Hydrophobic antibacterial preservative film and preparation method thereof

Abstract

This invention discloses a hydrophobic antibacterial food preservation film and its preparation method. The film uses a single polyethylene substrate layer with functional coatings on both sides. From the inside out, the coating consists of an adhesion-promoting layer and a hydrophobic antibacterial layer. The adhesion-promoting layer is covalently bonded to the substrate, and the hydrophobic antibacterial layer is cross-linked with it to form a three-dimensional network. Internally, hydrophobic components such as hydrophobic fumed silica, methyltrimethoxysilane, and stearic acid, as well as silanized chitosan quaternary ammonium salt contact antibacterial components, are covalently bonded. The substrate is composed of a compound of metallocene linear low-density polyethylene, low-density polyethylene, and linear low-density polyethylene. After single-layer blow molding, pre-corona discharge, and plasma activation, a primer and topcoat are simultaneously applied to both sides, followed by UV curing, stepped hot air curing, and aging. This method solves the problems of additive migration, easy coating peeling, and conflicting antibacterial and hydrophobic functions in traditional food preservation films. It also possesses long-lasting hydrophobic and anti-condensation effects with high-efficiency antibacterial properties, exhibiting excellent mechanical and optical properties.

Description

Technical Field

[0001] This invention relates to the field of food preservation film technology, and in particular to a hydrophobic antibacterial food preservation film and its preparation method. Background Technology

[0002] Plastic wrap is a type of plastic packaging product, typically made from ethylene through a polymerization reaction. Plastic wrap can be divided into three main categories: polyethylene (PE), polyvinyl chloride (PVC), and polyvinylidene chloride (PVDC). With the expansion of food distribution radius and the upgrading of consumer demand, the market has placed comprehensive requirements on plastic wrap, demanding features such as superhydrophobicity, anti-fogging, high-efficiency antibacterial properties, and food contact safety. Traditional single-function polyethylene plastic wrap can no longer meet the needs of high-end food preservation, making functional modification the mainstream trend in industry technology development.

[0003] Most existing antibacterial food preservation films are made by blending antibacterial masterbatch with polyethylene resin through blow molding. The core problem stems from the defects in the antibacterial mechanism: the antibacterial agent needs to migrate to the film surface and dissolve in the aqueous phase to play a role, resulting in a raw material utilization rate of less than 10%, and there are long-term problems of excessive release in the early stage and rapid decay in the later stage. At the same time, the migration behavior is uncontrollable, and it is easy to dissolve excessively in high-fat and high-acid food contact scenarios, which does not meet food contact safety standards. In addition, these antibacterial components rely on aqueous phase dissolution to play a role, which conflicts with the principle of hydrophobic and anti-condensation function, and the two cannot be synergistically achieved.

[0004] Existing hydrophobic modification technologies also have obvious drawbacks: physically coated hydrophobic coatings only bond with the substrate through physical adsorption, resulting in extremely poor adhesion and easy detachment and failure after friction or washing; adding hydrophobic powders will damage the mechanical properties and light transmittance of the film, leading to increased haze, and the hydrophobic groups are prone to migration and loss; although some fluorinated hydrophobic modifiers have good effects, they are persistent environmental pollutants and do not comply with global fluorine restriction regulations. Summary of the Invention

[0005] The main objective of this invention is to provide a hydrophobic antibacterial food preservation film and its preparation method. The aim is to solve the problems of food contact safety risks caused by the migration and leaching of additives in existing internally added food preservation films, the principle conflict between antibacterial and hydrophobic functions, and the easy peeling and failure of the coating by using a structural design of a single polyethylene substrate with double-sided functional coatings. The three-dimensional network formed by the covalent bonding of the adhesion promoting layer and the substrate and the cross-linking of the hydrophobic antibacterial layer and the adhesion promoting layer can covalently bond and fix the hydrophobic components and the contact antibacterial components.

[0006] To achieve the above objectives, the present invention proposes a hydrophobic and antibacterial food preservation film, comprising a substrate layer made of a single polyethylene material, and functional coatings symmetrically disposed on both sides of the substrate layer; the functional coatings, from the inside to the outside, are an adhesion promoting layer and a hydrophobic and antibacterial layer. The adhesion promoting layer is formed by curing a primer containing vinyltrimethoxysilane, which is covalently bonded to the substrate layer. The hydrophobic antibacterial layer and the adhesion promoting layer form a three-dimensional network structure through a cross-linking reaction. The hydrophobic antibacterial layer contains covalently bonded hydrophobic components and contact antibacterial components. The hydrophobic component includes hydrophobic fumed silica nanoparticles, methyltrimethoxysilane, and stearic acid; the contact antibacterial component includes silanized chitosan quaternary ammonium salt.

[0007] In one possible implementation, the substrate layer is composed of the following components in parts by weight: 60-70 parts of metallocene linear low-density polyethylene, 20-30 parts of low-density polyethylene, and 10 parts of linear low-density polyethylene.

[0008] In one possible implementation, the adhesion-promoting layer is formed by curing a primer liquid, wherein the dispersion medium of the primer liquid is a mixture of anhydrous ethanol and deionized water, and the solid components include vinyltrimethoxysilane and photoinitiator 1173.

[0009] In one possible implementation, the hydrophobic antibacterial layer further includes photoinitiator 1173 and polyether-modified siloxane dispersant.

[0010] In one possible implementation, the substrate layer has a thickness of 10-20 μm, the adhesion promoting layer has a dry film thickness of 200-250 nm, and the hydrophobic antibacterial layer has a dry film thickness of 600-750 nm.

[0011] A method for preparing a hydrophobic antibacterial food preservation film includes the following steps: S1: A single-layer blow molding process is used to prepare a single polyethylene substrate film, and the substrate film is pre-corona treated. S2: Perform low-temperature plasma activation treatment on the substrate film after unwinding; S3: Apply a primer containing vinyltrimethoxysilane to both sides of the activated substrate simultaneously, and perform UV pre-curing to obtain an adhesion-promoting layer. S4: Apply a topcoat containing hydrophobic components and silanized chitosan quaternary ammonium salt to both sides of the pre-cured adhesion promoting layer, and then perform UV curing and stepped hot air full curing in sequence to obtain a hydrophobic antibacterial layer. S5: The fully cured film is then subjected to a curing treatment, and then slit and rolled to obtain a hydrophobic and antibacterial food preservation film.

[0012] In one possible implementation, the temperature control of the screw in the single-layer blow molding process in step S1 is as follows: feeding section 135-140℃, compression section 145-155℃, metering section 155-165℃, die head temperature 160-165℃, blow ratio 3.0-3.5, and traction ratio 4.0-4.5.

[0013] In one possible implementation, the adhesion-promoting layer in step S3 is coated using a 180-line anilox roller microgravure coating with an ultraviolet curing energy of 800 mJ / cm²; the hydrophobic and antibacterial layer in step S4 is coated using a 220-line anilox roller microgravure coating with an ultraviolet curing energy of 1200 mJ / cm².

[0014] In one possible implementation, the silanized chitosan quaternary ammonium salt in the topcoat liquid is prepared by reacting hydroxypropyltrimethylammonium chloride chitosan with γ-glycidoxypropyltrimethoxysilane at a mass ratio of 3:1 at 55°C and pH 5.5.

[0015] In one possible implementation, the temperature of the stepped hot air drying tunnel in step S4 is controlled in sections of 60-70℃, 80-90℃, and 90-100℃; the curing treatment in step S5 is constant temperature curing at 40℃ for 24 hours.

[0016] Compared with the prior art, the beneficial effects of this application are as follows: This invention utilizes the room-temperature hydrolysis of vinyltrimethoxysilane in the adhesion promoting layer to generate silanol groups, which then undergo a dehydration condensation reaction with the hydroxyl groups on the surface of the plasma-activated polyethylene substrate to form Si-OC covalent bonds, achieving a stable bond between the adhesion promoting layer and the substrate. Furthermore, the silane component of the hydrophobic and antibacterial layer undergoes a cross-linking reaction with the vinyl group of the adhesion promoting layer to form a three-dimensional network structure, covalently fixing the hydrophobic and antibacterial components. This avoids the inherent defects of internal additive systems, such as the migration and dissolution of additives and the easy peeling of physically coated coatings, reducing food contact safety risks while ensuring long-term stable performance.

[0017] Meanwhile, by using covalently fixed contact quaternary ammonium salt antibacterial components, antibacterial activity can be achieved by contact disruption of bacterial cell membranes without the need for aqueous phase dissolution. This avoids the conflict between existing dissolution-type antibacterial and hydrophobic functions. Furthermore, the hydrophobic surface can reduce bacterial adhesion, thus creating a synergistic effect with the antibacterial function.

[0018] Furthermore, by concentrating the functional components on the surface nano-coating, there is no need to add functional powders into the substrate, thus avoiding the damage to the mechanical and light transmission properties of the substrate caused by internal modification. At the same time, a stable hydrophobic effect can be achieved without fluorine-containing additives. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0020] Figure 1 This is a layer structure diagram of the food preservation film of the present invention; Explanation of icon numbers: 1. Substrate layer; 2. Adhesion promoting layer; 3. Hydrophobic and antibacterial layer.

[0021] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0023] All raw materials used in this invention are commercially available conventional industrial products, which can be directly purchased and repeatedly prepared by those skilled in the art. The sources of each raw material are as follows: Polyethylene substrate raw materials: Metallocene linear low-density polyethylene (mLLDPE): Commercially available grade ExxonMobil 1018FA; Low-density polyethylene (LDPE): Commercially available grade Sinopec Maoming Petrochemical 2426H, a special substrate for cling film; Linear low-density polyethylene (LLDPE): Commercially available grade: Sinopec Zhejiang Petrochemical DFDA-7042.

[0024] Silane-based additives: Vinyltrimethoxysilane: Industrial grade, commercially available standard product; Methyltrimethoxysilane: Industrial grade, commercially available standard product; γ-glycidoxypropyltrimethoxysilane (KH560): Industrial grade, commercially available standard product.

[0025] Antibacterial core raw materials Hydroxypropyltrimethylammonium chloride chitosan: food contact grade, degree of deacetylation ≥90%, commercially available regular product.

[0026] Functional additives Hydrophobic fumed silica nanoparticles: specific surface area 200±20m² / g, brand: Evonik; Stearic acid: octadecanoic acid content ≥98%; Photoinitiator 1173 (2-hydroxy-2-methyl-1-phenyl-1-propanone): A commercially available, standard product; Polyether-modified siloxane dispersant: an additive for food contact coatings, a commercially available, standard product.

[0027] The experimental methods and processing equipment used in the embodiments of this invention are all conventional and standard equipment and methods in the field of food packaging film, without any special customized equipment. The specific equipment includes: a single screw blown film machine, an atmospheric pressure low-temperature plasma treatment machine, a double-sided synchronous microgravure coating machine, an ultraviolet curing machine, a three-stage stepped hot air drying tunnel, and a constant temperature and humidity curing chamber.

[0028] The silanized chitosan quaternary ammonium salt of this invention is prepared using a conventional constant-temperature reactor in the art, and the preparation method is as follows: First, hydroxypropyltrimethylammonium chloride chitosan and γ-glycidoxypropyltrimethoxysilane were added to anhydrous ethanol-deionized water (mass ratio 8:2) at a mass ratio of 3:1. The solid content of the system was controlled at 5wt%. KH560 was slowly added dropwise over 30 min to inhibit autohydrolysis. The pH of the system was adjusted to 5.5 with citric acid. The reaction was carried out at 55℃ with stirring at 300 r / min for 6 h. After the reaction was completed, the silane autocondensate was removed by centrifugation and the mixture was vacuum dried at 60℃ for 8 h to obtain silanized chitosan quaternary ammonium salt.

[0029] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention. Unless otherwise specified, the experimental methods used in the embodiments of this invention are conventional methods. Unless otherwise specified, the materials and reagents used in the embodiments of this invention are commercially available. Example 1

[0030] like Figure 1 As shown, this embodiment provides a hydrophobic and antibacterial food preservation film, including a substrate layer 1 made of a single polyethylene material, and functional coatings symmetrically disposed on both sides of the substrate layer 1; the functional coatings are, from the inside to the outside, an adhesion promoting layer 2 and a hydrophobic and antibacterial layer 3.

[0031] Specifically, the adhesion promoting layer 2 is covalently bonded to the substrate layer 1, and the hydrophobic antibacterial layer 3 is cross-linked with the adhesion promoting layer 2 to form a three-dimensional network structure; the hydrophobic antibacterial layer 3 contains covalently bonded hydrophobic components and contact antibacterial components.

[0032] The substrate layer 1 is composed of the following components in parts by weight: 65 parts of metallocene linear low-density polyethylene, 25 parts of low-density polyethylene, and 10 parts of linear low-density polyethylene; the thickness of the substrate layer 1 is 15 μm.

[0033] Among them, metallocene linear low-density polyethylene is used to improve the tensile strength, puncture resistance and transparency of the substrate, low-density polyethylene is used to improve the strength of blown melt and the flexibility of film wrapping, and linear low-density polyethylene is used to balance the mechanical uniformity and processing stability of the substrate.

[0034] The adhesion promoting layer 2 is formed by curing the primer, and its dry film thickness is 225 nm. The dispersion medium of the primer is a mixture of anhydrous ethanol and deionized water at a mass ratio of 8:2. Vinyltrimethoxysilane is first hydrolyzed at room temperature for 30 min, and then mixed with photoinitiator 1173 at a mass ratio of 96:4. The solid content of the primer is 4 wt%.

[0035] Among them, vinyltrimethoxysilane can form covalent bonds with the surface of polyethylene substrate after hydrolysis, which greatly improves the adhesion of the coating. Photoinitiator 1173 is used to initiate the polymerization reaction of vinyl, realize the pre-curing of the primer and retain active sites for crosslinking of the topcoat.

[0036] The hydrophobic antibacterial layer 3 is formed by curing the topcoat liquid, and its dry film thickness is 700 nm. The dispersion medium of the topcoat liquid is a mixture of anhydrous ethanol and deionized water at a mass ratio of 9:1. The solid components include: 3 parts of hydrophobic fumed silica, 4 parts of methyltrimethoxysilane, 1.5 parts of stearic acid, 2.5 parts of silanized chitosan quaternary ammonium salt, 0.8 parts of polyether modified siloxane dispersant, and 0.5 parts of photoinitiator 1173. The solid content of the topcoat liquid is 10 wt%.

[0037] Among them, hydrophobic fumed silica nanoparticles are used to construct micro-nano rough structures to improve hydrophobicity; methyltrimethoxysilane is used to reduce the surface energy of the coating and participate in the cross-linking of the system; stearic acid is used to further enhance hydrophobicity and improve the flexibility of the coating; silanized chitosan quaternary ammonium salt achieves contact antibacterial effect by destroying the cell membrane of microorganisms through electrostatic adsorption; polyether modified siloxane dispersant is used to uniformly disperse nanoparticles to avoid agglomeration; and photoinitiator 1173 is used to promote the complete cross-linking of the coating to form a stable three-dimensional network.

[0038] Based on the above-mentioned component ratio of the hydrophobic and antibacterial preservation film, its preparation method is as follows: S1. Preparation and pre-corona treatment of the substrate film: Weigh the metallocene linear low-density polyethylene, low-density polyethylene and linear low-density polyethylene according to the above weight parts, mix them evenly in a high-speed mixer (500r / min, 5min) and then add them to a single-screw blow molding machine to prepare the substrate film using a single-layer blow molding process.

[0039] The screw temperature is controlled in sections: 138℃ for the feeding section, 150℃ for the compression section, and 160℃ for the metering section. The die temperature is 162℃, the blow-up ratio is 3.2, and the traction ratio is 4.2. The resulting substrate film is then subjected to pre-corona treatment with a power of 2.5kW. After treatment, the surface wet tension of the substrate is ≥38mN / m.

[0040] S2. Atmospheric pressure low temperature plasma activation treatment: The substrate film after unwinding is subjected to atmospheric pressure low temperature air plasma activation treatment on both sides. The treatment power is 5.5kW, the treatment speed is 90m / min, and the wet tension of the substrate surface after treatment is ≥42mN / m.

[0041] S3. Primer coating and UV pre-curing: The activated substrate is coated with primer on both sides simultaneously using a 180-line anilox roller micro-gravure plate. The solvent is first evaporated by hot air at 60℃, and then UV pre-curing is performed. The UV curing energy is 800mJ / cm², resulting in a substrate film with adhesion promoting layer 2.

[0042] S4. Topcoat application, UV curing and stepped hot air curing: The topcoat is applied simultaneously on both sides of the pre-cured adhesion promoting layer 2 using a 220-line anilox roller micro-gravure plate. First, UV curing is performed with an energy of 1200 mJ / cm². Then, the material is sent into a stepped hot air drying tunnel for full curing. The film speed is 90 m / min, and the temperature of the stepped hot air drying tunnel is controlled in sections at 65℃, 85℃, and 95℃.

[0043] S5. Curing, Slitting and Rolling: The fully cured film is sent into the curing chamber and cured at a constant temperature of 40℃ for 24 hours. After curing, it is slitting and rolled to obtain the hydrophobic antibacterial preservation film. Example 2

[0044] This embodiment provides a hydrophobic antibacterial food preservation film, which differs from Embodiment 1 only in that: the substrate layer 1 is composed of the following components in parts by weight: The composition consists of 60 parts of metallocene linear low-density polyethylene, 30 parts of low-density polyethylene, and 10 parts of linear low-density polyethylene; the thickness of substrate layer 1 is 10 μm.

[0045] The adhesion promoting layer 2 has a dry film thickness of 200 nm and a liquid-to-solid content of 3 wt%. The hydrophobic and antibacterial layer 3 has a dry film thickness of 600 nm and a liquid-to-solid content of 8 wt%.

[0046] Based on the above components, the preparation method is as follows, which differs from Example 1 only in that: in S1, the temperature control of the screw segment of the single-layer blow molding is 135°C for the feeding section, 145°C for the compression section, and 155°C for the metering section, with a die head temperature of 160°C, a blow-up ratio of 3.0, and a traction ratio of 4.0; the pre-corona treatment power is 2.0kW.

[0047] The S2 medium-pressure low-temperature plasma activation treatment has a power of 5.0kW and a processing speed of 100m / min.

[0048] The S4 medium-stage hot air drying tunnel has segmented temperature control at 60℃, 80℃, and 90℃, with a film speed of 100m / min. Example 3

[0049] This embodiment provides a hydrophobic antibacterial food preservation film, which differs from Embodiment 1 only in that: the substrate layer 1 is composed of the following components in parts by weight: The composition consists of 70 parts of metallocene linear low-density polyethylene, 20 parts of low-density polyethylene, and 10 parts of linear low-density polyethylene; the thickness of substrate layer 1 is 20 μm.

[0050] The adhesion promoting layer 2 has a dry film thickness of 250 nm and a liquid-to-solid content of 5 wt%. The hydrophobic and antibacterial layer 3 has a dry film thickness of 750 nm and a liquid-to-solid content of 12 wt%.

[0051] The preparation method of the hydrophobic antibacterial preservation film in this embodiment differs from that in Example 1 only in that: in S1, the temperature control of the screw segment in the single-layer blow molding is 140°C for the feeding section, 155°C for the compression section, and 165°C for the metering section, with a die head temperature of 165°C, a blow-up ratio of 3.5, and a traction ratio of 4.5; the pre-corona treatment power is 3.0kW.

[0052] In S2, the low-temperature plasma activation treatment at atmospheric pressure has a power of 6.0 kW and a processing speed of 80 m / min. In S4, the stepped hot air drying tunnel has segmented temperature control at 70℃, 90℃, and 95℃, with a film flow rate of 80 m / min. Example 4

[0053] This embodiment provides a hydrophobic antibacterial food preservation film, which differs from Embodiment 1 only in that: The mass ratio of vinyltrimethoxysilane to photoinitiator 1173 in the primer is 94:6, and the solid content of the primer is 3.5wt%.

[0054] The solid components of the topcoat liquid include: 2 parts hydrophobic fumed silica nano-silica, 3 parts methyltrimethoxysilane, 1 part stearic acid, 2 parts silanized chitosan quaternary ammonium salt, 0.5 parts polyether modified siloxane dispersant, and 0.3 parts photoinitiator 1173. The solid content of the topcoat liquid is 9 wt%.

[0055] The preparation method of the hydrophobic antibacterial preservation film in this embodiment differs from that in Example 1 only in that: In S1, the screw temperature control for single-layer blow molding is as follows: feeding section 136℃, compression section 148℃, metering section 158℃, die head temperature 161℃, blow ratio 3.1, and traction ratio 4.1.

[0056] The S2 medium-pressure low-temperature plasma activation treatment has a power of 5.2kW and a processing speed of 95m / min. Example 5

[0057] This embodiment provides a hydrophobic antibacterial preservation film, which differs from Embodiment 1 only in that the solid components of the coating liquid include: The coating consists of 4 parts hydrophobic fumed silica, 5 parts methyltrimethoxysilane, 2 parts stearic acid, 3 parts silanized chitosan quaternary ammonium salt, 1 part polyether-modified siloxane dispersant, and 11730.8 parts photoinitiator. The liquid-solid content of the topcoat is 11 wt%.

[0058] The preparation method of the hydrophobic antibacterial preservation film in this embodiment differs from that in Example 1 only in that: In S1, the screw temperature control for single-layer blow molding is as follows: feeding section 139℃, compression section 152℃, metering section 163℃, die head temperature 164℃, blow ratio 3.4, and traction ratio 4.4.

[0059] The S2 medium-pressure low-temperature plasma activation treatment has a power of 5.8kW and a processing speed of 85m / min.

[0060] Comparative Example 1 This comparative example is a commercially available ordinary food-grade polyethylene cling film without a functional coating. The substrate is a single-layer film made of linear low-density polyethylene (DFDA-7042) and low-density polyethylene (2426H), with a thickness of 15μm. It is a commercially available conventional product.

[0061] Comparative Example 2 This comparative example provides a food preservation film, which differs from Example 1 only in that: the adhesion promoting layer 2 is not provided, and the topcoat liquid is directly applied to the surface of the substrate after plasma activation; the rest of the formulation and process are the same as in Example 1.

[0062] Comparative Example 3 This comparative example provides a food preservation film that differs from Example 1 only in that: silanized chitosan quaternary ammonium salt is not added to the top coating liquid of the hydrophobic antibacterial layer 3; the rest of the formulation and process are the same as in Example 1.

[0063] Comparative Example 4 This comparative example provides a food preservation film, which differs from Example 1 only in that: unmodified hydroxypropyltrimethylammonium chloride chitosan is used to replace the silanized chitosan quaternary ammonium salt in the topcoat liquid by mass, while the rest of the formulation and process are the same as in Example 1.

[0064] Comparative Example 5 This comparative example provides a food preservation film, which differs from Example 1 only in that: a functional coating is provided on only one side of the substrate layer 1, and the other side of the substrate has no coating; the rest of the formula and process are the same as in Example 1.

[0065] Comparative Example 6 This comparative example provides a food preservation film, which differs from Example 1 only in that: the S2 low-temperature plasma activation treatment is not performed in the preparation steps, and the adhesion promotion layer 2 is directly coated after only the S1 pre-corona treatment. The rest of the formula and process are the same as in Example 1.

[0066] Based on the food preservation film samples prepared in Examples 1-5 and Comparative Examples 1-6 above, this application conducted performance tests on them. All tests adopted the currently valid national standard methods in the field of food packaging films, which can be completed with conventional laboratory equipment and without special testing conditions. The test standards are as follows: Hydrophobic performance testing includes two sub-items: water contact angle testing and cold storage anti-condensation testing. Water contact angle testing is conducted strictly in accordance with the national standard GB / T30693-2014 "Measurement of water contact angle of plastic films and sheets". This standard is applicable to the determination of water contact angle of the surface of various plastic films and sheets, and can accurately characterize the hydrophobic properties of the material surface.

[0067] Test Procedure: Before testing, the plastic wrap samples of the examples and comparative examples were placed in a standard environment for conditioning. The ambient temperature was controlled at 25°C and the relative humidity was kept stable at 50%. A contact angle meter was used for testing. During the test, a flat area without defects or wrinkles was selected on the sample surface. Five different test points were randomly selected for each sample. After adding deionized water droplets, the contact angle values ​​were collected. Finally, the arithmetic mean of the five points was taken as the water contact angle test result of the sample. This avoids the error caused by single-point testing and ensures the accuracy and representativeness of the data.

[0068] Cold storage anti-condensation test: Conducted in accordance with the conventional evaluation methods for the preservation performance of food packaging; Test Procedure: During the test, take a 500mL beaker and fill it with deionized water at 25℃ to the standard mark. Completely cover the sample of plastic wrap to be tested and seal the mouth of the beaker, ensuring that there is no air leakage or curling at the seal. Then, place the sealed beaker in a refrigerated environment with a stable temperature of 4℃ for 24 hours. After the preset time, take out the sample and observe and record the condensation adhesion on the surface of the plastic wrap sample. The results are evaluated intuitively according to three levels: no condensation, slight condensation, and severe condensation. This test can simulate the actual anti-condensation effect of plastic wrap in the refrigerated food packaging scenario and is highly consistent with the actual application scenario of the product.

[0069] Antibacterial performance test: The test was conducted in strict accordance with the national standard GB / T21866-2025 "Determination of antiviral activity and antibacterial properties of coatings". This standard is the current effective specification for testing the antibacterial performance of coating materials and is applicable to the evaluation of the antibacterial effect of the hydrophobic antibacterial layer 3 of this invention.

[0070] Test Procedure: Common pathogenic bacteria in the food packaging industry were selected as test strains, namely Escherichia coli (ATCC25922) and Staphylococcus aureus (ATCC6538). Before the test, standard bacterial suspensions were prepared according to standard requirements, and the bacterial concentration was controlled within the standard range. The plastic wrap samples to be tested were cut into standard-sized specimens, fully contacted with the bacterial suspension, and placed under standard culture conditions for constant temperature culture. The culture temperature and culture time strictly followed the standard provisions. After the culture was completed, the inhibition rate of the sample against the two strains was calculated according to the standard formula, reflecting the initial antibacterial ability of the sample.

[0071] To verify the long-lasting antibacterial properties, an additional durability test simulating wear and tear was added. Test procedure: The sample surface was repeatedly wiped 50 times with food-grade ethanol, with the wiping force and amount of wiping medium kept constant. After wiping, the antibacterial rate was tested again according to the same standard method. The change in antibacterial rate before and after wiping was compared to evaluate the stability of the antibacterial performance.

[0072] In conjunction with food contact safety requirements, antimicrobial agent migration tests were conducted. These migration tests were strictly conducted in accordance with GB31604.1-2023 "National Food Safety Standard - General Rules for Migration Testing of Plastic Materials and Articles for Food Contact" and GB5009.156-2016 "Pretreatment Methods for Migration Testing of Food Contact Materials and Articles". Test Procedure: Based on the food contact usage scenario of the cling film, select the corresponding food simulant, conduct the migration test according to the migration temperature and migration time specified in the standard, and use high-precision detection equipment to determine the content of antibacterial agent in the migration liquid. Set the detection limit of antibacterial agent migration to 0.01 mg / kg to clarify the migration level of antibacterial agent in the sample and ensure that the test results meet the evaluation requirements for food contact safety.

[0073] The coating adhesion test adopts the cross-cut test method, strictly following the national standard GB / T9286-2021 "Cross-cut test of paints and varnishes". This standard is a general specification for evaluating the adhesion strength between the coating and the substrate, and is applicable to the adhesion test of the functional coating on the surface of the food preservation film of this invention.

[0074] Test Procedure: During testing, the sample of the plastic wrap to be tested is fixed flat on a hard plate to avoid stretching or wrinkling. A standard cross-cutting tool is used to cut the surface of the sample coating. The cutting force is uniform, ensuring that the cut penetrates the coating to the substrate surface, forming a standard grid pattern. The grid size and cutting depth meet the standard requirements. After cutting, the debris on the grid surface is gently swept away with a soft brush. Then, standard tape is used to firmly adhere to the grid area. After quickly removing the tape, the coating peeling is observed. The adhesion is judged according to the standard rating system from 0 to 5, where 0 is the best level, representing no coating peeling and a tight bond with the substrate, and 5 is the worst level, representing large-area coating peeling. This rating can intuitively reflect the bonding strength between the functional coating and the polyethylene substrate, and evaluate the effect of adhesion promoting layer 2 and plasma activation treatment on improving coating adhesion.

[0075] Optical performance testing includes two indicators: light transmittance and haze. It is conducted strictly according to the national standard GB / T2410-2006, "Determination of Light Transmittance and Haze of Transparent Plastics." This standard is applicable to the optical performance testing of transparent and semi-transparent plastic films and can accurately reflect the visual transparency of the food preservation film. Before testing, samples are cut to standard sizes, and defects such as stains and scratches that may affect the test results are removed from the sample surface. A light transmittance and haze meter is used for testing. The instrument is calibrated and adjusted in advance according to the standard requirements. During testing, the light source type and optical path conditions meet the standard specifications. The visible light transmittance and haze values ​​of the samples are measured separately. Light transmittance reflects the film's ability to transmit light; a higher value indicates better film transparency. Haze reflects the degree of light scattering by the film; a lower value indicates higher film clarity. The combination of these two indicators can comprehensively evaluate the optical performance of the hydrophobic and antibacterial food preservation film, verify whether the application of functional coatings has an adverse effect on the film's transparency and clarity, and ensure that the product meets the requirements for visual food packaging.

[0076] Mechanical performance testing targets two key indicators of cling film: tensile strength at break and elongation at break. It is strictly implemented in accordance with the national standard GB / T1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets". This standard is a dedicated specification for mechanical performance testing of plastic films and is suitable for the flexible film characteristics of cling film.

[0077] Test Procedure: Before testing, the sample to be tested is cut into a standard dumbbell-shaped specimen. The size, width, and thickness of the specimen are prepared according to the standard specifications. Multiple sets of parallel specimens are prepared for each sample to ensure data reliability. A universal electronic tensile testing machine is used for testing. The testing machine is calibrated for force and displacement in advance, and the tensile speed is set to 500 mm / min. This speed meets the testing requirements for film specimens in the standard. During the test, the two ends of the specimen are clamped and the specimen is stretched at a constant speed until it breaks. The maximum force value and the elongation at break are recorded during the tensile process. The tensile breaking strength and elongation at break are calculated according to the standard formula. The tensile breaking strength reflects the film's ability to resist tensile breakage and reflects the film's mechanical strength. The elongation at break reflects the film's flexibility and extensibility. These two indicators can comprehensively evaluate the film's resistance to damage and tensile strength during use, verify the influence of substrate formulation and functional coating on the film's mechanical properties, and ensure that the product meets the mechanical performance requirements for packaging use.

[0078] Based on the above performance testing methods, the following test results were obtained: Table 1: Results of Hydrophobicity Tests

[0079] Table 2: Results of Antibacterial Performance Test

[0080] Table 3: Overall Performance Test Results

[0081] The following conclusions can be drawn from the test results in Table 1-3 above: Hydrophobic properties: The water contact angle of Examples 1-5 of this invention is ≥115°, and there is no condensation after refrigeration at 4℃ for 24 hours, which is far superior to ordinary PE cling film sold in the market.

[0082] Among them, hydrophobic fumed nano silica, methyltrimethoxysilane, and stearic acid are the core hydrophobic components. The hydrophobic fumed nano silica constructs a micro-nano rough structure, methyltrimethoxysilane reduces the surface energy of the coating and crosslinks and fixes the nanoparticles, and stearic acid further reduces the surface energy and improves the flexibility of the coating. The three work together to construct a stable hydrophobic interface.

[0083] Comparative Example 4, due to the use of hydrophilic unmodified chitosan quaternary ammonium salt, disrupted the integrity of the hydrophobic interface, resulting in a water contact angle of 98° and slight condensation. Comparative Example 2 (without adhesion promoting layer 2) and Comparative Example 6 (without plasma activation) showed insufficient coating adhesion, preventing the hydrophobic components from being stably fixed and leading to a decrease in hydrophobic performance. Comparative Example 5, with single-sided coating and no hydrophobic components on the uncoated side, showed severe condensation on one side, verifying the necessity of double-sided coating and interfacial covalent bonding for stable hydrophobic effects.

[0084] Antibacterial performance: Examples 1-5 showed an antibacterial rate of ≥99.5% against pathogenic bacteria, with no significant attenuation after 50 wiping cycles, and the migration amount of the antibacterial agent was below the detection limit.

[0085] Among them, silanized chitosan quaternary ammonium salt is the core contact antibacterial component. It achieves sterilization through the electrostatic adsorption of quaternary ammonium salt cations to microbial cell membranes. The silanization modification allows it to be covalently bonded to the three-dimensional network of the coating, with no migration and long-term stability. Photoinitiator 1173 promotes the cross-linking of the coating, firmly fixing the antibacterial component and forming a synergy with the three-dimensional network of hydrophobic components, thus avoiding the precipitation of antibacterial agent.

[0086] Comparative Example 3 had no antibacterial components and completely lost its antibacterial effect; Comparative Example 4, the unsilanized antibacterial agent was water-soluble and could not be covalently bonded, making it easy to migrate and precipitate. After 50 wiping cycles, the antibacterial rate dropped significantly to 61.8%, and a migration amount of 0.85 mg / kg was detected, indicating a failure of long-term effectiveness; Comparative Examples 2 and 6 had poor coating adhesion, and after wiping, the coating partially peeled off, the antibacterial components were lost, and the antibacterial rate dropped significantly, verifying the core role of the covalently bonded antibacterial components in the stable bonding with the coating.

[0087] Overall performance: The coating adhesion of all examples is grade 0, and the light transmittance, haze and mechanical properties meet the requirements for use in food preservation films. The overall performance is better than that of conventional products.

[0088] Among them, the metallocene linear low-density polyethylene, low-density polyethylene and linear low-density polyethylene in the substrate layer 1 work together. The metallocene linear low-density polyethylene provides tensile strength, puncture resistance and transparency, the low-density polyethylene improves the strength of blow molding melt and the wrapping flexibility, and the linear low-density polyethylene balances mechanical uniformity and processing stability. The combination of the three ensures the basic performance of the substrate.

[0089] In the adhesion promoting layer 2, vinyltrimethoxysilane and photoinitiator 1173 work synergistically. After the vinyltrimethoxysilane is hydrolyzed, it covalently bonds with the substrate. The photoinitiator 1173 initiates polymerization to achieve pre-curing and retains active sites, thus building a connection bridge between the substrate and the hydrophobic antibacterial layer 3 and improving the interlayer adhesion.

[0090] In the hydrophobic antibacterial layer 3, the polyether-modified siloxane dispersant works synergistically with the hydrophobic fumed silica nanoparticles. The dispersant prevents the agglomeration of nanoparticles, ensuring the uniformity of the hydrophobic structure, while also helping to improve the leveling properties of the coating. The photoinitiator 1173 simultaneously initiates cross-linking of the primer and topcoat, enabling the adhesion promotion layer 2 and the hydrophobic antibacterial layer 3 to form a three-dimensional interpenetrating network, achieving seamless bonding between layers.

[0091] After process optimization, the film has no risk of thermal deformation. The synergistic effect of each component and structural layer gives the product excellent hydrophobicity, antibacterial properties, adhesion, optical and mechanical properties, meeting the requirements of industrial production and food contact safety.

[0092] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A hydrophobic antibacterial food preservation film, characterized in that, It includes a substrate layer (1) made of a single polyethylene material, and functional coatings are provided on both sides of the substrate layer (1); the functional coatings are, from the inside to the outside, an adhesion promoting layer (2) and a hydrophobic antibacterial layer (3). The adhesion promoting layer (2) is formed by curing a primer containing vinyltrimethoxysilane, and it is covalently bonded to the substrate layer (1). The hydrophobic antibacterial layer (3) and the adhesion promoting layer (2) form a three-dimensional network structure through a cross-linking reaction. The hydrophobic antibacterial layer (3) contains covalently bonded hydrophobic components and contact antibacterial components. The hydrophobic component includes hydrophobic fumed silica nanoparticles, methyltrimethoxysilane, and stearic acid; the contact antibacterial component includes silanized chitosan quaternary ammonium salt.

2. The hydrophobic antibacterial food preservation film according to claim 1, characterized in that, The substrate layer (1) is composed of the following components in parts by weight: 60-70 parts of metallocene linear low-density polyethylene, 20-30 parts of low-density polyethylene, and 10 parts of linear low-density polyethylene.

3. The hydrophobic antibacterial food preservation film according to claim 1, characterized in that, The adhesion promoting layer (2) is formed by curing a primer liquid. The dispersion medium of the primer liquid is a mixture of anhydrous ethanol and deionized water, and the solid components include vinyltrimethoxysilane and photoinitiator 1173.

4. The hydrophobic antibacterial food preservation film according to claim 1, characterized in that, The hydrophobic antibacterial layer (3) also includes photoinitiator 1173 and polyether-modified siloxane dispersant.

5. The hydrophobic antibacterial preservation film according to claim 1, characterized in that, The substrate layer (1) has a thickness of 10-20 μm, the adhesion promoting layer (2) has a dry film thickness of 200-250 nm, and the hydrophobic antibacterial layer (3) has a dry film thickness of 600-750 nm.

6. A method for preparing a hydrophobic antibacterial food preservation film as described in any one of claims 1-5, characterized in that, Includes the following steps: S1: A single-layer blow molding process is used to prepare a single polyethylene substrate film, and the substrate film is pre-corona treated. S2: Perform low-temperature plasma activation treatment on the substrate film after unwinding; S3: Apply a primer containing vinyltrimethoxysilane to both sides of the activated substrate simultaneously, and perform UV pre-curing to obtain an adhesion promoting layer (2). S4: Apply a topcoat containing hydrophobic components and silanized chitosan quaternary ammonium salt to both sides of the pre-cured adhesion promoting layer (2), and perform UV curing and step-by-step hot air curing in sequence to obtain a hydrophobic antibacterial layer (3). S5: The fully cured film is then subjected to a curing treatment, and then slit and rolled to obtain a hydrophobic and antibacterial food preservation film.

7. The method for preparing a hydrophobic antibacterial preservation film according to claim 6, characterized in that, In step S1, the temperature control of the screw in single-layer blow molding is as follows: feeding section 135-140℃, compression section 145-155℃, metering section 155-165℃, die head temperature 160-165℃, blow ratio 3.0-3.5, and traction ratio 4.0-4.

5.

8. The method for preparing a hydrophobic antibacterial food preservation film according to claim 6, characterized in that, In step S3, the adhesion promoting layer (2) is coated using a 180-line anilox roller micro-gravure coating with an ultraviolet curing energy of 800 mJ / cm²; in step S4, the hydrophobic antibacterial layer (3) is coated using a 220-line anilox roller micro-gravure coating with an ultraviolet curing energy of 1200 mJ / cm².

9. The method for preparing a hydrophobic antibacterial food preservation film according to claim 6, characterized in that, The surface coating liquid contains silanized chitosan quaternary ammonium salt, which is prepared by reacting hydroxypropyltrimethylammonium chloride chitosan with γ-glycidoxypropyltrimethoxysilane at a mass ratio of 3:1 under conditions of 55°C and pH 5.

5.

10. The method for preparing a hydrophobic antibacterial food preservation film according to claim 6, characterized in that, In step S4, the temperature of the stepped hot air drying tunnel is controlled in sections of 60-70℃, 80-90℃, and 90-100℃; in step S5, the curing treatment is constant temperature curing at 40℃ for 24 hours.

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