Preparation method and application of anti-sticking composite film

Abstract

This invention discloses a method for preparing and applying an anti-adhesion composite film, comprising: firstly, rolling a primer onto a heat-sealing substrate and drying and curing it, and then applying a topcoat onto the primer layer; the key is that, before the primer and / or topcoat are fully cured, the composite structure is micro-stretched by 0.5%–3%, thereby forming fine textures with a width of 20–200 nm and a depth of 5–50 nm in situ on the coating surface. This improves the anti-adhesion performance of the composite film and effectively solves the problem of residue of highly viscous contents inside packaging.

Description

Technical Field

[0001] This invention relates to the field of composite membrane technology, and specifically to a method for preparing and applying an anti-adhesive composite membrane. Background Technology

[0002] In the current food packaging industry, sticky products such as sauces, yogurt, and coffee often use ordinary plastic film as packaging material. However, this type of material is prone to causing the contents to adhere to the inner wall of the packaging during use, resulting in residue. This not only affects the consumer experience but also leads to product waste to some extent, failing to meet modern consumers' demands for convenience and sustainability.

[0003] To achieve the anti-stick function of packaging materials, traditional methods typically employ surface modification or the application of special coatings. For example, Chinese patent (CN114539580B) shows a non-stick milk coating on the inner layer of the cover film. The raw materials for this non-stick milk coating include solid particles, hydrophobic silanes, pH adjusters, and solvents, which are used to improve the anti-sticking effect in high-viscosity products and extend the anti-sticking time to more than three months. Another example is Chinese patent application (CN116691104A), which provides a method for preparing a paper-textured anti-fingerprint film, the film itself, and a packaging bag. On the inside of the base film, a textured layer is gravure-printed using a reverse printing process; on the outside of the base film, an anti-fouling layer is printed using a surface printing process; a heat-sealing layer is laminated onto the textured layer; and after a curing process, the paper-textured anti-fingerprint film is obtained.

[0004] While coating technology has improved anti-stick properties to some extent, its application still has certain limitations. For example, the uniformity of the coating and its stability during long-term use are currently unsatisfactory.

[0005] Therefore, it is essential to develop a packaging material that combines good non-stick properties, strong processing adaptability, and compliance with food safety requirements. Summary of the Invention

[0006] The purpose of this invention is to overcome at least one of the problems described in the background art and provide a method for preparing an anti-adhesion composite film, which has good anti-adhesion properties and a simple and efficient preparation process.

[0007] To achieve the above objectives, the technical solution provided by the present invention is as follows.

[0008] A method for preparing an anti-adhesive composite film includes the following steps: S001. Prepare the primer; S002. The primer liquid is selectively roller-coated onto the inner surface of the heat-sealing substrate using an anilox roller, followed by a drying process to form a primer coating layer. S003. The substrate with the base coating is cured once; S004. Prepare the topcoat liquid; S005. The topcoat liquid is selectively roller-coated onto the surface of the cured base coating by positioning coating, and then dried a second time to form the topcoat. S006. Before the topcoat has completely cooled, use an embossing roller to emboss it, then roll it up and perform a second curing. In S002 and / or S005, before the base coating and / or top coating are fully cured, they are heated together with the heat-sealing substrate and subjected to a stretching treatment. The stretching ratio of the stretching treatment is controlled at 0.5% to 3%, so that the surface of the base coating and / or top coating has a texture with a width of 20nm to 200nm and a depth of 5nm to 50nm.

[0009] As a preferred technical solution, the heat-sealing substrate includes at least one of biaxially oriented polypropylene, cast polypropylene, polyethylene, and linear low-density polyethylene film.

[0010] As a preferred technical solution, in the stretching process, the temperature is raised to 10°C to 50°C above the glass transition temperature of the heat-sealing substrate.

[0011] As a preferred technical solution, the stretching treatment is bidirectional stretching, with the longitudinal stretching ratio controlled at 0.5% to 2% and the transverse stretching ratio controlled at 1% to 3%.

[0012] As a preferred technical solution, when the top coating is stretched longitudinally or transversely, the bottom coating is stretched transversely or longitudinally accordingly.

[0013] As a preferred technical solution, the primer liquid comprises, by mass percentage, 12.2%~22.5% hydrogenated styrene-butadiene block copolymer, 14.8%~25.3% aliphatic polyurethane acrylate, 0.2%~5.8% γ-glycidyl etheroxypropyltrimethoxysilane, and the balance being a first solvent; the first solvent is one or a mixture of methyl isobutyl ketone, ethyl acetate, methyl ethyl ketone, and isopropanol.

[0014] As a preferred technical solution, the topcoat liquid comprises, by mass percentage, 25.2%~38.8% branched polyvinyl butyral, 12.4%~21.7% polyamide-imide, 2.5%~7.6% silica, with the balance being a second solvent; the second solvent is a mixed solvent composed of ethanol and propylene glycol methyl ether in a mass ratio of (2~1):1.

[0015] As a preferred technical solution, the conditions for the first curing are: curing at 35℃~50℃ for 12~24 hours; and the conditions for the second curing are: curing at room temperature for 24~48 hours.

[0016] As a preferred technical solution, the conditions for the first drying are: drying at a temperature of 60℃~90℃ for 1~3 minutes; the conditions for the second drying are: drying at a temperature of 70℃~110℃ for 2~5 minutes.

[0017] An anti-adhesion composite film is prepared by means of a method having at least one of the above-mentioned technical features.

[0018] The advantages and beneficial effects of this invention are as follows: This method introduces a controllable stretching process when the base coating and / or top coating are not fully cured, performed above the glass transition temperature of the heat-sealing substrate, inducing the formation of fine textures with a width of 20–200 nm and a depth of 5–50 nm on the coating surface. This not only improves the density and mechanical strength of the coating, but also further reduces the actual contact area of ​​the adhesion interface by controlling the surface morphology, thereby inhibiting the adhesion of high-viscosity substances.

[0019] In some embodiments of the present invention, the primer uses hydrogenated styrene-butadiene block copolymer and aliphatic polyurethane acrylate as the film-forming main body, supplemented by a silane coupling agent. This not only enhances the adhesion between the coating and the polyolefin substrate, but also improves the toughness and fatigue resistance of the coating through the flexibility of the molecular chains and the cross-linked structure. The topcoat introduces branched polyvinyl butyral and polyamide-imide as the main resins, combined with silica microparticles, to construct a surface with an anti-adhesive texture, so that the anti-adhesive composite film prepared by the present invention has good anti-adhesion and long-term stability. Attached Figure Description

[0020] Figure 1 This is a flowchart of the preparation method of the anti-adhesion composite film shown in this invention. Detailed Implementation

[0021] 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.

[0022] 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.

[0023] 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.

[0024] Please see Figure 1 This invention provides a method for preparing an anti-adhesive composite film. It utilizes a micro-stretching process performed while the coating is semi-cured to construct a stable micro-nano textured structure in situ on the coating surface, thereby physically reducing the actual contact area between the coating and its contents. Combined with a specially formulated double-layer coating system, it achieves a highly efficient and durable anti-adhesive effect. The method includes the following steps: S001. Prepare the primer; S002. The primer liquid is selectively roller-coated onto the inner surface of the heat-sealing substrate using an anilox roller, followed by a drying process to form a primer coating layer. S003. The substrate with the base coating is cured once; S004. Prepare the topcoat liquid; S005. The topcoat liquid is selectively roller-coated onto the surface of the cured base coating by positioning coating, and then dried a second time to form the topcoat. S006. Before the topcoat has completely cooled, emboss it using an embossing roller, then rewind it and perform a second curing.

[0025] In step S002, after the base coating is applied and dried, and / or in step S005, after the top coating is applied and dried, but before complete curing, the substrate system with coatings is heated and subjected to a small-scale stretching treatment, so that the surface of the base coating and / or top coating has a fine texture with a width of 20nm~200nm and a depth of 5nm~50nm.

[0026] The "before complete curing" state refers to the state after the coating has undergone a drying process to remove most of the solvent, but before the cross-linking reaction or glass transition of the polymer resin is fully completed. The coating is in a "soft solid" mechanical state. At this point, the coating material possesses sufficient bulk strength to maintain its macroscopic shape, while its polymer chains have adequate mobility and plasticity. If the coating is completely cured, the polymer chains are thoroughly solidified, and stretching will cause the coating to crack brittlely or peel off from the substrate. If the coating is stretched too early (due to excessive solvent content), it cannot effectively transfer and maintain tensile stress, resulting in unfixed deformation or sagging.

[0027] The purpose of the "stretching treatment" is to utilize the unique mechanical state of the coating at this time to apply a fine stretching ratio, far lower than that of traditional thin film orientation processes. This tiny stretching amount is sufficient to induce key changes in the coating at the molecular and microscopic scales. Under the action of tensile stress, the polymer molecular chains on the coating surface and near the surface region will undergo orientation and rearrangement along the stretching direction. Simultaneously, for the surface coating, the interface between the uniformly dispersed silica nanoparticles and the resin matrix will be adjusted under stress, and the resin around the particles will undergo local yielding and reconstruction, which will be fixed by the subsequent cooling and curing process, thereby growing a uniform and stable microtexture with a width of 20nm~200nm and a depth of 5nm~50nm on the coating surface.

[0028] The effects of stretching processes include, but are not limited to: First, it actively creates surface micro-roughness. This in-situ texture, combined with the low surface energy of the coating chemistry, reduces the adhesion of sticky substances to the film surface, conforming to the basic principles of the Cassie-Baxter hydrophobic model, where droplets are supported by the protrusions on the top of the texture and the trapped air, greatly reducing the solid-liquid contact area. Second, unlike methods that rely solely on added particles to create roughness or simply replicate surface structures through embossing, this texture, formed from the inside out through molecular chain orientation and interface regulation, has a stronger bond with the coating bulk and is an integral part of the coating's structure. This avoids the risk of particle detachment or texture wear failure under mechanical friction, improving the durability of anti-stick properties. Finally, moderate stretching also helps eliminate internal stresses formed during the drying process, making the coating structure denser and further enhancing its mechanical strength and adhesion to the substrate.

[0029] In some embodiments, the heat-sealing substrate includes at least one of biaxially oriented polypropylene (BOPP), cast polypropylene (CPP), polyethylene (PE), and linear low-density polyethylene (LLDPE) film. These materials are chosen because they possess good heat-sealing properties, mechanical strength, and food safety, making them commonly used substrates in the food packaging industry. The selection of the substrate must consider its compatibility with the base coating and its own mechanical and thermal properties to ensure stability during subsequent stretching and processing.

[0030] In some embodiments, the stretching process involves heating to a temperature 10°C to 50°C above the glass transition temperature (Tg) of the heat-sealing substrate. Stretching within this temperature range is crucial. If the temperature is too low, the substrate itself remains in a glassy state with poor ductility, making it difficult to deform in tandem with the coating. This can easily lead to interfacial delamination or coating cracking due to mismatched deformation between the substrate and the coating. If the temperature is too high, the substrate may become excessively softened, resulting in unstable macroscopic dimensions and even uncontrollable thermal shrinkage. Simultaneously, the coating may become excessively cross-linked or degraded due to overheating, losing its plasticity. Maintaining the temperature within 10°C to 50°C above the substrate's Tg ensures that the substrate is in a highly elastic state, possessing sufficient ductility to accommodate coating deformation, while simultaneously maintaining sufficient modulus to support and transfer tensile stress. This is a key thermodynamic condition for successful micro-stretching.

[0031] In some embodiments, the stretching process is bidirectional stretching, with the longitudinal (MD) stretching ratio controlled at 0.5%~2% and the transverse (TD) stretching ratio controlled at 1%~3%. Bidirectional stretching is used to induce texture formation evenly in both dimensions, obtaining a more isotropic anti-stick surface and avoiding performance directional differences caused by unidirectional texture. The longitudinal stretching ratio is slightly lower than the transverse stretching ratio, usually considering that the substrate already has a certain orientation in the longitudinal direction due to previous production processes; an excessively high longitudinal stretching ratio may increase the risk of film breakage. If the stretching ratio is too low, the applied stress may not be sufficient to effectively induce sufficient orientation of the coating molecular chains and reconstruction of the interface structure, making it difficult to form significant and uniform nanotextures, resulting in limited improvement in anti-sticking effect. Conversely, if the stretching ratio is too high, it may exceed the elastic limit of the coating in the semi-cured state, leading to excessively large and uneven textures, or even causing microcracks in the coating or delamination from the substrate. It will also adversely affect the flatness and dimensional stability of the substrate, increasing the difficulty of production process control and the scrap rate.

[0032] In some embodiments, to optimize the overall mechanical properties and structural stability of the composite membrane, the topcoat is longitudinally stretched while the bottomcoat is transversely stretched, or vice versa. This cross-stretching design allows for the formation of molecular chain orientations and microtextures in different directions in the bottom and topcoats, respectively, thereby creating a stable network structure within the composite membrane that mutually constrains and reinforces each other. This helps balance the internal stress of the film in different directions, prevents curling, and improves the overall dimensional stability and mechanical strength of the composite membrane.

[0033] In some embodiments, the primer comprises, by mass percentage: 12.2%–22.5% hydrogenated styrene-butadiene block copolymer (SEBS), 14.8%–25.3% aliphatic polyurethane acrylate, 0.2%–5.8% γ-glycidyl etheroxypropyltrimethoxysilane, with the balance being a first solvent. In this formulation, SEBS, as the elastomer matrix, provides flexibility and initial tack to the polyolefin substrate, and its saturated carbon-carbon backbone structure endows the coating with excellent anti-aging properties. The aliphatic polyurethane acrylate contributes to good film-forming properties, abrasion resistance, and adhesion. γ-glycidyl etheroxypropyltrimethoxysilane, as an adhesion promoter, has methoxy groups in its molecule that hydrolyze under the action of water vapor to generate silanol groups, which can form strong Si-OM (M is a substrate surface atom) covalent bonds with the hydroxyl groups on the substrate surface; simultaneously, its epoxy groups can react with the active groups in SEBS or polyurethane during the curing process, thereby connecting at the coating-substrate interface, enhancing interfacial adhesion, and preventing the coating from peeling off during use. The first solvent is one or a mixture of methyl isobutyl ketone (MIBK), ethyl acetate (EA), methyl ethyl ketone (MEK), and isopropanol (IPA). The choice of solvent system needs to balance the solubility of each component and the appropriate evaporation rate to ensure coating leveling, avoid pinholes, and prevent corrosion of the substrate.

[0034] In some embodiments, the topcoat liquid comprises, by mass percentage: 25.2%–38.8% branched polyvinyl butyral (PVB), 12.4%–21.7% polyamide-imide (PAI), 2.5%–7.6% silica, with the balance being a second solvent. The topcoat layer is a functional layer that directly contacts the contents. Branched PVB provides mechanical strength, toughness, and transparency; its branched structure helps form a denser three-dimensional network. PAI imparts extremely high heat resistance, surface hardness, and dimensional stability to the coating; the imide rings in its molecules can form strong intermolecular hydrogen bonds with the hydroxyl groups of PVB, enhancing the cohesive strength of the composite resin matrix. Silica nanoparticles serve as functional fillers, with functions including, but not limited to: acting as hard particles in the coating to improve wear resistance; acting as stress concentration points during micro-stretching to guide and stabilize the formation of micro / nano textures; and possessing low surface energy to construct an anti-stick surface with the resin. The second solvent is a mixture of ethanol and propylene glycol methyl ether in a mass ratio of (2–1):1. This mixed solvent system exhibits excellent solubility for both PVB and PAI. Ethanol, as the main solvent, evaporates quickly, which helps the coating to initially set. Propylene glycol methyl ether, as a high-boiling-point solvent, evaporates slowly, maintaining a certain fluidity of the coating during the drying process. This promotes the uniform distribution of silica particles and the final leveling of the coating, preventing silica agglomeration or coating cracking due to excessively rapid solvent evaporation.

[0035] In some embodiments, the primary curing conditions are: curing at 35°C to 50°C for 12 to 24 hours; the secondary curing conditions are: curing at room temperature (typically 20°C to 30°C) for 24 to 48 hours. The curing process is not simply the complete evaporation of the solvent, but a crucial physicochemical process. Primary curing mainly targets the base coat. Under these mild heating conditions, the polymer chains gain sufficient mobility for rearrangement and relaxation, helping to eliminate internal stress. More importantly, it provides sufficient time and energy for γ-glycidyl etheroxypropyltrimethoxysilane to complete hydrolysis and undergo condensation reactions with the substrate surface and coating polymers, forming strong chemical bonds, thereby maximizing adhesion. Secondary curing, carried out at room temperature, is an economical and effective final stabilization process, bringing the top coat and the entire composite film structure to a final thermodynamic equilibrium state, releasing residual stress, and ensuring long-term performance stability.

[0036] In some embodiments, the primary drying conditions are: drying at 60°C to 90°C for 1 to 3 minutes; the secondary drying conditions are: drying at 70°C to 110°C for 2 to 5 minutes. The purpose of the drying process is to safely and efficiently remove most of the solvent, allowing the coating to initially set. The primary drying temperature is relatively low, focusing on removing solvent from the primer while avoiding overheating deformation of the heat-sealing substrate (such as PE, PP). The secondary drying temperature is increased, partly to thoroughly remove potentially high-boiling-point solvents from the topcoat, and partly because the higher temperature facilitates further imidization of PAI in the topcoat and promotes the final crosslinking of the resin system, thereby improving the heat resistance, hardness, and mechanical properties of the topcoat. The drying time is matched with the temperature, coating speed, and coating thickness to ensure sufficient solvent evaporation without the formation of bubbles or defects.

[0037] [Example 1] This embodiment provides a method for preparing an anti-adhesion composite film, including the following steps: S001. Preparation of primer: By mass percentage, dissolve 15.0% of hydrogenated styrene-butadiene block copolymer (number average molecular weight approximately 50,000 g / mol), 20.0% of aliphatic polyurethane acrylate, and 3.0% of γ-glycidyl etheroxypropyltrimethoxysilane in the remaining first solvent, which is a mixture of methyl isobutyl ketone and ethyl acetate in a mass ratio of 1:1. Stir at 50°C until completely dissolved to obtain the primer.

[0038] S002. The primer liquid is selectively roller-coated onto the inner surface of the heat-sealing substrate (biaxially oriented polypropylene BOPP) using an anilox roller, and then dried at 75°C for 2 minutes to form the primer coating.

[0039] S003. The substrate with the base coating is cured at 40°C for 18 hours.

[0040] S004. Preparation of topcoat solution: By mass percentage, dissolve 30.0% of branched polyvinyl butyral (solution viscosity approximately 45 mPa·s), 17.0% of polyamide-imide, and 5.0% of fumed silica in the remaining second solvent, which is a mixed solvent of ethanol and propylene glycol methyl ether in a mass ratio of 1.5:1. Stir and disperse evenly at 35°C to obtain the topcoat solution.

[0041] S005. The topcoat liquid is selectively roller-coated onto the surface of the cured base coating by positioning coating, and then dried again at 90°C for 3 minutes to form the topcoat.

[0042] S006. Before the topcoat has completely cooled (temperature approximately 50°C), emboss it using an embossing roller, then roll it up and allow it to cure for 36 hours at room temperature.

[0043] In step S005, after the surface coating has dried for the second time and is before it is fully cured, it is heated together with the BOPP heat-sealing substrate to 100°C (the Tg of BOPP is about 0°C, and the temperature is raised to about 100°C above Tg), and longitudinal stretching is performed, with the stretching ratio controlled at 1.0%.

[0044] The anti-adhesive composite film prepared in this embodiment has a texture with a width of approximately 80 nm and a depth of approximately 20 nm on its surface. Its contact angle with water is 154°. The peel strength between the coating and the substrate is 4.9 N / cm. After 7 days of accelerated aging testing at 85°C and 85% relative humidity, the contact angle remained at 150°, and the coating showed no peeling or wrinkling.

[0045] [Example 2] This embodiment provides a method for preparing an anti-adhesion composite film, including the following steps: S001. Preparation of primer: By mass percentage, dissolve 18.0% of hydrogenated styrene-butadiene block copolymer (number average molecular weight approximately 70,000 g / mol), 22.0% of aliphatic polyurethane acrylate, and 4.5% of γ-glycidyl etheroxypropyltrimethoxysilane in the remaining first solvent, which is a mixture of methyl ethyl ketone and isopropanol in a mass ratio of 2:1. Stir at 55°C until completely dissolved to obtain the primer.

[0046] S002. Using an anilox roller, selectively roll-coat the primer onto the inner surface of the heat-sealing substrate (cast polypropylene CPP), and then dry it once at 80°C for 1.5 minutes to form the primer coating. S003. Allow the substrate with the primer coating to cure at 45°C for 15 hours.

[0047] S004. Preparation of topcoat solution: By mass percentage, dissolve 32.0% of branched polyvinyl butyral (solution viscosity approximately 50 mPa·s), 19.0% of polyamide-imide, and 6.5% of fumed silica in the remaining second solvent, which is a mixed solvent of ethanol and propylene glycol methyl ether in a mass ratio of 2:1. Stir and disperse evenly at 40°C to obtain the topcoat solution.

[0048] S005. The topcoat liquid is selectively roller-coated onto the surface of the cured base coating by positioning coating, and then dried again at 100°C for 2.5 minutes to form the topcoat.

[0049] S006. Before the topcoat has completely cooled (temperature approximately 55°C), emboss it using an embossing roller, then roll it up and allow it to cure for 48 hours at room temperature.

[0050] In step S002, after the base coating has dried once and is before it is fully cured, it is heated to 70°C together with the CPP heat-sealing substrate and subjected to transverse stretching treatment, with the stretching ratio controlled at 2.0%.

[0051] The anti-adhesive composite film prepared in this embodiment has a texture with a width of approximately 150 nm and a depth of approximately 35 nm on its surface. Its contact angle with water is 156°. The peel strength between the coating and the substrate is 5.0 N / cm. After 7 days of accelerated aging testing, the contact angle is 152°.

[0052] [Example 3] This embodiment provides a method for preparing an anti-adhesive composite film, the steps of which are basically the same as those in Embodiment 1, the difference being in the process parameters of the stretching treatment: In step S005, after the surface coating has dried a second time but before it is fully cured, it is heated to 100°C together with the BOPP heat-sealing substrate and subjected to biaxial stretching treatment, wherein the longitudinal stretching ratio is controlled at 0.8% and the transverse stretching ratio is controlled at 1.5%. The anti-adhesive composite film obtained in this embodiment has a texture with a width of approximately 100 nm and a depth of approximately 25 nm on its surface. The contact angle with water is 155°. The peel strength between the coating and the substrate is 5.3 N / cm. After 7 days of accelerated aging testing, the contact angle is 151°.

[0053] [Example 4] This embodiment provides a method for preparing an anti-adhesive composite film, the steps of which are basically the same as those in Embodiment 2, the difference being in the process parameters of the stretching treatment: In step S002, after the base coating has dried once but before it is fully cured, it is heated to 70°C together with the CPP heat-sealing substrate and subjected to biaxial stretching treatment, wherein the longitudinal stretching ratio is controlled at 1.5% and the transverse stretching ratio is controlled at 2.5%. The anti-adhesive composite film obtained in this embodiment has a texture with a width of approximately 180 nm and a depth of approximately 45 nm on its surface. The contact angle with water is 157°. The peel strength between the coating and the substrate is 4.8 N / cm. After 7 days of accelerated aging testing, the contact angle is 153°.

[0054] [Example 5] This embodiment provides a method for preparing an anti-adhesion composite film, the steps of which are basically the same as those in Embodiment 3, the difference being the use of a cross-stretching strategy: In step S002, the base coating is subjected to unidirectional transverse stretching at a stretching ratio of 2.0%; in step S005, the top coating is subjected to unidirectional longitudinal stretching at a stretching ratio of 1.0%. Both stretching operations are performed after the corresponding coating has dried but before it has fully cured, by heating the substrate together with the base coating to a temperature 20°C above its Tg.

[0055] The anti-adhesive composite film prepared in this embodiment has anisotropic but uniformly distributed nanotextures on its surface. The contact angle with water is 155°. Due to cross-stretching optimizing the internal stress distribution, the peel strength between the coating and the substrate is increased to 5.5 N / cm. After 7 days of accelerated aging testing, the contact angle is 152°.

[0056] [Example 6] This embodiment provides a method for preparing an anti-adhesive composite film, the steps of which are basically the same as those in Example 1, the difference being the use of a lower stretching ratio and a different substrate: The heat-sealing substrate is linear low-density polyethylene (LLDPE). In step S005, after the topcoat has dried a second time but before it is fully cured, it is heated together with the LLDPE heat-sealing substrate to 85°C (the Tg of LLDPE is approximately -120°C, so the temperature is raised to approximately 205°C above the Tg), and then subjected to unidirectional (longitudinal) stretching treatment, with the stretching ratio controlled at 0.6%.

[0057] The anti-adhesive composite film prepared in this embodiment has a finer texture on its surface, with a width of approximately 50 nm and a depth of approximately 10 nm. Its contact angle with water is 153°. The peel strength between the coating and the substrate is 4.7 N / cm. After 7 days of accelerated aging testing, the contact angle is 149°.

[0058] [Comparative Example 1] This comparative example provides an anti-adhesion composite film and its preparation method.

[0059] The anti-stick composite film comprises a heat-sealable substrate stacked together and an anti-stick coating partially covering the surface of the heat-sealable substrate. The heat-sealable substrate is a biaxially oriented polypropylene (BOPP) film. The anti-stick coating is applied to the inner surface of the BOPP film by positioning, such that the inner surface forms an anti-stick area with the anti-stick coating and a heat-sealable area without the anti-stick coating. The anti-stick coating comprises a base coating and a top coating sequentially along the direction away from the heat-sealable substrate.

[0060] Based on the total mass of the base coating, the base coating comprises, by mass percentage, 15.0% hydrogenated styrene-butadiene block copolymer, 20.0% aliphatic polyurethane acrylate, 3.0% γ-glycidyl etheroxypropyltrimethoxysilane, and the balance being a first solvent. The first solvent is a mixture of toluene and ethyl acetate in a mass ratio of 1:1.

[0061] Based on the total mass of the topcoat, the topcoat comprises, by mass percentage, 30.0% branched polyvinyl butyral, 17.0% polyamide-imide, 5.0% silica, with the balance being a second solvent. The second solvent is a mixture of ethanol and propylene glycol methyl ether in a mass ratio of 1.5:1.

[0062] Its preparation method includes the following steps: S001. Hydrogenated styrene-butadiene block copolymer and aliphatic polyurethane acrylate are dissolved in the first solvent and stirred at 50°C until completely dissolved. γ-glycidyl etheroxypropyltrimethoxysilane is added and stirred evenly to obtain the primer. S002. The primer liquid is selectively roller-coated onto the inner surface of the BOPP heat-sealing substrate using an anilox roller, and then dried at 75°C for 2 minutes to form the primer coating. S003. The substrate with the base coating is cured at 40°C for 18 hours. S004. Dissolve branched polyvinyl butyral and polyamide-imide in a second solvent and stir until completely dissolved. Then add silica and stir to disperse evenly at 35°C to obtain a topcoat liquid. S005. The topcoat liquid is selectively roller-coated onto the surface of the cured base coating by positioning coating, and then dried again at 90°C for 3 minutes to form the topcoat. S006. Before the topcoat has completely cooled, emboss it using an embossing roller, then roll it up and allow it to cure again at room temperature for 36 hours. After the anti-stick coating is applied and cured by the anilox roller, a texture with a width of 100 nm and a depth of 25 nm is formed on its surface.

[0063] The anti-stick composite film prepared in this comparative example has a contact angle of 152° with water in the anti-stick area. The peel strength is 4.5 N / cm. After 7 days of accelerated aging test at 85℃ and 85% relative humidity, the contact angle remains at 148°, and the coating shows no peeling or wrinkling.

[0064] [Comparative Example 2] The difference between this comparative example and Example 4 is that the micro-stretching treatment described above was not performed in step S002. The remaining steps and formulation are exactly the same as in Example 4. The composite film obtained in this comparative example has a regular surface texture but lacks a nanoscale fine structure. Its contact angle with water is 145°. The peel strength between the coating and the substrate is 4.1 N / cm. After 7 days of accelerated aging testing, the contact angle decreased to 135°.

[0065] [Comparative Example 3] This comparative example uses a commercially available packaging film with a fluorinated anti-stick coating. The contact angle of this commercially available film with water is 142°. Its peel strength from the substrate is 3.2 N / cm. After 7 days of accelerated aging testing, the contact angle decreased to 130°, and localized coating cracking occurred.

[0066] [Comparative Example 4] This comparative example uses commercially available ordinary polyethylene (PE) packaging film. The film surface has no functional anti-stick coating. The contact angle between this PE film and water is 85°. Its peel strength to its own substrate was not tested. After 7 days of accelerated aging testing, there was no significant change in the contact angle. Significant residue was observed in sauce-type products.

[0067] 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 an anti-adhesive composite film, characterized in that, Includes the following steps: S001. Prepare the primer; S002. The primer liquid is selectively roller-coated onto the inner surface of the heat-sealing substrate using an anilox roller, followed by a drying process to form a primer coating layer. S003. The substrate with the base coating is cured once; S004. Prepare the topcoat liquid; S005. The topcoat liquid is selectively roller-coated onto the surface of the cured base coating by positioning coating, and then dried a second time to form the topcoat. S006. Before the topcoat has completely cooled, use an embossing roller to emboss it, then roll it up and perform a second curing. In S002 and / or S005, before the base coating and / or top coating are fully cured, they are heated together with the heat-sealing substrate and subjected to a stretching treatment. The stretching ratio of the stretching treatment is controlled at 0.5% to 3%, so that the surface of the base coating and / or top coating has a texture with a width of 20nm to 200nm and a depth of 5nm to 50nm.

2. The preparation method according to claim 1, characterized in that, The heat-sealing substrate includes at least one of biaxially oriented polypropylene, cast polypropylene, polyethylene, and linear low-density polyethylene film.

3. The preparation method according to claim 2, characterized in that, In the stretching process, the temperature is raised to 10°C to 50°C above the glass transition temperature of the heat-sealing substrate.

4. The preparation method according to claim 2, characterized in that, The stretching process is bidirectional stretching, with the longitudinal stretching ratio controlled at 0.5% to 2% and the transverse stretching ratio controlled at 1% to 3%.

5. The preparation method according to claim 4, characterized in that, When the topcoat is stretched longitudinally or transversely, the bottomcoat is stretched transversely or longitudinally accordingly.

6. The preparation method according to claim 1, characterized in that, The primer, by mass percentage, comprises: 12.2%~22.5% hydrogenated styrene-butadiene block copolymer, 14.8%~25.3% aliphatic polyurethane acrylate, 0.2%~5.8% γ-glycidyl etheroxypropyltrimethoxysilane, with the balance being a first solvent; the first solvent is one or a mixture of methyl isobutyl ketone, ethyl acetate, methyl ethyl ketone, and isopropanol.

7. The preparation method according to claim 1, characterized in that, The topcoat liquid comprises, by mass percentage: 25.2%~38.8% branched polyvinyl butyral, 12.4%~21.7% polyamide-imide, 2.5%~7.6% silica, with the balance being a second solvent; the second solvent is a mixed solvent composed of ethanol and propylene glycol methyl ether in a mass ratio of (2~1):

1.

8. The preparation method according to any one of claims 1-7, characterized in that, The conditions for the first curing are: curing at 35℃~50℃ for 12~24 hours; the conditions for the second curing are: curing at room temperature for 24~48 hours.

9. The preparation method according to any one of claims 1-7, characterized in that, The conditions for the first drying are: drying at a temperature of 60℃~90℃ for 1~3 minutes; the conditions for the second drying are: drying at a temperature of 70℃~110℃ for 2~5 minutes.

10. An anti-adhesive composite film, characterized in that, It is prepared by the method described in any one of claims 1-7.

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