A multi-layer protective film and a preparation process thereof

Abstract

The application provides a multilayer protective film and a preparation process thereof. The structure of the multilayer protective film comprises an outer surface layer, a first adhesive layer, a support layer and a second adhesive layer arranged in sequence, wherein the support layer is a polyamide layer. The preparation process of the multilayer protective film adopts a co-extrusion process. Through the arrangement of the structure of the protective film and the reasonable compounding of the formula components, the structural strength and the heat resistance of the battery protective film are effectively improved on the basis of ensuring the safety performance and the insulation performance, the adhesive strength of the adhesive layer is improved, the protective film does not generate thermal shrinkage and thermal deformation in the use process, and the preparation process is simple and the preparation efficiency is high.

Description

Technical Field

[0001] This invention belongs to the field of battery protection materials technology, specifically, it relates to a multilayer protective film and its preparation process. Background Technology

[0002] Currently, most battery protective films on the market use polyethylene terephthalate (PET) as the outer layer and substrate to support the adhesive layer, ensuring the film's excellent structural strength. However, PET has poor temperature resistance, posing a risk of spontaneous combustion in the event of thermal runaway of the battery cell or external heat sources. This is detrimental to effective protection of the battery cell, and the protective film is more prone to thermal shrinkage and deformation. Therefore, those skilled in the art urgently need to solve the problems of the commonly used PET substrate being susceptible to high-temperature shrinkage, thermal runaway, complex manufacturing processes, and low efficiency. Summary of the Invention

[0003] The purpose of this invention is to provide a multilayer protective film. By setting the structure of the protective film and rationally compounding the formulation components, the structural strength and heat resistance of the battery protective film are effectively improved while ensuring safety and insulation performance. The bonding strength of the adhesive layer is also improved, so that the protective film does not produce thermal shrinkage and thermal deformation during use. Moreover, the preparation process is simple and the preparation efficiency is high.

[0004] According to a first aspect of the present invention, a multilayer protective film is provided, the structure of which includes an outer surface layer, a first adhesive layer, a support layer, and a second adhesive layer disposed sequentially, wherein the support layer is a polyamide layer. In this invention, by providing a polyamide support layer on the structure of the protective film, the problem of the outer surface layer's poor high-temperature resistance is specifically solved, enabling the protective film provided by the present invention to possess both excellent mechanical strength and temperature resistance, be less prone to thermal shrinkage, have excellent structural stability, better protect the battery cell, prevent thermal runaway, and improve the insulation performance of the protective film.

[0005] Preferably, the polyamide layer comprises polyamide MXD6. MXD6 has the characteristics of low water absorption, high tensile strength, high heat distortion temperature, low heat shrinkage, and good barrier properties against gases such as O2 and CO2.

[0006] Preferably, the outer membrane material comprises polyethylene terephthalate (PET). PET serves as a substrate to support the adhesive layer, providing a good bonding effect.

[0007] Preferably, the first adhesive layer comprises a polyolefin copolymer, wherein, by mass percentage, the raw materials of the polyolefin copolymer comprise 65-85% soft copolymer and 10-15% hard copolymer. The soft copolymer is obtained by polymerization of soft monomers, and the hard copolymer is obtained by polymerization of hard monomers. The combination of the soft copolymer and the hard copolymer to form the first adhesive layer facilitates better bonding between the first adhesive layer and the outer surface layer, achieving excellent bonding effects on both the support layer and the outer surface layer.

[0008] Preferably, the soft copolymer is a polyethylene copolymer, and the hard copolymer is a cyclic olefin copolymer. Using a polyethylene copolymer as the soft copolymer of the first adhesive layer not only improves the adhesion of the protective film but also ensures its high-temperature resistance. However, because polyethylene is relatively soft, it is prone to thickness reduction during hot pressing. Therefore, by using a cyclic olefin copolymer as the hard copolymer of the first adhesive layer, the flow of polyethylene molecular chains can be suppressed, thereby improving the adhesion performance of the first adhesive layer.

[0009] Preferably, the polyethylene copolymer includes at least one of ethylene-vinyl acetate copolymer, ethylene-octene copolymer, and ethylene-acrylic acid copolymer.

[0010] Preferably, the melt index of the cyclic olefin copolymer is 15-30 g / 10 min, and the Tg is 80-140 °C.

[0011] Preferably, the second adhesive layer comprises a polyaromatic elastomer, wherein the raw materials of the polyaromatic elastomer, by weight percentage, comprise 65-85% styrene thermoplastic elastomer and 10-30% copolymer polypropylene.

[0012] In another aspect of the present invention, a co-extrusion process for preparing a multilayer protective film as claimed in any one of claims 1 to 8 is provided, comprising the following steps: firstly, the raw materials of the first adhesive layer and the second adhesive layer are melt-blended and extruded into masterbatches, and then the masterbatches are melt-blended and co-extruded with the raw materials of the outer surface layer and the raw materials of the support layer and cast into a film.

[0013] Since the protective film provided by this invention is a multi-layer composite film, if the traditional transfer coating process is used to prepare the protective film provided by this invention, multiple transfer coating operations are required, which is cumbersome. Moreover, because a support layer is set between two adhesive layers, the traditional coating process of curing the film in stages makes it difficult to achieve tight adhesion between different composite layers. This can easily lead to gaps between the layers and poor film consistency. In addition, the coating process generally requires a large amount of volatile solvents to prepare the coating slurry, which may introduce a large amount of harmful substances into the construction environment, failing to meet the requirements of green and environmentally friendly construction. In contrast, this invention uses a co-extrusion process to prepare the encapsulation film, which can achieve simultaneous film formation and composite of different raw materials, and does not require the use of a large amount of solvents. This saves processing steps and raw materials, provides high control precision, and improves the efficiency of protective film production. Furthermore, it is worth noting that the co-extrusion process allows different film materials to be tightly bonded under the external force of the co-extrusion die, improving the tightness between film layers and maintaining excellent consistency and flatness of the film.

[0014] Preferably, the co-extrusion temperature of the co-extrusion process is 265–300°C. Since polyamide has a narrow melting temperature range, maintaining heating within this range during the preparation process can prevent die blockage due to polyamide solidification, ensuring smooth feeding.

[0015] Preferably, the melting temperature of the first adhesive layer and the second adhesive layer is 250°C to 280°C.

[0016] Specific implementation methods

[0017] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0018] Example 1

[0019] Processing Group 1

[0020] This embodiment provides a multilayer co-extruded protective film for power batteries with a thickness of 110μm, which is composed of PET, a first adhesive layer, polyamide MXD6, a second adhesive layer, and a release layer in sequence.

[0021] The PET layer thickness is 25μm;

[0022] The thickness of the first adhesive layer is 20 μm. The materials used to prepare the first adhesive layer include soft monomers and hard monomers. By mass, the soft copolymers include 60 parts of ethylene-vinyl acetate copolymer and 10 parts of ethylene-acrylic acid copolymer. The hard copolymers include 10 parts of cyclic olefin copolymer, wherein the cyclic olefin copolymer is Mitsui's COCAPL6013, with a melt index of 15 g / 10 min and a Tg of 125 °C. The materials used to prepare the first adhesive layer also include 8 parts of silica, 10 parts of phthalocyanine blue, 2 parts of ultramarine, 0.2 parts of triphenyl phosphite, and 0.1 parts of tert-butylperoxycarbonate-2-ethylhexyl ester.

[0023] The polyamide MXD6 layer has a thickness of 20 μm;

[0024] The thickness of the second adhesive layer is 20 μm. The materials used to prepare the second adhesive layer, by mass parts, include 75 parts of hydrogenated polystyrene-polybutadiene-polystyrene, 20 parts of copolymerized polypropylene, 10 parts of C9 resin, 1 part of triphenyl phosphite, and 0.2 parts of tert-butylperoxycarbonate-2-ethylhexyl ester; wherein the crystallinity of hydrogenated polystyrene-polybutadiene-polystyrene is ≤20%.

[0025] The release layer is a PET release layer with a thickness of 25μm.

[0026] The above-mentioned multilayer co-extruded protective film for power batteries is prepared by the following steps:

[0027] 1. The materials used to prepare the first adhesive layer and the second adhesive layer are melt-blended at 250°C and 280°C respectively, and then extruded into masterbatch;

[0028] 2. The above masterbatch is fed into a twin-screw extruder and heated to a molten state. Then, it is co-extruded and cast in the interlayer sequence and compounded. The extrusion temperature is set to 265℃~300℃. After cooling, slitting and winding, a multi-layer co-extruded protective film for power batteries is obtained.

[0029] Processing Group 2

[0030] This treatment group prepared a multilayer protective film according to treatment group 1 in Example 1. The difference between this treatment group and treatment group 1 in this example is that the support layer used is composed of polyamide PA6. Apart from the above differences, the materials and process operations used in this example are strictly consistent with those of treatment group 1 in this example.

[0031] Processing Group 3

[0032] This treatment group prepared a multilayer protective film according to treatment group 1 in Example 1. The difference between this treatment group and treatment group 1 in this example is that the support layer used is composed of polyamide PA11. Apart from the above differences, the materials and process operations used in this example are strictly consistent with those of treatment group 1 in this example.

[0033] Comparison group 1

[0034] This comparative treatment group prepared a multilayer protective film according to treatment group 1 in this embodiment. The difference between this embodiment and treatment group 1 in embodiment 1 is that the structure of the multilayer protective film only includes an outer surface layer and a second adhesive layer. Apart from the above differences, the materials and process operations used in this comparative treatment group are strictly consistent with those of treatment group 1 in this embodiment.

[0035] Comparison group 2

[0036] This comparative treatment group prepared a multilayer protective film according to treatment group 1 in this embodiment. The difference between this comparative treatment group and treatment group 1 in embodiment 1 is that the support layer used in this comparative treatment group is composed of polyethylene terephthalate (PET). Apart from the above differences, the materials and process operations used in this comparative treatment group are strictly consistent with those of treatment group 1 in this embodiment.

[0037] Comparison group 3

[0038] This comparative treatment group prepared a multilayer protective film according to treatment group 1 in this embodiment. The difference between this comparative treatment group and treatment group 1 in embodiment 1 is that the support layer used in this comparative treatment group is composed of polyimide (PI). Apart from the above differences, the materials and process operations used in this comparative treatment group are strictly consistent with those of treatment group 1 in this embodiment.

[0039] Test Example 1

[0040] 1. Test the build method

[0041] The test objects in this test example are the multilayer protective films prepared by treatment groups 1 to 3 and control treatment groups 1 to 3 in Example 1. The bonding strength of the steel plate, insulation resistance, shrinkage rate at 85°C, bonding strength at high temperature and humidity for 100 hours, and film surface condition at high temperature and humidity for 100 hours are tested.

[0042] (1) Steel plate bonding strength: The test was conducted in accordance with the contents specified in the national standard GB2792-2014. A 25mm protective film was attached to the steel plate, rolled 3 times with a 2kg roller, and placed in an environment of 23±1℃ and 50±5%RH for 20min. The peel force was tested at a speed of 300mm / min at 180°. The measured peel force is the steel plate bonding strength.

[0043] (2) Insulation resistance: The test was conducted using a HEX301 DC AC withstand voltage insulation tester. The test sample was prepared, and adhesive film was attached to both sides and the back of the substrate. The positive and negative electrodes were clamped to both sides of the substrate. The "insulation resistance test" was selected, and the test conditions were adjusted to DC 10000V, 60s. The test was then clicked and the test results were read.

[0044] (3) 85℃ high temperature shrinkage rate: The test was conducted in accordance with the contents specified in the national standard GB / T 34848-2017 "Test method for shrinkage performance of heat shrink film" and the test conditions were 85℃ for 6 hours.

[0045] (4) Bonding strength under high temperature and humidity for 100 hours: The test was conducted in accordance with the contents specified in the national standard GB2792-2014. A 25mm protective film was attached to the steel plate, rolled 3 times with a 2kg roller, and placed in an environment of 85℃ and 85%RH for 100 hours. The peel force was tested at a speed of 300mm / min at 180°. The measured peel force is the bonding strength of the steel plate.

[0046] 2. Test Results

[0047] Table 1 Performance test results of the multilayer protective film in Example 1

[0048]

[0049]

[0050] The performance test results of the multilayer protective films in treatment groups 1-3 and control groups 1-3 in Example 1 are shown in Table 1. As can be seen from Table 1, compared with control groups 1-3, the multilayer protective film provided by this invention, by setting a support layer and using a polyamide layer as the support layer, exhibits excellent temperature resistance, bonding strength, insulation performance, and film surface smoothness. Specifically, the high-temperature shrinkage rate at 100℃ is less than 0.1%, the steel plate bonding strength is greater than 14.0 N / 24 mm, and the insulation resistance is greater than 2.5 × 10⁻⁶. 3 MΩ, with good film surface flatness and no warping. In contrast, the multi-layer protective films provided in treatment groups 1-3 showed a high-temperature shrinkage rate of less than 1.5% at 100℃, a steel plate bonding strength of less than 14.0 N / 24 mm, and an insulation resistance of less than 2.0 × 10⁻⁶. 3 MΩ, film surface lifting. Compared to treatment groups 2-3, the multilayer protective film provided by treatment group 1 has better adhesive strength by using polyamide MXD6 as the polyamide layer.

[0051] Example 2

[0052] Processing Group 1

[0053] This treatment group prepares a multilayer protective film according to treatment group 1 of Example 1. The materials and process operations used in this treatment group are strictly consistent with those of treatment group 1 in this example.

[0054] Processing Group 2

[0055] This treatment group prepares a multilayer protective film according to treatment group 1 of this embodiment. The difference between this treatment group and treatment group 1 is that the raw materials used in the first adhesive layer, calculated by parts, include 70 parts of a soft copolymer and 15 parts of a hard copolymer. Apart from the above differences, the specific composition of the soft copolymer and hard copolymer used in this treatment group, the other raw materials of the protective film, and the process operation are strictly consistent with those of treatment group 1 in this embodiment.

[0056] Processing Group 3

[0057] This treatment group prepares a multilayer protective film according to treatment group 1 of this embodiment. The difference between this treatment group and treatment group 1 is that the raw materials used in the first adhesive layer, calculated by parts, include 70 parts of a soft copolymer and 5 parts of a hard copolymer. Apart from the above differences, the specific composition of the soft copolymer and hard copolymer used in this treatment group, the other raw materials of the protective film, and the process operation are strictly consistent with those of treatment group 1 in this embodiment.

[0058] Processing Group 4

[0059] This treatment group prepares a multilayer protective film according to treatment group 1 of this embodiment. The difference between this treatment group and treatment group 1 is that the raw materials used in the first adhesive layer, calculated by parts, include 70 parts of a soft copolymer and 25 parts of a hard copolymer. Apart from the above differences, the specific composition of the soft copolymer and hard copolymer used in this treatment group, the other raw materials of the protective film, and the process operation are strictly consistent with those of treatment group 1 in this embodiment.

[0060] Test Example 2

[0061] 1. Test the build method

[0062] The test objects in this test example are the multilayer protective films prepared by treatment groups 1 to 4 of Example 2. The bonding strength of the steel plate, insulation resistance, high temperature shrinkage rate at 85℃, bonding strength at high temperature and humidity for 100 hours, and film surface condition at high temperature and humidity for 100 hours are tested.

[0063] The testing method is the same as that used in Test Example 1.

[0064] 2. Test Results

[0065] Table 2 Performance test results of the multilayer protective film in Example 2

[0066]

[0067]

[0068] As shown in Table 2, compared with treatment groups 1 to 2, the multilayer protective film provided by treatment groups 3 to 4 in Example 2 has better bonding strength, high temperature resistance and film surface smoothness by using soft copolymers and hard copolymers with different ratios as raw materials for the first adhesive layer.

[0069] Example 3

[0070] Processing Group 1

[0071] This treatment group prepared a multilayer protective film according to treatment group 1 of Example 1. The materials and process operations used in this treatment group are strictly consistent with those of treatment group 1 of Example 1.

[0072] Processing Group 2

[0073] This treatment group prepares a multilayer protective film according to treatment group 1 of this embodiment. The difference between this treatment group and treatment group 1 is that the soft copolymer composed of ethylene-vinyl acetate copolymer and ethylene-acrylic acid copolymer used in the first adhesive layer is replaced with isooctyl acrylate. Apart from the above differences, the materials and process operations used in this treatment group are strictly consistent with those of treatment group 1 in this embodiment.

[0074] Processing Group 3

[0075] This treatment group prepares a multilayer protective film according to treatment group 1 of this embodiment. The difference between this treatment group and treatment group 1 is that the soft copolymer composed of ethylene-vinyl acetate copolymer and ethylene-acrylic acid copolymer used in the first adhesive layer is replaced with ethyl acrylate. Apart from the above differences, the materials and process operations used in this treatment group are strictly consistent with those of treatment group 1 in this embodiment.

[0076] Processing Group 4

[0077] This treatment group prepares a multilayer protective film according to treatment group 1 of this embodiment. The difference between this treatment group and treatment group 1 is that the soft copolymer composed of ethylene-vinyl acetate copolymer and ethylene-acrylic acid copolymer used in the first adhesive layer is replaced with butyl acrylate. Apart from the above differences, the materials and process operations used in this treatment group are strictly consistent with those of treatment group 1 in this embodiment.

[0078] Test Example 3

[0079] 1. Test the build method

[0080] The test objects in this test example are the multilayer protective films prepared by treatment groups 1 to 4 of Example 2. The bonding strength of the steel plate, insulation resistance, high temperature shrinkage rate at 85℃, bonding strength at high temperature and humidity for 100 hours, and film surface condition at high temperature and humidity for 100 hours are tested.

[0081] The testing method is the same as that used in Test Example 1.

[0082] 2. Test Results

[0083] Table 3 Performance test results of the multilayer protective film in Example 3

[0084]

[0085] As shown in Table 3, compared with treatment groups 2 to 4, the multilayer protective film provided by treatment group 1 in Example 3 has better bonding strength, high temperature resistance and film surface smoothness by using polyethylene copolymer as the raw material of the soft copolymer of the first adhesive layer.

[0086] Example 4

[0087] Processing Group 1

[0088] This treatment group prepared a multilayer protective film according to treatment group 1 of Example 1. The materials and process operations used in this treatment group are strictly consistent with those of treatment group 1 of Example 1.

[0089] Processing Group 2

[0090] This treatment group prepares a multilayer protective film according to treatment group 1 of this embodiment. The difference between this treatment group and embodiment 1 is that the polyethylene copolymer used in the first adhesive layer is composed of ethylene-octene copolymer. Apart from the above differences, the materials and process operations used in this treatment group are strictly consistent with those in embodiment 1.

[0091] Processing Group 3

[0092] This treatment group prepares a multilayer protective film according to treatment group 1 of this embodiment. The difference between this treatment group and embodiment 1 is that the polyethylene copolymer used in the first adhesive layer is composed of ethylene-vinyl acetate copolymer. Apart from the above differences, the materials and process operations used in this treatment group are strictly consistent with those in embodiment 1.

[0093] Processing Group 4

[0094] This treatment group prepares a multilayer protective film according to treatment group 1 of this embodiment. The difference between this treatment group and embodiment 1 is that the polyethylene copolymer used in the first adhesive layer is composed of ethylene-acrylic acid copolymer. Apart from the above differences, the materials and process operations used in this treatment group are strictly consistent with those in embodiment 1.

[0095] Test Example 4

[0096] 1. Test the build method

[0097] The test objects in this test example are the multilayer protective films prepared by treatment groups 1 to 4 of Example 2. The bonding strength of the steel plate, insulation resistance, high temperature shrinkage rate at 85℃, bonding strength at high temperature and humidity for 100 hours, and film surface condition at high temperature and humidity for 100 hours are tested.

[0098] The testing method is the same as that used in Test Example 1.

[0099] 2. Test Results

[0100] Table 4 Performance test results of the multilayer protective film in Example 4

[0101]

[0102]

[0103] As shown in Table 4, compared with treatment groups 2 to 4, the multilayer protective film provided in treatment group 1 in Example 4 has better high-temperature resistance by using ethylene-vinyl acetate copolymer and acrylic acid copolymer as raw materials for the first adhesive layer polyethylene copolymer.

[0104] Example 5

[0105] Processing Group 1-1

[0106] This treatment group prepares a multilayer protective film with reference to treatment group 1 of this embodiment. The materials and process operations used in this treatment group are strictly consistent with those of treatment group 1 in embodiment 1.

[0107] Treatment group 1-2

[0108] This treatment group prepared a multilayer protective film according to treatment group 1 of this embodiment. The difference between this treatment group and embodiment 1 is that the cyclic olefin copolymer used in the first adhesive layer is Mitsui APL6509, with a Tg of 80°C. Apart from the above differences, the materials and process operations used in this treatment group are strictly consistent with those in embodiment 1.

[0109] Treatment Groups 1-3

[0110] This treatment group prepared a multilayer protective film according to treatment group 1 of this embodiment. The difference between this treatment group and embodiment 1 is that the cyclic olefin copolymer used in the first adhesive layer is Mitsui APL5014D0 with a Tg of 132°C. Apart from the above differences, the materials and process operations used in this treatment group are strictly consistent with those in embodiment 1.

[0111] Treatment groups 1-4

[0112] This treatment group prepared a multilayer protective film according to treatment group 1 of this embodiment. The difference between this treatment group and embodiment 1 is that the cyclic olefin copolymer used in the first adhesive layer is Polyplastics 6015S-04, with a Tg of 158°C. Apart from the above differences, the materials and process operations used in this treatment group are strictly consistent with those in embodiment 1.

[0113] Treatment groups 1-5

[0114] This treatment group prepared a multilayer protective film according to treatment group 1 of this embodiment. The difference between this treatment group and embodiment 1 is that the cyclic olefin copolymer used in the first adhesive layer is TOPAS 8007F-600, with a Tg of 78°C. Apart from the above differences, the materials and process operations used in this treatment group are strictly consistent with those in embodiment 1.

[0115] Comparison treatment group 2-1

[0116] This comparative treatment group prepared a multilayer protective film according to treatment group 1 of this embodiment. The difference between this comparative treatment group and treatment group 1 of this embodiment is that the process of this comparative treatment group is to transfer and coat the raw materials of the multilayer protective film in the interlayer sequence using a coating machine, thereby obtaining the protective film of this comparative treatment group. Apart from the above differences, the materials used in this comparative treatment group are strictly consistent with those in Example 1.

[0117] Comparison treatment group 2-2

[0118] This comparative treatment group prepared a multilayer protective film according to treatment group 2 of this embodiment. The difference between this comparative treatment group and treatment group 2 of this embodiment is that the process of this comparative treatment group is to transfer and coat the raw materials of the multilayer protective film in the interlayer sequence using a coating machine, thereby obtaining the protective film of this embodiment. Apart from the above differences, the materials used in this comparative treatment group are strictly consistent with those in Example 1.

[0119] Comparison treatment group 2-3

[0120] This comparative treatment group prepared a multilayer protective film in accordance with treatment group 3 of this embodiment. The difference between this comparative treatment group and treatment group 3 of this embodiment is that the process of this comparative treatment group involves transferring and coating the raw materials of the multilayer protective film in the interlayer sequence using a coating machine, thereby obtaining the protective film of this comparative treatment group. Apart from the above differences, the materials used in this comparative treatment group are strictly consistent with those in Example 1.

[0121] Comparison treatment groups 2-4

[0122] This comparative treatment group prepared a multilayer protective film in accordance with treatment group 4 of this embodiment. The difference between this comparative treatment group and treatment group 4 of this embodiment is that the process of this comparative treatment group involves transferring and coating the raw materials of the multilayer protective film in the interlayer sequence using a coating machine, thereby obtaining the protective film of this comparative treatment group. Apart from the above differences, the materials used in this comparative treatment group are strictly consistent with those in Example 1.

[0123] Comparison treatment groups 2-5

[0124] This comparative treatment group prepared a multilayer protective film in accordance with treatment group 5 of this embodiment. The difference between this comparative treatment group and treatment group 5 of this embodiment is that the process of this comparative treatment group involves transferring and coating the raw materials of the multilayer protective film in the interlayer sequence using a coating machine, thereby obtaining the protective film of this comparative treatment group. Apart from the above differences, the materials used in this comparative treatment group are strictly consistent with those in Example 1.

[0125] Test Example 5

[0126] 1. Test the build method

[0127] The test objects in this test example are the multilayer protective films prepared by treatment groups 1 to 4 of Example 2. The bonding strength of the steel plate, insulation resistance, high temperature shrinkage rate at 85℃, bonding strength at high temperature and humidity for 100 hours, and film surface condition at high temperature and humidity for 100 hours are tested.

[0128] The testing method is the same as that used in Test Example 1.

[0129] 2. Test Results

[0130] Table 5 Performance test results of the multilayer protective film in Example 5

[0131]

[0132]

[0133] As shown in Table 5, compared with control groups 2-1 to 2-5, the multilayer protective films provided in control groups 1-1 to 1-5 of Example 5, prepared using a co-extrusion process, exhibit better adhesive strength, high-temperature resistance, and surface smoothness. Compared with control groups 1-4 to 1-5, the multilayer protective films provided in control groups 1-1 to 1-3 of Example 5, using cyclic olefin copolymers with suitable Tg values, exhibit better adhesive strength, high-temperature resistance, and surface smoothness.

[0134] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. A multilayer protective film, characterized in that, The structure of the multilayer protective film includes an outer outer layer, a first adhesive layer, a support layer, and a second adhesive layer arranged sequentially. The support layer is a polyamide layer. The second adhesive layer includes a polyaromatic elastomer, wherein, by mass percentage, the raw materials of the polyaromatic elastomer include 65-85% styrene thermoplastic elastomer and 10-30% copolymer polypropylene. The first adhesive layer comprises a polyolefin copolymer, wherein, by mass percentage, the raw materials of the polyolefin copolymer comprise 65-85% soft copolymer and 10-15% hard copolymer; The soft copolymer is a polyethylene copolymer, and the hard copolymer is a cyclic olefin copolymer; The polyethylene copolymer includes at least one of ethylene-vinyl acetate copolymer, ethylene-octene copolymer, and ethylene-acrylic acid copolymer; The glass transition temperature of the cyclic olefin copolymer is 80–140°C; The multilayer protective film is prepared by a co-extrusion process.

2. The multilayer protective film as described in claim 1, characterized in that, The polyamide layer comprises polyamide MXD6.

3. The multilayer protective film as described in claim 1, characterized in that, The outer membrane material includes polyethylene terephthalate.

4. The multilayer protective film as described in claim 1, characterized in that, The melt index of the cyclic olefin copolymer is 15-30 g / 10 min.

5. A co-extrusion process for preparing a multilayer protective film as described in any one of claims 1 to 4, characterized in that, The process includes the following steps: first, the raw materials of the first adhesive layer and the second adhesive layer are melt-blended and extruded into masterbatch, and then the masterbatch is melt-co-extruded with the raw materials of the outer surface layer and the raw materials of the support layer and cast into a film.

6. The co-extrusion process of the multilayer protective film as described in claim 5, characterized in that, The co-extrusion temperature of the co-extrusion process is 265–300°C.

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