 15% to 25%, and the melting point of the first polyolefin elastomer is 100 to 160°C, while the first polyolefin elastomer is not added to the core layer of Comparative Example 1, Comparative Example 2 does not meet the mass content of the rubber phase in the first polypropylene of 15% to 25% and the melting point of the first polyolefin elastomer of 100 to 160°C, Comparative Examples 3 to 4 do not meet the mass content of the rubber phase in the first polypropylene of 15% to 25%, and Comparative Examples 5 to 6 do not meet the melting point of the first polyolefin elastomer of 100 to 160°C, and the aluminum-plastic film of Examples 1 to 11 has excellent deep-drawing forming performance, high-temperature peeling strength greater than 3N / 15mm, electrolyte resistance greater than 7N / 15mm, and performance qualified data indicators, with good high-temperature resistance and electrolyte resistance, while the effect of the comparative example is not as good as that of the embodiment. Therefore, the present invention can significantly improve the deep-drawing forming performance, high-temperature resistance and electrolyte resistance of the aluminum-plastic film by introducing a polypropylene film that meets the above parameters.

[0122] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A polypropylene film for aluminum-plastic film, characterized in that: The polypropylene film (1) comprises a heat-sealing layer (13), a core layer (11) and a corona layer (12) which are stacked in sequence; The material forming the core layer (11) includes a first polypropylene and a first polyolefin elastomer, the mass content of the rubber phase in the first polypropylene is 15% to 25%, and the melting point of the first polyolefin elastomer is 100 to 160°C.

2. The polypropylene film according to claim 1, characterized in that Taking the thickness of the polypropylene film (1) as 100%, the thickness of the heat sealing layer (13) accounts for 5% to 20%, the thickness of the core layer (11) accounts for 60% to 90%, and the thickness of the corona layer (12) accounts for 5% to 20%.

3. The polypropylene film according to claim 1, characterized in that The mass content of ethylene in the rubber phase of the first polypropylene is 20% to 40%; and / or, The mass content of the first polyolefin elastomer in the material forming the core layer (11) is ≤30%; Preferably, in the material forming the core layer (11), the mass content of the first polypropylene is 70% to 95%, and the mass content of the first polyolefin elastomer is 5% to 30%.

4. The polypropylene film according to any one of claims 1 to 3, characterized in that The material forming the heat-sealing layer (13) includes a second polypropylene and a second polyolefin elastomer; Wherein, the mass content of the second polypropylene in the material forming the heat-sealing layer (13) is 90% to 97%, and the mass content of the second polyolefin elastomer is 3% to 10%; Preferably, the melting point of the second polyolefin elastomer is less than the melting point of the first polyolefin elastomer.

5. The polypropylene film according to claim 4, characterized in that The melting point of the second polyolefin elastomer is 50-80°C.

6. The polypropylene film according to claim 4, characterized in that The first polyolefin elastomer and the second polyolefin elastomer are each independently selected from at least one of ethylene-α-olefin elastomer and propylene-α-olefin elastomer; Preferably, the first polyolefin elastomer is copolymerized from propylene monomer and ethylene monomer, or the first polyolefin elastomer is copolymerized from propylene monomer and 1-butene monomer; Preferably, the second polyolefin elastomer is copolymerized from ethylene monomer and 1-butene monomer, or the second polyolefin elastomer is copolymerized from ethylene monomer and 1-octene monomer; Preferably, the weight average molecular weight of the first polyolefin elastomer is 150,000 to 250,000; Preferably, the weight average molecular weight of the second polyolefin elastomer is 120,000 to 200,000.

7. The polypropylene film according to claim 4, characterized in that The first polypropylene is a block copolymer polypropylene, and the second polypropylene is a binary random copolymer polypropylene or a ternary random copolymer polypropylene; Preferably, the first polypropylene is a block copolymer polymerized from propylene monomers and ethylene monomers; Preferably, the second polypropylene is a random copolymer formed by polymerizing propylene monomers and ethylene monomers; or, the second polypropylene is a random copolymer formed by polymerizing propylene monomers and butene monomers; or, the second polypropylene is a random copolymer formed by polymerizing ethylene monomers, propylene monomers and butene monomers; Preferably, the weight average molecular weight of the first polypropylene is 200,000 to 500,000, and the weight average molecular weight of the second polypropylene is 200,000 to 400,000.

8. The polypropylene film according to claim 4, characterized in that The material forming the corona layer (12) includes a third polypropylene, and the third polypropylene is a binary random copolymer polypropylene; Preferably, the third polypropylene is a binary random copolymer formed by polymerizing propylene monomer and ethylene monomer; or, the third polypropylene is a binary random copolymer formed by polymerizing propylene monomer and butene monomer; Preferably, the weight average molecular weight of the third polypropylene is 200,000 to 400,000.

9. An aluminum-plastic film, characterized in that: The aluminum-plastic film comprises an inner layer, an aluminum foil layer (2) and an outer layer (3) which are stacked in sequence; wherein the inner layer is the polypropylene film (1) for the aluminum-plastic film according to any one of claims 1 to 8, the corona layer (12) of the polypropylene film (1) is bonded to one surface of the aluminum foil layer (2), and the other surface of the aluminum foil layer (2) is bonded to the outer layer (3).

10. A battery, characterized in that: The battery comprises a battery cell and the aluminum-plastic film according to claim 9, wherein the aluminum-plastic film is used to encapsulate the battery cell.

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