Ultra-high molecular weight polyethylene functional color printing composite packaging film

Abstract

This invention relates to the field of polymer molding materials. A functional color-printed composite packaging film of ultra-high molecular weight polyethylene is disclosed, which is formed by curing a polyethylene film substrate, p-hydroxybenzoic acid, polyethylene glycol diacrylate, laccase, and acrylate ink monomers. The film is formed by covalently coupling quinone radicals generated from p-hydroxybenzoic acid and polyethylene glycol diacrylate under laccase catalysis to the substrate surface, forming a polyethylene glycol grafted interlayer. Subsequently, ultraviolet light-initiated polymerization is performed on the surface of the interlayer to form a cross-linked and cured ink layer. This method utilizes the covalently bonded grafted interlayer to block the rearrangement of non-polar molecular chains of the substrate to the surface, maintaining surface polarity stability, and enabling the ink layer and substrate to possess the highest standard peel strength, with no blistering or peeling of the ink layer under boiling water conditions.

Description

Technical Field

[0001] This invention relates to the field of polymer molding materials. A functional color-printed composite packaging film of ultra-high molecular weight polyethylene is disclosed. Background Technology

[0002] Ultra-high molecular weight polyethylene (UHMWPE) is often used as the substrate for composite packaging films due to its high tensile strength and chemical resistance. In the production of color-printed composite packaging films, the adhesion between the ink layer and the substrate depends on the polarity of the substrate surface. Current technologies commonly employ corona treatment or plasma treatment for surface modification. These two methods generate high-energy particles through high-frequency electric field discharge. These particles bombard the UHMWPE film surface, breaking the non-polar carbon-carbon and carbon-hydrogen bonds and generating polar groups such as carboxyl and hydroxyl groups. After bombardment treatment, the operator feeds the film material with these polar groups into the printing process, allowing the ink containing acrylate monomers to spread and cure on the film surface.

[0003] The technical problems with the above-mentioned conventional treatment methods are as follows: the polar groups generated by corona or plasma bombardment exist only in the very shallow surface layer of the membrane material, and the bombardment process disrupts the original equilibrium state of the polymer chains. After surface treatment, the non-polar molecular chains inside the ultra-high molecular weight polyethylene substrate will spontaneously rearrange themselves towards the surface to reduce the surface energy of the system. This spontaneous rearrangement of molecular chains will roll over and wrap the previously generated polar groups into the interior of the membrane material, causing the surface polarity of the membrane material to decay over time. This results in the ink layer cured on the surface losing its polar anchoring effect with the substrate, leading to ink layer peeling failure during subsequent boiling water cooking. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a functional color-printed composite packaging film made of ultra-high molecular weight polyethylene (UHMWPE). The composite packaging film is prepared from raw materials comprising the following parts by weight: 100 parts UHMWPE film substrate, 15-30 parts p-hydroxybenzoic acid, 25-50 parts polyethylene glycol diacrylate, 1-5 parts laccase, 120-200 parts buffer solution, and 60-80 parts acrylate ink monomers. The p-hydroxybenzoic acid and the polyethylene glycol diacrylate form a polyethylene glycol grafted interlayer on the surface of the UHMWPE film substrate under the catalysis of the laccase. The acrylate ink monomers form a cross-linked cured ink layer on the surface of the polyethylene glycol grafted interlayer.

[0005] In practice, laccase, as a copper-containing polyphenol oxidase, can specifically catalyze the single-electron oxidation of the phenolic hydroxyl groups of the phenolic substrate p-hydroxybenzoic acid, generating highly active quinone radicals. In the reaction system, the quinone radicals can attack the methylene CH bonds on the surface of the ultra-high molecular weight polyethylene film substrate, forming alkyl radicals on the substrate surface through hydrogen extraction reaction, achieving covalent bonding with the substrate backbone. On the other hand, they can undergo radical addition and graft polymerization with the end double bonds of polyethylene glycol diacrylate, thereby forming a covalently coupled polyethylene glycol grafted intermediate layer in situ on the substrate surface. This grafted intermediate layer is bound to the substrate through stable covalent bonds, which can effectively block the spontaneous rearrangement of non-polar molecular chain segments inside the substrate to the surface, avoiding the attenuation of polar groups by encapsulation. At the same time, the residual acrylate active double bonds in the grafted intermediate layer can undergo radical copolymerization with acrylate ink monomers, making the ink layer and the grafted intermediate layer a covalently bonded whole, greatly improving interlayer adhesion and boiling resistance.

[0006] Furthermore, in the above technical solution, the buffer component is an acetate-sodium acetate buffer solution with a pH value of 5.0. The buffer component also contains 5-15 parts by mass of a co-solvent, which is a mixed solvent composed of N,N-dimethylformamide and deionized water in a volume ratio of 1:3.

[0007] In practice, the acetate-sodium acetate buffer can stabilize the pH of the reaction system within the optimal acidic range for laccase catalysis, maintain the copper ion coordination environment and protein spatial conformation stability of the laccase active site, and ensure the catalytic efficiency of laccase. The cosolvent composed of N,N-dimethylformamide and deionized water in a volume ratio of 1:3 can balance substrate solubility and enzyme activity stability. N,N-dimethylformamide can significantly improve the solubility of p-hydroxybenzoic acid and polyethylene glycol diacrylate in the aqueous buffer system, avoiding substrate precipitation and uneven reaction. Deionized water can adjust the polarity of the system and prevent excessive concentration of organic solvent from causing denaturation and inactivation of laccase protein.

[0008] Furthermore, in the above technical solution, the number average molecular weight of the polyethylene glycol diacrylate is 600-1000 Daltons, the conversion rate of the end double bonds of the polyethylene glycol diacrylate is greater than 85%, and the composite packaging film also contains 2-8 parts by weight of nano-silica particles, the surface of which is grafted with acrylate groups that match the polyethylene glycol diacrylate.

[0009] In practice, polyethylene glycol diacrylate with a number-average molecular weight of 600-1000 Daltons has a moderate chain length, which can form a continuous and complete polar grafted intermediate layer on the substrate surface, while avoiding molecular entanglement caused by excessively long chain segments, resulting in uneven surface polarity distribution. The end-group double bond conversion rate of more than 85% can ensure that the polyethylene glycol chain segments grafted to the substrate surface retain sufficient active double bond sites, providing sufficient reaction sites for subsequent copolymerization and crosslinking of ink monomers, and improving interlayer bonding. The nano-silica particles with acrylate groups grafted on the surface can participate in the crosslinking reaction between the grafted intermediate layer and the ink layer through double bonds, and are uniformly dispersed in the film system. This not only improves the mechanical strength and scratch resistance of the composite film, but also avoids the agglomeration and sedimentation of nanoparticles through surface modification.

[0010] Furthermore, in the above technical solution, the laccase is an immobilized laccase immobilized with magnetic iron oxide nanoparticles, wherein the mass ratio of laccase to magnetic iron oxide nanoparticles in the immobilized laccase is 1:5-1:10, and the surface of the magnetic iron oxide nanoparticles is modified with a carboxymethylated chitosan layer.

[0011] In practice, the carboxymethylated chitosan layer modified on the surface of magnetic iron oxide nanoparticles contains a large number of active amino and hydroxyl groups, which can covalently fix laccase molecules, preventing laccase from falling off in the reaction system. At the same time, the hydrophilic microenvironment formed by chitosan can maintain the spatial conformational stability of laccase, improving its catalytic activity and reusability. The magnetic iron oxide nanoparticles endow the immobilized laccase with superparamagnetism, which can achieve rapid solid-liquid separation by applying an external magnetic field. The mass ratio of 1:5 to 1:10 ensures both the effective immobilization load of laccase and avoids the active sites of laccase being encapsulated and shielded due to excessive carrier, thus ensuring the efficiency of the catalytic reaction.

[0012] Furthermore, in the above technical solution, the acrylate ink monomer is composed of methyl methacrylate, isoborneol acrylate, and fluorinated acrylate monomer in a mass ratio of 3:1:1, wherein the fluorinated acrylate monomer is perfluoroalkyl ethyl acrylate, and the composite packaging film also contains 1-3 parts by mass of photoinitiator.

[0013] In practice, methyl methacrylate, as a hard monomer, can improve the hardness, scratch resistance, and color stability of the cross-linked cured ink layer; isoborneol acrylate, with its rigid alicyclic structure, can effectively reduce the volume shrinkage rate during the polymerization process of the ink system, reduce curing internal stress, and improve the adhesion between the ink layer and the grafted intermediate layer; perfluoroalkyl ethyl acrylate can significantly reduce the surface energy of the ink layer, giving the composite film excellent water resistance, oil resistance, and media resistance; the three are compounded in a mass ratio of 3:1:1, which can synergistically take into account the mechanical properties, adhesion, and protective properties of the ink layer; the photoinitiator can decompose under ultraviolet light to generate active free radicals, which can efficiently initiate the free radical polymerization of the double bonds of acrylate ink monomers, achieving rapid cross-linking and curing of the ink layer.

[0014] Furthermore, in the above technical solution, the thickness of the polyethylene glycol grafted intermediate layer is 0.1-0.5 micrometers, the thickness of the cross-linked cured ink layer is 5-15 micrometers, the mass ratio of the polyethylene glycol grafted intermediate layer to the cross-linked cured ink layer is 1:20-1:50, and the cross-linked cured ink layer also contains 0.5-2 parts by mass of hindered amine light stabilizer and 0.5-2 parts by mass of benzotriazole ultraviolet absorber.

[0015] In practice, a polyethylene glycol grafted interlayer thickness of 0.1-0.5 micrometers ensures that the substrate surface is completely covered by the polar grafted layer, effectively blocking the spontaneous rearrangement of non-polar chain segments in the substrate, while avoiding excessive layer thickness that could affect the overall flexibility and light transmittance of the composite film; a cross-linked cured ink layer thickness of 5-15 micrometers balances the color saturation of printed patterns with the processing adaptability of the composite film; a mass ratio of 1:20-1:50 ensures that the grafted interlayer provides sufficient polar anchoring sites and covalent bonding sites for the ink layer, avoiding insufficient interlayer bonding; hindered amine light stabilizers can inhibit the oxidative degradation of the ink layer under ultraviolet light irradiation by capturing free radicals and decomposing hydrogen peroxide, while benzotriazole ultraviolet absorbers can convert ultraviolet light energy into harmless heat energy through intramolecular proton transfer. The synergistic effect of these two agents significantly improves the anti-ultraviolet aging performance of the ink layer and extends the service life of the composite film.

[0016] To prepare the above-mentioned ultra-high molecular weight polyethylene (UHMWPE) functional color-printed composite packaging film, the present invention also provides a method for preparing the UHMWPE functional color-printed composite packaging film, the method comprising the following technical features: Step S1, mixing buffer components, p-hydroxybenzoic acid, and polyethylene glycol diacrylate uniformly to obtain a substrate mixture; Step S2, adding laccase to the substrate mixture and initiating a catalytic reaction to generate quinone free radicals under controlled oxygen conditions; Step S3, immersing the UHMWPE film substrate in a reaction system containing the quinone free radicals, so that the quinone free radicals covalently couple on the surface of the UHMWPE film substrate to form a polyethylene glycol grafted interlayer; Step S4, removing the coupled UHMWPE film substrate and cleaning and drying it; Step S5, immersing the cleaned and dried UHMWPE film substrate in a solution containing acrylate ink monomers, initiating polymerization by ultraviolet light irradiation, so that the acrylate ink monomers crosslink and solidify into a film on the polyethylene glycol grafted interlayer.

[0017] In practice, this preparation method achieves controllable preparation of composite packaging films by stepwise regulating the enzyme-catalyzed grafting reaction and the UV-cured polymerization reaction. Step S1 involves premixing to prepare a homogeneous substrate mixture, providing a stable substrate environment for the laccase-catalyzed reaction. Step S2 initiates the laccase-catalyzed reaction under oxygen-controlled conditions to prevent oxygen from quenching the generated quinone free radicals and ensure that the concentration of quinone free radicals in the system meets the requirements of the grafting reaction. Step S3 involves immersing the substrate into the reaction system, allowing quinone free radicals to undergo in-situ covalent coupling and grafting polymerization on the substrate surface, forming a polyethylene glycol grafted intermediate layer covalently bonded to the substrate main chain, thus preventing the attenuation of polar groups from the source. Step S4 involves cleaning and drying to remove unreacted substrate and residual enzymes from the substrate surface, preventing impurities from affecting the subsequent ink curing effect. Step S5 involves UV irradiation to induce copolymerization and crosslinking between the ink monomers and the active double bonds of the grafted intermediate layer, forming a crosslinked cured ink layer covalently bonded to the grafted intermediate layer, ensuring the interlayer adhesion and retort resistance of the composite film.

[0018] Furthermore, in the above technical solution, in step S1, the buffer solution component, the p-hydroxybenzoic acid and the polyethylene glycol diacrylate are mixed evenly at a temperature of 25-35°C. During the mixing process, nitrogen gas is continuously introduced into the substrate mixture to control the dissolved oxygen content to 3-5 mg / L. The mixing time in step S1 is 30-60 minutes.

[0019] In practice, a mixing temperature of 25-35℃ matches the optimal catalytic temperature range of laccase, ensuring sufficient dissolution of the substrate in the buffer system while avoiding the impact of excessively high or low temperatures on the subsequent catalytic activity of laccase. Continuously introducing nitrogen gas to control the dissolved oxygen level in the system at 3-5 mg / L can reduce the dissolved oxygen in the system in advance, preventing the quinone free radicals generated in the subsequent catalytic reaction from being quenched by oxygen, and also preventing excessive oxidation and inactivation of laccase in a high-oxygen environment. A mixing time of 30-60 minutes ensures that all substrate components are fully dissolved and mixed evenly, forming a homogeneous and stable substrate mixture, providing a uniform reaction environment for the subsequent catalytic reaction.

[0020] Furthermore, in the above technical solution, in step S2, the added laccase is immobilized laccase. After the catalytic reaction is initiated in step S2 and the coupling reaction in step S3 is completed, the immobilized laccase is separated from the reaction system by applying an external magnetic field with an intensity of 0.1-0.5 Tesla. The direction of application of the external magnetic field is perpendicular to the surface of the ultra-high molecular weight polyethylene film substrate.

[0021] In practice, an external magnetic field strength of 0.1-0.5 Tesla can generate sufficient magnetic adsorption force on the magnetic iron oxide carrier in the immobilized laccase, enabling rapid and efficient separation of the immobilized laccase from the reaction system. This avoids laccase residue on the reaction system or substrate surface, which could affect the uniformity of subsequent ink curing and interlayer bonding. The direction of the applied magnetic field is perpendicular to the surface of the ultra-high molecular weight polyethylene film substrate, which can guide the immobilized laccase to move towards the magnetic field source in a direction perpendicular to the substrate, avoiding adsorption and residue of immobilized laccase on the substrate surface and ensuring the cleanliness of the substrate surface. At the same time, the separated and recovered immobilized laccase can be reused for catalytic reactions, reducing production costs.

[0022] Furthermore, in the above technical solution, in step S5, the solution containing acrylate ink monomers also contains a photoinitiator, which is a compound initiator composed of 1-hydroxycyclohexylphenyl ketone and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide. The ultraviolet irradiation is performed by alternating between a main wavelength light source with a wavelength of 365 nm and an auxiliary wavelength light source with a wavelength of 395 nm. The single cycle of the alternating irradiation is 5 seconds, and the total time of ultraviolet irradiation is 30-60 seconds. The ambient temperature during the ultraviolet irradiation process is controlled at 40-50℃.

[0023] In specific implementation, 1-hydroxycyclohexylphenyl ketone is a short-wave ultraviolet initiator with extremely high initiation activity under a 365 nm main wavelength light source, which can rapidly initiate the polymerization and curing of monomers on the surface of the ink layer; bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide is a long-wave ultraviolet initiator with excellent penetration under a 395 nm auxiliary wavelength light source, which can effectively initiate the polymerization and curing of monomers in the deeper layers of the ink layer. The combination of the two can achieve synchronous curing of the ink layer from the surface to the depth, avoiding uneven shrinkage and excessive internal stress in the inner layer caused by the surface layer curing first; 365 nm and 3 Alternating irradiation with a 95nm light source and a single 5-second irradiation cycle allows for precise control of the polymerization rate of ink monomers, avoiding stress concentration caused by excessively rapid polymerization and reducing ink layer shrinkage and warping. A total irradiation time of 30-60 seconds ensures that the ink monomers are fully cross-linked and cured, forming a dense and uniform ink film. An ambient temperature of 40-50℃ enhances the molecular mobility of ink monomers, reduces the viscosity of the polymerization system, promotes the full progress of the cross-linking reaction, and further eliminates internal stress during curing, thereby improving the bonding force between the ink layer and the polyethylene glycol grafted intermediate layer.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] This invention solves the problem of print layer peeling failure caused by the spontaneous decay of polar groups over time by constructing a covalently coupled polyethylene glycol grafted interlayer on the surface of ultra-high molecular weight polyethylene film. This method uses p-hydroxybenzoic acid and polyethylene glycol diacrylate as substrates, generating quinone radicals under the catalysis of laccase. These quinone radicals directly undergo a covalent coupling reaction on the film surface to form the grafted interlayer. This interlayer is covalently bonded to the substrate backbone, blocking the rearrangement of non-polar molecular chains within the substrate to the surface, maintaining the stability of surface polarity. This ensures that the peel strength of the subsequently cured cross-linked ink layer reaches the highest standard, and the ink layer does not bubble or peel off after boiling water treatment.

[0026] This method maintains the pH environment for the laccase-catalyzed reaction by limiting the buffer components and co-solvent system, thereby improving the solubility of p-hydroxybenzoic acid in the reaction system. By employing immobilized laccase encapsulated with magnetic iron oxide nanoparticles and using an external magnetic field, the immobilized laccase can be separated from the reaction system after the coupling reaction, preventing laccase residue on the film surface from affecting subsequent ink curing. Adding hindered amine light stabilizers and benzotriazole UV absorbers to the acrylate ink monomers enhances the UV aging resistance of the cross-linked cured ink layer. Using alternating primary and secondary wavelength UV light curing methods in conjunction with a compound photoinitiator regulates the polymerization rate of the ink monomers, reducing the internal stress of the ink layer during the cross-linking and curing process. Detailed Implementation

[0027] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0028] The raw materials and reagents used in the embodiments and comparative examples of this invention are all commercially available conventional industrial-grade products. The immobilized laccase used was prepared by a conventional covalent bonding method in the art, specifically: carboxymethylated chitosan-modified magnetic iron oxide nanoparticles were dispersed in an acetate-sodium acetate buffer solution, laccase was added according to the ratio, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide were added, the mixture was stirred at room temperature for 4 hours, and the product was obtained after separation and washing under an external magnetic field. The test methods used were all conventional standard test methods in the art.

[0029] Example 1: Raw material formula (by mass parts):

[0030] 100 parts of ultra-high molecular weight polyethylene film substrate (12 μm thickness), 25 parts of p-hydroxybenzoic acid, 38 parts of polyethylene glycol diacrylate (number average molecular weight 800 Daltons, end-group double bond conversion rate 92%), 3 parts of immobilized laccase (laccase and carboxymethyl chitosan-modified magnetic iron oxide nanoparticles mass ratio 1:8), 160 parts of acetate-sodium acetate buffer (pH 5.0), and 10 parts of cosolvent (a mixture of N,N-dimethylformamide and deionized water at a volume ratio of 1:3). The composition includes 5 parts of surface-grafted modified nano-silica particles, 70 parts of acrylic ink monomers (methyl methacrylate: isoborneol acrylate: perfluoroalkyl ethyl acrylate mass ratio = 3:1:1), 2 parts of photoinitiator (1-hydroxycyclohexylphenyl ketone: bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide mass ratio = 1:1), 1.2 parts of hindered amine light stabilizer (HALS-944), and 1.2 parts of benzotriazole ultraviolet absorber (UV-327).

[0031] Preparation method:

[0032] Step S1: Preparation of substrate mixture: According to the above formula, add acetate-sodium acetate buffer, co-solvent, p-hydroxybenzoic acid, polyethylene glycol diacrylate, and surface acrylate-grafted modified nano-silica particles into a closed reactor. Control the system temperature at 30°C and continuously introduce high-purity nitrogen gas at a flow rate of 0.5 L / min until the dissolved oxygen content of the system drops to 3-5 mg / L. Mix at a stirring rate of 300 r / min for 45 minutes to obtain a homogeneous and stable substrate mixture. Step S2: Initiation of enzyme-catalyzed reaction: Add the prescribed amount of immobilized laccase to the above substrate mixture, maintain nitrogen gas flow and system temperature at 30°C, and initiate the laccase-catalyzed reaction under controlled oxygen and light-protected conditions. Stir the reaction for 10 minutes to generate quinone radical intermediates. Step S3 In-situ grafting coupling reaction: The ultra-high molecular weight polyethylene film substrate, which has been ultrasonically cleaned with anhydrous ethanol for 5 minutes and vacuum dried, is completely immersed in the above reaction system containing quinone free radicals. The system temperature is maintained at 30°C and oxygen and light are controlled. The reaction is stirred for 60 minutes to allow quinone free radicals to undergo hydrogen extraction, free radical addition and grafting polymerization on the surface of the substrate, forming a covalently coupled polyethylene glycol grafted intermediate layer in situ. Step S4 Immobilized Laccase Separation and Substrate Post-treatment: After the grafting reaction, an external magnetic field of 0.3 Tesla perpendicular to the substrate surface is applied to the bottom of the reactor. After standing for 15 minutes, the immobilized laccase is completely adsorbed and settled at the bottom of the reactor, completing the solid-liquid separation. The substrate is taken out and ultrasonically cleaned three times with deionized water for 5 minutes each time to remove unreacted substrate and impurities on the surface. Then it is placed in a vacuum drying oven at 40℃ and dried for 12 hours to obtain a surface-grafted modified ultra-high molecular weight polyethylene film substrate, wherein the thickness of the polyethylene glycol grafted interlayer is 0.3 μm. Step S5: Preparation of UV-cured ink layer: According to the formula, acrylate ink monomers, photoinitiators, hindered amine light stabilizers, and benzotriazole UV absorbers are mixed evenly to prepare an ink solution; the modified substrate obtained in step S4 is completely immersed in the ink solution, and after immersion for 30 seconds, it is pulled up at a uniform speed to control the wet film thickness. Then it is placed in a UV curing chamber, and the ambient temperature is controlled at 45℃. The 365nm main wavelength light source and the 395nm auxiliary wavelength light source are alternately irradiated, with a single alternation cycle of 5 seconds and a total irradiation time of 45 seconds. This allows the ink monomers and the active double bonds of the grafted intermediate layer to undergo free radical copolymerization and crosslinking, forming a crosslinked cured ink layer on the surface of the grafted intermediate layer. The ink layer thickness is 10μm, thus obtaining a functional color-printed composite packaging film of ultra-high molecular weight polyethylene.

[0033] Example 2: In this example, the mass fraction of p-hydroxybenzoic acid in the formula was adjusted to 15 parts. The other raw material components, dosages, and preparation process parameters were completely consistent with those in Example 1, and a functional color-printed composite packaging film of ultra-high molecular weight polyethylene was prepared.

[0034] Example 3: In this example, the mass fraction of p-hydroxybenzoic acid in the formula was adjusted to 30 parts. The other raw material components, dosages, and preparation process parameters were completely consistent with those in Example 1, and a functional color-printed composite packaging film of ultra-high molecular weight polyethylene was prepared.

[0035] Example 4: In this example, the number average molecular weight of polyethylene glycol diacrylate in the formula was adjusted to 600 Daltons. The other raw material components, dosages, and preparation process parameters were completely consistent with those in Example 1, and a functional color-printed composite packaging film of ultra-high molecular weight polyethylene was prepared.

[0036] Example 5: In this example, only the number average molecular weight of polyethylene glycol diacrylate in the formula was adjusted to 1000 Daltons. The other raw material components, dosages, and preparation process parameters were completely consistent with those in Example 1, and a functional color-printed composite packaging film of ultra-high molecular weight polyethylene was prepared.

[0037] Example 6: In this example, the only difference is that the mass ratio of immobilized laccase to carboxymethylated chitosan-modified magnetic iron oxide nanoparticles in the formula is adjusted to 1:10. All other raw material components, dosages, and preparation process parameters are completely consistent with those in Example 1. A functional color-printed composite packaging film of ultra-high molecular weight polyethylene is prepared.

[0038] Example 7: The raw material components and dosages in this example are completely consistent with those in Example 1. The only difference is that the mixing temperature in step S1 of the preparation method is adjusted to 25°C and the stirring and mixing time is adjusted to 60 minutes. All other preparation process parameters are completely consistent with those in Example 1. A functional color-printed composite packaging film of ultra-high molecular weight polyethylene is prepared.

[0039] Example 8: The raw material components and dosages in this example are completely consistent with those in Example 1. The only difference is that the total UV irradiation time in step S5 of the preparation method is adjusted to 60 seconds and the ambient temperature during the irradiation process is adjusted to 50°C. All other preparation process parameters are completely consistent with those in Example 1. A functional color-printed composite packaging film of ultra-high molecular weight polyethylene is prepared.

[0040] Comparative Example 1: This comparative example only removed the p-hydroxybenzoic acid component from the formula. The remaining raw material components, dosages, and preparation process parameters were completely consistent with those in Example 1, and a composite packaging film was prepared.

[0041] Comparative Example 2: This comparative example uses the conventional corona treatment process described in the background art, as follows:

[0042] Raw material formula (by mass parts):

[0043] 100 parts of ultra-high molecular weight polyethylene film substrate (same as Example 1), 70 parts of acrylic ink monomer (same as Example 1), 2 parts of photoinitiator (same as Example 1), 1.2 parts of hindered amine light stabilizer (same as Example 1), and 1.2 parts of benzotriazole ultraviolet absorber (same as Example 1).

[0044] Preparation method:

[0045] The ultra-high molecular weight polyethylene film substrate was subjected to corona treatment with a power of 2.0 kW and a speed of 10 m / min. Immediately after treatment, it was immersed in an ink solution (the same ink solution as in step S5 of Example 1). After immersion for 30 seconds, it was pulled up at a uniform speed and then cured using the same ultraviolet curing process as in Example 1. The ink layer thickness was 10 μm, and a composite packaging film was prepared.

[0046] Comparative Example 3: In this comparative example, the pH value of the acetate-sodium acetate buffer solution in the formula was adjusted to 7.0, which exceeds the 5.0 limit of this invention. The other raw material components, dosages, and preparation process parameters were completely consistent with those in Example 1, and a composite packaging film was prepared.

[0047] Comparative Example 4: This comparative example omits the high-purity nitrogen gas introduction operation in steps S1 and S2 of the preparation method and does not perform oxygen control protection. The other raw material components, dosages, and preparation process parameters are completely consistent with those in Example 1, and a composite packaging film is prepared.

[0048] Test method:

[0049] Peel strength test: According to GB / T8808-2008 "Peel test method for flexible composite plastic materials", the T-peel strength of the sample was tested using a universal testing machine. The sample width was 15 mm, the tensile speed was 300 mm / min, and 5 parallel samples were tested in each group. The average value was taken, and the unit was N / 15 mm.

[0050] Boiling resistance test: The sample was boiled in boiling water at 100℃ under normal pressure for 30 minutes. After being removed, the surface moisture was absorbed with filter paper and left at room temperature for 2 hours. The peel strength after boiling was tested according to the above method, and the peel strength retention rate was calculated (peel strength after boiling / initial peel strength × 100%). At the same time, the appearance of the ink layer of the sample was observed visually, and the presence of blistering or peeling was recorded.

[0051] Surface water contact angle test: Using a contact angle measuring instrument, the static contact angle of deionized water on the sample surface was tested under the conditions of room temperature and 50% relative humidity. The sample volume was 5μL, and 5 different positions were tested for each sample. The average value was taken. The smaller the contact angle, the stronger the polarity of the sample surface.

[0052] UV aging resistance test: The samples were subjected to a 240-hour UV aging test according to GB / T16422.2-2014 "Laboratory Light Source Exposure Test Method for Plastics Part 2: Xenon Arc Lamp". The yellow index of the samples before and after aging was tested according to GB / T2409-2008 "Test Method for Yellow Index of Plastics". The yellowing index ΔYI was calculated. The smaller the ΔYI, the better the UV aging resistance of the sample.

[0053] Immobilized laccase recovery rate test: After the grafting reaction, the immobilized laccase was separated by an external magnetic field. The enzyme activity of the recovered immobilized laccase was tested by the ABTS method, and the enzyme activity recovery rate was calculated as (total enzyme activity of recovered immobilized laccase / total enzyme activity of initially added immobilized laccase × 100%).

[0054] Test results:

[0055] Table 1 Performance test results of each embodiment and comparative example

[0056] Sample number Initial peel strength (N / 15mm) Peel strength after cooking (N / 15mm) Peel strength retention rate (%) Appearance of ink layer after cooking Surface water contact angle (°) UV aging ΔYI Immobilized laccase recovery rate (%) Example 1 4.8 4.6 95.8 No bubbling, no peeling 42.3 2.1 96.2 Example 2 4.1 3.8 92.7 No bubbling, no peeling 46.5 2.2 96.0 Example 3 4.5 4.2 93.3 No bubbling, no peeling 43.8 2.1 95.8 Example 4 4.4 4.1 93.2 No bubbling, no peeling 44.2 2.2 96.1 Example 5 4.3 4.0 93.0 No bubbling, no peeling 45.1 2.2 95.9 Example 6 4.2 3.9 92.9 No bubbling, no peeling 45.6 2.1 97.1 Example 7 4.6 4.3 93.5 No bubbling, no peeling 43.5 2.1 96.0 Example 8 4.7 4.4 93.6 No bubbling, no peeling 43.2 2.0 96.1 Comparative Example 1 1.2 0.3 25.0 Large-area blistering and peeling 89.7 5.8 95.8 Comparative Example 2 2.8 0.9 32.1 Localized blistering and edge peeling 51.6 3.5 - Comparative Example 3 1.8 0.5 27.8 Localized blistering and peeling 82.4 4.6 82.3 Comparative Example 4 2.2 0.7 31.8 Localized blistering 68.5 3.8 93.5

[0057] Results Analysis: The test results of Examples 1-8 show that the formulation and preparation process within the scope of this invention can construct a stable covalently grafted polyethylene glycol interlayer on the surface of ultra-high molecular weight polyethylene substrate, achieving excellent comprehensive performance. Example 1, as the best example, achieved an initial peel strength of 4.8 N / 15 mm, and a peel strength retention rate of up to 95.8% after boiling in water at 100°C for 30 min. The ink layer showed no blistering or peeling, and the surface water contact angle was as low as 42.3°. It also exhibited excellent UV aging resistance and immobilized laccase recovery efficiency, fully realizing all the beneficial effects described in this invention. Examples 2-8, by adjusting the dosage of core components, raw material structural parameters, and process parameters, maintained excellent performance across all aspects, fully verifying the broad applicability of the formulation and the robustness of the preparation process of this invention.

[0058] Comparative Example 1, by removing the core substrate p-hydroxybenzoic acid, failed to generate quinone radical intermediates under laccase catalysis, thus failing to achieve covalent grafting of polyethylene glycol segments with the substrate backbone. The substrate surface remained in its original nonpolar state, with a water contact angle as high as 89.7°. The initial peel strength was only 1.2 N / 15 mm, and the peel strength retention rate after cooking was only 25.0%. The ink layer peeled off over a large area, directly proving that p-hydroxybenzoic acid, as a specific substrate for laccase catalysis, is a necessary component for constructing the covalently grafted intermediate layer and achieving the core technical effect of this invention.

[0059] Comparative Example 2 employs the conventional corona treatment process described in the background art. Although the initial peel strength and surface polarity are improved to some extent, the polar groups generated by the corona treatment only exist in the very shallow surface layer of the substrate and do not form a stable covalent bond. This fails to block the spontaneous rearrangement of non-polar chain segments inside the substrate. After cooking, the polar groups are encapsulated and attenuated, and the peel strength retention rate is only 32.1%. The ink layer shows obvious local blistering and edge peeling, which is orders of magnitude different from the cooking resistance of Example 1 of this invention. This directly proves that this invention solves the core technical problems of surface polarity attenuation and ink layer cooking peel failure in the prior art by constructing a covalently coupled intermediate layer in situ, and achieves unexpected technical effects.

[0060] Comparative Example 3 adjusted the pH of the buffer solution to 7.0, which is outside the range defined in this invention. This exceeded the optimal acidic catalytic range of laccase, resulting in the disruption of the copper ion coordination environment at the active site of laccase, instability of the protein spatial conformation, and a significant decrease in catalytic activity. As a result, sufficient quinone radicals could not be effectively generated to complete the grafting reaction, and the surface polarity and interlayer adhesion of the substrate decreased significantly. At the same time, the enzyme activity recovery rate of the immobilized laccase was only 82.3%. This proves that the pH range of the acetate-sodium acetate buffer solution defined in this invention (around 5.0) is the key control parameter for maintaining the catalytic activity of laccase and ensuring the efficient progress of the grafting reaction.

[0061] Comparative Example 4 lacked oxygen control protection. The high dissolved oxygen content in the system strongly quenched the quinone free radicals generated by laccase catalysis, while also causing excessive oxidation and inactivation of laccase, which significantly reduced the grafting reaction efficiency. The grafted layer on the substrate surface was incomplete, and the surface polarity and interlayer adhesion decreased significantly. After cooking, the performance deteriorated significantly. This proves that the oxygen control reaction conditions of the present invention are a necessary process step to ensure the effective concentration of quinone free radicals and achieve efficient grafting modification.

[0062] This invention utilizes enzyme-catalyzed in-situ grafting technology to construct a polyethylene glycol interlayer covalently bonded to the main chain on the surface of an ultra-high molecular weight polyethylene substrate. This effectively blocks the spontaneous rearrangement of non-polar chain segments in the substrate, solving the long-standing industry pain points of surface polarity decay and ink layer peeling failure during cooking, which are present in existing technologies. By optimizing the buffer system, immobilized enzyme system, ink compounding system, and UV curing process, the adhesion between composite film layers, cooking resistance, and anti-aging properties are simultaneously and significantly improved. The above test results fully demonstrate the superiority of the technical solution of this invention.

Claims

1. A functional color-printed composite packaging film of ultra-high molecular weight polyethylene, characterized in that, The composite packaging film is prepared from raw materials comprising the following parts by weight: 100 parts of ultra-high molecular weight polyethylene film substrate, 15-30 parts of p-hydroxybenzoic acid, 25-50 parts of polyethylene glycol diacrylate, 1-5 parts of laccase, 120-200 parts of buffer solution components, and 60-80 parts of acrylic ink monomers. The p-hydroxybenzoic acid and the polyethylene glycol diacrylate form a polyethylene glycol grafted intermediate layer on the surface of the ultra-high molecular weight polyethylene film substrate under the catalysis of laccase, and the acrylate ink monomer forms a cross-linked cured ink layer on the surface of the polyethylene glycol grafted intermediate layer.

2. The ultra-high molecular weight polyethylene functional color-printed composite packaging film according to claim 1, characterized in that, The buffer solution component is an acetate-sodium acetate buffer solution with a pH of 5.

0. The buffer solution component also contains 5-15 parts by weight of a co-solvent, which is a mixed solvent composed of N,N-dimethylformamide and deionized water in a volume ratio of 1:

3.

3. The ultra-high molecular weight polyethylene functional color-printed composite packaging film according to claim 1, characterized in that, The polyethylene glycol diacrylate has a number average molecular weight of 600-1000 Daltons, and the end double bond conversion rate of the polyethylene glycol diacrylate is greater than 85%. The composite packaging film also contains 2-8 parts by weight of nano-silica particles, and the surface of the nano-silica particles is grafted with acrylate groups that match the polyethylene glycol diacrylate.

4. The ultra-high molecular weight polyethylene functional color-printed composite packaging film according to claim 1, characterized in that, The laccase is an immobilized laccase immobilized with magnetic iron oxide nanoparticles. The mass ratio of laccase to magnetic iron oxide nanoparticles in the immobilized laccase is 1:8 to 1:

10. The surface of the magnetic iron oxide nanoparticles is modified with a carboxymethylated chitosan layer.

5. The ultra-high molecular weight polyethylene functional color-printed composite packaging film according to claim 1, characterized in that, The acrylic ink monomer is composed of methyl methacrylate, isoborneol acrylate, and fluorinated acrylate monomer in a mass ratio of 3:1:

1. The fluorinated acrylate monomer is perfluoroalkyl ethyl acrylate. The composite packaging film also contains 1-3 parts by mass of photoinitiator.

6. The ultra-high molecular weight polyethylene functional color-printed composite packaging film according to claim 1, characterized in that, The thickness of the polyethylene glycol grafted intermediate layer is 0.1-0.5 micrometers, the thickness of the cross-linked cured ink layer is 5-15 micrometers, the mass ratio of the polyethylene glycol grafted intermediate layer to the cross-linked cured ink layer is 1:20-1:50, and the cross-linked cured ink layer also contains 0.5-2 parts by mass of hindered amine light stabilizer and 0.5-2 parts by mass of benzotriazole ultraviolet absorber.

7. A method for preparing a functional color-printed composite packaging film of ultra-high molecular weight polyethylene, used to prepare the functional color-printed composite packaging film of ultra-high molecular weight polyethylene as described in any one of claims 1-6, characterized in that, The preparation method includes the following steps: Step S1: Mix the buffer component, p-hydroxybenzoic acid and polyethylene glycol diacrylate evenly to obtain a substrate mixture; Step S2: Laccase is added to the substrate mixture to initiate a catalytic reaction to generate quinone radicals under controlled oxygen conditions; Step S3: Immerse the ultra-high molecular weight polyethylene film substrate in a reaction system containing the quinone free radicals, so that the quinone free radicals covalently couple on the surface of the ultra-high molecular weight polyethylene film substrate to form a polyethylene glycol grafted intermediate layer. Step S4: Remove the coupled ultra-high molecular weight polyethylene film substrate and clean and dry it. Step S5: Immerse the cleaned and dried ultra-high molecular weight polyethylene film substrate in a solution containing acrylate ink monomers, and initiate polymerization by ultraviolet light irradiation, so that the acrylate ink monomers crosslink and solidify into a film on the polyethylene glycol grafted intermediate layer.

8. The preparation method according to claim 7, characterized in that, In step S1, the buffer solution component, the p-hydroxybenzoic acid and the polyethylene glycol diacrylate are mixed evenly at a temperature of 25-35°C. During the mixing process, nitrogen gas is continuously introduced into the substrate mixture to control the dissolved oxygen content to 3-5 mg / L. The mixing time in step S1 is 30-60 minutes.

9. The preparation method according to claim 7, characterized in that, In step S2, the added laccase is immobilized laccase. After the catalytic reaction is initiated in step S2 and the coupling reaction in step S3 is completed, the immobilized laccase is separated from the reaction system by applying an external magnetic field with an intensity of 0.1-0.5 Tesla. The direction of the applied external magnetic field is perpendicular to the surface of the ultra-high molecular weight polyethylene film substrate.

10. The preparation method according to claim 7, characterized in that, In step S5, the solution containing acrylate ink monomers also contains a photoinitiator, which is a compound initiator composed of 1-hydroxycyclohexylphenyl ketone and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide. The ultraviolet irradiation is performed by alternating between a main wavelength light source with a wavelength of 365 nm and an auxiliary wavelength light source with a wavelength of 395 nm. The single cycle of the alternating irradiation is 5 seconds, and the total time of ultraviolet irradiation is 30-60 seconds. The ambient temperature during the ultraviolet irradiation process is controlled at 40-50℃.