A reclosable lidding film and method of making the same

Abstract

This invention discloses a reusable cover film and its preparation method, comprising: compositing an outer polyester film and an inner heat-sealable polyester film to form a pressure-sensitive adhesive layer and a release layer; coating an anti-fog coating on the outer side of the inner heat-sealable polyester film; performing bidirectional half-cutting on the cover film substrate to form staggered first and second half-cuts; and partially removing the pressure-sensitive adhesive at the starting end of the opening path to form a non-adhesive gripping part. A silver-based antibacterial agent and a silane coupling agent are added to the release layer, and an anionic polymer is added to the pressure-sensitive adhesive layer. The two react with electrostatic adsorption and coordination at the interface, and the aminated polymer in the pressure-sensitive adhesive can partially reduce silver ions to silver nanoparticles in situ, forming an interfacial gradient. This invention enables the cover film to have reusable opening, anti-fog, and antibacterial functions, stable opening force, reliable closing, and all layers are made of polyester material for easy recycling.

Description

Technical Field

[0001] This invention relates to composite membrane technology, specifically to a reusable cover membrane and a method for preparing the cover membrane. Background Technology

[0002] Packaging for fresh fruits and vegetables, meat, and convenience foods comes in various forms, mainly falling into two categories: flexible packaging and rigid packaging. In the flexible packaging sector, common technical solutions for achieving reusable opening include zippered bags or spouted bags. These packages use mechanical sealing strips or spouts on the bag body, allowing consumers to manually close the seal after opening to preserve the remaining contents. In the rigid packaging sector, common reusable opening solutions include the combination of a box body and a snap-on lid.

[0003] In other words, existing packaging mainly falls into two categories: one-time tear-off cap film and rigid snap-on cap film.

[0004] Single-use tear-off lids are typically made of heat-sealable materials and are securely sealed to the edges of the tray using a heat-sealing process. Once torn, the seal is irreversibly damaged and cannot be closed again. If consumers do not use the contents all at once, they cannot effectively seal and preserve the remaining portion and must use other containers or plastic wrap to wrap it separately, resulting in a poor user experience and easily causing food waste or cross-contamination of odors.

[0005] Rigid snap-on lids typically refer to rigid plastic lids that are separate from the tray, and are repeatedly opened and closed by engaging with the tray through a snap-on or hinge structure. However, this type of rigid lid has a mechanical fit with the tray, resulting in poor sealing.

[0006] Therefore, there is an urgent need to provide a cover film that can both securely seal with the tray and have a re-opening function. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a reusable cover film, as well as a method for preparing such a cover film.

[0008] To achieve the above objectives, the technical solution provided by the present invention is as follows.

[0009] In a first aspect, the present invention provides a method for preparing a reusable cover film, comprising the following steps: S1, an outer polyester film is laminated with an inner heat-sealable polyester film, and a pressure-sensitive adhesive layer and a release layer are formed between the two; the release layer is located between the pressure-sensitive adhesive layer and the inner heat-sealable polyester film; S2, an anti-fog coating liquid is applied to the surface of the inner heat-sealable polyester film away from the pressure-sensitive adhesive layer, and after drying, an anti-fog coating is formed to obtain a cover film substrate; S3, the cover film substrate is partially cut in both the upper and lower directions to form a first half-cut and a second half-cut; the first half-cut is cut from the outer polyester film side and extends to the pressure-sensitive adhesive layer, and the second half-cut is cut from the inner heat-sealable polyester film side and extends to the pressure-sensitive adhesive layer, and the first half-cut and the second half-cut are staggered in the plane direction of the cover film. S4, in the starting area defined by the first half-cut and the second half-cut, the pressure-sensitive adhesive layer is partially removed to form a gripping part.

[0010] As a preferred technical solution, in S1, the pressure-sensitive adhesive layer is formed by coating with an acrylic pressure-sensitive adhesive emulsion, with a dry coating amount of 10-20 g / ㎡ and a thickness of 10-20 μm; the release layer is formed by coating with an organosilicon release coating liquid, with a dry coating amount of 0.1-2 g / ㎡ and a release force controlled at 0.3-1.8 N / 25 mm.

[0011] As a preferred technical solution, in step S2, the anti-fog coating liquid includes one or a mixture of sodium oleate, sodium lauryl ester, sorbitan laurate, and polyoxyethylene ether glycerol stearate, and the solvent is ethanol or ethyl acetate; it is applied by gravure coating, with a wet coating amount of 2-8 g / m² and a dry coating amount of 0.1-1 g / m² after drying.

[0012] As a preferred technical solution, in step S3, the first half-cut and the second half-cut are formed by die-cutting; the misalignment distance between the first half-cut and the second half-cut in the width direction of the cover film is 2-15mm; the first half-cut and the second half-cut are provided with discontinuities, which are uncut areas on the half-cuts, the length of the discontinuities is 0.5-3mm, and the spacing between adjacent discontinuities is 1-10mm.

[0013] As a preferred technical solution, in step S1, before applying the release coating liquid, a micro-nano imprinting process is used to form regularly arranged microstructures on the surface of the inner heat-sealable polyester film. The depth of the microstructures is 0.5-5μm, the feature size is 1-20μm, and the area coverage of the microstructures is 10%-50%. Then, an organosilicon release coating liquid is applied to the surface with the microstructures, and after drying, a release layer with surface microstructures is formed.

[0014] As a preferred technical solution, in step S1, the pressure-sensitive adhesive layer uses a UV-curable acrylic pressure-sensitive adhesive; after coating, a first curing treatment is performed from the outer polyester film side, with a curing energy of 100-300 mJ / cm². 2 Then, a second curing process is performed from the inner heat-sealable polyester film side, with a curing energy of 50-150 mJ / cm². 2 This creates a curing gradient along the thickness direction.

[0015] As a preferred technical solution, the pressure-sensitive adhesive layer uses a pressure-sensitive adhesive latex that includes anionic polymers, wherein the anionic polymers include one or more of chitosan, carboxymethyl chitosan, ε-polylysine, acryloyllysine copolymer, and methacryloylarginine copolymer, and the amount of the added polymer is 1%-5% of the total mass of the pressure-sensitive adhesive latex.

[0016] As a preferred technical solution, a silver-based antibacterial agent and a silane coupling agent are added to the release layer; the amount of the silver-based antibacterial agent added is 0.1%-1.5% of the total mass of the release coating liquid; the amount of the silane coupling agent added is 0.5%-3.0% of the total mass of the release coating liquid; the silver-based antibacterial agent is one or more of silver nanoparticles, silver ion exchangers, or silver salts; the silane coupling agent is one or more of mercaptopropyltrimethoxysilane, aminopropyltrimethoxysilane, and sodium carboxyethylsilane triol.

[0017] As a preferred technical solution, the anionic polymer is modified with amino groups. After the release coating liquid is applied and dried, the surface of the release layer is activated by corona treatment. Then, the pressure-sensitive adhesive latex is applied to the activated surface of the release layer. During the coating and drying process, the amino polysaccharide polymers in the pressure-sensitive adhesive latex reduce some of the silver ions in the release layer to silver nanoparticles in situ.

[0018] Secondly, the present invention provides a reusable cover film, characterized in that it is prepared by the preparation method described in any of the above technical features.

[0019] The advantages and beneficial effects of this invention are as follows: By setting a pressure-sensitive adhesive layer and a release layer between the outer polyester film and the inner heat-sealable polyester film, the cover film can still be repeatedly closed multiple times after the initial opening due to the initial tack of the pressure-sensitive adhesive; by forming a preset opening path through the staggered first and second half-cuts, the opening stress is accurately transmitted along this path, preventing tearing force from spreading to the heat-sealed edge and ensuring the integrity of the cover film structure after multiple openings and closings; by setting a local adhesive removal area at the beginning of the opening path, the difficulty of the first opening is reduced, and the user experience is improved; by setting an intermittent part on the die-cutting line, the time interval of the first opening time will cause irreversible breakage, forming an intuitive anti-theft opening indication.

[0020] This invention adds a silver-based antibacterial agent and a silane coupling agent to the release layer. Silver ions are fixed in the organosilicon matrix by the silane coupling agent, giving the release layer a long-lasting antibacterial function. Anionic polymers such as chitosan are added to the pressure-sensitive adhesive layer and modified with amino groups, so that they can electrostatically adsorb and coordinate with silver ions in the release layer at the interface. At the same time, during the coating and drying process, the amino polysaccharide reduces some silver ions in situ to silver nanoparticles, forming a silver ion concentration gradient from the inside of the release layer to the interface. This not only enhances the interfacial bonding force between the pressure-sensitive adhesive layer and the release layer, making the opening force more stable and the closing more reliable, but also realizes the gradient release of silver ions, taking into account both long-lasting antibacterial effect and food safety. Attached Figure Description

[0021] Figure 1 This is one of the structural schematic diagrams of the present invention.

[0022] Figure 2 This is the second structural schematic diagram of the present invention.

[0023] Figure 3 This is the third structural schematic diagram of the present invention.

[0024] 1-Outer polyester film, 2-Inner heat-sealable polyester film, 3-Pressure-sensitive adhesive layer, 4-Release layer, 5-First half-cut, 6-Second half-cut, 7-Interruption, 8-Printing layer, 9-Anti-fog coating. Detailed Implementation

[0025] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, it should be noted that, for ease of description, only the parts relevant to this application are shown in the accompanying drawings, not the entire structure. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0026] The terms “comprising” and “having”, and any variations thereof, used in this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0027] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly or implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0028] This invention provides a method for preparing a reusable cover film. This method combines a multi-layer composite structure design with precise post-processing techniques, resulting in a cover film that possesses multiple functions including reusable opening, anti-fogging, and antibacterial properties. The preparation method includes four steps: S1 composite base film preparation, S2 anti-fogging coating application, S3 double-sided die-cutting, and S4 localized adhesive removal.

[0029] In S1, an outer polyester film is laminated with an inner heat-sealable polyester film, and a pressure-sensitive adhesive layer and a release layer are formed between the two; the release layer is located between the pressure-sensitive adhesive layer and the inner heat-sealable polyester film.

[0030] The outer polyester film (PET) serves as the support layer for the cover film, typically 12-50 μm thick, and offers excellent mechanical strength, transparency, and printability. The inner heat-sealable polyester film, also made of polyester and 15-50 μm thick, exhibits excellent heat-sealing compatibility with APET trays, achieving a heat-sealing strength of over 8 N / 15 mm. A release layer lies between the pressure-sensitive adhesive layer and the inner heat-sealable polyester film, maintaining a peelable bond under normal conditions. When the cover film is first opened, the pressure-sensitive adhesive layer separates from the release layer; upon re-closure, the pressure-sensitive adhesive layer re-adheres to the release layer surface due to its initial tack, allowing for repeated opening and closing. Insufficient release force may cause the cover film to open unexpectedly, while excessive force will result in difficult opening. Maintaining the release force within the range of 0.3-1.8 N / 25 mm achieves an optimal balance between sealing strength and smooth opening.

[0031] The lamination process can be carried out by dry lamination or solvent-free lamination. Specifically, for solution-type or emulsion-type pressure-sensitive adhesives, a dry lamination process can be used to bond the outer polyester film and the inner heat-sealable polyester film together, with the core layer being pressure-sensitive adhesive.

[0032] For solvent-free pressure-sensitive adhesives, a solvent-free lamination process can be used to bond the outer polyester film and the inner heat-sealable polyester film together, with the core layer being the pressure-sensitive adhesive.

[0033] S2 applies an anti-fogging coating liquid to the surface of the inner heat-sealable polyester film away from the pressure-sensitive adhesive layer. After drying, an anti-fogging coating is formed, resulting in a cover film substrate. The anti-fogging coating liquid contains hydrophilic and lipophilic small molecule compounds, such as sodium oleate, sodium laurate, sorbitan laurate, and polyoxyethylene ether glycerol stearate, or a mixture thereof. These compounds contain both hydrophilic and lipophilic groups in their molecular structure: the lipophilic groups have good affinity with the polyester film surface, ensuring coating adhesion; the hydrophilic groups face inwards towards the cover film, reducing the surface tension during water vapor condensation, allowing the condensed water to spread in a uniform water film form rather than forming droplets. From a thermodynamic perspective, the introduction of the anti-fogging coating changes the contact angle of water on the film surface, transforming the original hydrophobic surface into a hydrophilic surface, changing the nucleation mode of water vapor condensation from bead-like condensation to film-like condensation, thereby maintaining transparency.

[0034] The anti-fog coating liquid is applied using a gravure coating method, with a wet coating amount controlled at 2-8 g / m², and a dry coating amount of 0.1-1 g / m² after drying. If the coating amount is too low, the anti-fog effect will not be durable; if the coating amount is too high, it will affect the heat-sealing effect. Corona treatment of the inner heat-sealable polyester film before coating can increase the surface polar groups and enhance the interfacial adhesion between the anti-fog coating liquid and the film.

[0035] S3, Double-sided half-die cutting: The cover film substrate is partially cut in both the upper and lower directions to form a first half-cut and a second half-cut. The first half-cut enters from the outer polyester film side and extends to the pressure-sensitive adhesive layer, while the second half-cut enters from the inner heat-sealable polyester film side and extends to the pressure-sensitive adhesive layer. The first and second half-cuts are staggered in the cover film plane direction. The first half-cut enters from the outer polyester film side, and the cutting depth is controlled to be the thickness of the outer polyester film plus 10%-50% of the pressure-sensitive adhesive layer thickness, ensuring that the blade tip touches the pressure-sensitive adhesive layer but does not cut into the release layer. The second half-cut enters from the inner heat-sealable polyester film side, and the cutting depth is controlled to be the thickness of the inner heat-sealable polyester film plus 10%-50% of the pressure-sensitive adhesive layer thickness. The two half-cuts are staggered in the cover film plane direction, with a stagger distance of 2-20mm, preferably 5-15mm.

[0036] It should be noted that, considering the thinness of the release layer and the difficulty in controlling the cutting depth, the second half-cut can cut through the release layer and stop the cut at the pressure-sensitive adhesive layer, without affecting the realization of the repeated opening function.

[0037] The presence of a semi-cut slit introduces a pre-existing crack within the cover film. When a consumer applies force from the initial point, the stress concentrates at the tip of the semi-cut slit, causing the peeling process to precisely extend along a predetermined path, rather than randomly tearing. The first and second semi-cut slits are formed using a circular die-cutting method. The die-cutting blade has a cutting edge angle of 30°-60°, a blade hardness of HRC58-62, a die-cutting pressure of 0.2-0.8 MPa, and a die-cutting speed of 10-50 m / min. Discontinuities, i.e., uncut areas on the semi-cut slits, are provided on both the first and second semi-cut slits. The length of these discontinuities is 0.5-3 mm, and the spacing between adjacent discontinuities is 5-30 mm. These discontinuities maintain the complete appearance of the cover film when it is not opened; when the cover film is opened for the first time, the discontinuities inevitably break and cannot be restored to their original state without leaving a trace, thus forming a visually obvious anti-theft indication.

[0038] S4 performs localized removal of the pressure-sensitive adhesive layer in the starting area defined by the first and second half-cuts, creating a non-adhesive gripping area. In this starting area, the pressure-sensitive adhesive layer is completely removed using methods such as mechanical wiping, laser ablation, or solvent dissolution, exposing the inner heat-sealable polyester film surface and forming a non-adhesive gripping area. From an ergonomic perspective, the localized adhesive removal area eliminates the need for consumers to pry open the cover film upon first opening; they can simply pinch the adhesive-free area to apply force smoothly. The localized removal process references adhesive removal techniques used in the self-adhesive label industry, employing a lint-free cloth dampened with an organic solvent (ethanol, ethyl acetate, or a mixture) to wipe the starting area of ​​the preset opening path. The solvent evaporates without residue, ensuring the cleanliness and hygiene of the gripping area.

[0039] In some embodiments, to optimize the basic properties of the pressure-sensitive adhesive layer and the release layer, the thickness, coating amount, and release force of both are precisely controlled. The pressure-sensitive adhesive layer is formed by coating with an acrylic pressure-sensitive adhesive emulsion, with a dry basis coating amount of 10-20 g / m² and a thickness of 10-20 μm. Acrylic pressure-sensitive adhesives have excellent initial tack, holding power, and aging resistance. The carboxyl and ester groups in their molecular chains can form hydrogen bonds and van der Waals forces with various surfaces, ensuring adhesive stability during repeated opening and closing. If the coating amount is less than 10 g / m², the pressure-sensitive adhesive layer is too thin, and adhesion may decrease after repeated opening and closing; if the coating amount is greater than 20 g / m², it may cause the adhesive layer to overflow or the opening force to be too large.

[0040] The release layer is formed by coating with a silicone release coating liquid, with a dry coating amount of 0.1-2 g / m², and the release force is controlled between 0.3-1.8 N / 25 mm. The silicone release coating examples exhibit low surface energy characteristics, and the silicon-oxygen bonds (Si-O-Si) in its molecular chain endow the coating with good thermal stability and chemical inertness, ensuring a peelable bond with the pressure-sensitive adhesive layer. The release force is controlled by adjusting the degree of crosslinking and the coating amount of the silicone: excessive crosslinking or insufficient coating amount increases the release force; conversely, it decreases it. The range of 0.3-1.8 N / 25 mm is the optimal range verified through extensive experimentation, ensuring that the cover film will not be accidentally opened during transportation and storage, while providing a smooth peel feel when actively opened by the consumer.

[0041] In some embodiments, to optimize the performance and coating process of the anti-fog coating, the composition and coating parameters of the anti-fog coating liquid are defined. The anti-fog coating liquid includes one or a mixture of sodium oleate, sodium laurate, sorbitan laurate, and polyoxyethylene ether glycerol stearate, with ethanol or ethyl acetate as the solvent. These hydrophilic and lipophilic small molecule compounds typically have molecular weights between 200-600 Da and can rapidly migrate to the surface to form a hydrophilic layer during coating drying. Gravure coating is used, with a wet coating amount of 2-8 g / m² and a dry coating amount of 0.1-1 g / m² after drying. Controlling the wet coating amount requires comprehensive consideration of the solid content of the coating liquid and the coating speed: if the wet coating amount is less than 2 g / m², the coating is too thin, and the anti-fog effect is not durable; if the wet coating amount is greater than 8 g / m², it may lead to an excessively thick coating, which can easily cause cracks or decreased adhesion during drying, insufficient drying, excessive residual solvent or strong solvent odor, and decreased heat-sealing performance. The drying temperature should be controlled between 50-90℃ to ensure rapid solvent evaporation, while avoiding excessively high temperatures that could lead to the loss of hydrophilic small molecules.

[0042] In some embodiments, to achieve precise control over the processing accuracy of the half-cut slits, the die-cutting method and the parameters of the interrupted sections are defined. The first and second half-cut slits are formed using a rotary die-cutting method, which has the advantages of high processing speed, high precision, and suitability for mass production. The misalignment distance between the first and second half-cut slits in the width direction of the cover film is 2-20mm. The selection of the misalignment distance needs to comprehensively consider the thickness of the cover film and the opening force requirements: if the misalignment distance is too small, the stress guiding effect is not obvious; if the misalignment distance is too large, it may lead to an excessively long opening path, affecting the user experience. Interrupted sections are provided on the first and second half-cut slits. The interrupted sections are uncut areas on the half-cut slits, with a length of 0.5-3mm and a spacing of 5-30mm between adjacent interrupted sections. The interrupted sections ensure that the cover film remains intact in the unopened state, and their length and spacing need to be precisely matched: if the interrupted sections are too long, the opening force is too large; if the interrupted sections are too short, they may break accidentally during transportation.

[0043] In some embodiments, to further reduce the opening force and improve its stability, a micro-nano imprinting process is used to form regularly arranged microstructures on the surface of the release layer. Before applying the release coating liquid, a regularly arranged microstructure is formed on the surface of the inner heat-sealable polyester film using a micro-nano imprinting process. The depth of the microstructure is 0.5-5 μm, the feature size is 1-20 μm, and the area coverage of the microstructure is 10%-50%. Then, an organosilicon release coating liquid is applied to the surface with the microstructure, and after drying, a release layer with surface microstructures is formed. From the perspective of interfacial mechanics, the presence of microstructures reduces the actual contact area between the pressure-sensitive adhesive layer and the release layer, reducing the peel force by 20%-40%. At the same time, the microstructures form stress concentration points at the interface, making the stress distribution more uniform during opening and avoiding fluctuations in opening force caused by excessive local stress. The depth and feature size of the microstructure need to be matched with the thickness of the pressure-sensitive adhesive layer: if the microstructure is too shallow, the area reduction effect is not obvious; if the microstructure is too deep, it may lead to incomplete filling of the pressure-sensitive adhesive, affecting the repeat adhesion performance.

[0044] In some embodiments, the pressure-sensitive adhesive layer is a UV-curable acrylic pressure-sensitive adhesive; after coating, a first curing treatment is performed from the outer polyester film side, with a curing energy of 100-300 mJ / cm². 2 Then, a second curing process is performed from the inner heat-sealable polyester film side, with a curing energy of 50-150 mJ / cm². 2 This creates a curing gradient along the thickness direction. From the perspective of photocuring kinetics, ultraviolet light attenuates as it penetrates the thin film layer. By controlling the curing energy on both sides, the crosslinking density of the pressure-sensitive adhesive layer near the outer layer can be higher (60%-80%), providing good cohesive strength; while the crosslinking density of the pressure-sensitive adhesive layer near the release layer is lower (30%-50%), maintaining high initial tack. This curing gradient along the thickness direction allows the pressure-sensitive adhesive layer to possess both high cohesive strength and excellent initial tack, avoiding the performance defects caused by a single crosslinking density.

[0045] Unlike photocurable pressure-sensitive adhesives, some embodiments use emulsion-type pressure-sensitive adhesives. In order to impart electrostatic adsorption between the pressure-sensitive adhesive layer and the release layer, an anionic polymer is added to the pressure-sensitive adhesive emulsion.

[0046] The pressure-sensitive adhesive layer uses a pressure-sensitive adhesive latex containing anionic polymers. These anionic polymers are one or more of chitosan, carboxymethyl chitosan, ε-polylysine, acryloyllysine copolymer, and methacryloylarginine copolymer, and their addition amount is 1%-5% of the total mass of the pressure-sensitive adhesive latex. These anionic polymer molecules contain a large number of carboxyl groups (-COO) on their molecular chains. -The amino group (-NH2, which becomes positively charged under acidic conditions) can electrostatically adsorb the charged components in the release layer. From a polymer physics perspective, the introduction of electrostatic adsorption increases the bonding strength between the pressure-sensitive adhesive layer and the release layer, requiring additional bonding forces to be overcome during repeated opening and closing, thus improving the stability of the closed state. Simultaneously, the electrostatic adsorption is reversible, being disrupted during opening and reformed during closing, reducing the opening force attenuation rate after multiple openings and closings to less than 10%.

[0047] In some embodiments, to impart long-lasting antibacterial function to the release layer, a silver-based antibacterial agent and a silane coupling agent are added to the release coating solution. The silver-based antibacterial agent is added at an amount of 0.1%-1.5% of the total mass of the release coating solution; the silane coupling agent is added at an amount of 0.5%-3.0% of the total mass of the release coating solution; the silver-based antibacterial agent is one or more of silver nanoparticles, silver ion exchangers, or silver salts; the silane coupling agent is one or more of mercaptopropyltrimethoxysilane, aminopropyltrimethoxysilane, and sodium carboxyethylsilane triol. From a coordination chemistry perspective, the thiol (-SH), amino (-NH2), or carboxyl (-COOH) groups at one end of the silane coupling agent molecule can form stable coordination bonds with silver ions, anchoring them within the organosilicon matrix. The trimethoxysilane or triethoxysilane groups at the other end undergo hydrolysis and condensation in the presence of moisture, forming Si-O-Si bonds that cross-link with the organosilicon release layer. This ligand bridging structure solves the problem of easy aggregation and migration of silver ions in organosilicon, ensuring uniform distribution and slow release of silver ions within the release layer. If the amount of silver-based antibacterial agent added is less than 0.1%, the antibacterial effect is not significant; if the amount added is greater than 1.5%, it may affect the release force stability of the release layer or lead to excessive silver ion migration. The amount of silane coupling agent added needs to be matched with the amount of silver-based antibacterial agent added to ensure that silver ions are adequately anchored.

[0048] In some embodiments, in order to establish the interaction between the pressure-sensitive adhesive layer and the release layer and form an interfacial gradient structure, the anionic polymer is modified with amino groups, and a corona treatment activation and in-situ reduction process is employed.

[0049] The anionic polymer is modified with amino groups; after the release coating liquid is applied and dried, the surface of the release layer is activated by corona treatment; then the pressure-sensitive adhesive latex is applied to the activated surface of the release layer, and the amino-modified anionic polymer in the pressure-sensitive adhesive latex reduces some of the silver ions in the release layer to silver nanoparticles in situ during the coating and drying process.

[0050] From the perspective of interfacial reaction kinetics, corona treatment introduces active groups onto the release layer surface, enhancing its reactivity. The amino groups (-NH2) in the aminated anionic polymers possess strong reducing properties, capable of reducing silver ions to elemental form at a reduction rate of 20%-60%. The in-situ reduction process creates a silver ion concentration gradient at the interface between the release layer and the pressure-sensitive adhesive layer. Silver ions near the interface are reduced to silver nanoparticles, while those further away remain in ionic form. In this gradient structure, the silver nanoparticles at the interface provide long-lasting antibacterial effects; unreduced silver ions form electrostatic adsorption with the anionic polymer in the pressure-sensitive adhesive layer, enhancing the release force; and the silver ion concentration gradient ensures the sustainability of silver release, extending the antibacterial lifespan. The power and time of the corona treatment need to be controlled: too low a power or too short a time will result in insufficient activation; too high a power or too long a time may damage the release layer surface or cause changes in the release force.

[0051] Example 1 This embodiment provides a method for preparing a reusable cover film.

[0052] In step S1, the outer polyester film is a 12μm thick printable polyester film, and the inner heat-sealable polyester film is a 30μm thick co-extruded heat-sealable polyester film. The pressure-sensitive adhesive layer is formed by coating with an acrylic pressure-sensitive adhesive emulsion, with a dry coating amount of 10g / ㎡ and a thickness of approximately 10μm; the release layer is formed by coating with an organosilicon release coating liquid, with a dry coating amount of 0.3g / ㎡ and a release force controlled at 100g / 25mm. A dry lamination process is used, with a polyurethane-based two-component adhesive, a coating amount of 3g / ㎡, and curing at 50℃ for 48 hours after lamination.

[0053] In step S2, the anti-fog coating liquid uses sorbitol laurate, the solvent is ethanol, the solid content is 5%, and it is applied by gravure coating method with a wet coating amount of 4 g / ㎡ and a dry coating amount of 0.2 g / ㎡ after drying.

[0054] In step S3, the first and second half-cuts are formed by circular die cutting, with a misalignment distance of 5mm, a discontinuity length of 1mm, and a spacing of 10mm between adjacent discontinuities.

[0055] In step S4, a mechanical wiping method is used to locally remove adhesive from the starting area, with a removal width of 10mm and a length of 15mm. After heat sealing the resulting cover film with the APET tray, the heat seal strength is >6N / 15mm, the initial opening force is 0.65N / 15mm, the adhesion force after 10 repeated adhesions is 0.35N / 15mm, and the anti-fog level is 1.

[0056] Example 2 The difference between this embodiment and Embodiment 1 is that in step S1, the pressure-sensitive adhesive layer uses a UV-curable acrylic pressure-sensitive adhesive, and after coating, the first curing treatment is performed from the outer layer side (curing energy 200mJ / cm). 2 Then, a second curing process (curing energy 100mJ / cm2) is performed from the inner layer side to form a curing gradient in the thickness direction. The initial opening force of the resulting cover film is 0.70N / 15mm, and the adhesive force is 0.40N / 15mm after 10 repeated applications, indicating a decrease in the opening force attenuation rate.

[0057] Example 3 The difference between this embodiment and Embodiment 1 is that, in step S1, before applying the release coating liquid, a micro-nano imprinting process is used to form regularly arranged microstructures on the surface of the inner heat-sealable polyester film. The microstructures have a depth of 2 μm, a feature size of 5 μm, and an area coverage of 30%. The initial opening force of the resulting cover film is 0.50 N / 15 mm, which is 23% lower than that of Embodiment 1.

[0058] Example 4 The difference between this embodiment and Example 1 is as follows: In step S1, an emulsion-type pressure-sensitive adhesive is used, and chitosan (an anionic polymer) is added to the pressure-sensitive adhesive emulsion at a concentration of 3% of the total mass of the emulsion. 0.5% silver nanoparticles (silver-based antibacterial agent) and 1.0% mercaptopropyltrimethoxysilane (silane coupling agent) are added to the release coating solution. The resulting capping film exhibits antibacterial rates >99% against both *Escherichia coli* and *Staphylococcus aureus*, and the antibacterial rate remains >95% after 10 repeated opening and closing cycles.

[0059] Example 5 The difference between this embodiment and Embodiment 4 is that the anionic polymer is modified with amino groups; after the release coating liquid is applied and dried, the surface of the release layer is activated by corona treatment with a power of 1 kW and a treatment time of 20 seconds; then, the pressure-sensitive adhesive emulsion is applied to the activated release layer surface, and the aminated chitosan in the pressure-sensitive adhesive emulsion partially reduces silver ions to silver nanoparticles in situ during the coating and drying process. The resulting cover film has an initial opening force of 0.55 N / 15 mm, an adhesion force of 0.38 N / 15 mm after 10 repeated applications, an antibacterial rate of >99%, and XPS analysis shows a significant silver ion concentration gradient at the interface.

[0060] Comparative Example 1 The cover film is a commercially available, standard, one-time tear-off type. It is a single-layer heat-sealable polyester film, 40μm thick, and heat-sealed to the APET tray. This cover film does not have a pressure-sensitive adhesive layer or a release layer, is not semi-die-cut, and does not have a designated adhesive removal area.

[0061] Testing revealed that the heat-sealing structure of the lid was completely destroyed after the first opening, making it impossible to close again. Consumers who do not finish using the contents must use cling film or other containers for storage, resulting in a poor user experience. This comparative example illustrates that the invention achieves a reusable lid function through the cooperation of the pressure-sensitive adhesive layer and the release layer.

[0062] Comparative Example 2 The preparation method is basically the same as in Example 1, except that: in step S1, no release layer is coated, and the pressure-sensitive adhesive layer is directly bonded to the inner heat-sealable polyester film.

[0063] Tests revealed that when the cover was first opened, there was no release layer separating the pressure-sensitive adhesive layer from the inner heat-sealable polyester film, resulting in a peel force as high as 3.5 N / 15 mm, making opening difficult. Furthermore, the pressure-sensitive adhesive transferred during the peeling process, with some remaining on the surface of the inner heat-sealable polyester film. This caused the adhesive force to rapidly decrease during repeated closing, and after three repetitions, the adhesive force dropped to below 0.1 N / 15 mm, making effective sealing impossible.

[0064] Comparative Example 3 The preparation method is basically the same as in Example 1, except that: in step S3, only the first half-cut slit (cutting in from the outer layer) is set, and the second half-cut slit is not set, so the staggered opening path is not formed.

[0065] Testing revealed that when the cover was first opened, the tearing force could not be accurately transmitted along the preset path. Instead, the stress randomly diffused to the heat-sealed edge, causing the heat-sealed edge to tear and the cover itself to deform irreversibly. After being closed twice, the heat-sealed edge was severely damaged, the cover detached from the tray, and could no longer be used.

[0066] Comparative Example 4 The preparation method is basically the same as in Example 1, except that in step S3, the first half-cut and the second half-cut are continuous cuts without any interruptions.

[0067] Testing revealed that during transportation and storage, the continuous half-cut slit allowed the film to open along the slit under slight external force, leading to a decrease in packaging seal and making it impossible to visually determine if the film had been accidentally opened. This comparative example illustrates that the intermediate break in this invention creates an uncut connection point, maintaining the film's integrity when closed. Upon first opening, the break point irreversibly fractures, providing a clear anti-theft indication.

[0068] Comparative Example 5 The preparation method is basically the same as in Example 5 (containing silver antibacterial agent), except that: micro-nano imprinting is not performed in step S1, and the release layer surface is a conventional smooth surface.

[0069] Testing revealed that the initial opening force of the cover film was 0.85 N / 15 mm; the standard deviation of the opening force was 0.12 N, higher than the 0.03 N in Example 5. SEM observation showed that the release layer without the micro-nano imprint structure had a smooth surface, and the actual contact area between the pressure-sensitive adhesive layer and the release layer was large, resulting in a higher opening force with greater fluctuations.

[0070] Comparative Example 6 The preparation method is basically the same as in Example 2, except that the pressure-sensitive adhesive layer is cured by single-sided ultraviolet light (curing only from the outer layer side, with a curing energy of 300 mJ / cm). 2 No curing gradient was formed in the thickness direction.

[0071] Testing revealed that the initial opening force of the cover film was 0.68 N / 15 mm, comparable to Example 2 (0.70 N / 15 mm). However, after 10 repeated applications, the adhesive force decreased to 0.28 N / 15 mm, lower than the 0.40 N / 15 mm of Example 2. DSC analysis showed that the crosslinking density of the single-sided cured pressure-sensitive adhesive layer was uniform in the thickness direction (approximately 65%), but the crosslinking density near the release layer was too high, resulting in insufficient initial tack and a decrease in adhesive force after repeated opening and closing.

[0072] Comparative Example 7 The preparation method is basically the same as in Example 4 (containing silver antibacterial agent), except that no anionic polymers such as chitosan are added to the pressure-sensitive adhesive latex.

[0073] Testing revealed that the initial opening force of the cover film was 0.75 N / 15 mm; after 10 repeated applications, the adhesive force was 0.30 N / 15 mm, lower than the 0.38 N / 15 mm of Example 4. XPS analysis showed that there was no significant electrostatic adsorption at the interface between the pressure-sensitive adhesive layer and the release layer of this comparative example cover film, indicating a low interfacial bonding energy. Antibacterial performance testing showed that the antibacterial rate of this comparative example cover film was 85%, lower than the 99% of Example 4, indicating that the anionic polymer in the pressure-sensitive adhesive layer not only enhanced the interfacial bonding force but also promoted the slow release of silver ions through electrostatic interaction.

[0074] Comparative Example 8 The preparation method is basically the same as in Example 4 (containing silver antibacterial agent), except that only silver nanoparticles (0.5%) are added to the release coating liquid, and no silane coupling agent is added.

[0075] Testing revealed that silver nanoparticles agglomerated during the fabrication of the cover film, resulting in visible black spots on the release layer surface. Release force testing showed significant fluctuations (0.4-2.1 N / 25 mm), far exceeding the stable range of Example 4 (0.5-0.7 N / 25 mm). Antibacterial performance testing showed an initial antibacterial rate of 95%, but this dropped to 70% after five repeated opening and closing cycles. Silver ion migration testing indicated excessive silver migration.

[0076] Comparative Example 9 The preparation method is basically the same as in Example 5, except that: no corona activation treatment is performed, and the pressure-sensitive adhesive latex is directly coated on the surface of the unactivated release layer.

[0077] Testing revealed that the initial opening force of the cover film was 0.68 N / 15 mm; after 10 repeated applications, the adhesive force was 0.32 N / 15 mm, lower than the 0.38 N / 15 mm in Example 5. TEM observation showed no obvious silver nanoparticle distribution at the interface between the release layer and the pressure-sensitive adhesive layer of this comparative example cover film, and no silver ion concentration gradient was formed. Antibacterial performance testing showed that the cover film had an antibacterial rate of 92%, and the antibacterial rate decreased rapidly after repeated opening and closing.

[0078] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a reusable opening cover film, characterized in that, Includes the following steps: S1, an outer polyester film is laminated with an inner heat-sealable polyester film, and a pressure-sensitive adhesive layer and a release layer are formed between the two; the release layer is located between the pressure-sensitive adhesive layer and the inner heat-sealable polyester film; S2, an anti-fog coating liquid is applied to the surface of the inner heat-sealable polyester film away from the pressure-sensitive adhesive layer, and after drying, an anti-fog coating is formed to obtain a cover film substrate; S3, the cover film substrate is partially cut in both the upper and lower directions to form a first half-cut and a second half-cut; the first half-cut is cut from the outer polyester film side and extends to the pressure-sensitive adhesive layer, and the second half-cut is cut from the inner heat-sealable polyester film side and extends to the pressure-sensitive adhesive layer, and the first half-cut and the second half-cut are staggered in the plane direction of the cover film. S4. In the starting area defined by the first half-cut and the second half-cut, the pressure-sensitive adhesive layer is partially removed to form a non-adhesive gripping part.

2. The preparation method according to claim 1, characterized in that, In step S1, the pressure-sensitive adhesive layer is formed by coating with an acrylic pressure-sensitive adhesive emulsion, with a dry coating amount of 10-20 g / m² and a thickness of 10-20 μm; the release layer is formed by coating with an organosilicon release coating liquid, with a dry coating amount of 0.1-2 g / m² and a release force controlled at 0.3-1.8 N / 25 mm.

3. The preparation method according to claim 2, characterized in that, In step S2, the anti-fog coating liquid includes one or a mixture of sodium oleate, sodium lauryl ester, sorbitan laurate, and polyoxyethylene ether glyceryl stearate, and the solvent is ethanol or ethyl acetate; it is applied by gravure coating, with a wet coating amount of 2-8 g / m² and a dry coating amount of 0.1-1 g / m² after drying.

4. The preparation method according to claim 2, characterized in that, In step S3, the first and second half-cuts are formed by circular die-cutting; the misalignment distance between the first and second half-cuts in the width direction of the cover film is 2-15mm; the first and second half-cuts are provided with discontinuities, which are uncut areas on the half-cuts, the length of the discontinuities is 0.5-3mm, and the spacing between adjacent discontinuities is 5-30mm.

5. The preparation method according to claim 3, characterized in that, In step S1, before applying the release coating liquid, a micro-nano imprinting process is used to form regularly arranged microstructures on the surface of the inner heat-sealable polyester film. The depth of the microstructures is 0.5-5μm, the feature size is 1-20μm, and the area coverage of the microstructures is 10%-50%. Then, an organosilicon release coating liquid is applied to the surface with microstructures, and after drying, a release layer with surface microstructures is formed.

6. The preparation method according to claim 3, characterized in that, In step S1, the pressure-sensitive adhesive layer uses a UV-curable acrylic pressure-sensitive adhesive; after coating, a first curing treatment is performed from the outer polyester film side, with a curing energy of 100-300 mJ / cm². 2 Then, a second curing process is performed from the inner heat-sealable polyester film side, with a curing energy of 50-150 mJ / cm². 2 This creates a curing gradient along the thickness direction.

7. The preparation method according to claim 1, characterized in that, In step S1, the pressure-sensitive adhesive layer uses a pressure-sensitive adhesive latex containing anionic polymers. The anionic polymers are one or more of chitosan, carboxymethyl chitosan, ε-polylysine, acryloyllysine copolymer, and methacryloylarginine copolymer, and their addition amount is 1%-5% of the total mass of the pressure-sensitive adhesive latex.

8. The preparation method according to claim 7, characterized in that, In step S1, a silver-based antibacterial agent and a silane coupling agent are added to the release layer; the amount of the silver-based antibacterial agent added is 0.1%-1.5% of the total mass of the release coating liquid; the amount of the silane coupling agent added is 0.5%-3.0% of the total mass of the release coating liquid; the silver-based antibacterial agent is one or more of silver nanoparticles, silver ion exchangers, or silver salts; the silane coupling agent is one or more of mercaptopropyltrimethoxysilane, aminopropyltrimethoxysilane, and sodium carboxyethylsilane triol.

9. The preparation method according to claim 8, characterized in that, The anionic polymer is modified with amino groups; in step S1, after the release coating liquid is applied and dried, the surface of the release layer is activated by corona treatment; then the pressure-sensitive adhesive emulsion is applied to the activated surface of the release layer, and the aminated anionic polymer in the pressure-sensitive adhesive emulsion reduces some of the silver ions in the release layer to silver nanoparticles in situ during the coating and drying process.

10. A reusable opening cover film, characterized in that, It is prepared by any one of the preparation methods according to claims 1-9.

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