Ultra-thin tensile strength reinforced packaging film

Abstract

This invention discloses an ultra-thin, tensile-reinforced packaging film, relating to the field of agricultural packaging film technology. The film has a seven-layer co-extruded structure with a total thickness of 15–22 micrometers. It comprises an outer surface unwinding weather-resistant layer, an inner surface adhesive layer, a core layer with pinhole self-sealing in the middle, and tensile-reinforced crack-blocking layers on both sides. The core layer contains a polyisobutylene sealing phase, a dynamic ionic framework composed of a blend of sodium and zinc ionomers and unneutralized ethylene-acid copolymer, and a compatibilizer containing epoxy-based ethylene copolymers. The molar ratio of epoxy to free acid groups is 0.05–0.25, resulting in polyisobutylene forming a sealing microdomain with a median particle size of 0.3–1.2 micrometers and 90% of the particles having a diameter no greater than 2.5 micrometers. The blocking layer contains a microfibrillated reinforcing phase. Under pre-tension, the film can quickly seal pinholes and reduce oxygen intrusion, while simultaneously inhibiting the migration of the sealing phase, reducing in-roll adhesion and downtime for repairs.

Description

Technical Field

[0001] This invention relates to the field of agricultural packaging film technology, specifically to ultra-thin tensile-strength reinforced packaging film. Background Technology

[0002] After hay, alfalfa, silage, or straw are compacted into round or square bales by balers in the field, they are typically wrapped in multiple turns of thermoplastic stretch wrapping film. This utilizes the binding force generated by pre-stretching and the overlap between layers to create a relatively low-oxygen storage environment, allowing for fermentation or preservation in the open air for several months to over a year. This application requires the wrapping film to be compatible with the high linear speed and pre-stretching conditions of the wrapping equipment (such as the approximately 55%–70% pre-stretching and at least multiple layers used in standards like EN14932), while also withstanding environmental loads such as outdoor UV aging, temperature and humidity cycles, and handling friction. This places comprehensive demands on the film's tensile strength, tear resistance, puncture resistance, single-sided adhesion, and unwinding stability.

[0003] In existing technologies, bundling packaging films mostly adopt a multi-layer co-extruded structure based on polyethylene. By selecting high-performance linear low-density polyethylene, elastomer toughening, surface adhesion and slip systems, and weather-resistant stabilizers, the mechanical properties per unit thickness are improved while ensuring wrapability. Meanwhile, to reduce material usage and transportation costs, the industry is trending towards thinner thicknesses. For airtightness and preservation requirements, there are also solutions to reduce oxygen penetration by increasing the number of coating layers, improving puncture resistance, or using barrier layer structures. However, these improvements mainly focus on reducing the probability of breakage or improving the overall barrier level; airtightness failure may still occur in unavoidable localized damage conditions in the field.

[0004] During actual operation and stacking, the surface of the bale may have geometric protrusions such as hard straw stalks, square bale edges, and impurity particles. Friction from handling forks, ground gravel, bird pecking, and rodent gnawing can all cause pinhole-level penetrating damage. Because the packaging film is in a state of continuous tension and stress relaxation after pre-stretching, stress concentration and localized yielding easily occur at the edges of the perforations. The pore size may expand or tear under repeated external loads and temperature and humidity changes. Simultaneously, the area around the pores is often contaminated with straw juice, dust, or water film, affecting interlayer adhesion and the effective bonding of the patch material, making it difficult to detect and reliably seal the micropores in a timely manner. Even small micropores can form continuous gas exchange channels, leading to oxygen intrusion, localized aerobic heating, and mold growth, resulting in dry matter and nutrient loss, decreased feed quality, potential mycotoxin risks, and additional inspection and repair costs.

[0005] Therefore, the technical problem faced in this field is: in the application of ultra-thin stretch film for baling and packaging of hay, straw, etc., when the packaging film suffers pinhole-level penetrating damage under high pre-stretch and surface contamination conditions, how to control the continuous air leakage and oxygen intrusion caused by the micropores and inhibit the sealing failure caused by the expansion of the pores. Summary of the Invention

[0006] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides an ultra-thin, tensile-reinforced packaging film. This film has a seven-layer co-extruded structure with a total thickness of 15–22 micrometers. It comprises an outer unwinding weather-resistant layer, an inner adhesive layer, a core layer with self-sealing pinholes in the middle, and tensile-reinforced crack-blocking layers on both sides. Under pre-tension, the film can quickly seal pinholes and reduce oxygen intrusion, while simultaneously inhibiting sealant phase migration, reducing in-roll adhesion and downtime for repairs; thus solving the technical problems described in the background art.

[0007] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: The ultra-thin tensile-strength packaging film comprises a seven-layer co-extrusion molding process with a total thickness of 15-22 micrometers, which sequentially includes an outer surface unwound weather-resistant layer, an outer tough load-bearing layer, an outer tensile-strength / crack-blocking layer, a pinhole self-sealing core layer, an inner tensile-strength / crack-blocking layer, an inner tough load-bearing layer, and an inner surface adhesive layer. The pinhole self-sealing core layer contains a polyisobutylene sealing phase, a dynamic ionic framework, and a reactive compatibilizer. The polyisobutylene sealing phase exists in dispersed sealing microdomains, with a median particle size of 0.3–1.2 μm and 90% of the particles having a size ≤2.5 μm. The dynamic ionic framework is a blend of sodium ion-type ethylene-acid ionomers and zinc ion-type ethylene-acid ionomers, and contains unneutralized ethylene-acid copolymers. The reactive compatibilizer is an epoxy-containing ethylene copolymer, with a molar ratio of epoxy groups to free acid groups of 0.05–0.25. Both tensile reinforcement / crack blocking layers contain microfibrillated reinforcing phases.

[0008] Furthermore, the polyisobutylene sealing phase is a bimodal polyisobutylene system, comprising medium-to-high molecular weight polyisobutylene with a number average molecular weight of 80,000 to 200,000 and low molecular weight polyisobutylene with a number average molecular weight of 5,000 to 20,000. The proportion of low molecular weight polyisobutylene in the polyisobutylene sealing phase is no more than 20%, and the content of the polyisobutylene sealing phase is 3 to 12% by mass, based on the total amount of the self-sealing core layer with pinholes.

[0009] Furthermore, the dynamic ionic skeleton is obtained by blending sodium ionic ethylene-methacrylic acid ionomer and zinc ionic ethylene-methacrylic acid ionomer at a mass ratio of 20:80 to 80:20, and further contains 6 to 12% by mass of unneutralized ethylene-methacrylic acid copolymer with an acid content of 6%. The degree of neutralization of the carboxylic acid groups in the dynamic ionic skeleton is 40 to 70%, sodium neutralization is 10 to 40%, zinc neutralization is 10 to 30%, and the balance is unneutralized carboxylic acid groups.

[0010] Furthermore, the reactive compatibilizer is an ethylene-glycidyl methacrylate copolymer, the content of epoxy functional group monomer in the reactive compatibilizer is 3-8% by mass, the melt flow rate is 2-10 g / 10 min, and the content of the reactive compatibilizer is 0.5-3.0% by mass based on the total amount of the self-sealing core layer of pinholes.

[0011] Furthermore, the microfibrillated reinforcing phase is ultra-high molecular weight polyethylene or ultra-high viscosity polyethylene, the weight-average molecular weight of the microfibrillated reinforcing phase is 1,000,000 to 3,000,000 g / mol, the melt flow rate is not greater than 0.1 g / 10 min, and the content of the microfibrillated reinforcing phase is 0.3 to 3.0% by mass based on the total amount of the whole film.

[0012] Furthermore, based on the total amount of the outer surface unwound weather-resistant layer, the outer surface unwound weather-resistant layer contains 0.05–0.25% by mass of slip agent, 0.05–0.25% by mass of anti-blocking agent, and 0.10–0.60% by mass of UV stabilizer. The anti-blocking agent is silica or talc with a median particle size of 1.5–3.5 micrometers and 90% of the particles having a particle size of no more than 6 micrometers. The inner surface adhesive layer contains homogeneous branched ultra-low density polyethylene with a density of 0.870–0.900 g / cm³ and a melt flow rate greater than 1 g / 10 min.

[0013] A method for preparing an ultra-thin tensile-reinforced packaging film, wherein the packaging film is formed by seven-layer co-extrusion, with a total thickness of 15-22 micrometers, and includes at least a pinhole-sealing core layer and tensile-reinforced / crack-blocking layers on both sides; the method includes: To prepare tensile-strength masterbatch, ultra-high molecular weight polyethylene powder and metallocene linear low-density polyethylene are melt-blended in a twin-screw extruder and granulated under vacuum. To prepare sealing micro-domain masterbatch, a dynamic ionic skeleton, metallocene linear low-density polyethylene, and a reactive compatibilizer are melt-blended and subjected to an acid-epoxy reaction, with the molar ratio of epoxy groups to free acid groups controlled at 0.05–0.25. Then, a polyisobutylene sealing phase is injected in the middle and later stages and dispersed by strong mixing and shearing, followed by vacuum granulation. During seven-layer co-extrusion blown film or cast film production, the sealing micro-domain masterbatch is fed into the pinhole self-sealing core layer, and the tensile-strength masterbatch is fed into the tensile-strength / crack-blocking layers on both sides, and then co-extruded into a film.

[0014] Furthermore, the raw material ratio of the tensile strength masterbatch is based on a total masterbatch weight of 100 parts by mass, including 30 parts by mass of ultra-high molecular weight polyethylene powder and 70 parts by mass of metallocene linear low density polyethylene. During the blending and granulation process in a twin-screw extruder, the temperature is gradually increased from 160 degrees Celsius to 200-210 degrees Celsius, the screw speed is 200-400 revolutions per minute, and vacuum exhaust is activated.

[0015] Furthermore, the raw material ratio of the sealing microdomain masterbatch, based on a total masterbatch volume of 100 parts by mass, includes 30 parts by mass of polyisobutylene sealing phase, 55 parts by mass of dynamic ionic skeleton, 5 parts by mass of reactive compatibilizer, and 10 parts by mass of metallocene linear low-density polyethylene. Specifically, the dynamic ionic skeleton, metallocene linear low-density polyethylene, and reactive compatibilizer are added first in the front section, and then the polyisobutylene sealing phase is injected in the middle and rear sections through side feeding or metering pump. The extrusion process temperature is 170-210 degrees Celsius and vacuum degassing is activated. The median particle size of the resulting polyisobutylene sealing microdomain is 0.3-1.2 micrometers, and 90% of the particles have a diameter not greater than 2.5 micrometers.

[0016] Furthermore, during the seven-layer co-extrusion blown film process, the blow-up ratio is 2.2–3.0, the freeze line height is not less than 4 times the die diameter, and based on the total amount of the outer tensile reinforcement / crack blocking layer and the inner tensile reinforcement / crack blocking layer, the addition amount of tensile reinforcement masterbatch on both sides is 6% by mass. Based on the total amount of the pinhole self-sealing core layer, the polyisobutylene sealing phase is 6–10% by mass, the dynamic ionic skeleton is 15–25% by mass, and the reactive compatibilizer is 1–4% by mass through the formulation of the sealing micro-domain masterbatch.

[0017] (III) Beneficial Effects This invention provides an ultra-thin tensile-strength reinforced packaging film, which has the following beneficial effects: The seven-layer co-extruded ultrathin tensile-reinforced packaging film forms controlled-size polyisobutylene sealing microdomains within the self-sealing core layer of pinholes. These microdomains are then encapsulated by an ion polymer skeleton composed of sodium and zinc ion polymers. This allows the sealing phase to quickly wet the pore edges and block gas channels under the continuous tension and rebound compression of the bundle when pinholes occur, thereby significantly reducing the risk of localized heating and mold spread caused by oxygen intrusion.

[0018] The ionomer backbone and reactive compatibilizer form a chemically anchored interface during melt blending, inhibiting the migration and seepage of the sealing phase to the surface, reducing the probability of in-roll adhesion and equipment roller surface contamination, and maintaining the stable overlap sealing performance of the inner surface adhesive layer. The tensile-strength crack-blocking layers on both sides of the core layer contain reinforcing phases that can form microfibrillated structures, dispersing stress concentration around pinholes and inhibiting hole expansion and tear propagation, further synergistically improving the sealing speed and sealing reliability under pre-stretch conditions with the self-sealing core layer.

[0019] The outer surface unwound weather-resistant layer provides low-friction and anti-adhesion properties, working in conjunction with the weather-resistant system to improve surface integrity and scratch resistance during outdoor storage. This ensures stable machine operation even under thinning conditions, reduces downtime due to film breakage and the frequency of manual patching, and decreases packaging material usage. The overall formulation is primarily based on a polyolefin system, and through interlayer functional partitioning, it achieves mutual support between adhesion, unwinding, reinforcement, and self-sealing, resulting in technical effects that exceed the linear summation of individual adhesion or reinforcement. The self-sealing component is located in the core layer and is anchored, allowing for more stable and reliable sealing even when contaminated. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the 7-layer co-extruded packaging film structure and thickness distribution of the present invention; Figure 2 This is an enlarged schematic diagram of the microstructure of the self-sealing pinhole core layer of the present invention; Figure 3 This is a diagram illustrating the microfiber skeleton and crack blocking mechanism of the tensile reinforcement layer of the present invention. Figure 4 This is a flowchart illustrating the preparation process of the sealing micro-domain masterbatch for this invention. Figure 5 This is a schematic diagram of the 7-layer co-extrusion blown film forming system of the present invention; Figure 6 This is a timing diagram of the cooperative self-closing mechanism after the pinhole is formed according to the present invention; Figure 7 This is a flowchart illustrating the preparation process of the tensile-strength-enhancing masterbatch for this invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Please see Figures 1-7This invention provides an ultra-thin tensile-strength reinforced packaging film, proposing a 7-layer co-extrusion (blown or cast) ultra-thin tensile-strength reinforced packaging film with a total thickness of 15–22 micrometers (e.g., 18 micrometers), featuring a single-sided adhesive and single-sided unwinding structure; a pinhole self-sealing functional layer (self-sealing core layer) is set in the middle to form a sealed microdomain with controllable particle size: the sealed microdomain is composed of a highly viscoelastic hydrocarbon sealing phase (mainly polyisobutylene); ethylene-acid ionomer neutralized by bimetallic ions serves as a dynamic ionic framework / embedded phase; and an epoxy-functionalized polyethylene reactive compatibilizer undergoes an acid-epoxy reaction during melt blending to form a chemically anchored interface shell layer around the sealed microdomain, thereby locking the sealing phase inside the core layer (reducing migration) and stabilizing the sealed microdomain at a submicron to micrometer particle size, avoiding stress concentration defects in ultra-thin films.

[0023] Tensile reinforcement / crack blocking layers are arranged on both sides of the self-sealing core layer: a small amount of ultra-high molecular weight polyethylene or ultra-high viscosity polyethylene microfibrillated reinforcing phase is used to form a microfibrillated skeleton along the machine direction under blown film traction orientation, which improves tear resistance and anti-pore expansion, and confines the damage to the vicinity of the pinhole, giving the self-sealing layer time and pressure conditions.

[0024] The symmetrical design of single-sided adhesive (inner surface) and single-sided low-tack smooth (outer surface) satisfies the overlapping adhesion for bundling and wrapping while avoiding blockage during winding; and adopts a conventional agricultural film weather-resistant system (hindered amine light stabilizer, ultraviolet absorber, etc.).

[0025] The self-sealing component of this scheme can adopt (i) a sealed phase microdomain structure or (ii) a sealed phase microcapsule structure. Preferably, (i) a sealed phase microdomain structure is adopted, that is, a sealed phase dispersion microdomain with controlled particle size is formed in the self-sealing core layer, and the interface is anchored by an ionomer framework and a reactive compatibilizer to suppress migration.

[0026] The following parts by weight / percentages by weight are described based on a single layer or the entire film.

[0027] Component A: A robust resin matrix system that provides the main load-bearing framework for the film, blown film stability, pre-stretch window, and basic puncture resistance. May include the following sub-components: A1: Metallocene linear low-density polyethylene: Density: 0.915–0.922 g / cm³; Melt flow rate (190°C / 2.16 kg): 0.5–2.5 g / 10 min; Dosage (whole film): 30–70%; Used for core load-bearing and tear resistance.

[0028] A2: Conventional linear low-density polyethylene: Density: 0.918–0.930 g / cm³; Melt flow rate: 1–8 g / 10 min; Dosage (whole film): 0–30%; A3: High-density polyethylene: Density: 0.948–0.956 g / cm³; Melt flow rate: 0.05–0.8 g / 10 min; Dosage (whole film): 0–20%; Component B: Elastic rebound and anti-hole expansion system: Provides rebound and continuous clamping force under pre-stretch and stress conditions, so that the periphery of the pinhole generates compression / drive of the sealing phase.

[0029] B1: Ethylene-α-olefin copolymer elastomers (e.g., ethylene-octene copolymers): Density: 0.860–0.890 g / cm³; Melt flow rate: 0.5–5 g / 10 min; Dosage (whole film): 10–40%; Component C: Tensile reinforcement / crack blocking system: Inhibits tear propagation and improves porosity resistance under ultrathin conditions, preventing pinholes from tearing into cracks under tension. It inhibits tear propagation non-linearly by inducing the formation of a fibrous framework through film-forming traction (the crack propagation path is rewritten). May contain: C1: Microfibrillated reinforcing phase (preferably ultra-high molecular weight polyethylene or ultra-high viscosity polyethylene); Material selection criteria (resin in powder or concentrated masterbatch): Weight-average molecular weight: 1,000,000–3,000,000 g / mol (higher options available); Melt flow rate (190°C / 2.16 kg): ≤0.1 g / 10 min (extremely low flow, which is beneficial for the formation of microfibrillated skeletons during traction orientation). Final content (whole film): 0.3–3.0%; Morphological indicators (microfibrillated structures formed within the reinforcing layer): Equivalent diameter of microfibrillated structure: 0.1–1.0 micrometers (target); Aspect ratio: ≥20 (target); Component D: Surface functional system: The function of D is to meet the core operating conditions of bundled film: adhesive overlap on the inner surface, unwinding capability on the outer surface without sticking to the rollers; and to provide outdoor weather resistance (UV protection). It may include: D1: Outer surface unwinding / smooth anti-stick system (placed on the outer surface layer); Lubricant: 0.05–0.25% (e.g., erucamide or oleamide); Anti-blocking agent: 0.05–0.25% (e.g., silica / talc, median particle size 2–6 microns); UV stabilizer package: 0.10–0.60% (hindered amine light stabilizer + UV absorber combination); D2: Inner surface adhesive system (placed in the inner surface layer): Homogeneous branched ultra-low density polyethylene is used as the adhesive substrate: Density: 0.870–0.900 g / cm³; Melt flow rate: >1 g / 10 min; Component E: Pinhole self-sealing system: When a pinhole occurs, rapid pore plugging is achieved at room temperature by a micro-domain sealing phase + dynamic ionic framework + chemical anchoring interface, and the pore remains sealed under tension.

[0030] E1: Sealing phase (highly viscoelastic hydrocarbon sealing material): Preferred polyisobutylene bimodal system: E1a: Medium to high molecular weight polyisobutylene, number average molecular weight 80,000–200,000; apparent viscosity (or equivalent viscoelasticity) at 25°C meets the requirement of being flowable but not leaky.

[0031] E1b: Low molecular weight polyisobutylene, number average molecular weight 5,000–20,000, used to improve wetting and micropore filling; its proportion in the sealing phase can be ≤30% to avoid migration risk.

[0032] E1 content within the self-sealing layer: 3–12%; converted to whole membrane: 0.5–4%.

[0033] E2: Bimetallic ion-neutralized ethylene-acid ionomer (dynamic ionic framework / embedded phase) Material selection: ethylene-methacrylic acid ionomer or ethylene-acrylic acid ionomer (belonging to ionomers); ionomers can be used for blown film / co-extrusion.

[0034] Sodium-ionized ethylene-methacrylic acid ionomer (sodium ionomer) and zinc-ionized ethylene-methacrylic acid ionomer (zinc ionomer) are selected and mixed in a mass ratio of (20:80)–(80:20) (preferably (40:60)–(60:40)) to form a macroscopically mixed bimetallic ion network. A certain proportion of unneutralized ethylene-acid copolymer (e.g., ethylene-methacrylic acid copolymer, acid content 6–12%) is further added to provide reactive acid groups.

[0035] Acid content: 7–12% (mass fraction); Neutralization degree: 40–70%; The neutralizing cation is a sodium + zinc combination (bimetallic): Sodium neutralization: 10–40% (mole fraction of acid groups); Zinc neutralization: 10–30% (mole fraction of acid group); The remainder consists of unneutralized acid groups, which provide reaction sites for subsequent reactive compatibilizers; Melt flow rate: 2–20 g / 10 min E3: Reactive compatibilizer (polyethylene-epoxy functional group copolymer): Preferred: Ethylene-glycidyl methacrylate copolymer (containing epoxy groups); Epoxy functional group monomer content: 3–8% (mass fraction); Melt flow rate: 2–10 g / 10 min; Content: 0.5–3.0% in the self-sealing layer; 0.1–1.0% in the whole film; During melt blending, it reacts with the unneutralized acid groups of E2 to form a chemically anchored interface, stabilizing the micro-particle size of the sealing micro-domain and inhibiting the migration / leakage of the sealing phase.

[0036] E4: Structural parameters of the sealed micro-domain: Within the self-sealed core layer, the E1 sealing phase exists as dispersed microdomains: Median particle size in volume distribution: 0.3–1.2 μm; 90% volume distribution particle size: ≤2.5 μm; The method for measuring the particle size of the sealed micro-domain is as follows: the core sample is frozen and fractured with liquid nitrogen; the fracture surface is then metal-sprayed. The particle size was observed using a scanning electron microscope; the median and 90% particle size were obtained by statistically analyzing the equivalent circle diameter using image analysis software.

[0037] The micro-domain is enriched with an E2 / E3 reactive interface layer, which keeps it stable under extrusion and high pre-stretching, preventing it from evolving into large-sized oil droplet defects and avoiding the fatal gel / fisheye / stress concentration points of ultrathin films.

[0038] In the core layer, the molar ratio of epoxy groups to free acid groups is controlled to be 0.05–0.25 (preferably 0.08–0.18) so that it can act as an interface anchor / compatibility rather than a bulk crosslinking.

[0039] During reactive extrusion (preparation of sealed micro-domain masterbatch): The preferred maximum melt temperature is 190–210°C; The preferred dwell time is ≤120 seconds; Vacuum exhaust must be activated; If increased gelation is found, the epoxy copolymer in L4 can be reduced from 2.0% to 1.0–1.8%, and the source of unneutralized acid groups in the ionomer can be controlled at 2–6% (adjusted by adding the proportion of unneutralized acid copolymer).

[0040] V. Example 1: 18-micron, 7-layer, pinhole self-sealing / tensile-strength reinforced bundling packaging film 1) Membrane layer structure and thickness distribution (total thickness 18 micrometers) From the outside in (outer side is the unrolled surface, inner side is the adhesive surface): Layer 1: Outer surface unrolled weather-resistant layer: 1.2 micrometers; Second layer: Outer tough load-bearing layer: 2.4 micrometers; Layer 3: Outer tensile reinforcement / crack blocking layer: 3.0 micrometers; Layer 4: Pinhole self-sealing core layer (critical functional layer): 4.8 micrometers; Layer 5: Inner tensile reinforcement / crack blocking layer: 3.0 micrometers; 6th layer: Inner tough load-bearing layer: 2.4 micrometers; 7th layer: Inner surface adhesive layer: 1.2 micrometers; 2) Specific formula for each layer (based on a total volume of 100 parts by mass for that layer) Layer 1 (outer surface unrolled weather-resistant layer, 1.2 micrometers): A2 linear low-density polyethylene (density 0.920; melt flow rate 2–4): 55.00 parts; A3 high-density polyethylene (density 0.954; melt flow rate 0.2–0.5): 30.00 parts; B1 ethylene-octene copolymer elastomer (density 0.870; melt flow rate 1–3): 14.32 parts; D1 slip agent (either erucamide or oleamide): 0.15 parts; D1 antiblocking agent (precipitated silica, antiblocking agent particle size: median 1.5–3.5 microns, 90% particle size ≤ 6 microns): 0.15 parts; UV stabilizer package (hindered amine light stabilizer + UV absorber): 0.30 parts; Antioxidant pack (hindered phenol + phosphite): 0.08 parts; Second layer (outer tough load-bearing layer, 2.4 micrometers): A1 metallocene linear low-density polyethylene (density 0.918; melt flow rate 0.8–1.5): 72.00 parts; B1 ethylene-octene copolymer elastomer (density 0.870; melt flow rate 1–3): 27.87 parts; Antioxidant packet: 0.08 parts; Blown film processing aid (fluoropolymer, optional): 0.05 parts; Third layer (outer tensile reinforcement / crack blocking layer, 3.0 micrometers): A1 metallocene linear low-density polyethylene: 55.00 parts; A2 linear low-density polyethylene: 15.00 parts; B1 Ethylene-Octene Copolymer Elastomer: 21.92 parts; C1 tensile-strength masterbatch (see masterbatch composition below): 6.00 parts; E2 ionomer (same as layer 4, used to form gradient compatibility / strain hardening contribution): 2.00 parts; Antioxidant packet: 0.08 parts; The recipe for layer 5 is the same as that for layer 3.

[0041] Layer 4 (Pinhole self-sealing core layer, 4.8 micrometers): A1 metallocene linear low-density polyethylene: 44.87 parts; B1 Ethylene-Octene Copolymer Elastomer: 25.00 parts; E2 bimetallic ion neutralization of ethylene-acid ionomer (sodium + zinc): 20.00 parts; E1 polyisobutylene sealed phase (bimodal polyisobutylene system): 8.00 parts; E3 ethylene-epoxy functional group copolymer (reactive compatibilizer): 2.00 parts; Antioxidant packet: 0.08 parts; Blown film processing aid (fluoropolymer, optional): 0.05 parts; 6th layer (inner tough load-bearing layer, 2.4 micrometers): A1 metallocene linear low-density polyethylene: 70.00 parts; B1 Ethylene-Octene Copolymer Elastomer: 27.92 parts; E2 ionomer: 2.00 parts; Antioxidant packet: 0.08 parts; 7th layer (inner surface adhesive layer, 1.2 micrometers): D2 homogeneous branched ultra-low density polyethylene (density 0.870–0.900; melt flow rate >1): 70.00 parts; B1 Ethylene-Octene Copolymer Elastomer: 25.00 parts; E2 ionomer: 4.92 parts; Antioxidant packet: 0.08 parts.

[0042] VI. Preparation method: Step 1: Preparation of tensile-strength masterbatch (C1 masterbatch) Raw material ratio (masterbatch = 100 parts by weight): The masterbatch was dispersed by a twin-screw extruder, and microscopic examination of the masterbatch sections showed no gel exceeding 80 micrometers. Ultra-high molecular weight polyethylene powder (weight average molecular weight 1,000,000–3,000,000; average particle size 5–20 micrometers): 30 parts; A1 metallocene linear low-density polyethylene: 70 parts; Process: A twin-screw extruder was used for melt blending and granulation. Temperature setting: Gradually increase from 160°C in the feeding section to 200–210°C in the head section; Screw speed: 200–400 rpm (ideally to ensure even distribution without excessive shearing and heat generation); Vacuum exhaust: Turn on to reduce the risk of volatiles and gels; After granulation and cooling, seal and package for later use.

[0043] Step 2: Preparation of sealing micro-domain masterbatch (E-system masterbatch) Stable, fine polyisobutylene sealing microdomains are formed under processable conditions, and locked inside the core layer through the synergy of E2 / E3.

[0044] Raw material ratio (masterbatch = 100 parts by weight): E1 polyisobutylene sealing phase: 30 parts; Of which: E1a (Mn80000–200000) accounts for 80% of the sealing phase; E1b (Mn5000–20000) accounts for 20%; E2 bimetallic ion neutralization of ethylene-acid ionomer (sodium + zinc, neutralization degree 40–70%): 55 parts; E3 ethylene-epoxy functional group copolymer: 5 parts; A1 metallocene linear low-density polyethylene: 10 parts; Process: Twin-screw extruder: First, add E2, A1, and E3 to the front section and allow them to fully melt and mix to form a continuous phase; E1 (polyisobutylene sealing phase) is injected in the middle and later stages via side feeding or metering pump. A strong mixing and kneading element is set in the rear section to shear and disperse E1 into micro-domains, while simultaneously promoting the reaction of E3 and the unneutralized acid groups of E2 and their enrichment at the interface. Temperature: 170–210°C; Vacuum exhaust: On; Granulation and cooling for later use.

[0045] Quality control: After slicing, the E1 micro-domain particle size is examined using a scanning electron microscope or a transmission electron microscope to ensure that the median volume distribution is 0.3–1.2 μm and 90% is ≤2.5 μm.

[0046] Step 3: 7-layer co-extrusion film formation Equipment: 7 extruders + 7-layer annular co-extrusion die head, air ring cooling, traction winding system.

[0047] Feeding at each level: The fourth layer (self-sealing core layer) is precisely controlled using a masterbatch + resin method: The sealing micro-domain masterbatch is added in proportion to make the final E1=8%, E2=20%, and E3=2% of the layer (this can be achieved through batching calculations if the masterbatch formula is as above). Add 6% tensile-strength masterbatch to the 3rd and 5th layers.

[0048] Temperature (reference range): Polyethylene / elastomer extruders: 160–220°C gradient; Fourth-layer extruder with high ionomer content: 170–210°C (ensuring melt homogeneity and avoiding localized overheating). Ionomers can be used in blown film processing.

[0049] Blown film parameters (range): Inflation ratio 2.2–3.0; Traction ratio (depending on linear speed / extrusion rate): to obtain stable bubble shape and achieve a certain orientation; Cooling: Air ring + internal cooling optional (improves thickness reduction stability); Take-up tension: The window between not inducing adhesion and not producing wrinkles.

[0050] The height of the freezing line is ≥ 4 times the die diameter (to ensure a certain orientation and crystal locking). Low melt flow rate high-density polyethylene (190°C / 2.16kg0.05–0.3g / 10min) can replace part of ultra-high molecular weight polyethylene, while still providing crack blocking and anti-porous expansion, and is easier to process.

[0051] Step 4: Application Method The 18-micron film is wound on a winding machine with a pre-stretch of 50–80% (e.g., 70%), and covered with 6–8 layers of winding. When pinholes are formed, the film is under tension and pre-stretch, and local tearing and retraction will occur at the edge of the pinhole. In the fourth layer, the E1 sealing micro-domain is subjected to severe shearing and stretching near the orifice edge, resulting in micro-domain rupture / connection. The sealing phase is driven to migrate into the orifice and wet the orifice edge.

[0052] Simply adding polyisobutylene to polyethylene will lead to typical problems such as migration, oil separation, roller sticking, and decreased mechanical strength. By forming an ionic aggregate framework through E2 (ionomer), and then reacting E3 with the unneutralized acid groups of E2, a chemical anchoring interface is formed around the sealed micro-domain, thereby: inhibiting the migration of E1 to the surface at room temperature (reducing contamination and uncontrolled adhesion); inhibiting the growth of the micro-domain into defective oil droplets under extrusion / stretching; and maintaining the high pre-stretching stability of the ultrathin film.

[0053] E2 ionic bonds are dynamically reversible: they can temporarily dissociate in high-strain local areas, allowing the sealing phase to be extruded and spread; after strain is released, ionic aggregates are rebuilt, enhancing the cohesion and retention at the pore edges.

[0054] The microfibrillated reinforcement skeleton in the 3rd and 5th layers rearranges the crack propagation path, making it more difficult for cracks to expand from pinholes into tears; Once the damage is confined to the vicinity of the pore, the compression at the pore edge becomes more concentrated, which is more conducive to the formation of a stable blockage by the fourth sealing phase at the pore. This is a synergistic relationship between mechanical positioning and effective operation of the sealing phase: without the C layer, the pore is prone to expand into a crack, and even the strongest E layer will not be able to block it in time.

[0055] Experimental grouping: uniform structure (all samples are identical); 7-layer co-extruded blown film, total thickness: 18μm (±0.6μm); Thickness distribution: L1 / L7 12% each, L2 / L6 14% each, L3 / L5 14% each, L4 (core layer) 20%; Outer surface L1: Low friction / anti-stick (smooth and anti-stick masterbatch consistent); Inner surface L7: Adhesive layer (maintain consistency to avoid interference from adhesion differences in comparison); Only the core layer L4 (self-sealing system E) and the reinforcing layers L3 / L5 (tensile reinforcement system C) are changed.

[0056] IE1 (Example) L4 core layer (self-enclosed system, mass percentage, based on L4): A (main polyethylene phase: mLLDPE / VLDPE mixture) = 44–55%; B (toughening / resilience phase: POE) = 20–30%; E1 (highly viscoelastic self-closing phase: polyisobutylene PIB microdomains) = 6–10%; E2 (ionic polymer backbone: Na / Zn bimetallic ionic polymer) = 15–25%; E3 (reactive anchoring phase: ethylene copolymer containing glycidyl groups) = 1–4%; (Total amount of antioxidants / processing aids: 0.2–0.5%, consistent across groups); L3 / L5 reinforcement layer (tensile reinforcement system C): A microfiber network containing microfibrillable ultra-high molecular weight polyethylene (or equivalent microfibrillable polyolefin), with approximately 2–6% C in the reinforcing layer (based on the reinforcing layer) and the remainder being A / B phase.

[0057] During processing / post-curing, E3 and E2 form an interface anchor, stabilizing the PIB microdomains of E1 near the ionic framework, forming a self-sealing phase that is flowable but not prone to uncontrolled migration; the C microfiber network inhibits the pores from growing larger under pre-stretching residual stress, creating a window period for the viscoelastic flow of E1 to seal the pores → the self-sealing speed is significantly improved and more reliable.

[0058] Five comparative experimental groups (CE1–CE5) CE1 (reference membrane: no self-sealing, no reinforcement), L4: conventional A / B system (A 60–75%, B 25–40%), without E1 / E2 / E3; L3 / L5: without C; CE2 (enhanced only: contains C, but no self-closing); L4: same as CE1 (without E1 / E2 / E3); L3 / L5: contains C (2–6%). CE3 (E1 only: direct blend of PIB, no ionic framework / no anchoring); L4: E1 (6–10%) added to the A / B base of CE1, but E2=0, E3=0; L3 / L5: no C; CE4 (E1+E2: has an ionic framework, but no E3 reaction anchoring); L4: A / B+E1 (6–10%)+E2 (15–25%), but E3=0; L3 / L5: no C; CE5 (complete E1+E2+E3, but without enhanced C): L4: same as IE1 (including E1 / E2 / E3); L3 / L5: no C; 3) Testing standards and methods: ISO 291: Conditioning of plastic specimens and standard environment (23°C / 50%RH).

[0059] ISO 527-3: Tensile strength and elongation at break of films are tested.

[0060] ISO 6383-2: Film tear test (Elmendorf).

[0061] ASTM D1709 (Method A): 50% failure weight of a film under dart impact.

[0062] ASTM D5748: Stretch packaging film protrusion puncture performance (pear-shaped 19mm probe; example speed 10in / min).

[0063] ASTM D5458: Adhesion of stretch membrane (measured under tensile stress).

[0064] ASTM D3354: Film resistance load.

[0065] ASTM F2096: Underwater bubble method for leak detection (basic standard for evaluating pinhole self-sealing): Sample pretreatment: Prepare film bags from samples (heat seal 3 sides → inflate → seal); Install the small bag on the stretching frame and apply 70% stretch along the main stretching direction; A needle hole is formed by vertically piercing the hole with a 1.0mm stainless steel needle; Maintain the internal pressure of the bag at 2 kPa, immerse it in water for ≥25 mm, and record: The time (in minutes) required for continuous bubbling to stop = self-closing time; The number of bubbles (bubbles / min) measured after repressurization at 30 min and 24 h = residual leakage.

[0066] 4) Performance test data (target / measured values) and comparison table: Table 1: Mechanical and Surface Windows (Average values, recommended n≥5; dart drop n≥20) Unit description: Tensile strength: MPa / % Tearing: cN (1cN = 0.01N); Falling dart: g (50% failureweight); Puncture: N (maximum force); Adhesion: N / 25mm (equivalent width); Resistance to adhesion: g (resistance load); Group Key differences (relative to IE1) Total thickness (μm) Tensile strength MD / TD (MPa) Elongation at break MD / TD (%) Elmendorf tear MD / TD(cN) Dart impact D1709-A(g) Maximum force (N) for puncturing D5748 70% tensile adhesion D5458 (N / 25mm) Insulating agent D3354(g) IE1 (This invention) E1+E2+E3+C (Complete Collaboration) 18.0 36 / 28 500 / 640 200 / 600 198 26 2.8 60 CE1 No E, no C 18.0 34 / 23 520 / 680 150 / 520 170 24 2.8 90 CE2 Only C, no E 18.0 35 / 24 500 / 660 180 / 560 185 26 2.8 90 CE3 Only E1 (PIB blend), no E2 / E3, no C 18.0 32 / 22 560 / 700 140 / 480 175 25 3.0 180 CE4 E1+E2, no E3, no C 18.0 33 / 23 540 / 680 155 / 520 180 26 2.9 130 CE5 E1+E2+E3, no C 18.0 35 / 24 520 / 660 170 / 560 195 27 2.8 70 CE2 demonstrates that the reinforcing layer C significantly improves tear / puncture resistance, but does not resolve pinhole leakage (see Table 2).

[0067] CE3 proves that PIB (E1) alone does have a tendency to seal holes, but it leads to a significant increase in adhesion resistance (increased risk of processing / unwinding / roller sticking) and poor sealing stability.

[0068] CE4 / CE5 demonstrates that the ionic framework (E2) + reaction anchoring (E3) can pull the flow sealing of E1 from uncontrollable migration back to the usable window, significantly reducing resistance and adhesion without significant sacrifice of mechanics.

[0069] The key difference between IE1 and CE5 is the addition of C, whose value is mainly reflected in the sealing speed / reliability under real tension conditions (see Table 2).

[0070] Table 2: Self-sealing / self-healing capability of pinholes (ASTM F2096 foundation + 70% tensile condition) Test conditions: 70% tension fixation, 1.0mm pinhole, 2kPa gauge pressure inside the bag, underwater observation; record the continuous bubbling stop time and residual bubbling.

[0071] Group Self-closing time (stopping continuous bubbling, min) 30-minute residual leakage (bubbles / min) 24-hour residual leakage (bubbles / min) Summary of Phenomena and Failure Modes IE1 (This invention) 3 ≤3 ≤1 (occasional or none) The pinhole edges are not significantly enlarged; after sealing, re-pressure basically stops continuous bubbling. CE1 >60 (does not stop) ≥200 (continuous bubble flow) ≥200 Typical pinhole leaks with no self-sealing function. CE2 >60 (does not stop) ≥200 ≥200 Higher strength but continued leakage proves that reinforcement ≠ self-sealing CE3 18 40 20 It has some sealing properties, but the resistance to adhesion is high and the sealing fluctuations are large (PIB migration / micro-domain coarsening). CE4 10 15 8 While dispersion has improved, anchoring is lacking, resulting in insufficient sealing speed / stability; residual leakage remains significant. CE5 6 8 2 Micro-domains are more stable and have lower resistance to adhesion; however, without C, the aperture edges are more easily pulled open under tension, and the sealing speed and reliability are still inferior to IE1. Conclusion: Under 70% tensile tension (in the application range of bonding and bundling), the self-sealing time of IE1 is ≈3min, and the residual leakage after 24h is ≤1bubbles / min; while CE1 / CE2 are completely unsealed and continuously leak air within 60min (≥200bubbles / min).

[0072] Enhancement only (CE2): tearing / puncture improved, but sealing still failed → indicating that C is not a sufficient condition for self-closure.

[0073] PIB (CE3) only: It can seal holes but has severe adhesion and poor stability → This indicates that using E1 alone will introduce new process / application pain points.

[0074] E1+E2+E3 (CE5): The resistance to adhesion is significantly reduced and pore sealing can occur → This indicates that the ionic framework + reactive anchoring has indeed pulled the viscoelastic pore sealing of E1 from uncontrollable migration back to a usable window.

[0075] IE1 (CE5+C): Sealing time decreased from 6 min to 3 min, and residual leakage further decreased. C inhibits hole expansion (creating a time window for sealing); E1 flows rapidly to fill the wells in the stable micro-domains of E2 / E3 (completing the sealing). The combination of the two brings about a new effect of sealing the hole even when tension exists, which is difficult to achieve with either element alone.

[0076] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An ultra-thin, tensile-strength reinforced packaging film, characterized in that: include, It adopts a seven-layer co-extrusion molding process with a total thickness of 15-22 micrometers, which includes an outer surface uncoiled weather-resistant layer, an outer tough load-bearing layer, an outer tensile reinforcement / crack blocking layer, a pinhole self-sealing core layer, an inner tensile reinforcement / crack blocking layer, an inner tough load-bearing layer, and an inner surface adhesive layer. The pinhole self-sealing core layer contains a polyisobutylene sealing phase, a dynamic ionic framework, and a reactive compatibilizer. The polyisobutylene sealing phase exists in dispersed sealing microdomains, with a median particle size of 0.3–1.2 μm and 90% of the particles having a size ≤2.5 μm. The dynamic ionic framework is a blend of sodium ion-type ethylene-acid ionomers and zinc ion-type ethylene-acid ionomers, and contains unneutralized ethylene-acid copolymers. The reactive compatibilizer is an epoxy-containing ethylene copolymer, with a molar ratio of epoxy groups to free acid groups of 0.05–0.

25. Both tensile reinforcement / crack blocking layers contain microfibrillated reinforcing phases.

2. The ultra-thin tensile-strength reinforced packaging film according to claim 1, characterized in that: The polyisobutylene sealing phase is a bimodal polyisobutylene system, including medium-to-high molecular weight polyisobutylene with a number average molecular weight of 80,000 to 200,000 and low molecular weight polyisobutylene with a number average molecular weight of 5,000 to 20,000. The proportion of low molecular weight polyisobutylene in the polyisobutylene sealing phase is no more than 20%, and the content of the polyisobutylene sealing phase is 3 to 12% by mass, based on the total amount of the self-sealing core layer with pinholes.

3. The ultra-thin tensile-strength reinforced packaging film according to claim 1, characterized in that: The dynamic ionic skeleton is obtained by blending sodium ionic ethylene-methacrylic acid ionomer and zinc ionic ethylene-methacrylic acid ionomer at a mass ratio of 20:80 to 80:20, and further contains 6 to 12% by mass of unneutralized ethylene-methacrylic acid copolymer with an acid content of 6%. The degree of neutralization of the carboxylic acid groups in the dynamic ionic skeleton is 40 to 70%, sodium neutralization is 10 to 40%, zinc neutralization is 10 to 30%, and the balance is unneutralized carboxylic acid groups.

4. The ultra-thin tensile-strength reinforced packaging film according to claim 1, characterized in that: The reactive compatibilizer is an ethylene-glycidyl methacrylate copolymer. The content of epoxy functional group monomer in the reactive compatibilizer is 3-8% by mass, the melt flow rate is 2-10 g / 10 min, and the content of the reactive compatibilizer is 0.5-3.0% by mass based on the total amount of the self-sealing core layer of pinholes.

5. The ultra-thin tensile-strength reinforced packaging film according to claim 1, characterized in that: The microfiber-reinforcing phase is ultra-high molecular weight polyethylene or ultra-high viscosity polyethylene. The weight-average molecular weight of the microfiber-reinforcing phase is 1,000,000 to 3,000,000 g / mol, the melt flow rate is not greater than 0.1 g / 10 min, and the content of the microfiber-reinforcing phase is 0.3 to 3.0% by mass based on the total amount of the film.

6. The ultra-thin tensile-strength reinforced packaging film according to claim 1, characterized in that: Based on the total amount of the outer surface unwound weather-resistant layer, the outer surface unwound weather-resistant layer contains 0.05-0.25% by mass of slip agent, 0.05-0.25% by mass of anti-blocking agent, and 0.10-0.60% by mass of UV stabilizer. The anti-blocking agent is silica or talc with a median particle size of 1.5-3.5 micrometers and 90% of the particles having a particle size of no more than 6 micrometers. The inner surface adhesive layer contains homogeneous branched ultra-low density polyethylene with a density of 0.870-0.900 g / cm³ and a melt flow rate greater than 1 g / 10 min.

7. A method for preparing an ultra-thin tensile-strength reinforced packaging film, characterized in that: The packaging film is produced by seven-layer co-extrusion molding, with a total thickness of 15–22 micrometers, and includes at least a pinhole self-sealing core layer and tensile reinforcement / crack-blocking layers on both sides; the method includes: To prepare tensile-strength masterbatch, ultra-high molecular weight polyethylene powder and metallocene linear low-density polyethylene are melt-blended in a twin-screw extruder and granulated under vacuum. To prepare sealing micro-domain masterbatch, a dynamic ionic skeleton, metallocene linear low-density polyethylene, and a reactive compatibilizer are melt-blended and subjected to an acid-epoxy reaction, with the molar ratio of epoxy groups to free acid groups controlled at 0.05–0.

25. Then, a polyisobutylene sealing phase is injected in the middle and later stages and dispersed by strong mixing and shearing, followed by vacuum granulation. During seven-layer co-extrusion blown film or cast film production, the sealing micro-domain masterbatch is fed into the pinhole self-sealing core layer, and the tensile-strength masterbatch is fed into the tensile-strength / crack-blocking layers on both sides, and then co-extruded into a film.

8. The preparation method according to claim 7, characterized in that: The raw material ratio of the tensile strengthening masterbatch is based on a total masterbatch weight of 100 parts by mass, including 30 parts by mass of ultra-high molecular weight polyethylene powder and 70 parts by mass of metallocene linear low density polyethylene. During the blending and granulation process in a twin-screw extruder, the temperature is gradually increased from 160 degrees Celsius to 200-210 degrees Celsius, the screw speed is 200-400 revolutions per minute, and vacuum exhaust is turned on.

9. The preparation method according to claim 7, characterized in that: The raw material ratio of the sealing microdomain masterbatch is based on a total masterbatch of 100 parts by mass, including 30 parts by mass of polyisobutylene sealing phase, 55 parts by mass of dynamic ionic skeleton, 5 parts by mass of reactive compatibilizer, and 10 parts by mass of metallocene linear low-density polyethylene. The dynamic ionic skeleton, metallocene linear low-density polyethylene, and reactive compatibilizer are added first in the front section, and then the polyisobutylene sealing phase is injected in the middle and rear sections through side feeding or metering pump. The extrusion process temperature is 170-210 degrees Celsius and vacuum degassing is turned on. The median particle size of the obtained polyisobutylene sealing microdomain is 0.3-1.2 micrometers and 90% of the particles have a diameter not greater than 2.5 micrometers.

10. The preparation method according to claim 7, characterized in that: When using a seven-layer co-extrusion blown film, the blow-up ratio is 2.2 to 3.0, the freeze line height is not less than 4 times the die diameter, and based on the total amount of the outer tensile reinforcement / crack blocking layer and the inner tensile reinforcement / crack blocking layer, the addition amount of tensile reinforcement masterbatch on both sides is 6% by mass. Based on the total amount of the pinhole self-sealing core layer, the polyisobutylene sealing phase is 6% to 10% by mass, the dynamic ionic skeleton is 15% to 25% by mass, and the reactive compatibilizer is 1% to 4% by mass through the formulation of the sealing micro-domain masterbatch.

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