Multifunctional high-barrier polypropylene recyclable packaging film and preparation method thereof

Abstract

The invention relates to the field of high polymer materials, and discloses a multifunctional high-barrier polypropylene recyclable packaging film and a preparation method thereof, and the film structure sequentially comprises an anti-ultraviolet BOPP film, a first functional bonding layer, a composite barrier middle layer, a second functional bonding layer and a puncture-resistant CPP film from outside to inside. Wherein the outer layer of the anti-ultraviolet BOPP film contains nano zinc oxide and a high-molecular-weight hindered amine light stabilizer; ultra-high molecular weight polyethylene is introduced into the supporting layer of the puncture-resistant CPP film through a reactive extrusion process; the puncture-resistant granules are prepared through reactive extrusion, the composite barrier middle layer is prepared through magnetron sputtering and plasma treatment, and finally all the layers are subjected to hot-pressing compounding through the bonding layer containing the silane coupling agent. The film prepared by the invention has excellent ultraviolet resistance, puncture resistance, high barrier property, interlayer bonding strength and high-temperature dimensional stability.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a multifunctional high-barrier recyclable polypropylene packaging film and its preparation method. Background Technology

[0002] Polypropylene (PP) films, especially biaxially oriented polypropylene (BOPP) films and cast polypropylene (CPP) films, have gained widespread use in flexible packaging due to their cost-effectiveness, excellent processability, transparency, and recyclability potential within a single material system. To meet increasingly stringent protection requirements for contents such as food, pharmaceuticals, and precision electronic components, single-layer polypropylene films often fall short, leading to the development of multilayer composite film technology.

[0003] However, existing polypropylene-based multilayer composite films still have many shortcomings in terms of overall performance. Firstly, to achieve efficient barrier properties against oxygen and water vapor, inorganic oxide barrier layers (such as silicon oxide or aluminum oxide) or metallized layers are typically introduced. These inorganic layers have weak interfacial adhesion to the non-polar polypropylene substrate, making them highly susceptible to interlayer delamination under mechanical stresses such as bending and rubbing, or in humid and hot environments such as high-temperature cooking. This leads to a sharp decline in barrier performance or even complete failure. This limits their application in conditions requiring high durability and resistance to cooking.

[0004] Secondly, the mechanical properties of conventional polypropylene films, especially their puncture resistance, are insufficient for some specialized applications, such as packaging products with sharp edges or requiring vacuum sealing to create a tight seal. While this can be improved by adding toughening agents, it is often difficult to achieve the desired results or may sacrifice other key properties of the film.

[0005] Furthermore, polypropylene itself has poor resistance to ultraviolet radiation. Under prolonged exposure to light, its molecular chains degrade, leading to aging phenomena such as yellowing, embrittlement, and decreased mechanical properties in the film. This not only affects the appearance and integrity of the packaging but also fails to provide effective protection for photosensitive contents. Currently used single-anti-UV additive solutions often have limited durability of their protective effect. Meanwhile, the dimensional stability (i.e., low heat shrinkage) and surface antistatic properties of traditional polypropylene films during high-temperature processing are also performance indicators that urgently need improvement in practical applications.

[0006] Therefore, developing a multifunctional packaging film that can simultaneously achieve high barrier properties, high-strength interlayer bonding, excellent puncture resistance, long-lasting UV resistance, and good thermal stability within a single polypropylene material system is a current technical challenge in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a multifunctional high-barrier recyclable polypropylene packaging film and its preparation method, which solves the problems of existing polypropylene-based composite films, such as difficulty in balancing barrier performance and mechanical properties, weak interlayer bonding leading to rapid performance degradation under humid heat or dynamic stress, and insufficient UV resistance.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution: a multifunctional high-barrier polypropylene recyclable packaging film, comprising, from the outside to the inside: an anti-UV BOPP film, a first functional adhesive layer, a composite barrier intermediate layer, a second functional adhesive layer, and a puncture-resistant CPP film.

[0009] The UV-resistant BOPP film has a three-layer co-extruded structure, comprising an outer layer, a core layer, and an inner surface layer. The outer layer is a blend of random copolymer polypropylene granules and modified polypropylene granules, containing 0.5-1.0 wt% nano-zinc oxide. The semiconductor band structure of the nano-zinc oxide enables it to absorb ultraviolet light within a specific wavelength range. Furthermore, the outer layer further contains 0.1-0.3 wt% of a hindered amine light stabilizer with a molecular weight greater than 2500 g / mol. The molecular structure of this hindered amine light stabilizer allows it to capture light-induced free radicals, thereby inhibiting the degradation of the polymer matrix. The inner surface layer is a blend of random copolymer polypropylene granules and modified polypropylene granules, wherein the modified polypropylene granules contain 0.3-0.5 wt% carbon nanotubes. As a one-dimensional nanomaterial, carbon nanotubes dispersed in the polymer matrix can form a reinforcing network.

[0010] Preferably, the puncture-resistant CPP film has a three-layer co-extruded structure, comprising a composite layer, a support layer, and a heat-sealing layer. The support layer is made of a blend of random copolymer polypropylene granules, modified polypropylene granules, a polyolefin elastomer, and 1-2 wt% ultra-high molecular weight polyethylene. The weight ratio of the random copolymer polypropylene granules, modified polypropylene granules, and polyolefin elastomer is 100:(5-10):(20-25). The long molecular chains of ultra-high molecular weight polyethylene form a physically entangled network in the matrix, which can absorb and dissipate energy under stress.

[0011] Preferably, the composite barrier interlayer is a multilayer inorganic composite structure. Specifically, this composite structure consists of a silicon oxide layer, a graphene layer, and a silicon nitride layer deposited sequentially. The graphene layer is composed of two-dimensional sheet-like graphene, whose sheet structure can extend the permeation path of gas molecules. The silicon nitride layer covers the graphene layer, providing physical protection.

[0012] Preferably, the graphene layer surface has oxygen-containing functional groups. These functional groups are formed by plasma treatment of the graphene surface and serve as active sites for subsequent chemical reactions.

[0013] Preferably, the first and second functional adhesive layers are adhesive layers formed by adding 0.2-0.3 wt% of γ-aminopropyltriethoxysilane to a polyurethane-acrylate blend adhesive. γ-aminopropyltriethoxysilane is a bifunctional molecule, whose amino group at one end can react with specific groups in the polymer, and whose silanol group formed after hydrolysis at the other end can chemically bond with inorganic surfaces.

[0014] A method for preparing a multifunctional high-barrier recyclable polypropylene packaging film includes the following steps:

[0015] a) Prepare the UV-resistant BOPP film and the puncture-resistant CPP film respectively;

[0016] b) The composite barrier intermediate layer is prepared using a vacuum deposition process;

[0017] c) The UV-resistant BOPP film, the composite barrier interlayer, and the puncture-resistant CPP film are composited and molded using a functional adhesive layer.

[0018] Preferably, the process for preparing the granules used in step a) of the puncture-resistant CPP film includes a reactive extrusion step. In this step, 50-200 ppm of peroxide is added to the polypropylene melt blend. The peroxide decomposes at the extrusion temperature to generate free radicals, which induces the breakage of polypropylene molecular chains, thereby reducing the melt viscosity of the system. This is beneficial for the uniform dispersion of ultra-high molecular weight polyethylene in the subsequent process.

[0019] Preferably, the process for preparing the UV-resistant BOPP film in step a) includes transverse stretching and heat setting at a temperature of 180-190°C, which is conducive to the formation of a highly oriented crystal structure. The process for preparing the puncture-resistant CPP film includes casting and cooling on a cooling roller at 15-25°C, which is conducive to the formation of a fine grain structure.

[0020] Preferably, in step b), the process for preparing the composite barrier interlayer includes an additional plasma surface functionalization step after the graphene layer is deposited and before the silicon nitride layer is deposited. This step is a low-temperature oxygen plasma treatment performed in an oxygen atmosphere to introduce oxygen-containing functional groups onto the graphene surface.

[0021] Preferably, the composite molding process in step c) employs hot-pressing. This process is carried out at a temperature of 80-90°C and a pressure of 0.3-0.5 MPa. These temperature and pressure conditions promote physical adhesion between the film layers and provide the necessary energy for the chemical reaction between γ-aminopropyltriethoxysilane at the interface and the functional groups on the surface of adjacent layers.

[0022] In summary, the present invention has at least one of the following beneficial technical effects:

[0023] 1. The packaging film of the present invention possesses enhanced and long-lasting UV resistance. By compounding nano-zinc oxide and a high molecular weight hindered amine light stabilizer into the outer layer of the BOPP film, a protective system combining physical shielding and chemical stabilization is constructed. Nano-zinc oxide is responsible for shielding UV rays, while the hindered amine light stabilizer captures free radicals initiated by light and those that may be generated by nano-zinc oxide under light, thereby simultaneously protecting both the packaging contents and the film substrate itself, extending the effective protection period of the product.

[0024] 2. The packaging film of the present invention exhibits significantly improved puncture resistance. By employing a reactive extrusion process in the preparation of the support layer of the CPP film, the rheological properties of the polypropylene matrix are first reduced by using peroxide to lower its melt viscosity, and then ultra-high molecular weight polyethylene is introduced. This method improves the uniformity of ultra-high molecular weight polyethylene dispersion in the matrix and effectively preserves its molecular chain length, allowing for a more complete formation of its long-chain entanglement network, thereby enhancing the film's resistance to puncture by external sharp objects.

[0025] 3. The packaging film of this invention achieves stable and reliable high barrier performance. After plasma treatment, the graphene layer in its composite barrier interlayer generates oxygen-containing functional groups on its surface. These functional groups chemically bond with the silane coupling agent in the functional adhesive layer. This cross-interface chemical anchoring structure tightly connects the inorganic barrier layers with the organic adhesive layer, effectively suppressing the risk of interlayer delamination under bending or temperature and humidity changes, ensuring the integrity and long-term effectiveness of the barrier structure. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0027] The following is in conjunction with the appendix Figure 1 The present invention will be further described in detail below.

[0028] The main raw materials and reagents used in the following examples are as follows. Unless otherwise specified, all reagents are commercially available analytical grade or higher grade products.

[0029] 1. Polymer resin

[0030] Random copolymer polypropylene granules A (PP-RA): Melt index (MFI, 230℃ / 2.16kg) is 2.0g / 10min.

[0031] Random copolymer polypropylene granules B (PP-RB): Melt index (MFI, 230℃ / 2.16kg) is 8.0g / 10min.

[0032] Highly crystalline homopolymer polypropylene granules (PPH): Melt index (MFI, 230℃ / 2.16kg) is 2.5g / 10min.

[0033] Ultra-high molecular weight polyethylene (UHMWPE): weight average molecular weight approximately 5.0 × 10⁻⁶ 6 g / mol, in powder form.

[0034] 2. Elastomers and Modifiers

[0035] Maleic anhydride-grafted polyolefin elastomer (POE-g-MAH): maleic anhydride (CAS No.: 108-31-6) grafting rate 1.0%, MFI (190℃ / 2.16kg) 1.7g / 10min.

[0036] Polyolefin elastomer (POE): MFI (190℃ / 2.16kg) is 2.8g / 10min.

[0037] 3. Functional nanofillers and additives

[0038] Multi-walled carbon nanotubes (MWCNTs): diameter 10-20 nm, length 5-15 μm, purity >95%.

[0039] Nano zinc oxide (ZnO): CAS No.: 1314-13-2, average particle size 80nm, purity >99.5%, surface hydrophobic treatment.

[0040] High molecular weight hindered amine light stabilizer (HALS): The reaction product of poly[N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine-2,4-dichloro-6-(4-morpholinyl)-1,3,5-triazine], CAS No.: 65447-77-0, molecular weight approximately 3000-4000 g / mol.

[0041] Reactive extrusion peroxide: 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, CAS No.: 78-63-7.

[0042] 4. Adhesives and coupling agents

[0043] Two-component high-temperature resistant polyurethane adhesive: commercially available.

[0044] Two-component high-temperature resistant acrylic adhesive: commercially available.

[0045] Silane coupling agent: γ-aminopropyltriethoxysilane (KH-550), CAS No.: 919-30-2, purity ≥98%.

[0046] 5. Sputtering target and gas

[0047] Silicon target (Si): 99.99% purity.

[0048] High-purity graphite target (C): purity 99.995%.

[0049] Process gases: Argon (Ar, 99.999%), Oxygen (O2, 99.999%), Nitrogen (N2, 99.999%).

[0050] 6. Temporary baseband

[0051] Biaxially oriented polyethylene terephthalate (PET) film: 12μm thick, commercially available.

[0052] Example 1

[0053] This embodiment provides a multifunctional high-barrier polypropylene recyclable packaging film and its preparation method.

[0054] 1. Preparation of CNT-reinforced granules for the inner surface layer of BOPP

[0055] 100 parts by weight of random copolymer polypropylene granules A, 12 parts by weight of POE-g-MAH, 0.4 parts by weight of MWCNT, and 0.8 parts by weight of conventional antioxidant were mixed in a high-speed mixer at 1200 rpm for 8 minutes. The mixture was then fed into a 1.5 cm thick layer on a vibrating feeder and irradiated with 365 nm wavelength and 3 kW ultraviolet light for 4 minutes. The irradiated material was then fed into a twin-screw extruder with a length-to-diameter ratio of 44:1. The temperatures of each zone were set as follows: Zone 1-2: 185℃, Zone 3-5: 215℃, Zone 6-8: 225℃, and the die temperature: 225℃. The screw speed was 400 rpm. The melt was then water-cooled, pelletized, and dried for later use.

[0056] 2. Preparation of Rheology-Controlled Puncture-Resistant Granules for CPP Support Layer

[0057] 100 parts by weight of random copolymer polypropylene granules B, 8 parts by weight of modified polypropylene granules, and 25 parts by weight of POE were premixed in a mixer. Reactive extrusion was performed using a twin-screw extruder. In the second zone of the extruder, 150 ppm of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane was injected; in the fifth zone, 1.5 parts by weight of UHMWPE powder was added through a side feed port. The extruder zone temperatures were set as follows: Zone 1-3: 205℃, Zone 4-6: 235℃, Zone 7-9: 225℃, and the die temperature was 225℃. The screw speed was 400 rpm. The melt was pelletized using an underwater pelletizing system, dried, and then sealed in packaging for later use.

[0058] 3. Preparation of various functional thin films

[0059] UV-resistant BOPP film: A three-layer co-extrusion process was used. The outer layer (layer A) consisted of 100 parts by weight of PP-RA, 0.8 parts by weight of nano-ZnO, and 0.2 parts by weight of HALS. The core layer (layer B) consisted of 100 parts by weight of PPH. The inner layer (layer C) used CNT-reinforced granules prepared in step 1. After co-extrusion casting, the film underwent a 4x longitudinal stretch, followed by a 9x transverse stretch in a tenter frame. The stretching and heat-setting temperature was 185°C. After corona treatment to 44 dyne / cm, the film was wound up to obtain a BOPP film with a total thickness of 20 μm.

[0060] Puncture-resistant CPP film: A three-layer co-extrusion process is used. The support layer (layer B) uses the granules prepared in step 2. The granules are cast through a co-extrusion die onto a cooling roller at a surface temperature of 20°C for rapid cooling, resulting in a CPP film with a total thickness of 60 μm.

[0061] 4. The composite barrier interlayer was prepared on a 12 μm thick PET temporary substrate using a multi-target magnetron sputtering system, with the chamber vacuum level evacuated to 5.0 × 10⁻⁶. -3 Below Pa, the following deposition processes occur sequentially:

[0062] (1) SiOx layer: sputtering power 3kW, working pressure 0.4Pa, deposition thickness 4μm.

[0063] (2) Graphene layer: sputtering power 4kW, working pressure 0.2Pa, deposition thickness 2.5μm.

[0064] (3) Plasma treatment: The baseband is sent into the online plasma treatment unit, O2 gas is introduced, the working pressure is controlled at 10Pa, 200W radio frequency power is applied, and the treatment time is 15 seconds.

[0065] (4) SiNx layer: sputtering power 4kW, working pressure 0.3Pa, deposition thickness 12μm.

[0066] 5. Overall Composite Molding and Curing: A two-component polyurethane adhesive and a two-component acrylic adhesive are mixed at a solid content weight ratio of 3.5:1. KH-550, accounting for 0.25 wt% of the total solid content of the adhesive, is added to prepare a functional adhesive. A dry lamination process is used. First, the BOPP film is laminated with the composite barrier interlayer. After removing the PET base tape, it is then laminated with the CPP film. The pre-laminated film roll is then hot-pressed in a hot-pressing unit at a temperature of 85℃ and a pressure of 0.4 MPa. The laminated film roll is then placed in a curing chamber at 45℃ for 72 hours.

[0067] Example 2

[0068] This embodiment provides a multifunctional high-barrier polypropylene recyclable packaging film and its preparation method. The preparation method is basically the same as that in Example 1, except that:

[0069] When preparing CNT-reinforced granules for the inner surface layer of BOPP, the amount of MWCNT added is 0.5 parts by weight.

[0070] When preparing rheology-controlled puncture-resistant granules for CPP support layers, the amount of UHMWPE added is 2.0 parts by weight, and the amount of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane injected is 200 ppm.

[0071] In the preparation of the UV-resistant BOPP film, the amount of nano-ZnO added in the outer layer (A layer) formulation is 1.0 parts by weight, and the amount of HALS added is 0.3 parts by weight.

[0072] During the integral composite molding process, the hot pressing temperature is 90℃.

[0073] Comparative Example 1

[0074] A conventional composite film was prepared by laminating commercially available general-purpose BOPP film and CPP film at room temperature using a conventional polyurethane adhesive without silane coupling agents. This comparative example does not contain any special functional additives, composite barrier interlayers, or special preparation processes described in this invention.

[0075] Comparative Example 2

[0076] The difference compared to Example 1 is as follows:

[0077] In preparing the outer layer of the UV-resistant BOPP film, only nano-zinc oxide was added, without the addition of high molecular weight hindered amine light stabilizer (HALS). The remaining components and preparation steps were the same as in Example 1.

[0078] Comparative Example 3

[0079] The difference compared to Example 1 is as follows:

[0080] In preparing the rheology-controlled puncture-resistant granules for the CPP support layer, ultra-high molecular weight polyethylene was directly blended and extruded with other components in a twin-screw extruder, without using 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane for reactive extrusion. The remaining components and preparation steps were the same as in Example 1.

[0081] Comparative Example 4

[0082] The difference compared to Example 1 is as follows:

[0083] In the preparation of the composite barrier intermediate layer, after depositing the graphene layer, no low-temperature oxygen plasma surface treatment is performed, and the silicon nitride layer is directly deposited.

[0084] In the integral composite molding process, γ-aminopropyltriethoxysilane (KH-550) was not added to the functional adhesive used. The remaining components and preparation steps were the same as in Example 1.

[0085] Test Example 1: Performance Testing

[0086] To verify the technical solution of the present invention, the thin film samples prepared in Examples 1-2 and Comparative Examples 1-4 were subjected to the following performance tests.

[0087] 1. Barrier performance test

[0088] Oxygen permeability (OTR): Tested using a differential pressure gas permeameter according to GB / T19789-2005 standard. Test conditions were: temperature 23℃, relative humidity 50%RH, and oxygen test pressure 0.1MPa. Three parallel samples were tested for each sample, and the average value was taken.

[0089] Water vapor transmission rate (WVTR): Tested using the cup method according to GB / T1037-1988 standard. Test conditions were 38℃ and 90% RH relative humidity. Three parallel samples were tested for each sample, and the average value was taken.

[0090] 2. Mechanical property testing

[0091] Puncture resistance: Tested according to ASTM F1306 standard using an electronic universal testing machine. A 3.2 mm diameter hemispherical probe was used at a testing speed of 250 mm / min. The maximum force when the probe punctured the film was recorded. Five parallel samples were tested for each sample, and the average value was taken.

[0092] Interlayer composite strength (peel strength): Tested according to GB / T8808-1988A method (180° peel). The sample was cut into 15mm wide specimens and peeled at a speed of 300mm / min on an electronic universal testing machine. The average peel force between the BOPP layer and the CPP layer was recorded. Five parallel samples were tested for each sample, and the average value was taken.

[0093] 3. Weather resistance test

[0094] UV resistance: The samples were placed in a xenon lamp artificial climate aging test chamber and accelerated aging was performed according to GB / T16422.2-2014 standard. The irradiation intensity was set to 0.51 W / (m²). 2• 340nm), blackboard temperature 63℃, continuous illumination for 48 hours. Test the elongation at break of the sample before and after aging (according to GB / T1040.3-2006), and calculate the elongation at break retention rate (%).

[0095] 4. Thermal stability test

[0096] Heat shrinkage rate: Cut the sample into 200mm × 200mm pieces and mark a 150mm × 150mm square in the center area. Place the sample horizontally in an oven at 121℃ for 30 minutes. After removal, cool it in a standard environment (23℃, 50% RH) for 30 minutes, and measure the longitudinal (MD) and transverse (TD) dimensions of the marked square again. Calculate the longitudinal and transverse heat shrinkage rates and take their average value.

[0097] Test results: The performance test data of the samples obtained from Examples 1-2 and Comparative Examples 1-4 are summarized in Table 1.

[0098] Table 1. Performance test data of the examples and comparative examples

[0099]

[0100] As shown in Table 1, the oxygen and water vapor permeability of the films prepared in Examples 1 and 2 were significantly lower than those in Comparative Examples 1 and 4. This result is attributed to the introduction of graphene sheets in the composite barrier interlayer, whose two-dimensional structure elongates the permeation path of gas molecules. Comparing the data of Example 1 and Comparative Example 4, the latter, due to the absence of plasma treatment and the use of silane coupling agents, exhibited significantly reduced interlayer peel strength and deteriorated barrier performance. This indicates that forming oxygen-containing functional groups on the graphene surface through plasma treatment and then chemically bonding them with the inorganic surface and polymer matrix using silane coupling agents is an effective way to construct a stable, high-strength interlayer interface and maintain the integrity of the barrier structure.

[0101] Comparing the puncture resistance data of Example 1 and Comparative Example 3, under the condition that the only difference is the reactive extrusion process, the puncture resistance of Example 1 is significantly higher than that of Comparative Example 3. This is because during the reactive extrusion process, the peroxide induces controlled degradation of the polypropylene matrix, reducing the melt viscosity and thus providing a better dispersion environment for the high-viscosity ultra-high molecular weight polyethylene. The uniformly dispersed ultra-high molecular weight polyethylene can form a more effective physical entanglement network in the matrix, thereby absorbing and dissipating more energy when subjected to external forces, improving the material's puncture resistance.

[0102] Furthermore, regarding weather resistance, Example 1 exhibited a higher elongation at break retention rate than Comparative Example 2, which contained only nano-zinc oxide. This indicates that the addition of a high-molecular-weight hindered amine light stabilizer can inhibit the photocatalytic degradation of nano-zinc oxide under light irradiation through a free radical scavenging mechanism, thereby forming a synergistic protective effect with the UV absorption function of nano-zinc oxide. The thermal shrinkage rates of Examples 1 and 2 were both lower than those of Comparative Example 1, which was prepared using a conventional process. This confirms that using a higher heat-setting temperature during BOPP film preparation is beneficial for forming a more complete and stable crystal structure, thereby improving the dimensional stability of the final composite film.

[0103] Test Example 2: Stability Testing of Specific Functions and Applications

[0104] To further verify the performance of the technical solution of the present invention in specific application scenarios, the following supplementary tests were performed on the thin film samples prepared in Examples 1-2 and some comparative examples.

[0105] 1. Surface resistivity test

[0106] Test objective: To evaluate the electrostatic dissipation capability of the thin film surface.

[0107] Test Procedure: Following ASTM D257 standard, a high-resistivity meter was used for testing. The prepared UV-resistant BOPP film (before lamination) was taken, and the test electrode was placed on the surface of its inner layer (C layer containing CNTs). The test environment was 23°C, 50% RH, with an applied voltage of 100V. The surface resistivity after stabilization was recorded. For the comparative film without CNTs, the inner surface in contact with the adhesive layer was also tested. Five different locations were tested for each sample, and the average value was taken.

[0108] 2. Test for resistance to boiling

[0109] Test objective: To evaluate the structural stability and interlayer bonding retention of composite films under high temperature and high humidity conditions.

[0110] Test steps:

[0111] (1) Cut the final composite films prepared in Examples 1-2 and Comparative Examples 1 and 4 into 100mm×100mm samples.

[0112] (2) Place the sample in a high-temperature and high-pressure cooking pot (sterilizer) and treat it for 30 minutes under saturated steam conditions of 121℃ and 0.15MPa.

[0113] (3) After the treatment is completed, the sample is taken out and placed in a standard environment (23℃, 50%RH) for 24 hours to adjust its condition.

[0114] (4) Observe whether there are any changes in appearance such as layering, bubbling, or wrinkles on the surface of the sample.

[0115] (5) For the adjusted sample, test its interlayer composite strength (peel strength) after cooking according to the GB / T8808-1988A method described in Test Example 1.

[0116] The test results are summarized in Table 2, which presents the supplementary performance test data of the samples obtained from Examples 1-2 and the relevant comparative examples.

[0117] Table 2. Specific functional and stability test data of the examples and comparative examples

[0118]

[0119] Table 2 shows the surface resistivity data, indicating that the surface resistivity of the inner layer of the BOPP film in Examples 1 and 2 is within the electrostatic dissipation range, while the film surface in the comparative example exhibits insulating properties. This difference stems directly from the introduction of multi-walled carbon nanotubes into the inner layer of the BOPP film in the examples. These carbon nanotubes form conductive pathways within the polypropylene matrix, endowing the surface of this layer with the ability to dissipate static charge. This function is technically valuable for packaging applications requiring antistatic properties.

[0120] The peel strength and appearance results after steaming revealed the differences in stability of different interlayer bonding mechanisms under humid and hot conditions. Samples from Examples 1 and 2 maintained their intact structure and high interlayer peel strength after being steamed at 121°C. In contrast, the interlayer peel strength of sample from Comparative Example 4 dropped sharply to near zero, and severe delamination occurred. This indicates that in the absence of plasma surface functionalization and silane coupling agents, interlayer bonding mainly relies on physical adsorption, and this force is easily disrupted by the combined effects of water molecules and thermal energy.

[0121] Comprehensive analysis shows that the strategy employed in this approach—introducing oxygen-containing functional groups onto the surface of the inorganic barrier layer through plasma treatment and then utilizing silane coupling agent molecules to form chemical bonds between the inorganic surface and the organic adhesive—is key to achieving a moisture- and heat-resistant, high-strength interlayer bond. This stable chemical bond structure effectively resists corrosion from high-temperature and high-humidity environments, ensuring that the composite film maintains its structural integrity and barrier functionality even under harsh processing conditions such as boiling, thereby expanding the application range of the film.

[0122] Test Example 3: Performance and Durability Testing under Dynamic Stress and Composite Environments

[0123] To evaluate the film's ability to retain performance under simulated dynamic bending and long-term light aging conditions that may be encountered in actual use, the following durability tests were performed on the film samples prepared in Examples 1-2 and some comparative examples.

[0124] 1. Dynamic bending fatigue test (FlexDurability)

[0125] Test objective: To evaluate the ability of composite films to retain their barrier properties under repeated bending and rubbing.

[0126] Test Procedure: The test was conducted using a Gelbo bending tester according to ASTM F392 standard. The sample was fixed in the test station, and the program was set to perform 1000 cycles of rubbing and twisting. After the test, the sample was removed and laid flat. For the sample that underwent dynamic bending treatment, its oxygen permeability was tested according to GB / T19789-2005 standard as described in Test Example 1.

[0127] 2. Mechanical property retention test after UV aging

[0128] Test objective: To evaluate the retention of key mechanical properties (puncture resistance) of composite films after undergoing accelerated UV aging.

[0129] Test steps:

[0130] (1) The sample was subjected to accelerated aging treatment for 48 hours in a xenon lamp artificial climate aging test chamber according to the UV resistance test method described in Test Example 1.

[0131] (2) Take out the aged sample and place it in a standard environment (23℃, 50%RH) for 24 hours to adjust its condition.

[0132] (3) Test the puncture resistance of the conditioned specimen according to the ASTM F1306 standard described in Test Example 1.

[0133] (4) Calculate the puncture strength retention rate (%) based on the puncture strength values ​​before and after aging.

[0134] The test results are summarized in Table 3, which presents the durability test data of the samples obtained from Examples 1-2 and the relevant comparative examples.

[0135] Table 3. Performance and durability test data under dynamic stress and composite environments

[0136]

[0137] The results of the dynamic bending fatigue test in Table 3 show that after 1000 cycles of bending, the oxygen permeability of the samples in Examples 1 and 2 only increased slightly, while the sample in Comparative Example 4 deteriorated rapidly, essentially losing its barrier performance. This phenomenon reveals the role of interlayer bonding strength in maintaining the durability of the barrier layer. In the example samples, the plasma-treated graphene layer and the polymer matrix formed a stable chemical bond interface through a silane coupling agent. This interface effectively absorbed and dispersed the stress generated by bending, preventing microcracks or interlayer delamination in the inorganic barrier layer, thereby protecting the integrity of the barrier structure.

[0138] Mechanical property data after UV aging showed that the puncture strength retention rates of samples in Examples 1 and 2 remained at approximately 90% after 48 hours of accelerated aging. In contrast, Comparative Example 2, lacking a high-molecular-weight hindered amine light stabilizer, exhibited a puncture strength retention rate that decreased to 56.9%. This difference confirms a synergistic protective mechanism between the UV absorber (nano-zinc oxide) and the free radical scavenger (hindered amine light stabilizer). This mechanism not only slows down photoaging of the material surface but, more importantly, inhibits degradation reactions such as chain breakage and cross-linking induced by light within the polymer matrix, effectively maintaining the structural integrity of the polypropylene molecular chains and thus protecting the material's bulk mechanical properties.

[0139] In summary, the long-term stability of the composite film constructed using this technical solution stems from the synergistic effect of multiple structural designs. The puncture resistance is based on an ultra-high molecular weight polyethylene (UHMWPE) reinforced network optimized through reactive extrusion, while the long-term effectiveness of this network depends on the comprehensive protection of the polymer matrix provided by the composite UV-resistant system. Simultaneously, the high-strength chemically bonded interfaces ensure that the inorganic barrier layer remains adhered to the protected polymer matrix under dynamic stress, continuously fulfilling its barrier function. These design features collectively ensure the functional reliability of the film in complex application environments.

Claims

1. A multifunctional high-barrier polypropylene recyclable packaging film, characterized in that, From the outside to the inside, it includes: UV-resistant BOPP film, first functional adhesive layer, composite barrier intermediate layer, second functional adhesive layer and puncture-resistant CPP film; The outer layer of the UV-resistant BOPP film contains 0.5-1.0 wt% nano-zinc oxide; The support layer of the puncture-resistant CPP film contains 1-2 wt% ultra-high molecular weight polyethylene; The composite barrier intermediate layer is a multilayer inorganic composite structure containing a graphene layer.

2. The multifunctional high-barrier polypropylene recyclable packaging film according to claim 1, characterized in that, The outer surface layer of the UV-resistant BOPP film further comprises 0.1-0.3 wt% of a hindered amine light stabilizer with a molecular weight greater than 2500 g / mol; and / or the modified polypropylene granules used in the inner surface layer of the UV-resistant BOPP film contain 0.3-0.5 wt% of carbon nanotubes.

3. The multifunctional high-barrier polypropylene recyclable packaging film according to claim 1, characterized in that, The composite barrier intermediate layer is a three-layer composite structure consisting of a silicon oxide layer, a graphene layer and a silicon nitride layer deposited sequentially, and the surface of the graphene layer has oxygen-containing functional groups generated after plasma treatment.

4. The multifunctional high-barrier polypropylene recyclable packaging film according to claim 1, characterized in that, Both the first and second functional adhesive layers are adhesive layers formed by adding 0.2-0.3 wt% γ-aminopropyltriethoxysilane to a polyurethane-acrylate blend adhesive.

5. The multifunctional high-barrier polypropylene recyclable packaging film according to claim 1, characterized in that, The support layer of the puncture-resistant CPP film is made of random copolymer polypropylene granules B, modified polypropylene granules, polyolefin elastomer B and ultra-high molecular weight polyethylene, wherein the weight ratio of random copolymer polypropylene granules B, modified polypropylene granules and polyolefin elastomer B is 100:(5-10):(20-25).

6. A method for preparing a multifunctional high-barrier polypropylene recyclable packaging film, applied to the multifunctional high-barrier polypropylene recyclable packaging film according to any one of claims 1-5, characterized in that, Includes the following steps: a) Prepare UV-resistant BOPP film and puncture-resistant CPP film respectively; b) The composite barrier interlayer was prepared using a vacuum deposition process; c) The UV-resistant BOPP film, the composite barrier interlayer, and the puncture-resistant CPP film are laminated together using a functional adhesive layer; wherein the preparation method comprises a combination of at least one of the following technical features: i) When preparing the granules used to make the puncture-resistant CPP film, a reactive extrusion process is used, and the rheological properties of the polypropylene matrix are controlled by adding chemical reagents. ii) In step b), the deposited graphene layer is subjected to plasma surface functionalization treatment; iii) In step c), the composite molding adopts a hot-pressing composite process.

7. The method for preparing a multifunctional high-barrier polypropylene recyclable packaging film according to claim 6, characterized in that, In step a), preparing the UV-resistant BOPP film includes transverse stretching and shaping at a temperature of 180-190°C; and / or preparing the puncture-resistant CPP film includes casting and cooling on a cooling roller at 15-25°C.

8. The method for preparing a multifunctional high-barrier polypropylene recyclable packaging film according to claim 6, characterized in that, The reactive extrusion process described in i) involves adding 50-200 ppm of peroxide to the melt blend to reduce the melt viscosity of the polypropylene matrix.

9. In the method for preparing a multifunctional high-barrier polypropylene recyclable packaging film according to claim 6, the plasma surface functionalization treatment in ii) is a low-temperature oxygen plasma treatment performed in an oxygen atmosphere to generate oxygen-containing functional groups on the graphene surface.

10. The preparation method of a multifunctional high-barrier polypropylene recyclable packaging film according to claim 6, wherein the conditions of the hot-pressing composite process in iii) are: temperature 80-90℃, pressure 0.3-0.5MPa.

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