A multi-layer composite self-adhesive label for food packaging and a method for preparing the same

Abstract

The application discloses a kind of multilayer composite self-adhesive label for food packaging and preparation method thereof, it is related to label material technical field, including base paper layer, adhesive layer, surface paper layer, the base paper layer selects the kraft paper coated with silicon oil, the side of surface paper layer away from adhesive layer is coated with polyvinyl alcohol coating, and adhesive layer uses acrylate adhesive.The polyvinyl alcohol coating is arranged on the surface paper layer of self-adhesive label in the application, realizes high barrier property, solves the problem that traditional label only has identification function without protection ability, solves the problem that traditional label is easily eroded by environment, improves the adaptability of label in high humidity environment.

Description

Technical Field

[0001] This invention relates to the field of label material technology, specifically to a multi-layer composite self-adhesive label for food packaging and its preparation method. Background Technology

[0002] Modern consumers are increasingly concerned about information such as the source of ingredients, nutritional value, and shelf life of food products. Self-adhesive labels offer ample surface area and excellent printability, allowing them to clearly and completely convey this mandatory and promotional information. Globalized logistics necessitates long-distance transportation and multiple handling of food products, placing higher demands on label durability.

[0003] Traditional single-material labels have significant limitations in complex food packaging applications, failing to effectively prevent the penetration of water vapor, oxygen, and oils. For foods with high moisture, high oil content, or those sensitive to oxygen, such as dairy products, fried snacks, and meats, the degradation of label performance can indirectly affect the integrity of the packaging.

[0004] Patent CN114043780B discloses a self-adhesive label and its preparation method. The above patent achieves reinforcement in the tearing direction of the self-adhesive label, avoids the paper bending phenomenon after tearing the self-adhesive label, and reduces the probability of the label curling phenomenon when using the self-adhesive label.

[0005] The aforementioned patent pastes high-basis-weight coated paper on both sides of the core paper to increase the overall thickness of the paper, thus solving the problem that peeled self-adhesive labels tend to curl in the tearing direction, making them difficult to use and prone to label contamination. However, there is still room for improvement in label protection. This application solves the problem that traditional labels only have marking functions but no protective capabilities by setting a coating on the self-adhesive label.

[0006] Therefore, this application proposes a method for preparing a multilayer composite self-adhesive label for high-barrier food packaging. Summary of the Invention

[0007] The purpose of this invention is to provide a multi-layer composite self-adhesive label for food packaging and its preparation method, so as to solve the technical problem mentioned in the background art that traditional labels only have identification functions but no protective capabilities.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a multi-layer composite self-adhesive label for food packaging, characterized in that it comprises a base paper layer, an adhesive layer, and a face paper layer. The base paper layer is made of kraft paper coated with silicone oil. The face paper layer is coated with a polyvinyl alcohol coating on the side away from the adhesive layer. The adhesive layer uses an acrylic adhesive. The polyvinyl alcohol coating comprises the following components by weight: 80 parts polyvinyl alcohol, 10-15 parts hydrophobic modifier, 10-15 parts vanillin Schiff base derivative, 5-10 parts nanofiller, 2-5 parts ε-polylysine, and 5-10 parts alkylated chitosan.

[0009] Preferably, the hydrophobic modifier is glyceryl monostearate, and the nanofiller is nanocellulose.

[0010] Preferably, the polyvinyl alcohol coating is made of polyvinyl alcohol coating liquid, and the preparation method of the polyvinyl alcohol coating liquid includes the following steps:

[0011] Polyvinyl alcohol was dissolved in deionized water to prepare a 10% (w / w) aqueous solution. Nanocellulose, ε-polylysine, vanillin Schiff base derivative, glyceryl monostearate, and alkylated chitosan were added and stirred until homogeneous to obtain the polyvinyl alcohol coating solution.

[0012] Preferably, the vanillin Schiff base derivative is a vanillin-amino acid Schiff base derivative, and the preparation method of the vanillin-amino acid Schiff base derivative includes the following steps:

[0013] Glycine was poured into ethanol, potassium hydroxide was added, and the mixture was stirred in a 50°C water bath for 3 hours to obtain a glycine salt solution.

[0014] Vanillin was poured into ethanol, and glycine salt solution was slowly added dropwise. After washing and drying, vanillin-amino acid Schiff base derivatives were obtained.

[0015] Preferably, the preparation method of the acrylate adhesive includes the following steps:

[0016] Acrylic acid, styrene, methyl methacrylate, propylene glycol methyl ether acetate, azobisisobutyronitrile, vinyl polysiloxane, and vinyl quaternary ammonium salt were poured into a reaction vessel and stirred at 100°C for 2 hours. Then, a nano-dispersion was added and stirred for 30 minutes to obtain an acrylate adhesive.

[0017] Preferably, the method for preparing the alkylated chitosan includes the following steps:

[0018] Mix isopropanol and sodium hydroxide solution, add chitosan, add glycidyl ammonium chloride, heat to 70°C, filter, wash and dry to obtain alkylated chitosan.

[0019] Preferably, the preparation method of the glycidyl ammonium chloride includes the following steps:

[0020] Dodecyl dimethylamine was added dropwise to epichlorohydrin and the temperature was raised to 50°C to obtain epichlorohydrin ammonium chloride.

[0021] Preferably, the preparation method of the nano-dispersion includes the following steps:

[0022] Carbon nanotubes were added to propylene glycol methyl ether acetate and ultrasonically dispersed to obtain a nano-dispersion.

[0023] Preferably, the method for preparing the self-adhesive label includes the following steps:

[0024] S1. Apply polyvinyl alcohol coating liquid to one side of the face paper layer and immediately send it into the drying chamber for drying and curing treatment to form a polyvinyl alcohol coating.

[0025] S2. Using a coating machine, apply acrylic adhesive to the side of the face paper layer away from the polyvinyl alcohol coating to form an adhesive layer.

[0026] S3. Adhere the side of the backing paper coated with silicone oil to the side of the face paper coated with acrylic adhesive to obtain a composite self-adhesive label.

[0027] Preferably, the method for preparing the self-adhesive label further includes the following steps:

[0028] S11. Discharge treatment is performed on the surface of the paper layer using a high-voltage corona treatment machine.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. This invention achieves high barrier properties by setting a polyvinyl alcohol coating on the face paper layer of the self-adhesive label, solving the problem that traditional labels only have marking functions but no protective capabilities, solving the problem that traditional labels are easily corroded by the environment, and improving the adaptability of the label in high humidity environments;

[0031] 2. By introducing glyceryl monostearate and nanocellulose, this invention achieves hydrophobicity of the coating surface, maintains the microstructural integrity and density of the label coating in humid environments, improves the functional reliability and service life of the label in humid circulation environments, and enhances the barrier performance stability of the coating in high humidity environments.

[0032] 3. By introducing vanillin Schiff base derivatives and ε-polylysine, this invention achieves high durability of the label's UV shielding function and high stability of its appearance quality, thereby improving the label's functional reliability and solving the problem of label discoloration that easily occurs in complex circulation environments.

[0033] 4. By introducing alkylated chitosan, the good compatibility and hydrogen bonding between the molecular chains of alkylated chitosan and the polyvinyl alcohol matrix enhance the coating structure, effectively reducing the risk of cross-contamination caused by microbial contamination on the label surface, and improving the hygienic quality and consumer safety of food. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the self-adhesive label manufacturing process of the present invention;

[0035] Figure 2 This is a schematic diagram of the preparation process of the polyvinyl alcohol coating liquid of the present invention;

[0036] Figure 3 This is a schematic diagram of the preparation process of the acrylate adhesive of the present invention;

[0037] Figure 4 This is a schematic diagram of the glycine salt solution preparation process of the present invention;

[0038] Figure 5 This is a schematic diagram of the preparation process of vanillin Schiff base derivatives according to the present invention.

[0039] Figure 6 This is a schematic diagram of the alkylated chitosan preparation process of the present invention;

[0040] Figure 7 This is a schematic diagram of the preparation process of glycidyl ammonium chloride according to the present invention;

[0041] Figure 8 This is a schematic diagram of the preparation process of the nano-dispersion of the present invention. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Example 1, please refer to Figure 1 and Figure 2 A multi-layer composite self-adhesive label for food packaging, the method for preparing the self-adhesive label includes the following steps:

[0044] Dissolve 80 parts of polyvinyl alcohol in deionized water to prepare a 10% (w / w) aqueous solution. Add 10 parts of nanocellulose, 5 parts of ε-polylysine, 15 parts of vanillin Schiff base derivative, 15 parts of glyceryl monostearate, and 10 parts of alkylated chitosan. Stir until homogeneous to obtain a polyvinyl alcohol coating solution.

[0045] A high-voltage corona treatment machine is used to discharge the surface of the face paper layer, and polyvinyl alcohol coating liquid is applied to one side of the face paper layer. The paper is then immediately sent into a drying chamber for drying and curing to form a polyvinyl alcohol coating. An acrylic adhesive is then applied to the side of the face paper layer away from the polyvinyl alcohol coating using a coating machine to form an adhesive layer. The side of the back paper layer coated with silicone oil is then bonded to the side of the face paper layer coated with acrylic adhesive to obtain a self-adhesive label.

[0046] Furthermore, polyvinyl alcohol (PVA) serves as the film-forming matrix of the coating, providing its basic framework. Nanocellulose, as a nano-reinforcing filler, forms a three-dimensional network structure within the PVA matrix. Through its large specific surface area, it generates strong hydrogen bonds with the PVA molecular chains, effectively transferring and dispersing stress, resulting in significant reinforcement and toughening effects. This allows the label surface to resist damage caused by scratches and friction, ensuring the integrity of printed graphics during distribution and shelving. ε-polylysine, as a biomacromolecule, can form a cross-linked network with other components in the coating, thereby improving its physical properties. The hydrogen bonds formed between the amino groups of ε-polylysine and the hydroxyl groups on the PVA molecular chains increase the cross-linking density between PVA molecular chains, making the coating structure denser. This enhances the coating's barrier properties against small molecules, reduces its free volume and porosity, making it difficult for water molecules to diffuse within the coating, effectively reducing water vapor permeability and improving the coating's intrinsic moisture barrier properties. Glyceryl monostearate, as a nonionic surfactant, has a molecular structure with a hydrophilic glyceryl ester group at one end and a long-chain alkane at the other. During the coating film formation process, the hydrophobic ends of glyceryl monostearate tend to migrate to the coating-air interface, enriching the coating surface with a layer of non-polar methyl groups. This hinders the initial wetting of the coating by liquid water and reduces the overall hygroscopicity of the coating. In food packaging environments, when the label comes into contact with moisture, condensation, detergents, or accidentally spilled liquids, the polyvinyl alcohol coating effectively prevents moisture from penetrating into the label, avoiding blurring and fading of printed text and patterns caused by moisture. This ensures that important information such as production date and shelf life remains clear during storage and transportation. The cross-linking network formed by ε-polylysine strengthens the structural stability of the coating, maintaining its barrier properties in long-term humid environments and preventing swelling or peeling of the coating due to moisture erosion. The hydrophobic layer formed by glyceryl monostearate on the coating surface reduces the adhesion time of liquids on the label surface and reduces the possibility of moisture penetration through the surface. This synergistically improves the water resistance and durability of the label, ensuring the information integrity and appearance stability of food packaging labels under complex storage and transportation conditions.

[0047] Example 2, please refer to Figure 1 , Figure 2 , Figure 4 and Figure 5A multi-layer composite self-adhesive label for food packaging, the method for preparing the self-adhesive label includes the following steps:

[0048] Glycine was poured into ethanol, potassium hydroxide was added, and the mixture was stirred in a 50°C water bath for 3 hours to obtain a glycine salt solution. Vanillin was poured into ethanol, and the glycine salt solution was slowly added dropwise. After washing and drying, vanillin-amino acid Schiff base derivatives were obtained, namely vanillin Schiff base derivatives.

[0049] Dissolve 80 parts of polyvinyl alcohol in deionized water to prepare a 10% (w / w) aqueous solution. Add 9 parts of nanocellulose, 5 parts of ε-polylysine, 14 parts of vanillin Schiff base derivative, 14 parts of glyceryl monostearate, and 9 parts of alkylated chitosan. Stir until homogeneous to obtain a polyvinyl alcohol coating solution.

[0050] The surface of the face paper layer is subjected to electrical discharge treatment. Polyvinyl alcohol coating liquid is applied to one side of the face paper layer and dried and cured to form a polyvinyl alcohol coating. Acrylic adhesive is applied to the face paper layer to form an adhesive layer. The back paper layer is then bonded to the face paper layer to obtain a self-adhesive label.

[0051] Furthermore, vanillin Schiff base derivatives, as ultraviolet absorbers, can convert harmful ultraviolet rays into harmless heat energy, achieving protection. Compared with the raw material vanillin, the derivatives exhibit a red shift in their maximum absorption wavelength due to the expansion of the conjugated system, resulting in a wider ultraviolet absorption range and enhanced absorption capacity for ultraviolet rays, achieving more comprehensive protection. The imine bonds in the vanillin Schiff base derivative molecule are the source of its ultraviolet shielding function, but they are prone to hydrolysis or protonation in humid environments, leading to a decrease in the ultraviolet absorption capacity of the coating. This results in discoloration and distortion of patterns and text printed on labels, affecting the label's information readability. The ε-polylysine molecular chain is rich in positively charged amino groups, which can interact with vanillin Schiff base derivatives. The nitrogen atoms with partial negative charges in the imine bonds of the material undergo strong electrostatic attraction to form a stable complex, thereby effectively inhibiting the discoloration problem of vanillin Schiff base derivatives in high humidity environments. This ensures the stability of label color and the clarity of printed text throughout the entire distribution process, and prevents the label's UV shielding function from rapidly decaying due to environmental humidity. In addition, the complexation of ε-polylysine with vanillin Schiff base derivatives, as well as the hydrogen bond network formed between ε-polylysine and polyvinyl alcohol and alkylated chitosan, constitute a dense three-dimensional cross-linked structure, enhancing the label's wear and scratch resistance. This makes the label surface less prone to scratches or wear during handling, shelving, and consumer handling, thus protecting the printed information from damage.

[0052] Example 3, please refer to Figure 1 , Figure 2 , Figure 3 and Figure 8A multi-layer composite self-adhesive label for food packaging, the method for preparing the self-adhesive label includes the following steps:

[0053] Carbon nanotubes were added to propylene glycol methyl ether acetate and ultrasonically dispersed to obtain a nano-dispersion. Acrylic acid, styrene, methyl methacrylate, propylene glycol methyl ether acetate, azobisisobutyronitrile, vinyl polysiloxane, and vinyl quaternary ammonium salt were poured into a reaction vessel and stirred at 100°C for 2 hours. The nano-dispersion was then added and stirred for 30 minutes to obtain an acrylate adhesive.

[0054] Dissolve 80 parts of polyvinyl alcohol in deionized water to prepare a 10% (w / w) aqueous solution. Add 8 parts of nanocellulose, 4 parts of ε-polylysine, 13 parts of vanillin Schiff base derivative, 13 parts of glyceryl monostearate, and 8 parts of alkylated chitosan. Stir until homogeneous to obtain a polyvinyl alcohol coating solution.

[0055] The surface of the face paper layer is subjected to electrical discharge treatment. Polyvinyl alcohol coating liquid is applied to one side of the face paper layer and dried and cured to form a polyvinyl alcohol coating. Acrylic adhesive is applied to the face paper layer to form an adhesive layer. The back paper layer is then bonded to the face paper layer to obtain a self-adhesive label.

[0056] Furthermore, the adhesive's main chain backbone is formed by free radical copolymerization of acrylic acid, methyl methacrylate, and styrene. Acrylic acid provides carboxyl groups, methyl methacrylate provides ester groups, and styrene provides a benzene ring structure. The synergistic effect of these three groups endows the adhesive with excellent bonding performance and chemical stability. Carboxyl groups can form hydrogen bonds or chemical bonds with the surface of the adherend, enhancing interfacial bonding. Ester groups impart a certain rigidity and hardness to the polymer chain, preventing the label from slipping due to an overly soft adhesive layer. The benzene ring structure further enhances the cohesive strength of the polymer. Vinyl polysiloxane segments tend to migrate to the adhesive-air interface and the adhesive-substrate interface, forming a hydrophobic layer that effectively blocks the penetration of water vapor and polar liquids in the environment, thereby improving the adhesive's water resistance. Vinyl quaternary ammonium salt acts as a dual ionic crosslinking point. The quaternary ammonium cations in the vinyl quaternary ammonium salt form ionic bonds with the carboxyl groups of acrylic acid, enhancing the adhesive's cohesive strength and crosslinking density. At the same time, the quaternary ammonium cations also impart certain properties to the adhesive. The antibacterial properties of the labels prevent bacterial growth in humid environments, thus protecting food packaging safety. Carbon nanotubes dispersed in the adhesive form a three-dimensional network with the polymer chains, effectively blocking solvent molecule penetration and reducing adhesive swelling. Stress dispersion also enhances adhesion durability. The main chain is constructed through free radical copolymerization, with ionic bonding strengthening the cohesion. Hydrophobic protection is achieved through vinyl polysiloxane migration, and a nano-reinforcing network is built through carbon nanotube doping. This ensures high bonding strength while also providing excellent water resistance, solvent resistance, and mechanical stability, providing reliable assurance for the long-term stable use of self-adhesive labels in complex food packaging environments. It solves the problems of traditional self-adhesive labels easily detaching and swelling in humid, multi-solvent environments, and reduces the potential risks to the overall hygiene of food packaging caused by microbial growth. This further improves the comprehensive performance and reliability of self-adhesive labels for food packaging.

[0057] Example 4, please refer to Figure 1 , Figure 2 , Figure 6 and Figure 7 A multi-layer composite self-adhesive label for food packaging, the method for preparing the self-adhesive label includes the following steps:

[0058] Dodecyl dimethylamine was added dropwise to epichlorohydrin and heated to 50°C to obtain epipropylammonium chloride. Isopropanol and sodium hydroxide solution were mixed, chitosan was added, epipropylammonium chloride was added, and the temperature was raised to 70°C. The mixture was filtered, washed, and dried to obtain alkylated chitosan.

[0059] Dissolve 80 parts of polyvinyl alcohol in deionized water to prepare a 10% (w / w) aqueous solution. Add 7 parts of nanocellulose, 3 parts of ε-polylysine, 12 parts of vanillin Schiff base derivative, 12 parts of glyceryl monostearate, and 7 parts of alkylated chitosan. Stir until homogeneous to obtain a polyvinyl alcohol coating solution.

[0060] The surface of the face paper layer is subjected to electrical discharge treatment. Polyvinyl alcohol coating liquid is applied to one side of the face paper layer and dried and cured to form a polyvinyl alcohol coating. Acrylic adhesive is applied to the face paper layer to form an adhesive layer. The back paper layer is then bonded to the face paper layer to obtain a self-adhesive label.

[0061] Furthermore, the amino and hydroxyl groups on the alkylated chitosan backbone form intermolecular hydrogen bonds with the hydroxyl groups of polyvinyl alcohol and nanocellulose. This three-dimensional hydrogen bond network acts as physical crosslinking points, effectively dispersing stress and making the coating matrix more robust and flexible. Simultaneously, the amino groups in the ε-polylysine molecule can form additional hydrogen bonds with the hydroxyl groups of polyvinyl alcohol, further enhancing the stability of the network structure. Alkylated chitosan also improves the interfacial compatibility between polyvinyl alcohol and nanocellulose, anchoring nanocellulose more uniformly within the polyvinyl alcohol matrix through hydrogen bonding, reducing agglomeration, achieving more effective stress transfer, and forming a rigid reinforcing network. Moreover, strong hydrophobic interactions and van der Waals forces exist between the hydrophobic long-chain alkyl groups of alkylated chitosan and the hydrophobic alkyl chains of glyceryl monostearate, causing the hydrophobic ends of alkylated chitosan and glyceryl monostearate molecules to migrate and align towards the coating-air interface, thus forming a stable, low-surface-energy region rich in long-chain alkyl groups on the coating surface, increasing the hydrophobic contact angle of the coating. Inside the coating, alkylated chitosan and glyceryl monostearate... The hydrophobic segments of the ester self-assemble through hydrophobic interactions, intertwining with the hydrophilic network of the material to form a dense structure. This effectively prolongs the diffusion paths of water and oxygen molecules, thus significantly reducing water vapor permeability. Vanillin Schiff base derivatives possess a certain degree of hydrophobicity. The hydrophobic cavities of alkylated chitosan, or through hydrophobic interactions, can encapsulate or bind vanillin Schiff base molecules, reducing their spontaneous aggregation and ensuring uniform dispersion of vanillin Schiff base derivatives within the polyvinyl alcohol matrix. Furthermore, the cationic quaternary ammonium salt groups of alkylated chitosan act on the negatively charged bacterial cell membrane through electrostatic adsorption, disrupting the integrity of the cell membrane structure and leading to leakage of cell contents. ε-Polylysine, as a positively charged small molecule polypeptide, more easily enters the cell after the alkylated chitosan disrupts the cell membrane integrity. It binds to intracellular targets such as ribosomes, inhibiting protein synthesis, interfering with metabolism, and leading to cell death. This achieves an antibacterial effect, inhibiting bacterial growth on the label surface, improving the hygiene and safety of the label, and preventing mold growth from affecting the label's appearance and hygiene.

[0062] Example 5, please refer to Figure 1 and Figure 2 A multi-layer composite self-adhesive label for food packaging, the method for preparing the self-adhesive label includes the following steps:

[0063] Dissolve 80 parts of polyvinyl alcohol in deionized water to prepare a 10% (w / w) aqueous solution. Add 6 parts of nanocellulose, 2 parts of ε-polylysine, 11 parts of vanillin Schiff base derivative, 11 parts of glyceryl monostearate, and 6 parts of alkylated chitosan. Stir until homogeneous to obtain a polyvinyl alcohol coating solution.

[0064] The surface of the face paper layer is subjected to electrical discharge treatment. Polyvinyl alcohol coating liquid is applied to one side of the face paper layer and dried and cured to form a polyvinyl alcohol coating. Acrylic adhesive is applied to the face paper layer to form an adhesive layer. The back paper layer is then bonded to the face paper layer to obtain a self-adhesive label.

[0065] Example 6, please refer to Figure 1 and Figure 2 A multi-layer composite self-adhesive label for food packaging, the method for preparing the self-adhesive label includes the following steps:

[0066] Dissolve 80 parts of polyvinyl alcohol in deionized water to prepare a 10% (w / w) aqueous solution. Add 5 parts of nanocellulose, 2 parts of ε-polylysine, 10 parts of vanillin Schiff base derivative, 10 parts of glyceryl monostearate, and 5 parts of alkylated chitosan. Stir until homogeneous to obtain a polyvinyl alcohol coating solution.

[0067] The surface of the face paper layer is subjected to electrical discharge treatment. Polyvinyl alcohol coating liquid is applied to one side of the face paper layer and dried and cured to form a polyvinyl alcohol coating. Acrylic adhesive is applied to the face paper layer to form an adhesive layer. The back paper layer is then bonded to the face paper layer to obtain a self-adhesive label.

[0068] Comparative Example 1: A multi-layer composite self-adhesive label for food packaging, wherein the preparation method of the self-adhesive label includes the following steps:

[0069] Dissolve 80 parts of polyvinyl alcohol in deionized water to prepare a 10% (w / w) aqueous solution. Add 10 parts of nanocellulose, 5 parts of ε-polylysine, 15 parts of glyceryl monostearate, and 10 parts of alkylated chitosan. Stir until homogeneous to obtain a polyvinyl alcohol coating solution.

[0070] The surface of the face paper layer is subjected to electrical discharge treatment. Polyvinyl alcohol coating liquid is applied to one side of the face paper layer and dried and cured to form a polyvinyl alcohol coating. Acrylic adhesive is applied to the face paper layer to form an adhesive layer. The back paper layer is then bonded to the face paper layer to obtain a self-adhesive label.

[0071] Comparative Example 2: A multi-layer composite self-adhesive label for food packaging, wherein the preparation method of the self-adhesive label includes the following steps:

[0072] Dissolve 80 parts of polyvinyl alcohol in deionized water to prepare a 10% (w / w) aqueous solution. Add 10 parts of nanocellulose, 5 parts of ε-polylysine, 15 parts of vanillin Schiff base derivative, and 10 parts of alkylated chitosan. Stir until homogeneous to obtain a polyvinyl alcohol coating solution.

[0073] The surface of the face paper layer is subjected to electrical discharge treatment. Polyvinyl alcohol coating liquid is applied to one side of the face paper layer and dried and cured to form a polyvinyl alcohol coating. Acrylic adhesive is applied to the face paper layer to form an adhesive layer. The back paper layer is then bonded to the face paper layer to obtain a self-adhesive label.

[0074] Performance testing

[0075] Test 1 Water vapor barrier performance test: The polyvinyl alcohol coating liquid prepared in Examples 1-6 and Comparative Examples 1-2 was coated on PE film to obtain samples. The samples were tested using a water vapor transmission test system. According to GB / T1037-2021 standard, the test conditions were 38℃ and 90%RH.

[0076] Test 2: Surface hydrophobicity test: The polyvinyl alcohol coating solutions prepared in Examples 1-6 and Comparative Examples 1-2 were coated on PE films to obtain samples. 1 μL of ultrapure water droplets were dropped onto the sample surface through a microsyringe, according to GB / T30693-2014 standard.

[0077] Test 3 Optical performance test: The polyvinyl alcohol coating liquid prepared in Examples 1-6 and Comparative Examples 1-2 was coated on PE film to obtain samples. The samples were tested using a transmittance / haze tester according to GB / T 18830-2009 standard.

[0078] Test 4 Antibacterial performance test: The polyvinyl alcohol coating solutions prepared in Examples 1-6 and Comparative Examples 1-2 were coated on plates. The resulting coatings were cut into 1cm×1cm samples. The samples were immersed in centrifuge tubes containing 1 mL of bacterial suspension and incubated at 37°C for 2 hours. 100 μL of bacterial suspension was then taken and serially diluted 10 times.

[0079]

[0080]

[0081] In summary, through performance tests in Examples 1-6 and Comparative Examples 1-2, the addition of vanillin Schiff base derivatives to the polyvinyl alcohol coating improved the UV shielding performance of the coating; the introduction of glyceryl monostearate improved the water vapor barrier performance, effectively reduced the material's sensitivity to moisture and transmittance, reduced the surface energy of the coating, and improved hydrophobicity.

[0082] Working principle: The polyvinyl alcohol coating is located on the outside of the face paper layer, serving as a barrier for the label. The hydroxyl groups on the polyvinyl alcohol molecular chain provide abundant reaction sites for other components in the polyvinyl alcohol coating. Through hydrogen bonds, it combines with nanocellulose, alkylated chitosan, ε-polylysine, etc., to form a dense cross-linked network, further enhancing the barrier performance of the coating.

[0083] The network structure of nanocellulose can extend the diffusion path of small molecules such as water vapor and oxygen in the coating, and synergistically improve the barrier performance of the coating. The hydrophobic long-chain alkane of glyceryl monostearate effectively reduces the surface energy of the coating, increases the water contact angle of the coating, slows down the adsorption and penetration of water vapor, and maintains the stability of the barrier performance of the coating in high humidity environment.

[0084] ε-polylysine and vanillin Schiff base derivatives form a stable complex through electrostatic interaction, which inhibits the hydrolysis of imine bonds in vanillin Schiff base derivatives under high humidity conditions, thereby maintaining the long-term effectiveness of the coating's UV shielding performance.

[0085] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A multi-layer composite self-adhesive label for food packaging, characterized in that: It includes a base paper layer, an adhesive layer, and a face paper layer. The base paper layer is made of kraft paper coated with silicone oil. The face paper layer is coated with a polyvinyl alcohol coating on the side away from the adhesive layer. The adhesive layer uses an acrylic adhesive. The polyvinyl alcohol coating includes the following components by weight: 80 parts polyvinyl alcohol, 10-15 parts hydrophobic modifier, 10-15 parts vanillin Schiff base derivative, 5-10 parts nanofiller, 2-5 parts ε-polylysine, and 5-10 parts alkylated chitosan.

2. The multi-layer composite self-adhesive label for food packaging according to claim 1, characterized in that: The hydrophobic modifier is glyceryl monostearate, and the nanofiller is nanocellulose.

3. The multi-layer composite self-adhesive label for food packaging according to claim 1, characterized in that: The polyvinyl alcohol coating is made of polyvinyl alcohol coating liquid, and the preparation method of polyvinyl alcohol coating liquid includes the following steps: Polyvinyl alcohol was dissolved in deionized water to prepare a 10% (w / w) aqueous solution. Nanocellulose, ε-polylysine, vanillin Schiff base derivative, glyceryl monostearate, and alkylated chitosan were added and stirred until homogeneous to obtain the polyvinyl alcohol coating solution.

4. The multi-layer composite self-adhesive label for food packaging according to claim 1, characterized in that: The vanillin Schiff base derivative is a vanillin-amino acid Schiff base derivative, and the preparation method of the vanillin-amino acid Schiff base derivative includes the following steps: Glycine was poured into ethanol, potassium hydroxide was added, and the mixture was stirred in a 50°C water bath for 3 hours to obtain a glycine salt solution. Vanillin was poured into ethanol, and glycine salt solution was slowly added dropwise. After washing and drying, vanillin-amino acid Schiff base derivatives were obtained.

5. The multi-layer composite self-adhesive label for food packaging according to claim 1, characterized in that: The preparation method of the acrylate adhesive includes the following steps: Acrylic acid, styrene, methyl methacrylate, propylene glycol methyl ether acetate, azobisisobutyronitrile, vinyl polysiloxane, and vinyl quaternary ammonium salt were poured into a reaction vessel and stirred at 100°C for 2 hours. Then, a nano-dispersion was added and stirred for 30 minutes to obtain an acrylate adhesive.

6. The multi-layer composite self-adhesive label for food packaging according to claim 1, characterized in that: The preparation method of the alkylated chitosan includes the following steps: Mix isopropanol and sodium hydroxide solution, add chitosan, add glycidyl ammonium chloride, heat to 70°C, filter, wash and dry to obtain alkylated chitosan.

7. A multi-layer composite self-adhesive label for food packaging according to claim 6, characterized in that: The preparation method of the glycidyl ammonium chloride includes the following steps: Dodecyl dimethylamine was added dropwise to epichlorohydrin and the temperature was raised to 50°C to obtain epichlorohydrin ammonium chloride.

8. A multi-layer composite self-adhesive label for food packaging according to claim 5, characterized in that: The preparation method of the nano-dispersion includes the following steps: Carbon nanotubes were added to propylene glycol methyl ether acetate and ultrasonically dispersed to obtain a nano-dispersion.

9. A method for preparing a multi-layer composite self-adhesive label for food packaging, applicable to the multi-layer composite self-adhesive label for food packaging as described in any one of claims 1-8, characterized in that: The method for preparing the self-adhesive label includes the following steps: S1. Apply polyvinyl alcohol coating liquid to one side of the face paper layer and immediately send it into the drying chamber for drying and curing treatment to form a polyvinyl alcohol coating. S2. Using a coating machine, apply acrylic adhesive to the side of the face paper layer away from the polyvinyl alcohol coating to form an adhesive layer. S3. Adhere the side of the backing paper coated with silicone oil to the side of the face paper coated with acrylic adhesive to obtain a self-adhesive label.

10. A method for preparing a multilayer composite self-adhesive label for food packaging according to claim 9, characterized in that: The method for preparing self-adhesive labels further includes the following steps: S11. Discharge treatment is performed on the surface of the paper layer using a high-voltage corona treatment machine.

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