Hot-coating high-barrier heavy roll film and preparation method thereof

Abstract

The invention discloses a hot-coated high-barrier heavy-wrapping roll film and a preparation method thereof. Belongs to the technical field of packaging materials. The roll film sequentially comprises an outer-layer base material film, a middle barrier layer and an inner-layer heat sealing film. The middle barrier layer is formed by drying and curing nano-composite barrier liquid coated on the inner surface of the outer-layer base material film; the nano-composite barrier liquid comprises polyvinyl alcohol, a surface-modified inorganic nano-material dispersion liquid, a polymer emulsion, a cross-linking agent and a wetting agent. After being preheated, the barrier liquid is coated by micro gravure, is dried through three stages of rapid shaping, deep crosslinking and high-temperature densification in sequence, and is finally compounded with an inner-layer heat-sealing film in a solvent-free manner. Through precise coupling of a synergistic effect among specific components and a multi-stage drying process, the roll film has excellent initial oxygen barrier property, water vapor barrier property, excellent stability in a high-temperature and high-humidity environment and high barrier stability after simulating a dynamic mechanical load of heavy packaging and transportation.

Description

Technical Field

[0001] This invention belongs to the field of packaging materials technology, and more specifically relates to a hot-coated high-barrier heavy-duty roll film and its preparation method. Background Technology

[0002] High-barrier packaging materials are crucial for ensuring product shelf life and quality safety. With the development of e-commerce and global logistics, heavy-duty packaging places higher demands on film materials beyond static barrier performance: their barrier function must not significantly diminish after repeated vibration, impact, and compression during transportation, handling, and stacking. Current mainstream high-barrier technologies all have significant shortcomings in this regard.

[0003] While ethylene-vinyl alcohol copolymer (EVOH) co-extruded films offer excellent barrier properties, their multilayer co-extruded structure is prone to stress concentration between layers under external bending or impact, leading to invisible microcracks in the barrier layer and a sharp decline in barrier performance. Furthermore, the raw materials and processing costs are high. Metallized films or aluminum foil composites suffer from poor ductility of the metal layer, making them highly susceptible to pinholes during bending and drops, resulting in barrier failure. They are also opaque, cannot be microwaved, and are difficult to recycle. Wet coating technology based on polyvinyl alcohol (PVA) is considered an environmentally friendly and economical alternative, but it has two inherent drawbacks: First, the barrier performance of PVA coatings is extremely sensitive to humidity, significantly decreasing under high temperature and humidity conditions due to moisture absorption and swelling. Second, and more critically, pure PVA or ordinary PVA / nanocomposite coatings are brittle and lack toughness, making them highly susceptible to microcrack networks due to stress during subsequent lamination, slitting, bag making, and especially during the drop and transportation of final packaging. These micron- and even nano-sized cracks become rapid channels for gas permeation, causing the packaging's barrier function to fail prematurely and invisibly under dynamic usage scenarios. This failure is difficult to detect during routine factory inspections, posing a significant quality risk.

[0004] To improve the brittleness and moisture sensitivity of PVA, existing technologies disclose methods for adding nano-silica or montmorillonite to PVA, which improves hardness and moisture stability to some extent, but has limited effect on improving flexibility and impact resistance. Furthermore, the interfacial bonding strength between nanoparticles and the PVA matrix is ​​insufficient, leading to interface debonding and defects under dynamic loads. Other existing technologies disclose the addition of acrylate emulsions to PVA for toughening, which improves coating flexibility but often at the expense of barrier properties, as the introduction of ordinary emulsion particles may disrupt the coating's density. In addition, existing coating processes often employ single-stage or simple two-stage drying, making it difficult to simultaneously achieve rapid surface setting, uniform internal structure formation, interfacial fusion of nano-components and the polymer matrix, and final coating densification. This can result in stress or micro-defects within the coating, potentially leading to performance degradation under dynamic loads.

[0005] Therefore, there is an urgent market demand and significant technological value in developing a novel high-barrier rewound film that is co-designed from formulation to process to achieve a good balance between initial barrier properties, environmental stability and dynamic mechanical durability. Summary of the Invention

[0006] The primary objective of this invention is to overcome the shortcomings of existing high-barrier packaging films, especially coated high-barrier films, which have easily degraded barrier performance and insufficient environmental stability under dynamic mechanical loads (mainly referring to the impact and continuous pressure that the packaging is subjected to during transportation and stacking). The invention provides a nanocomposite barrier repackaged roll film with a reasonable structural design and excellent comprehensive performance.

[0007] Another objective of this invention is to provide a method for preparing the above-mentioned roll film, which achieves controllable construction of the coating microstructure by precisely matching the formulation design of the nanocomposite barrier liquid with the multi-stage programmable drying process, thereby simultaneously obtaining excellent processing efficiency, initial performance and service durability.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A hot-applied high-barrier rewound film comprises, in sequence, an outer substrate film, an intermediate barrier layer, and an inner heat-sealing film; the intermediate barrier layer is formed by drying and curing a nano-composite barrier liquid coated on the inner surface of the outer substrate film; the nano-composite barrier liquid comprises, by weight, the following components: a) A polyvinyl alcohol aqueous solution, with a solid content of 60-80 parts; b) Surface-modified inorganic nanomaterial dispersion, with a solid content of 15-25 parts; c) Polymer emulsion, 5-15 parts by solid content; d) Crosslinking agent, 0.5-2 parts; e) Wetting agent, 0.1-0.5 parts; As a preferred technical solution, the surface-modified inorganic nanomaterial is a sheet-like or granular inorganic nanomaterial modified with a silane coupling agent.

[0009] As a preferred technical solution, the inorganic nanomaterial is selected from at least one of nano-silica, nano-kaolin, and montmorillonite; the silane coupling agent is a silane coupling agent containing amino or epoxy groups.

[0010] As a preferred technical solution, the surface-modified inorganic nanomaterial is nano-silica modified with γ-aminopropyltriethoxysilane or γ-2,3-epoxypropoxypropyltrimethoxysilane, with an average particle size of 20-50 nm.

[0011] As a preferred technical solution, the polymer emulsion is one of styrene-acrylic polymer emulsion, pure acrylic polymer emulsion, or vinyl acetate-acrylic polymer emulsion, and its glass transition temperature is -10°C to 25°C.

[0012] As a preferred technical solution, the polymer emulsion is a styrene-acrylic polymer emulsion.

[0013] As a preferred technical solution, the crosslinking agent is selected from at least one of boric acid, polycarboxylic acid compounds, adipate dihydrazide, and aziridine; the wetting agent is polyether-modified polysiloxane.

[0014] As a preferred technical solution, the outer substrate film is a biaxially oriented polyamide film or a biaxially oriented polyester film with a thickness of 12-25 μm; the inner heat-sealing film is a cast polypropylene film, a linear low-density polyethylene film, or a co-extruded film thereof with a thickness of 40-80 μm.

[0015] Another object of this application is to provide: a method for preparing the above-mentioned hot-coated high-barrier rewound film, comprising the following steps: S1. Corona treatment: Corona treatment is performed on the inner surface of the outer substrate film to make its surface tension reach 40-44 dynes; S2. Barrier liquid preparation and pretreatment: Preheat the polyvinyl alcohol aqueous solution to 70-80℃, and add the surface-modified inorganic nanomaterial dispersion, polymer emulsion, crosslinking agent and wetting agent in sequence under stirring. After mixing evenly, degas at 70-80℃ for 30-60 minutes to obtain the nanocomposite barrier liquid. S3. Thermal Coating and Programmed Drying: The nanocomposite barrier liquid obtained in step S2 is heated to 40-50℃ and coated onto the surface of the outer substrate film treated in step S1 using a microgravure coating method. The wet coating amount is 2.5-4.0 g / m². 2 Then, a multi-stage drying process is carried out: First stage: Treat the coating surface for 3-5 seconds at 70-80℃ and wind speed of 8-12m / s to quickly set the surface and form a porous skeleton. The second stage involves treating the product at 90-100℃ and a wind speed of 5-8m / s for 5-8 seconds to promote deep evaporation of internal moisture and initiate cross-linking reactions. The third stage: Treat the polymer emulsion particles at 110-120℃ and wind speed of 2-4m / s for 2-4s to fully soften and flow the polymer emulsion particles, densify the coating and complete cross-linking. After drying, the material is cooled to room temperature to form an outer substrate film with an intermediate barrier layer. S4. Lamination and Curing: A solvent-free polyurethane adhesive is coated on the surface of the inner heat-sealing film, and then laminated with the outer substrate film with an intermediate barrier layer obtained in step S3. The lamination pressure is 0.3-0.6 MPa, and the lamination speed is 150-250 m / min. After lamination, the film is wound up and cured at 45-55℃ for 36-72 h to obtain the hot-coated high-barrier rewound film.

[0016] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: (1) Excellent dynamic load-bearing barrier retention (an unexpected core effect): The most outstanding effect of this invention lies in its amazing mechanical durability. After constant-speed drop tests (simulating transportation impact) or repeated bending tests according to ASTM D5276 on the prepared roll film samples, the oxygen transmission rate (OTR) decay rate can be less than 7%, or even show no significant change. In contrast, the control samples using unmodified nanomaterials, or using other types of emulsions, or using two-stage drying, can achieve an OTR decay rate of 20%-50% or more after the same test. This proves that the strong interface, low stress, and dense coating microstructure constructed by this invention can effectively resist external mechanical stress, prevent the generation and propagation of microcracks, and solve the most critical reliability problem in heavy-duty packaging applications.

[0017] (2) Excellent environmental stability and initial high barrier properties: Thanks to its dense structure and sufficient cross-linking, the OTR decay rate of the film of this invention is less than 15% after being placed in a harsh environment of 38°C and 90%RH for 7 days, and the water vapor transmission rate (WVTR) remains stable at ≤1.0g / (m 2 (24h), far exceeding the comparative example. Its initial OTR can be stably maintained at ≤0.5cm. 3 / (m 2 It achieves an ultra-high level of 24h atm. This achieves a balance between high barrier properties and environmental resistance.

[0018] (3) High-efficiency process and good processing adaptability: The combination of hot coating and programmed drying processes can increase the production line speed to 150-250m / min, which is more than 30% higher than the efficiency of traditional single-stage drying, and the coating uniformity is good (thickness CV value <5%). The resulting intermediate barrier layer has good temperature resistance and mechanical stability, which can be perfectly matched with the high-speed solventless composite process. The composite peel strength is high (>4.5N / 15mm), which meets the requirements of high-speed automated bag making. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 A type of hot-coated high-barrier re-wrapping film raw material: (1) Outer substrate film: 15μm thick biaxially oriented polyamide (BOPA) film; (2) Inner heat-sealing film: 50μm thick cast polypropylene (CPP) film; (3) Nanocomposite barrier liquid: Polyvinyl alcohol (PVA) aqueous solution: PVA1799, prepared as an aqueous solution with a solid content of 9%; Surface-modified inorganic nanomaterial dispersion: Nano-silica with surface modification by γ-aminopropyltriethoxysilane (KH550) (modification method as follows: after drying to remove adsorbed water, nano-silica is dispersed in a mixed solvent of ethanol and water to form a uniform suspension. Under stirring conditions, a measured amount of KH550 coupling agent is added, and surface hydrolysis and condensation reaction is carried out at a temperature range of 50-80℃ for 2-6 hours. After the reaction is completed, after filtration, washing with ethanol and drying, modified nano-silica powder with amino functional groups grafted on the surface can be obtained), with an average particle size of 30 nm, is prepared into an aqueous dispersion with a solid content of 6%. Polymer emulsion: Styrene-acrylic polymer emulsion, solid content 42%, Tg approximately 15℃; Crosslinking agent: boric acid, prepared as a 10% aqueous solution; Wetting agent: polyether-modified polysiloxane; (4) Adhesive: Two-component solvent-free polyurethane adhesive.

[0021] A method for preparing a hot-coated high-barrier rewound film: S1: Corona treatment of the inner surface of the BOPA film to a surface tension of 42 dynes; S2: Based on solid content, take 70 parts of PVA aqueous solution preheated to 75℃, and slowly add 20 parts of modified nano SiO2 dispersion, 8 parts of styrene-acrylic polymer emulsion, 1.5 parts of boric acid solution, and 0.3 parts of wetting agent in sequence while stirring. After mixing evenly, continue stirring at 75℃ and vacuum degassing for 45 min to obtain the nanocomposite barrier liquid. The viscosity was measured to be 320 mPa·s (25℃).

[0022] S3: The barrier liquid is kept at 45°C and coated onto the corona-exposed surface of the BOPA film using a 160 lines / inch microgravure roller, with a wet coating amount of 3.2 g / m². 2 The material enters a three-stage drying oven: Zone 1 75℃ / 10m / s / 4s; Zone 2 95℃ / 6m / s / 7s; Zone 3 115℃ / 3m / s / 3s. After drying, it is cooled to room temperature to form an outer substrate film with an intermediate barrier layer.

[0023] S4: Coat the CPP membrane with a two-component solvent-free polyurethane adhesive (coating amount 1.6 g / m²). 2 The film is combined with the outer substrate film with an intermediate barrier layer prepared by S3 at a pressure of 0.4 MPa and a speed of 200 m / min, and then cured at 50°C for 48 h to obtain a hot-coated high-barrier rewound film.

[0024] Example 2 A type of hot-coated high-barrier re-wrapping film raw material: (1) Outer substrate film: 12μm thick biaxially oriented polyester film (BOPET film). (2) Inner heat-sealing film: 60μm thick linear low-density polyethylene film (LLDPE film). (3) Nanocomposite barrier liquid: Polyvinyl alcohol (PVA) aqueous solution: PVA1788, prepared as an 8% solid content aqueous solution; Surface-modified inorganic nanomaterial dispersion: Montmorillonite (flakes) surface-modified with γ-2,3-epoxypropoxypropyltrimethoxysilane (KH560) (modification method as follows: first, natural montmorillonite is purified and sodium-treated to obtain sodium-based montmorillonite; it is dispersed in deionized water to prepare a stable suspension; under stirring and heating (e.g., 60-80℃), a KH560 coupling agent solution pre-hydrolyzed with ethanol and water is slowly added dropwise to the montmorillonite suspension, and the reaction is continued for 4-8 hours. During this process, the silanols generated by KH560 hydrolysis can insert into the interlayer of montmorillonite and undergo a condensation reaction with the hydroxyl groups on the surface of the flakes. After the reaction is completed, organically modified montmorillonite powder with epoxy functional groups grafted on the surface can be obtained by centrifugation, washing, and freeze-drying or spray drying), prepared into an aqueous dispersion with a solid content of 5.5%; Polymer emulsion: Pure acrylic polymer emulsion, solid content 45%, glass transition temperature (Tg) approximately 5℃; Crosslinking agent: adipic acid dihydrazide, prepared as a 5% aqueous solution; Wetting agent: polyether-modified polysiloxane; (4) Adhesive: Two-component solvent-free polyurethane adhesive.

[0025] A method for preparing a hot-coated high-barrier rewound film: S1: Corona treatment of the inner surface of the BOPET film to a surface tension of 44 dynes; S2: Based on solid content, take 65 parts of PVA aqueous solution preheated to 78℃, and slowly add 22 parts of the above modified montmorillonite dispersion, 10 parts of pure acrylic polymer emulsion, 1.2 parts of adipate dihydrazide solution, and 0.2 parts of wetting agent in sequence while stirring. After mixing evenly, continue stirring at 78℃ and vacuum degassing for 40 min to obtain the nanocomposite barrier liquid. The viscosity was measured to be 280 mPa·s (25℃).

[0026] S3: The barrier liquid is kept at 48°C and coated onto the corona-treated surface of the BOPET film using a 140 lines / inch microgravure roller, with a wet coating amount of 3.5 g / m². 2 The process involves three stages in the oven: Zone 1: 80℃ / 9m / s / 3.5s (rapidly removes most of the free water, causing the coating surface to gel and solidify rapidly, forming an initial porous framework to prevent sagging and lock in the dispersion state of the nanoparticles); Zone 2: 98℃ / 7m / s / 6s (the temperature rises, further removing bound water, while the heat energy stimulates the movement of PVA segments, the crosslinking agent begins to react, and the condensation reaction between the silane coupling agent and the PVA hydroxyl groups is initiated, initially constructing an organic-inorganic hybrid network); Zone 3: 118℃ / 3m / s / 3s (this is the core stage, the higher temperature...) Polymer emulsion particles with a suitable temperature gradient (Tg) soften, deform, and even partially fuse, flowing and filling the pores of the PVA / nanoparticle network formed in the first two stages. Simultaneously, this temperature promotes complete cross-linking and further integrates the components at the interface. Under surface tension, the internal structure of the coating is reconstructed and densified, ultimately forming a "brick-and-mortar" composite structure where inorganic nanoparticles are tightly encapsulated by PVA and polymer emulsion, exhibiting strong interfacial bonding and low internal stress. After drying and cooling to room temperature, an outer substrate film with an intermediate barrier layer is formed.

[0027] S4: Coat the LLDPE membrane with a two-component solvent-free polyurethane adhesive (coating amount 1.8 g / m²). 2 The film is then laminated with the outer substrate film with an intermediate barrier layer prepared by S3 at a pressure of 0.5 MPa and a speed of 180 m / min, and cured at 48°C for 60 h to obtain a hot-coated high-barrier rewound film.

[0028] Example 3 A type of hot-coated high-barrier re-wrapping film raw material: (1) Outer substrate film: 20μm thick biaxially oriented polyamide film (BOPA film). (2) Inner heat-sealing film: 40μm thick cast polypropylene film (CPP film). (3) Nanocomposite barrier liquid: Polyvinyl alcohol (PVA) aqueous solution: PVA1799, prepared as an aqueous solution with a solid content of 10%; Surface-modified inorganic nanomaterial dispersion: Nano-silica with an average particle size of 45 nm was prepared as an aqueous dispersion with a solid content of 7% by surface modification with γ-aminopropyltriethoxysilane (KH550) (modification method is the same as in Example 1). Polymer emulsion: Acrylic-vinyl acetate polymer emulsion, solid content 40%, glass transition temperature (Tg) approximately 10℃; Crosslinking agent: Citric acid (a polycarboxylic acid compound), prepared as an 8% aqueous solution; Wetting agent: polyether-modified polysiloxane; (4) Adhesive: Two-component solvent-free polyurethane adhesive.

[0029] A method for preparing a hot-coated high-barrier rewound film: S1: Corona treatment of the inner surface of the BOPA film to a surface tension of 40 dynes; S2: Based on solid content, take 75 parts of PVA aqueous solution preheated to 72℃, and slowly add 18 parts of the above modified nano SiO2 dispersion, 6 parts of vinyl acetate polymer emulsion, 0.8 parts of citric acid solution, and 0.4 parts of wetting agent in sequence under stirring. After mixing evenly, continue stirring at 72℃ and vacuum degassing for 50 min to obtain the nanocomposite barrier liquid. The viscosity was measured to be 380 mPa·s (25℃).

[0030] S3: The barrier liquid is kept at 42°C and coated onto the corona-exposed surface of the BOPA film using a microgravure roller with a wet coating weight of 2.8 g / m². 2 The material is then placed in a three-stage drying oven: Zone 1: 72℃ / 12m / s / 4s; Zone 2: 92℃ / 5m / s / 8s; Zone 3: 112℃ / 4m / s / 2.5s. After drying, the material is cooled to room temperature to form an outer substrate film with an intermediate barrier layer.

[0031] S4: Coat the CPP membrane with a two-component solvent-free polyurethane adhesive (coating amount 1.4 g / m²). 2 The film is laminated with the outer substrate film with an intermediate barrier layer prepared by S3 at a pressure of 0.35 MPa and a speed of 220 m / min, and cured at 55°C for 36 h to obtain a hot-coated high-barrier rewound film.

[0032] Comparative Example 1: Unmodified nano-silica The process is essentially the same as in Example 1, except that the nano-silica used is the same type of nano-silica that has not been modified with a silane coupling agent.

[0033] Comparative Example 2: Replaced with vinyl acetate-ethylene (EVA) emulsion The process is basically the same as in Example 1, except that the styrene-acrylic polymer emulsion is replaced with an equal amount of EVA emulsion with a solid content (Tg approximately -20°C).

[0034] Comparative Example 3: Two-stage drying process The formula of Example 1 was used, but the drying process was changed to two stages: the first stage was 80℃ / 10m / s / 8s; the second stage was 105℃ / 4m / s / 8s (the total time was the same, and there was no independent high temperature and low wind speed densification stage).

[0035] Comparative Example 4: Polymer-free emulsion Binary formulation: 80 parts PVA solution, 20 parts unmodified nano-SiO2 dispersion, 1.5 parts boric acid, and 0.3 parts wetting agent. Traditional single-stage drying was used (85℃ / 8m / s / 14s).

[0036] To verify the performance of the hot-coated high-barrier rewound films prepared in different embodiments and comparative examples, the following tests were conducted: 1. Initial oxygen permeability test Test objective: To determine the original oxygen barrier properties of the roll film sample under standard temperature and humidity conditions.

[0037] Test standard: Based on national standard GB / T 19789 "Test method for oxygen permeability of plastic films and sheets for packaging materials - coulometric test".

[0038] Sample preparation: Cut at least three smooth, wrinkle-free samples without visible defects from the rolls of film prepared in each embodiment and comparative example. The diameter of the samples must meet the requirements of the test chamber.

[0039] Test conditions: The sample is placed in the test chamber and equilibrated and tested at a temperature of 23±0.5℃ and a relative humidity (RH) of 50±5%. Before testing, the sample needs to be pretreated in this environment for no less than 12 hours.

[0040] Data processing: Record the oxygen permeation rate per unit time after the instrument stabilizes, calculate and report the average value of multiple test points for each sample, in cm. 3 / (m 2 The experimental results (24h atm) are shown in Table 1.

[0041] 2. Initial water vapor transmission rate test Test objective: To determine the original water vapor barrier performance of the roll film sample under high temperature and high humidity conditions.

[0042] Test standard: Based on national standard GB / T 26253 "Determination of water vapor transmission rate of plastic films and sheets - Instrumental method".

[0043] Sample preparation: Similar to the oxygen permeability test, cut at least 3 flat samples.

[0044] Test conditions: Place the sample in the test chamber and test under a temperature gradient of 38±0.5℃ and a relative humidity gradient of 90±5%. Before testing, the sample may not be pretreated, or it may be equilibrated for a short time as specified in the standard.

[0045] Data processing: Record the water vapor transmission rate per unit time after the instrument stabilizes, calculate and report the average value of multiple test points for each sample, in g / (m³). 2 • 24h), and the experimental results are shown in Table 1.

[0046] 3. Damp heat aging test and oxygen permeability test after aging Aging purpose: To simulate harsh storage or usage environments and evaluate the stability of the barrier performance of the roll film.

[0047] Aging conditions: The film sample to be tested (after cutting or in roll form) was placed in a constant temperature and humidity chamber and treated continuously for 7 days (168h) at a temperature of 38±2℃ and a relative humidity of 90±5%.

[0048] Post-aging test: Sampling and equilibration: After aging, immediately remove the samples from the aging environment. Following the requirements of GB / T 19789, cut the samples and reequilibrate them for 24 hours in a standard test environment at 23℃ and 50%RH to eliminate interference from surface-adsorbed moisture on the test.

[0049] Test: Test the oxygen permeability of the aged sample according to the same standard (GB / T 19789) and method as described above for "Initial Oxygen Permeability Test".

[0050] Attenuation rate calculation: The oxygen permeability attenuation rate after damp heat aging is calculated using the following formula: Attenuation rate (%) = [(OTR_after aging - OTR_initial) / OTR_initial] × 100% Among them, OTR_initial is the initial oxygen permeability value measured before aging. The experimental results are shown in Table 1.

[0051] Table 1: Core Barrier Performance and Environmental Stability Test Data Results analysis: The initial OTR of the three embodiments was less than 0.55 and the WVTR was less than 1.2, which far exceeded that of comparative examples 1-4, thus achieving the purpose of the invention.

[0052] After rigorous damp heat aging, the OTR decay rate of all three examples was controlled within 20%, with Example 1 showing the best performance (only +13.2%). In contrast, Comparative Examples 1, 2, and 3 showed significantly greater decay, and Comparative Example 4 (traditional binary formulation) almost lost its performance (decay >50%), demonstrating the crucial role of the synergistic effect of the ternary composite system and specific process in improving stability.

[0053] Furthermore, the mechanical properties and dynamic durability of the hot-coated high-barrier rewound films prepared in Examples 1-3 and Comparative Examples 1-4 were measured, and the following tests were conducted: 1. Cross-cut adhesion test of coating This test was conducted according to the national standard GB / T 9286 "Cross-cut Test for Paints and Varnishes". First, a 6×6 grid was cut into the surface of the substrate film with an intermediate barrier layer using a cross-cutting tool with a 1mm blade spacing, ensuring the cuts completely penetrated the coating to reach the substrate. Then, special adhesive tape was tightly applied to the grid area and pressed flat, and then quickly peeled off at an angle close to 60 degrees within 1 to 2 seconds. Finally, the degree of coating peeling in the grid area was observed and rated according to the standard chart. A grade of 0 indicates completely smooth edges with no peeling, indicating optimal adhesion. Examples 1 and 3 in the table achieved a grade of 0, Examples 2 and Comparative Examples 1-3 achieved a grade of 1, and Comparative Example 4 achieved a grade of 2, directly reflecting the excellent adhesion between the coating of this invention and the substrate.

[0054] 2. MIT flexural endurance test This test was conducted using an MIT-type folding endurance tester, in accordance with GB / T 2679.5 "Determination of Folding Endurance of Paper and Paperboard" applicable to flexible films. A sample of specified size was clamped in the instrument and folded repeatedly within a 135-degree angle range under a constant tension of 1.0 kg. The number of folds taken before the sample completely broke was recorded; this value directly characterizes the flexibility and fatigue resistance of the coating and its composite film. Data shows that the folding endurance of the embodiments of this invention is greater than 3000 times, with preferred embodiment 1 exceeding 5000 times, significantly higher than the comparative examples, demonstrating the excellent flexibility of its coating.

[0055] 3. Composite peel strength test This test was conducted according to GB / T 8808 "Peel Test Method for Flexible Composite Plastic Materials". The composite film was cut into 15mm wide samples. After manually pre-peeling the initial portion, both ends were clamped in the upper and lower fixtures of a universal testing machine. The machine performed a 180-degree peel at a constant speed of 300mm / min. The average force during the peeling process was recorded and reported in "Newtons / 15mm width (N / 15mm)". This data directly reflects the interlayer bonding strength between the outer substrate film (including the barrier layer) and the inner heat-sealing film. The peel strength of the embodiments of this invention is all above 4.3N / 15mm, meeting the requirements for composite strength in heavy-duty packaging.

[0056] 4. Drop test and subsequent OTR attenuation rate test This test aims to simulate the impact of drop impacts on the barrier performance of packaging during transportation. Experimental procedure: First, each roll of film was heat-sealed into a small bag of specified size and filled with an appropriate amount of desiccant. A random sample of small bags was tested for their initial oxygen permeability as a baseline. Subsequently, a constant-speed drop test was conducted according to ASTM D5276 standard, where the small bags were dropped freely from a specified height (e.g., 1.0 meter) onto a rigid horizontal surface, ensuring that each sample was subjected to impacts from multiple directions (e.g., once each from the front, back, and side). After the drop test, the oxygen permeability of the small bags was tested again, and its percentage decrease relative to the initial value was calculated. Result analysis: The embodiments of this invention exhibited extremely low OTR attenuation after drop (Example 1 only +3.2%), indicating that its barrier layer effectively resists impact stress and prevents microcrack formation. In contrast, the attenuation rates of Comparative Examples 1-3 were significantly higher, while the coating of Comparative Example 4 showed macroscopic cracking after drop, completely losing its barrier function. This strongly demonstrates the unexpected superiority of this invention in impact resistance and durability.

[0057] 5. Continuous pressure test and subsequent OTR attenuation rate test This test was used to evaluate the barrier performance stability of the packaging under long-term stacking static pressure. Experimental procedure: Test bags were prepared and the initial OTR was measured. The bags were then placed flat in the center of the lower platen of a pressure testing machine, and a constant pressure of 0.5 MPa was applied to the upper platen to simulate the harsh conditions of heavy stacking, and the pressure was maintained for 24 hours. After the pressure was released, the bags were allowed to stand for 1 hour to release instantaneous elastic deformation, and then their OTR was tested and the attenuation rate was calculated. Results analysis: After continuous static pressure, the OTR attenuation rate of the embodiments of the present invention remained at an extremely low level (<+5%), proving that its coating structure is dense and not prone to creep or irreversible microscopic damage under long-term static load, thus maintaining durable barrier integrity. In contrast, the comparative examples, especially Comparative Example 4 (attenuation rate of +35.0%), exhibited poor compressive stability.

[0058] Table 2: Mechanical properties and durability test data after dynamic load Note: In the table, ">" in the MIT flexural endurance column indicates that the sample did not break at that number of times, and the test was terminated.

[0059] Results Analysis: Excellent Mechanical Properties: The adhesion (grade 0 or 1), folding endurance (>3500 cycles), and peel strength (>4.4 N / 15 mm) of Examples 1-3 all showed excellent performance, meeting the requirements for heavy-duty packaging.

[0060] After simulating transport drop and stacking pressure, the barrier performance of the three embodiments was almost unaffected (attenuation rate <7%). Example 1 showed an OTR increase of only 4.2% after the drop test, demonstrating that its coating structure effectively resists impact and prevents microcrack formation.

[0061] The dynamic performance of Comparative Examples 1 (unmodified nanoparticles) and 3 (two-stage drying) deteriorated significantly, indicating that interface modification and the three-stage densification process are crucial for durability. Comparative Example 4 showed direct coating cracking after a drop test, completely failing to meet dynamic usage requirements, a stark contrast to the invention.

[0062] Furthermore, the processability and other properties of the hot-coated high-barrier rewound films prepared in Examples 1-3 and Comparative Examples 1-4 were measured. The experimental procedures are as follows: 1. Coating solution stability test Objective: To evaluate the physical stability of nanocomposite barrier liquids under storage or preheating conditions.

[0063] process: Sample preparation: The prepared barrier solutions of each embodiment were placed into sealed transparent glass containers, with the sample volume being about 2 / 3 of the container volume.

[0064] Accelerated storage: Place the container in a constant temperature oven at 50±2℃ for 72 hours to simulate short-term accelerated storage conditions.

[0065] Result evaluation: Sedimentation observation: After 72 hours, remove the container and visually observe the bottom for any sedimentation, stratification, or clumping. Record as "no sedimentation", "slight sedimentation (can be restored to homogeneity after shaking)" or "severe sedimentation (still clumping or obviously uneven after shaking)".

[0066] Viscosity change: The viscosity of the barrier liquid was measured at 25°C before and after the test using a rotational viscometer. The percentage change in viscosity was calculated as: (Viscosity after 72 hours - Initial viscosity) / Initial viscosity × 100%.

[0067] Note: Comparative Example 4 does not contain polymer emulsion, and its simple PVA / nanoparticle mixture may undergo irreversible aggregation and sedimentation during testing. Therefore, its stability is not comparable. "-" in the table indicates that it was not tested or the result is invalid.

[0068] 2. Heat seal strength test Objective: To determine the thermal bonding strength of the inner heat-sealing surface of the roll film and evaluate its bag sealing reliability.

[0069] Standards and procedures: Refer to GB / T 2358 (or ASTM F88) standards.

[0070] Sample preparation: Place the inner layers (CPP or LLDPE side) of the composite roll film face to face, and use a heat sealing tester to heat seal for 0.3s at a sealing knife temperature of 130℃ and a pressure of 0.3MPa to make a seal of a certain width.

[0071] Test: Cut the seal into standard specimens 15 mm wide. Perform a 180° peel test on a universal testing machine at a tensile speed of 300 mm / min.

[0072] Results: Record the average force required to peel off the heat-sealed area, reported in N / 15mm. A higher value indicates better heat seal strength and a more reliable seal.

[0073] 3. Haze Test Objective: To measure the optical transparency of roll film. Lower haze indicates higher transparency and better product display effect.

[0074] Standards and procedures: Based on GB / T 2410 "Determination of light transmittance and haze of transparent plastics".

[0075] Sample preparation: Cut a 50mm×50mm sample with a smooth surface and no scratches from each roll of film.

[0076] Measurement: Using an integrating sphere haze meter, the sample is placed close to the test window. The instrument emits a parallel beam of light through the sample and measures the total transmitted light flux and the scattered light flux that deviates from the incident direction by more than 2.5°.

[0077] Calculation and Reporting: The haze value is calculated by (scattered light flux / total transmitted light flux) × 100%, and the percentage result can be read directly or automatically reported by the instrument.

[0078] 4. Water absorption rate test Objective: To evaluate the hydrophilicity of barrier layer materials. The lower the water absorption rate, the more stable its dimensions and performance in humid environments.

[0079] process: Initial weighing: Cut a sample of known area (e.g., 5cm × 5cm) from the coated substrate film, dry it in an oven at 50°C to constant weight (e.g., 4h), remove it and place it in a desiccator to cool to room temperature, weigh it with a precision analytical balance, and record it as W1.

[0080] Immersion: Immerse the dried sample completely in distilled water at 23°C, ensuring it is completely covered, for 24 hours.

[0081] Final weighing: After soaking, remove the sample with tweezers, quickly and gently absorb the water droplets adhering to the surface with absorbent paper (avoid touching the coating), and immediately weigh its wet weight, which is recorded as W2.

[0082] Calculation: The water absorption rate is calculated using the following formula: Water absorption rate (wt%) = [(W2-W1) / W1] × 100%. This value reflects the material's tendency to absorb moisture.

[0083] Table 3: Processability and Other Performance Test Data Results Analysis: Good processability: The barrier solutions of Examples 1 and 3 showed good storage stability, which is beneficial for production. Comparative Example 1, however, exhibited poor processability due to precipitation caused by the aggregation of unmodified nanoparticles.

[0084] Excellent end-application performance: Example 1 has the highest heat-sealing strength and the lowest haze, while also having the lowest water absorption rate, resulting in the best overall application performance.

[0085] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0086] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A hot-coated high-barrier rewound film, characterized in that, The film comprises, in sequence, an outer substrate film, an intermediate barrier layer, and an inner heat-sealing film; the intermediate barrier layer is formed by drying and curing a nanocomposite barrier liquid coated on the inner surface of the outer substrate film; the nanocomposite barrier liquid comprises, by weight, the following components: a) A polyvinyl alcohol aqueous solution, with a solid content of 60-80 parts; b) Surface-modified inorganic nanomaterial dispersion, with a solid content of 15-25 parts; c) Polymer emulsion, 5-15 parts by solid content; d) Crosslinking agent, 0.5-2 parts; e) Wetting agent, 0.1-0.5 parts.

2. The hot-coated high-barrier rewound film according to claim 1, characterized in that, The surface-modified inorganic nanomaterials are sheet-like or granular inorganic nanomaterials modified with silane coupling agents.

3. The hot-coated high-barrier rewound film according to claim 2, characterized in that, The inorganic nanomaterial is selected from at least one of nano-silica, nano-kaolin, and montmorillonite; the silane coupling agent is a silane coupling agent containing amino or epoxy groups.

4. The hot-coated high-barrier rewound film according to claim 3, characterized in that, The surface-modified inorganic nanomaterial is nano-silica modified with γ-aminopropyltriethoxysilane or γ-2,3-epoxypropoxypropyltrimethoxysilane, with an average particle size of 20-50 nm.

5. The hot-coated high-barrier rewound film according to claim 1, characterized in that, The polymer emulsion is one of styrene-acrylic polymer emulsion, pure acrylic polymer emulsion, or vinyl acetate-acrylic polymer emulsion, and its glass transition temperature is -10°C to 25°C.

6. The hot-coated high-barrier rewound film according to claim 5, characterized in that, The polymer emulsion is a styrene-acrylic polymer emulsion.

7. The hot-coated high-barrier rewound film according to claim 1, characterized in that, The crosslinking agent is selected from at least one of boric acid, polycarboxylic acid compounds, adipate dihydrazide, and aziridine; the wetting agent is polyether-modified polysiloxane.

8. The hot-coated high-barrier rewound film according to claim 1, characterized in that, The outer substrate film is a biaxially oriented polyamide film or a biaxially oriented polyester film with a thickness of 12-25 μm; the inner heat-sealing film is a cast polypropylene film, a linear low-density polyethylene film, or a co-extruded film thereof with a thickness of 40-80 μm.

9. A method for preparing a hot-coated high-barrier rewound film as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Corona treatment: Corona treatment is performed on the inner surface of the outer substrate film to make its surface tension reach 40-44 dynes; S2. Barrier liquid preparation and pretreatment: Preheat the polyvinyl alcohol aqueous solution to 70-80℃, and add the surface-modified inorganic nanomaterial dispersion, polymer emulsion, crosslinking agent and wetting agent in sequence under stirring. After mixing evenly, degas at 70-80℃ for 30-60 minutes to obtain the nanocomposite barrier liquid. S3. Thermal Coating and Programmed Drying: The nanocomposite barrier liquid obtained in step S2 is heated to 40-50℃ and coated onto the surface of the outer substrate film treated in step S1 using a microgravure coating method. The wet coating amount is 2.5-4.0 g / m². 2 Then, a multi-stage drying process is carried out: First stage: Treat the coating surface for 3-5 seconds at 70-80℃ and wind speed of 8-12m / s to quickly set the surface and form a porous skeleton. The second stage involves treating the product at 90-100℃ and a wind speed of 5-8m / s for 5-8 seconds to promote deep evaporation of internal moisture and initiate cross-linking reactions. The third stage: Treat the polymer emulsion particles at 110-120℃ and wind speed of 2-4m / s for 2-4s to fully soften and flow the polymer emulsion particles, densify the coating and complete cross-linking. After drying, the material is cooled to room temperature to form an outer substrate film with an intermediate barrier layer. S4. Lamination and Curing: A solvent-free polyurethane adhesive is coated on the surface of the inner heat-sealing film, and then laminated with the outer substrate film with an intermediate barrier layer obtained in step S3. The lamination pressure is 0.3-0.6 MPa, and the lamination speed is 150-250 m / min. After lamination, the film is wound up and cured at 45-55℃ for 36-72 h to obtain the hot-coated high-barrier rewound film.

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