Environment-friendly printing ink for cigarette case packaging paper and preparation method thereof

Abstract

This invention relates to the field of packaging ink technology, specifically to an environmentally friendly printing ink for cigarette box packaging paper and its preparation method. This invention overcomes the problems of poor environmental performance and overall poor performance of traditional inks. By using deionized water as the dispersion medium, volatile organic compound emissions are reduced; through the synergistic effect of a free radical-cationic dual-initiator system, a rigid-flexible interpenetrating network is formed; through chemical bonding modification and nano-silica reinforcement, the ink's adhesion and abrasion resistance are significantly improved; casein, through hydrolysis modification and dynamic cross-linking, constructs a hydrophobic-durable composite structure, enhancing heat resistance and water resistance; the combination of infrared pre-drying and dual curing processes ensures rapid and dense ink layer formation; the polyurethane microsphere core-shell structure absorbs thermal stress and inhibits high-temperature deformation; and the synergistic optimization of each component and the reasonable matching between preparation parameters enable the ink to possess adhesion, abrasion resistance, heat resistance, and environmental friendliness.

Description

Technical Field

[0001] This invention relates to the field of packaging ink technology, specifically to an environmentally friendly printing ink for cigarette box packaging paper and its preparation method. Background Technology

[0002] As the outer packaging of cigarette products, the printing quality and safety of cigarette boxes directly affect the product image and consumer health. Currently, cigarette box printing inks are mainly divided into solvent-based inks and water-based inks.

[0003] While traditional solvent-based inks offer advantages such as fast drying, good adhesion, and high gloss, they contain large amounts of volatile organic compounds (VOCs), such as toluene, xylene, and ethyl acetate. These VOCs are released into the atmosphere during ink production, printing, and waste disposal, polluting the environment and posing a potential threat to the health of production workers and end consumers. Furthermore, potentially harmful solvents remaining in solvent-based inks may migrate into cigarette products, posing a safety hazard to human health.

[0004] With increasingly stringent global environmental regulations and growing consumer awareness of environmental protection, the development of environmentally friendly printing materials has become an industry trend. Water-based inks, using water as the primary solvent, significantly reduce VOC emissions and are considered an ideal alternative to solvent-based inks. However, existing water-based inks still face some challenges when applied to substrates such as cigarette packaging paper, which are typically coated and have low surface energy. After printing, water-based resins have relatively weak wetting and penetration capabilities on non-absorbent or low-absorbent coated paper, potentially leading to insufficient adhesion and easy peeling during subsequent processing or use. Water evaporates more slowly than organic solvents, which may affect printing efficiency. After drying, the abrasion resistance and water stability of water-based ink films are sometimes inferior to those of solvent-based inks. The rheological properties and transfer properties of water-based inks need to be precisely controlled to meet specific printing requirements.

[0005] Therefore, developing a water-based printing ink that meets environmental protection requirements, achieves excellent printing performance on cigarette packaging paper, and has good abrasion resistance and water resistance is of great practical significance and market demand.

[0006] To address this, an environmentally friendly printing ink for cigarette box packaging paper and its preparation method are proposed. Summary of the Invention

[0007] The purpose of this invention is to provide an environmentally friendly printing ink for cigarette box packaging paper and its preparation method. By using deionized water as the dispersion medium, volatile organic compound emissions are reduced. A rigid-flexible interpenetrating network is formed through the synergistic effect of a free radical-cationic dual-initiation system. Chemical bonding modification and nano-silica reinforcement significantly improve ink adhesion and abrasion resistance. Casein is modified by hydrolysis and dynamically cross-linked to construct a hydrophobic-durable composite structure, enhancing heat resistance and water resistance. The combination of infrared pre-drying and dual-curing processes ensures rapid and dense ink layer formation. The polyurethane microsphere core-shell structure absorbs thermal stress and inhibits high-temperature deformation. Synergistic optimization of the components and reasonable matching of preparation parameters enable the ink to possess adhesion, abrasion resistance, heat resistance, and environmental friendliness.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention provides a method for preparing environmentally friendly printing ink for cigarette box packaging paper. The preparation method is as follows:

[0010] The S1 prepolymer synthesis involves adding isophorone diisocyanate, polytetrahydrofuran ether diol, dimethylolpropionic acid, and pentaerythritol triacrylate to a reactor, heating, adding a catalyst, reacting, adding KH550, continuing the reaction, cooling, adding glycidyl methacrylate dropwise, maintaining the temperature, reacting again, adding triethylamine, transferring to a disperser, and adding deionized water to obtain the prepolymer emulsion. This process is under nitrogen protection and kept completely dark. After dispersion, the prepolymer emulsion has a particle size D50 ≤ 150 nm; the polytetrahydrofuran ether diol has a molecular weight of 1000.

[0011] S2 modified casein preparation: After partial hydrolysis of casein, cystamine, perfluorooctyltriethoxysilane, EDC and NHS are added to react and obtain cystamine-modified casein; cystamine-modified casein is added to a hydroxymethyl diacetone acrylamide solution, N-hydroxymethyl acrylamide is added after heating, and the mixture is refluxed and dried to obtain modified casein.

[0012] S3 nano-silica was added to the prepolymer emulsion and dispersed to obtain a prepolymer dispersion; the particle size of the acrylated nano-silica was 20-50 nm.

[0013] S4 ink is prepared by mixing a prepolymer dispersion, polyethylene glycol, triethylene glycol divinyl ether, diglycidyl ether, polyurethane microspheres, and modified casein, then adding a free radical initiator, iodonium salt, water-based pigment, wetting agent, and defoamer. After ball milling, the ink to be cured is obtained. The preparation process is carried out in the dark. Finally, the ink is filtered and sealed. The filter bag used for filtration has a size of 5μm. The polyurethane microspheres have a particle size of 100-200nm, and the average molecular weight of polyethylene glycol is 400.

[0014] Water-based pigments can be red, or they can be yellow, blue, green, or other colors.

[0015] After printing and coating using the S5 curing process, the ink is pre-dried and then cured by UV-thermal dual curing to obtain the printing ink.

[0016] By first performing UV curing followed by thermosetting, UV curing rapidly initiates the free radical polymerization of acrylate double bonds, forming a rigid network structure that provides initial hardness and surface abrasion resistance. Subsequent thermosetting triggers the ring-opening reaction of epoxy groups, catalyzing the formation of a flexible cross-linked network that interpenetrates with the rigid acrylate network. Pre-curing with high-temperature initiation of early epoxy ring-opening depletes the activity of iodonium salts, leading to insufficient free radical polymerization during UV curing, an imbalance in the dual-network structure, side reactions between the thermosetting agent's cationic initiator and the free radical initiator, reducing cross-linking efficiency, and a mismatch between the UV and thermosetting timescales, resulting in localized over-curing or uncured areas. Prioritizing UV curing rapidly forms a rigid framework, fixing the ink morphology and preventing structural deformation caused by subsequent thermosetting. Thermosetting then supplements the rigid network, constructing flexible cross-links through epoxy ring-opening, forming a "rigid-flexible" network structure that optimizes overall performance.

[0017] Material deformation risk: Unformed resin is prone to flow during thermosetting, leading to uneven coating or uncontrolled thickness.

[0018] Preferably, the mass ratio of isophorone diisocyanate, polytetrahydrofuran ether diol, dimethylolpropionic acid, pentaerythritol triacrylate, glycidyl methacrylate and triethylamine in S1 is 35-50:55-65:5-9:20-30:13-18:4.0-6.5; the heating temperature is 70-80℃; the temperature is lowered to 55℃; and the reaction time is 1.5-2.5h.

[0019] Preferably, the method for preparing modified casein in S2 is as follows:

[0020] Deionized water was added to hydroxymethyl diacetone acrylamide and stirred until completely dissolved to obtain a hydroxymethyl diacetone acrylamide solution. Cystamine-modified casein was added to the hydroxymethyl diacetone acrylamide solution, stirred evenly, and then heated. When the temperature reached 80°C, N-hydroxymethyl acrylamide was added dropwise at a rate of 5 drops / s, and a 5% potassium sulfate aqueous solution was added dropwise at a rate of 5 drops / s. The pH of the system was adjusted to 9, and the temperature was increased at a rate of 20°C / min. The mixture was refluxed for 2.5 h to obtain a modified casein precursor. The modified casein precursor was poured onto the surface of a tetrafluoroethylene plate and dried to obtain modified casein.

[0021] A preferred method for preparing cystamine-modified casein is as follows: Casein is dispersed in a phosphate buffer solution preheated to 50°C with a solid-liquid ratio of 1:10 and a pH of 8.0. The solution is stirred at 300 rpm for 2 hours at 60°C until completely dissolved, forming a homogeneous colloidal solution. The pH is adjusted to 8.5 using 1M NaOH solution. Two parts of alkaline protease are added to the solution, and the temperature is maintained at 50°C. The mixture is continuously stirred at 200 rpm while maintaining the pH at 8.5 for 1 hour. The reaction is terminated by cooling the reaction vessel in ice water, ultimately yielding a partially hydrolyzed casein solution with a final degree of hydrolysis of 5%-8%.

[0022] A partially hydrolyzed casein solution was placed in a reaction vessel, and cystamine and perfluorooctyltriethoxysilane were slowly added under stirring. The pH was adjusted to 8, and the reaction was carried out at 45°C for 3 hours. After the reaction was completed, unreacted cystamine and other impurities were removed by ultrafiltration to obtain cystamine-modified casein.

[0023] A preferred method for preparing perfluorooctyltriethoxysilane is as follows: deionized water is added to perfluorooctyltriethoxysilane; then 3% hydrochloric acid is added dropwise to adjust the pH of the reaction system to 3; the reaction mixture is heated to 60°C under stirring and refluxed for 4 hours to obtain crude perfluorooctyltriethoxysilane; after the reaction is completed, unreacted substances and water in the crude product are removed by vacuum distillation to obtain perfluorooctyltriethoxysilane.

[0024] Preferably, the mass ratio of acrylated nano-silica in S3 to polyurethane microspheres and modified casein in S4 is 3-5:2-3.5:20-25; the prepolymer dispersion obtained after dispersing nano-silica is confirmed by laser particle size analyzer to have a D50≤100nm.

[0025] Preferably, the mass ratio of the dry weight of the prepolymer dispersion, polyethylene glycol, triethylene glycol divinyl ether, diglycidyl ether, polyurethane microspheres and modified casein in S4 is 60-75:10-15:5-8:3.5-5:3-3.5:1.8-2.2.

[0026] Preferably, the coating amount for printing and coating in S5 is 2.0 ± 0.2 g / m³. 2 The pre-drying time is 1.5-3 seconds; the energy density of UV curing in the UV-thermal dual curing process is 200-280 mJ / cm³. 2 .

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. Through water-based system design and dual-curing process optimization, the environmental friendliness and curing efficiency of the ink are significantly improved. Using water-based polyurethane acrylate prepolymer as the base material and deionized water as the main dispersion medium, combined with a low-VOC co-solvent, the volatile organic compound emissions of the ink are greatly reduced. By introducing a free radical-cationic dual-initiation system, under the synergistic effect of ultraviolet light irradiation and thermal activation, the ink rapidly forms a rigid-flexible interpenetrating network structure. Nitrogen protection and complete light-shielding operation effectively avoid side reactions, ensuring the stability of prepolymer synthesis. Simultaneously, carboxyl neutralization and silane coupling technology significantly improve emulsion dispersibility and storage stability. The cured ink surface is dense and defect-free, suitable for printing requirements, and meets stringent environmental standards.

[0029] 2. Through chemical bonding design and nano-reinforcement technology, the adhesion and abrasion resistance of the ink are synergistically improved. Epoxy groups and polyfunctional acrylates are introduced into the prepolymer, forming a chemical cross-linked network during the dual curing process, enhancing the chemical bonding force with the substrate. Nano-silica particles, after surface modification, are uniformly embedded into the polyurethane network through high-speed dispersion and ultrasonic treatment, forming a rigid reinforcing phase that effectively suppresses frictional stress concentration. Simultaneously, casein, after hydrolysis modification and dynamic cross-linking, exhibits short peptide chains that synergistically work with components such as fluorosilanes and cystamine to construct a hydrophobic-durable composite structure. Ultimately, this results in inks that possess both excellent adhesion and abrasion resistance after curing.

[0030] 3. Through dynamic cross-linking networks and nanocomposite reinforcement strategies, the heat resistance and high-temperature stability of the ink are significantly improved. The disulfide bonds and fluorocarbon chains introduced into the modified casein can dissipate heat energy through reversible fracture at high temperatures, thus delaying thermal degradation; acrylated silica is chemically bonded into the polyurethane network, improving the material's thermal conductivity and rigidity; the core-shell structure of polyurethane microspheres absorbs thermal stress, reducing microcrack propagation; the interpenetrating network formed by the dual-curing process further balances rigidity and toughness, inhibiting molecular chain breakage at high temperatures; the ink maintains structural integrity after heat treatment, with no discoloration or cracking on the surface, making it suitable for high-temperature processing environments.

[0031] 4. Through the synergistic design of multifunctional components and precise control of process parameters, comprehensive optimization of ink performance was achieved. Hydrolytic modification of casein and silane coupling technology enhanced its compatibility with the polyurethane matrix, while the introduction of reactive diluents and initiators optimized curing performance. Nanoparticle dispersion technology and thickener control ensured the stability of ink viscosity. The combination of infrared pre-drying and dual-curing processes effectively removed moisture and accelerated film formation, avoiding curing defects. The synergistic effect of these preparation methods and parameters enabled the ink to achieve a balance in adhesion, abrasion resistance, heat resistance, and environmental friendliness, providing a high-performance solution for cigarette box packaging. Attached Figure Description

[0032] Figure 1These are the test results for the heat resistance of the ink of this invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Please see Figure 1 This invention provides an environmentally friendly printing ink for cigarette box packaging paper and its preparation method. The technical solution is as follows: Unless otherwise specified, all "parts" in this invention refer to "parts by weight".

[0035] The material information used in this invention is as follows:

[0036] Isophorone diisocyanate CAS: 4098-71-9; Dimethylolpropionic acid CAS: 4767-03-7; Pentaerythritol triacrylate CAS: 3524-68-3; Glycidyl methacrylate CAS: 106-91-2; γ-aminopropyltriethoxysilane (KH550) CAS: 919-30-2; Triethylamine CAS: 121-44-8; Zinc acetylacetone CAS: 14024-63-6; Triethylene glycol divinyl ether CAS: 765-12-8; Water-dispersible iodonium salt (UVI-6976), diphenyl[4-(phenylthio)phenyl]-sulfonium hexafluoroantimonyate CAS: 71449-78-0; Casein CAS: 9000-71-9; Cystamine CAS: 51-85-4; Perfluorooctyltriethoxysilane CAS: 51851-37-7; Hydroxymethyl diacetone acrylamide CAS: 255-936-4; Tris(N-nitroso-N-phenylhydroxylamine) aluminum salt CAS: 15305-07-4; Alkaline protease CAS: 9014-01-1; 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) CAS: 1892-57-5; N-hydroxysuccinimide (NHS) CAS: 6066-82-6; Acrylate-esterified nano silica was purchased from Xi'an Qiyue Biotechnology Co., Ltd.; Free radical photoinitiator (TPO-L) was purchased from Shanghai Kaiyin Chemical Co., Ltd.; Waterborne pigments were purchased from BASF; Wetting agent (BYK) Dynwet 800N was purchased from Guangzhou Haoyi New Material Technology Co., Ltd.; defoamer (BYK-024) was purchased from BYK Chemical Additives, Germany; HEUR thickener was purchased from Nanjing Kaishengtong New Material Co., Ltd.; and polyurethane microspheres were purchased from Suzhou Zhiyi Microsphere Technology Co., Ltd.

[0037] Example 1

[0038] S1 prepolymer synthesis

[0039] 40 parts of isophorone diisocyanate, 60 parts of polytetrahydrofuran ether diol, 8 parts of dimethylolpropionic acid, and 25 parts of pentaerythritol triacrylate were added to a reactor. The temperature was raised to 75°C, and 0.1 parts of zinc acetylacetonate were added. The stirring speed was 300 rpm. The NCO content was measured every 30 min. After reacting for 30 min, 4 parts of KH550 were added, and the reaction was continued for 3 h to prepare a polyurethane main chain with an NCO content of 3%. The temperature was lowered to 55°C, and 15 parts of glycidyl methacrylate were slowly added dropwise at a rate of 5 drops / min. The reaction was maintained at this temperature for 1.5 h, and the NCO value was monitored until it reached 0.1%. The temperature was lowered to 45°C, and 5.5 parts of triethylamine were added to neutralize the carboxyl groups and the pH was adjusted to 7.5. The prepolymer was transferred to a high-speed disperser, and 200 parts of deionized water were slowly added. The mixture was dispersed at 2000 rpm for 1 h to obtain a prepolymer emulsion.

[0040] Preparation of S2 modified casein

[0041] Preparation of partially hydrolyzed casein solution: 100 parts of casein were dispersed in phosphate buffer preheated to 50℃, with a solid-liquid ratio of 1:10 (w / v) and a pH of 8.0. The solution was stirred at 300 rpm for 2 hours at 60℃ until completely dissolved, forming a homogeneous colloidal solution. The pH was adjusted to 8.5 with 1M NaOH solution. Two parts of alkaline protease were added to the solution, and the temperature was maintained at 50℃. The solution was stirred continuously at 200 rpm while maintaining the pH at 8.5 for 1 hour. The reaction was terminated by cooling the reaction vessel in ice water, and the partially hydrolyzed casein solution was finally obtained.

[0042] In a reaction vessel equipped with a stirrer and a reflux condenser, 5 parts of perfluorooctyltriethoxysilane were added, followed by 30 parts of deionized water. 3% hydrochloric acid was then added dropwise to adjust the pH of the reaction system to 3. The reaction mixture was heated to 60°C under stirring and refluxed for 4 hours to obtain crude perfluorooctyltriethoxysilane. After the reaction was complete, unreacted substances and water were removed from the crude product by vacuum distillation to obtain perfluorooctyltriethoxysilane.

[0043] 142 parts of partially hydrolyzed casein solution were placed in a reaction vessel. Under stirring, 6.0 parts of cystamine, 2 parts of perfluorooctyltriethoxysilane, 0.1 parts of EDC and 0.1 parts of NHS were slowly added. The pH of the reaction system was adjusted to 8 with sodium hydroxide solution, and the reaction was refluxed at 45°C for 3 hours. After the reaction was completed, unreacted cystamine, other impurities and solvents were removed by ultrafiltration to obtain cystamine-modified casein.

[0044] Add 150 parts of deionized water to 19.9 parts of hydroxymethyl diacetone acrylamide and stir until completely dissolved to obtain a hydroxymethyl diacetone acrylamide solution. Transfer the hydroxymethyl diacetone acrylamide solution to a four-necked flask and add 40 parts of cystamine-modified casein. Stir well and start heating. When the temperature reaches 80℃, add 4.5 parts of N-hydroxymethyl acrylamide dropwise to the solution at a rate of 5 drops / s. At the same time, add 5 parts of 5% potassium sulfate aqueous solution at a rate of 5 drops / s and adjust the pH of the system to 9. Heat to 110℃ at a rate of 20℃ / min and reflux for 2.5h to obtain a modified casein precursor. Pour the modified casein precursor onto the surface of a tetrafluoroethylene plate and dry at room temperature for 24h until there are no bubbles on the film surface. Then dry in an oven at 60.0℃ for 6h to obtain a cured film, i.e., modified casein.

[0045] S3 nano silica dispersion

[0046] Nanoparticle dispersion: 3 parts of acrylated nano-silica were added to the prepolymer emulsion and dispersed at high speed of 2000 rpm for 1 h; then ultrasonically assisted treatment was carried out at 300 W power and 40 kHz frequency for 30 min to ensure no visible agglomeration, thus obtaining the prepolymer dispersion.

[0047] S4 Ink Formulation

[0048] Take 60 parts (dry weight) of the prepolymer dispersion, 10 parts of polyethylene glycol, 5 parts of triethylene glycol divinyl ether, 3.5 parts of diglycidyl ether, 2 parts of polyurethane microspheres, and 20 parts of modified casein, and stir in the dark for 20 minutes. Then add 3 parts of free radical initiator, 2 parts of water-dispersible iodonium salt, 30 parts of red water-based pigment, 0.2 parts of wetting agent, and 0.3 parts of defoamer. Ball mill for 2 hours at 500 rpm, with zirconia beads of 0.5 mm particle size, ensuring that the pigment particle size is ≤1 μm. Add 0.5 parts of thickener pre-diluted in 5 parts of deionized water. Add deionized water to a total mass of 160 parts, filter, and store in a sealed container.

[0049] S5 curing process

[0050] Printing and Coating: Gravure printing machine, 250 mesh, coating amount 2.0 g / m² 2 ;

[0051] Pre-drying: Infrared drying at 85℃, infrared wavelength 5μm, curing time 2s, residual moisture ≤5%;

[0052] UV-thermal dual curing: UV curing: mercury lamp irradiation for 3 seconds, mercury lamp's main peak is 365nm, light intensity is 80mW / cm². 2 Energy density 240 mJ / cm³ 2Thermosetting: Circulate hot air at 90℃ for 2 minutes to trigger deep cross-linking of epoxy groups, and finally dry at room temperature.

[0053] The preparation methods of Examples 2-4 are generally the same as those of Example 1, but some parameters of the preparation methods in the synthesis of S1 prepolymer are changed, as shown in Table 1.

[0054] In Comparative Example 1S1, polytetrahydrofuran ether diol was not added, and the other preparation methods were consistent with those in Example 1.

[0055] In Comparative Example 2S1, no dimethylolpropionic acid was added, and the other preparation methods were consistent with those in Example 1.

[0056] Comparative Example 3S1 did not contain glycidyl methacrylate and pentaerythritol triacrylate, and the other preparation methods were consistent with those in Example 1.

[0057] In Comparative Example 4S1, triethylamine was not used for carboxyl neutralization, and the other preparation methods were consistent with those in Example 1.

[0058] After the polyurethane backbone was prepared in Comparative Example 5S1, no cooling treatment was performed, and the temperature remained at 75°C.

[0059] The total mass of Comparative Example 6S4 after adding deionized water was 600 parts.

[0060] Table 1. Preparation parameters for the synthesis of S1 prepolymer

[0061]

[0062] Experimental Example 1

[0063] The viscosity of the inks obtained in the above examples and comparative examples was tested before the S5 curing process, specifically according to the method in GB / T14623-2009 "Determination of Rheological Properties of Inks"; after the S5 curing process, the adhesion was tested according to the method in GB / T 13217.7—2023 "Test Method for Adhesion of Inks". The substrate used was cigarette box packaging paper, and the test results are shown in Table 2.

[0064] Table 2. Ink viscosity and adhesion test results

[0065] Example 1 1320 95 Example 2 1300 90 Example 3 1380 98 Example 4 1310 88 Comparative Example 1 1250-1390 72 Comparative Example 2 1400 64 Comparative Example 3 1250 44 Comparative Example 4 1320 51 Comparative Example 5 1450 59 Comparative Example 6 859 37

[0066] The printing ink for shape-retaining cigarette box packaging paper prepared by this invention has a viscosity of 1300-1380 mPa·s and an adhesion of 88%-95% under the conditions of Examples 1-4. A prepolymer was prepared under nitrogen protection and complete light avoidance conditions. The isocyanate groups in isophorone diisocyanate undergo a stepwise addition polymerization reaction with the hydroxyl groups in polytetrahydrofuran ether diol to form a polyurethane backbone. The content of isocyanate groups was controlled by the reaction process. The hydroxyl groups in dimethylolpropionic acid react with the isocyanate groups to introduce carboxyl groups into the polyurethane backbone, providing conditions for subsequent emulsification and water-based treatment. At the same time, the amino group of KH550 undergoes a condensation reaction with the group of the system during the reaction. The epoxy group of glycidyl methacrylate partially opens under heating conditions and reacts with the isocyanate group and carboxyl group of the system. Triethylamine neutralizes the carboxyl group to form a carboxylate, making the prepolymer hydrophilic. The introduced pentaerythritol triacrylate and glycidyl methacrylate provide chemical bonding reaction active sites for the subsequent crosslinking and curing reaction, so that the ink has a moderate viscosity before curing and good adhesion to packaging paper after curing. The ink obtained in Comparative Example 1 exhibited unstable viscosity. The lack of polytetrahydrofuran ether diol resulted in excessively high rigidity. The absence of PETA reduced crosslinking density, significantly decreasing adhesion. Furthermore, the failure to form a stable prepolymer led to uneven dispersion, causing viscosity fluctuations. Ink samples taken from different points within the same container showed varying viscosities. In Comparative Example 2, the absence of carboxyl groups resulted in emulsion instability, poor ink film-forming properties, reduced adhesion, and the unneutralized prepolymer's tendency to agglomerate, leading to excessively high viscosity. In Comparative Example 3, the absence of glycidyl methacrylate and pentaerythritol triacrylate hindered subsequent thermosetting and photocuring processes, relying solely on physical adsorption, resulting in insufficient adhesion and a significant decrease in viscosity. In Comparative Example 4, unneutralized carboxyl groups caused emulsion stratification, preventing uniform ink film formation, reducing adhesion, and showing no significant change in viscosity. In Comparative Example 5, after obtaining the polyurethane backbone, no cooling treatment was performed. At high temperatures, the self-polymerization of glycidyl methacrylate and side reactions damaged the prepolymer structure, leading to decreased adhesion, molecular chain breakage or uneven crosslinking, and abnormally high viscosity. Comparative Example 6 showed that excessive dilution resulted in low solid content, incomplete film formation, extremely poor adhesion, and significantly reduced viscosity.

[0067] In Examples 5-6, the ink preparation and curing process parameters for S4 and S5 were changed, as shown in Table 3. Other preparation steps remained the same as in Example 3. The adjustment of the ultraviolet energy density was achieved through irradiation time; the irradiation time in Example 5 was 2.5 s, and in Example 6 it was 3.5 s.

[0068] Table 3. S4 Ink Formulation and S5 Curing Process Parameters

[0069]

[0070]

[0071] In Comparative Example 7, the dry weight of the prepolymer dispersion is 100 parts, and other preparation steps are kept the same as those in Example 3.

[0072] In Comparative Example 8, no prepolymer dispersion is added, and other preparation steps are kept the same as those in Example 3.

[0073] In Comparative Example 9, no polyethylene glycol is added, and other preparation steps are kept the same as those in Example 3.

[0074] In Comparative Example 10, no triethylene glycol divinyl ether is added, and other preparation steps are kept the same as those in Example 3.

[0075] In Comparative Example 11, no diglycidyl ether is added, and other preparation steps are kept the same as those in Example 3.

[0076] In Comparative Example 12, no free radical initiator and water-dispersible iodonium salt are added, and other preparation steps are kept the same as those in Example 3.

[0077] Comparative Example 13 has a coating weight of 4.0g / m 2 , and other preparation steps are kept the same as those in Example 3.

[0078] In Comparative Example 14, no pre-drying process is performed, and other preparation steps are kept the same as those in Example 3.

[0079] In Comparative Example 15, nano-silica instead of acrylated nano-silica is added in step S3, and other preparation steps are kept the same as those in Example 3.

[0080] In Comparative Example 16, no acrylated nano-silica is added in step S3 and no polyurethane microspheres are added in step S4, and other preparation steps are kept the same as those in Example 3.

[0081] Experimental Example 2

[0082] The abrasion resistance test is carried out on the inks obtained in the above examples and comparative examples. A standard eraser with a hardness of 70 Shore A is used to rub the ink layer at a constant pressure of 500g and a speed of 40 times / min. The number of frictions before the ink layer falls off is recorded. Cigarette pack ink is qualified only when the number of frictions is ≥1500 times (no substrate exposure). The final test results are shown in Table 4.

[0083] Table 4 Abrasion resistance test results of Example 3, Example 5-6, Comparative Example 3 and Comparative Example 7-16

[0084] Example 3 1800 Comparative Example 10 1100 Example 5 2100 Comparative Example 11 900 Example 6 1950 Comparative Example 12 700 Comparative Example 3 800 Comparative Example 13 900 Comparative Example 7 1150 Comparative Example 14 600 Comparative Example 8 600 Comparative Example 15 1500 Comparative Example 9 1300 Comparative Example 16 450

[0085] The ink prepared according to the method of this invention exhibited a wear resistance of 1800-2100 cycles under the conditions of Examples 3, 5, and 6. In step S3, during the dispersion of nano-silica, high-speed dispersion and ultrasonic treatment ensured uniform dispersion of nanoparticles in the prepolymer emulsion. The surface modification of the introduced nano-silica enabled it to form chemical bonds with the polyurethane matrix. The silica particles embedded in the polyurethane network through chemical bonds and physical adsorption, forming a rigid reinforcing phase and enhancing wear resistance. In step S4, when preparing the ink, the prepolymer emulsion, reactive diluent, initiator, and other additives were mixed. Polyethylene glycol diacrylate served as a reactive diluent, reducing viscosity and participating in free radical polymerization. The added prepolymer provided dual curing sites, including acrylate and epoxy groups. Triethylene glycol divinyl ether synergistically cationically cured the epoxy groups, forming... A flexible network is formed. The free radical initiator TPO-L decomposes into free radicals under ultraviolet light, initiating the polymerization of acrylate double bonds. The water-dispersible iodonium salt is activated by ultraviolet I-6976 at 90°C to release hydrogen ions, catalyzing the ring-opening polymerization of epoxy groups to form an interpenetrating network structure. This network, together with nano-silica, synergistically enhances the abrasion resistance of the ink. In the S5 curing process, infrared pre-drying is performed to remove moisture, followed by ultraviolet-initiated free radical polymerization. Thermal curing promotes the ring-opening polymerization of epoxy groups. This dual curing mechanism ensures rapid ink layer formation and a dense structure. The rigid acrylate network and the flexible epoxy network are interpenetrating, synergistically enhancing the abrasion resistance of the ink with nano-silica and polyurethane microspheres.

[0086] Comparative Example 3, lacking glycidyl methacrylate and pentaerythritol triacrylate, lacked chemical crosslinking sites, resulting in a loose cured network and significantly reduced abrasion resistance. Comparative Example 7, with excessive prepolymer dispersion and high solids content, led to uneven dispersion and decreased abrasion resistance. Comparative Example 8, lacking prepolymer dispersion, lacked film-forming substances, failing to form an effective protective layer and significantly reducing abrasion resistance. Comparative Example 9, lacking reactive diluent, resulted in insufficient crosslinking and reduced abrasion resistance. Comparative Example 10, lacking triethylene glycol divinyl ether, hindered cationic curing, resulting in insufficient epoxy crosslinking and reduced ink performance. Comparative Example 11, lacking diglycidyl ether, resulted in missing epoxy crosslinking points and a loose cured network. Comparative Example 12, lacking initiator, prevented ink curing, deteriorated film formation, and only modified casein played a film-forming role, leading to reduced abrasion resistance. Comparative Example 13, with excessive coating and an overly thick ink layer, resulted in uneven internal stress and decreased abrasion resistance. Comparative Example 14 was not pre-dried, and residual moisture caused curing defects, making the ink layer easy to peel off. Comparative Example 15 added nano-silica instead of acrylated nano-silica; the surface of the nanoparticles did not contain substances that cross-link with the system, resulting in a decrease in wear resistance compared to Example 3. Comparative Example 16 did not add acrylated nano-silica or polyurethane microspheres, and the number of friction cycles decreased significantly, resulting in reduced wear resistance.

[0087] In Comparative Example 17S2, casein was modified directly without hydrolysis, that is, 142 parts of partially hydrolyzed casein solution were replaced with 142 parts of casein dispersion. The 142 parts of casein dispersion contained 12.9 parts of casein, and the remainder was phosphate buffer. Other preparation steps were the same as in Example 3.

[0088] Comparative Example 18S2 did not contain cystamine, and the other preparation steps were the same as in Example 3.

[0089] Comparative Example 19S2 did not contain perfluorooctyltriethoxysilane, and the other preparation steps were the same as in Example 3.

[0090] In Comparative Example 19S2, hydroxymethyl diacetone acrylamide was not added, and the other preparation steps were the same as in Example 3.

[0091] In Comparative Example 20S2, N-hydroxymethylacrylamide was not added, and the other preparation steps were the same as in Example 3.

[0092] In Comparative Example 21S2, no casein was modified, and the other preparation steps were the same as in Example 3.

[0093] Comparative Example 22S4 did not contain modified casein, and the other preparation steps were the same as in Example 3.

[0094] In the synthesis of Comparative Example 23S1 prepolymer, KH550 was not added, and other preparation steps were consistent with those in Example 3.

[0095] Experimental Example 3

[0096] The inks prepared in Examples 3, 5, and Comparative Examples 17-22 were tested for abrasion resistance and hydrophilicity. The abrasion resistance was tested according to the test method of Experiment 2; the hydrophilicity was tested according to the water contact angle test method. The test results are shown in Table 5.

[0097] Table 5 Results of abrasion resistance and hydrophilicity tests

[0098] Example 3 1800 100 Example 5 2100 102 Comparative Example 17 1500 60 Comparative Example 18 1000 64 Comparative Example 19 1750 45 Comparative Example 20 1100 77 Comparative Example 21 1800 51 Comparative Example 22 450 40 Comparative Example 23 1800 73

[0099] By modifying casein and using it as a raw material for ink preparation, the rubbing cycles in Examples 3 and 5 were 1800 and 2100, respectively, and the water contact angles were 100° and 102°, respectively. In S2, casein was hydrolyzed and modified. First, a hydrolysis process was carried out, in which alkaline protease selectively hydrolyzed the peptide bonds of casein to generate short peptide chains, reducing the molecular weight and improving solubility and fluidity. The short peptide chains exposed more amino and hydroxyl groups, providing active sites for subsequent chemical modification. Perfluorooctyltriethoxysilane was hydrolyzed under acidic conditions to perfluorooctylsilanol, which condensed with the amino or hydroxyl groups of casein to form Si-OC / N bonds, introducing fluorocarbon chains. Cystamine was introduced for modification, and the amino group of cystamine (containing disulfide bonds) reacted with the carboxyl or amino group of the short casein peptide. The condensation of the base forms a dynamic disulfide bond crosslinking network, which enhances mechanical properties and improves water resistance, thereby increasing the water contact angle. The hydroxymethyl group of N-hydroxymethylacrylamide condenses with the casein amino group, and the hydroxyl group in hydroxymethyl diacetone acrylamide condenses with the casein group. At the same time, its vinyl group participates in subsequent free radical polymerization, providing crosslinking active sites, improving compatibility with acrylate monomers and other substances containing unsaturated double bonds in the ink, forming a reinforcing phase, and improving hydrophobic effect. The introduction of KH550 in S1 also improves the water resistance of the ink after curing.

[0100] Comparative Example 17: Unhydrolyzed casein has a long molecular chain, poor solubility, insufficient exposure of modification sites, low crosslinking density, weak hydrophobicity, and a decrease in the content of crosslinkable curable groups, resulting in reduced abrasion resistance. Comparative Example 18: Without cystamine, it lacks dynamic disulfide crosslinking, resulting in poor water resistance and reduced abrasion resistance and hydrophobicity. Comparative Example 19: Without the introduction of fluorocarbon chains, hydrophobicity decreased significantly, and water penetration led to a sharp drop in abrasion resistance. Comparative Example 20: Without hydroxymethyl diacetone acrylamide, crosslinking active sites were missing, acrylate binding was insufficient, and abrasion resistance and hydrophobicity were limited. Comparative Example 21: No casein modification treatment was performed; the original casein had poor solubility and could not participate in crosslinking, resulting in a loose ink film with extremely low abrasion resistance and hydrophobicity. Comparative Example 22: Without modified casein, it lacked a casein reinforcing phase and film-forming substances, resulting in a fragile ink structure and a significant decrease in abrasion resistance and hydrophobicity. In Comparative Example 23, no KH550 was added during the synthesis of the S1 prepolymer. The wear resistance remained unchanged, but the water contact angle was reduced compared to Example 3.

[0101] Example 7

[0102] In S3, the amount of acrylated nano-silica added is 5 parts, the amount of polyurethane microspheres added is 3 parts, and the amount of modified casein added is 25 parts. Other preparation steps are the same as those in Example 5.

[0103] Example 8

[0104] In S3, the amount of acrylated nano-silica added is 4.5 parts, the amount of polyurethane microspheres added is 3.5 parts, and the amount of modified casein added is 22 parts. Other preparation steps are the same as those in Example 5.

[0105] Experiment Example 4

[0106] The inks obtained in Examples 5, 7, and 8, as well as Comparative Examples 16 and 22, were subjected to heat resistance tests. According to GB / T 1735-2009 "Determination of Heat Resistance of Paints and Varnishes", the heat resistance test method for inks is as follows: the cured ink coating was placed in a constant temperature oven, heated to a set temperature of 120°C, and maintained for 1 hour. After cooling, the surface condition of the coating (such as discoloration, blistering, and cracking) was observed, and the adhesion retention rate was tested. The test results are shown in Table 6 and... Figure 1 As shown.

[0107] Table 6 Results of Heat Resistance Test

[0108] Example 5 95 92 No discoloration, no cracks Example 7 97 95 No discoloration, no cracks Example 8 93 89 No discoloration, no cracks Comparative Example 16 60 45 Noticeable cracking and blistering Comparative Example 22 45 28 Severe discoloration and peeling

[0109] The ink prepared by this invention exhibits excellent heat resistance. Under the conditions of Examples 5, 7, and 8, the adhesion before heat treatment was 93%-97%, and the adhesion after heat treatment was 89%-95%, with no discoloration or cracking on the ink surface. Modified casein, after hydrolysis and fluorosilane modification, forms a dynamic cross-linked network (disulfide bonds and fluorocarbon chains), maintaining structural stability at high temperatures. Hydroxymethylacrylamide grafting provides heat-resistant cross-linking sites. Acrylated silica is embedded in the polyurethane network through chemical bonds, enhancing thermal stability. Its synergistic use with polyurethane microspheres, along with the core-shell structure absorbing thermal stress and reducing crack propagation, and the interpenetrating network formed by infrared-ultraviolet-thermal dual curing balancing rigidity and toughness, inhibits molecular chain breakage at high temperatures, collectively improving the ink's heat resistance. Comparative Example 16, without acrylated silica and polyurethane microspheres, lacks a reinforcing phase, resulting in uneven thermal conduction and cracking. Comparative Example 22, without modified casein, relies on a single polyurethane network, softening and deforming at high temperatures, leading to decreased heat resistance.

[0110] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an environmentally friendly printing ink for cigarette box packaging paper, characterized in that: The preparation method is as follows: Ink formulation: A prepolymer dispersion, polyethylene glycol, triethylene glycol divinyl ether, diglycidyl ether, polyurethane microspheres, and modified casein are mixed. A free radical initiator, iodonium salt, water-based pigment, wetting agent, and defoamer are then added. After ball milling, deionized water and a thickener are added to obtain the ink to be cured. The modified casein is obtained by enzymatic hydrolysis of casein followed by treatment with cystamine, perfluorooctyltriethoxysilane, hydroxymethyl diacetone acrylamide, and N-hydroxymethyl acrylamide. Curing process: After the ink to be cured is printed and coated, it is pre-dried and UV-thermal dual curing is performed to obtain the printing ink; The prepolymer dispersion is prepared as follows: 35-50 parts of isophorone diisocyanate, 55-65 parts of polytetrahydrofuran ether diol, 5-9 parts of dimethylolpropionic acid, and 20-30 parts of pentaerythritol triacrylate are added to a reactor. After heating, a catalyst is added, followed by reaction. γ-aminopropyltriethoxysilane is added, and the reaction continues. The temperature is then lowered, and 13-18 parts of glycidyl methacrylate are added dropwise. The reaction is maintained at this temperature, and 4.0-6.5 parts of triethylamine are added and transferred to a disperser. Deionized water is added to obtain a prepolymer emulsion. Acrylated nano-silica is added to the prepolymer emulsion and dispersed to obtain the prepolymer dispersion. The heating temperature is 70-80℃; the temperature is then lowered to 55℃; the holding time is 1.5-2.5 hours. The modified casein is prepared as follows: Deionized water is added to the hydroxymethyl diacetone acrylamide and stirred until completely dissolved to obtain a hydroxymethyl diacetone acrylamide solution; cystamine-modified casein is added to the hydroxymethyl diacetone acrylamide solution, stirred evenly, and then heated. When the temperature reaches 80°C, N-hydroxymethyl acrylamide is added dropwise, and potassium sulfate aqueous solution is added dropwise simultaneously. After heating, the mixture is refluxed to obtain a modified casein precursor; the modified casein precursor is poured onto the surface of a tetrafluoroethylene plate and dried to obtain the modified casein. The preparation method of the cystamine-modified casein is as follows: the casein is dispersed in preheated phosphate buffer and completely dissolved to form a homogeneous colloidal solution; alkaline protease is added to the homogeneous colloidal solution and stirred continuously at a speed of 200 rpm; after the reaction, the reaction vessel is placed in ice water to cool and terminate the reaction, and finally a partially hydrolyzed casein solution is obtained. The partially hydrolyzed casein solution was placed in a reaction vessel, and under stirring conditions, the cystamine and the perfluorooctyltriethoxysilane were added; after the reaction was completed, the cystamine-modified casein was obtained by ultrafiltration.

2. The method for preparing an environmentally friendly printing ink for cigarette box packaging paper according to claim 1, characterized in that: The preparation method of the perfluorooctyltriethoxysilane is as follows: deionized water is added to perfluorooctyltriethoxysilane; the reaction mixture is heated and refluxed under stirring to obtain crude perfluorooctyltriethoxysilane; after the reaction is completed, unreacted substances and water in the crude product are removed by vacuum distillation to obtain the perfluorooctyltriethoxysilane.

3. The method for preparing an environmentally friendly printing ink for cigarette box packaging paper according to claim 1, characterized in that: The mass ratio of the acrylated nano-silica, the polyurethane microspheres, and the modified casein is 3-5:2-3.5:20-25.

4. The method for preparing an environmentally friendly printing ink for cigarette box packaging paper according to claim 1, characterized in that: The ratio of the dry weight of the prepolymer dispersion, the mass of polyethylene glycol, the triethylene glycol divinyl ether, the diglycidyl ether, the polyurethane microspheres, and the modified casein is 60-75:10-15:5-8:3.5-5:3-3.5:1.8-2.

2.

5. The method for preparing an environmentally friendly printing ink for cigarette box packaging paper according to claim 1, characterized in that: In the curing process, the coating amount of the printing coating is 1.8-2.2 g / m². 2 The pre-drying time is 1.5-3 seconds; the energy density of UV curing in the UV-thermal dual curing process is 200-280 mJ / cm³. 2 .

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