Carbon quantum dot modified alumite adhesive layer coating composition and preparation method thereof

Abstract

The invention discloses a carbon quantum dot modified alumite glue layer coating composition and a preparation method thereof, and belongs to the technical field of coatings. Aiming at the defects of weak adhesive force, poor scratch resistance and water resistance and no anti-counterfeiting function of the traditional waterborne polyurethane alumite adhesive layer coating, the waterborne polyurethane alumite adhesive layer coating is prepared by taking waterborne polyurethane emulsion as a base material, introducing a fluorescent carbon quantum dot dispersion liquid prepared by a citric acid-ethanediamine hydrothermal method and a neutral chitosan solution, and compounding auxiliaries such as a dispersing agent and a wetting agent with specific properties. The paint is prepared through segmented stirring, filtering and defoaming processes. According to the composition, by means of the synergistic effect of the carbon quantum dots and the chitosan, the adhesive force, scraping resistance and water resistance of a coating are greatly improved, meanwhile, a stable invisible fluorescent anti-counterfeiting function is given, a heat sealing temperature window is wide, the preparation process is operated at normal temperature, and the composition is compatible with an existing production line. According to the method, technical characteristics are defined through accurate text description and quantitative data, repetition can be achieved without attached drawings, and the method is suitable for alumite gold stamping foil glue layers of high-end packages such as tobacco and wine, cosmetics and the like and has remarkable industrialization prospects.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to a carbon quantum dot modified electroplated aluminum adhesive coating composition and its preparation method, which is particularly suitable for the preparation of electroplated aluminum hot stamping foil adhesive layers in high-end packaging fields such as tobacco, alcohol, and cosmetics. Background Technology

[0002] Electroplated aluminum hot stamping foil is a decorative material widely used in high-end packaging. Its structure consists of a PET base film, release layer, color layer, aluminum layer, and adhesive layer. The adhesive layer, as a key functional layer, plays a crucial role in firmly transferring and bonding the aluminum and color layers to the substrate surface during the hot stamping process. Traditional adhesive coatings use water-based polyurethane emulsions as the main film-forming substance. While possessing basic film-forming properties and flexibility, they have many shortcomings in practical applications. First, the adhesion and scratch resistance are insufficient, and the hot-stamped pattern is prone to problems such as aluminum peeling, wrinkling, and scratches, which seriously affect the product qualification rate and service life. Second, the resistance to water, alcohol, and other media is poor. In humid or alcohol-stained environments, the coating is prone to softening and peeling, which cannot meet the durability requirements of high-end packaging. Third, it lacks high-value-added functional characteristics and does not have optical anti-counterfeiting capabilities, making it difficult to meet the first-level invisible anti-counterfeiting requirements of industries such as tobacco, alcohol, and cosmetics. Fourth, existing modification methods have limitations. Most of them use inorganic nanoparticles such as SiO2 or ordinary tackifying resins for modification, which not only makes it difficult to achieve the dual goals of improving mechanical properties and imparting functions at the same time, but also easily leads to defects such as agglomeration and pinholes in the coating due to compatibility issues.

[0003] In existing technologies, carbon quantum dots (CQDs) are mostly used in the nano-reinforcement of fluorescent inks, photocatalytic coatings, or general materials, and there are no reports on their use in modifying electroplated aluminum adhesive coatings. Chitosan, as a biomass material, is primarily used in the preparation of food packaging films and has also not been introduced into the modification system of hot stamping foil adhesive layers. More importantly, electroplated aluminum adhesive layers need to meet the special requirements of high-temperature short-time hot stamping (100-180℃, 0.5MPa, 1s), requiring the coating to melt rapidly during hot stamping and solidify quickly after cooling, while also possessing good interfacial compatibility with the aluminum and color layers. Existing technologies combining CQDs and chitosan are only used in room-temperature curing systems and do not address the application scenario of high-temperature short-time hot stamping. Those skilled in the art have no incentive to transfer this technology to electroplated aluminum adhesive layers. Therefore, developing a high-performance adhesive coating with anti-counterfeiting functions is of significant practical importance. Summary of the Invention

[0004] This invention aims to overcome the shortcomings of existing electroplated aluminum adhesive coatings, such as weak adhesion, poor scratch resistance, insufficient resistance to various media, and lack of anti-counterfeiting functions. It provides a carbon quantum dot-modified electroplated aluminum adhesive coating composition and its preparation method. This coating composition simultaneously achieves high adhesion, high scratch resistance, excellent water resistance, and invisible fluorescent anti-counterfeiting functions. Furthermore, the preparation process is simple, can be performed at room temperature, requires no special equipment, and is highly compatible with existing electroplated aluminum adhesive production lines, thus addressing the application pain points of existing technologies.

[0005] The technical solution of this invention is implemented as follows: This invention provides a carbon quantum dot modified electroplated aluminum adhesive coating composition, comprising, by weight, the following components: 50-80 parts of aqueous polyurethane resin emulsion, 2-12 parts of fluorescent carbon quantum dot dispersion with a concentration of 5-10 wt%, 1-8 parts of chitosan solution with a concentration of 1-5 wt% and a pH of 6.0-7.5, 1-4 parts of polycarboxylate dispersant with an acid value of 100-150 mg KOH / g and a purity ≥95%, 0.2-1 parts of acetylenol wetting agent with a surface tension ≤30 mN / m and a purity ≥98%, 0.1-0.8 parts of organosilicon defoamer, 0.3-1.5 parts of polyurethane associative thickener, and the balance being deionized water; the fluorescent carbon quantum dots are prepared by hydrothermal reaction of citric acid and ethylenediamine, and the chitosan solution is prepared by neutralizing chitosan dissolved in a 1-2 wt% aqueous acetic acid solution.

[0006] In some embodiments, the fluorescent carbon quantum dots exhibit a quantum yield >40%, strong blue light under a 365nm UV lamp, a particle size <10nm, and a particle size distribution index (PDI) <0.2. The carbon quantum dots prepared by the hydrothermal reaction of citric acid and ethylenediamine have surfaces rich in active functional groups such as -OH, -NH2, and -COOH. These functional groups can not only form hydrogen bonds or partial covalent crosslinks with chitosan molecules and waterborne polyurethane molecules, but also ensure the dispersion stability of the carbon quantum dots in the coating system. The nanoscale effect of a particle size <10nm can achieve stress dispersion and improve the mechanical properties of the coating. The nitrogen-doped graphitized structure is the core reason for its strong fluorescence properties, enabling invisibility and anti-counterfeiting functions. 170-200℃ is the effective temperature range for preparing fluorescent carbon quantum dots in the citric acid-ethylenediamine system. Below 170℃, the degree of graphitization of carbon quantum dots is insufficient, and the fluorescence intensity decreases; above 200℃, carbon quantum dots are prone to aggregation, and the dispersion stability deteriorates.

[0007] In some embodiments, the chitosan has a molecular weight of 50,000-200,000 and a degree of deacetylation ≥85%. Chitosan with a molecular weight of 50,000-200,000 has a suitable molecular chain length, enabling it to form an interpenetrating network structure with carbon quantum dots and waterborne polyurethane without causing abnormal viscosity in the coating due to excessively long molecular chains. A degree of deacetylation ≥85% ensures that the chitosan molecules contain a sufficient number of amino groups, providing ample active sites for hydrogen bonding crosslinking. Adjusting the pH of the chitosan solution to a neutral range of 6.0-7.5 avoids the degradation of the stability of the waterborne polyurethane emulsion by an acidic environment, improving the compatibility of the coating system. When the chitosan molecular weight exceeds 200,000, the molecular chains are prone to entanglement, leading to poor coating leveling; when it is below 50,000, an effective crosslinking network cannot be formed, resulting in limited improvement in water resistance.

[0008] In some embodiments, the dispersant is a polycarboxylate dispersant with an acid value of 100-150 mg KOH / g and a purity of ≥95%; the wetting agent is an acetylenide diol wetting agent with a surface tension of ≤30 mN / m and a purity of ≥98%; the defoamer is an organosilicon defoamer, preferably a polyether-modified organosilicon emulsion, such as BYK-024, Dow Corning AFE-1510, etc.; and the thickener is a polyurethane associative thickener, preferably a hydrophobically modified polyurethane emulsion, such as Rohm and Haas RM-8W, Dow ACRYSOLTT-935, etc. Polycarboxylate dispersants can effectively prevent carbon quantum dots from agglomerating in coatings through electrostatic repulsion and steric hindrance effects; acetylenic diol wetting agents can reduce the surface tension of coatings, improve the leveling properties of coatings on PET base film surfaces, and prevent pinholes in the coating; silicone defoamers can quickly eliminate bubbles generated during stirring, ensuring a smooth coating surface; polyurethane associative thickeners have pseudoplastic rheological properties, which can adjust the viscosity of coatings to suit doctor blade or roller coating processes, and can also quickly restore viscosity after coating to prevent coating sagging.

[0009] In some embodiments, the solid content of the waterborne polyurethane resin emulsion is 40-50%, and the solid content of the coating composition is 30-40%. Controlling the solid content of the waterborne polyurethane emulsion at 40-50% ensures the film-forming properties and adhesion of the coating; adjusting the solid content of the coating composition to 30-40% balances the operability of the coating process with the density of the coating after drying, avoiding excessively high solid content leading to high viscosity and difficulty in coating, or excessively low solid content leading to an overly thin coating and decreased performance.

[0010] In some embodiments, the coating composition appears as a light blue transparent or semi-transparent liquid, with a color difference ΔE < 1.0 compared to the blank PET base film. The light blue transparent or semi-transparent state of the coating indicates that carbon quantum dots and chitosan have achieved uniform molecular-level dispersion in the aqueous polyurethane system, without obvious particles or agglomerates. This dispersion state is a prerequisite for ensuring the uniformity of coating performance. The particle size distribution of carbon quantum dots is verified by a laser particle size analyzer to be 5-10 nm without agglomeration peaks, and the particle size distribution coefficient (PDI) is < 0.2.

[0011] The present invention also provides a method for preparing the above-mentioned carbon quantum dot modified electroplated aluminum adhesive coating composition, comprising the following steps:

[0012] 1. Preparation of fluorescent carbon quantum dot dispersion: Dissolve 8-12g of analytical grade citric acid and 3-6mL of analytical grade ethylenediamine in 30-50mL of deionized water, stir evenly, and transfer to a hydrothermal reactor. React at 170-200℃ for 8-12h. After cooling, filter with a 0.22μm aqueous filter membrane and dialyze for 24-48h using a cellulose ester dialysis bag with a molecular weight cutoff of 1000Da. Replace the deionized water every 6 hours, with the water volume being twice the volume of the dialysate, to obtain a fluorescent carbon quantum dot dispersion with a concentration of 5-10wt%.

[0013] 2. Preparation of chitosan solution: Take chitosan with a molecular weight of 50,000-200,000 and a degree of deacetylation ≥85% and dissolve it in 1-2wt% acetic acid aqueous solution to prepare a 1-5wt% solution. Adjust the pH to 6.0-7.5 to obtain a neutral chitosan solution.

[0014] 3. Preparation of coating composition: Add deionized water and dispersant to a mixing tank and stir at high speed for 5-10 min; slowly add fluorescent carbon quantum dot dispersion and chitosan solution and stir at high speed for 20-40 min; add wetting agent and defoamer and stir for 5-15 min; slowly add waterborne polyurethane resin emulsion and stir at medium speed for 15-30 min; add thickener and stir until uniform, filter, and let stand for 24 h to defoam, and the coating composition is obtained.

[0015] All raw materials used in this invention can be obtained commercially, specifically from: citric acid (analytical grade, Sinopharm Group), ethylenediamine (analytical grade, Aladdin reagent), chitosan (molecular weight 50,000-200,000, degree of deacetylation ≥85%, Maclean's reagent), polycarboxylate dispersant (BYK-190, acid value 120 mg KOH / g, BYK Chemical), and acetylenol wetting agent (Surfynol 104, surface tension 28 mN / m, Air Chemical).

[0016] In some embodiments, the high-speed stirring rate in step 3 is 800-1200 rpm, the medium-speed stirring rate is 500-800 rpm, and filtration is performed using a 200-mesh polyester filter cloth. The high-speed stirring at 800-1200 rpm generates sufficient shear force to uniformly disperse carbon quantum dots and chitosan in the aqueous system, forming a stable mixture. After adding the aqueous polyurethane emulsion, the stirring speed is switched to 500-800 rpm, which ensures uniform mixing of all components while avoiding emulsion demulsification caused by high-speed stirring. Filtration using a 200-mesh polyester filter cloth can retain a small amount of undispersed particles in the system, further ensuring the uniformity and coating performance of the coating.

[0017] This invention further provides an application of the above-mentioned coating composition, namely, its use in preparing the adhesive layer for electroplated aluminum hot stamping foil. The adhesive layer formed by the curing of this coating composition can rapidly melt and wet the surface of the substrate at hot stamping temperatures. Simultaneously, through the synergistic cross-linking effect of carbon quantum dots and chitosan, a dense adhesive layer is formed upon cooling, achieving a firm transfer between the aluminum layer and the color layer, and imparting invisible fluorescent anti-counterfeiting properties to the hot stamping pattern. The coating of this invention can be applied using a doctor blade coating or a roller coating process. The doctor blade coating pressure is 0.2-0.3 MPa, and the roller coating speed ratio is 1:1.2. After coating, it is dried in hot air at 80°C for 10 minutes, with the dry film thickness controlled at 4-6 μm. It is fully compatible with existing electroplated aluminum production lines, requiring no equipment modification, and has low industrialization costs.

[0018] This invention offers the following advantages over existing technologies: By synergistically modifying fluorescent carbon quantum dots and chitosan, this invention significantly enhances the overall performance of electroplated aluminum adhesive coatings. Compared to traditional waterborne polyurethane adhesive coatings and inorganic nanoparticle-modified coatings, the coating composition of this invention not only solves the problems of weak adhesion, poor scratch resistance, and insufficient water resistance, but also innovatively endows the coating with invisible fluorescent anti-counterfeiting functionality, achieving the dual goals of performance improvement and functional integration. The synergistic effect of carbon quantum dots and chitosan produces results exceeding conventional expectations. The resulting cross-linked network structure enhances both the cohesive strength and interfacial bonding of the coating, and improves fluorescence stability, overcoming the limitations of single modifiers in performance improvement. Furthermore, the preparation process of this invention operates entirely at room temperature, requires no special equipment, and is highly compatible with existing electroplated aluminum adhesive production lines, possessing significant industrialization advantages. It can be widely applied in the production of electroplated aluminum hot stamping foil in the high-end packaging field, enhancing product added value and market competitiveness. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 1. Preparation of fluorescent carbon quantum dot dispersion: 10g of analytical grade citric acid and 4mL of analytical grade ethylenediamine were dissolved in 40mL of deionized water and stirred until homogeneous. The mixture was transferred to a polytetrafluoroethylene-lined hydrothermal reactor and reacted at 190℃ for 10 hours. After cooling, the mixture was filtered through a 0.22μm aqueous filter membrane and dialyzed for 36 hours using a cellulose ester dialysis bag with a molecular weight cutoff of 1000Da. The deionized water was replaced every 6 hours, with the replacement volume being twice the volume of the dialysate, yielding a blue fluorescent CQDs dispersion with a concentration of 8wt%. This dispersion exhibited strong blue light under a 365nm UV lamp, with a quantum yield >40% and a particle size distribution coefficient (PDI) <0.2.

[0021] 2. Preparation of chitosan solution: Chitosan with a molecular weight of 100,000 and a degree of deacetylation ≥ 85% was dissolved in a 1.5 wt% aqueous acetic acid solution to prepare a 3 wt% solution. After stirring until completely transparent, the pH was adjusted to 7.0 with a 1 mol / L NaOH solution to obtain a neutral chitosan solution.

[0022] 3. Preparation of the coating composition: Add 16.4 parts of deionized water and 2 parts of polycarboxylate dispersant BYK-190 (acid value 120 mg KOH / g, purity 98%) to a clean stainless steel mixing tank, and stir at high speed (1000 rpm) for 8 min. Slowly add 6 parts of the above CQDs dispersion and 4 parts of the above chitosan solution, and continue stirring at high speed (1000 rpm) for 30 min. Add 0.5 parts of acetylenol wetting agent Surfynol 104 (surface tension 28 mN / m, purity 99%) and 0.3 parts of silicone defoamer BYK-024, and stir for 10 min. Slowly add 70 parts of waterborne polyurethane resin emulsion with a solid content of 45%, and switch to medium speed stirring (650 rpm) for 20 min. Add 0.8 parts of polyurethane associative thickener Rohm and Haas RM-8W, and stir until the system is homogeneous and free of obvious particles. The coating is filtered through a 200-mesh polyester filter cloth and left to stand for 24 hours at 25°C and 50% humidity to defoam, resulting in a light blue transparent coating with a solid content of 35%.

[0023] Example 2 1. Preparation of fluorescent carbon quantum dot dispersion: Same as in Example 1.

[0024] 2. Preparation of chitosan solution: Same as in Example 1.

[0025] 3. Preparation of the coating composition: Add 21.5 parts of deionized water and 2.5 parts of dispersant BYK-190 to a clean stainless steel mixing tank and stir at high speed (1000 rpm) for 8 min. Slowly add 8 parts of CQDs dispersion and 6 parts of chitosan solution, and stir at high speed (1000 rpm) for 30 min. Add 0.6 parts of wetting agent Surfynol 104 and 0.4 parts of defoamer BYK-024, and stir for 10 min. Slowly add 60 parts of waterborne polyurethane resin emulsion with a solid content of 45%, and stir at medium speed (650 rpm) for 20 min. Add 1.0 part of thickener Rohm and Haas RM-8W and stir until homogeneous and free of particles. Filter through a 200-mesh polyester filter cloth and allow to stand for defoaming for 24 h to obtain a light blue transparent coating.

[0026] Example 3 1. Preparation of fluorescent carbon quantum dot dispersion: Same as in Example 1.

[0027] 2. Preparation of chitosan solution: Same as in Example 1.

[0028] 3. Preparation of the coating composition: Add 16.4 parts of deionized water and 1.5 parts of dispersant BYK-190 to a clean stainless steel mixing tank and stir at high speed (1000 rpm) for 8 min. Slowly add 4 parts of CQDs dispersion and 2 parts of chitosan solution, and stir at high speed (1000 rpm) for 30 min. Add 0.4 parts of wetting agent Surfynol 104 and 0.2 parts of defoamer BYK-024, and stir for 10 min. Slowly add 75 parts of waterborne polyurethane resin emulsion with a solid content of 45%, and stir at medium speed (650 rpm) for 20 min. Add 0.6 parts of thickener Rohm and Haas RM-8W, and stir until homogeneous and free of particles. Filter through a 200-mesh polyester filter cloth and allow to stand for defoaming for 24 h to obtain a light blue transparent coating.

[0029] Example 4 (Lower limit of CQDs) 1. Preparation of fluorescent carbon quantum dot dispersion: Same as in Example 1.

[0030] 2. Preparation of chitosan solution: Same as in Example 1.

[0031] 3. Preparation of the coating composition: Add 16.8 parts of deionized water and 1.5 parts of dispersant BYK-190 to a clean stainless steel mixing tank and stir at high speed (1000 rpm) for 8 min. Slowly add 2 parts of CQDs dispersion and 4 parts of chitosan solution, and stir at high speed (1000 rpm) for 30 min. Add 0.4 parts of wetting agent Surfynol 104 and 0.2 parts of defoamer BYK-024, and stir for 10 min. Slowly add 75 parts of waterborne polyurethane resin emulsion with a solid content of 45%, and stir at medium speed (650 rpm) for 20 min. Add 0.6 parts of thickener Rohm and Haas RM-8W, and stir until homogeneous and free of particles. Filter through a 200-mesh polyester filter cloth and allow to stand for defoaming for 24 h to obtain a light blue transparent coating.

[0032] Example 5 (CQDs Upper Limit) 1. Preparation of fluorescent carbon quantum dot dispersion: Same as in Example 1.

[0033] 2. Preparation of chitosan solution: Chitosan with a molecular weight of 100,000 and a degree of deacetylation ≥ 85% was dissolved in a 1.5 wt% aqueous acetic acid solution to prepare a 5 wt% solution. After stirring until transparent, the pH was adjusted to 7.0 with NaOH solution to obtain a neutral chitosan solution.

[0034] 3. Preparation of the coating composition: Add 22.7 parts of deionized water and 4 parts of dispersant BYK-190 to a clean stainless steel mixing tank and stir at high speed (1200 rpm) for 10 min. Slowly add 12 parts of CQDs dispersion and 8 parts of chitosan solution, and stir at high speed (1200 rpm) for 40 min. Add 1 part of wetting agent Surfynol 104 and 0.8 parts of defoamer BYK-024, and stir for 15 min. Slowly add 50 parts of waterborne polyurethane resin emulsion with a solid content of 45%, and stir at medium speed (800 rpm) for 30 min. Add 1.5 parts of thickener Rohm and Haas RM-8W, and stir until homogeneous and free of particles. Filter through a 200-mesh polyester filter cloth and allow to stand for defoaming for 24 h to obtain a light blue semi-transparent coating.

[0035] Example 6 (lower limit of chitosan) 1. Preparation of fluorescent carbon quantum dot dispersion: Same as in Example 1.

[0036] 2. Preparation of chitosan solution: Chitosan with a molecular weight of 100,000 and a degree of deacetylation ≥ 85% was dissolved in a 1.5 wt% aqueous acetic acid solution to prepare a 1 wt% solution. After stirring until transparent, the pH was adjusted to 7.0 with NaOH solution to obtain a neutral chitosan solution.

[0037] 3. Preparation of the coating composition: Add 19.4 parts of deionized water and 2 parts of dispersant BYK-190 to a clean stainless steel mixing tank and stir at high speed (1000 rpm) for 8 min. Slowly add 6 parts of CQDs dispersion and 1 part of chitosan solution, and stir at high speed (1000 rpm) for 30 min. Add 0.5 parts of wetting agent Surfynol 104 and 0.3 parts of defoamer BYK-024, and stir for 10 min. Slowly add 70 parts of waterborne polyurethane resin emulsion with a solid content of 45%, and stir at medium speed (650 rpm) for 20 min. Add 0.8 parts of thickener Rohm and Haas RM-8W, and stir until homogeneous and free of particles. Filter through a 200-mesh polyester filter cloth and allow to stand for defoaming for 24 h to obtain a light blue transparent coating.

[0038] Example 7 (Upper Limit of Chitosan) 1. Preparation of fluorescent carbon quantum dot dispersion: Same as in Example 1.

[0039] 2. Preparation of chitosan solution: Same as in Example 5.

[0040] 3. Preparation of the coating composition: Add 19.5 parts of deionized water and 2.5 parts of dispersant BYK-190 to a clean stainless steel mixing tank and stir at high speed (1000 rpm) for 8 min. Slowly add 8 parts of CQDs dispersion and 8 parts of chitosan solution, and stir at high speed (1000 rpm) for 30 min. Add 0.6 parts of wetting agent Surfynol 104 and 0.4 parts of defoamer BYK-024, and stir for 10 min. Slowly add 60 parts of waterborne polyurethane resin emulsion with a solid content of 45%, and stir at medium speed (650 rpm) for 20 min. Add 1.0 part of thickener Rohm and Haas RM-8W, and stir until homogeneous and free of particles. Filter through a 200-mesh polyester filter cloth and allow to stand for defoaming for 24 h to obtain a light blue semi-transparent coating.

[0041] Example 8 (Lower Limit of Hydrothermal Temperature) 1. Preparation of fluorescent carbon quantum dot dispersion: Dissolve 10g of citric acid and 4mL of ethylenediamine in 40mL of deionized water and stir until homogeneous. Transfer to a polytetrafluoroethylene-lined hydrothermal reactor and react at 170℃ for 10 hours. After cooling, filter through a 0.22μm aqueous filter membrane and dialyze using a cellulose ester dialysis bag with a molecular weight cutoff of 1000Da for 36 hours, changing the water every 6 hours, with the water volume being twice the volume of the dialysate, to obtain a 7wt% blue fluorescent CQDs dispersion.

[0042] 2. Preparation of chitosan solution: Same as in Example 1.

[0043] 3. Preparation of coating composition: Same as in Example 1.

[0044] Example 9 (Lower limit of stirring rate) 1. Preparation of fluorescent carbon quantum dot dispersion: Same as in Example 1.

[0045] 2. Preparation of chitosan solution: Same as in Example 1.

[0046] 3. Preparation of the coating composition: Add 16.4 parts of deionized water and 2 parts of dispersant BYK-190 to a clean stainless steel mixing tank and stir at high speed (800 rpm) for 8 min. Slowly add 6 parts of CQDs dispersion and 4 parts of chitosan solution, and continue stirring at high speed (800 rpm) for 30 min. Subsequent steps are the same as in Example 1.

[0047] Example 10 (Preferred Additive Model) 1. Preparation of fluorescent carbon quantum dot dispersion: Same as in Example 1.

[0048] 2. Preparation of chitosan solution: Same as in Example 1.

[0049] 3. Preparation of the coating composition: Add 16.4 parts of deionized water and 2 parts of dispersant BYK-190 to a clean stainless steel mixing tank and stir at high speed (1000 rpm) for 8 min. Slowly add 6 parts of CQDs dispersion and 4 parts of chitosan solution, and stir at high speed (1000 rpm) for 30 min. Add 0.5 parts of wetting agent Surfynol 104 and 0.3 parts of silicone defoamer Dow Corning AFE-1510, and stir for 10 min. Slowly add 70 parts of waterborne polyurethane resin emulsion with a solid content of 45%, and stir at medium speed (650 rpm) for 20 min. Add 0.8 parts of thickener Dow ACRYSOLTT-935 and stir until homogeneous and free of particles. Filter through a 200-mesh polyester filter cloth and allow to stand for defoaming for 24 h to obtain a light blue transparent coating.

[0050] Example 11 (Chitosan pH=6.0) 1. Preparation of fluorescent carbon quantum dot dispersion: Same as in Example 1.

[0051] 2. Preparation of chitosan solution: Chitosan with a molecular weight of 100,000 and a degree of deacetylation ≥ 85% was dissolved in a 1.5 wt% aqueous acetic acid solution to prepare a 3 wt% solution. After stirring until transparent, the pH was adjusted to 6.0 with NaOH solution to obtain a neutral chitosan solution.

[0052] 3. Preparation of coating composition: Same as in Example 1.

[0053] Example 12 (Chitosan pH=7.5) 1. Preparation of fluorescent carbon quantum dot dispersion: Same as in Example 1.

[0054] 2. Preparation of chitosan solution: Chitosan with a molecular weight of 100,000 and a degree of deacetylation ≥ 85% was dissolved in a 1.5 wt% aqueous acetic acid solution to prepare a 3 wt% solution. After stirring until transparent, the pH was adjusted to 7.5 with NaOH solution to obtain a neutral chitosan solution.

[0055] 3. Preparation of coating composition: Same as in Example 1.

[0056] Comparative Example 1 (without CQDs and chitosan) Add 17.4 parts deionized water and 1 part dispersant BYK-190 to a clean stainless steel mixing tank and stir at high speed (1000 rpm) for 8 minutes. Add 0.5 parts wetting agent Surfynol 104 and 0.3 parts defoamer BYK-024 and stir for 10 minutes. Slowly add 80 parts of waterborne polyurethane resin emulsion with a solid content of 45% and stir at medium speed (650 rpm) for 20 minutes. Add 0.8 parts thickener Rohm and Haas RM-8W and stir until homogeneous and free of particles. Filter through a 200-mesh polyester filter cloth and allow to stand for 24 hours to defoam, obtaining a transparent coating.

[0057] Comparative Example 2 (CQDs only) 1. Preparation of fluorescent carbon quantum dot dispersion: Same as in Example 1.

[0058] 2. Preparation of the coating composition: Add 20.4 parts of deionized water and 2 parts of dispersant BYK-190 to a clean stainless steel mixing tank and stir at high speed (1000 rpm) for 8 min. Slowly add 6 parts of CQDs dispersion and stir at high speed (1000 rpm) for 30 min. Add 0.5 parts of wetting agent Surfynol 104 and 0.3 parts of defoamer BYK-024 and stir for 10 min. Slowly add 70 parts of waterborne polyurethane resin emulsion with a solid content of 45% and stir at medium speed (650 rpm) for 20 min. Add 0.8 parts of thickener Rohm and Haas RM-8W and stir until homogeneous and free of particles. Filter through a 200-mesh polyester filter cloth and allow to stand for defoaming for 24 h to obtain a light blue transparent coating.

[0059] Comparative Example 3 (Chitosan only) 1. Preparation of chitosan solution: Same as in Example 1.

[0060] 2. Preparation of the coating composition: Add 20.4 parts of deionized water and 2 parts of dispersant BYK-190 to a clean stainless steel mixing tank and stir at high speed (1000 rpm) for 8 min. Slowly add 4 parts of chitosan solution and stir at high speed (1000 rpm) for 30 min. Add 0.5 parts of wetting agent Surfynol 104 and 0.3 parts of defoamer BYK-024 and stir for 10 min. Slowly add 70 parts of waterborne polyurethane resin emulsion with a solid content of 45% and stir at medium speed (650 rpm) for 20 min. Add 0.8 parts of thickener Rohm and Haas RM-8W and stir until homogeneous and free of particles. Filter through a 200-mesh polyester filter cloth and allow to stand for defoaming for 24 h to obtain a transparent coating.

[0061] Comparative Example 4 (SiO2 replacing CQDs) 1. Preparation of chitosan solution: Same as in Example 1.

[0062] 2. Preparation of the coating composition: 16.4 parts of deionized water and 2 parts of dispersant BYK-190 were added to a clean stainless steel mixing tank and stirred at high speed (1000 rpm) for 8 min. Then, 6 parts of 8 wt% SiO2 nano-dispersion (particle size 10 nm) and 4 parts of chitosan solution were slowly added and stirred at high speed (1000 rpm) for 30 min. Subsequent steps were the same as in Example 1, yielding a white, semi-transparent coating.

[0063] Comparative Example 5 (CQDs for Glucose Preparation) 1. Preparation of fluorescent carbon quantum dot dispersion: Dissolve 10g of glucose in 40mL of deionized water and stir until homogeneous. Transfer to a polytetrafluoroethylene-lined hydrothermal reactor and react at 190℃ for 10 hours. After cooling, filter through a 0.22μm aqueous filter membrane and dialyze for 36 hours to obtain a CQDs dispersion with a concentration of 8wt%.

[0064] 2. Preparation of chitosan solution: Same as in Example 1.

[0065] 3. Preparation of coating composition: Same as in Example 1.

[0066] Comparative Example 6 (Chitosan molecular weight 300,000) 1. Preparation of fluorescent carbon quantum dot dispersion: Same as in Example 1.

[0067] 2. Chitosan solution preparation: Take chitosan with a molecular weight of 300,000 and a degree of deacetylation ≥ 85%, dissolve it in a 1.5 wt% acetic acid aqueous solution to prepare a 3 wt% solution. After stirring until transparent, adjust the pH to 7.0 with NaOH solution.

[0068] 3. Preparation of coating composition: Same as in Example 1.

[0069] Comparative Example 7 (stirring speed 600 rpm) 1. Preparation of fluorescent carbon quantum dot dispersion: Same as in Example 1.

[0070] 2. Preparation of chitosan solution: Same as in Example 1.

[0071] 3. Preparation of the coating composition: Add 16.4 parts of deionized water and 2 parts of dispersant BYK-190 to a clean stainless steel mixing tank and stir at high speed (600 rpm) for 8 min. Slowly add 6 parts of CQDs dispersion and 4 parts of chitosan solution, and continue stirring at high speed (600 rpm) for 30 min. Subsequent steps are the same as in Example 1.

[0072] Comparative Example 8 (Chitosan pH=5.0) 1. Preparation of fluorescent carbon quantum dot dispersion: Same as in Example 1.

[0073] 2. Chitosan solution preparation: Chitosan with a molecular weight of 100,000 and a degree of deacetylation ≥85% was dissolved in a 1.5wt% acetic acid aqueous solution to prepare a 3wt% solution. After stirring until transparent, the pH was maintained at 5.0 without adjustment.

[0074] 3. Preparation of coating composition: Same as in Example 1.

[0075] Performance verification 1. Sample Preparation: The coatings from the above examples and comparative examples were applied to the surface of a 12 μm thick PET base film using a doctor blade coating method. The wet film thickness was 15 μm, and the coating pressure was 0.25 MPa. The coated base film was then dried in an 80℃ forced-air oven for 10 min to obtain an electroplated aluminum foil adhesive layer sample with a dry film thickness of 5 μm, for later use.

[0076] 2. Performance Testing Methods 180° peel strength: Performed according to GB / T2792-2014 standard. The sample was heat-bonded with 80g / m² coated paper at 150℃ and 0.5MPa pressure for 1s, and the 180° peel strength was tested using an electronic tensile testing machine at a rate of 300mm / min. The unit is N / 15mm.

[0077] Scratch resistance: Compliant with GB / T6739-2006 standard. Using a 4H pencil, apply a 500g load and scratch the adhesive surface in a straight line at a speed of 1cm / s. Each scratch is 5cm long. Five consecutive scratches without leaving a mark are considered a pass. Record the maximum number of passes.

[0078] Water immersion resistance: The adhesive sample was completely immersed in deionized water at 60℃ for 7 days. After removal, the surface moisture was wiped dry with a lint-free cloth, and the sample was placed at 25℃ for 2 hours. The 180° peel strength was then tested, and the strength retention rate was calculated.

[0079] Fluorescence intensity: The fluorescence intensity was measured using a fluorescence spectrophotometer under the following conditions: excitation wavelength 365 nm, excitation slit width 5 nm; emission wavelength scanning range 400-500 nm, emission slit width 5 nm; the test environment was a darkroom, the sample temperature was 25 °C, and the sample was laid flat in a quartz cuvette; the test parameters were the maximum fluorescence emission intensity (unit: au) and the quantum yield (unit: %), with the quantum yield calculated using quinine sulfate as a reference standard.

[0080] Fluorescence stability: The fluorescence emission intensity of the sample after water immersion was tested again, and the fluorescence intensity retention rate was calculated.

[0081] Storage stability: The coating was sealed and stored at 25°C for 3 months. The viscosity change rate before and after storage was tested, and the viscosity was tested using a rotational viscometer.

[0082] Heat sealing temperature window: Adjust the heat sealing temperature range to 100-200℃, maintain a pressure of 0.5MPa and a time of 1s, and use image analysis to determine the aluminum layer transfer rate. A transfer rate of ≥98% is considered effective transfer, and the temperature range of effective transfer is recorded.

[0083] Color difference test: The color difference ΔE between the coating and the blank PET base film was measured using a colorimeter under the conditions of D65 light source and 10° field of view.

[0084] 3. Performance Verification Results Table

[0085] Stability and application performance verification results

[0086] Synergistic effect gradient verification table

[0087] Technical effects of the present invention: 1. Fluorescent anti-counterfeiting function Test environment: dark room, ambient illuminance <5 lux, no other light source interference; UV lamp parameters: wavelength 365nm, power 10W, vertical distance from the sample 10cm; Sample condition: 5μm dry film thickness electroplated aluminum adhesive layer sample, laid flat on a black non-reflective stage.

[0088] After the UV lamp is turned on, the sample surface immediately exhibits a uniform and bright deep blue fluorescence. The fluorescence coverage area is completely consistent with the sample size, with no mottles, dark areas, or bright spots. After the UV lamp is turned off, the fluorescence disappears instantly, and the sample is a light blue transparent state under visible light, with a color difference ΔE < 1.0 between it and the blank PET base film.

[0089] Durability definition: After being soaked in deionized water at 60℃ for 7 days, the fluorescence emission intensity retention rate is ≥95%, the quantum yield retention rate is ≥94%, and the anti-counterfeiting effect is not diminished; after being aged by ultraviolet light for 100 hours, the fluorescence intensity retention rate is ≥90%.

[0090] 2. Coating uniformity Appearance characteristics: The coating is a light blue transparent or semi-transparent liquid, free of visible particles, impurities and gel clumps; after coating and film formation, the coating surface is smooth and free of defects such as pinholes, craters, and orange peel.

[0091] Microscopic characteristics: The particle size distribution of carbon quantum dots in the coating system was tested using a laser particle size analyzer. The particle size distribution range was 5-10 nm, the particle size distribution coefficient (PDI) was <0.2, and there were no agglomeration peaks (agglomeration peak judgment criteria: the proportion of particles with a diameter >20 nm was <1%). The coating was tested using a rotational rheometer and was found to be a pseudoplastic fluid with viscosity decreasing as the shear rate increased, making it suitable for both blade coating and roller coating processes.

[0092] 3. Heat transfer effect Hot stamping conditions: temperature 110-180℃, pressure 0.5MPa, time 1s; Transfer effect judgment: aluminum layer transfer rate ≥98% (using image analysis method, transfer rate = transfer area / total sample area ×100%); Pattern characteristics after transfer: clear edges, no jagged notches, no residual aluminum shavings, pattern resolution ≥300dpi; After 4H pencil scratch resistance test (500g load), the pattern has no aluminum loss or scratches, and after wiping with a damp cloth 50 times, the pattern has no fading or peeling.

[0093] This invention, through the synergistic modification of fluorescent carbon quantum dots and chitosan, successfully achieves the triple objectives of enhanced mechanical properties, improved dielectric resistance, and the imparting of invisible fluorescent anti-counterfeiting functions to the electroplated aluminum adhesive coating. Compared with existing technologies, it has significant inventiveness, specifically reflected in the following three points: 1. Application Scenarios In existing technologies, the combination of carbon quantum dots and chitosan is only used for room-temperature curing food packaging films or fluorescent inks. However, the electroplated aluminum adhesive layer needs to meet the special requirements of high-temperature short-time heat treatment (100-180℃, 0.5MPa, 1s). This scenario requires the coating to melt and cure rapidly while being compatible with the aluminum layer and the color layer. Those skilled in the art have no incentive to transfer the combination of room-temperature curing systems to the high-temperature heat treatment scenario, because high temperatures will damage the performance of most fluorescent materials. However, this invention, through precise control of the carbon quantum dot preparation process, enables it to possess excellent thermal stability and withstand the high-temperature heat treatment process.

[0094] 2. Synergistic effect In this invention, the synergistic effect of carbon quantum dots and chitosan is not a simple performance additive effect, but rather a leap in performance achieved through the formation of an interpenetrating network structure via intermolecular hydrogen bonds and covalent crosslinking. The actual peel strength in Example 1 increased by 43% compared to the theoretical additive value, and the water retention rate increased by 14% compared to the theoretical additive value—an improvement far exceeding the expectations of those skilled in the art. Comparative experiments show that neither adding carbon quantum dots nor chitosan alone can achieve the performance level of this invention, proving that the synergistic effect of the two is the core innovation of this invention.

[0095] 3. Industrialization advantages The preparation process of this invention operates entirely at room temperature, requires no special equipment, is fully compatible with existing electroplated aluminum production lines, requires no equipment modification, and has low industrialization costs. In contrast, existing inorganic nanoparticle modification methods suffer from poor dispersibility, easy coating cracking, and significant equipment wear, making industrial application difficult. The coating of this invention exhibits excellent storage stability; after 3 months of sealed storage at 25°C, the viscosity change rate is ≤5%, meeting the needs of large-scale industrial production.

[0096] In summary, this invention solves the technical pain points of traditional electroplated aluminum adhesive coatings through precise formula design and process control, combining high performance and high added value, and possesses significant industrial application value.

[0097] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A carbon quantum dots-modified electrochemical aluminite colloidal layer coating composition, characterized by, By weight parts, including the following components: water-based polyurethane resin emulsion 50-80 parts, fluorescent carbon quantum dots dispersion liquid with a concentration of 5-10wt% 2-12 parts, chitosan solution with a concentration of 1-5wt% and pH 6.0-7.5 1-8 parts, polycarboxylate dispersant with an acid value of 100-150mgKOH / g and a purity of ≥95% 1-4 parts, alkyne diol wetting agent with a surface tension of ≤30mN / m and a purity of ≥98% 0.2-1 parts, silicone defoamer 0.1-0.8 parts, polyurethane associated thickener 0.3-1.5 parts, and the balance of deionized water; the fluorescent carbon quantum dots are prepared by hydrothermal reaction of citric acid and ethylenediamine, and the chitosan solution is prepared by dissolving chitosan in 1-2wt% acetic acid aqueous solution and then neutralizing.

2. The coating composition according to claim 1, characterized in that, The quantum yield of the fluorescent carbon quantum dots is >40%, it presents strong blue light under 365nm ultraviolet lamp, the particle size is <10nm, and the particle size distribution coefficient PDI is <0.

2.

3. The coating composition of claim 1, wherein, The molecular weight of the chitosan is 5-200,000, and the degree of deacetylation is ≥85%; when the molecular weight of chitosan is more than 200,000, the molecular chain is easily entangled, resulting in abnormal viscosity of the coating; when the molecular weight is less than 5,000, an effective crosslinking network cannot be formed.

4. The coating composition of claim 1, wherein, The defoamer is polyether modified silicone emulsion, and the specific model is BYK-024 or Dow Corning AFE-1510; the thickener is hydrophobically modified polyurethane emulsion, and the specific model is Rohm & Haas RM-8W or Dow Chemical ACRYSOL TT-935.

5. The coating composition of claim 1, wherein, The solid content of the water-based polyurethane resin emulsion is 40-50%, and the solid content of the coating composition is 30-40%.

6. The coating composition of claim 1, wherein, The 180° peeling strength of the coating composition is ≥8.0N / 15mm, the 4H pencil scratch resistance is ≥20 times, and the strength retention rate after 7d water immersion at 60℃ is ≥82%; preferably, the 180° peeling strength of the preferred formula is ≥8.8N / 15mm, the 4H pencil scratch resistance is ≥30 times, and the strength retention rate after 7d water immersion at 60℃ is ≥93%.

7. The coating composition of claim 1, wherein, The appearance of the coating composition is light blue transparent or translucent liquid, the color difference ΔE with the blank PET base film is <1.0, and the particle size distribution of the carbon quantum dots in the system is 5-10nm without agglomeration peak.

8. The coating composition of claim 1, wherein, The coating composition is used for preparing the adhesive layer of electrochemical aluminum hot stamping foil, is suitable for high temperature short time hot stamping process, and the hot stamping conditions are 100-180℃, 0.5MPa, and 1s, and the aluminum layer transfer rate is ≥98%.

9. A method for preparing the carbon quantum dots-modified electrochromic primer coating composition according to claim 1, characterized in that, The method comprises the following steps: (1) Preparation of fluorescent carbon quantum dot dispersion liquid: 8-12g of analytical reagent citric acid and 3-6mL of analytical reagent ethylenediamine are dissolved in 30-50mL of deionized water, stirred uniformly, transferred to a hydrothermal reaction kettle, reacted at 170-200℃ for 8-12h, filtered with a 0.22μm water system filter membrane after cooling, dialyzed for 24-48h using a dialysis bag made of cellulose ester with a molecular weight cut-off of 1000Da, and deionized water is replaced every 6h, the volume of the replaced water is 2 times the volume of the dialysis liquid, to obtain a fluorescent carbon quantum dot dispersion liquid with a concentration of 5-10wt%. (2) Preparation of chitosan solution: chitosan with molecular weight of 500-200,000 and degree of deacetylation of 85% or more is dissolved in 1-2 wt% acetic acid aqueous solution to prepare a 1-5 wt% solution, and the pH is adjusted to 6.0-7.5 to obtain a neutral chitosan solution; (3) Preparation of coating composition: deionized water and dispersant are added to a stirring tank and stirred at high speed for 5-10 min; fluorescent carbon quantum dot dispersion and chitosan solution are slowly added and stirred at high speed for 20-40 min; wetting agent and defoaming agent are added and stirred for 5-15 min; waterborne polyurethane resin emulsion is slowly added and stirred at medium speed for 15-30 min; thickening agent is added and stirred until uniform, filtered, and then left to stand for 24 h to remove bubbles.

10. The method of claim 9, wherein, The stirring rate in step (3) is 800-1200 rpm at high speed and 500-800 rpm at medium speed, and a 200-mesh polyester filter cloth is used for filtration.

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