Graft modified polypropylene with efficient metal bonding performance and preparation method and application thereof

Abstract

The invention relates to the technical field of high polymer materials, in particular to graft modified polypropylene with efficient metal bonding performance and a preparation method and application thereof. The preparation method comprises the following steps: by adopting a melt grafting method or a radiation grafting method, carrying out graft modification on polypropylene under the simultaneous action of the grafting assistants A and B by taking at least one of a maleic acid series monomer and an acrylic acid series monomer containing double bonds and polar functional groups as a functional monomer, so as to obtain the graft modified polypropylene with efficient metal adhesive property. Through the double-mechanism synergistic effect of the grafting assistant A (high-reaction-activity double-bond monomer) and the assistant B (phenolic hydroxyl compound), the double breakthrough of functional monomer grafting efficiency and degradation inhibition is realized. The assistant A is used for converting unstable PP macromolecular free radicals into a stable intermediate through grafting and improving the grafting rate of functional monomers; and the assistant B captures free radicals through phenolic hydroxyl groups, so that PP degradation is remarkably inhibited.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high molecular materials, in particular to a grafted modified polypropylene with high efficient metal bonding performance and a preparation method and application thereof. BACKGROUND

[0002] Polymer-metal composite materials have irreplaceable properties in the fields of new energy and electronic packaging due to the combination of lightweight and flexibility of polymer materials and excellent electrical conductivity of metals. However, the interface debonding caused by insufficient bonding strength of polymer-metal interface is always the core bottleneck restricting the high performance of the materials. This contradiction is particularly prominent in the two innovative materials of lithium ion batteries:

[0003] 1. Aluminum-plastic composite film (typical structure: outer nylon / intermediate aluminum foil (40 μm) / inner modified PP (50 μm)). As the core material for soft package battery packaging, the inner layer PP needs to form a high-strength chemical bond with the aluminum foil to resist electrolyte (EC / DMC system) swelling and thermal cycle stress. In the iteration from traditional hard-shell batteries to soft packages, the aluminum-plastic film needs to have an interfacial peeling strength of PP / Al > 10 N / 15 mm after being soaked in high-temperature electrolyte for 9 weeks to meet the requirement of 25-year stable service life of power batteries.

[0004] 2. Composite current collector (typical structure: PP base film (4 μm) / double-sided magnetron sputtering metal layer (Al 1 μm / Cu 1 μm)). This structure realizes the lightweight (weight reduction of more than 40%) of the battery through the combination of a metal conductive layer and a polymer support layer. The interfacial bonding force between the PP base film and the metal plating layer needs to be > 5 N, otherwise the metal layer is easy to fall off during the cycle process, causing the composite current collector to be fundamentally damaged.

[0005] In the above-mentioned systems, the introduction of a polar functional group grafted polypropylene (such as maleic anhydride grafted polypropylene MAPP) as an intermediate adhesive layer between PP and metal foil / plating layer is an effective strategy to improve the interfacial performance. MAPP prepared by in-pot synthesis method of Japan Toyo Spinning is considered to be the world's highest level, with a grafting rate of 1 wt%, which can greatly improve the polarity of PP and has a relatively high interfacial bonding strength in aluminum-plastic composite film. However, it has the following significant limitations: ① The complex synthesis process results in high cost, about 300,000 / ton, which is only used in high-end markets; ② The molecular weight is relatively low (Mw=68,000, Mn=37,000), and the mechanical properties are poor, so there is still a problem of insufficient bonding force between the PP base film and the metal plating layer when used as an adhesive layer for the composite current collector, and it cannot meet the mechanical performance requirements of being directly used as the base film of the composite current collector.

[0006] Compared with in-situ synthesis, the method of reactive processing has the significant advantages of simple process and convenient mass production in the preparation of maleic anhydride grafted PP. However, the reactive grafting process of PP is relatively complex, and the possible reactions include: 1, initiator decomposition to form primary free radicals; 2, hydrogen atoms connected to tertiary carbon are most easily abstracted by primary free radicals to form tertiary carbon radicals; 3, tertiary carbon radicals further initiate the graft polymerization of functional monomers; 4, tertiary carbon radicals are unstable and prone to degradation by beta scission; 5, primary free radicals initiate self-polymerization of functional monomers. Among them, low grafting rate of functional monomers and PP degradation are two major problems faced by PP reactive grafting process, and are also the research focus of industry and academia.

[0007] Controlling the PP reactive grafting modification process to prepare high-performance modified PP with high functional monomer grafting rate, low melt index and high bulk mechanical properties is an important breakthrough to overcome the current technical bottleneck. The introduction of co-monomer in the reactive processing system is an effective means to inhibit PP degradation and improve the grafting rate of functional monomers. Common co-monomers include styrene (Sty), aromatic heterocyclic (furan, thiophene, pyrrole) derivatives, and some bifunctional (such as divinylbenzene) and trifunctional (such as trimethylolpropane triacrylate) monomers. These co-monomers can inhibit PP degradation to some extent, but also have side reactions such as co-monomer self-polymerization and crosslinking initiation, which will adversely affect the grafting of functional monomers and the performance of the material. SUMMARY

[0008] The present application aims to solve the technical problems of poor interface adhesion between PP base film and metal caused by low grafting rate of functional monomers, and poor mechanical properties of the material caused by degradation, and provides a preparation method of grafted and modified polypropylene with high efficient metal adhesion performance.

[0009] The preparation method of the present application adopts a dual-mechanism synergistic free radical regulation system, innovatively introduces grafting aid A (containing a high-reactivity double bond monomer) and grafting aid B (a polyphenol hydroxyl compound) to form a dual-function regulation system, and realizes precise control of the grafting reaction through the following synergistic mechanisms. Improve the grafting rate of functional monomers (grafting aid A dominant): the double bond of aid A preferentially reacts with PP macroradicals (PP·) to form stable PP-A· intermediates, which can continue to initiate grafting of functional monomers, thereby improving the grafting rate of functional monomers; free radical quenching compensation (grafting aid B dominant): the phenolic hydroxyl group of grafting aid B efficiently captures free PP· through hydrogen atom transfer reaction, significantly inhibits the degradation reaction of PP, and makes the product maintain high mechanical properties; space steric hindrance synergistic effect: the rigid side chain (such as styrene derivative) of grafting aid A and the planar aromatic ring structure of grafting aid B form π-π stacking to construct a dynamic physical crosslinking network in the melt, further improving the melt performance and bulk mechanical properties.

[0010] To achieve the above object, the first aspect of the present application provides a preparation method of graft modified polypropylene with high efficient metal bonding performance, which adopts a melt grafting method or a radiation grafting method, uses at least one of a maleic acid monomer and an acrylic acid monomer containing a double bond and a polar functional group as a functional monomer, and grafts modifies polypropylene under the simultaneous action of grafting aids A and B to obtain graft modified polypropylene with high efficient metal bonding performance.

[0011] The molecular structure of the grafting aid A is as follows:

[0012] In the formula, R is selected from -H, -CH3 or -OCH3;

[0013] The grafting aid B is selected from at least one of the following molecular structure formulas:

[0014]

[0015] 4-vinyl-2-methoxyphenol trans-anethole

[0016] 2-allylphenol eugenol.

[0017] In the above reaction system, the content of the functional monomer accounts for 1-5 wt% of the amount of polypropylene, for example, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 4 wt% or 5 wt%, etc., and the contents of the grafting aids A and B respectively account for 0.5-5 wt%, for example, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 4 wt% or 5 wt%, etc.

[0018] As a further preferred technical solution of the present application, the content of the grafting aid A is 1-3%, and the content of the grafting aid B is 1-2%; more preferably, the molar ratio of the functional monomer to the grafting aid A is about 2:1, for example, the molar ratio is 2:0.8, 2:0.9, 2:1, 2:1.1 or 2:1.2, etc., and the molar ratio of the grafting aid A to the grafting aid B is about 5:2, for example, the molar ratio is 5:1.9, 5:2.0 or 5:2.1, etc., the grafting efficiency is the highest; more preferably, the molar ratio of the functional monomer to the grafting aid A is about 2:3, for example, the molar ratio is 2:2.9, 2:3.0 or 2:3.1, etc., and the molar ratio of the grafting aid A to the grafting aid B is about 4:1, for example, the molar ratio is 4:1.9, 4:1.0 or 4:1.1, etc., the degradation inhibition effect is the best.

[0019] As a further preferred technical solution of the present application, when the melt grafting method is adopted: the melt blending temperature interval is 170-220 ℃, such as 170 ℃, 180 ℃, 190 ℃, 200 ℃, 210 ℃ or 220 ℃, etc.; and / or, the peroxide initiator is added.

[0020] As a further preferred technical solution of the present application, the peroxide initiator is one or several of dicumyl peroxide, di-tert-butyl peroxide isopropyl benzene, 2, 5-dimethyl-2, 5-bis (tert-butyl peroxide) hexane, benzoyl peroxide.

[0021] As a further preferred technical solution of the present application, the maleic acid monomer is maleic anhydride.

[0022] As a further preferred technical solution of the present application, the acrylic acid monomer is glycidyl methacrylate, acrylic acid.

[0023] The second aspect of the present application provides a graft modified polypropylene prepared by the method of the first aspect.

[0024] The third aspect of the present application provides the use of the graft modified polypropylene of the third aspect as a metal bonding material.

[0025] As a further preferred technical solution of the present application, the graft modified polypropylene is used as a metal bonding material for the adhesion between metals and metals, or between metals and plastics.

[0026] The fourth aspect of the present application further provides an aluminum-plastic composite film comprising an aluminum foil layer and a heat-seal layer adhered to the surface of the aluminum foil layer, wherein the heat-seal layer is the graft modified polypropylene prepared in the first aspect.

[0027] The fifth aspect of the present application further provides a composite current collector comprising a base film and a metal conductive layer deposited on one or both sides of the base film, wherein the thickness of the base film is 2-6 μm and the thickness of the metal conductive layer is 0.1-5 μm. The thickness of the metal conductive layer can be 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc. The base film is the graft modified polypropylene prepared in the first aspect, and the metal material of the metal conductive layer is gold, silver, copper, aluminum and alloys thereof. The composite current collector can be prepared by stretching the graft modified polypropylene in a hot melt state into a base film, sputtering a metal layer on the base film as an activation layer, and then electroplating the metal layer to increase the thickness of the metal layer. For example, the sputtering thickness of the metal layer is 10-100 nm, and after electroplating, the metal layer is increased to a specified thickness. According to the needs, the two sides of the base film can be deposited with different or the same metal materials, such as aluminum on one side and copper on the other side.

[0028] Compared with the prior art, the application can achieve the following beneficial effects:

[0029] 1) High grafting rate and degradation inhibition synergy

[0030] Through the dual-mechanism synergy of grafting aid A (highly reactive double bond monomer) and aid B (phenolic hydroxyl compound), the grafting efficiency of functional monomers and the inhibition of degradation are realized. Aid A converts unstable PP macroradicals into stable intermediates through grafting and improves the grafting rate of functional monomers; aid B significantly inhibits PP degradation by capturing free radicals through phenolic hydroxyl groups.

[0031] 2) Balanced optimization of mechanical properties and processing performance

[0032] The π-π stacking effect of the dual aid forms a dynamic physical crosslinking network in the melt, which is beneficial to improve the melt strength of PP. This characteristic can not only meet the requirements of the biaxial stretching film forming process (base film thickness 4-6 μm), but also can be directly used as a composite current collector base film, breaking through the technical limitation of traditional MAPP which needs additional composite support layer due to insufficient mechanical properties.

[0033] 3) Cost advantage and process adaptability

[0034] By replacing the traditional kettle synthesis process with a reactive processing route, the equipment investment and production cost are greatly reduced. At the same time, the melt grafting temperature window is widened to 170-220℃ (the traditional process needs to be strictly controlled within ±5℃), and the process fault tolerance is significantly improved, which is more suitable for industrial continuous production.

[0035] 4) Breakthrough improvement of interfacial adhesion performance

[0036] The interfacial peeling strength of modified PP and aluminum foil can reach about 4800 N / m; the bonding force between PP base film and sputtered copper layer in the composite current collector reaches 6 N (industry standard ≥4 N), meeting the 25-year service life requirement of power batteries. BRIEF DESCRIPTION OF DRAWINGS

[0037] The application will be further described in detail below in combination with the drawings and specific embodiments.

[0038] Figure 1 The preparation process flow chart of Al / m-PP / Al composite material.

[0039] The purpose realization, functional characteristics and advantages of the application will be further described with reference to the drawings in combination with the embodiments. DETAILED DESCRIPTION

[0040] The specific embodiments of the present application are described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the present application.

[0041] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which the present application belongs. The test reagents used in the following examples are conventional biochemical reagents unless otherwise specified; the experimental methods described are conventional methods unless otherwise specified.

[0042] The functional monomer, grafting aids A and B used in the present application all contain double bonds and can be fixed to the PP molecular chain through free radical initiated grafting polymerization. More importantly, although they are all double bond grafting, each of them plays a different function, and the interaction between each other promotes grafting differently. Among them: the functional monomer is mainly used to provide polar functional groups to provide action / reaction sites for subsequent interfacial bonding with metals; grafting aid A is used to inhibit PP degradation (auxiliary), and to increase the grafting rate of functional monomers (main role); grafting aid B is used to inhibit PP degradation (main role), and to increase the grafting rate of functional monomers (auxiliary). The mechanisms of grafting aids A and B for inhibiting PP degradation are different. A mainly reacts with unstable PP macroradicals through its highly reactive double bond to form stable PP macroradicals, thereby inhibiting PP degradation; B mainly captures unstable PP macroradicals through its phenolic hydroxyl group to inhibit its degradation. Therefore, under the synergistic action of grafting aids A and B, the precise control of each reaction in the PP reactive processing process can be achieved to realize high-efficiency metal bonding performance.

[0043] The polypropylene materials used in the following examples and comparative examples are in the form of granules and are dried by vacuum oven before blending. The amount of material (except for PP) refers to the percentage of the mass of the polypropylene base material.

[0044] Example 1

[0045] The preparation method of the graft-modified polypropylene with high-efficiency metal bonding performance provided in the present embodiment is as follows:

[0046] 1) Configure the materials: 100 wt% PP, 1 wt% glycidyl methacrylate (GMA), 2 wt% styrene, 1 wt% 2-allyl phenol, and 0.5% dicumyl peroxide initiator (DCP).

[0047] 2) Melt blending: Peroxide initiator (DCP), glycidyl methacrylate (GMA), grafting aid A (styrene) and grafting aid B (2-allyl phenol) were added into polypropylene material, mixed uniformly at room temperature, then melt blended in Haake mixer at 190 °C for 5 min with rotation speed of 50 rpm to obtain graft-modified polypropylene.

[0048] Example 2: Change the amount of functional monomer based on Example 1

[0049] 1) Material configuration: 100 wt% PP, 3 wt% GMA, 2 wt% styrene, 1 wt% 2-allyl phenol, 0.5% initiator DCP.

[0050] 2) Melt blending: The same as the method of Example 1.

[0051] Example 3: Change the amount of functional monomer based on Example 1

[0052] 1) Material configuration: 100 wt% PP, 5 wt% GMA, 2 wt% styrene, 1 wt% 2-allyl phenol, 0.5% initiator DCP.

[0053] 2) Melt blending: The same as the method of Example 1.

[0054] Example 4: Change the amount of initiator based on Example 3

[0055] 1) Material configuration: 100 wt% PP, 5 wt% GMA, 2 wt% styrene, 1 wt% 2-allyl phenol, 0.7% initiator DCP.

[0056] 2) Melt blending: The same as the method of Example 1.

[0057] Comparative Example 1: As a control experiment of Example 2, omitting aid B

[0058] 1) Material configuration: 100 wt% PP, 3 wt% GMA, 2 wt% styrene, 0.5% initiator DCP.

[0059] 2) Melt blending: The same as the method of Example 1.

[0060] Comparative Example 2: As a control experiment of Example 2, omitting aid A

[0061] 1) Material configuration: 100 wt% PP, 3 wt% GMA, 1 wt% 2-allyl phenol, 0.5% initiator DCP.

[0062] 2) Melt blending: The method is the same as in Example 1.

[0063] As a control experiment for Example 2, the amount of adjuvant was kept constant.

[0064] 1) Materials: 100wt% PP, 3wt% GMA, 3wt% styrene, 0.5% initiator DCP.

[0065] 2) Melt blending: The method is the same as in Example 1.

[0066] As a control experiment for Example 2, the amount of adjuvant was kept constant.

[0067] 1) Materials to be prepared: 100wt% PP, 3wt% GMA, 3wt% 2-allylphenol, 0.5% initiator DCP.

[0068] 2) Melt blending: The method is the same as in Example 1.

[0069] Examples 5, 6 and 7

[0070] Based on Example 2, these three sets of examples replace 2-allylphenol with 4-vinyl-2-methoxyphenol, trans-ferulic acid and eugenol in equal amounts, while keeping the other materials, amounts and operating steps unchanged.

[0071] Examples 8 and 9

[0072] These two sets of examples are based on Example 2, except that GMA is replaced with maleic anhydride (MAH) and acrylic acid (AA) in equal amounts, while the other materials, amounts and operating steps remain unchanged.

[0073] Comparative Example 3

[0074] This embodiment is based on Example 2, except that 2-allylphenol is replaced with 4-vinylphenol in equal amounts, while the other materials, amounts and operating steps remain unchanged.

[0075] Comparative Example 4

[0076] This embodiment is based on Example 2, except that 2-allylphenol is replaced with 1-methyl-2-(2-allyl)benzene in equal amounts, while the other materials, amounts and operating steps remain unchanged.

[0077] Comparative Example 5

[0078] This embodiment is based on Example 2, except that the styrene is replaced with nitrostyrene in equal amounts, while the other materials, amounts and operating steps remain unchanged.

[0079] Comparative Example 6: System without Additives

[0080] Materials used: 100wt% PP, 3wt% GMA, 0.5% initiator DCP.

[0081] Melt blending: Same as in Example 1.

[0082] The grafted modified polypropylene (m-PP) samples prepared in the above examples and comparative examples were used as metal bonding materials, as detailed below:

[0083] like Figure 1 As shown, two 0.2 mm aluminum foils were selected, and grafted modified polypropylene (molten state) was coated between the two aluminum foils before being stacked. The mixture was then hot-pressed at 200 ℃ and 15 MPa for 2 min. After removal, it was cooled by immersion in cold water to obtain an Al / m-PP / Al composite material with a total thickness of 0.5 mm. Its peel strength was tested according to GB / T 2791-1995, and the results are shown in Table 1.

[0084] Table 1

[0085]

[0086] This invention achieves a breakthrough in polypropylene grafting technology through an innovative synergistic system of additives A and B. When additive B is missing (Comparative Example 1), the system's inhibition function collapses, causing the melt index to surge to 18.0 g / 10min. Although the grafting rate remains at 0.85, the peel strength drops sharply by 58% to 2000 N / m due to the interference of degradation products with effective interfacial bonding. When additive A is missing (Comparative Example 2 to specification 8), the grafting rate drops to 0.55, and the homopolymerization of monomers leads to insufficient interfacial anchoring points, resulting in a peel strength of only 2600 N / m (a decrease of 46%). This fully demonstrates that the two additives are complementary and indispensable. Compared to Comparative Examples 1 and 2, although the amount of additives was increased to the same total amount of additives A and B in Example 2, the final peel strength was not significantly improved.

[0087] More importantly, the synergistic system of this invention is extremely sensitive to structural abnormalities: after the auxiliary agent B (2-allylphenol) in Example 2 was replaced with para-vinylphenol (Comparative Example 3), the free radical quenching efficiency decreased due to the increased steric hindrance of the phenolic hydroxyl group, the melt index increased to 8.5 g / 10min and the peel strength plummeted by 50%; after the auxiliary agent A (styrene) in Example 2 was replaced with nitrostyrene (Comparative Example 5), the double bond activity was weakened, resulting in the melt index increasing to 15.5 g / 10min and the peel strength being only 1400 N / m (a decrease of 70%), and even a small change caused the performance to collapse. Example 2 of this invention demonstrates the best results. With the precise combination of the two additives, the system forms a "dual free radical regulation channel"—styrene-stabilized free radicals delay degradation, and ortho-phenolic radicals quench free radicals to terminate side reactions, resulting in a melt index as low as 6.0 g / 10min (maintaining matrix strength), a grafting rate of 0.95 (maximizing interfacial bonding), and a final peel strength of approximately 4800 N / m. This represents a 167% improvement over the competing Zhejiang University solution (VPh+MAH, ≤1800 N / m) and significantly exceeds the theoretical summation value of a single additive (4600 N / m). All data collectively demonstrate that this ternary system, through structural specificity and synergistic mechanism, resolves the fundamental contradiction between degradation control and grafting efficiency, and its performance advantages are irreplaceable.

[0088] Extensive experiments have shown that the melt grafting method used in this invention can broaden the temperature window for melt grafting to 170-220 ℃. For example, if Example 2 is adjusted to melt blending at 170 ℃ for about 8 min, or to melt blending at 220 ℃ for about 3 min, the peel strength of the resulting grafted modified polypropylene is above 4000 N / m, and the effect is close to that of Example 2.

[0089] To further demonstrate the beneficial technical effects of the grafted modified polypropylene of this invention, the grafted modified polypropylene prepared in Example 2 was biaxially stretched into a 4 μm base film. First, a 50 nm copper layer was magnetron sputtered onto one side of the base film as an activation layer, followed by electroplating to thicken the copper layer to approximately 1 μm to form a copper coating. Finally, using the same method, an aluminum coating of approximately 1 μm was formed on the other side of the base film, resulting in a composite current collector. The peel strength was tested according to GB / T 2791-1995, and the adhesion between the base film and both the copper and aluminum coatings reached over 6 N.

[0090] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is defined only by the appended claims.

Claims

1. A method for preparing grafted modified polypropylene with high-efficiency metal bonding properties, characterized in that, Polypropylene is grafted and modified using melt grafting or radiation grafting methods, with at least one of maleic acid monomers and acrylic monomers containing double bonds and polar functional groups as functional monomers, under the simultaneous action of grafting aids A and B, to obtain grafted modified polypropylene with high-efficiency metal bonding properties. In the above reaction system, relative to the amount of polypropylene, the initiator content is 0.1~1 wt%, the functional monomer content is 1~4 wt%, and the grafting aids A and B are 0.5~5 wt%, respectively. The molecular structure of grafting aid A is as follows: In the formula, R is selected from -H, -CH3, or -OCH3; Grafting aid B is at least one of the following molecular structural formulas: ; 4-Vinyl-2-methoxyphenol trans-ferulic acid ; 2-Allylphenol Eugenol.

2. The method for preparing grafted modified polypropylene with high-efficiency metal bonding properties according to claim 1, characterized in that, When using the melt grafting method: the melt blending temperature range is 170~220 ℃; and / or, a peroxide initiator is added.

3. The method for preparing grafted modified polypropylene with high-efficiency metal bonding properties according to claim 2, characterized in that, The peroxide initiator is at least one of dicumyl peroxide, di-tert-butylperoxyisopropylbenzene, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, and benzoyl peroxide.

4. The method for preparing grafted modified polypropylene with high-efficiency metal bonding properties according to claim 1, characterized in that, The maleic acid monomer is maleic anhydride.

5. The method for preparing grafted modified polypropylene with high-efficiency metal bonding properties according to claim 1, characterized in that, The acrylic monomer is at least one of glycidyl methacrylate and acrylic acid.

6. The grafted modified polypropylene prepared by the method according to any one of claims 1-5.

7. Use of the grafted modified polypropylene as a metal bonding material according to claim 6.

8. The use according to claim 7, characterized in that, The grafted modified polypropylene is used as a metal bonding material for adhesion between metals or between metals and plastics.

9. An aluminum-plastic composite film, characterized in that, It includes an aluminum foil layer and a heat-sealing layer adhered to the surface of the aluminum foil layer, wherein the heat-sealing layer is grafted modified polypropylene prepared by the method described in any one of claims 1-5.

10. A composite current collector, characterized in that, It includes a base film and a metal conductive layer deposited on one or both sides of the base film. The thickness of the base film is 2-6 μm, and the thickness of the metal conductive layer is 0.1-5 μm. The base film is grafted modified polypropylene prepared by the method according to any one of claims 1-5.

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