Modified polypropylene resin molded article for polypropylene film and process for producing the same

Abstract

The present application relates to the field of high polymer film material and packaging technology, specifically to a modified polypropylene resin forming body for polypropylene film and a processing technology thereof; the forming body comprises an outer layer containing a composite antibacterial master batch, a core layer containing a barrier master batch, and an inner layer; the forming body combines the specific thickness proportion of each layer to construct a three-layer structure; the core is to use amino-nano-silver, modified polydimethylsiloxane and tannic acid to react to form a composite antibacterial system with a core-shell structure, and to use hydrophobic two-dimensional inorganic sheet layer, ethylene-vinyl alcohol copolymer and maleic anhydride grafted polypropylene to form a fine layered barrier structure through strong shearing mixing; the present application effectively overcomes the defect that the traditional co-extrusion process needs to add an independent adhesive resin layer, solves the problems of easy aggregation of antibacterial agents and easy peeling of polar materials and non-polar matrix through core-shell wrapping and interfacial compatibility modification, prolongs the antibacterial effective period and improves the barrier performance.

Description

Technical Field

[0001] This invention relates to the field of polymer film materials and packaging technology, specifically to modified polypropylene resin molded articles for use in polypropylene films and their processing technology. Background Technology

[0002] Existing polypropylene packaging films suffer from insurmountable technical defects when attempting to achieve multifunctionality: In single-layer blend films, the addition of antibacterial agents often disrupts the continuity of the polymer matrix or interferes with the directional arrangement of barrier fillers, leading to a significant decrease in gas barrier performance; inorganic nano-silver readily aggregates in the non-polar PP matrix and easily migrates to the surface, resulting in rapid precipitation and a short antibacterial shelf life; natural phenolic antibacterial agents have poor heat resistance and are prone to thermo-oxidative degradation and volatilization during PP melt extrusion; polar barrier materials lack interfacial bonding with non-polar PP, and direct co-extrusion easily leads to interlayer delamination. Traditional solutions require multiple independent bonding resin layers, resulting in complex processing equipment structures, cumbersome processes, and hindering the subsequent recycling and regeneration of materials. Summary of the Invention

[0003] The purpose of this invention is to provide a modified polypropylene resin molded body for polypropylene films and its processing technology, aiming to solve the problems of existing polypropylene packaging films where antibacterial agents easily agglomerate and migrate, resulting in a short antibacterial period, and where the interfacial bonding between polar barrier materials and non-polar matrix is ​​poor, and co-extrusion is prone to peeling, requiring the addition of an adhesive layer and leading to complex equipment. Specifically, the technical solution of this invention is as follows: A modified polypropylene resin molded body for use in polypropylene films, comprising an outer layer, a core layer, and an inner layer; Based on thickness percentage, the outer layer accounts for 15%-25%, the core layer accounts for 45%-55%, and the inner layer accounts for 20%-35%, and the sum of the thickness percentages of the outer layer, core layer, and inner layer is 100%; the total thickness of the molded body is 30-100μm. The outer layer comprises the following raw materials, by mass parts: 80-90 parts homopolymer polypropylene, 10-20 parts composite antibacterial masterbatch; The core layer comprises the following raw materials, by mass parts: 70-90 parts homopolymer polypropylene and 10-30 parts barrier masterbatch. The inner layer comprises the following raw materials, by mass: 80-100 parts of ternary copolymer polypropylene, 1-3 parts of erucamide, and 0.5-2 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid].

[0004] Preferably, the preparation of the composite antibacterial masterbatch includes the following steps: mixing the composite antibacterial system with homopolymer polypropylene at a mass ratio of 1:(4-9), and then melt-extruded and granulating the mixture using a twin-screw extruder at 180-200°C to obtain the composite antibacterial masterbatch; The composite antibacterial system comprises the following raw materials, by mass: 10-20 parts aminated nano-silver, 30-50 parts allyl glycidyl ether modified polydimethylsiloxane, 15-25 parts tannic acid, 80-120 parts N,N-dimethylformamide, and 1-3 parts alkaline catalyst or phase transfer catalyst; wherein, the allyl glycidyl ether modified polydimethylsiloxane is prepared by hydrosilylation reaction of hydrogen-containing polydimethylsiloxane and allyl glycidyl ether under the action of chloroplatinic acid catalyst; the preparation of the composite antibacterial system includes the following steps: S1: Nano-silver was ultrasonically dispersed in an aqueous ethanol solution, and after surface micro-oxidation treatment with a trace amount of hydrogen peroxide, 3-aminopropyltriethoxysilane was added to undergo a dehydration condensation reaction. After centrifugation, washing and vacuum drying, aminated nano-silver was obtained. S2: The above-mentioned aminated nano-silver and allyl glycidyl ether modified polydimethylsiloxane are added to N,N-dimethylformamide and stirred at 60-80℃ to undergo a ring-opening addition reaction of amino and epoxy groups to form a silver nucleus precursor. S3: Add tannic acid and the catalyst to the silver nucleus precursor, and stir and reflux at 70-90°C under nitrogen protection to carry out a ring-opening etherification reaction. Then add anhydrous diethyl ether to precipitate and remove the solvent to obtain the composite antibacterial system.

[0005] Preferably, the preparation of the barrier masterbatch includes the following steps: dispersing two-dimensional nano-inorganic sheets in a mixture of ethanol and water, adding a long-chain alkylsilane coupling agent, hydrolyzing under weakly acidic conditions and performing surface grafting coating, filtering and drying to obtain hydrophobic two-dimensional inorganic sheets; mixing 5-15 parts by mass of the hydrophobic two-dimensional inorganic sheets, 15-30 parts by mass of ethylene-vinyl alcohol copolymer, 5-10 parts by mass of maleic anhydride-grafted polypropylene and 50-70 parts by mass of homopolymer polypropylene at high speed, and then granulating the mixture by strong shearing at 190-210°C using a twin-screw extruder to obtain the barrier masterbatch.

[0006] Preferably, the two-dimensional nano-inorganic sheets are a mixture of nano-montmorillonite, nano-kaolinite and nano-talc in a mass ratio of 1:2:1; the long-chain alkylsilane coupling agent is hexadecyltrimethoxysilane.

[0007] Preferably, in S1, the particle size of the nano-silver is 15-30 nm; the aqueous ethanol solution is a 95% (w / w) aqueous ethanol solution; and the mass ratio of the nano-silver to 3-aminopropyltriethoxysilane is 1:(0.1-0.3).

[0008] Preferably, in S3, the catalyst is triethylamine or tetrabutylammonium bromide.

[0009] Preferably, the ternary copolymer polypropylene is a propylene-ethylene-butene copolymer.

[0010] Preferably, the processing technology of the modified polypropylene resin molded body for polypropylene film includes the following steps: The outer layer raw materials are mixed and then added to the first extruder; After the core layer raw materials are mixed, they are added to the second extruder. The length-to-diameter ratio of the second extruder is controlled to be ≥30:1, and the melt temperature is distributed in a stepped manner at 190℃, 210℃, and 220℃. The inner layer raw materials are mixed and then added to the third extruder; The three melt streams are distributed according to thickness ratio by a distributor and then converge into a T-die. The temperature of the T-die is controlled at 220-230℃, and the shear rate in the high shear rate zone of the T-die is controlled to be greater than 100 s⁻¹. After extrusion, the melt is pressed against a quenching roller with a cooling water temperature of 15-25℃ for rapid cooling and shaping. After edge trimming, corona treatment and winding, a modified polypropylene resin molded body for use in polypropylene film is obtained.

[0011] The beneficial effects of this invention are as follows: This invention utilizes the reaction of aminated nano-silver, modified polydimethylsiloxane, and tannic acid to construct a core-shell structured composite antibacterial system, effectively inhibiting the activity decay and aggregation of the silver component during processing, achieving a long-lasting and highly efficient antibacterial effect, with an antibacterial rate of up to 99.9% against Escherichia coli and Staphylococcus aureus; Meanwhile, through the strong shear mixing of hydrophobic two-dimensional inorganic sheets, ethylene-vinyl alcohol copolymer, and maleic anhydride-grafted polypropylene, a highly uniform and fine layered barrier structure is formed in the film core layer, which prolongs the diffusion path of gas and water vapor. The oxygen permeability of the film is as low as 0.8cc / (m²·day·atm), and the water vapor permeability is as low as 1.6g / (m²·day). The specific three-layer structure of this invention ensures excellent interlayer bonding and heat-sealing strength (heat-sealing strength reaches 16.8N / 15mm) without the need for an additional adhesive resin layer, significantly improving the overall physical properties of polypropylene packaging film. Detailed Implementation

[0012] The technical solutions in the embodiments of the present invention will be clearly and completely described below; the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0013] Example 1: This example provides a multifunctional antibacterial high-barrier multilayer polypropylene composite film with a total thickness of 60 μm. The thickness ratios of the outer layer, core layer, and inner layer are 20%, 50%, and 30%, respectively. The specific steps include: S1. Preparation of allyl glycidyl ether modified polydimethylsiloxane: Hydrogen-containing polydimethylsiloxane and allyl glycidyl ether are mixed at a mass ratio of 10:1, and 20 ppm of chloroplatinic acid catalyst is added. The mixture is reacted at 80°C for 4 hours to carry out a hydrosilylation reaction, and allyl glycidyl ether modified polydimethylsiloxane is obtained. As a macromolecular crosslinking agent, it provides a flexible silicone oil skeleton and reactive groups for subsequent reactions. S2. Preparation of aminated silver nanoparticles: Take 1 part of silver nanoparticles with a particle size of 20 nm, ultrasonically disperse them in 50 parts of 95% ethanol aqueous solution, add 3-aminopropyltriethoxysilane, and control the mass ratio of silver nanoparticles to 3-aminopropyltriethoxysilane to be 1:0.2. Stir and react at 60℃ for 2 hours. After surface micro-oxidation treatment of the silver nanoparticles with a trace amount of hydrogen peroxide, the abundant hydroxyl groups generated on the surface of the silver nanoparticles cause them to undergo dehydration condensation reaction. After the reaction is completed, centrifuge, wash and vacuum dry to obtain aminated silver nanoparticles. Surface amination improves the dispersibility and reactivity of silver nanoparticles in organic systems. S3. Preparation of a composite antibacterial system: Take 100 parts of N,N-dimethylformamide, add 15 parts of aminated nano-silver and 40 parts of allyl glycidyl ether modified polydimethylsiloxane, stir and mix at 70℃ for 3 hours to allow the amino and epoxy groups to undergo a ring-opening addition reaction to form a silver core precursor; add 20 parts of tannic acid to the silver core precursor, add 2 parts of triethylamine under nitrogen protection, stir and reflux at 80℃ for 4 hours to allow the phenolic hydroxyl groups in the tannic acid to undergo a ring-opening etherification reaction with the remaining epoxy groups; after the reaction, add anhydrous diethyl ether to precipitate and purify, remove the solvent, and obtain a composite antibacterial system. This system has a core-shell structure, which can effectively inhibit the activity decay of the silver component and improve the stability of the system. S4. Preparation of composite antibacterial masterbatch: The composite antibacterial system is mixed with homopolymer polypropylene at a mass ratio of 1:6, and then melt-extruded and granulated at 190°C using a twin-screw extruder to obtain the composite antibacterial masterbatch, which facilitates the uniform dispersion of the antibacterial system in the polypropylene matrix. S5. Preparation of hydrophobic two-dimensional inorganic sheets: Take 1 part of two-dimensional nano-inorganic sheets and disperse them in a mixture of 20 parts of ethanol and water. The two-dimensional nano-inorganic sheets are composed of nano-montmorillonite, nano-kaolinite and nano-talc in a mass ratio of 1:2:1. Add 0.05 parts of hexadecyltrimethoxysilane, hydrolyze under weakly acidic conditions at 60°C and carry out surface grafting coating reaction for 2 hours. After filtration and drying, hydrophobic two-dimensional inorganic sheets are obtained. Their surface energy is reduced, thereby significantly improving their compatibility and dispersibility in the polymer matrix. S6. Preparation of barrier masterbatch: Take 10 parts of hydrophobic two-dimensional inorganic sheets, 25 parts of ethylene-vinyl alcohol copolymer, 8 parts of maleic anhydride grafted polypropylene and 57 parts of homopolymer polypropylene, mix them at high speed, and then granulate them by strong shearing at 200°C using a twin-screw extruder to obtain barrier masterbatch, so that the barrier phase forms a fine layered barrier structure in the matrix. S7. Prepare a three-layer composite film; take 85 parts by mass of homopolymer polypropylene and 15 parts by mass of composite antibacterial masterbatch for the outer layer, mix them and add them to the first extruder; take 80 parts by mass of homopolymer polypropylene and 20 parts by mass of barrier masterbatch for the core layer, mix them and add them to the second extruder, control the length-to-diameter ratio of the second extruder to be 32:1, and the melt temperature is distributed in a stepped manner at 190℃, 210℃ and 220℃. The inner layer raw materials consist of 95 parts by weight of propylene-ethylene-butene copolymer, 2 parts by weight of erucamide, and 1 part by weight of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid], which are then mixed and added to the third extruder. The three melt streams are distributed according to their thickness ratios by a distributor and then converge into the T-die. The temperature of the T-die is controlled at 225°C, and the shear rate in the high shear rate region is controlled at 120 s. -1 After the melt is extruded, it is rapidly cooled and shaped on a quenching roller with a cooling water temperature of 20°C. After edge trimming, corona treatment, and winding, a multifunctional antibacterial high-barrier multilayer polypropylene composite film is obtained.

[0014] Example 2: This example provides a multifunctional antibacterial high-barrier multilayer polypropylene composite film with a total thickness of 30 μm. The thickness ratios of the outer layer, core layer, and inner layer are 15%, 55%, and 30%, respectively. The preparation steps are basically the same as in Example 1, except that: In S1, hydrogen-containing polydimethylsiloxane and allyl glycidyl ether are mixed at a mass ratio of 8:1. The number average molecular weight of the hydrogen-containing polydimethylsiloxane is 1500, and the hydrogen content is 0.8wt%. The amount of chloroplatinic acid catalyst is 15ppm of the total mass. The reaction temperature is 70℃, and the reaction time is 3 hours. The obtained allyl glycidyl ether-modified polydimethylsiloxane serves as a macromolecular crosslinking agent, providing a flexible silicone oil framework and reactive groups for subsequent reactions. In S2, one part of 15 nm silver nanoparticles was ultrasonically dispersed in 40 parts of 95% ethanol aqueous solution, with a mass ratio of silver nanoparticles to 3-aminopropyltriethoxysilane of 1:0.1. The mixture was stirred at 55 °C for 1.5 hours, and a dehydration condensation reaction was carried out using the hydroxyl groups generated by the natural oxidation of the silver nanoparticles. After surface amination treatment, the dispersibility and reactivity of the silver nanoparticles in the organic system were significantly improved. In S3, the raw materials of the composite antibacterial system, by mass parts, are: 10 parts of aminated nano-silver, 30 parts of allyl glycidyl ether modified polydimethylsiloxane, 15 parts of tannic acid, 80 parts of N,N-dimethylformamide, and 1 part of tetrabutylammonium bromide; the ring-opening addition reaction temperature is 60℃, and the reaction time is 2 hours; the ring-opening etherification reaction temperature is 70℃, and the reaction time is 3 hours; the obtained composite antibacterial system can effectively inhibit the activity decay of the silver component and improve the stability of the system; In S4, the mass ratio of the composite antibacterial system to homopolymer polypropylene is 1:9, and the extrusion temperature is 180℃; the resulting composite antibacterial masterbatch facilitates the uniform dispersion of the antibacterial system in the polypropylene matrix. In S5, 1 part of two-dimensional nano-inorganic sheets was dispersed in a mixture of 15 parts of ethanol and water, and 0.03 parts of hexadecyltrimethoxysilane were added. The mixture was hydrolyzed at 55°C and subjected to a surface grafting coating reaction for 1.5 hours. The resulting hydrophobic two-dimensional inorganic sheets had reduced surface energy, which improved their compatibility and dispersibility in the polymer matrix. In S6, the raw materials of the barrier masterbatch are, by mass parts: 5 parts hydrophobic two-dimensional inorganic sheets, 15 parts ethylene-vinyl alcohol copolymer, 5 parts maleic anhydride grafted polypropylene and 70 parts homopolymer polypropylene; the mixing temperature is 190℃; the obtained barrier masterbatch enables the barrier phase to form a fine layered barrier structure in the matrix. In S7, the outer layer material consists of 90 parts homopolymer polypropylene and 10 parts composite antibacterial masterbatch; the core layer material consists of 70 parts homopolymer polypropylene and 30 parts barrier masterbatch; and the inner layer material consists of 100 parts propylene-ethylene-butene copolymer, 1 part erucamide, and 0.5 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]. The second extruder has an aspect ratio of 30:1, a T-die temperature of 220℃, and a shear rate of 105 s in the high shear rate zone. -1 The cooling water temperature for the rapid cooling roller is 25℃.

[0015] Example 3: This example provides a multifunctional antibacterial high-barrier multilayer polypropylene composite film with a total thickness of 100 μm. The thickness ratios of the outer layer, core layer, and inner layer are 25%, 45%, and 30%, respectively. The preparation steps are basically the same as in Example 1, except that: In S1, when hydrogen-containing polydimethylsiloxane and allyl glycidyl ether are mixed and reacted at a mass ratio of 12:1, chloroplatinic acid catalyst accounting for 25 ppm of the total mass is added, and the reaction is carried out at 90°C for 5 hours. The resulting allyl glycidyl ether-modified polydimethylsiloxane serves as a macromolecular crosslinking agent, providing a flexible silicone oil framework and reactive groups for subsequent reactions. In S2, one part of nano-silver with a particle size of 30 nm was ultrasonically dispersed in 60 parts of a 95% ethanol aqueous solution. The mass ratio of nano-silver to 3-aminopropyltriethoxysilane was 1:0.3. The mixture was stirred at 65 °C for 2.5 hours, and a dehydration condensation reaction was carried out using the hydroxyl groups generated by the natural oxidation of the nano-silver surface. After surface amination treatment, the dispersibility and reactivity of the nano-silver in the organic system were significantly improved. In S3, the raw materials of the composite antibacterial system, by mass parts, are: 20 parts of aminated nano-silver, 50 parts of allyl glycidyl ether modified polydimethylsiloxane, 25 parts of tannic acid, 120 parts of N,N-dimethylformamide, and 3 parts of triethylamine; the ring-opening addition reaction temperature is 80℃, and the reaction time is 4 hours; the ring-opening etherification reaction temperature is 90℃, and the reaction time is 5 hours; the obtained composite antibacterial system can effectively inhibit the activity decay of the silver component and improve the stability of the system; In S4, the mass ratio of the composite antibacterial system to homopolymer polypropylene is 1:4, and the extrusion temperature is 200℃; the resulting composite antibacterial masterbatch facilitates the uniform dispersion of the antibacterial system in the polypropylene matrix. In S5, 1 part of two-dimensional inorganic nanosheets was dispersed in a mixture of 25 parts of ethanol and water, and 0.08 parts of hexadecyltrimethoxysilane were added. The mixture was hydrolyzed at 65°C and subjected to a surface grafting coating reaction for 2.5 hours. The resulting hydrophobic two-dimensional inorganic sheets had reduced surface energy, which improved their compatibility and dispersibility in the polymer matrix. In S6, the raw materials of the barrier masterbatch are, by mass parts: 15 parts hydrophobic two-dimensional inorganic sheets, 30 parts ethylene-vinyl alcohol copolymer, 10 parts maleic anhydride grafted polypropylene and 50 parts homopolymer polypropylene; the mixing temperature is 210℃; the obtained barrier masterbatch enables the barrier phase to form a fine layered barrier structure in the matrix. In S7, the outer layer material is 80 parts homopolymer polypropylene and 20 parts composite antibacterial masterbatch; the core layer material is 90 parts homopolymer polypropylene and 10 parts barrier masterbatch; and the inner layer material is 80 parts propylene-ethylene-butene copolymer, 3 parts erucamide, and 2 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. The second extruder has an aspect ratio of 34:1, a T-die temperature of 230℃, and a shear rate of 130s in the high shear rate zone. -1 The cooling water temperature for the rapid cooling roller is 15℃.

[0016] Example 4: This example provides a multifunctional antibacterial high-barrier multilayer polypropylene composite film with a total thickness of 50 μm. The thickness ratios of the outer layer, core layer, and inner layer are 18%, 52%, and 30%, respectively. The preparation steps are basically the same as in Example 1, except that: In S2, the nano-silver particles have a diameter of 25 nm, and the mass ratio of nano-silver to 3-aminopropyltriethoxysilane is 1:0.25. In S3, the raw materials of the composite antibacterial system are as follows by mass: 18 parts of aminated nano-silver, 45 parts of allyl glycidyl ether modified polydimethylsiloxane, 22 parts of tannic acid, 110 parts of N,N-dimethylformamide and 2 parts of tetrabutylammonium bromide; the ring-opening addition reaction temperature is 75℃, and the ring-opening etherification reaction temperature is 85℃. In S4, the mass ratio of the composite antibacterial system to homopolymer polypropylene is 1:5, and the extrusion temperature is 195℃. In S6, the raw materials of the barrier masterbatch are, by mass parts: 12 parts hydrophobic two-dimensional inorganic sheets, 22 parts ethylene-vinyl alcohol copolymer, 7 parts maleic anhydride grafted polypropylene and 59 parts homopolymer polypropylene; the mixing temperature is 205℃. In S7, the outer layer raw material is 88 parts homopolymer polypropylene and 12 parts composite antibacterial masterbatch, the core layer raw material is 75 parts homopolymer polypropylene and 25 parts barrier masterbatch, and the inner layer raw material is 92 parts propylene-ethylene-butene copolymer, 2 parts erucamide and 1.5 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]; the length-to-diameter ratio of the second extruder is 31:1, the T-die temperature is 228℃, the shear rate in the high shear rate zone is 115s⁻¹, and the cooling water temperature of the quench roll is 18℃.

[0017] Comparative Example 1: The difference between this comparative example and Example 1 is that tannic acid is omitted in S3, while the other operating steps and process parameters are exactly the same as in Example 1.

[0018] Comparative Example 2: The difference between this comparative example and Example 1 is that the surface amination treatment of nano-silver with 3-aminopropyltriethoxysilane in S2 is omitted, while the other operation steps and process parameters are exactly the same as in Example 1.

[0019] Comparative Example 3: The difference between this comparative example and Example 1 is that the hydrophobication treatment of the two-dimensional nano-inorganic sheets by hexadecyltrimethoxysilane in S5 is omitted, while the other operation steps and process parameters are exactly the same as in Example 1.

[0020] Comparative Example 4: The difference between this comparative example and Example 1 is that maleic anhydride grafted polypropylene is omitted in S6, while the other operating steps and process parameters are exactly the same as in Example 1.

[0021] Comparative Example 5: The difference between this comparative example and Example 1 is that the length-to-diameter ratio of the second extruder in S7 is replaced by 24:1 instead of 32:1. Other operating steps and process parameters are exactly the same as in Example 1.

[0022] Comparative Example 6: The difference between this comparative example and Example 1 is that in S7, the shear rate in the high shear rate region of the T-die is reduced from 120 s. -1 Replace with 80s -1Other operating steps and process parameters are exactly the same as in Example 1.

[0023] Comparative Example 7: The difference between this comparative example and Example 1 is that in S7, the thickness ratio of the three layers is replaced from 20%:50%:30% to 33%:34%:33%, while the other operating steps and process parameters are exactly the same as in Example 1.

[0024] The oxygen permeability of the membrane was determined according to standard GB / T1038-2000, with a test temperature of 23℃ and a relative humidity of 50%, and the result is expressed as cc / (m²·day·atm); the water vapor permeability was determined according to standard GB / T1037-2021, with a test temperature of 38℃ and a relative humidity of 90%, and the result is expressed as g / (m²·day); the antibacterial rate against Escherichia coli and Staphylococcus aureus was determined according to standard GB / T31402-2015; the heat seal strength was determined according to industry standard QB / T2358-1998, with a test temperature of 130℃, a heat seal pressure of 0.3MPa, and a heat seal time of 1.0s, and the result is expressed as N / 15mm. Table 1. Performance test results of thin films in each embodiment and comparative example. As can be seen from the comparison of the test results of Example 1 and Comparative Example 1 in Table 1, omitting tannic acid leads to a decrease in antibacterial rate. After tannic acid participates in the ring-opening etherification reaction of the remaining epoxy groups in the silicone oil skeleton, it can form a stable polyphenol shell outside the silver core. This shell expands the antibacterial activity range on the one hand, and inhibits the activity decay of the silver component during processing on the other hand. After omitting this feature, the composite antibacterial system retains only the silver component, the types of antibacterial activity are reduced, and the stability of the outer antibacterial micro-region decreases. Therefore, the antibacterial rates of Escherichia coli and Staphylococcus aureus both decrease. As can be seen from the comparison of the test results of Example 1 and Comparative Example 2 in Table 1, omitting the amination treatment on the surface of the nano-silver leads to a decrease in antibacterial rate and a certain decrease in barrier performance. The amination treatment provides a reaction site for the ring-opening addition reaction between nano-silver and modified polydimethylsiloxane, which can improve the coating degree and dispersion uniformity of the silver core in the silicone oil. After omitting this feature, the nano-silver is more prone to agglomeration, and the outer antibacterial micro-regions are unevenly distributed, resulting in a reduction in the effective contact area. At the same time, local agglomeration will destroy the continuity of the film matrix, shortening the permeation path of oxygen and water vapor, thus reducing both the antibacterial rate and barrier performance. As can be seen from the comparison of the test results of Example 1 and Comparative Example 3 in Table 1, omitting the hydrophobic treatment of the two-dimensional nano-inorganic sheets leads to a significant increase in oxygen permeability and water vapor permeability. The hydrophobic treatment reduces the surface energy of the inorganic sheets, improves their dispersibility in the polypropylene matrix, and facilitates the alignment of the sheets along the film surface during shear flow. After omitting this feature, there are interfacial bonding defects between the inorganic sheets and polypropylene, which easily lead to agglomeration. The sheets cannot effectively extend the gas diffusion path, thus significantly reducing the barrier performance. As can be seen from the comparison of the test results of Example 1 and Comparative Example 4 in Table 1, omitting the maleic anhydride-grafted polypropylene leads to a further increase in oxygen and water vapor permeability. Maleic anhydride-grafted polypropylene can improve the interfacial bonding between the continuous polypropylene phase and the dispersed phase of the ethylene-vinyl alcohol copolymer, enabling the ethylene-vinyl alcohol copolymer to form a stable, high aspect ratio layered fine structure under shear action, and together with the two-dimensional inorganic sheets, it forms a continuous barrier path. After omitting this feature, the interfacial bonding force is weakened, the ethylene-vinyl alcohol copolymer is difficult to maintain its layered morphology, and interfacial defects are more likely to form inside the barrier layer, thus significantly increasing the gas and water vapor permeability. As can be seen from the comparison of the test results of Example 1 and Comparative Example 5 in Table 1, replacing the length-to-diameter ratio of the second extruder from 32:1 to 24:1 leads to a decrease in barrier performance. Increasing the length-to-diameter ratio parameter of the equipment is beneficial for the barrier layer raw material to obtain more complete melt mixing and dispersion during the extrusion process, so that the ethylene-vinyl alcohol copolymer and the two-dimensional inorganic sheets form a highly uniform finely dispersed phase in the polypropylene matrix. After the length-to-diameter ratio is reduced, the mixing effect is weakened, the barrier phase is not sufficiently dispersed, and it is difficult to form a continuous and well-oriented barrier structure. Therefore, the oxygen permeability and water vapor permeability increase. As can be seen from the comparison of the test results of Example 1 and Comparative Example 6 in Table 1, replacing the shear rate in the high shear rate region of the T-die with 80 s⁻¹ resulted in a decrease in barrier performance. Increasing the high shear rate in the die can cause the ethylene-vinyl alcohol copolymer dispersed phase to be further stretched from the initial spherical dispersed particles into high aspect ratio sheets, and at the same time cause the two-dimensional nano-inorganic sheets to be oriented along the film surface, thereby extending the permeation path. After the shear rate is reduced, the degree of deformation of the dispersed phase is insufficient, the degree of sheet orientation decreases, and the tortuous diffusion path in the barrier layer is shortened, thus increasing the oxygen permeability and water vapor permeability. As can be seen from the comparison of the test results of Example 1 and Comparative Example 7 in Table 1, replacing the thickness ratio of the three layers from 20%:50%:30% to 33%:34%:33% resulted in a decrease in barrier performance, antibacterial performance, and heat-sealing strength. After the core layer thickness ratio decreased, the effective proportion of the high-barrier structure in the total film thickness decreased, which shortened the gas barrier path. Although the thickness of the outer antibacterial layer and the inner heat-sealing layer increased, the overall barrier performance still decreased significantly after the core layer function was weakened. Meanwhile, the effective structural proportion of ternary copolymer polypropylene in the inner layer material failed to remain within the effective threshold range for maintaining interlayer strength, resulting in a decrease in the continuity and load-bearing capacity of the heat-sealing interface and thus a reduction in heat-sealing strength; changes in the thickness of the outer functional layer also affected the distribution of antibacterial components in the unit thickness direction, leading to a slight decrease in the antibacterial rate.

[0025] The above are merely specific embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any conventional modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A modified polypropylene resin molded article for use in polypropylene films, characterized in that: Includes outer layer, core layer and inner layer; Based on thickness percentage, the outer layer accounts for 15%-25%, the core layer accounts for 45%-55%, and the inner layer accounts for 20%-35%, and the sum of the thickness percentages of the outer layer, core layer, and inner layer is 100%; the total thickness of the molded body is 30-100μm. The outer layer comprises the following raw materials, by mass parts: 80-90 parts homopolymer polypropylene, 10-20 parts composite antibacterial masterbatch; The core layer comprises the following raw materials, by mass parts: 70-90 parts homopolymer polypropylene and 10-30 parts barrier masterbatch. The inner layer comprises the following raw materials, by mass: 80-100 parts of ternary copolymer polypropylene, 1-3 parts of erucamide, and 0.5-2 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid].

2. The modified polypropylene resin molded body for polypropylene film according to claim 1, characterized in that, The preparation of the composite antibacterial masterbatch includes the following steps: The composite antibacterial system is mixed with homopolymer polypropylene at a mass ratio of 1:(4-9), and then melt-extruded and granulated at 180-200℃ using a twin-screw extruder to obtain the composite antibacterial masterbatch. The composite antibacterial system comprises the following raw materials, by mass: 10-20 parts aminated nano-silver, 30-50 parts allyl glycidyl ether modified polydimethylsiloxane, 15-25 parts tannic acid, 80-120 parts N,N-dimethylformamide, and 1-3 parts alkaline catalyst or phase transfer catalyst; wherein, the allyl glycidyl ether modified polydimethylsiloxane is prepared by hydrosilylation reaction of hydrogen-containing polydimethylsiloxane and allyl glycidyl ether under the action of chloroplatinic acid catalyst; the preparation of the composite antibacterial system includes the following steps: S1: Nano-silver was ultrasonically dispersed in an aqueous ethanol solution, and after surface micro-oxidation treatment with a trace amount of hydrogen peroxide, 3-aminopropyltriethoxysilane was added to undergo a dehydration condensation reaction. After centrifugation, washing and vacuum drying, aminated nano-silver was obtained. S2: The above-mentioned aminated nano-silver and allyl glycidyl ether modified polydimethylsiloxane are added to N,N-dimethylformamide and stirred at 60-80℃ to undergo a ring-opening addition reaction of amino and epoxy groups to form a silver nucleus precursor. S3: Add tannic acid and the catalyst to the silver nucleus precursor, and stir and reflux at 70-90°C under nitrogen protection to carry out a ring-opening etherification reaction. Then add anhydrous diethyl ether to precipitate and remove the solvent to obtain the composite antibacterial system.

3. The modified polypropylene resin molded body for polypropylene film according to claim 1, characterized in that: The preparation of the barrier masterbatch includes the following steps: dispersing two-dimensional nano-inorganic sheets in a mixture of ethanol and water, adding a long-chain alkylsilane coupling agent, hydrolyzing under weakly acidic conditions and performing surface grafting and coating, filtering and drying to obtain hydrophobic two-dimensional inorganic sheets; mixing 5-15 parts by mass of the hydrophobic two-dimensional inorganic sheets, 15-30 parts by mass of ethylene-vinyl alcohol copolymer, 5-10 parts by mass of maleic anhydride-grafted polypropylene and 50-70 parts by mass of homopolymer polypropylene at high speed, and then granulating the mixture by strong shearing at 190-210℃ using a twin-screw extruder to obtain the barrier masterbatch.

4. The modified polypropylene resin molded body for polypropylene film according to claim 3, characterized in that: The two-dimensional nano-inorganic sheets are a mixture of nano-montmorillonite, nano-kaolinite and nano-talc in a mass ratio of 1:2:1; the long-chain alkylsilane coupling agent is hexadecyltrimethoxysilane.

5. A modified polypropylene resin molded body for use in polypropylene films according to claim 2, characterized in that: In S1, the particle size of the nano-silver is 15-30 nm; the aqueous ethanol solution is a 95% (w / w) aqueous ethanol solution; and the mass ratio of the nano-silver to 3-aminopropyltriethoxysilane is 1:(0.1-0.3).

6. The modified polypropylene resin molded body for polypropylene film according to claim 2, characterized in that: In S3, the catalyst is triethylamine or tetrabutylammonium bromide.

7. The modified polypropylene resin molded body for polypropylene film according to claim 1, characterized in that: The ternary copolymer polypropylene is a propylene-ethylene-butene copolymer.

8. A processing method for preparing a modified polypropylene resin molded body for use in polypropylene films as described in any one of claims 1-7, characterized in that, Includes the following steps: The outer layer raw materials are mixed and then added to the first extruder; After the core layer raw materials are mixed, they are added to the second extruder. The length-to-diameter ratio of the second extruder is controlled to be ≥30:1, and the melt temperature is distributed in a stepped manner at 190℃, 210℃, and 220℃. The inner layer raw materials are mixed and then added to the third extruder; The three melt streams, after being distributed according to thickness ratios by a distributor, converge and enter the T-die. The temperature of the T-die is controlled at 220-230℃, and the shear rate in the high-shear rate region of the T-die is controlled to be greater than 100s. -1 After the melt is extruded, it is rapidly cooled and shaped on a quenching roller with a cooling water temperature of 15-25℃. After edge trimming, corona treatment and winding, a modified polypropylene resin molded body for use in polypropylene film is obtained.

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