Multilayer coextruded polyolefin evaporation film, method for producing same, and use thereof

Abstract

The application discloses a kind of multilayer co-extrusion polyolefin evaporation film and its preparation method and application.The composite film uses four-layer structure design: substrate layer is blended by linear low-density polyethylene and metallocene polyethylene with (2-5):1 ratio, and high tough support layer is formed by 160-180 ℃ melt processing;Adhesive layer uses maleic anhydride grafted polyolefin (grafting rate 1.2-1.8%, acid value 15-25 mg KOH / g) to enhance interface bonding;Isolation layer selects biaxial stretching polypropylene (longitudinal / transverse tensile ratio 4-5:1, crystallinity 55-60%) or polyamide to realize interlayer isolation;Binding layer is grafted by ethylene-acrylic acid copolymer 8-12% glycidyl methacrylate, and chemical bonding is formed with evaporation layer by using epoxy group.The thickness ratio of each layer is (5-10):(1-1.6):(2-3):(1-1.6), and the application significantly improves the bonding strength of evaporation layer by polar group grafting and chemical bonding mechanism, especially suitable for packaging field needing high adhesion evaporation.

Description

Technical Field

[0001] This invention relates to the field of practical composite membrane technology, specifically to polyolefin composite membranes, and more specifically to a multilayer co-extruded polyolefin vapor-deposited membrane, as well as to the preparation method and application of such composite membranes. Background Technology

[0002] In selecting the isolation layer for composite films, the mainstream choices include vapor-deposited composite films and aluminized composite films. Compared to aluminized composite films, vapor deposition technology can deposit various materials such as aluminum, silicon oxide, copper, and silver to meet different requirements, including transparency, conductivity, and electromagnetic shielding, and provides higher oxygen and water vapor barrier properties for the composite film. Furthermore, vapor-deposited layers are chemically stable, more resistant to acids, alkalis, and high temperatures, and their thickness can be controlled between 20-100 nm. Their barrier performance is comparable to micron-level aluminized layers, but their thickness is only 1 / 10 that of aluminized layers, while also exhibiting superior bending resistance. Based on these principles and the designable structures of vapor-deposited layers, their application prospects in electronic products and new energy fields are broader.

[0003] Evaporated composite films are formed by depositing one or more layers of functional materials onto a substrate using an evaporation process to create a continuous, layered metal or dielectric film. For non-polar substrates, the film surface needs to be corona-treated or coated with an adhesive layer before evaporation to improve adhesion. However, while corona treatment can temporarily increase surface energy and thus improve bonding strength, its effect easily diminishes over time, and the treatment depth is difficult to control uniformly, leading to unstable adhesion of the evaporated layer. For coating processes, the difference in thermal expansion coefficients between the adhesive layer and the substrate can easily cause interfacial stress concentration, making interlayer delamination prone to occur under bending or high-temperature conditions. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a multilayer co-extruded polyolefin composite film that meets the requirements of direct vapor deposition and improves its bonding effect with the vapor-deposited layer.

[0005] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0006] A multilayer co-extruded polyolefin vapor-deposited film, comprising, from the inside out:

[0007] Substrate layer: a blend of linear low-density polyethylene and metallocene polyethylene;

[0008] Adhesive layer: maleic anhydride-grafted polyolefin;

[0009] Separation layer: Biaxially oriented polypropylene or polyamide layer;

[0010] Binding layer: ethylene-acrylic acid copolymer, wherein the ethylene-acrylic acid is further grafted with glycidyl methacrylate, and the grafting rate of glycidyl methacrylate is 8-12%;

[0011] The thickness ratio of the substrate layer, adhesive layer, isolation layer, and bonding layer is (5-10): (1-1.6): (2-3): (1-1.6).

[0012] Furthermore, the blending ratio of the linear low-density polyethylene to the metallocene polyethylene is (2-5):1.

[0013] Furthermore, the linear low-density polyethylene has a melt index of 0.8-1.5 g / 10min, and the metallocene polyethylene has a density of 0.915-0.930 g / cm³. 3 The blending and melting temperature of the two is controlled at 160-180℃.

[0014] Furthermore, the grafting rate of the maleic anhydride-grafted polyolefin is 1.2-1.8%.

[0015] Furthermore, the acid value of the maleic anhydride-grafted polyolefin is 15-25 mg KOH / g.

[0016] Furthermore, the longitudinal / transverse stretch ratio of the biaxially oriented polypropylene in the isolation layer is (4-5): 1, and the crystallinity of the biaxially oriented polypropylene is ≤60% for 55% ≤ 60%.

[0017] This invention also provides a method for preparing a multilayer co-extruded polyolefin vapor-deposited film, comprising the following steps:

[0018] S1: Blend linear low-density polyethylene with metallocene polyethylene and then melt-granulate.

[0019] S2: Melt grafting of ethylene-acrylic acid copolymer with glycidyl methacrylate;

[0020] S3: Using multi-layer co-extrusion equipment, the raw materials for the substrate layer, adhesive layer, isolation layer and bonding layer are extruded from independent extruders in sequence. The extrusion temperature and melt flow rate of the extruder corresponding to each layer are controlled. The extruder die of each layer is extruded into film bubbles through a conical die.

[0021] S4: After the membrane bubbles of each layer of the composite film are cooled and shaped, the membrane bubbles of each layer are flattened together by rollers and rolled up into a composite film.

[0022] Furthermore, the extrusion temperature of each layer in S3 is controlled as follows: substrate layer 160-180℃, adhesive layer 170-190℃, isolation layer 200-250℃, and bonding layer 180-200℃; the flow rate of each layer is adjusted according to the thickness ratio; the die gap of the conical stacked die is 0.5-1.2 mm, and the blow-up ratio is 2.5-3.5.

[0023] Furthermore, the isolation layer is made of biaxially oriented polypropylene, and the extruder end of the isolation layer is also equipped with a biaxial stretching unit. The longitudinal stretching temperature of the biaxial stretching unit is 120-135℃, the transverse stretching temperature is 145-155℃, and the heat setting temperature is 160-170℃.

[0024] The present invention also provides applications of the above-mentioned multilayer co-extruded polyolefin composite film, including the bonding layer being bonded to the side of the bonding layer away from the substrate layer by a vapor deposition process.

[0025] The advantages and beneficial effects of this invention are as follows:

[0026] 1. The substrate layer uses a blend of LLDPE and mPE to achieve high strength and toughness while supporting the membrane structure. The substrate layer and the adhesive layer enhance the interlayer adhesion by grafting polar groups of maleic anhydride onto polyolefin, preventing peeling failure. The isolation layer uses biaxially oriented polypropylene or polyamide to provide physical isolation between the adhesive layer and the bonding layer, preventing them from competing for vapor deposition bonding sites. The bonding layer uses GMA grafted with EAA, and achieves chemical bonding with the vapor deposition layer through epoxy groups, significantly improving the bonding strength between the vapor deposition layer and the composite membrane.

[0027] 2. The multilayer composite membrane structure can be co-extruded, optionally combined with biaxially oriented polypropylene membrane or polyamide membrane, and formed in one step to reduce interface defects, and can achieve a high recycling rate of all-olefin structure. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the composite membrane shown in this invention;

[0029] Figure 2 This is a process flow diagram of the composite membrane preparation process shown in this invention;

[0030] In the diagram: 1-substrate layer, 2-adhesive layer, 3-isolation layer, 4-bonding layer, 5-evaporation layer. Detailed Implementation

[0031] This invention provides a multilayer co-extruded polyolefin vapor-deposited film, its preparation method, and its application. The technical principle is as follows.

[0032] The substrate layer employs a blend of linear low-density polyethylene (LLDPE) and metallocene polyethylene (mPE). LLDPE provides excellent flexibility and tear resistance, while mPE enhances mechanical strength and improves processing rheology through its narrow molecular weight distribution and uniform branched structure. The optimal blending ratio is 2-5:1 to balance toughness and rigidity; and the melting temperature is selected at 160-180℃ to ensure compatibility. mPE acts as the dispersed phase to reinforce the matrix, while the continuous LLDPE phase absorbs impact energy, forming an "island structure" that achieves a balance between rigidity and toughness, preventing phase separation. As the core support layer of the film, the substrate layer resists the high temperatures of the vapor deposition process and the mechanical stresses during subsequent use, preventing film deformation or warping.

[0033] The adhesive layer incorporates carboxylic acid groups grafted with maleic anhydride, with an acid value of 15-25 mg KOH / g, enhancing the interfacial bonding with the substrate layer and the release layer. The carboxylic acid groups bond with the nonpolar segments of LLDPE / mPE via van der Waals forces, forming a weak interfacial layer to buffer stress. The carboxylic acid groups also form hydrogen or ionic bonds with the polar surfaces of BOPP / PA (such as the carbonyl groups in BOPP), with the bonding strength progressively increasing. By adjusting the distribution concentration of the grafted polyolefin, a polar gradient is created from the substrate layer to the release layer, preventing interlayer delamination caused by stress concentration.

[0034] The isolation layer can be selected from biaxially oriented polypropylene (BOPP) or polyamide (PA). BOPP is preferred, as its longitudinal / transverse stretch ratio (4-5:1) induces high molecular chain orientation, improving tensile strength and crystallinity, and optimizing barrier properties and heat resistance. Its function is to prevent the migration of maleic anhydride polar groups from the adhesive layer to the bonding layer, thus preventing them from competing with the vapor-deposited layer for bonding sites. The temperature resistance of BOPP and polyamide ensures minimal thermal shrinkage of the isolation layer during the vapor deposition process, meeting the requirements of the vapor deposition process.

[0035] The bonding layer utilizes ethylene-acrylic acid copolymer (EAA) to provide carboxylic acid groups, and then introduces epoxy groups by grafting glycidyl methacrylate (GMA). These epoxy groups form covalent bonds with the metal vapor-deposited layer through a ring-opening reaction, significantly improving the adhesion of the vapor-deposited layer. It is important to note that the GMA grafting rate needs to be precisely controlled; excessively high rates may lead to rigidification of the EAA segments, resulting in a decrease in the flow index of the EAA melt and affecting the uniformity of film formation.

[0036] The vapor-deposited film shown in this invention can be prepared using a multi-layer co-extrusion molding process. The extrusion temperature of each layer is matched with the material properties to avoid delamination caused by thermal stress. The die gap and blow-up ratio of the conical die control the uniformity of the film bubble and reduce interface defects. During the extrusion process, the extruder flow rate is adjusted according to the thickness ratio to ensure accurate thickness of each layer. The specific steps are based on the following principles.

[0037] The extrusion temperature of each layer is controlled according to the material properties. The substrate layer must match the melt viscosity of the LLDPE / mPE blend to avoid overheating and mPE degradation. The adhesive layer ensures that the maleic anhydride-grafted polyolefin is fully melted and that the polar groups do not decompose. The release layer meets the melt strength requirements before biaxial stretching. The bonding layer needs to balance the flowability and grafting stability of EAA-GMA.

[0038] As a preferred technical solution, when BOPP is used for the isolation layer, longitudinal stretching is performed at a temperature of 120-135℃ to induce the molecular chains to align along the extrusion direction and improve longitudinal strength; transverse stretching is performed at a temperature of 145-155℃ to enhance transverse tear resistance and balance the anisotropy caused by BOPP stretching. Finally, heat setting is performed at a temperature of 160-170℃ to stabilize the crystalline structure and prevent subsequent shrinkage.

[0039] The vapor-deposited film of this invention, after aluminum or silicon oxide is deposited on the bonding layer surface, can be applied to moisture-proof and antioxidant packaging for food and pharmaceuticals. The high adhesion of the bonding layer also allows for the vapor deposition of metal electrodes for use in flexible circuit substrates. By adjusting the proportions of each layer (e.g., thickening the insulating layer), oxygen / water barrier properties can be customized to meet the needs of different scenarios.

[0040] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0041] Example 1

[0042] A multilayer co-extruded polyolefin vapor-deposited film, the composition of which is:

[0043] Substrate layer: 50μm thick, made of LLDPE and mPE blend. LLDPE melt index is 1.0g / 10min; LLDPE / mPE mass ratio is 3:1; mPE density is 0.915g / cm³; melt blending temperature is 170℃.

[0044] Adhesive layer: 10μm thick, using MAH-g-PE with a grafting rate of 1.5% and an acid value of 20mg KOH / g.

[0045] Isolation layer: 20μm thick, made of BOPP, with a longitudinal and transverse stretch ratio of 4.5:1, and its crystallinity is measured to be 58%.

[0046] Bonding layer: 10 μm thick, using GMA-g-EAA with a grafting rate of 10%. The acrylic acid content in EAA is 10 wt%.

[0047] The preparation process includes blending and melting LLDPE and mPE at 170°C, followed by granulation using a twin-screw extruder (screw speed 200 rpm). EAA and GMA are melt-grafted at 180°C for 30 min, with dicumyl peroxide (DCP, 0.1 wt%) as the initiator.

[0048] During co-extrusion molding, the extrusion temperatures for each layer are: substrate layer 170℃, adhesive layer 180℃, release layer 220℃, and bonding layer 190℃. The die gap of the conical stack die is 0.8mm, the blow-up ratio is 3.0, and the melt flow rates for each layer are: substrate layer: 12kg / h, adhesive layer: 3kg / h, release layer: 6kg / h, and bonding layer: 3kg / h.

[0049] Each layer of the film bubble is air-cooled and shaped at 25℃. The longitudinal stretching temperature of BOPP is 130℃, and the stretching rate is 5m / min. The transverse stretching temperature is 150℃, and the stretching speed is 5m / min. The heat setting temperature is 165℃, and the time is 10s.

[0050] Example 2

[0051] A multilayer co-extruded polyolefin vapor-deposited film, which differs from Example 1 only in that...

[0052] Adhesive layer: 10μm thick, using MAH-g-PP with a grafting rate of 1.8% and an acid value of 25mg KOH / g.

[0053] Bonding layer: 10 μm thick, using GMA-g-EAA with a grafting rate of 12%. The acrylic acid content in EAA is 12 wt%.

[0054] The only difference in the preparation process is that...

[0055] The grafting reaction temperature of EAA and GMA in the adhesive layer was increased to 190℃, the amount of initiator DCP was increased to 0.15wt%, and the reaction time was extended to 35min.

[0056] During co-extrusion molding, the extrusion temperatures for each layer are: substrate layer 170℃, adhesive layer 190℃, release layer 220℃, and bonding layer 195℃. The die gap of the conical stack die is 0.7mm, the blow-up ratio is 3.2, and the melt flow rates for each layer are: substrate layer: 12kg / h, adhesive layer: 3kg / h, release layer: 6kg / h, and bonding layer: 2.55kg / h.

[0057] Example 3

[0058] A multilayer co-extruded polyolefin vapor-deposited film, which differs from Example 1 only in that...

[0059] The isolation layer, 25 μm thick, is made of PA.

[0060] The manufacturing process includes the following: during co-extrusion molding, the extrusion temperature of the isolation layer is 250℃, the melt flow rate is 6kg / h, the die gap of the conical stacked die is 1.0mm, and the blow-up ratio is 2.8.

[0061] Example 4

[0062] A multilayer co-extruded polyolefin vapor-deposited film, the composition of which is:

[0063] Substrate layer: 80μm thick, made of LLDPE and mPE blend. LLDPE melt index is 1.5g / 10min; LLDPE / mPE mass ratio is 5:1; mPE density is 0.930g / cm³; melt blending temperature is 180℃.

[0064] Adhesive layer: 12.8μm thick, using MAH-g-PP with a grafting rate of 1.2% and an acid value of 15mg KOH / g.

[0065] Isolation layer: 24μm thick, made of BOPP, with a longitudinal and transverse stretch ratio of 5:1, and its crystallinity is measured to be 60%.

[0066] Bonding layer: 12.8 μm thick, using GMA-g-EAA with a grafting rate of 8%. The acrylic acid content in EAA is 12 wt%.

[0067] The preparation process includes blending and melting LLDPE and mPE at 180°C, followed by granulation using a twin-screw extruder (screw speed 250 rpm). EAA and GMA are melt-grafted at 180°C for 30 minutes, with 0.1 wt% 1DCP as the initiator.

[0068] During co-extrusion molding, the extrusion temperatures for each layer are: substrate layer 180℃, adhesive layer 190℃, release layer 240℃, and bonding layer 200℃. The die gap of the conical stack die is 0.5mm, the blow-up ratio is 3.5, and the melt flow rates for each layer are: substrate layer: 20kg / h, adhesive layer: 4.8kg / h, release layer: 9.6kg / h, and bonding layer: 4.8kg / h.

[0069] Each layer of the film bubble is air-cooled and shaped at 20℃. The longitudinal stretching temperature of BOPP is 135℃, and the stretching rate is 5m / min. The transverse stretching temperature is 145℃, and the stretching speed is 5m / min. The heat setting temperature is 165℃, and the time is 15s.

[0070] Example 5

[0071] A multilayer co-extruded polyolefin vapor-deposited film, the composition of which is:

[0072] Substrate layer: 50μm thick, made of LLDPE and mPE blend. LLDPE melt index is 1.0g / 10min; LLDPE / mPE mass ratio is 3:1; mPE density is 0.915g / cm³; melt blending temperature is 170℃.

[0073] Adhesive layer: 10μm thick, using MAH-g-PE with a grafting rate of 1.5% and an acid value of 20mg KOH / g.

[0074] Isolation layer: 20μm thick, made of BOPP, with a longitudinal and transverse stretch ratio of 4.5:1 and a crystallinity of 58%.

[0075] Bonding layer: 10μm thick, made of unmodified EAA, with an acrylic acid content of 10wt%.

[0076] The preparation process includes: blending and melting LLDPE and mPE at 170°C, and granulating them through a twin-screw extruder (screw speed 200 rpm).

[0077] During co-extrusion molding, the extrusion temperatures for each layer are: substrate layer 170℃, adhesive layer 180℃, release layer 220℃, and bonding layer 190℃. The die gap of the conical stack die is 0.8mm, the blow-up ratio is 3.0, and the melt flow rates for each layer are: substrate layer 12kg / h, adhesive layer 3kg / h, release layer 6kg / h, and bonding layer 3kg / h.

[0078] Each layer of the membrane bubble is air-cooled and shaped at 25℃. The longitudinal stretching temperature of BOPP is 130℃, the transverse stretching temperature is 150℃, and the heat setting temperature is 165℃.

[0079] The composite membranes shown in the above embodiments have the following technical effects:

[0080] Test Project Heat shrinkage rate, %, 150℃, 30min <![CDATA[Water vapor barrier property, g / (m 2 ·24 h)]]> <![CDATA[Oxygen barrier property, cm 3 / (m 2 ·24 h·0.1 MPa)]]> Test Standards ASTMD1204 ASTM F1249 ASTM D3985 Example 1 1.2 12 55 Example 2 0.8 12 63 Example 3 1.1 4.2 110 Example 4 1.3 18 87 Example 5 1.5 15 70

[0081] The composite film shown in the above embodiments is used to produce a vapor-deposited film through a vapor deposition process, referred to as a preparation example, and the specific structure is as follows.

[0082] Preparation Example 1: The composite film obtained in Example 1 was used to prepare a vapor-deposited layer using a vacuum evaporation machine with a vacuum degree ≤ 5 × 10⁻⁶. - 4 Under Torr conditions, aluminum wire was placed in a tungsten boat and heated to 1400°C for evaporation, with an ambient humidity of 40%. The evaporation rate was 20 nm / s, and an aluminum metal layer with a thickness of 30 nm was deposited on the outside of the bonding layer.

[0083] Preparation Example 2: The composite membrane obtained in Example 2 was deposited with a 100 nm thick silicon oxide layer on the outside of the bonding layer by vapor deposition using SiH4 and N2O with a flow ratio of 0.25, a pressure of 0.5 Torr, a substrate temperature of 80 °C, an RF power of 500 W, and a deposition rate of 5 nm / s.

[0084] Preparation Example 3: The composite film obtained in Example 3 was deposited with trimethylaluminum and H2O at a deposition temperature of 150°C and a pressure of 0.1 Torr for 200 cycles, and an aluminum oxide layer with a thickness of 50 nm was attached to the outside of its bonding layer.

[0085] Preparation Example 4: The composite film obtained in Example 4 was used to attach an 80 nm thick indium tin oxide layer outside the bonding layer at an In2O3:SnO2 ratio of 90:10 wt%, a pressure of 0.003 Torr, an argon atmosphere, a substrate temperature of 120 °C, and a sputtering rate of 0.8 nm / s.

[0086] Preparation Example 5: The composite film obtained in Example 5 was directly subjected to a vapor deposition process: vacuum degree ≤ 5 × 10 -4 Under Torr conditions, aluminum wire was placed in a tungsten boat and heated to 1400°C for evaporation, with an ambient humidity of 38%. The evaporation rate was 20 nm / s, and an aluminum metal layer with a thickness of 30 nm was deposited on the outside of the bonding layer.

[0087] Preparation Example 6: The composite film obtained in Example 5 was corona treated with parameters of 5kW power and 10m / min processing speed, and then, in the same manner as in Preparation Example 5, an aluminum metal layer with a thickness of 30nm was formed on the outer side of the composite film bonding layer.

[0088] Peeling tests and water vapor and oxygen barrier tests were conducted on each preparation example at room temperature. The water vapor and oxygen test environment was 25°C and 50%RH. The folding resistance test method was to continuously fold the sample in half and unfold it, repeat the cycle, and record the number of times the vapor-deposited layer peeled off.

[0089] Test Project Peel strength, N / 15mm <![CDATA[Water vapor barrier property, g / (m 2 ·24 h)]]> <![CDATA[Oxygen barrier property, cm 3 / (m 2 ·24 h·0.1 MPa)]]> Flexural endurance test, times Test Standards ASTM D1876 ASTM F1249 ASTM D3985 ASTM D5264 Preparation Example 1 12.9 ≤1.0 ≤0.1 1000 Preparation Example 2 12.6 ≤1.8 ≤0.2 850 Preparation Example 3 15.4 N / A N / A 750 Preparation Example 4 13.7 N / A N / A 800 Preparation Example 5 1.2 ≤5.2 ≤2 200 Preparation Example 6 10.7 ≤3.8 ≤1 650

[0090] As shown in the table above, Preparation Examples 1-4, by grafting EAA onto GMA, form covalent bonds with the vapor-deposited layer through epoxy groups, which significantly improves the bonding and isolation between the vapor-deposited layer and the composite film. Preparation Examples 1-2, which also include a vapor-deposited layer, exhibit excellent water vapor and oxygen barrier properties. The peel strength between the untreated composite film and the vapor-deposited layer is extremely low, relying solely on physical adsorption and van der Waals forces, easily leading to the peeling and detachment of the vapor-deposited layer. In contrast, the composite film structure provided by this invention exhibits a superior bonding effect between the composite film structure and the vapor-deposited layer compared to prior art corona treatment (Preparation Example 6), providing stronger peel strength and significantly improving its folding resistance.

[0091] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A multilayer co-extruded polyolefin vapor-deposited film, characterized in that, Including the following settings from the inside out: The substrate layer is composed of a blend of linear low-density polyethylene and metallocene polyethylene; The adhesive layer is composed of maleic anhydride-grafted polyolefin; The isolation layer is made of biaxially oriented polypropylene or polyamide; The bonding layer is composed of an ethylene-acrylic acid copolymer, wherein the ethylene-acrylic acid copolymer is grafted with glycidyl methacrylate; the thickness ratio of the substrate layer, adhesive layer, release layer and bonding layer is (5-10):(1-1.6):(2-3):(1-1.6). The mass ratio of linear low-density polyethylene to metallocene polyethylene is (2-5):1, the melt index of the linear low-density polyethylene is 0.8-1.5 g / 10 min, and the density of the metallocene polyethylene is 0.915-0.930 g / cm³. 3 Furthermore, the blending and melting temperature of the two is controlled at 160-180℃; The grafting rate of the maleic anhydride-grafted polyolefin is 1.2-1.8%, and the acid value of the maleic anhydride-grafted polyolefin is 15-25 mg KOH / g. The grafting rate of the glycidyl methacrylate in the ethylene-acrylic acid copolymer is 8-12%.

2. The multilayer co-extruded polyolefin vapor-deposited film according to claim 1, characterized in that, When the isolation layer is biaxially oriented polypropylene, its longitudinal / transverse stretch ratio is (4-5):1, and its crystallinity is 55%-60%.

3. A method for preparing a multilayer co-extruded polyolefin vapor-deposited film as described in claim 1, characterized in that, Includes the following steps: S1: Linear low-density polyethylene is blended with metallocene polyethylene and then melt-granulated; S2: Melt grafting of ethylene-acrylic acid copolymer with glycidyl methacrylate; S3: Using multi-layer co-extrusion equipment, the raw materials of the substrate layer, adhesive layer, isolation layer and bonding layer are respectively extruded through independent extruders, and the extrusion temperature and melt flow rate of each layer are controlled. The melt of each layer is extruded through a conical die to form a film bubble. S4: After the composite film bubble is air-cooled and shaped, it is flattened by rollers and then wound up.

4. The preparation method according to claim 3, characterized in that, The extrusion temperatures of each layer in S3 are as follows: substrate layer 160-180℃, adhesive layer 170-190℃, isolation layer 200-250℃, and bonding layer 180-200℃; the die gap of the conical stacked die is 0.5-1.2mm, and the blow-up ratio is 2.5-3.

5.

5. The preparation method according to claim 3, characterized in that, When the isolation layer is biaxially oriented polypropylene, a biaxial stretching unit is configured at the end of the extruder, with a longitudinal stretching temperature of 120-135℃, a transverse stretching temperature of 145-155℃, and a heat setting temperature of 160-170℃.

6. An application of the multilayer co-extruded polyolefin composite film as described in claim 1, characterized in that, A vapor-deposited layer is formed on the side of the bonding layer away from the substrate layer by a vapor deposition process.

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