Antique verdigris coating treatment method for inner surface of packaging box

Abstract

The invention belongs to the technical field of coatings, and discloses an antique verdigris coating treatment method for the inner surface of a packaging box, and the treatment method comprises the following steps: adding a catechol derivative into a cationic polyurethane solution, and uniformly mixing to obtain an adhesive solution, the cationic group contained in the cationic polyurethane solution being a quaternary ammonium group; adjusting the pH value of the adhesion liquid to alkalescence, coating the adhesion liquid to the inner surface of the packaging box, pre-curing to form an adhesion layer, scattering copper powder and fixing the copper powder to the surface of the adhesion layer to obtain a copper layer; the verdigris inducer is added into a polymer solution to obtain a reaction solution, the reaction solution is applied to the surface of the copper layer, curing and standing reaction are carried out, the antique verdigris coating is obtained, the polymer contains a hydrophilic monomer and a hydrophobic monomer, and the toughness of the antique verdigris coating is improved after curing. By means of the method, the adhesion and toughness of the antique verdigris coating can be effectively improved.

Description

Technical Field

[0001] This application relates to the field of coating technology, and in particular to a method for applying an antique-style verdigris coating to the inner surface of a packaging box. Background Technology

[0002] In the high-end packaging sector, antique bronze patina coating is widely used for surface treatment of packaging boxes to imbue products with a unique sense of historical weight, artistic value, and luxurious style. The core of this process lies in the use of antique bronze patina paint. Its core function is not simply coloring, but rather, through complex materials science, precisely simulating the basic copper carbonate rust that forms on the packaging substrate over centuries in a natural environment. This effect instantly enhances the visual impact and cultural narrative of the packaging, making the product stand out in the consumer experience and satisfying the market's pursuit of personalized and high-quality appearance. To achieve a more realistic antique effect, modern antique bronze patina paint typically employs a sophisticated component system. Its foundation is a metallic primer rich in copper or bronze powder, providing a base for subsequent chemical reactions. The key lies in the bronze patina reactant, which contains chlorides, ammonium salts, and weak acids to accelerate and control the corrosion of the copper layer, generating a colorful copper salt rust layer. Finally, a layer of transparent matte protective varnish is applied on top to fix the effect and provide basic durability.

[0003] However, despite its remarkable visual appeal, this coating system suffers from inherent physical defects, particularly on substrates like packaging boxes that require bending and compression. Firstly, the porous copper oxide layer formed by chemical corrosion is inherently loose and brittle. Combined with the internal stress arising from differences in composition and drying shrinkage rates among the multiple layers of primer, reaction layer, and protective varnish, the overall coating lacks flexibility. When the packaging box deforms during opening, closing, or transportation, the coating is prone to cracking or even peeling at creases. Secondly, the adhesion of this complex coating system to various commonly used packaging substrates is challenging. Improper pretreatment or inadequate primer compatibility can lead to the coating peeling off entirely from the substrate surface due to poor adhesion, severely impacting the product's usability and lifespan. Summary of the Invention

[0004] The technical problem to be solved by this invention is to propose an antique-style patina treatment method for the inner surface of a packaging box, which aims to solve the problem of reduced adhesion and toughness of the patina coating caused by internal stress generated by the multi-layer coating process.

[0005] To address the aforementioned technical problems, this invention proposes a method for applying an antique-style verdigris coating to the inner surface of a packaging box, comprising the following steps: S1. Add catechol derivatives to cationic polyurethane solution, mix well to obtain an adhesive liquid, wherein the cationic polyurethane solution contains quaternary ammonium groups. S2. Adjust the pH of the adhesive solution to weak alkalinity, apply it to the inner surface of the packaging box, pre-cur it to form an adhesive layer, sprinkle copper powder on it and fix it to the surface of the adhesive layer to obtain a copper layer. S3. Add the verdigris initiator to the polymer solution to obtain a reaction solution, coat it onto the surface of the copper layer, cure it, and allow it to stand to react, thereby obtaining an antique verdigris coating. The polymer is used to improve the toughness of the antique verdigris coating after curing.

[0006] In some embodiments, the catechol derivatives in step S1 include at least one of 3,4-dihydroxybenzoic acid, 3,4-dihydroxyphenylpropionic acid, 3,4-dihydroxyhydrogenated cinnamic acid, sodium 1,2-dihydroxynaphthalene-4-sulfonate, and 3,4-dihydroxymandelic acid.

[0007] In some embodiments, step S1 includes: S1.1 A mixture of diol and diisocyanate is heated to 75-80℃ and reacted for 2-3 hours. The mixture is then cooled to 40-45℃, and the tertiary amine chain extender N-methyldiethanolamine is added, and the reaction continues for 1-2 hours. Dimethyl sulfate is then added dropwise, and the reaction continues for 2-3 hours. The mixture is cooled, neutralized with glacial acetic acid to a pH of 4.5-6.5, and emulsified with water under stirring at 800-1200 rpm. The mixture is then distilled under reduced pressure at 40-50℃ to obtain a cationic polyurethane solution, wherein the diol and diisocyanate... The molar ratio of ester: N-methyldiethanolamine: dimethyl sulfate is 1:(1.5~2.0):(0.1~0.4):(0.1~0.4), the diol includes at least one of polypropylene glycol, polyether glycol, and polyester glycol, the diisocyanate includes at least one of isophorone diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane-4,4'-diisocyanate, and the concentration of cationic polyurethane in the cationic polyurethane solution is 40~50 wt%. S1.2 Under stirring conditions of 800~1200rpm, add long-chain alkyl quaternary ammonium salt to the cationic polyurethane solution, mix evenly to obtain an adhesive liquid, and coat it onto the inner surface of the packaging box. Pre-cur at 60~75℃ for 5~15min to obtain an adhesive layer. The concentrations of catechol derivative and long-chain alkyl quaternary ammonium salt in the cationic polyurethane solution are 5~15wt% and 1~5wt%, respectively. The long-chain alkyl quaternary ammonium salt includes at least one of hexadecyltrimethylammonium bromide, octadecyltrimethylammonium chloride, and dodecyldimethylammonium chloride.

[0008] In some embodiments, the method of fixing copper powder in step S2 includes applying pressure or using a fixing liquid. The method of applying pressure includes pressing with a roller and / or a plate. The fixing liquid is composed of polyimide, a crosslinking agent, and a ruthenium catalyst.

[0009] In some embodiments, the specific steps of fixing copper powder with a fixative are as follows: S2.1 In an inert atmosphere, an equimolar amount of diamine is mixed with furan-2,5-dicarboxylic acid and the antioxidant triphenyl phosphite. The mixture is first heated to 180-220°C and reacted for 2-4 hours, then heated to 240-260°C and reacted for 1-2 hours. The mixture is then cooled to 120-150°C and a furan-termining agent is added and reacted for 30-60 minutes to obtain furan-terminated polyamide. The mass ratio of diamine: antioxidant: furan-termining agent is 100:(0.1-0.5):(5-15). The diamine includes at least one of 1,6-hexanediamine, m-phenylenediamine, and 1,12-dodecanediamine. The furan-termining agent includes at least one of 5-methylfuran-2-carboxyl chloride, 2-furanacryloyl chloride, and 2,5-furandicarboxyl chloride. S2.2 Add crosslinking agent and ruthenium catalyst to furan-terminated polyamide, stir evenly, add copper powder to obtain a bonding liquid, adjust the pH of the bonding liquid to 8.0, coat it onto the inner surface of the packaging box, pre-cur at 80℃ for 20 min to form a bonding layer, then coat the bonding liquid onto the surface of the bonding layer, pre-cur at 90~110℃ for 20~40 min to obtain a bonding layer, wherein the mass ratio of furan-terminated polyamide: copper powder: crosslinking agent: ruthenium catalyst is 100:(50~80):(8~15):(0.5~1.5).

[0010] In some embodiments, the crosslinking agent comprises at least one of 1,1'-(methylenedi-4,1-phenylene)bismaleimide, 1,6-bismaleimide hexane, and 1,3-bis(3-maleimide phenoxy)benzene, and the ruthenium catalyst comprises at least one of trichlorotris(triphenylphosphine)ruthenium, tris(dibenzylideneacetone)diruthenium, and dichloro(p-methylisopropylbenzene)ruthenium dimer.

[0011] In some embodiments, the aureorrhea inducer in step S3 is composed of ammonium chloride and sodium benzoate in a mass ratio of 70-80:30-20.

[0012] In some embodiments, step S3 includes: S3.1. Dissolve the hydrophilic and hydrophobic monomers in ethyl acetate, add azobisisobutyronitrile initiator and dodecyl mercaptan chain transfer agent, heat to 65-75℃ and react for 6-8 hours to obtain a polymer. Add deionized water to the polymer while stirring at 400-600 rpm, and distill under reduced pressure at 40-50℃ to obtain a polymer solution. The hydrophilic monomer includes at least one of polyethylene glycol methyl ether methacrylate, 2-hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, and acrylamide, and the hydrophobic monomer includes at least one of methyl methacrylate, n-butyl methacrylate, isobornyl methacrylate, and lauryl methacrylate. The mass ratio of hydrophilic monomer to hydrophobic monomer is (40-60):(60-40), and the concentration of polymer in the polymer solution is 30-40 wt%. S3.2 Add the verdigris inducer to the polymer solution, mix evenly to obtain a reaction solution, coat it onto the surface of the copper layer, bake in an oven at 60~70℃ for 15~20 minutes to cure, and let it stand to react to obtain an antique verdigris coating.

[0013] In addition, a packaging box is provided, the inner surface of which contains a copper oxide coating obtained by the above-described method for treating the inner surface of a packaging box with an antique copper oxide coating.

[0014] The beneficial effects of this invention are: The substrate adhesion layer utilizes the quaternary ammonium salt groups of cationic polyurethane to generate strong electrostatic adsorption with the cellulose inside the packaging box. Simultaneously, catechol derivatives form a dense anchoring network with the paper fibers through multiple hydrogen bonds and coordination bonds. This dynamic interface effectively buffers and disperses stress, improving adhesion to the packaging box surface. Secondly, the top layer uses an amphiphilic comb-like polymer. Its cured nanophase-separated structure allows hydrophilic microdomains to act as toughening points, absorbing energy through induced crazing and shear banding, while the hydrophobic matrix maintains overall strength, thus endowing the coating with excellent bulk toughness and crack resistance. During the copper layer coating process, the weakly alkaline pre-cured adhesion layer exposes activated catechol groups. These groups not only form coordination bonding nodes with the copper powder but also form hydrogen bond bridges through the amphiphilic polymer permeating the gaps between the copper powder particles. Furthermore, the polymer's penetration into the gaps between the copper powder particles creates a three-dimensional mechanical interlock. This dual mechanism of chemical bonding and physical anchoring converts internal stress into interfacial bonding energy, reducing interlayer internal stress and improving interlayer adhesion. Finally, the amphiphilic comb-like polymer cured on the surface layer forms a continuous three-dimensional network channel composed of hydrophilic segments through its nanophase separation structure. These hydrophilic microdomains can efficiently adsorb and transport water molecules and oxygen in the environment, thereby continuously providing the necessary reactants for the copper powder oxidation reaction during the static stage, driving the continuous formation of basic copper salt, namely verdigris. Attached Figure Description

[0015] Figure 1This is a flowchart illustrating a method for applying an antique-style verdigris coating to the inner surface of a packaging box according to an embodiment of the present invention. Detailed Implementation

[0016] In the description of this application, it should be noted that, unless specific conditions are specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0017] Please refer to Figure 1 This invention provides a method for applying an antique-style verdigris coating to the inner surface of a packaging box, comprising the following steps: S1. Add catechol derivatives to cationic polyurethane solution, mix well to obtain an adhesive liquid, wherein the cationic polyurethane solution contains quaternary ammonium groups. The catechol derivatives in step S1 include at least one of 3,4-dihydroxybenzoic acid, 3,4-dihydroxyphenylpropionic acid, 3,4-dihydroxyhydrocinnamic acid, sodium 1,2-dihydroxynaphthalene-4-sulfonate, and 3,4-dihydroxymandelic acid.

[0018] The quaternary ammonium salt groups of cationic polyurethane generate strong electrostatic adsorption with the cellulose inside the packaging box. At the same time, the catechol derivative forms a dense anchoring network with the paper fibers through multiple hydrogen bonds and coordination bonds. This dynamic interface can effectively buffer and disperse stress, and improve adhesion to the surface of the packaging box.

[0019] Step S1 includes: S1.1 A mixture of diol and diisocyanate is heated to 75-80℃ and reacted for 2-3 hours. The mixture is then cooled to 40-45℃, and the tertiary amine chain extender N-methyldiethanolamine is added, and the reaction continues for 1-2 hours. Dimethyl sulfate is then added dropwise, and the reaction continues for 2-3 hours. The mixture is cooled, neutralized with glacial acetic acid to a pH of 4.5-6.5, and emulsified with water under stirring at 800-1200 rpm. The mixture is then distilled under reduced pressure at 40-50℃ to obtain a cationic polyurethane solution, wherein the diol and diisocyanate... The molar ratio of ester: N-methyldiethanolamine: dimethyl sulfate is 1:(1.5~2.0):(0.1~0.4):(0.1~0.4), the diol includes at least one of polypropylene glycol, polyether glycol, and polyester glycol, the diisocyanate includes at least one of isophorone diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane-4,4'-diisocyanate, and the concentration of cationic polyurethane in the cationic polyurethane solution is 40~50 wt%. S1.2 Under stirring conditions of 800~1200rpm, add catechol derivatives and long-chain alkyl quaternary ammonium salts to the cationic polyurethane solution, mix evenly to obtain an adhesive liquid, and coat it onto the inner surface of the packaging box. Pre-cur at 60~75℃ for 5~15min to obtain an adhesive layer. The concentrations of catechol derivatives and long-chain alkyl quaternary ammonium salts in the cationic polyurethane solution are 5~15wt% and 1~5wt%, respectively. The long-chain alkyl quaternary ammonium salts include at least one of hexadecyltrimethylammonium bromide, octadecyltrimethylammonium chloride, and dodecyldimethylammonium chloride.

[0020] S2. Adjust the pH of the adhesive solution to weak alkalinity, apply it to the inner surface of the packaging box, pre-cur it to form an adhesive layer, sprinkle copper powder on it and fix it to the surface of the adhesive layer to obtain a copper layer. The method of fixing copper powder in step S2 includes applying pressure or using a fixing liquid. The method of applying pressure includes pressing with a roller and / or a plate. The fixing liquid is composed of polyimide, a crosslinking agent and a ruthenium catalyst.

[0021] By adjusting the system to a weakly alkaline environment, the catechol groups are oxidized to form highly reactive o-quinone structures. These structures act as strong electrophiles, undergoing Michael addition reactions with metal atoms or ions on the copper powder surface to form robust covalent bonds. Simultaneously, the oxygen atoms in the catechol / o-quinone structures also exhibit strong coordination with copper, further enhancing interfacial bonding. On the other hand, the quaternary ammonium groups in the cationic polyurethane carry a positive charge, which can attract the slightly negatively charged copper powder surface naturally present in the atmosphere through electrostatic adsorption, achieving initial and rapid capture and fixation. Finally, polyurethane itself, as a polymer with excellent film-forming properties, forms a thin film with suitable micro-adhesion during curing, allowing copper powder particles to be partially embedded within it. This physical anchoring effect distributes stress and prevents powder detachment.

[0022] The method of fixing copper powder in step S2 includes applying pressure or using a fixing liquid. The method of applying pressure includes pressing with a roller and / or a plate. The fixing liquid is composed of polyimide, a crosslinking agent and a ruthenium catalyst.

[0023] The crosslinking agent includes at least one of 1,1'-(methylenedi-4,1-phenylene)bismaleimide, 1,6-bismaleimide hexane, and 1,3-bis(3-maleimide phenoxy)benzene, and the ruthenium catalyst includes at least one of trichlorotris(triphenylphosphine)ruthenium, tris(dibenzylideneacetone)diruthenium, and dichloro(p-methylisopropylbenzene)ruthenium dimer.

[0024] The specific steps for fixing copper powder using a fixative are as follows: S2.1 In an inert atmosphere, an equimolar amount of diamine is mixed with furan-2,5-dicarboxylic acid and the antioxidant triphenyl phosphite. The mixture is first heated to 180-220°C and reacted for 2-4 hours, then heated to 240-260°C and reacted for 1-2 hours. The mixture is then cooled to 120-150°C and a furan-termining agent is added, and the reaction is carried out for 30-60 minutes to obtain furan-terminated polyamide. The mass ratio of diamine: antioxidant: furan-termining agent is 100:(0.1-0.5):(5-15). The diamine includes at least one of 1,6-hexanediamine, m-phenylenediamine, and 1,12-dodecanediamine. The furan-termining agent includes at least one of 5-methylfuran-2-carboxyl chloride, 2-furanacryloyl chloride, and 2,5-furandicarboxyl chloride.

[0025] First, by using an inert atmosphere and adding antioxidants, the high-temperature oxidative degradation of the polymer can be effectively prevented, ensuring the integrity of the molecular chain. A two-stage heating strategy of 180~220℃ and 240~260℃ is adopted. In the early stage, the diamine and furan dicarboxylic acid are fully polycondensed to form amide bonds and control the molecular weight. In the later stage, solid-state polymerization is completed at a higher temperature to significantly improve the crystallinity and mechanical strength of the polymer. Finally, a specific furan end-capping agent is added at a moderate temperature of 120~150℃. This can achieve precise end-capping through the efficient reaction of acyl chloride and polymer chain terminal amino groups, introducing furan rings that can participate in the subsequent Diels-Alder crosslinking reaction. It can also avoid the decomposition of the end-capping agent or side reactions caused by excessively high temperatures, thus ensuring that the final product has excellent thermal stability, a clear end-group structure, and the reaction potential as a reversible crosslinking material.

[0026] S2.2 Add the crosslinking agent and ruthenium catalyst to the furan-terminated polyamide, stir evenly, add copper powder to obtain the bonding liquid, adjust the pH of the bonding liquid to 8.0, coat it onto the inner surface of the packaging box, pre-cur at 80℃ for 20 min to form the bonding layer, then coat the bonding liquid onto the surface of the bonding layer, pre-cur at 90~110℃ for 20~40 min to obtain the bonding layer, wherein the mass ratio of furan-terminated polyamide:copper powder:crosslinking agent:ruthenium catalyst is 100:(50~80):(8~15):(0.5~1.5); In the connecting layer, furan-terminated polyamide undergoes a Diels-Alder cycloaddition reaction with bismaleimide in the crosslinking agent. The diene of furan and the diephilic body of maleimide form a thermally reversible oxabicyclo-heptene structure through electron rearrangement, constructing a bulk crosslinking network that can dissipate mechanical energy. Furthermore, the ruthenium catalyst selectively activates the CH bonds of the catechol aromatic ring in the bottom layer to generate a ruthenium-aryl intermediate, which then undergoes an insertion / elimination process with the unreacted maleimide double bond in the bismaleimide to form an aryl-olefin covalent bridge, thus realizing interlayer click chemical bonding.

[0027] In one embodiment, to accelerate the oxidation of copper powder to form verdigris, manganese dioxide at 1-3 wt% of the copper powder mass can be mixed with the copper powder and then fixed together onto the surface of the adhesion layer. The specific fixing method is as follows: The pH of the adhesive solution is adjusted to a slightly alkaline state, applied to the inner surface of the packaging box, pre-cured to form an adhesive layer, a mixture of copper powder and calcium peroxide is sprinkled on, and a roller is used to fix it to the surface of the adhesive layer to obtain a copper layer.

[0028] Manganese oxide undergoes a reduction reaction in the acidic microenvironment created by the subsequent copper oxide initiator, ammonium chloride, continuously releasing oxygen and generating soluble divalent manganese ions. The in-situ generated oxygen provides an efficient and uniformly distributed oxidation source for copper oxidation, directly accelerating the initial conversion of copper to cuprous oxide / copper oxide. The dissolved manganese ions, as a strong electrolyte, significantly improve the conductivity of the micro-regions within the coating, synergistically promoting the electrochemical corrosion cycle of copper with chloride ions. This allows copper powder to be converted into copper oxide products such as basic copper carbonate more quickly and uniformly. After final curing, the trace amounts of manganese chloride in the system present a light pink underlayer covering approximately 1-3% of the total coating area. This warm tone intertwines and overlaps with the blue-green copper oxide main body covering approximately 97-99%, forming a richer, deeper visual layer that closely resembles the color of natural bronze rust. This enhances the artistic authenticity of the antique effect, thus effectively shortening the curing and reaction time of the process and optimizing the visual aesthetics of the final product without affecting the coating adhesion and overall performance.

[0029] S3. Add the verdigris initiator to the polymer solution to obtain a reaction solution, coat it onto the surface of the copper layer, cure it, and allow it to stand for reaction to obtain an antique verdigris coating. The polymer contains hydrophilic and hydrophobic monomers, which are used to improve the toughness of the antique verdigris coating after curing.

[0030] In step S3, the aureorrhea inducer is composed of ammonium chloride and sodium benzoate in a mass ratio of 70-80:30-20.

[0031] The surface layer uses an amphiphilic comb-like polymer. The nano-phase separation structure formed after curing not only makes the hydrophilic micro-regions act as toughening points, absorbing energy by inducing crazes and shear bands, while the hydrophobic matrix maintains the overall strength, thus giving the coating excellent bulk toughness and crack resistance; it also enables the continuous three-dimensional network channels composed of hydrophilic segments to efficiently adsorb and transport water molecules and oxygen in the environment, thereby continuously providing the necessary reactants for the copper powder oxidation reaction during the static stage, driving the continuous formation of basic copper salt, i.e., verdigris.

[0032] Step S3 includes: S3.1 Dissolve the hydrophilic and hydrophobic monomers in ethyl acetate, add azobisisobutyronitrile initiator and dodecyl mercaptan chain transfer agent, heat to 65-75℃ and react for 6-8 hours to obtain a polymer. Add deionized water to the polymer while stirring at 400-600 rpm, and distill under reduced pressure at 40-50℃ to obtain a polymer solution. The hydrophilic monomer includes at least one of polyethylene glycol methyl ether methacrylate, 2-hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, and acrylamide, and the hydrophobic monomer includes at least one of methyl methacrylate, n-butyl methacrylate, isobornyl methacrylate, and lauryl methacrylate. The mass ratio of hydrophilic monomer to hydrophobic monomer is (40-60):(60-40), and the concentration of polymer in the polymer solution is 30-40 wt%.

[0033] Hydrophilic and hydrophobic monomers were copolymerized at a mass ratio of (40~60):(60~40), precisely controlling the amphiphilic balance of the polymer. This enabled the formation of a nanoscale phase-separated structure after curing, creating continuous transport channels for water molecules and ions while maintaining the overall integrity of the coating through a hydrophobic matrix. Specific types of monomers were selected to provide side chain flexibility, strong hydrogen bonding ability, or steric hindrance effect, which together enhanced the toughness and adhesion of the coating. Ethyl acetate as a solvent and a reaction temperature of 65~75℃ ensured a stable and uniform copolymerization reaction, while the addition of dodecyl mercaptan effectively controlled the molecular weight and avoided excessive crosslinking and embrittlement. Finally, a stable dispersion with a solid content of 30~40wt% was obtained through phase inversion emulsification and vacuum distillation.

[0034] S3.2 Add the verdigris inducer to the polymer solution, mix evenly to obtain a reaction solution, coat it onto the surface of the copper layer, bake in an oven at 60~70℃ for 15~20 minutes to cure, and let it stand to react to obtain an antique verdigris coating.

[0035] The copper oxide initiator is uniformly dispersed in the polymer solution, ensuring a spatially homogeneous distribution of reactive components in the coating, laying the material foundation for subsequent uniform corrosion throughout the entire area. The medium-temperature curing process of 60~70℃ effectively removes solvents, promotes polymer chain entanglement to form a tough film, and activates some initiator components to form an initial corrosion environment, while avoiding excessive acceleration of the copper powder oxidation process by high temperature. The curing time of 15~20 minutes allows for the migration of the initiator to the copper layer interface while ensuring sufficient film formation. In the subsequent static stage, the natural penetration of ambient moisture, guided by the hydrophilic network of the polymer, forms a galvanic cell reaction system with the copper powder, allowing copper ions and the initiator to slowly generate basic copper salt crystals at the solid-liquid interface, ultimately forming a realistic copper oxide effect with strong adhesion, natural color, and stable structure.

[0036] This application also provides a packaging box, the inner surface of which contains a copper oxide coating obtained by the above-described method for treating the inner surface of a packaging box with an antique copper oxide coating.

[0037] For example, the present invention provides the following specific embodiments to illustrate the specific preparation method: Example 1 S1.1. Polypropylene glycol and isophorone diisocyanate were mixed and heated to 75°C for 2.5 h. The mixture was then cooled to 45°C, and the tertiary amine chain extender N-methyldiethanolamine was added, and the reaction continued for 1.5 h. Dimethyl sulfate was then added dropwise, and the reaction continued for 2.3 h. The mixture was cooled, neutralized with glacial acetic acid to pH 5.5, emulsified with water under stirring at 1000 rpm, and distilled under reduced pressure at 45°C to obtain a cationic polyurethane solution. The molar ratio of polypropylene glycol:isophorone diisocyanate:N-methyldiethanolamine:dimethyl sulfate was 1:1.8:0.25:0.25, and the concentration of cationic polyurethane in the cationic polyurethane solution was 45 wt%. S1.2 Under stirring at 1000 rpm, 3,4-dihydroxybenzoic acid and hexadecyltrimethylammonium bromide were added to the cationic polyurethane solution and mixed evenly to obtain an adhesion liquid, wherein the concentrations of 3,4-dihydroxybenzoic acid and hexadecyltrimethylammonium bromide in the cationic polyurethane solution were 10 wt% and 3 wt%, respectively. S2. Adjust the pH of the adhesive solution to 8.0, apply it to the inner surface of the packaging box, pre-cur at 80℃ for 20 minutes to form an adhesive layer, sprinkle copper powder on it and use a roller to fix it to the surface of the adhesive layer to obtain a copper layer. S3.1. Polyethylene glycol methyl ether methacrylate and methyl methacrylate are dissolved in ethyl acetate, and azobisisobutyronitrile initiator and dodecyl mercaptan chain transfer agent are added. The mixture is heated to 70°C and reacted for 7 hours to obtain a polymer. Deionized water is added to the polymer while stirring at 500 rpm, and the mixture is distilled under reduced pressure at 45°C to obtain a polymer solution. The mass ratio of polyethylene glycol methyl ether methacrylate to methyl methacrylate is 50:50, and the polymer concentration in the polymer solution is 35 wt%. S3.2 Add the copper alumina initiator, composed of ammonium chloride and sodium benzoate in a mass ratio of 75:25, to the polymer solution, mix evenly to obtain a reaction solution, coat it onto the copper layer surface, bake it in an oven at 65℃ for 18 minutes for curing, and let it stand to react to obtain an antique copper alumina coating. The concentration of the copper alumina initiator in the polymer solution is 10wt%.

[0038] Example 2 The process is basically the same as in Example 1, except that in step S2, the copper powder is doped with 2 wt% manganese dioxide by weight of the copper powder to form a copper layer containing both manganese dioxide and copper powder.

[0039] Example 3 The process is basically the same as in Example 1, except that in step S2, the copper powder is fixed using a fixing liquid. The specific fixing steps are as follows: S2.1 In an inert atmosphere, 1,6-hexanediamine and furan-2,5-dicarboxylic acid are mixed in equimolar amounts, and then the antioxidant triphenyl phosphite is added. The mixture is heated to 200°C and reacted for 3 hours, then heated to 250°C and reacted for 1.5 hours. Finally, the mixture is cooled to 135°C and 5-methylfuran-2-carboxyl chloride is added and reacted for 45 minutes to obtain furan-terminated polyamide. The mass ratio of 1,6-hexanediamine: antioxidant: 5-methylfuran-2-carboxyl chloride is 100:0.3:10. S2.2 Add 1,6-bismaleimide hexane and ruthenium dichlorotris(triphenylphosphine) to furan-terminated polyamide, stir evenly, add copper powder to obtain a bonding liquid, adjust the pH of the bonding liquid to 8.0, coat it onto the inner surface of the packaging box, pre-cur at 80℃ for 20 min to form an adhesive layer, then coat the bonding liquid onto the surface of the adhesive layer, pre-cur at 100℃ for 30 min to obtain a bonding layer, wherein the mass ratio of furan-terminated polyamide: copper powder: 1,6-bismaleimide hexane: ruthenium dichlorotris(triphenylphosphine) is 100:65:12:1.0.

[0040] Comparative Example 1 It is basically the same as Example 1, except that the adhesive liquid does not contain catechol derivatives.

[0041] Comparative Example 2 It is basically the same as Example 1, except that dimethyl sulfate was not added to the adhesive solution for reaction, that is, the polyurethane does not contain quaternary ammonium salt cations.

[0042] Comparative Example 3 The process is basically the same as in Example 1, except that the pH of the adhesive solution was not adjusted to weak alkalinity and it was directly applied to the inner surface of the packaging box.

[0043] Comparative Example 4 It is basically the same as Example 1, except that the polymer contains only hydrophilic monomers.

[0044] Performance testing: Antique bronze patina coating toughness: The sample coated with the sample paint film is bent 180° on a shaft of a certain diameter and the paint film is checked for cracking or peeling from the substrate. Toughness is expressed by the minimum shaft diameter (mm) at which the paint film is not damaged. The smaller the shaft diameter, the better the toughness.

[0045] Antique bronze patina coating adhesion: Using specialized adhesive, a small aluminum or steel ingot (pull-out head) is vertically attached to the surface of the antique bronze patina coating. After the adhesive has fully cured, a pull-out adhesion tester is used to pull the ingot vertically with a uniform force until the coating is pulled off. The instrument records the maximum pulling force at which the coating breaks.

[0046] The antique bronze coatings prepared in Examples 1-3 and Comparative Examples 1-4 were used as samples for testing. The test results are shown in Table 1. Table 1 Performance of Antique Bronze Green Coating As can be seen from the performance data of the antique coating in Table 1, the antique copper green coatings prepared in Examples 1-3 all have good adhesion and toughness. Further observation of Comparative Examples 1-4 shows that the absence of catechol derivatives (Comparative Example 1), the absence of quaternary ammonium salt cations (Comparative Example 2), the failure to adjust the pH of the adhesive solution to weak alkalinity (Comparative Example 3), and the absence of hydrophobic monomers in the polymer (Comparative Example 4) have a significant impact on the adhesion and toughness of the antique copper green coating.

[0047] The above embodiments are preferred embodiments of this application, but the implementation of this application is not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of this application shall be considered equivalent substitutions and shall be included within the protection scope of this application.

Claims

1. A method for applying an antique-style verdigris coating to the inner surface of a packaging box, characterized in that, Includes the following steps: S1. Add catechol derivatives to cationic polyurethane solution, mix well to obtain an adhesive liquid, wherein the cationic polyurethane solution contains quaternary ammonium groups. S2. Adjust the pH of the adhesive solution to weak alkalinity, apply it to the inner surface of the packaging box, pre-cur it to form an adhesive layer, sprinkle copper powder on it and fix it to the surface of the adhesive layer to obtain a copper layer. S3. Add the verdigris initiator to the polymer solution to obtain a reaction solution, coat it onto the surface of the copper layer, cure it, and allow it to stand for reaction to obtain an antique verdigris coating. The polymer contains hydrophilic and hydrophobic monomers, which are used to improve the toughness of the antique verdigris coating after curing.

2. The method for applying an antique-style verdigris coating to the inner surface of a packaging box according to claim 1, characterized in that, The catechol derivatives in step S1 include at least one of 3,4-dihydroxybenzoic acid, 3,4-dihydroxyphenylpropionic acid, 3,4-dihydroxyhydrocinnamic acid, sodium 1,2-dihydroxynaphthalene-4-sulfonate, and 3,4-dihydroxymandelic acid.

3. The method for applying an antique-style verdigris coating to the inner surface of a packaging box according to claim 1, characterized in that, Step S1 includes: S1.1 A mixture of diol and diisocyanate is heated to 75-80℃ and reacted for 2-3 hours. The mixture is then cooled to 40-45℃, and the tertiary amine chain extender N-methyldiethanolamine is added, and the reaction continues for 1-2 hours. Dimethyl sulfate is then added dropwise, and the reaction continues for 2-3 hours. The mixture is cooled, neutralized with glacial acetic acid to a pH of 4.5-6.5, and emulsified with water under stirring at 800-1200 rpm. The mixture is then distilled under reduced pressure at 40-50℃ to obtain a cationic polyurethane solution, wherein the diol and diisocyanate... The molar ratio of ester: N-methyldiethanolamine: dimethyl sulfate is 1:(1.5~2.0):(0.1~0.4):(0.1~0.4), the diol includes at least one of polypropylene glycol, polyether glycol, and polyester glycol, the diisocyanate includes at least one of isophorone diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane-4,4'-diisocyanate, and the concentration of cationic polyurethane in the cationic polyurethane solution is 40~50 wt%. S1.2 Under stirring conditions of 800~1200rpm, add catechol derivatives and long-chain alkyl quaternary ammonium salts to the cationic polyurethane solution, mix evenly to obtain an adhesive liquid, and coat it onto the inner surface of the packaging box. Pre-cur at 60~75℃ for 5~15min to obtain an adhesive layer. The concentrations of catechol derivatives and long-chain alkyl quaternary ammonium salts in the cationic polyurethane solution are 5~15wt% and 1~5wt%, respectively. The long-chain alkyl quaternary ammonium salts include at least one of hexadecyltrimethylammonium bromide, octadecyltrimethylammonium chloride, and dodecyldimethylammonium chloride.

4. The method for applying an antique-style verdigris coating to the inner surface of a packaging box according to claim 1, characterized in that, The method of fixing copper powder in step S2 includes applying pressure or using a fixing liquid. The method of applying pressure includes using a roller and / or a plate. The fixing liquid consists of polyimide, a crosslinking agent, and a ruthenium catalyst.

5. The method for applying an antique-style verdigris coating to the inner surface of a packaging box according to claim 4, characterized in that, The specific steps for fixing copper powder using a fixative are as follows: S2.1 In an inert atmosphere, an equimolar amount of diamine is mixed with furan-2,5-dicarboxylic acid and the antioxidant triphenyl phosphite. The mixture is first heated to 180-220°C and reacted for 2-4 hours, then heated to 240-260°C and reacted for 1-2 hours. The mixture is then cooled to 120-150°C and a furan-termining agent is added and reacted for 30-60 minutes to obtain furan-terminated polyamide. The mass ratio of diamine: antioxidant: furan-termining agent is 100:(0.1-0.5):(5-15). The diamine includes at least one of 1,6-hexanediamine, m-phenylenediamine, and 1,12-dodecanediamine. The furan-termining agent includes at least one of 5-methylfuran-2-carboxyl chloride, 2-furanacryloyl chloride, and 2,5-furandicarboxyl chloride. S2.2 Add crosslinking agent and ruthenium catalyst to furan-terminated polyamide, stir evenly, add copper powder to obtain a bonding liquid, adjust the pH of the bonding liquid to 8.0, coat it onto the inner surface of the packaging box, pre-cur at 80℃ for 20 min to form a bonding layer, then coat the bonding liquid onto the surface of the bonding layer, pre-cur at 90~110℃ for 20~40 min to obtain a bonding layer, wherein the mass ratio of furan-terminated polyamide: copper powder: crosslinking agent: ruthenium catalyst is 100:(50~80):(8~15):(0.5~1.5).

6. A method for applying an antique-style verdigris coating to the inner surface of a packaging box according to claim 4 or 5, characterized in that, The crosslinking agent includes at least one of 1,1'-(methylenedi-4,1-phenylene)bismaleimide, 1,6-bismaleimide hexane, and 1,3-bis(3-maleimide phenoxy)benzene, and the ruthenium catalyst includes at least one of trichlorotris(triphenylphosphine)ruthenium, tris(dibenzylideneacetone)diruthenium, and dichloro(p-methylisopropylbenzene)ruthenium dimer.

7. The method for applying an antique-style verdigris coating to the inner surface of a packaging box according to claim 1, characterized in that, In step S3, the aureorrhea inducer is composed of ammonium chloride and sodium benzoate in a mass ratio of 70-80:30-20.

8. The method for applying an antique-style verdigris coating to the inner surface of a packaging box according to claim 1, characterized in that, Step S3 includes: S3.

1. Dissolve the hydrophilic and hydrophobic monomers in ethyl acetate, add azobisisobutyronitrile initiator and dodecyl mercaptan chain transfer agent, heat to 65-75℃ and react for 6-8 hours to obtain a polymer. Add deionized water to the polymer while stirring at 400-600 rpm, and distill under reduced pressure at 40-50℃ to obtain a polymer solution. The hydrophilic monomer includes at least one of polyethylene glycol methyl ether methacrylate, 2-hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, and acrylamide, and the hydrophobic monomer includes at least one of methyl methacrylate, n-butyl methacrylate, isobornyl methacrylate, and lauryl methacrylate. The mass ratio of hydrophilic monomer to hydrophobic monomer is (40-60):(60-40), and the concentration of polymer in the polymer solution is 30-40 wt%. S3.2 Add the verdigris inducer to the polymer solution, mix evenly to obtain a reaction solution, coat it onto the copper layer surface, bake in an oven at 60~70℃ for 15~20 minutes for curing, and let it stand to react to obtain an antique verdigris coating. The concentration of the verdigris inducer in the polymer solution is 5~15wt%.

9. A packaging box, characterized in that, The inner surface of the packaging box contains a copper oxide coating obtained by the antique copper oxide treatment method for the inner surface of the packaging box as described in any one of claims 1-8.

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