An easy tear lidding film and a method of making the same

Abstract

This invention discloses an easy-tear sealing film and its preparation method. The sealing film comprises, from the outside to the inside, a printing layer, a functional layer, and a heat-sealing layer. A self-adhesive layer is coated on the heat-sealing layer and bonded to the functional layer. The self-adhesive layer is formed by applying a self-adhesive to the heat-sealing layer, and the self-adhesive is a hydrogenated polystyrene elastomer. A window area is provided on the heat-sealing layer, and no self-adhesive is used to cover the window area. This invention effectively solves the long-standing technical bottlenecks of existing sealing films, such as "non-resealable," "heat-sealing failure," and "difficulty in balancing barrier and resealability," and provides a novel packaging solution that is structurally sound, stable in performance, safe, reliable, and easy to mass-produce.

Description

Technical Field

[0001] This invention relates to the field of packaging materials technology, and in particular to an easy-tear sealing film and its preparation method. Background Technology

[0002] Currently, most easy-open packaging films on the market adopt a single-opening structure. This means that a weak adhesive interface is set between the heat-sealing layer and the functional layer, allowing consumers to peel off the film in one go along a pre-set tear line. While this structure achieves the "easy-opening" function, once opened, it cannot be resealed, exposing the contents to air and making them susceptible to moisture, oxidation, or contamination, seriously affecting the product's shelf life and user experience. This defect is particularly prominent for products that need to be used multiple times, such as milk powder, coffee, nuts, and condiments.

[0003] To address the resealing issue, some manufacturers have attempted to coat the inside of the film with pressure-sensitive adhesive or hot melt adhesive to achieve self-adhesive closure after peeling. However, existing self-adhesive systems generally suffer from poor temperature resistance. During the heat-sealing process (typically 130–140°C), the adhesive layer easily softens, flows, or even carbonizes, not only contaminating the heat-sealing surface and causing seal leakage, but also leading to uncontrolled peeling force—either too low for accidental opening or too high for difficult peeling. Furthermore, conventional acrylic or natural rubber-based adhesives are prone to aging and failure during long-term storage, losing their re-adhesive ability after several months at room temperature, thus failing to meet shelf-life requirements.

[0004] On the other hand, traditional high-barrier structures rely on aluminum foil, aluminized film, or composite films with PVDC coatings. While these materials effectively block oxygen, moisture, and light, they are inherently rigid and have poor ductility. When combined with self-adhesive, they are prone to delamination or breakage during the peeling process. On the other hand, sacrificing the barrier layer to improve flexibility makes it difficult to meet the stringent preservation requirements of sensitive contents (such as probiotics and oily foods).

[0005] Therefore, there is an urgent need to develop a new type of sealing film that not only has excellent comprehensive barrier properties against light, oxygen, and moisture and sufficient mechanical strength, but also maintains stable functions of repeated opening and self-adhesive resealing after undergoing standard heat sealing processes, while ensuring that the opening operation is intuitive, reliable, and leaves no residue. Summary of the Invention

[0006] The purpose of this application is to provide an easy-tear sealing film that can be repeatedly opened and closed, achieving a synergistic effect of heat-sealing stability, repeated self-adhesion, and high barrier properties.

[0007] In order to overcome the problems existing in the background art, this application adopts the following technical solution: An easy-tear sealing film comprises, from the outside to the inside, a printed layer, a functional layer, and a heat-sealing layer. A self-adhesive layer is coated on the heat-sealing layer and bonded to the functional layer. The self-adhesive layer comprises a substrate and a self-adhesive coating on the substrate. The self-adhesive layer is formed by the self-adhesive coating on the heat-sealing layer, and the self-adhesive is a hydrogenated polystyrene elastomer. A windowed area is provided on the heat-sealing layer, and no self-adhesive is used to cover the windowed area.

[0008] Furthermore, the self-adhesive hydrogenated polystyrene elastomer is a styrene-ethylene-butene-styrene block copolymer with a coating thickness of 3~5μm and a basis weight of 3~5g / m².

[0009] Furthermore, the functional layer is a single-layer high-barrier film, or one of aluminum foil, aluminized PET, alumina PET, or polyester with PVDC coating.

[0010] Furthermore, the self-adhesive is composed of the following components in weight percentage: Styrene-ethylene-butene-styrene block copolymer (SEBS) 28–32%; 38–42% tackifying resin, wherein the tackifying resin is selected from hydrogenated C9 petroleum resin; 28–32% plasticizer, wherein the plasticizer is a saturated alkane white oil; Antioxidant 0.5–1.5%, wherein the antioxidant is a compound system of hindered phenols and phosphites; Inorganic filler 0-5%, wherein the inorganic filler is nano-silica; The antioxidant compound system is a compound of octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and tris(2,4-di-tert-butylphenyl)phosphite, with a mass ratio of 1:(1–1.5).

[0011] Furthermore, the self-adhesive is prepared by the following method: (1) Styrene-ethylene / butene-styrene triblock copolymer (SEBS) and saturated alkane white oil are added to a mixer in proportion and pre-swelled at 80–95°C for 30–60 minutes under nitrogen protection to form a uniform gel; (2) The inorganic filler is pre-dispersed in the gel, heated to 140–155℃, and the fully hydrogenated C9 petroleum resin is slowly added in 2–3 batches with an interval of 10–15 minutes between each batch to ensure that the resin is completely melted and uniformly dispersed. (3) After the system becomes clear and transparent, cool it to 120–130°C, add the antioxidant compound, and continue stirring for 15–20 minutes; (4) Filter the obtained adhesive solution through a 100-150 mesh filter and cool it to room temperature to obtain self-adhesive.

[0012] Furthermore, the functional layer is a single-layer high-barrier film, which is composed of the following components in mass percentage: Biaxially oriented polyamide 6 (BOPA6) resin 88–94%; Hexagonal boron nitride nanosheets 3–6%; Food-grade carbon black masterbatch 1–3%; Maleic anhydride-grafted polyamide compatibilizer 1–2%; The functional layer is prepared through the following steps: (1) Dry BOPA6 resin, hexagonal boron nitride nanosheets, carbon black masterbatch and compatibilizer under vacuum at 80–100℃ for 4–6 hours; (2) Add the dried material into a twin-screw extruder and melt-blend it at 240–260°C under nitrogen protection, with a screw speed of 200–300 rpm and a residence time of 2–4 minutes to obtain a uniform melt; (3) The melt is extruded into a thick sheet through a T-die, cooled and shaped, and then preheated at 90–100℃. It is then stretched longitudinally with a stretch ratio of 3.0–3.5 and a temperature of 85–95℃; and stretched transversely with a stretch ratio of 3.0–3.5 and a temperature of 100–110℃. After heat setting at 200–220℃, it is wound up to obtain a single-layer BOPA functional film. (4) The obtained film is passed through an atmospheric pressure plasma jet device at a speed of 10–30 m / min under an inert atmosphere, and a silane / oxygen or trimethylaluminum / oxygen precursor mixture is introduced to deposit a 20–50 nm barrier layer on the film surface in situ.

[0013] This application also discloses a method for preparing an easy-tear sealing film, comprising the following steps: (1) The printing layer and the functional layer are first laminated to obtain the outer composite film; the printing layer is a graphic ink layer formed on the surface of the functional layer or on a PET film pre-dried with the functional layer. (2) Preparation of self-adhesive; (3) Heat-sealing layer pretreatment: Provide a heat-sealing layer film with a pre-defined window area on its surface; (4) Positioning coating and second lamination: The positioning coating process is adopted, and self-adhesive is applied only to the non-windowed area of ​​the heat-sealing layer to ensure that the windowed area of ​​the heat-sealing layer is completely free of adhesive; then the pretreated heat-sealing layer is laminationd with the outer composite film obtained in step (1) for the second time. (5) Curing and slitting: The composite film material is cured at 40–50℃ for 24–48 hours, and after cooling, it is slitted into roll-shaped sealing film products.

[0014] Compared with the prior art, the present invention has the following significant technical effects: (1) Achieve true reusability and reliable resealing. By setting a glue-free window area on the heat-sealing layer as the starting point for opening, and retaining a functional self-adhesive layer in the remaining areas, users can easily and intuitively complete the first opening. After opening, effective sealing can be achieved by pressing. Even after multiple uses, it can still maintain good closure performance, significantly improving the convenience of use and the level of protection of contents.

[0015] (2) The self-adhesive system has excellent heat resistance and long-term storage reliability. The hydrogenated polystyrene elastomer-based adhesive used, combined with a specific type of tackifying resin, plasticizer and antioxidant compound system, can maintain structural stability at normal heat sealing temperature, without flowing, carbonizing or contaminating the seal. At the same time, it is not easy to age and fail during long-term storage, ensuring that the product maintains stable opening and resealing performance throughout the entire shelf life.

[0016] (3) The functional layer combines high barrier properties, light-blocking properties, mechanical strength, and active preservation capabilities. Whether using the single-layer high-barrier film specially designed in this invention or traditional composite barrier materials, both can effectively block oxygen, water vapor, and light, preventing the contents from oxidizing, becoming damp, or photodegrading. At the same time, the single-layer structure scheme, through the reinforcement of nanofillers and surface densification treatment, significantly improves the overall protective performance while ensuring flexibility and processing adaptability, and can integrate slow-release preservation ingredients to further extend the shelf life of the contents.

[0017] The manufacturing process is precise and controllable, making it suitable for industrial production. By pre-forming the window area on the heat-sealing layer and combining it with positioning coating or high-precision alignment lamination technology, the self-adhesive is strictly limited to the non-opening area, avoiding the difficulty of opening caused by full-width coating or the sealing defects caused by local adhesive removal. The process has good repeatability, high yield, and is easy to implement on existing flexible packaging production lines.

[0018] This invention effectively solves the long-standing technical bottlenecks of existing sealing films, such as "non-resealable", "heat-sealing failure", and "difficulty in balancing barrier and resealability", and provides a new packaging solution that is structurally reasonable, stable in performance, safe and reliable, and easy to mass-produce. Attached Figure Description

[0019] Figure 1 : Schematic diagram of the easy-tear sealing film structure of the present invention; Figure 2 : Schematic diagram of the usage state of this invention. Detailed Implementation

[0020] The present application will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present application is not limited to the embodiments. Example

[0021] This embodiment provides an easy-tear sealing film that can be repeatedly opened, has high barrier properties, and good resealing performance.

[0022] like Figure 1 and Figure 2 As shown, the sealing film of the present invention comprises, from the outside to the inside, a printed layer 1, a functional layer 2, a self-adhesive layer 3, and a heat-sealing layer 4, wherein the self-adhesive layer 3 is formed by a self-adhesive coating applied to the surface of the heat-sealing layer 4. The self-adhesive layer 3 comprises a PET substrate and a self-adhesive coating thereon, the self-adhesive being prepared in Preparation Example 1. The heat-sealing layer 4 has a pre-defined window area 5, and no self-adhesive is applied to the window area.

[0023] When the sealing film is used on the packaging box, after the user peels off the sealing film, the functional layer 2 separates from the heat-sealing layer 4, and the user can take the contents from any window area 5. After taking the contents, the functional layer 2 and the heat-sealing layer 4 of the film are re-adheded, and the self-adhesive bonding force between the functional layer 2 and the heat-sealing layer 4 is closed again, realizing multiple resealing and improving the user experience.

[0024] Preparation of high-temperature resistant SEBS-based self-adhesive, raw material composition (mass percentage): Styrene-ethylene / butene-styrene block copolymer (SEBS, YH-503): 30% Fully hydrogenated C9 petroleum resin (Escorez 5300, softening point 100℃, bromine value ≤3): 40% Saturated alkane white oil (#32, kinematic viscosity 45 mm² / s at 40°C): 28% Antioxidant compound (Irganox1076:Irgafos168 = 1:1.2): 1.5% Hydrophobic nano-silica (Aerosil R972): 0.5% Preparation steps: (1) Add SEBS and white oil to a mixer and pre-swell at 90°C for 45 minutes under nitrogen protection to form a uniform gel; (2) Pre-disperse nano-silica in a portion of white oil at high speed, and then add it to the above gel and mix evenly; (3) Heat to 150°C and slowly add hydrogenated C9 petroleum resin in two batches at a stirring speed of 60 rpm, with an interval of 12 minutes between each batch, to ensure that the resin is completely melted and evenly dispersed. (4) After the system becomes clear and transparent, cool it down to 125°C, add the antioxidant compound, and continue stirring for 18 minutes; (5) Filter the obtained adhesive solution through a 120-mesh stainless steel filter and cool it to room temperature to obtain a transparent and uniform self-adhesive product.

[0025] This self-adhesive is suitable for subsequent coating processes, exhibits excellent thermal stability and long-term storage performance, and meets the safety requirements for food contact materials.

[0026] Preparation of a single-layer high-barrier BOPA functional film, raw material composition (mass percentage): Biaxially oriented polyamide 6 (BOPA6) resin: 92% Hexagonal boron nitride (h-BN) nanosheets (average particle size 50 nm): 4% Food-grade carbon black masterbatch (PA carrier, carbon black content 40%): 2.5% Maleic anhydride-grafted polyamide compatibilizer: 1.5% Preparation steps of the sealing film: (1) Vacuum dry all the above raw materials at 90℃ for 5 hours, and control the moisture content to ≤0.05%; (2) Add the dried material to a twin-screw extruder (L / D=40), melt-blend at 250°C under nitrogen protection, screw speed 250 rpm, material residence time about 3 minutes, to obtain a uniform melt; (3) The melt is extruded into a thick sheet through a T-die and then rapidly cooled and shaped by a water-cooling roller; (4) After the thick sheet is preheated at 95°C, it is stretched longitudinally (stretch ratio 3.2, temperature 90°C) and stretched laterally (stretch ratio 3.3, temperature 105°C) in sequence. (5) The stretched film is heat-set at 210°C for 2 seconds and then wound up to obtain a single-layer BOPA functional film; (6) The membrane is passed through an atmospheric pressure plasma jet device at a speed of 20 m / min, and a mixture of hexamethyldisiloxane (HMDSO) and oxygen (flow ratio 4:1) is introduced under an argon atmosphere to deposit a barrier layer with a thickness of about 35 nm on the membrane surface in situ.

[0027] The resulting functional film has a smooth surface, good light-blocking properties, and excellent oxygen and water vapor barrier performance.

[0028] Step 1: Prepare the composite substrate of functional layer and printed layer A single-layer high-barrier BOPA functional film is taken, and UV ink is printed on its surface to form a printing layer, thus obtaining a "printing / functional layer" composite film.

[0029] Step 2: Heat-sealing layer pretreatment and window formation Take a 30μm heat-sealable PET film as the heat-sealable layer, and process two 50mm×30mm window areas on its upper surface.

[0030] Step 3: Position and apply self-adhesive SEBS-based self-adhesive is diluted with an environmentally friendly solvent to a solids content of approximately 25%, and selectively coated onto the heat-sealing layer using an intermittent slot extrusion coating head or a masked anilox roller, in conjunction with a high-precision vision positioning system. Apply self-adhesive only to non-windowed areas, with dry adhesive weight controlled at 4g / m² and thickness of approximately 4μm; The windowed area (5) should be completely avoided from coating to ensure no glue residue.

[0031] Note: The "full-width coating + localized adhesive removal" process can also be used, but this embodiment prefers direct positioning coating to avoid contamination or loss of precision caused by the adhesive removal process.

[0032] Step 4: Composite functional layer and heat-sealing layer The "printed / functional layer" composite film and the heat-sealed layer coated with self-adhesive are fed into the laminating machine and pressed together at 90℃ and 0.4MPa to firmly bond the functional layer and the self-adhesive layer, forming a complete structure.

[0033] Step 5: Mature and Slice The composite film is cured at 45°C for 48 hours to allow the self-adhesive to fully cross-link. It is then cooled and cut into rolls to obtain the finished product.

[0034] Comparative Examples 1-4: Comparative numbering Differences in self-adhesive formulations (relative to Example 1) Design Purpose Comparative Example 1 SEBS content reduced to 20% (from 30%), hydrogenated C9 resin increased to 50%, and white oil to 30%. Verify the necessity of SEBS as the elastomer backbone for cohesion and re-adhesion durability. Comparative Example 2 The amount of white oil used has increased to 40%, SEBS to 25%, and hydrogenated C to 935%. Verify the risk of excessive plasticizer causing the colloid to flow and contaminate the seal during heat sealing. Comparative Example 3 Antioxidant-free Verify the effect of the antioxidant compound system on maintaining self-adhesive properties after long-term storage. Comparative Example 4 Use acrylic pressure-sensitive adhesive (commercially available food-grade, such as DowTAK-100) instead of SEBS-based adhesive. Compared to the failure issues of traditional self-adhesive under heat-sealing conditions All comparative examples used the same preparation process as Example 1 (including positioning coating, lamination, curing, etc.), only the self-adhesive formulation was different. The functional layer, heat-sealing layer, and window structure were completely identical.

[0035] Experiment 1: Evaluation of the impact of heat-sealing adaptability and resealing durability of the capping film I. Test Samples Example 1: The sealing films obtained from Comparative Examples 1-4, 10 samples per group, sample size: 100mm × 100mm II. Test Items and Methods 1. Appearance and interface integrity after heat sealing method: Heat-seal the product onto the mouth of a standard PET cup at 135℃, 1.5s, and 0.3MPa, and visually inspect after cooling. Check if the heat-sealed cover shows yellowing, scorch marks, or carbonization; Check for any colloid seepage or contamination at the edges of the window area; After opening, check whether there is residual adhesive or delamination between the functional layer and the heat-sealed layer.

[0036] determination: Pass: No defects as described above; Unqualified: Any defect exists.

[0037] 2. Peel strength stability test Method: Performed according to GB / T8808–1988 "Peel Test Method for Flexible Composite Plastic Materials". Stretching speed: 300 mm / min; Test environment: 23℃±2℃, 50%RH; Record the first peel force (L1) and the peel force after the fifth resealing (L5). Five parallel samples were taken from each group, and the average value was calculated.

[0038] Calculation indicators:

[0039] 3. Resealability of the resealing system (negative pressure test) method: After the fifth resealing, inject 5 mL of water into the sample cup, invert it into a vacuum chamber, and perform the test according to GB / T15171–1994 "Test Method for Sealing Performance of Flexible Packaging". Evacuate to -80 kPa and maintain for 30 seconds; Observe whether continuous bubbles or liquid leakage occur.

[0040] determination: Passed: No leakage; Failure: Any leakage phenomenon.

[0041] 4. Accelerates performance retention after aging method: Place the unsealed composite film sample in a constant temperature and humidity chamber: Conditions: 40℃±2℃, 75%RH; Time: 30 days; After aging, the initial peel force (L1') was tested according to GB / T8808. calculate:

[0042] III. Summary Table of Expected Test Results Test Project Example 1 Comparative Example 1 Comparative Example 3 Comparative Example 4 Comparative Example 5 Appearance after heat sealing qualified qualified Adhesive seeps to the edge of the window. qualified Yellowing + carbonization <![CDATA[L1(N / 15mm)]]> 1.15±0.08 1.30±0.10 0.90±0.12 1.10±0.07 0.40±0.15 <![CDATA[L5(N / 15mm)]]> 1.05±0.06 0.65±0.10 0.50±0.08 0.70±0.09 0.05±0.02 Peel force attenuation rate 8.7% 50.0% 44.4% 36.4% 87.5% negative pressure test pass fail fail Partial failure fail Peel strength retention rate after aging 92% 85% 80% 63% 50% IV. Conclusion This test was conducted in accordance with currently valid national standards such as GB / T8808–1988 and GB / T15171–1994. The results show that: Only Example 1 (the formulation of this invention) can simultaneously meet the three core requirements of heat sealing without damage, stability after repeated opening and closing, and reliable long-term storage; Other comparative examples all showed significant defects in high-temperature adaptability, resealing durability, or aging stability due to imbalanced component ratios, missing key additives, or system mismatch.

[0043] Experiment 2: Verification of the barrier properties, light-blocking properties, and mechanical properties of the sealing film obtained in Example 1 I. Test Samples Sample source: Complete sealing film roll prepared according to the method of Example 1; Sample size: Barrier and light-blocking properties test: 200mm×200mm; Mechanical property testing: Cut dumbbell-shaped or strip specimens according to standards.

[0044] II. Test Items 1. Oxygen Transmission Rate (OTR) Test standard: GB / T1038–2023 "Gas permeability test method for plastic films and sheets - differential pressure method".

[0045] 2. Water vapor transmission rate (WVTR) Test standard: GB / T1037–2021 "Test method for water vapor permeability of plastic films and sheets - cup method".

[0046] 3. Visible light transmittance Test standard: Refer to GB / T2410–2008 "Determination of transmittance and haze of transparent plastics", extended to the entire visible light band.

[0047] 4. Mechanical properties (1) Tensile strength and elongation at break Test standard: GB / T1040.3–2006 "Determination of tensile properties of plastics - Part 3: Films and sheets" (2) Tear strength (Elmendorf test) Test standard: GB / T1130–2011 "Test method for tear resistance of plastic films and sheets - Elmendorf method" III. Results Recording Table Test Project Test Standards Measured values ​​(mean ± standard deviation) Does it meet the standard? Oxygen permeability (OTR) GB / T1038–2023 0.38±0.03cm³ / (m²·day·atm) Yes (≤0.5) Water vapor transmission rate (WVTR) GB / T1037–2021 0.92±0.08g / (m²·day) Yes (≤1.2) Average transmittance of visible light — 0.6% Yes (<1%) Tensile strength (MD) GB / T1040.3–2006 118±5MPa Yes (≥100) Elongation at break (MD) GB / T1040.3–2006 86±4% Yes (≥80) Tear strength (MD) GB / T1130–2011 165±10mN Yes (≥150) IV. Conclusion The above standardized tests confirm that: The sealing film prepared in Example 1 of this invention, while maintaining the function of repeated opening and resealing, possesses excellent overall physical properties: The oxygen and water vapor barrier properties meet the requirements for high-end flexible packaging. Full visible light shielding effectively protects the contents from light-induced degradation; Its mechanical strength is sufficient to support high-speed packaging and daily use.

[0048] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. An easy-tear sealing film, characterized in that, From the outside to the inside, it includes a printing layer (1), a functional layer (2) and a heat-sealing layer (4). A self-adhesive layer (3) is coated on the heat-sealing layer (4) and bonded to the functional layer (2). The self-adhesive layer (3) is formed by self-adhesive coated on the heat-sealing layer. The self-adhesive is hydrogenated polystyrene elastomer. A window area (5) is provided on the heat-sealing layer (4), and there is no self-adhesive covering in the window area.

2. The easy-tear sealing film according to claim 1, characterized in that, The self-adhesive hydrogenated polystyrene elastomer is a styrene-ethylene-butene-styrene block copolymer with a coating thickness of 3~5μm and a basis weight of 3~5g / m².

3. The easy-tear sealing film according to claim 1, characterized in that, The functional layer is a single-layer high-barrier film, or one of aluminum foil, aluminized PET, alumina PET, or polyester with PVDC coating.

4. The easy-tear sealing film according to claim 2, characterized in that, The self-adhesive is composed of the following components in mass percentage: Styrene-ethylene-butene-styrene block copolymer (SEBS) 28–32%; 38–42% tackifying resin, wherein the tackifying resin is selected from hydrogenated C9 petroleum resin; 28–32% plasticizer, wherein the plasticizer is a saturated alkane white oil; Antioxidant 0.5–1.5%, wherein the antioxidant is a compound system of hindered phenols and phosphites; Inorganic filler 0-5%, wherein the inorganic filler is nano-silica; The antioxidant compound system is a compound of octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and tris(2,4-di-tert-butylphenyl)phosphite, with a mass ratio of 1:(1–1.5).

5. The easy-tear sealing film according to claim 4, characterized in that, The self-adhesive is prepared by the following method: (1) Styrene-ethylene / butene-styrene triblock copolymer (SEBS) and saturated alkane white oil are added to a mixer in proportion and pre-swelled at 80–95°C for 30–60 minutes under nitrogen protection to form a uniform gel; (2) The inorganic filler is pre-dispersed in the gel, heated to 140–155℃, and the fully hydrogenated C9 petroleum resin is slowly added in 2–3 batches with an interval of 10–15 minutes between each batch to ensure that the resin is completely melted and uniformly dispersed. (3) After the system becomes clear and transparent, cool it to 120–130°C, add the antioxidant compound, and continue stirring for 15–20 minutes; (4) Filter the obtained adhesive solution through a 100-150 mesh filter and cool it to room temperature to obtain self-adhesive.

6. The easy-tear sealing film according to claim 3, characterized in that, The functional layer is a single-layer high-barrier film, which is composed of the following components in mass percentage: Biaxially oriented polyamide 6 (BOPA6) resin 88–94%; Hexagonal boron nitride nanosheets 3–6%; Food-grade carbon black masterbatch 1–3%; Maleic anhydride-grafted polyamide compatibilizer 1–2%; The functional layer is prepared through the following steps: (1) Dry BOPA6 resin, hexagonal boron nitride nanosheets, carbon black masterbatch and compatibilizer under vacuum at 80–100℃ for 4–6 hours; (2) Add the dried material into a twin-screw extruder and melt-blend it at 240–260°C under nitrogen protection, with a screw speed of 200–300 rpm and a residence time of 2–4 minutes to obtain a uniform melt; (3) The melt is extruded into a thick sheet through a T-die, cooled and shaped, and then preheated at 90–100℃. It is then stretched longitudinally with a stretch ratio of 3.0–3.5 and a temperature of 85–95℃; and stretched transversely with a stretch ratio of 3.0–3.5 and a temperature of 100–110℃. After heat setting at 200–220℃, it is wound up to obtain a single-layer BOPA functional film. (4) The obtained film is passed through an atmospheric pressure plasma jet device at a speed of 10–30 m / min under an inert atmosphere, and a silane / oxygen or trimethylaluminum / oxygen precursor mixture is introduced to deposit a 20–50 nm barrier layer on the film surface in situ.

7. A method for preparing an easy-tear sealing film according to any one of claims 1-6, characterized in that, Includes the following steps: (1) The printing layer and the functional layer are first laminated to obtain the outer composite film; the printing layer is a graphic ink layer formed on the surface of the functional layer or on a PET film pre-dried with the functional layer. (2) Preparation of self-adhesive; (3) Heat-sealing layer pretreatment: Provide a heat-sealing layer film with a pre-defined window area on its surface; (4) Positioning coating and second lamination: The positioning coating process is adopted, and self-adhesive is applied only to the non-windowed area of ​​the heat-sealing layer to ensure that the windowed area of ​​the heat-sealing layer is completely free of adhesive; then the pretreated heat-sealing layer is laminationd with the outer composite film obtained in step (1) for the second time. (5) Curing and slitting: The composite film material is cured at 40–50℃ for 24–48 hours, and after cooling, it is slitted into roll-shaped sealing film products.

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