Ink based on modified cellulose nanocrystals and method for its preparation

Abstract

The application provides an ink based on modified cellulose nanocrystals and a preparation method thereof, and relates to the technical field of ink materials.The ink based on modified cellulose nanocrystals comprises the following materials in parts by weight: 35-45 parts of an epoxy-modified acrylic acid-chitosan graft copolymer, 8-12 parts of modified cellulose nanocrystals, 30-40 parts of deionized water, 10-14 parts of inorganic pigments, 1-2 parts of a wet dispersing agent and 0.2-0.4 parts of a defoaming agent.The ink based on modified cellulose nanocrystals improves the water resistance, wear resistance and stability of the ink through the epoxy-modified acrylic acid-chitosan graft copolymer and the modified cellulose nanocrystals, meets the demand of the high-end printing market for high-quality ink, expands the application range of the modified cellulose nanocrystals in the ink field, and has wide market prospects and application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ink materials, in particular to an ink based on modified cellulose nanocrystals and a preparation method thereof. BACKGROUND

[0002] With the continuous development of printing technology, ink as a key material in the printing process directly affects the quality and application range of printed matter. The existing water-based gravure ink with PVA as the base material meets the basic needs of printing to some extent, but performs poorly in water resistance. Generally, such ink is prone to delamination after being in contact with water for more than 48 hours, resulting in a significant decrease in the durability of printed matter. In addition, the gloss of PVA-based ink is relatively low, generally less than 60°, which is difficult to meet the demand of high-end printing market for high-gloss products.

[0003] Cellulose nanocrystals are a nanoscale material extracted from natural cellulose, which has high strength, high modulus, high specific surface area, and good biocompatibility. Due to its unique physical and chemical properties, cellulose nanocrystals have shown wide application prospects in composite materials, coatings, inks, and other fields.

[0004] However, although the ink based on modified cellulose nanocrystals has made some progress in performance, there are still some problems to be solved. The hydrophobicity of cellulose nanocrystals can be improved by surface modification, but the existing ink is still prone to delamination, discoloration, and other phenomena when in contact with water or in a high-humidity environment for a long time, which seriously affects the durability and aesthetics of printed matter. Although the addition of cellulose nanocrystals can improve the wear resistance of ink, in some high-demand application scenarios such as packaging printing and label printing, the wear resistance of existing ink is still insufficient to meet the long-term use requirements. The ink is prone to yellowing, discoloration, cracking, and other phenomena when exposed to ultraviolet light, high temperature, high humidity, and other harsh environments for a long time, affecting the shelf life and use effect of printed matter.

[0005] To solve the above problems, the present application proposes an ink based on modified cellulose nanocrystals and a preparation method thereof. The purpose of the present application is to optimize the surface modification process of cellulose nanocrystals, select appropriate resin systems and additives, and prepare an ink with excellent water resistance, wear resistance, and aging resistance. SUMMARY

[0006] The purpose of the present application is to provide an ink based on modified cellulose nanocrystals and a preparation method thereof, which improves the water resistance, wear resistance, and stability of the ink.

[0007] On the one hand, the present invention provides an ink based on modified cellulose nanocrystals, comprising the following materials in parts by weight: 35-45 parts of epoxy-modified acrylic acid-chitosan graft copolymer, 8-12 parts of modified cellulose nanocrystals, 30-40 parts of deionized water, 10-14 parts of inorganic pigments, 1-2 parts of wetting and dispersing agents, and 0.2-0.4 parts of defoaming agents.

[0008] Furthermore, the preparation method of the epoxy-modified acrylic acid-chitosan graft copolymer comprises: dispersing chitosan quaternary ammonium salt in deionized water, adding acetic acid to adjust the pH to 6-7, stirring until the chitosan quaternary ammonium salt solution is completely dissolved, adding epoxy acrylate and bis(2-mercaptoethyl) ether to the solution, passing nitrogen to remove oxygen for 20-30 minutes, heating to 65-70° C., slowly adding an aqueous ammonium persulfate solution dropwise, reacting at a constant temperature for 5-6 hours, cooling to room temperature, adjusting the pH to 7-8 with an aqueous NaOH solution, dialysis purification, and freeze-drying to obtain the epoxy-modified acrylic acid-chitosan graft copolymer.

[0009] Furthermore, the weight ratio of the chitosan quaternary ammonium salt, epoxy acrylate, bis(2-mercaptoethyl) ether and ammonium persulfate is (10-20): (60-80): (0.3-0.6): (2.4-3.2).

[0010] Furthermore, the preparation method of the modified cellulose nanocrystals includes: pre-treating bamboo pulp cellulose by soaking it in alkali solution, and treating it with a citric acid-sodium ferrate system; centrifuging and washing it, and then drying it to obtain carboxylated cellulose nanocrystals, which are then dispersed in deionized water, and glycidyl methacrylate and ammonium persulfate are added. After the reaction is completed, dialyzing and drying are performed to obtain the modified cellulose nanocrystals.

[0011] Furthermore, the weight ratio of the carboxylated cellulose nanocrystals, deionized water, glycidyl methacrylate and ammonium persulfate is 1:(20-30):(1-2):(0.005-0.009).

[0012] Furthermore, the ink further comprises 5-8 parts of ε-polylysine / nano zinc oxide composite capsules.

[0013] Furthermore, the preparation method of the ε-polylysine / nano-zinc oxide composite capsules includes: ultrasonically dispersing nano-zinc oxide in deionized water, adding ε-polylysine and stirring to obtain a suspension; mixing the suspension with a sodium alginate aqueous solution, adding Tween 80 for high-speed emulsification to form an emulsion, adding the emulsion to an acetic acid solution of chitosan, adding a calcium chloride aqueous solution and stirring to obtain the ε-polylysine / nano-zinc oxide composite capsules after centrifugation, washing, and freeze-drying.

[0014] Furthermore, the inorganic pigment includes one or more of carbon black, titanium dioxide, and iron oxide red; the wetting dispersant is BYK-163 dispersant; and the defoaming agent is BYK-088 defoaming agent.

[0015] On the other hand, the present invention also provides a method for preparing an ink based on modified cellulose nanocrystals, comprising the steps of:

[0016] (1) Mix deionized water, dispersant, and defoamer, and stir at 500-600 rpm for 10-15 minutes for pre-dispersion;

[0017] (2) Add epoxy-modified acrylic acid-chitosan copolymer, heat to 50-60°C, and stir for 2-3 hours until completely dissolved;

[0018] (3) Slowly add modified cellulose nanocrystals and ultrasonicate at 20-30 kHz for 20-30 min;

[0019] (4) Add the inorganic pigment to the colloid obtained in step (3), and simultaneously add the ε-polylysine / nano zinc oxide composite capsules, and stir at a low speed of 160-200 rpm for 2-3 hours to avoid breaking the capsules.

[0020] Furthermore, the inorganic filler is a pretreated inorganic filler, and the pretreatment step includes: placing the inorganic pigment in a supercritical CO2 reactor, maintaining it at 30-40°C and 7-8 MPa for 30-40 minutes, and obtaining the pretreated inorganic pigment after decompression.

[0021] The beneficial effects of the present invention are:

[0022] The present invention designs a new type of epoxy-modified acrylic acid-chitosan graft copolymer. Through a specific synthesis path and reaction conditions, the performance of the copolymer is optimized, so that it forms a good interface bond with modified cellulose nanocrystals. Among them, bis(2-mercaptoethyl) ether is used as a cross-linking agent to enhance the network structure of the copolymer, thereby improving the mechanical strength and aging resistance of the coating. The presence of the cross-linking agent allows more chemical bonds to be formed between the molecular chains of the copolymer, increasing the cohesion and stability of the coating; and chitosan has good biocompatibility and film-forming properties, but its mechanical properties and water solubility are limited. Through the grafting modification of epoxy acrylate, more cross-linking points and active groups are introduced, thereby enhancing the network structure and mechanical strength of the copolymer; at the same time, the quaternary ammonium salt treatment of chitosan improves its water solubility, so that the copolymer can be evenly dispersed in the ink and form a good coating;

[0023] The present invention introduces cellulose nanocrystals that have undergone specific chemical modifications, significantly improving their compatibility with epoxy-modified acrylic acid-chitosan copolymers through surface functionalization (such as carboxylation and grafting with glycidyl methacrylate). The modified cellulose nanocrystals are grafted with glycidyl methacrylate through carboxylation, achieving surface multifunctionality. The carboxyl group (-COOH) can undergo a ring-opening reaction with the epoxy group in the epoxy-modified acrylic acid-chitosan copolymer to form a chemical bond. Simultaneously, the grafted glycidyl methacrylate also provides additional reaction sites, enhancing the interaction between the nanocrystals and the copolymer. Furthermore, the compatibility of the surface-functionalized cellulose nanocrystals with the epoxy-modified acrylic acid-chitosan copolymer is significantly improved, allowing the nanocrystals to be more evenly dispersed in the copolymer matrix, thereby enhancing the adhesion, wear resistance, and water resistance of the coating.

[0024] This invention utilizes supercritical CO2 pretreatment technology to improve the dispersibility of inorganic pigments, reduce interfacial defects, and enhance coating uniformity. Supercritical CO2 possesses unique solubility and permeability, penetrating deep into pigment particles to remove surface-adsorbed impurities and moisture, resulting in purer and more evenly dispersed pigment particles. Furthermore, supercritical CO2 treatment reduces pigment particle agglomeration, improving the gloss and uniformity of the coating.

[0025] The present invention incorporates ε-polylysine / nano-zinc oxide composite capsules, which further enhance the ink's aging and wear resistance through antibacterial and cross-linking-enhancing properties. The ε-polylysine in the composite capsules has antibacterial properties, inhibiting the growth of microorganisms in the ink; while the nano-zinc oxide provides enhanced cross-linking, further improving the coating's aging and wear resistance. The addition of the composite capsules significantly improves the ink's overall performance through their dual antibacterial and cross-linking-enhancing properties. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is described clearly and completely below. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention. It should be noted that the raw materials can be obtained commercially.

[0027] Epoxy acrylate CAS No. 71281-65-7 was purchased from Jiangsu Boquan Biotechnology Co., Ltd.; chitosan quaternary ammonium salt model C768944 was purchased from Macklin.

[0028] Example 1

[0029] This embodiment provides an ink based on modified cellulose nanocrystals, comprising the following materials in parts by weight: 40 parts of epoxy-modified acrylic acid-chitosan graft copolymer, 10 parts of modified cellulose nanocrystals, 35 parts of deionized water, 12 parts of carbon black, 1.5 parts of BYK-163 wetting and dispersing agent, and 0.3 parts of BYK-088 defoaming agent.

[0030] The preparation method of the epoxy-modified acrylic acid-chitosan graft copolymer comprises: dispersing 1.5 g of chitosan quaternary ammonium salt in 100 mL of deionized water, adding acetic acid to adjust the pH to 6.5, stirring until completely dissolved to obtain a chitosan quaternary ammonium salt solution, adding 7 g of epoxy acrylate and 50 mg of bis(2-mercaptoethyl) ether thereto, passing nitrogen to remove oxygen for 25 minutes, heating to 68° C., slowly adding an aqueous ammonium persulfate solution (the aqueous ammonium persulfate solution is prepared by dissolving 280 mg of ammonium persulfate in 20 mL of deionized water), reacting at a constant temperature for 5.5 hours, cooling to room temperature, adjusting the pH to 7.5 with an aqueous NaOH solution, placing the product into a dialysis bag with a molecular weight cutoff of 10,000 Da, dialyzing it in deionized water for 24 hours, changing the water every 6 hours, and freeze-drying it at −80° C. for 12 hours to obtain the epoxy-modified acrylic acid-chitosan graft copolymer;

[0031] Among them, the preparation method of the modified cellulose nanocrystals includes: pre-treating bamboo pulp cellulose by soaking it in a sodium hydroxide aqueous solution with a mass concentration of 5% for 24 hours, the amount ratio of bamboo pulp cellulose and sodium hydroxide aqueous solution is 1g:20mL, filtering, rinsing with deionized water to neutrality, and then drying at 60°C to constant weight to obtain pre-treated bamboo pulp cellulose, treating it at 80°C for 6 hours in a citric acid-sodium ferrate system with a weight ratio of 1:0.5, and the amount ratio of the pre-treated bamboo pulp cellulose and the citric acid-sodium ferrate system is 1g:50mL; washing with deionized water after centrifugation, freeze-drying at -50°C for 24 hours to obtain carboxylated cellulose nanocrystals for use, and then dispersing it in deionized water, adding methacrylic acid glycidyl ester and ammonium persulfate, in this step, the weight ratio of carboxylated cellulose nanocrystals, deionized water, methacrylic acid glycidyl ester and ammonium persulfate is 1:25:1.5:0.007, and after the reaction is completed, the product is loaded into a 3500 molecular weight cut-off ... The Da dialysis bag was dialyzed in deionized water for 72 hours, with the water changed every 6 hours, and freeze-dried at -40°C for 20 hours to obtain the modified cellulose nanocrystals;

[0032] The method for preparing the ink based on modified cellulose nanocrystals comprises the following steps:

[0033] (1) Mix deionized water, dispersant, and defoamer, and stir at 550 rpm for 12 minutes for pre-dispersion;

[0034] (2) Add epoxy-modified acrylic acid-chitosan copolymer, heat to 55°C, and stir for 2.5 hours until completely dissolved;

[0035] (3) Slowly add modified cellulose nanocrystals and ultrasonicate at 25 kHz for 25 min;

[0036] (4) Add the inorganic pigment carbon black to the colloid obtained in step (3), and stir at a low speed of 180 rpm for 2.5 hours to obtain the product.

[0037] Example 2

[0038] This embodiment provides an ink based on modified cellulose nanocrystals, comprising the following materials in parts by weight: 35 parts of epoxy-modified acrylic acid-chitosan graft copolymer, 8 parts of modified cellulose nanocrystals, 30 parts of deionized water, 10 parts of carbon black, 1 part of BYK-163 wetting and dispersing agent, and 0.2 parts of BYK-088 defoaming agent.

[0039] The preparation method of the epoxy-modified acrylic acid-chitosan graft copolymer comprises: dispersing 1 g of chitosan quaternary ammonium salt in 100 mL of deionized water, adding acetic acid to adjust the pH to 6, stirring until completely dissolved to obtain a chitosan quaternary ammonium salt solution, adding 6 g of epoxy acrylate and 30 mg of bis(2-mercaptoethyl) ether to the solution, passing nitrogen to remove oxygen for 20 minutes, heating to 65° C., slowly adding dropwise an ammonium persulfate aqueous solution (the ammonium persulfate aqueous solution is prepared by dissolving 240 mg of ammonium persulfate in 20 mL of deionized water), reacting at a constant temperature for 5 hours, cooling to room temperature, adjusting the pH to 7 with a NaOH aqueous solution, placing the product into a dialysis bag with a molecular weight cutoff of 10,000 Da, dialyzing it in deionized water for 24 hours, changing the water every 6 hours, and freeze-drying it at -80° C. for 12 hours to obtain the epoxy-modified acrylic acid-chitosan graft copolymer;

[0040] The preparation method of the modified cellulose nanocrystals includes: pre-treating bamboo pulp cellulose by soaking it in a sodium hydroxide aqueous solution with a mass concentration of 5% for 24 hours, the amount ratio of bamboo pulp cellulose to sodium hydroxide aqueous solution is 1g:20mL, filtering, rinsing with deionized water to neutrality, and then drying at 60°C to constant weight to obtain pre-treated bamboo pulp cellulose, treating it at 80°C for 6 hours in a citric acid-sodium ferrate system with a weight ratio of 1:0.5, and the amount ratio of the pre-treated bamboo pulp cellulose to the citric acid-sodium ferrate system is 1g:50mL; washing with deionized water after centrifugation, freeze-drying at -50°C for 24 hours to obtain carboxylated cellulose nanocrystals for use, and then dispersing it in deionized water, adding methacrylic acid glycidyl ester and ammonium persulfate, in this step, the weight ratio of carboxylated cellulose nanocrystals, deionized water, methacrylic acid glycidyl ester and ammonium persulfate is 1:20:1:0.005, and after the reaction is completed, the product is loaded into a 3500 molecular weight cut-off cellulose nanocrystal. The Da dialysis bag was dialyzed in deionized water for 72 hours, with the water changed every 6 hours, and freeze-dried at -40°C for 20 hours to obtain the modified cellulose nanocrystals;

[0041] The method for preparing the ink based on modified cellulose nanocrystals comprises the following steps:

[0042] (1) Mix deionized water, dispersant, and defoamer, and stir at 500 rpm for 10 minutes for pre-dispersion;

[0043] (2) Add epoxy-modified acrylic acid-chitosan copolymer, heat to 50°C, and stir for 2 h until completely dissolved;

[0044] (3) Slowly add modified cellulose nanocrystals and ultrasonicate at 20 kHz for 20 min;

[0045] (4) placing the inorganic pigment carbon black in a supercritical CO2 reactor, maintaining it at 35°C and 7.5 MPa for 35 minutes, and releasing the pressure to obtain the pretreated inorganic pigment;

[0046] (5) Add the pretreated inorganic pigment to the colloid obtained in step (3), and stir at a low speed of 160 rpm for 2 hours to obtain the colloid.

[0047] Example 3

[0048] This embodiment provides an ink based on modified cellulose nanocrystals, comprising the following materials in parts by weight: 45 parts of epoxy-modified acrylic acid-chitosan graft copolymer, 12 parts of modified cellulose nanocrystals, 40 parts of deionized water, 14 parts of carbon black, 2 parts of BYK-163 wetting and dispersing agent, and 0.4 parts of BYK-088 defoaming agent;

[0049] The preparation method of the epoxy-modified acrylic acid-chitosan graft copolymer comprises: dispersing 2 g of chitosan quaternary ammonium salt in 100 mL of deionized water, adding acetic acid to adjust the pH to 7, stirring until completely dissolved to obtain a chitosan quaternary ammonium salt solution, adding 8 g of epoxy acrylate and 60 mg of bis(2-mercaptoethyl) ether to the solution, passing nitrogen to remove oxygen for 30 minutes, heating to 70° C., slowly adding dropwise an ammonium persulfate aqueous solution (the ammonium persulfate aqueous solution is prepared by dissolving 320 mg of ammonium persulfate in 20 mL of deionized water), reacting at a constant temperature for 6 hours, cooling to room temperature, adjusting the pH to 8 with a NaOH aqueous solution, placing the product into a dialysis bag with a molecular weight cutoff of 10,000 Da, and dialyzing it in deionized water for 24 hours, changing the water every 6 hours, and freeze-drying it at -80° C. for 12 hours to obtain the epoxy-modified acrylic acid-chitosan graft copolymer;

[0050] Among them, the preparation method of the modified cellulose nanocrystals includes: pre-treating bamboo pulp cellulose by soaking it in a sodium hydroxide aqueous solution with a mass concentration of 5% for 24 hours, the amount ratio of bamboo pulp cellulose and sodium hydroxide aqueous solution is 1g:20mL, filtering, rinsing with deionized water to neutrality, and then drying at 60°C to constant weight to obtain pre-treated bamboo pulp cellulose, treating it at 80°C for 6 hours in a citric acid-sodium ferrate system with a weight ratio of 1:0.5, and the amount ratio of the pre-treated bamboo pulp cellulose and the citric acid-sodium ferrate system is 1g:50mL; washing with deionized water after centrifugation, freeze-drying at -50°C for 24 hours to obtain carboxylated cellulose nanocrystals for use, and then dispersing it in deionized water, adding methacrylic acid glycidyl ester and ammonium persulfate, in this step, the weight ratio of carboxylated cellulose nanocrystals, deionized water, methacrylic acid glycidyl ester and ammonium persulfate is 1:30:2:0.009, and after the reaction is completed, the product is loaded into a 3500 molecular weight cut-off cellulose nanocrystal. The Da dialysis bag was dialyzed in deionized water for 72 hours, with the water changed every 6 hours, and freeze-dried at -40°C for 20 hours to obtain the modified cellulose nanocrystals;

[0051] The method for preparing the ink based on modified cellulose nanocrystals comprises the following steps:

[0052] (1) Mix deionized water, dispersant, and defoamer, and stir at 600 rpm for 15 minutes for pre-dispersion;

[0053] (2) Add epoxy-modified acrylic acid-chitosan copolymer, heat to 60°C, and stir for 3 hours until completely dissolved;

[0054] (3) Slowly add modified cellulose nanocrystals and ultrasonicate at 30 kHz for 30 min;

[0055] (4) placing the inorganic pigment carbon black in a supercritical CO2 reactor, maintaining it at 35°C and 7.5 MPa for 35 minutes, and releasing the pressure to obtain the pretreated inorganic pigment;

[0056] (5) Add the pretreated inorganic pigment to the colloid obtained in step (3), and stir at a low speed of 200 rpm for 3 hours to obtain the colloid.

[0057] Example 4

[0058] This embodiment provides an ink based on modified cellulose nanocrystals, comprising the following materials in parts by weight: 35 parts of epoxy-modified acrylic acid-chitosan graft copolymer, 12 parts of modified cellulose nanocrystals, 30 parts of deionized water, 14 parts of carbon black, 1 part of BYK-163 wetting and dispersing agent, and 0.4 parts of BYK-088 defoaming agent;

[0059] The preparation method of the epoxy-modified acrylic acid-chitosan graft copolymer comprises: dispersing 1 g of chitosan quaternary ammonium salt in 100 mL of deionized water, adding acetic acid to adjust the pH to 6, stirring until completely dissolved to obtain a chitosan quaternary ammonium salt solution, adding 8 g of epoxy acrylate and 30 mg of bis(2-mercaptoethyl) ether to the solution, passing nitrogen to remove oxygen for 30 minutes, heating to 65° C., slowly adding dropwise an ammonium persulfate aqueous solution (the ammonium persulfate aqueous solution is prepared by dissolving 320 mg of ammonium persulfate in 20 mL of deionized water), reacting at a constant temperature for 6 hours, cooling to room temperature, adjusting the pH to 7 with a NaOH aqueous solution, placing the product into a dialysis bag with a molecular weight cutoff of 10,000 Da, and dialyzing it in deionized water for 24 hours, changing the water every 6 hours, and freeze-drying it at -80° C. for 12 hours to obtain the epoxy-modified acrylic acid-chitosan graft copolymer;

[0060] The preparation method of the modified cellulose nanocrystal comprises the following steps: pretreating bamboo pulp cellulose by immersing the bamboo pulp cellulose in a 5% sodium hydroxide aqueous solution for 24 hours, wherein the dosage ratio of the bamboo pulp cellulose to the sodium hydroxide aqueous solution is 1 g:20 mL; filtering and washing the bamboo pulp cellulose with deionized water until neutral; drying the bamboo pulp cellulose at 60°C until constant weight to obtain pretreated bamboo pulp cellulose; treating the pretreated bamboo pulp cellulose in a citric acid-sodium ferrite system with a weight ratio of 1:0.5 at 80°C for 6 hours, wherein the dosage ratio of the pretreated bamboo pulp cellulose to the citric acid-sodium ferrite system is 1 g:50 mL; centrifuging and washing the pretreated bamboo pulp cellulose with deionized water; and freeze-drying the pretreated bamboo pulp cellulose at-50°C for 24 hours to obtain carboxylated cellulose nanocrystals, which are then dispersed in deionized water, glycidyl methacrylate and ammonium persulfate are added, wherein the weight ratio of the carboxylated cellulose nanocrystals, the deionized water, the glycidyl methacrylate and the ammonium persulfate is 1:30:2:0.005; after the reaction is completed, the product is placed in a dialysis bag with a molecular weight cut-off of 3500 Da and dialyzed in deionized water for 72 hours, the water is changed every 6 hours; and the product is freeze-dried at-40°C for 20 hours to obtain the modified cellulose nanocrystals.

[0061] The preparation method of the ink based on the modified cellulose nanocrystals comprises the following steps:

[0062] (1) mixing deionized water, a dispersing agent and a defoaming agent, and pre-dispersing the mixture at 500 rpm for 15 minutes;

[0063] (2) adding an epoxy-modified acrylic-chitosan copolymer, and stirring the mixture at 50°C for 3 hours until the epoxy-modified acrylic-chitosan copolymer is completely dissolved;

[0064] (3) slowly adding the modified cellulose nanocrystals, and ultrasonically treating the mixture at 20 kHz for 30 minutes;

[0065] (4) placing inorganic pigments carbon black in a supercritical CO2 reaction kettle, and keeping the inorganic pigments carbon black in the supercritical CO2 reaction kettle at 35°C and 7.5 MPa for 35 minutes, and obtaining pretreated inorganic pigments after pressure relief;

[0066] (5) adding the pretreated inorganic pigments into the colloid obtained in step (3), and stirring the mixture at a low speed of 160 rpm for 3 hours to obtain the ink.

[0067] Comparative Example 1

[0068] Different from Example 1, the raw materials of the ink in Comparative Example 1 further comprise ε-polylysine / nano-zinc oxide composite capsules 6 parts.

[0069] The preparation method of the epsilon-polylysine / nano zinc oxide composite capsule comprises: 1g of nano zinc oxide is added into 50mL of deionized water, dispersed by ultrasonic treatment under the condition of a power of 300W for 30min, 1g of epsilon-polylysine is added, and stirring mixing is carried out under the condition of 500rpm for 1h to obtain a suspension, 2g of sodium alginate is dissolved in 100mL of deionized water, and stirring is carried out at 60℃ until complete dissolution to obtain a sodium alginate aqueous solution; 1g of chitosan is dissolved in 100mL of acetic acid aqueous solution with a volume concentration of 1%, and stirring is carried out to obtain a chitosan solution; the suspension and the sodium alginate aqueous solution are mixed, 0.5g of Tween 80 is added, high-speed emulsification is carried out under the condition of 10000rpm for 10min to form an emulsion, the emulsion is added dropwise into the chitosan solution under the condition of stirring at a speed of 500rpm, 0.3g of calcium chloride aqueous solution with a mass concentration of 5% is added, stirring is carried out under the condition of 300rpm for 30min, after centrifugation, washing is carried out with deionized water for 3 times, and after freeze-drying under the condition of-50℃ for 24h, the epsilon-polylysine / nano zinc oxide composite capsule is obtained.

[0070] The preparation method of the ink based on the modified cellulose nanocrystal comprises the following steps:

[0071] (1) Deionized water, dispersant and defoaming agent are mixed, and pre-dispersion is carried out under the condition of stirring at 550rpm for 12min;

[0072] (2) Epoxy-modified acrylic acid-chitosan copolymer is added, the temperature is increased to 55℃, and stirring is carried out for 2.5h until complete dissolution;

[0073] (3) Modified cellulose nanocrystal is slowly added, and ultrasonic treatment is carried out under the condition of 25kHz for 25min;

[0074] (4) Inorganic pigment is added into the colloid obtained in step (3), and epsilon-polylysine / nano zinc oxide composite capsule is synchronously added, and low-speed stirring is carried out under the condition of 180rpm for 2.5h, and then the ink based on the modified cellulose nanocrystal is obtained.

[0075] Comparative Example 2

[0076] Different from Example 1, in Comparative Example 2, the inorganic pigment is not pretreated.

[0077] Comparative Example 3

[0078] Different from Example 1, in Comparative Example 3, cellulose nanocrystal is prepared according to the prior art CN116589881B, and the specific steps comprise: 80mL of sulfuric acid solution with a concentration of 64wt% is taken, 5g of defatted cotton is added, stirring is carried out at 42℃ for 2.5h, 800mL of deionized water is added, stirring is carried out until uniform, centrifugation, washing, dialysis and drying are carried out, and then cellulose nanocrystal is obtained.

[0079] This comparative example provides an ink based on modified cellulose nanocrystals, comprising the following materials in parts by weight: 40 parts of epoxy-modified acrylic acid-chitosan graft copolymer, 10 parts of modified cellulose nanocrystals, 35 parts of deionized water, 12 parts of carbon black, 1.5 parts of BYK-163 wetting and dispersing agent, and 0.3 parts of BYK-088 defoaming agent;

[0080] The preparation method of the epoxy-modified acrylic acid-chitosan graft copolymer comprises: dispersing 1.5 g of chitosan quaternary ammonium salt in 100 mL of deionized water, adding acetic acid to adjust the pH to 6.5, stirring until completely dissolved to obtain a chitosan quaternary ammonium salt solution, adding 7 g of epoxy acrylate and 50 mg of bis(2-mercaptoethyl) ether thereto, passing nitrogen to remove oxygen for 25 minutes, heating to 68° C., slowly adding an aqueous ammonium persulfate solution (the aqueous ammonium persulfate solution is prepared by dissolving 280 mg of ammonium persulfate in 20 mL of deionized water), reacting at a constant temperature for 5.5 hours, cooling to room temperature, adjusting the pH to 7.5 with an aqueous NaOH solution, placing the product into a dialysis bag with a molecular weight cutoff of 10,000 Da, dialyzing it in deionized water for 24 hours, changing the water every 6 hours, and freeze-drying it at −80° C. for 12 hours to obtain the epoxy-modified acrylic acid-chitosan graft copolymer;

[0081] The obtained cellulose nanocrystals are added to glycidyl methacrylate and ammonium persulfate. In this step, the weight ratio of cellulose nanocrystals, deionized water, glycidyl methacrylate and ammonium persulfate is 1:25:1.5:0.007. After the reaction is completed, the product is placed in a dialysis bag with a molecular weight cutoff of 3500 Da and dialyzed in deionized water for 72 hours, with the water changed every 6 hours. The modified cellulose nanocrystals are obtained after freeze-drying at -40°C for 20 hours.

[0082] The method for preparing the ink based on modified cellulose nanocrystals comprises the following steps:

[0083] (1) Mix deionized water, dispersant, and defoamer, and stir at 550 rpm for 12 minutes for pre-dispersion;

[0084] (2) Add epoxy-modified acrylic acid-chitosan copolymer, heat to 55°C, and stir for 2.5 hours until completely dissolved;

[0085] (3) Slowly add modified cellulose nanocrystals and ultrasonicate at 25 kHz for 25 min;

[0086] (4) Add the inorganic pigment carbon black to the colloid obtained in step (3), and stir at a low speed of 180 rpm for 2.5 hours to obtain the product.

[0087] Comparative Example 4

[0088] Different from Example 1, the modification method of cellulose nanocrystals in Comparative Example 4 is different. Referring to the prior art CN116589881B, the specific steps include: taking 0.55 g of dodecafluoroheptyl methacrylate and 20 mL of N,N-dimethylformamide, stirring evenly to obtain a dodecafluoroheptyl methacrylate solution; taking 2 g of cellulose nanocrystals and 150 mL of deionized water, ultrasonically dispersing for 15 minutes, adding ammonia water to adjust the pH value to 9.5, adding 0.2 g of tannic acid, stirring for 23 hours, adding dodecafluoroheptyl methacrylate solution, reacting at 57°C for 9 hours, centrifuging, and washing to obtain modified cellulose nanocrystals.

[0089] Comparative Example 5

[0090] Different from Example 1, the modified cellulose nanocrystals in Comparative Example 5 are replaced by unmodified cellulose nanocrystals.

[0091] Comparative Example 6

[0092] Different from Example 1, the modified cellulose nanocrystals in Comparative Example 6 are replaced by ammonium thiocyanate.

[0093] Comparative Example 7

[0094] Different from Example 1, in Comparative Example 7, no bis(2-mercaptoethyl) ether crosslinking agent was added during the synthesis of the epoxy-modified acrylic acid-chitosan graft copolymer, and other conditions remained unchanged.

[0095] Comparative Example 8

[0096] Different from Example 1, in Comparative Example 8, the amount of epoxy-modified acrylic acid-chitosan copolymer was reduced from 40 parts to 20 parts, while the proportions of other ingredients remained unchanged.

[0097] Comparative Example 9

[0098] Different from Example 1, in Comparative Example 9, in step (4), an inorganic pigment is added to the colloid obtained in step (3), and the mixture is stirred at 300 rpm.

[0099] Experimental Example 1: The performance of the ink based on modified cellulose nanocrystals prepared in the above Examples 1-4 and Comparative Examples 1-9 was investigated.

[0100] 1. Water resistance: Apply the ink to a plastic film, cut it into 10×10 cm specimens after curing, immerse the specimen in deionized water (25±1℃) for 24 hours, remove it, dry it at room temperature for 1 hour, and spray it continuously for 48 hours at a water pressure of 0.1 MPa. Observe whether the coating has blistering, peeling, or discoloration.

[0101] 2. Adhesion test: The samples after water resistance test are graded according to the ASTM D1647 tape method, with grade 0 being no peeling and grade 5 being complete peeling.

[0102] 3. Abrasion resistance: Apply the ink to a plastic film, cure it, and cut it into circular specimens with a diameter of 100 mm. Taber abrasion testing was performed according to ASTM D4060 using a CS-17 abrasive wheel, a load of 500 g / wheel, a total load of 1000 g, a rotation speed of 60 rpm, and 1000 cycles. The specimens were weighed before and after the test, and the mass loss per unit area was calculated.

[0103] 4. Aging resistance: 85℃, relative humidity 85%, after aging for 1000h, use spectrophotometer (X-Rite Ci64) to measure the Lab value of the sample before aging, re-measure the same position after aging, and calculate the color difference ΔE. .

[0104] The performance test results are shown in Table 1 below:

[0105] Table 1: Performance Test

[0106] Coating status after water resistance test Adhesion (grade) Mass loss per unit area (mg / cm²) Color difference ΔE Example 1 No blistering, no peeling, no discoloration Level 0 0.12 1.32 Example 2 No blistering, no peeling, no discoloration Level 0 0.18 1.37 Example 3 No blistering, no peeling, no discoloration Level 0 0.15 1.41 Example 4 No blistering, no peeling, no discoloration Level 1 0.21 1.45 Comparative Example 1 No blistering, no peeling, no discoloration Level 0 0.09 1.28 Comparative Example 2 Slight blistering, partial peeling, slight discoloration Level 3 0.45 2.65 Comparative Example 3 No peeling but partial discoloration Level 2 0.32 1.85 Comparative Example 4 No blistering, slight peeling Level 2 0.28 1.20 Comparative Example 5 Blistering and noticeable peeling Level 3 0.38 2.11 Comparative Example 6 Severe peeling and discoloration Level 5 0.80 3.55 Comparative Example 7 Partial peeling and blistering Level 3 0.42 2.46 Comparative Example 8 Large area peeling Level 4 0.55 2.90 Comparative Example 9 Uneven, localized peeling Level 3 0.35 2.05

[0107] Combined with the above table, the addition of ε-polylysine / nano-zinc oxide composite capsules in Comparative Example 1 showed lower color difference (ΔE=1.28) and mass loss (0.09 mg / cm²), indicating that the composite capsules can further improve aging resistance and wear resistance through antibacterial and enhanced cross-linking. In Comparative Example 2, the adhesion dropped to level 3 and the mass loss increased, indicating that supercritical CO2 pretreatment can improve pigment dispersion, reduce interfacial defects, and improve coating uniformity. In Comparative Example 3, the sulfate ester groups (-OSO3 -Compared to the carboxylated cellulose nanocrystals (-COOH) in Example 1, the polarity match with the epoxy-modified acrylic acid-chitosan copolymer is poor, resulting in weakened interfacial bonding and decreased adhesion. Furthermore, sulfuric acid hydrolysis may produce shorter or more irregular cellulose nanocrystals, which reduces their uniformity of dispersion in the colloid and causes local stress concentration in the coating, leading to discoloration and deterioration of wear resistance. Furthermore, the sulfate group is easily hydrolyzed in a hot and humid environment, releasing acidic substances that accelerate coating degradation, resulting in a significantly higher color difference ΔE than in the Example. In Comparative Example 4, the fluorine chain of dodecafluoroheptyl methacrylate imparts strong hydrophobicity to the nanocrystals, but has poor compatibility with the hydrophilic epoxy-modified acrylic acid-chitosan copolymer, resulting in weak interfacial bonding and slight flaking. Furthermore, without carboxylation treatment, the nanocrystal surface lacks active reaction sites with the copolymer, relying solely on physical adsorption, resulting in lower wear resistance than in the Example. Furthermore, the chemical inertness of fluoride minimizes the color difference ΔE, but due to insufficient adhesion, long-term use may accelerate aging due to interfacial peeling. The performance of Comparative Examples 5 and 6 decreased significantly, indicating that the modified cellulose nanocrystals improved their compatibility with the epoxy-modified acrylic acid-chitosan copolymer through surface functionalization, thereby enhancing adhesion, wear resistance and water resistance. The adhesion and wear resistance of Comparative Example 7 deteriorated significantly, indicating that the crosslinking agent improved the mechanical strength and aging resistance of the coating by strengthening the copolymer network structure. Comparative Example 8 caused a significant decrease in adhesion and wear resistance, indicating that the copolymer, as the main film-forming substance, needs to maintain a sufficient proportion to form a dense coating. Comparative Example 9 caused uneven coating and local peeling, indicating that low-speed stirring helps maintain colloidal stability and avoid structural damage.

[0108] Test Example 2: Referring to ASTM E2149, the inks of Example 1 and Comparative Example 1 were each printed using a laboratory gravure printing press (IGT F1) at a pressure of 0.2 MPa and a speed of 50 m / min, ensuring sufficient contact between the ink and the PET film. The inks were then coated onto a PET film (0.1 mm thick) and, after curing, cut into 5 × 5 cm specimens.

[0109] Preparation of bacterial solution: Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 6538P) were diluted to 1×10 5 CFU / mL, 0.1 mL of bacterial solution was evenly spread on the sample surface, covered with a sterile film, and incubated at 37°C for 24 hours. The bacteria were eluted and diluted, and the plate count was used to calculate the inhibition rate. The inhibition rate results are shown in Table 2 below.

[0110] Table 2: Inhibition rate

[0111] sample Escherichia coli inhibition rate (%) Staphylococcus aureus inhibition rate (%) Example 1 99.25 98.72 Comparative Example 1 99.95 99.91

[0112] In combination with the above data, the antibacterial rate of the comparative example 1 is significantly improved (more than 99.9%) due to the addition of the epsilon-polylysine / nano zinc oxide composite capsule, and the nano zinc oxide enhances the long-acting antibacterial property through photocatalysis, thereby meeting the antibacterial requirement of food packaging.

[0113] Finally, it should be noted that the above examples are only used to illustrate the technical solutions described in the present application and not to limit the present application; those skilled in the art should understand that the present application can still be modified or replaced equivalently; and all technical solutions and improvements that do not deviate from the spirit and scope of the present application should be covered in the scope of the claims of the present application.

Claims

1. An ink based on modified cellulose nanocrystals, characterized in that: The invention comprises the following materials in parts by weight: 35-45 parts of epoxy-modified acrylic acid-chitosan graft copolymer, 8-12 parts of modified cellulose nanocrystals, 30-40 parts of deionized water, 10-14 parts of inorganic pigment, 1-2 parts of wetting and dispersing agent and 0.2-0.4 parts of defoaming agent; The preparation method of the epoxy-modified acrylic acid-chitosan graft copolymer comprises: dispersing chitosan quaternary ammonium salt in deionized water, adding acetic acid to adjust the pH to 6-7, stirring until the chitosan quaternary ammonium salt solution is completely dissolved, adding epoxy acrylate and bis(2-mercaptoethyl) ether to the chitosan quaternary ammonium salt solution, passing nitrogen to remove oxygen for 20-30 minutes, heating to 65-70° C., slowly adding an ammonium persulfate aqueous solution dropwise, reacting at a constant temperature for 5-6 hours, cooling to room temperature, adjusting the pH to 7-8 with a NaOH aqueous solution, dialysis purification, and freeze-drying to obtain the epoxy-modified acrylic acid-chitosan graft copolymer; The preparation method of the modified cellulose nanocrystals comprises: pre-treating bamboo pulp cellulose by soaking it in alkali solution, and then treating it with a citric acid-sodium ferrate system; centrifuging and washing it, and then drying it to obtain carboxylated cellulose nanocrystals; then dispersing it in deionized water, adding glycidyl methacrylate and ammonium persulfate, and dialyzing and drying it after the reaction is completed to obtain the modified cellulose nanocrystals.

2. The ink based on modified cellulose nanocrystals according to claim 1, characterized in that: The weight ratio of the chitosan quaternary ammonium salt, epoxy acrylate, bis(2-mercaptoethyl) ether and ammonium persulfate is (10-20): (60-80): (0.3-0.6): (2.4-3.2).

3. The ink based on modified cellulose nanocrystals according to claim 1, characterized in that: The weight ratio of the carboxylated cellulose nanocrystals, deionized water, glycidyl methacrylate and ammonium persulfate is 1:(20-30):(1-2):(0.005-0.009).

4. The ink based on modified cellulose nanocrystals according to claim 1, characterized in that: The ink further comprises 5-8 parts of epsilon-polylysine / nano zinc oxide composite capsules.

5. The ink based on modified cellulose nanocrystals according to claim 4, characterized in that: The preparation method of the ε-polylysine / nano-zinc oxide composite capsules comprises: ultrasonically dispersing nano-zinc oxide in deionized water, adding ε-polylysine and stirring to obtain a suspension; mixing the suspension with a sodium alginate aqueous solution, adding Tween 80 for high-speed emulsification to form an emulsion, adding the emulsion to an acetic acid solution of chitosan, adding a calcium chloride aqueous solution and stirring to obtain the ε-polylysine / nano-zinc oxide composite capsules after centrifugation, washing, and freeze-drying.

6. The ink based on modified cellulose nanocrystals according to claim 1, characterized in that: The inorganic pigment includes one or more of carbon black, titanium dioxide, and iron oxide red; the wetting dispersant is BYK-163 dispersant; and the defoaming agent is BYK-088 defoaming agent.

7. A method for preparing an ink based on modified cellulose nanocrystals according to any one of claims 1 to 6, characterized in that the steps include: (1) Mix deionized water, dispersant, and defoamer, and stir at 500-600 rpm for 10-15 minutes for pre-dispersion; (2) Add epoxy-modified acrylic acid-chitosan copolymer, heat to 50-60°C, and stir for 2-3 hours until completely dissolved; (3) Slowly add modified cellulose nanocrystals and ultrasonicate at 20-30 kHz for 20-30 min; (4) After the inorganic pigment is depressurized, it is added to the colloid obtained in step (3), and ε-polylysine / nano zinc oxide composite capsules are added simultaneously. The mixture is stirred at a low speed of 160-200 rpm for 2-3 hours to obtain the product.

8. The method for preparing ink based on modified cellulose nanocrystals according to claim 7, characterized in that: The inorganic pigment is a pretreated inorganic pigment, and the pretreatment step includes: placing the inorganic pigment in a supercritical CO2 reactor, maintaining it at 30-40°C and 7-8 MPa for 30-40 minutes, and releasing the pressure to obtain the pretreated inorganic pigment.