Metal-plastic composite film, preparation method thereof and secondary battery

Abstract

The invention discloses a metal-plastic composite film, a preparation method thereof and a secondary battery, and relates to the technical field of secondary batteries. The composition of the hot melting resin layer is improved, the polypropylene block copolymer and the ethylene-alpha-olefin copolymer are introduced on the basis of the polypropylene random copolymer, the content of each component is controlled, and the polypropylene block copolymer can enable the metal-plastic composite film to have good electrolyte barrier property and high heat sealing strength; the ethylene-alpha-olefin copolymer can reduce the hardness of the welding resin layer to a certain extent, improve the softness of the welding resin layer and improve the matching property with most tab films. The metal-plastic composite film provided by the invention does not generate an adhesion problem after being baked, and also has relatively good heat sealing performance.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular to a metal-plastic composite film, a preparation method thereof, and a secondary battery. Background Art

[0002] Currently, lithium-ion batteries primarily fall into three categories: cylindrical, prismatic, and soft-pack. Cylindrical and prismatic batteries, made of materials like aluminum alloy and stainless steel, are rigid, limiting battery design. Soft-pack batteries, on the other hand, significantly improve the rigidity of rigid-pack batteries and are gradually gaining a significant share of the lithium-ion battery market.

[0003] Soft-pack batteries are often manufactured using a metal-plastic composite film molding process. The commonly used metal-plastic composite film consists, from the outside inward, of an outer base resin layer, an outer adhesive layer, an intermediate metal layer, a thermal bonding resin layer, and a heat-melting resin layer. The heat-melting resin layer, primarily made of polypropylene, provides insulation to prevent short circuits and heat-seals the battery components during assembly.

[0004] The manufacturing process of soft pack batteries generally includes: (1) lamination; (2) welding the tabs to form a battery cell; (3) forming a metal-plastic composite film; (4) placing the battery cell in the pit after the metal-plastic composite film is formed and pre-packaging; (5) high-temperature baking to reduce the moisture in the battery cell and the aluminum-plastic composite film; (6) injecting electrolyte from the pre-reserved injection port and sealing; (7) standing under high temperature or room temperature conditions and performing chemical formation; (8) exhausting air and sealing the two sides along the edge of the battery cell. The soft pack battery is basically formed. During step (5), the baking is generally carried out at 70-110℃. The heat-melting resin layer of the metal-plastic composite film contacts each other under the combined action of heat and pressure, and it is easy to form adhesion, which is called initial heat sealing, or low-condition heat sealing, or false heat sealing state, which affects the efficiency of injecting electrolyte in step 6). Increasing the melting point of the heat-welding resin layer is beneficial to improving the adhesion problem, but it will cause other heat-sealing problems, increase the heat-sealing starting temperature, narrow the heat-sealing condition window of the metal-plastic composite film on the client side, and reduce its application performance.

[0005] The sticking property refers to that one side (referring to the hot melt adhesive layer) of the metal-plastic composite film is bonded to each other under the joint action of heat and pressure, so that the hot melt adhesive layer and the hot adhesive layer are separated by external force in the subsequent process. The above-mentioned sticking property is related to the composition of the hot melt adhesive layer. It is generally believed that the low molecular weight component, or the low melting point component, or the high melt index MFR component, or the component with poor compatibility with the main resin of the hot melt adhesive layer will migrate under the action of heat, migrate to the surface of the hot melt adhesive layer, and thus be bonded to the other side of the hot melt adhesive layer. Therefore, increasing the melting point, molecular weight and compatibility of each component in the hot melt adhesive layer becomes the main way to improve the sticking property of the metal-plastic composite film in the application process.

[0006] As the outer packaging material of lithium ion battery, the metal-plastic composite film not only requires good anti-sticking property, but also requires other good properties. Specifically, the hot melt adhesive layer involves heat sealing performance, including initial heat sealing performance, heat sealing performance after resistance to electrolyte, and top sealing performance with positive and negative tabs. By increasing the melting point, molecular weight and reducing the melt index MFR of each component in the hot melt adhesive layer, the initial heat sealing performance and the top sealing performance with positive and negative tabs are affected first, and the window of heat sealing conditions is narrowed. The heat sealing conditions include the temperature, pressure and heat sealing time of the heat sealing knife. The heat sealing conditions affect the efficiency and energy consumption of battery production. Customers generally hope that the window of heat sealing conditions is as wide as possible, that is, lower heat sealing temperature, lower pressure and shorter heat sealing time.

[0007] Therefore, it is urgent to improve the metal-plastic composite film to obtain good heat sealing performance while ensuring that the metal-plastic composite film has no sticking.

[0008] In view of this, the present application is proposed. SUMMARY

[0009] The purpose of the present application is to provide a metal-plastic composite film and a preparation method thereof and a secondary battery, which aims to solve the sticking problem of the metal-plastic composite film after baking in the application process on the premise of ensuring the heat sealing performance.

[0010] The present application is realized as follows:

[0011] In a first aspect, the present application provides a metal-plastic composite film, comprising a metal layer, a hot adhesive resin layer and a hot melt adhesive layer arranged in sequence.

[0012] The hot melt adhesive layer comprises at least one of polypropylene random copolymer, polypropylene block copolymer and ethylene-alpha-olefin copolymer;

[0013] The extreme difference in heat seal strength of the metal-plastic composite film obtained at a heat seal temperature range of 160°C to 195°C is ≤15N / 15mm;

[0014] And / or, after being stored at any temperature between 100° C. and 130° C. for 12 hours, the difference between the nanoindentation hardness H2 obtained by nanoindentation testing and the initial nanoindentation hardness H1 is ≤1.0 MPa.

[0015] In an optional embodiment, the heat-welding resin layer contains, by mass percentage, 55%-90% of a polypropylene random copolymer, 0%-15% of a polypropylene block copolymer, and 10%-30% of an ethylene-α-olefin copolymer;

[0016] The main chain of polypropylene random copolymer is composed of ethylene and propylene;

[0017] Polypropylene block copolymer is a block copolymer formed by ethylene and propylene.

[0018] In an optional embodiment, the heat-welding resin layer contains, by mass percentage, 65%-80% of a polypropylene random copolymer, 5%-10% of a polypropylene block copolymer, and 15%-25% of an ethylene-α-olefin copolymer;

[0019] and / or, the ratio of the length of the ethylene segments in the polypropylene random copolymer to the total segment length of the polypropylene random copolymer is (10-20):100;

[0020] and / or the number average molecular weight of the polypropylene random copolymer is 100,000 to 180,000;

[0021] And / or, at 230° C., the melt index MFR of the polypropylene random copolymer is ≤25 g / 10 min; preferably 7 g / 10 min-20 g / 10 min.

[0022] In an optional embodiment, the ratio of the length of the ethylene segments in the polypropylene block copolymer to the total segment length of the polypropylene block copolymer is (10-20):100;

[0023] and / or the polypropylene block copolymer has a melting point of less than 160° C.;

[0024] And / or, the crystallinity of the polypropylene block copolymer is less than or equal to 40%.

[0025] In an optional embodiment, the ethylene-α-olefin copolymer is formed by polymerizing ethylene as a main monomer and an α-olefin as a comonomer, wherein the α-olefin is selected from at least one of 1-butene, 1-pentene and 1-hexene; preferably 1-butene;

[0026] Preferably, the ratio of the ethylene segment length to the total segment length of the ethylene-α-olefin copolymer is (50-90):100, more preferably (80-90):100;

[0027] And / or, the melting point of the ethylene-α-olefin copolymer is 60°C to 170°C.

[0028] In an optional embodiment, the thickness of the metal layer is 40 μm-200 μm, the thickness of the thermal adhesive resin layer is 20 μm-50 μm, and the thickness of the thermal welding resin layer is 20 μm-50 μm;

[0029] And / or, the material of the metal layer is selected from at least one of aluminum, aluminum alloy, stainless steel, steel, titanium steel and nickel-plated iron;

[0030] And / or, the material of the thermal adhesive resin layer is modified polyolefin; the polyolefin in the modified polyolefin is selected from at least one of polypropylene resin and propylene-ethylene copolymer; the modified raw material is selected from at least one of acrylic acid, methacrylic acid, maleic acid, anhydrous maleic anhydride and polyamide.

[0031] In an optional embodiment, the heat-welding resin layer further contains 200-5000 ppm of a slip agent and 0.1%-0.2% of an opening agent;

[0032] Preferably, the lubricant is an amide compound;

[0033] Preferably, the opening agent is selected from at least one of silicon oxide, aluminum oxide, sodium aluminosilicate and potassium aluminosilicate.

[0034] In an optional embodiment, an outer base resin layer is provided on a side of the metal layer away from the thermal adhesive resin layer, and the material of the outer base resin layer is selected from at least one of polyester, polyamide, and polyurethane; preferably, a lubricant is coated on the surface of the outer base resin layer; and / or a lubricant is coated on the thermal adhesive resin layer; more preferably, the lubricant is an amide lubricant;

[0035] Preferably, a first anti-corrosion layer is provided between the metal layer and the thermal adhesive resin layer;

[0036] Preferably, a second anti-corrosion layer is provided between the metal layer and the outer base resin layer.

[0037] In a second aspect, the present invention provides a method for preparing the metal-plastic composite film according to any one of the aforementioned embodiments, comprising: sequentially preparing a metal layer, a thermal adhesive resin layer, and a thermal welding resin layer, and ensuring that the parameters of each layer meet the requirements.

[0038] In a third aspect, the present invention provides a secondary battery comprising the metal-plastic composite film according to any one of the aforementioned embodiments.

[0039] The present invention has the following beneficial effects: It improves the composition of the heat-welding resin layer by introducing a polypropylene block copolymer and an ethylene-α-olefin copolymer based on a polypropylene random copolymer, and controlling the content of each component. The polypropylene block copolymer enables the metal-plastic composite film to have excellent electrolyte barrier properties and high heat-seal strength; the ethylene-α-olefin copolymer can reduce the hardness of the welded resin layer to a certain extent, increase its softness, and improve compatibility with most tab adhesives. The metal-plastic composite film provided by the present invention does not cause adhesion problems after baking and also has good heat-seal performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0041] Figure 1 This is a structural diagram of the metal-plastic composite film provided by an embodiment of the present invention.

[0042] Icon: 101 - thermally fused resin layer; 102 - thermally adhesive resin layer; 103 - metal layer; 104 - outer base material resin layer. DETAILED DESCRIPTION

[0043] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0044] Please refer to Figure 1 An embodiment of the present invention provides a metal-plastic composite film, which includes at least a heat-melting resin layer 101, a heat-adhesive resin layer 102 and a metal layer 103 arranged in sequence. By improving the heat-melting resin layer 101, the metal-plastic composite film will not have adhesion problems after baking and also has good heat sealing performance.

[0045] [Thermal fusion resin layer 101]

[0046] The heat-welding resin layer 101 is mainly polyolefin resin, and contains at least one of polypropylene random copolymer, polypropylene block copolymer and ethylene-α-olefin copolymer. The heat-welding resin layer 101 contains at least any one, two or three of the above.

[0047] In some embodiments, the heat-welding resin layer 101 comprises, by mass percentage, 55%-90% polypropylene random copolymer, 0%-15% polypropylene block copolymer, and 10%-30% ethylene-α-olefin copolymer. The improved heat-welding resin layer 101 of the present invention comprises at least a polypropylene random copolymer and an ethylene-α-olefin copolymer, and preferably comprises a polypropylene random copolymer, a polypropylene block copolymer, and an ethylene-α-olefin copolymer. By introducing the polypropylene block copolymer and the ethylene-α-olefin copolymer and controlling the added amounts, the adhesion problem caused by baking can be improved without reducing the heat-sealing performance.

[0048] It should be noted that the hot-melt resin layer of the polypropylene random copolymer system basically has good heat-sealing properties. On this basis, adding some polypropylene block copolymer components can make the metal-plastic composite film have good electrolyte barrier properties, higher heat-sealing strength, appearance transparency and anti-whitening properties; ethylene-α-olefin copolymer is added to the hot-melt resin as an elastomer, which can further reduce the hardness of the hot-melt resin layer, improve its softness, and thereby improve its compatibility with most ear glues.

[0049] Specifically, in the hot-melt resin layer 101, the content of polypropylene random copolymer can be 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% and the like; the content of polypropylene block copolymer can be 0%, 3%, 5%, 8%, 10%, 13%, 15% and the like. A content of polypropylene block copolymer exceeding 15% is not conducive to the heat sealing condition window; the content of ethylene-α-olefin copolymer can be 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30% and the like.

[0050] In a preferred embodiment, the heat-sealing resin layer 101 comprises, by mass, 65%-80% polypropylene random copolymer, 5%-10% polypropylene block copolymer, and 15%-25% ethylene-α-olefin copolymer. The amounts of each component are preferably controlled within the above ranges to further enhance heat-sealing strength, improve transparency, and enhance electrolyte resistance. The thickness of the heat-sealing resin layer 101 is 20 μm-50 μm, which further enhances heat-sealing performance.

[0051] The polypropylene random copolymer makes the hot melt adhesive resin layer 101 have basic heat sealing performance and good electrolyte resistance. The polypropylene random copolymer can be composed of one molecular structure or two or more different molecular structures of polypropylene random copolymer, the main chain of which is composed of ethylene and propylene, and the ratio of the length of the ethylene segment to the total length of the polypropylene random copolymer is (10-20):100, such as 10:100, 13:100, 15:100, 18:100, 20:100, etc. The number average molecular weight of the polypropylene random copolymer is 100-180, such as 100, 120, 140, 160, 180, etc. The melt index MFR of the polypropylene random copolymer is ≤25 g / 10 min at 230°C, such as 25 g / 10 min, 20 g / 10 min, 15 g / 10 min, 10 g / 10 min, 7 g / 10 min, 5 g / 10 min, etc., preferably 7 g / 10 min-20 g / 10 min. The melting point span is 120-160°C, and the polypropylene random copolymer can be composed of one molecular structure or two or more different molecular structures. The hot melt adhesive resin layer is used to ensure the initial heat sealing performance, and the heat sealing strength at a heat sealing temperature of 190°C is >130 N / 15 mm. The above parameters of the polypropylene random copolymer are adjusted to further improve the heat sealing performance and electrolyte resistance of the hot melt adhesive resin layer 101.

[0052] The polypropylene block copolymer is a block copolymer composed of ethylene and propylene, and the melting point is prioritized to achieve heat sealing effect, and the melting point is less than 160°C. The ratio of the length of the ethylene segment to the total length of the polypropylene block copolymer is (10-20):100, such as 10:100, 13:100, 15:100, 18:100, 20:100, etc. The crystallinity of the polypropylene block copolymer is less than or equal to 40%, such as 40%, 35%, 30%, 25%, 20%, etc., and too high crystallinity will bring adverse effects of whitening. The above parameters of the polypropylene block copolymer are adjusted to further improve the electrolyte barrier performance of the hot melt adhesive resin layer 101 and improve the heat sealing strength.

[0053] The ethylene-α-olefin copolymer is formed by polymerization of the main monomer ethylene and the comonomer α-olefin, the α-olefin is selected from at least one of 1-butene, 1-pentene and 1-hexene, the α-olefin can be any one or several of the above, and is preferably 1-butene. By regulating the type of α-olefin, the hardness of the hot melt adhesive layer 101 is further reduced, and the softness is improved, which is more matched with the tab glue. The ethylene-α-olefin copolymer is composed of one molecular structure or two or more different molecular structures of ethylene-α-olefin copolymer, and the melting point of the ethylene-α-olefin copolymer is 60-170°C, such as 60°C, 80°C, 100°C, 120°C, 150°C, 170°C, etc. The ratio of the length of the ethylene segment to the total length of the ethylene-α-olefin copolymer is (50-90):100, such as 50:100, 60:100, 70:100, 80:100, 90:100, etc., and is preferably (80-90):100.

[0054] It should be noted that the ethylene-α-olefin copolymer has better compatibility with the polypropylene system resin in the hot melt adhesive layer than other types of elastomers, and is not easy to precipitate and aggregate to the surface of the hot melt adhesive layer to cause adhesion problems. At the same time, it has good plasticizing ability to the polypropylene resin, which is beneficial to improve the softness of the hot melt adhesive layer and improve its matching with most tab glues. The improvement of this performance is especially reflected in the heat sealing condition window of the metal-plastic composite film.

[0055] It should be noted that the metal-plastic composite film added with the ethylene-α-olefin copolymer is verified according to the heat sealing condition window, and the heat sealing strength is in a constant force range when the heat sealing temperature is in the span interval from 160°C to 195°C. The difference between the maximum and minimum values of the heat sealing strength corresponding to any temperature (referred to as the range in the present application) is ≤15N / 15mm, and is preferably ≤10N / 15mm.

[0056] In some embodiments, the heat-sealing resin layer 101 also contains 200-5000 ppm of a lubricant and 0.1%-0.2% of an opening agent. The addition of a lubricant can improve the formability of the metal-plastic composite film. The lubricant is one or more amide compounds with different melting points added to the heat-sealing resin layer in a specific ratio. The amide compounds gradually precipitate from the heat-sealing resin layer over time and as the ambient temperature changes, accumulating on the surface of the heat-sealing resin layer. This reduces the viscosity of the polypropylene resin itself, providing a lubricating effect and preventing adhesion between the heat-sealing resin layer and the outer substrate layer. The addition of an opening agent can also help reduce the adhesion of the metal-plastic composite film. The opening agent can be one or more inorganic substances added to the heat-sealing resin layer in a specific ratio. In some embodiments, the opening agent is selected from at least one of silicon oxide, aluminum oxide, sodium aluminosilicate, and potassium aluminosilicate. Any one or more of these opening agents can help reduce the adhesion of the metal-plastic composite film.

[0057] [Thermal Adhesive Resin Layer 102]

[0058] Thermal adhesive resin layer 102 primarily serves to bond metal layer 103 to thermally bonded resin layer 101. Thermal adhesive resin layer 102 may be formed from a modified polyolefin, modified cyclic polyolefin, or the like, to enhance adhesion between metal layer 103 and thermally bonded resin layer 101. The modified polyolefin is selected from at least one of polypropylene resin and propylene-ethylene copolymer, and may be any one or more of these. The modifying raw material is selected from at least one of acrylic acid, methacrylic acid, maleic acid, anhydrous maleic anhydride, and polyamide, and may be any one or more of these.

[0059] In some embodiments, the thickness of the thermal adhesive resin layer 102 is 20 μm-50 μm to better bond the metal layer 103 and the thermal adhesive resin layer 101 .

[0060] Taking a metal-plastic composite film having a total thickness of 80 μm of the heat-melting resin layer 101 and the heat-adhesive resin layer 102 as an example, the heat sealing temperature is set to any temperature in the range of 160° C. to 195° C., and the metal-plastic composite film is heat-sealed. A 15 mm width test area is used as the test area. The ultimate difference in heat seal strength obtained by the test is ≤15 N / 15 mm, preferably ≤10 N / 15 mm.

[0061] [Metal layer 103]

[0062] The metal layer 103 mainly functions to inhibit the entry of external moisture and solvent into the battery cell and to provide the metal-plastic composite film with good formability. The metal layer 103 is made of at least one selected from the group consisting of aluminum, aluminum alloy, stainless steel, steel, titanium steel, and nickel-plated iron. The metal layer 103 can be made of any one or a combination of two or more of the above materials, and is preferably made of aluminum alloy, nickel-plated iron, stainless steel, or the like. The thickness of the metal layer 103 is in the range of 40 μm to 200 μm, and can be, for example, 40 μm, 50 μm, 80 μm, 100 μm, 130 μm, 150 μm, 180 μm, or 200 μm.

[0063] [Outer base resin layer 104]

[0064] In some embodiments, the outer base resin layer 104 is provided on the side of the metal layer 103 away from the heat-adhesive resin layer 102. The outer base resin layer 104 functions as a base material for the metal-plastic composite film used as a packaging material for lithium-ion batteries, and is provided on the outer side of the metal-plastic composite film. The outer base resin layer 104 has at least an insulating property.

[0065] The outer base resin layer 104 is made of at least two selected from the group consisting of polyester, polyamide, and polyurethane, and has a layered structure of two or more layers. The outer base resin layer 104 can be a composite film formed by the action of an adhesive, or a resin composite film having two or more layers formed by co-extrusion of resins. The polyester can be polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyethylene isophthalate, or a copolymer polyester, and the polyamide can be aliphatic polyamide such as nylon 6, nylon 66, nylon 610, nylon 12, nylon 46, or a copolymer of nylon 6 and nylon 66.

[0066] In some embodiments, the outer base resin layer 104 can be manufactured by a stepwise biaxial stretching method, a film blowing method, a simultaneous stretching method, or a coating method, and has a film material with a stretched property.

[0067] In some embodiments, to improve the formability of the metal-plastic composite film as an outer package material for lithium ion batteries, the surface of the outer base resin layer 104 can be coated with a lubricant, and the hot melt resin layer 101 can also be coated with a lubricant. The lubricant on the surface of the outer base resin layer 104 and the hot melt resin layer 101 is not particularly limited, and is preferably an amide-based lubricant. Amide-based lubricants include saturated fatty acid amides, unsaturated fatty acid amides, substituted amides, hydroxymethyl amides, saturated fatty acid bisamides, unsaturated fatty acid bisamides, fatty acid amides and aromatic bisamides, etc. Taking saturated fatty acid amides as an example, lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, hydroxystearic acid amide, etc. can be used. Taking unsaturated fatty acid amides as an example, oleic acid amide, erucic acid amide, etc. can be mentioned. Substituted amides include N-oleopalmitamide, N-stearic amide, N-stearic amide, N-oleostearic amide and N-stearic amide.

[0068] In addition to the above layer structure, in some embodiments, a first corrosion-resistant layer is provided between the metal layer 103 and the hot bonding resin layer 102. The first corrosion-resistant layer functions to avoid corrosion of the metal layer surface by hydrogen fluoride produced by electrolyte and water, and prevents delamination of the metal layer 103 and the hot bonding resin layer 102. The first corrosion-resistant layer can mainly include a film obtained by drying treatment of a coating-type corrosion-resistant liquid mainly composed of at least two components selected from the group consisting of trivalent chromium compounds, inorganic acids, organic resins, bridging agents, water and solvents.

[0069] Similarly, in some embodiments, a second corrosion-resistant layer is provided between the metal layer 103 and the outer base resin layer 104. The second corrosion-resistant layer can stabilize the surface uniformity of the metal layer 103, reduce the adhesion (wettability) variation, and has the effect of preventing delamination between the outer base resin layer 104 and the metal layer 103 of the metal-plastic composite film during long-term storage in a high-temperature and high-humidity environment. The second corrosion-resistant layer can mainly include a film obtained by drying treatment of a coating-type corrosion-resistant liquid mainly composed of at least two components selected from the group consisting of trivalent chromium compounds, inorganic acids, organic resins, bridging agents, water and solvents.

[0070] The embodiments of the present application also provide a method for preparing a metal-plastic composite film, which comprises: sequentially preparing a metal layer 103, a hot bonding resin layer 102 and a hot melt resin layer 101, and making the parameters of each layer meet the requirements. The preparation method of each layer is not limited, and the current preparation method is within the scope of protection of the present application. The main steps are as follows:

[0071] (1) The two sides of the metal layer are coated with an anticorrosion liquid, and the anticorrosion liquid is heat treated at high temperature for a period of time, and dried to form an anticorrosion layer. The coating can be completed at one time, that is, by double-sided coating; the coating can also be completed twice, that is, first by single-sided coating, and then by coating the other side after the anticorrosion layer is dried, to finally obtain a metal with anticorrosion layers on both sides. The coating of the anticorrosion liquid can be implemented by means of bar coating, roll coating, gravure coating, or dipping, and one of the coating methods or a combination of two coating methods can be selected. The high-temperature drying of the anticorrosion liquid is carried out at a temperature condition range of 110°C-210°C, and the temperature of the surface of the metal layer in the coating process is controlled in real time to promote the full high-temperature chemical reaction on the surface of the intermediate metal layer, and the wet film amount of the anticorrosion liquid coated on the intermediate metal layer is in the range of 1.6-3.2 g / m 2 .

[0072] (2) The intermediate metal layer is provided with an outer substrate layer or a heat-bonding resin layer and a heat-fusing resin layer, and the order of arrangement is not limited, for example, the heat-bonding resin layer and the heat-fusing resin layer can be arranged first, and then the outer substrate layer is arranged; or the outer substrate resin layer can be arranged first, and then the heat-bonding resin layer and the heat-fusing resin layer are arranged. The outer substrate layer is a multi-layer composite material composed of at least two or more of polyester, polyamide, and polyurethane, which can be bonded and attached to the intermediate metal layer by heating and compounding together at the same time, or the polyurethane solution polymer can be arranged on any one of the polyester, polyamide, and intermediate metal layer by coating, and then dried at a temperature in the range of 60-100°C to obtain a solid polyurethane layer with bonding force, and then the polyurethane layer through which at least two or more layers of the polyester, polyamide, and intermediate metal layer can be bonded and attached to each other.

[0073] In the present application, the heat-bonding resin layer and the heat-fusing resin layer are heat-fused and film-coated onto the intermediate metal layer, and heat treated at a high temperature condition of 120-200°C to improve the bonding force between the heat-bonding resin layer and the intermediate metal layer, and the bonding force of the heat-bonding resin layer and the intermediate metal layer after heat treatment at a high temperature condition is required to be ≥8 N / 25 mm, and in order to ensure that the heat-bonding resin layer and the heat-fusing resin layer have a good appearance, a relatively low temperature condition of 0-50°C is used for post-treatment immediately after heat treatment to promote rapid crystallization of the inner layer PP and reduce the crystallinity. For the arrangement of the slip agent, a slip agent and an opening agent are added to the heat-fusing resin layer, and the slip arrangement of the inner layer is completed at the same time as the heat-fusing and film-coating onto the intermediate metal layer.

[0074] For the arrangement of the slip agent of the outer substrate resin layer, a coating method is used, and specifically, the slip agent can be coated on the surface by bar coating, roll coating, gravure coating, or dipping.

[0075] The embodiment of the present application also provides a secondary battery comprising the metal plastic composite film, and the secondary battery can also comprise a positive electrode, a negative electrode, an electrolyte, etc., and the secondary battery can be in the form of a soft package battery, but is not limited thereto.

[0076] The features and performances of the present application are further described in detail below in combination with embodiments.

[0077] It should be noted that the following examples and comparative examples are prepared to test the anti-blocking property and heat sealing performance of the metal plastic composite film, and the anti-blocking property is evaluated by the following two test methods: nanoindentation test and blocking test; and the heat sealing performance is evaluated by the test of heat sealing window condition.

[0078] (1) Nanoindentation test of the metal plastic composite film

[0079] The nanoindentation test is used to characterize the hardness of the hot melt adhesive layer in the metal plastic composite film, and the nanoindentation hardness and indentation depth of the hot melt adhesive layer are obtained under certain test conditions. The hot melt adhesive layer is required to have a certain softness, and the compatibility between the internal components of the hot melt adhesive layer is still good after a certain high-temperature baking, and the softness is still unchanged.

[0080] The nanoindentation test is mainly used to study the mechanical properties of materials in micro-nano structure. A certain shaped indenter is pressed into the material at a uniform or non-uniform rate, a certain load P is usually applied on the indenter, and the indenter reaches the maximum depth at a certain fixed time, at which time a maximum indentation depth parameter value h is obtained, and the projection area A of the contact area between the indenter and the material is also obtained. According to the load / projection area (P / A), the nanoindentation hardness H parameter of the material is obtained, and the material physical index-Young's modulus E parameter is also obtained, and the related formula is as follows:

[0081]

[0082] In formula (a), H represents hardness, unit: MPa; P represents the load applied on the indenter, unit: N; A represents the projection area of the contact area between the indenter and the material, unit: mm 2 .

[0083] In formula (b), S represents stiffness, unit: N / mm; π represents the circular ratio constant; β represents the geometric shape related constant of the indenter, without unit; Er represents the simple Young's modulus, which is the modulus data directly obtained by the machine, unit: GPa.

[0084] In formula (c), E represents the Young's modulus of the test material, unit: GPa; Ei represents the Young's modulus of the indenter, unit: GPa; Vi represents the Poisson's ratio of the indenter, without unit; V represents the Poisson's ratio of the test material, without unit.

[0085] According to the above formula, the greater the maximum indentation depth h of the material, the greater the contact projection area A, the smaller the hardness H, and the smaller the Young's modulus E. The change trend of hardness H with the maximum indentation depth h is the same as that of the Young's modulus E with the maximum indentation depth h. The Young's modulus of a polymer material is a inherent property of the polymer material, which is related to the molecular chain structure, molecular weight and its distribution, crosslinking degree, crystallinity, orientation, etc. The molecular chain structure, molecular weight and its distribution of the hot melt adhesive layer are similar, and there is no crosslinking degree problem. The hardness H and the Young's modulus E are mainly related to the crystallinity, orientation, and the state of the elastomer and small molecule additives existing between the chain segments.

[0086] (2) Adhesion test of metal-plastic composite film

[0087] The metal-plastic composite film product is prepared to have a size of TD=76 mm and MD=200 mm. The metal-plastic composite film is folded along the MD edge, so that the hot melt adhesive layers are attached to each other, and the outer substrate resin layer faces outward. The folded sample is placed in an oven at a certain high temperature. The bottom of the sample is kept flat, and a 1 kg weight is placed on top of the sample to apply pressure. The temperature of the oven can be set at 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C and above, with an increment or decrement of 5°C or 10°C. The storage time can be set for 6 hours or 12 hours. After moving away the 1 kg weight, the sample is taken out of the oven, and the unfolding of the folded sample is observed immediately. Five samples per group are tested in parallel, and the results are determined by visual observation.

[0088] (3) Heat sealing window condition test of metal-plastic composite film

[0089] A finished metal-plastic composite film was prepared with dimensions of TD = 76 mm and MD = 200 mm. The film was folded in half along the MD edge, so that the heat-melting resin layers adhered to each other and the outer substrate resin layer was exposed to the outside. The folded sample was then placed under a heat-sealing knife and heat-sealed along the TD edge. DOE validation was performed on multiple factors, with heat-sealing knife temperatures of 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, and 195°C, heat-sealing knife pressures of 0.5 MPa, 1.0 MPa, and 1.5 MPa, and heat-sealing times of 2 seconds, 3 seconds, and 4 seconds. In the present invention, a surface pressure of 1.0 MPa and a heat-sealing time of 2 seconds were preferred. The heat-sealed samples were cut into strips with the size of TD=15mm, MD=100mm, and the heat-sealing strength was tested using a tensile testing device. The tensile test speed was 150-300mm / min. In the present invention, a tensile rate of 300mm / min was preferred. A T-type peeling with a peeling surface of 180° was performed to obtain the maximum peeling value at the heat seal. 3 samples / group were tested in parallel. The strength force values ​​under each heat-sealing condition and the heat-sealing and unsealing interface damage were compared to verify the width of the heat-sealing condition window of the sample. If a higher heat-sealing strength and good interface damage performance can be obtained under low conditions, it is defined as a sample with a wider window of heat-sealing conditions, and stronger applicability to the client.

[0090] To further characterize the temperature-dependent compatibility of the ethylene-α-olefin copolymer in the heat-welding resin layer 101, the heat-welding resin layer was tested for hardness and penetration depth using a nanoindenter. Specifically, a Berkovich indenter with a regular triangular pyramidal shape was pressed into the surface of the heat-welding resin layer using the nanoindenter at 25°C and 50% relative humidity. The indenter load was maintained at 10 mN. During the indentation process, a vibration frequency of 220 Hz and an amplitude of 2 nm were applied to the indenter via the piezoelectric ceramic. The indentation was stopped after 40 seconds. The maximum penetration depth h1 of the heat-welding resin layer was 3.5-4.2 μm, resulting in a nanoindentation hardness H1 of 32-39 MPa, preferably 30-35 MPa.

[0091] After the metal plastic composite film is stored at any temperature in the range of 100°C to 130°C for 12 hours, the surface of the hot melt adhesive resin layer is pressed by a Berkovich indenter in the shape of an equilateral triangular pyramid using a nanoindenter in an environment with a temperature of 25°C and a relative humidity of 50%, the load of the indenter is kept constant at 10 mN, a vibration frequency of 220 Hz is applied to the indenter by a piezoelectric ceramic during the pressing process, the amplitude is 2 nm, the pressing process is stopped after 40 s, the maximum pressing depth h2 of the hot melt adhesive resin layer is still 3.4-4.3 μm, the nanoindentation hardness H2 of the hot melt adhesive resin layer obtained at this time is still 31-40 MPa, preferably 30-35 MPa. The difference between the pressing depth h2 and the pressing depth h1 is ≤0.2 μm. The difference between the nanoindentation hardness H2 and the nanoindentation hardness H1 is ≤1.0 MPa.

[0092] That is, after the metal plastic composite film is stored at any temperature in the range of 100°C to 130°C for 12 hours, the difference between the nanoindentation hardness H2 obtained by nanoindenter testing and the initial nanoindentation hardness H1 is ≤1.0 MPa.

[0093] It should be noted that the metal plastic composite film provided in the embodiment has good adhesion properties. The hot melt adhesive resin layer of the metal plastic composite film is adhered to the hot melt adhesive resin layer, a force of 1 kg is applied to press down, and at the same time, the metal plastic composite film is stored at any temperature in the range of 100°C to 130°C for 12 hours, then taken out and placed in an environment with a temperature of 25°C and a relative humidity of 50% to cool, and then observed. The hot melt adhesive resin layer of the metal plastic composite film and the hot melt adhesive resin layer are separated from each other, and there is no adhesion phenomenon.

[0094] Example 1

[0095] The embodiment provides a metal plastic composite film and a preparation method thereof, and specifically as follows:

[0096] The metal plastic composite film provided in the embodiment has a layered structure of an outer substrate resin layer, a metal layer, a hot adhesive resin layer and a hot melt adhesive resin layer.

[0097] The hot melt resin layer (40 μm in thickness) contains 85% of a polypropylene random copolymer and 15% of an ethylene-α-olefin copolymer. The polypropylene random copolymer is a commercially available material, the ratio of the length of the ethylene segment to the total length of the polypropylene random copolymer is 20%, the number average molecular weight of the polypropylene random copolymer is 150,000, the melt index MFR (230°C) of the polypropylene random copolymer is 12 g / 10 min, and the melting point interval of the polypropylene random copolymer is 140-160°C. The ethylene-α-olefin copolymer is formed by polymerization of the main monomer ethylene and the comonomer 1-butene, the melting point interval of the ethylene-α-olefin copolymer is 60-80°C, and the melt index MFR (230°C) of the ethylene-α-olefin copolymer is 7.0 g / 10 min.

[0098] As the metal-plastic composite film of the present application, the other side of the metal layer closely attached to the hot adhesive resin layer is further provided with an outer substrate resin layer, and the outer substrate resin layer is provided to play the basic performance of the metal-plastic composite film as a packaging material for lithium ion batteries. The outer substrate resin layer is a composite film sequentially containing polyethylene terephthalate, polyurethane, nylon 6, and polyurethane in an outer-to-inner layer four-layer structure, and the thickness of the outer substrate resin layer is 33 μm, wherein the thickness of the polyethylene terephthalate is 12 μm, the thickness of the nylon-6 is 15 μm, and the thickness of the polyurethane is 3 μm.

[0099] The hot adhesive resin layer mainly plays a role in bonding the metal layer and the hot melt resin layer, and the hot adhesive resin layer is a modified polyolefin, specifically a commercially available maleic anhydride modified propylene-ethylene copolymer, and the thickness is 40 μm. The metal layer mainly plays a role in inhibiting the entry of external moisture and solvent into the battery cell and providing good forming performance of the metal-plastic composite film, and the material of the metal layer is aluminum, and the thickness of the metal layer is 50 μm. The inner and outer surfaces of the metal layer are provided with an anti-corrosion layer.

[0100] The present embodiment also provides a preparation method of a metal-plastic composite film, and the steps are as follows:

[0101] (1) The two surfaces of the metal layer are coated with a commercially available anti-corrosion liquid, and the anti-corrosion liquid is mainly composed of a trivalent chromium compound, an inorganic acid, an organic polymer resin containing a hydroxyl group, a crosslinking agent, and water. The wet film amount of the anti-corrosion liquid is 2.5 g / m 2 , and then heat treated at 200°C for 1 min.

[0102] (2) First, the hot adhesive resin layer and the hot melt resin layer are prepared, and then the outer substrate layer is provided.

[0103] The thermal bonding resin layer and the hot melt resin layer are melted and coated on the intermediate metal layer by hot melting, and then heat treated at a high temperature of 150°C. The bonding force between the thermal bonding resin layer and the intermediate metal layer after the heat treatment is required to be ≥8 N / 25 mm. After the heat treatment, a post-treatment is immediately performed at a relatively low temperature of 25°C. For the setting of the slip agent, the slip agent and the opening agent are preferably added to the hot melt resin layer, and the slip setting of the inner layer is completed at the same time when the hot melt resin layer is melted and coated on the intermediate metal layer.

[0104] Performance test:

[0105] To further characterize the influence of temperature on the compatibility of the ethylene-α-olefin copolymer in the hot melt resin layer, the hardness and indentation depth of the hot melt resin layer were tested by a nanoindenter. Specifically, the Berkovich indenter in the shape of an equilateral triangular pyramid was pressed onto the surface of the hot melt resin layer using a nanoindenter in an environment with a temperature of 25°C and a relative humidity of 50%. The load of the indenter was kept constant at 10 mN. During the indentation process, a vibration frequency of 220 Hz was applied to the indenter by a piezoelectric ceramic, and the amplitude was 2 nm. The indentation was stopped when the indentation time reached 40 s. At this time, the maximum indentation depth h1 of the hot melt resin layer was 3.83 μm, and the nanoindentation hardness H1 of the hot melt resin layer was 35.2 MPa.

[0106] After the metal plastic composite film was stored at any temperature in the range of 100°C to 130°C for 12 hours, it was taken out and cooled, and then the Berkovich indenter in the shape of an equilateral triangular pyramid was pressed onto the surface of the hot melt resin layer using a nanoindenter in an environment with a temperature of 25°C and a relative humidity of 50%. The load of the indenter was kept constant at 10 mN. During the indentation process, a vibration frequency of 220 Hz was applied to the indenter by a piezoelectric ceramic, and the amplitude was 2 nm. The indentation was stopped when the indentation time reached 40 s. At this time, the maximum indentation depth h2 of the hot melt resin layer was as shown in Table 1-1, and the nanoindentation hardness H2 of the hot melt resin layer was as shown in Table 1-1.

[0107] Table 1-1 Test results of h2 and H2 at different temperatures

[0108] Temperature (°C) 100 105 110 115 120 125 130 Maximum indentation depth h2 3.79 3.81 3.92 3.77 3.88 3.97 3.84 Nanohardness H2 35.4 35.3 34.7 35.7 35.1 34.2 34.8

[0109] The difference between the indentation depth h2 and the indentation depth h1 was ≤0.14 μm. The difference between the nanoindentation hardness H2 and the nanoindentation hardness H1 was ≤1.0 MPa. After the metal plastic composite film was stored at 100-130°C, the change in the mechanical properties of the hot melt resin layer in the compression direction was small, and the elastomer had not been significantly precipitated from the hot melt resin layer.

[0110] The metal-plastic composite film provided in this embodiment has good encapsulation capabilities with most tab adhesives and a wide window of heat-sealing conditions. Taking a metal-plastic composite film having a total thickness of 153 μm and a total heat-adhesive resin layer of 80 μm and a total heat-melting resin layer as an example, the heat-sealing temperature is set to any temperature within the range of 160°C to 195°C, and a surface pressure of 1.0 MPa and a heat-sealing time of 2 seconds are used to heat-seal the metal-plastic composite film. The heat-seal strength obtained by the test is shown in Table 1-2 below, with a 15 mm width as the test area. The range of the heat-seal strength force value is ≤8 N / 15 mm, indicating a wide window of heat-sealing conditions, with conditions from 160°C to 195°C being effective heat-sealing conditions.

[0111] Table 1-2 Heat seal strength test results at different temperatures

[0112] Temperature (°C) 160 165 170 175 180 185 190 195 Heat seal strength N / 15 mm 134 134 134 135 127 128 132 135

[0113] The metal-plastic composite film provided in this embodiment also exhibits excellent adhesion properties. When the heat-melting resin layer and the heat-melting resin layer of the metal-plastic composite film were bonded together and pressed downward with a constant force of 1 kg, the films were simultaneously stored at any temperature between 100°C and 130°C for 12 hours. The films were then removed and cooled in an environment of 25°C and 50% relative humidity. The films were then observed to show that the heat-melting resin layer and the heat-melting resin layer of the metal-plastic composite film were separated from each other without any adhesion, as shown in Tables 1-3 below.

[0114] Table 1-3 Adhesion performance test results at different temperatures

[0115] Temperature (°C) 100 105 110 115 120 125 130 Whether blocking Not blocking Not blocking Not blocking Not blocking Not blocking Not blocking Not blocking

[0116] Example 2

[0117] The only difference from Example 1 is that the polypropylene random copolymer is composed of two polypropylene random copolymers with different molecular structures. The ratio of the ethylene segment length in the first polypropylene random copolymer to the total segment length of the polypropylene random copolymer is 20%, the number average molecular weight is 180,000, the melt index (MFR) (230°C) is 20 g / 10 min, and the melting point is between 120°C and 154°C. The ratio of the ethylene segment length in the second polypropylene random copolymer to the total segment length of the polypropylene random copolymer is 10%, the number average molecular weight is 120,000, the melt index (MFR) (230°C) is 7 g / 10 min, and the melting point is between 130°C and 145°C.

[0118] To further characterize the influence of temperature on the compatibility of the ethylene-α-olefin copolymer in the hot melt adhesive resin layer, the hardness and indentation depth of the hot melt adhesive resin layer were tested by a nanoindenter. Specifically, under the condition of a temperature of 25°C and a relative humidity of 50%, a Berkovich indenter in the shape of a regular triangular pyramid was pressed onto the surface of the hot melt adhesive resin layer using a nanoindenter, the load of the indenter was kept constant at 10 mN, a vibration frequency of 220 Hz was applied to the indenter by a piezoelectric ceramic during the indentation process, the amplitude was 2 nm, the indentation time was 40 s, and the indentation was stopped at this time, at which the maximum indentation depth h1 of the hot melt adhesive resin layer was 4.18 μm, and the nanoindentation hardness H1 of the hot melt adhesive resin layer obtained at this time was 32.4 MPa.

[0119] After the metal plastic composite film was stored at any temperature in the range of 100°C to 130°C for 12 hours, it was taken out and cooled, and then a Berkovich indenter in the shape of a regular triangular pyramid was pressed onto the surface of the hot melt adhesive resin layer using a nanoindenter under the condition of a temperature of 25°C and a relative humidity of 50%, the load of the indenter was kept constant at 10 mN, a vibration frequency of 220 Hz was applied to the indenter by a piezoelectric ceramic during the indentation process, the amplitude was 2 nm, the indentation time was 40 s, and the indentation was stopped at this time, at which the maximum indentation depth h2 of the hot melt adhesive resin layer was as shown in Table 2-1 below, and the nanoindentation hardness H2 of the hot melt adhesive resin layer obtained at this time was as shown in Table 2-1 below.

[0120] Table 2-1 Test results of h2 and H2 at different temperatures

[0121] Temperature (°C) 100 105 110 115 120 125 130 Maximum indentation depth h2 4.22 4.15 4.19 4.09 4.25 4.23 4.2 Nanohardness H2 32.1 32.6 32.5 33.1 31.9 32.1 32.4

[0122] The difference between the indentation depth h2 and the indentation depth h1 was ≤0.09 μm. The difference between the nanoindentation hardness H2 and the nanoindentation hardness H1 was ≤0.7 MPa, indicating that the compatibility of the ethylene-α-olefin copolymer with the above-mentioned polypropylene random copolymer system was still good after storage at any temperature in the range of 100-130°C.

[0123] The metal plastic composite film of the embodiment of the present application has good packaging capacity with most tab rubbers, and the window of the heat sealing condition is relatively wide. Taking a metal plastic composite film with a total layer thickness of the hot adhesive resin layer and the heat sealing resin layer of 80 μm and a total thickness of 152 μm as an example, the heat sealing temperature was set to be any temperature in the range of 160°C to 195°C, the heat sealing surface pressure was 1.0 MPa, the heat sealing time was 2 seconds, the metal plastic composite film was heat sealed, the heat sealing strength obtained by testing according to a test area with a width of 15 mm is shown in Table 2-2 below, and the range of the heat sealing strength was ≤8 N / 15 mm, indicating that the window of the heat sealing condition is relatively wide.

[0124] Table 2-2 Test results of heat sealing strength at different temperatures

[0125] Temperature (°C) 160 165 170 175 180 185 190 195 Heat seal strength N / 15 mm 133 134 135 136 128 131 133 129

[0126] The metal-plastic composite film of the present embodiment also exhibits good adhesion properties. The hot melt resin layer of the metal-plastic composite film is adhered to another hot melt resin layer, and a force of 1 kg is applied to press down on the layers, and the layers are stored at any temperature in the range of 100°C to 130°C for 12 hours. After being removed and cooled in an environment of 25°C and 50% relative humidity, the layers are observed. The hot melt resin layer of the metal-plastic composite film and the hot melt resin layer are separated from each other without any adhesion, as shown in Tables 2-3 below.

[0127] Table 2-3 Adhesion property test results at different temperatures

[0128] Temperature (°C) 100 105 110 115 120 125 130 Whether blocking Not blocking Not blocking Not blocking Not blocking Not blocking Not blocking Not blocking

[0129] Example 3

[0130] The difference from Example 1 is only that the type of α-olefin is different. The ethylene-α-olefin copolymer is formed by polymerization of the main monomer ethylene and the comonomer α-olefin, and the α-olefin is 1-pentene. The melting point of the ethylene-α-olefin copolymer is 60-70°C, and the melt index MFR (230°C) = 7 g / 10 min.

[0131] To further characterize the change in the compatibility of the ethylene-α-olefin copolymer in the hot melt resin layer affected by temperature, the hardness and indentation depth of the hot melt resin layer are tested by a nanoindenter. Specifically, the surface of the hot melt resin layer is indented with a Berkovich indenter in the shape of an equilateral triangular pyramid using a nanoindenter in an environment of 25°C and 50% relative humidity. The load of the indenter is constant at 10 mN, and a vibration frequency of 220 Hz is applied to the indenter by a piezoelectric ceramic during the indentation process. The amplitude is 2 nm, and the indentation time is 40 s when the indentation is stopped. At this time, the maximum indentation depth h1 of the hot melt resin layer is 3.84 μm, and the nanoindentation hardness H1 of the hot melt resin layer obtained at this time is 35.7 MPa.

[0132] The metal-plastic composite film is stored at any temperature in the range of 100°C to 130°C for 12 hours, removed and cooled, and then the surface of the hot melt resin layer is indented with a Berkovich indenter in the shape of an equilateral triangular pyramid using a nanoindenter in an environment of 25°C and 50% relative humidity. The load of the indenter is constant at 10 mN, and a vibration frequency of 220 Hz is applied to the indenter by a piezoelectric ceramic during the indentation process. The amplitude is 2 nm, and the indentation time is 40 s when the indentation is stopped. At this time, the maximum indentation depth h2 of the hot melt resin layer is shown in Table 3-1 below, and the nanoindentation hardness H2 of the hot melt resin layer obtained at this time is shown in Table 3-1 below.

[0133] Table 3-1 Test results of h2 and H2 at different temperatures

[0134] Temperature (°C) 100 105 110 115 120 125 130 Maximum indentation depth h2 3.82 3.85 3.87 3.84 3.83 3.79 3.81 Nanohardness H2 35.8 35.9 35.4 35.6 35.8 36 36.1

[0135] The difference between the indentation depth h2 and the indentation depth h1 is ≤0.05 μm. The difference between the nanoindentation hardness H2 and the nanoindentation hardness H1 is ≤0.4 MPa, indicating that the ethylene-α-olefin copolymer still has good compatibility with the above-mentioned polypropylene random copolymer system under storage at any temperature in the range of 100-130°C.

[0136] The metal-plastic composite film of the embodiment of the present application has good packaging capacity with most tab adhesives, and the window of heat sealing conditions is relatively wide. Taking a metal-plastic composite film with a total layer thickness of 80 μm of the heat-adhesion resin layer and the hot-melt resin layer and a total thickness of 152 μm as an example, the heat sealing temperature is set to be any temperature in the range of 160°C to 195°C, the heat sealing surface pressure is 1.0 MPa, and the heat sealing time is 2 seconds. The metal-plastic composite film is heat sealed, and the heat sealing strength obtained by testing according to a test area of 15 mm in width is shown in Table 3-2 below. The range of the heat sealing strength is ≤8 N / 15 mm, indicating that the window of heat sealing conditions is relatively wide.

[0137] Table 3-2 Test results of heat sealing strength at different temperatures

[0138] Temperature (°C) 160 165 170 175 180 185 190 195 Heat seal strength N / 15 mm 137 136 138 137 139 135 135 136

[0139] The metal-plastic composite film of the embodiment of the present application also has good adhesion properties. The hot-melt resin layer and the hot-melt resin layer of the metal-plastic composite film are adhered to each other, a constant force of 1 KG is applied to press down, and at the same time, the metal-plastic composite film is stored at any temperature in the range of 100°C to 130°C for 12 hours. After being taken out, the metal-plastic composite film is cooled in an environment with a temperature of 25°C and a relative humidity of 50%, and then observed. The hot-melt resin layer and the hot-melt resin layer of the metal-plastic composite film are separated from each other without any adhesion phenomenon, as shown in Table 3-3 below.

[0140] Table 3-3 Test results of adhesion properties at different temperatures

[0141] Temperature (°C) 100 105 110 115 120 125 130 Whether blocking Not blocking Not blocking Not blocking Not blocking Not blocking Not blocking Not blocking

[0142] Example 4

[0143] The difference from Example 1 is that the hot melt resin layer is composed of a mixed resin of 75% polypropylene random copolymer, 10% polypropylene block copolymer, and 15% ethylene-α-olefin copolymer. The parameters of the polypropylene random copolymer refer to Example 1. The parameters of the ethylene-α-olefin copolymer refer to Example 1. The polypropylene block copolymer is a block copolymer formed by ethylene and propylene, with a melting point range of 150-160°C, a crystallinity of the polypropylene block copolymer = 40%, and a length ratio of ethylene segments in the polypropylene block copolymer to the total length of segments = 15%.

[0144] Performance test:

[0145] To further characterize the influence of temperature on the compatibility of the ethylene-α-olefin copolymer in the hot melt resin layer, the hardness and indentation depth of the hot melt resin layer were tested by a nanoindenter. Specifically, under the condition of a temperature of 25°C and a relative humidity of 50%, a Berkovich indenter in the shape of a regular triangular pyramid was pressed onto the surface of the hot melt resin layer using a nanoindenter, the load of the indenter was kept constant at 10 mN, and a vibration frequency of 220 Hz was applied to the indenter by a piezoelectric ceramic during the indentation process, with an amplitude of 2 nm. The indentation was stopped after 40 s, at which time the maximum indentation depth h1 of the hot melt resin layer was 3.56 μm, and the nanoindentation hardness H1 of the hot melt resin layer was 38.7 MPa.

[0146] After the metal plastic composite film was stored at any temperature in the range of 100-130°C for 12 hours, it was taken out and cooled, and then a Berkovich indenter in the shape of a regular triangular pyramid was pressed onto the surface of the hot melt resin layer using a nanoindenter under the condition of a temperature of 25°C and a relative humidity of 50%, the load of the indenter was kept constant at 10 mN, and a vibration frequency of 220 Hz was applied to the indenter by a piezoelectric ceramic during the indentation process, with an amplitude of 2 nm. The indentation was stopped after 40 s, at which time the maximum indentation depth h2 of the hot melt resin layer was as shown in Table 4-1 below, and the nanoindentation hardness H2 of the hot melt resin layer was as shown in Table 4-1 below.

[0147] Table 4-1 Test results of h2 and H2 at different temperatures

[0148] Temperature (°C) 100 105 110 115 120 125 130 Maximum indentation depth h2 3.52 3.61 3.58 3.69 3.67 3.45 3.68 Nanohardness H2 39.1 38.5 38.5 38.2 38.3 39.2 38.3

[0149] The difference between the indentation depth h2 and the indentation depth h1 is ≤0.12 μm. The difference between the nanoindentation hardness H2 and the nanoindentation hardness H1 is ≤0.5 MPa, indicating that after storage at any temperature in the range of 100-130°C, the ethylene-α-olefin copolymer still has good elasticity and compatibility with the hot melt resin layer.

[0150] The metal plastic composite film provided by the embodiment of the present application has good packaging capacity with most tab rubber, and the window of heat sealing condition is relatively wide. Taking the metal plastic composite film with the total layer thickness of the heat bonding resin layer and the heat fusion resin layer being 80 μm and the total thickness being 152 μm as an example, the heat sealing temperature is set to be any temperature in the interval of 160-195 ℃, the heat sealing surface pressure is 1.0 MPa, and the heat sealing time is 3 seconds. The heat sealing of the metal plastic composite film is carried out, and the heat sealing strength is tested according to the test area of 15 mm width, and the heat sealing strength is shown in Table 4-2, and the range of the heat sealing strength is ≤N / 15 mm, which indicates that the window of the heat sealing condition is relatively wide.

[0151] Table 4-2 Heat sealing strength test results at different temperatures

[0152] Temperature (°C) 160 165 170 175 180 185 190 195 Heat seal strength N / 15 mm 142 143 143 140 138 141 143 144

[0153] The metal plastic composite film of the present application also has good adhesion properties. The heat fusion resin layer of the metal plastic composite film is adhered to the heat fusion resin layer, a force of 1 kg is applied to press down, and at the same time, the temperature is stored at any temperature in the interval of 100-130 ℃ for 12 hours, then taken out, placed in an environment with a temperature of 25 ℃ and a relative humidity of 50% to cool, and then observed. The heat fusion resin layer and the heat fusion resin layer of the metal plastic composite film are separated from each other, and there is no adhesion phenomenon, as shown in Table 4-3.

[0154] Table 4-3 Adhesion property test results at different temperatures

[0155] Temperature (°C) 100 105 110 115 120 125 130 Whether blocking Not blocking Not blocking Not blocking Not blocking Not blocking Not blocking Not blocking

[0156] Example 5

[0157] The difference between the embodiment 4 and the embodiment 5 is that the proportion of the ethylene-α-olefin copolymer and the melting point are different, and the proportion of the polypropylene random copolymer and the polypropylene block copolymer is also adjusted accordingly. The heat fusion resin layer is composed of a mixed resin of 68% of the polypropylene random copolymer, 7% of the polypropylene block copolymer and 25% of the ethylene-α-olefin copolymer. The raw material parameters of the polypropylene random copolymer and the polypropylene block copolymer are the same as those in the embodiment 3. The ethylene-α-olefin copolymer is formed by polymerization of the main monomer ethylene and the comonomer 1-butene, and the melting point interval is 100-110 ℃, and the melt index MFR (230 ℃) is 7.0 g / 10 min.

[0158] Performance test:

[0159] To further characterize the temperature-dependent compatibility of the ethylene-α-olefin copolymer in the heat-welding resin layer, the heat-welding resin layer was tested for hardness and penetration depth using a nanoindenter. Specifically, a Berkovich indenter with a regular triangular pyramidal shape was pressed into the surface of the heat-welding resin layer using the nanoindenter at 25°C and 50% relative humidity. The indenter load was maintained at 10 mN. During the indentation process, a vibration frequency of 220 Hz and an amplitude of 2 nm were applied to the indenter via the piezoelectric ceramic. The indentation was stopped after 40 seconds. The maximum penetration depth h1 of the heat-welding resin layer was 3.76 μm, resulting in a nanoindentation hardness H1 of 36.8 MPa.

[0160] The metal-plastic composite film was stored at any temperature within the range of 100° C. to 130° C. for 12 hours. The film was taken out and cooled. Then, a Berkovich indenter with a regular triangular pyramid shape was pressed into the surface of the heat-welding resin layer using a nanoindenter at a temperature of 25° C. and a relative humidity of 50%. The load of the indenter was constant at 10 mN. During the pressing process, a vibration frequency of 220 Hz and an amplitude of 2 nm were applied to the indenter through the piezoelectric ceramic. The pressing was stopped when the pressing time was 40 s. The maximum indentation depth h2 of the heat-welding resin layer obtained at this time is shown in Table 5-1 below. The nanoindentation hardness H2 of the heat-welding resin layer obtained at this time is shown in Table 5-1 below.

[0161] Table 5-1 Test results of h2 and H2 at different temperatures

[0162] Temperature (°C) 100 105 110 115 120 125 130 Maximum indentation depth h2 3.74 3.71 3.78 3.69 3.67 3.71 3.73 Nanohardness H2 36.8 36.8 36.5 37.0 37.2 36.9 36.5

[0163] The difference between the indentation depth h2 and the indentation depth h1 is ≤0.09 μm. The difference between the nanoindentation hardness H2 and the nanoindentation hardness H1 is ≤0.4 MPa, indicating that the elastic compatibility of the ethylene-α-olefin copolymer with the heat-welding resin layer remains good after storage at any temperature within the range of 100-130°C.

[0164] The metal-plastic composite film provided by the embodiments of the present invention has good encapsulation capabilities with most tab adhesives and a wide window of heat-sealing conditions. Taking a metal-plastic composite film having a total thickness of 152 μm, with a combined heat-adhesive resin layer and a heat-melting resin layer of 80 μm, as an example, the heat-sealing temperature is set to any temperature within the range of 160°C to 195°C, the heat-sealing pressure is 1.0 MPa, and the heat-sealing time is 3 seconds. The metal-plastic composite film is heat-sealed using a 15 mm width as the test area. The heat-sealing strength is shown in Table 5-2 below. The range of the heat-sealing strength is ≤ N / 15 mm, indicating a wide window of heat-sealing conditions.

[0165] Table 5-2 Heat seal strength test results at different temperatures

[0166] Temperature (°C) 160 165 170 175 180 185 190 195 Heat seal strength N / 15 mm 148 147 148 145 146 147 146 148

[0167] As the metal plastic composite film of the present application, the adhesion property is also good. The hot melt adhesive resin layer of the metal plastic composite film is adhered to each other, and a force of 1 kg is applied to press down, and at the same time, it is stored at any temperature condition in the range of 100 to 130 °C for 12 hours, then taken out, cooled in an environment of temperature 25 °C and relative humidity 50%, and then observed. The hot melt adhesive resin layer of the metal plastic composite film is separated from each other, and there is no adhesion phenomenon. The test results of adhesion property at different temperatures are shown in Table 5-3.

[0168] Table 5-3 Test results of adhesion property at different temperatures

[0169] Temperature (°C) 100 105 110 115 120 125 130 Whether blocking Not blocking Not blocking Not blocking Not blocking Not blocking Not blocking Not blocking

[0170] The metal plastic composite film prepared in the above Example 1-5 does not have adhesion phenomenon of the hot melt adhesive resin layer after storage at 100 to 130 °C for 12 hours, and the nanoindentation test results show that the compatibility of each component in the hot melt adhesive resin layer remains good, and there is no extremely obvious differentiation in hardness and maximum indentation depth. The mechanical properties of the hot melt adhesive resin in the compression layer have not changed significantly, which further indicates that the compatibility of each component in the hot melt adhesive resin layer remains good. In addition, the hot sealing conditions of the metal plastic composite film still maintain a relatively wide window, which is effective at a hot sealing temperature of 160 to 195 °C.

[0171] Comparative Example 1

[0172] The difference from Example 2 is that the ethylene-α-olefin copolymer is replaced by an equal amount of other types of elastomers, and the other elastomer is a 1-butene-based elastomer, which is formed by copolymerization of the main monomer 1-butene and the comonomer propylene. The melting point of the 1-butene-based elastomer is in the range of 110 to 140 °C, and the melt index MFR (230 °C) = 7.0 g / 10 min.

[0173] Performance test:

[0174] To further characterize the influence of temperature on the compatibility of the elastomer in the hot melt adhesive layer, the hardness and indentation depth of the hot melt adhesive layer were tested by nanoindentation. Specifically, under the conditions of temperature 25°C and relative humidity 50%, a Berkovich indenter in the shape of a regular triangular pyramid was used to press the surface of the hot melt adhesive layer using a nanoindenter, the load of the indenter was kept constant at 10 mN, and during the indentation process, a vibration frequency of 220 Hz was applied to the indenter by piezoelectric ceramics, the amplitude was 2 nm, the indentation time was 40 s, and the maximum indentation depth h1 of the hot melt adhesive layer was 4.2 μm, and the nanoindentation hardness H1 of the hot melt adhesive layer was 38.5 MPa.

[0175] After the metal plastic composite film was stored at any temperature in the range of 100°C to 130°C for 12 hours, it was removed and cooled, and then a Berkovich indenter in the shape of a regular triangular pyramid was used to press the surface of the hot melt adhesive layer using a nanoindenter under the conditions of temperature 25°C and relative humidity 50%, the load of the indenter was kept constant at 10 mN, and during the indentation process, a vibration frequency of 220 Hz was applied to the indenter by piezoelectric ceramics, the amplitude was 2 nm, the indentation time was 40 s, and the maximum indentation depth h2 of the hot melt adhesive layer was as shown in Table 4-1, and the nanoindentation hardness H2 of the hot melt adhesive layer was as shown in Table 4-1.

[0176] Table 4-1 Test results of h2 and H2 at different temperatures

[0177] Temperature (°C) 100 105 110 115 120 125 130 Maximum indentation depth h2 4.06 4.08 4.03 3.98 4 3.99 3.99 Nanohardness H2 39.1 38.9 39.4 39.8 39.5 39.9 39.6

[0178] The difference between the indentation depth h2 and the indentation depth h1 was ≤0.22 μm. The difference between the nanoindentation hardness H2 and the nanoindentation hardness H1 was ≤1.4 MPa. Compared with Comparative Examples 1-3, the difference in indentation depth and the difference in hardness nanoindentation hardness increased significantly, indicating that the compatibility of the components in the hot melt adhesive layer had changed, resulting in a significant change in the mechanical properties of the hot melt adhesive layer in terms of compression.

[0179] The metal plastic composite film had good packaging ability with most tab adhesives and a relatively wide window for heat sealing conditions. Taking a metal plastic composite film with a total thickness of 152 μm and a total thickness of the hot adhesive layer and the hot melt adhesive layer of 80 μm as an example, the heat sealing temperature was set to any temperature in the range of 160°C to 195°C, the heat sealing surface pressure was 1.0 MPa, and the heat sealing time was 2 seconds, the metal plastic composite film was heat sealed, and the test area was 15 mm wide, the heat sealing strength obtained by the test was as shown in Table 4-2, the range of heat sealing strength was ≤7 N / 15 mm, and the heat sealing condition window was not affected by the compatibility of the hot melt adhesive layer.

[0180] Table 4-2 Heat seal strength test results at different temperatures

[0181] Temperature (°C) 160 165 170 175 180 185 190 195 Heat seal strength N / 15 mm 134 133 134 129 130 133 134 136

[0182] However, the adhesion properties of the metal-plastic composite film of Comparative Example 1 need to be improved. The heat-sealing resin layers of the metal-plastic composite film were bonded together and pressed down with a constant force of 1 kg. The films were then stored at any temperature between 100°C and 130°C for 12 hours. The films were then removed and cooled in an environment with a temperature of 25°C and a relative humidity of 50%. The results were then observed. Table 4-3 shows the results.

[0183] Table 4-3 Adhesion performance test results at different temperatures

[0184] Temperature (°C) 100 105 110 115 120 125 130 Whether blocking Not blocking Not blocking Blocking Blocking Blocking Blocking Blocking

[0185] Comparative Example 2

[0186] The only difference from Example 2 is that the ethylene-α-olefin copolymer is replaced with an equal amount of another type of elastomer. The other elastomer is a propylene-based elastomer formed by copolymerizing propylene as the primary monomer with 1-butene as the comonomer. The 1-butene-based elastomer accounts for 15% by weight of the heat-sealable resin layer. The propylene-based elastomer has a melting point in the range of 70-90°C and a melt index (MFR) (230°C) of 7.0 g / 10 min.

[0187] Performance testing:

[0188] To further characterize the temperature-dependent compatibility of the elastomer within the heat-welding resin layer, the heat-welding resin layer was tested for hardness and penetration depth using a nanoindenter. Specifically, a Berkovich indenter with a regular triangular pyramidal shape was pressed into the surface of the heat-welding resin layer using the nanoindenter at 25°C and 50% relative humidity. The indenter applied a constant load of 10 mN. During the indentation process, a 220 Hz vibration frequency and 2 nm amplitude were applied to the indenter via the piezoelectric ceramic. The indentation was stopped after 40 seconds. The maximum penetration depth h1 of the heat-welding resin layer was 4.16 μm, resulting in a nanoindentation hardness H1 of 38.8 MPa.

[0189] The metal plastic composite film was stored at any temperature in the range of 100°C to 130°C for 12 hours, then removed and cooled, and then the surface of the hot melt adhesive layer was pressed with a Berkovich indenter in the shape of an equilateral triangular pyramid using a nanoindenter in an environment with a temperature of 25°C and a relative humidity of 50%, the load of the indenter was kept constant at 10 mN, a vibration frequency of 220 Hz was applied to the indenter by a piezoelectric ceramic during the pressing process, the amplitude was 2 nm, the pressing time was 40 s, and the pressing was stopped at this time, at which time the maximum pressing depth h2 of the hot melt adhesive layer was obtained, as shown in Table 5-1, and the nanoindentation hardness H2 of the hot melt adhesive layer obtained at this time was as shown in Table 5-1.

[0190] Table 5-1 Test results of h2 and H2 at different temperatures

[0191] Temperature (°C) 100 105 110 115 120 125 130 Maximum indentation depth h2 4.09 4.05 4.03 3.98 3.94 3.95 3.96 Nanohardness H2 39.5 39.6 39.6 39.8 39.9 40 39.8

[0192] The difference between the pressing depth h2 and the pressing depth h1 was ≤0.22 μm. The difference between the nanoindentation hardness H2 and the nanoindentation hardness H1 was ≤1.1 MPa. Compared with Examples 1-3, the difference in pressing depth and the difference in hardness nanoindentation hardness increased significantly, indicating that the compatibility of the components in the hot melt adhesive layer had changed, resulting in a significant change in the mechanical properties of the hot melt adhesive layer in terms of compression.

[0193] The metal plastic composite film had good packaging ability with most tab adhesives and a relatively wide window for heat sealing conditions. For example, the total thickness of the hot adhesive resin layer and the hot melt adhesive layer of the metal plastic composite film was 80 μm, the total thickness was 152 μm, the heat sealing temperature was set to any temperature in the range of 160°C to 195°C, the heat sealing surface pressure was 1.0 MPa, and the heat sealing time was 2 seconds. The metal plastic composite film was heat sealed, and the test area was 15 mm wide. The heat sealing strength obtained by the test is shown in Table 5-2, and the range of heat sealing strength is ≤3 N / 15 mm. The heat sealing condition window was not affected by the compatibility of the hot melt adhesive layer.

[0194] Table 5-2 Test results of heat sealing strength at different temperatures

[0195] Temperature (°C) 160 165 170 175 180 185 190 195 Heat seal strength N / 15 mm 135 134 134 135 136 137 136 135

[0196] However, the metal plastic composite film of Comparative Example 2 had to be improved in terms of adhesion properties. The hot melt adhesive layer of the metal plastic composite film was adhered to the hot melt adhesive layer, a constant force of 1 KG was applied to press down, and at the same time, the metal plastic composite film was stored at any temperature in the range of 100°C to 130°C for 12 hours, then removed and placed in an environment with a temperature of 25°C and a relative humidity of 50% to cool, and then observed, and the results are shown in Table 5-3.

[0197] Table 5-3 Adhesion property test results at different temperatures

[0198] Temperature (°C) 100 105 110 115 120 125 130 Whether blocking Blocking Blocking Blocking Blocking Blocking Blocking Blocking

[0199] Comparative Example 3

[0200] The difference from Example 2 is that no ethylene-a-olefin copolymer is added, and the hot melt adhesive layer only contains polypropylene random copolymer.

[0201] Performance test:

[0202] In this comparative example, no elastomer component is added, and the hardness and indentation depth of the hot melt adhesive layer are tested by a nanoindenter. Specifically, under the condition of temperature 25°C and relative humidity 50%, a Berkovich indenter in the shape of an equilateral triangular pyramid is pressed onto the surface of the hot melt adhesive layer using a nanoindenter, the load of the indenter is kept constant at 10 mN, and during the indentation process, a vibration frequency of 220 Hz is applied to the indenter by a piezoelectric ceramic, the amplitude is 2 nm, the indentation time is 40 s, and the indentation is stopped at this time. At this time, the maximum indentation depth h1 of the hot melt adhesive layer is 2.83 μm, and the nanoindentation hardness H1 of the hot melt adhesive layer obtained at this time is 50.0 MPa.

[0203] After the metal plastic composite film is stored at any temperature in the range of 100°C to 130°C for 12 hours, it is taken out and cooled, and then a Berkovich indenter in the shape of an equilateral triangular pyramid is pressed onto the surface of the hot melt adhesive layer using a nanoindenter under the condition of temperature 25°C and relative humidity 50%. The load of the indenter is kept constant at 10 mN, and during the indentation process, a vibration frequency of 220 Hz is applied to the indenter by a piezoelectric ceramic, the amplitude is 2 nm, the indentation time is 40 s, and the indentation is stopped at this time. At this time, the maximum indentation depth h2 of the hot melt adhesive layer is as follows in Table 6-1, and the nanoindentation hardness H2 of the hot melt adhesive layer obtained at this time is as follows in Table 6-1.

[0204] Table 6-1 Test results of h2 and H2 at different temperatures

[0205] Temperature (°C) 100 105 110 115 120 125 130 Maximum indentation depth h2 2.76 2.82 2.74 2.89 2.9 2.94 2.95 Nanohardness H2 50.1 50.0 50.2 50 49.8 49.8 49.7

[0206] The difference between the indentation depth h2 and the indentation depth h1 is ≤0.12 μm. The difference between the nanoindentation hardness H2 and the nanoindentation hardness H1 is ≤0.3 MPa. Since no elastomer component is added in this comparative example, the compatibility of each component does not change after high temperature treatment, and the mechanical properties of the hot melt adhesive layer in compression do not change significantly.

[0207] The total thickness of the metal-plastic composite film with a heat-adhesive resin layer and a hot-melt adhesive resin layer of 80 μm and a total thickness of 152 μm was taken as an example, the heat-sealing temperature was set to any temperature in the range of 160-195 °C, the heat-sealing surface pressure was 1.0 MPa, and the heat-sealing time was 2 seconds. The metal-plastic composite film was heat-sealed, and the heat-sealing strength was tested according to the test area of 15 mm width. The heat-sealing strength was as shown in Table 6-2, and the range of heat-sealing strength was ≤39 N / 15 mm, which was significantly higher than that of Example 1-3.

[0208] Table 6-2 Heat-sealing strength test results at different temperatures

[0209] Temperature (°C) 160 165 170 175 180 185 190 195 Heat seal strength N / 15 mm 101 128 126 140 134 135 140 138

[0210] It can be seen that the heat-sealing window of Comparative Example 3 is narrow (a narrow heat-sealing window means that the heat-sealing conditions require high temperature or pressure or time).

[0211] The metal-plastic composite film of the present comparative example has good blocking properties because no elastomer is added. The hot-melt adhesive resin layer of the metal-plastic composite film was adhered to the hot-melt adhesive resin layer, and a force of 1 KG was applied to press down, and at the same time, it was stored at any temperature in the range of 100-130 °C for 12 hours, then taken out and cooled in an environment of temperature 25 °C and relative humidity 50%, and then observed. The results are shown in Table 6-3.

[0212] Table 6-3 Blocking property test results at different temperatures

[0213] Temperature (°C) 100 105 110 115 120 125 130 Whether blocking Not blocking Not blocking Not blocking Not blocking Not blocking Not blocking Not blocking

[0214] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. The present application can be variously modified and changed by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A metal-plastic composite film, characterized in that: It includes a metal layer, a heat-adhesive resin layer and a heat-melting resin layer arranged in sequence; The heat-welding resin layer comprises at least one of a polypropylene random copolymer, a polypropylene block copolymer, and an ethylene-α-olefin copolymer; The extreme difference in heat sealing strength of the metal-plastic composite film obtained at a heat sealing temperature range of 160° C. to 195° C. is ≤15N / 15mm; And / or, after being stored at any temperature between 100° C. and 130° C. for 12 hours, the difference between the nanoindentation hardness H2 obtained by nanoindentation testing and the initial nanoindentation hardness H1 is ≤1.0 MPa.

2. The metal-plastic composite film according to claim 1, characterized in that The heat-welding resin layer contains, by mass percentage, 55%-90% of a polypropylene random copolymer, 0%-15% of a polypropylene block copolymer, and 10%-30% of an ethylene-α-olefin copolymer; The main chain of the polypropylene random copolymer is composed of ethylene and propylene; The polypropylene block copolymer is a block copolymer formed by ethylene and propylene.

3. The metal-plastic composite film according to claim 2, characterized in that: The heat-welding resin layer contains, by mass percentage, 65%-80% of a polypropylene random copolymer, 5%-10% of a polypropylene block copolymer, and 15%-25% of an ethylene-α-olefin copolymer; and / or, the ratio of the length of the ethylene segments in the polypropylene random copolymer to the total segment length of the polypropylene random copolymer is (10-20):100; And / or, the number average molecular weight of the polypropylene random copolymer is 100,000-180,000; And / or, at 230° C., the melt index MFR of the polypropylene random copolymer is ≤25 g / 10 min; preferably 7 g / 10 min-20 g / 10 min.

4. The metal-plastic composite film according to claim 2, characterized in that: The ratio of the length of the ethylene segments in the polypropylene block copolymer to the total segment length of the polypropylene block copolymer is (10-20):100; and / or, the melting point of the polypropylene block copolymer is less than 160° C.; And / or, the crystallinity of the polypropylene block copolymer is less than or equal to 40%.

5. The metal-plastic composite film according to claim 1, characterized in that: The ethylene-α-olefin copolymer is formed by polymerizing ethylene as a main monomer and an α-olefin as a comonomer, wherein the α-olefin is selected from at least one of 1-butene, 1-pentene and 1-hexene; preferably 1-butene; Preferably, the ratio of the ethylene segment length to the total segment length of the ethylene-α-olefin copolymer is (50-90):100, more preferably (80-90):100; And / or, the melting point of the ethylene-α-olefin copolymer is 60°C-170°C.

6. The metal-plastic composite film according to any one of claims 1 to 5, characterized in that: The thickness of the metal layer is 40 μm-200 μm, the thickness of the thermal adhesive resin layer is 20 μm-50 μm, and the thickness of the thermal welding resin layer is 20 μm-50 μm; And / or, the material of the metal layer is selected from at least one of aluminum, aluminum alloy, stainless steel, steel, titanium steel and nickel-plated iron; And / or, the material of the thermal adhesive resin layer is modified polyolefin; the polyolefin in the modified polyolefin is selected from at least one of polypropylene resin and propylene-ethylene copolymer; the modified raw material is selected from at least one of acrylic acid, methacrylic acid, maleic acid, anhydrous maleic anhydride and polyamide.

7. The metal-plastic composite film according to any one of claims 1 to 5, characterized in that: The heat-welding resin layer also contains 200-5000ppm of a lubricant and 0.1%-0.2% of an opening agent; Preferably, the lubricant is an amide compound; Preferably, the opening agent is selected from at least one of silicon oxide, aluminum oxide, sodium aluminosilicate and potassium aluminosilicate.

8. The metal-plastic composite film according to any one of claims 1 to 5, characterized in that: An outer base resin layer is provided on a side of the metal layer away from the thermal adhesive resin layer, wherein the material of the outer base resin layer is selected from at least one of polyester, polyamide and polyurethane; preferably, a lubricant is coated on the surface of the outer base resin layer; and / or a lubricant is coated on the thermal adhesive resin layer; more preferably, the lubricant is an amide lubricant; Preferably, a first anti-corrosion layer is provided between the metal layer and the thermal adhesive resin layer; Preferably, a second anti-corrosion layer is provided between the metal layer and the outer base resin layer.

9. A method for preparing the metal-plastic composite film according to any one of claims 1 to 8, characterized in that: include: The metal layer, the thermal adhesive resin layer and the thermal melting resin layer are prepared in sequence, and the parameters of each layer are made to meet the requirements.

10. A secondary battery, characterized in that: The invention comprises the metal-plastic composite film according to any one of claims 1 to 8.

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