Composite ink, method for preparing the same and use thereof

Abstract

The application provides a composite ink and a preparation method and application thereof. The composite ink comprises the following components in parts by weight: 20-35 parts of lignin, 10-15 parts of cellulose nanofibril, 40-60 parts of solvent, 10-30 parts of colorant, 0.1-1 parts of dispersing agent, 0.05-0.5 parts of defoaming agent and 0.05-0.5 parts of wetting agent. The composite ink takes lignin, a by-product of paper industry, as the main raw material, and the hydrogen bond network formed by lignin and nanocellulose endows the coating with excellent mechanical strength, flexibility and rapid film-forming performance. The composite ink is particularly suitable for printing of honeycomb paperboard, does not permeate ink and does not need to be coated with a petroleum-based primer to improve the printing suitability. In the recycling and pulping process of the honeycomb paperboard, no petroleum-based adhesive is generated, the strength of the regenerated paper pulp is well preserved, and efficient recycling of the honeycomb paperboard is realized.

Description

Technical Field

[0001] This application belongs to the field of ink technology, and in particular relates to a composite ink, its preparation method and application. Background Technology

[0002] With the deepening of dual-carbon goals and the full implementation of plastic restriction policies, the packaging and printing industry is accelerating its transformation towards green, low-carbon, and environmentally friendly practices. Paper packaging, due to its recyclability and biodegradability, is gradually becoming the mainstream development direction in the packaging field. However, traditional solvent-based inks contain 20%-40% petroleum-based synthetic resins and a large amount of volatile organic compounds (VOCs), which not only cause organic waste gas pollution during the printing process but also have a fundamental contradiction with the paper packaging recycling system: when the printed paper packaging is recycled and pulped, the petroleum-based resins cannot be completely separated through the pulping process and will adhere to the surface of the paper fibers, resulting in a 15%-20% decrease in the strength of the recycled paper. In severe cases, it may even lead to the entire batch of waste paper being unrecyclable, affecting the economic benefits of the recycling industry chain.

[0003] Therefore, developing fully bio-based, environmentally friendly green inks compatible with paper recycling systems has become a common industry need. To address these issues, extensive research on bio-based inks has been conducted both domestically and internationally. Among these, plant-based ink technologies, represented by soybean oil and flaxseed oil, are already quite mature and are gradually achieving mass production and initial commercial applications. However, these inks have not completely eliminated their dependence on petroleum-based raw materials. To ensure moldability and printability, a certain proportion of petroleum-based resins still needs to be added to the formulation as a binder, resulting in a limited overall bio-based content and making it difficult to achieve the goal of being fully bio-based. Furthermore, certain recycling compatibility issues still exist in the paper packaging recycling pulping process.

[0004] As the largest byproduct of the papermaking industry, lignin has a global annual output of over 50 million tons, but less than 5% is utilized for high-value purposes. The majority of the rest is either incinerated or landfilled. Currently, it is an ideal bio-based film-forming material. However, existing lignin-based inks have three inherent defects: (1) The branched structure of lignin molecules makes them rigid. When used as film-forming resins, they are generally brittle and lack flexibility, making it difficult to meet the requirements of printed materials for film strength and durability. Therefore, petroleum resins are usually added to improve film-forming performance; (2) The adhesion between lignin and uncoated paper is poor. Especially after printing, when subjected to friction and external force, the ink layer is prone to wear or peeling, affecting the quality of printed materials; (3) The drying and curing time of lignin-based ink systems is long, which limits their adaptability to high-speed printing equipment and makes it difficult to meet the requirements of continuous and high-efficiency operation in large-scale packaging production.

[0005] The aforementioned problems exhibit even more pronounced adaptability issues in the context of honeycomb paperboard printing: the high surface roughness and porosity of honeycomb paperboard make it prone to defects such as ink bleed-through, uneven coloring, and white showing when printed with ordinary inks. Existing solutions, in order to ensure print quality, involve applying an additional petroleum-based coating to seal the paper pores. This not only adds a printing step and increases printing costs but also introduces new petroleum-based components, contradicting the trend towards green and environmentally friendly development. Furthermore, recycling remains a challenge after disposal. In addition, its printing speed is limited, making it difficult to meet the demands of high-speed printing production.

[0006] Therefore, developing a fully bio-based composite ink that is completely free of petroleum-based resins, has excellent film-forming properties, and can simultaneously achieve paper reinforcement and printing, and is compatible with high-speed flexible printing on honeycomb paperboard, is a technical problem that the packaging and printing industry urgently needs to solve. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this application is to provide a composite ink, its preparation method, and its application. The composite ink has high bio-based carbon content, low VOC content, good flexibility, high adhesion to the substrate, and fast drying speed. It is suitable for printing on honeycomb paperboard, improves the strength of the base paper, does not bleed ink, is compatible with high-speed flexographic printing production lines, and has low raw material costs. It achieves a balance between film-forming performance, environmental friendliness, economy, and printability.

[0008] To achieve this objective, the following technical solution is adopted in this application: In a first aspect, this application provides a composite ink, which comprises the following components by weight: 20-35 parts lignin; 10-15 parts of cellulose nanofibers; Solvent 40-60 parts; Colorant 10-30 parts; Dispersant 0.1-1 part; Defoamer 0.05-0.5 parts; 0.05-0.5 parts of wetting agent.

[0009] This application uses lignin and cellulose nanofibers as the core film-forming materials, which form a network structure through intermolecular hydrogen bonding. On the one hand, the introduction of cellulose nanofibers improves the mechanical strength of the composite ink, thereby enhancing its adhesion to the substrate; on the other hand, the intermolecular hydrogen bond network formed by lignin and cellulose nanofibers exhibits thixotropy, resulting in good flowability of the composite ink under external force, which is beneficial for coating processing; after standing, the viscosity of the system increases, endowing the composite ink with excellent rheological properties.

[0010] The composite ink of this application completely abandons petroleum-based raw materials, using bio-based materials as the core component. This results in a high bio-based carbon content and extremely low VOC content, enabling the printed paperboard to achieve 100% recycled pulping, with no adhesive residue, achieving a completely green and pollution-free process. The composite ink possesses excellent mechanical strength and good flexibility, dries quickly, and achieves excellent film-forming performance without the need for any film-forming aids, making it suitable for high-speed industrial flexible printing production lines.

[0011] The composite ink of this application is particularly suitable for printing on honeycomb paperboard. It breaks through the traditional technical route of separating paper reinforcement and printability, and innovatively uses an ink system composed of lignin and nanocellulose materials as both a printing ink binder and a reinforcing agent for the base paper of honeycomb paperboard. Through the hydrogen bond network formed between lignin and nanocellulose, an interface-free transition layer is formed between the coating and the paper, which significantly improves the adhesion between the coating and the base paper. This achieves an integrated design of "substrate-ink", fundamentally solving the problem of ink bleeding of bio-based ink on high-porosity honeycomb paperboard. It completely eliminates the step of pre-coating a petroleum-based coating to improve printability in traditional processes, and achieves a synergistic improvement in base paper reinforcement and flexographic printing.

[0012] This application uses lignin, a byproduct of the papermaking industry, as the main raw material, realizing the high-value utilization of lignin. The printed honeycomb paperboard can be 100% recycled for pulping, with no petroleum resin residue, and will not affect the strength of recycled paper, thus having excellent environmental and economic benefits.

[0013] This application utilizes intermolecular hydrogen bonds formed between lignin and nanocellulose to create a film that combines high adhesion, high toughness, and fast drying properties. It is particularly suitable for printing on honeycomb paperboard, eliminating the need for an additional petroleum-based coating. This achieves a synergistic improvement in both paper reinforcement and printing performance, making it compatible with high-speed flexographic printing production lines. Furthermore, in the recycled pulping process, there is no petroleum-based resin residue, allowing for 100% closed-loop recycling of the pulp. This composite ink system fills the gap in the industrial application of fully bio-based, petroleum-free resin inks in the honeycomb paperboard field.

[0014] The amount of lignin used can be 20 parts, 22 parts, 24 parts, 26 parts, 28 parts, 30 parts, 32 parts, 34 parts, 35 parts, etc.

[0015] The amount of cellulose nanofibers used can be 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, etc.

[0016] The amount of solvent used can be 40 parts, 42 parts, 44 parts, 46 parts, 48 ​​parts, 50 parts, 52 parts, 54 parts, 56 parts, 58 parts, 60 parts, etc.

[0017] The amount of the colorant can be 10 parts, 12 parts, 14 parts, 16 parts, 18 parts, 20 parts, 22 parts, 24 parts, 26 parts, 28 parts, 30 parts, etc.

[0018] The amount of the dispersant can be 0.1 parts, 0.3 parts, 0.5 parts, 0.7 parts, 1 part, etc.

[0019] The amount of the defoamer can be 0.05 parts, 0.1 parts, 0.2 parts, 0.3 parts, 0.5 parts, etc.

[0020] The amount of the wetting agent can be 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, etc.

[0021] The following are preferred technical solutions of this application, but are not intended to limit the technical solutions provided in this application. The purpose and beneficial effects of this application can be better achieved through the following preferred technical solutions.

[0022] In some embodiments, the dispersant comprises any one or a combination of at least two of polyacrylate, polycarboxylate, lignin sulfonate or fatty alcohol polyoxyethylene ether, preferably polyacrylate.

[0023] In some embodiments, the defoamer includes any one or a combination of at least two of polyether defoamers, silicone defoamers, or mineral oil defoamers, preferably polyether defoamers.

[0024] In some embodiments, the wetting agent includes any one or a combination of at least two of acetylenic diol wetting agents, polyether-modified siloxane wetting agents, or fatty alcohol polyoxyethylene ether wetting agents, preferably acetylenic diol wetting agents.

[0025] In some embodiments, the lignin comprises enzymatically hydrolyzed lignin and / or alkali lignin.

[0026] In some embodiments, the purity of the lignin is ≥90%, such as 90%, 92%, 94%, 96%, 98%, 100%, etc.

[0027] In some embodiments, the weight-average molecular weight of the lignin is 3000-8000 g / mol, such as 3000 g / mol, 4000 g / mol, 5000 g / mol, 6000 g / mol, 7000 g / mol, 8000 g / mol, etc. If the weight-average molecular weight of the lignin is too low, it will result in insufficient film-forming strength; if the weight-average molecular weight is too high, it will result in poor solubility and difficulty in dispersion. This application controls the weight-average molecular weight of the lignin within the above-mentioned range, thus achieving both excellent solubility and film-forming properties.

[0028] In some embodiments, the molecular weight distribution index (PDI) of the lignin is 1.5-3.0, such as 1.5, 1.8, 2.0, 2.2, 2.5, 2.8, 3.0, etc.

[0029] In some embodiments, the cellulose nanofibers include carboxylated cellulose nanofibers.

[0030] In some embodiments, the diameter of the cellulose nanofibers is 3-20 nm, such as 3 nm, 5 nm, 7 nm, 9 nm, 10 nm, 12 nm, 14 nm, 16 nm, 18 nm, 20 nm, etc.

[0031] In some embodiments, the length of the cellulose nanofibers is 300-10000nm, such as 300nm, 500nm, 1000nm, 2000nm, 3000nm, 4000nm, 5000nm, 6000nm, 7000nm, 8000nm, 9000nm, 10000nm, etc.

[0032] The cellulose nanofibers described in this application have a diameter of 3-20 nm and a length of 300-10000 nm. Within this range, cellulose can form a sufficiently strong hydrogen bond network with lignin. If the aspect ratio decreases (the diameter is too large or the length is too small), the specific surface area of ​​the cellulose nanofibers decreases, the number of hydroxyl and carboxyl groups on the surface that can participate in hydrogen bond formation decreases, and the strength of the hydrogen bond network is insufficient, resulting in high brittleness of the composite ink film and reduced adhesion to the substrate. If the aspect ratio is too high (the diameter is too small or the length is too large), the cellulose nanofibers are prone to entanglement and aggregation, resulting in excessively high ink viscosity, reduced dispersibility, and easy formation of particles during grinding and coating, affecting printing quality. Furthermore, an excessively high aspect ratio will make the ink too thixotropic, resulting in poor leveling properties during high-speed printing and easy formation of defects such as dagger marks and streaks.

[0033] In some embodiments, the surface carboxyl content of the cellulose nanofibers is 0.5-1.5 mmol / g, such as 0.5 mmol / g, 0.7 mmol / g, 0.9 mmol / g, 1.1 mmol / g, 1.3 mmol / g, 1.5 mmol / g, etc.

[0034] In some embodiments, the solvent includes water and / or alcohol solvents.

[0035] In some embodiments, the colorant includes any one or a combination of at least two of carbon black, titanium dioxide, phthalocyanine blue, or permanent red.

[0036] In some embodiments, the alcohol solvent includes bio-alcohols.

[0037] In some embodiments, the bioethanol includes ethanol and / or propylene glycol.

[0038] In some embodiments, the mass ratio of water to alcohol solvent is (1.5-4):1, for example 1.5:1, 1.7:1, 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1, 4:1, etc.

[0039] Secondly, this application provides a method for preparing the composite ink as described in the first aspect, the method comprising the following steps: (1) The lignin and solvent are mixed for the first time to obtain a lignin solution; (2) Add dispersant and colorant for a second mixing to obtain color paste; (3) Add cellulose nanofibers for a third mixing, add defoamer and wetting agent and mix evenly to obtain the composite ink.

[0040] In some embodiments, the temperature of the first mixing is 45-55°C, such as 45°C, 47°C, 49°C, 51°C, 53°C, 55°C, etc.

[0041] In some embodiments, the first mixing is carried out in the presence of an alkaline substance.

[0042] In some embodiments, the alkaline substance includes sodium hydroxide.

[0043] In some embodiments, an alkaline substance is added to maintain the pH of the system at 8.5-9.0 (e.g., 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, etc.). Under weakly alkaline conditions, lignin gradually dissolves to obtain a dark brown solution. If there are a small number of undissolved particles, they are dispersed with ice bath ultrasonic assistance.

[0044] In some embodiments, the first mixing time is 30-50 minutes, such as 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, etc.

[0045] In some embodiments, the second mixing method includes second stirring and grinding.

[0046] In some embodiments, after adding the dispersant, the mixture is stirred at 800-1200 rpm for 5-10 minutes until completely dissolved; then the colorant is added, and the mixture is dispersed at high speed at 1500-2000 rpm for 20-25 minutes to obtain a coarse color paste; then the coarse color paste is transferred to a grinding mill, 0.8-1 mm zirconia grinding beads are added, and the mill is ground at 2000-2500 rpm for 30-40 minutes, with cooling water circulating during the grinding process to control the material temperature ≤60℃; during this process, the fineness is tested using a scraper fineness gauge, and when D90 ≤ 1... After 0 μm, the sample is filtered to obtain a color paste. The 800-1200 rpm can be 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, etc., the 5-10 min can be 5 min, 8 min, 10 min, etc., the 1500-2000 rpm can be 1500 rpm, 1700 rpm, 1800 rpm, 2000 rpm, etc., and the 20-25 min can be 20 min, 23 min, 25 min, etc.

[0047] In some embodiments, the third mixing time is 15-20 minutes, such as 15 minutes, 17 minutes, 20 minutes, etc.

[0048] In some embodiments, the third mixing method includes a third stirring.

[0049] In some embodiments, the second stirring speed is 1000-2000 rpm, such as 1000 rpm, 1200 rpm, 1400 rpm, 1600 rpm, 1800 rpm, 2000 rpm, etc.

[0050] In some embodiments, the second stirring time is 20-30 minutes, such as 20 minutes, 22 minutes, 24 minutes, 26 minutes, 28 minutes, 30 minutes, etc.

[0051] In some embodiments, the grinding is performed in a sand mill.

[0052] In some embodiments, the grinding time is 30-40 minutes, such as 30 minutes, 32 minutes, 34 minutes, 36 minutes, 38 minutes, 40 minutes, etc.

[0053] In some embodiments, the rotation speed of the third stirring is 700-900 rpm, such as 700 rpm, 750 rpm, 800 rpm, 850 rpm, 900 rpm, etc.

[0054] This application requires strict control of the third stirring speed. If the speed is too high, the high shear force will break the cellulose fibers, resulting in a decrease in the aspect ratio, weakening the hydrogen bond network strength between lignin and cellulose, leading to increased film brittleness and decreased coating adhesion. If the speed is too low, the cellulose nanofibers cannot be evenly dispersed, easily forming agglomerates, resulting in increased ink fineness, particles and pinholes after coating, affecting printing quality and adhesion.

[0055] In some embodiments, the process of mixing thoroughly further includes adjusting the pH value, filtering, and degassing.

[0056] In some embodiments, the speed of the grinding machine is 2000-2500 rpm, such as 2000 rpm, 2100 rpm, 2200 rpm, 2300 rpm, 2400 rpm, 2500 rpm, etc.

[0057] In some embodiments, the pH adjustment is performed using citric acid.

[0058] In some embodiments, the pH value is adjusted to 7.5-8.0, such as 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, etc.

[0059] In some embodiments, the degassing includes vacuum degassing or static degassing.

[0060] Thirdly, this application provides an application of the composite ink as described in the first aspect in printed packaging.

[0061] In some embodiments, the substrate of the printed packaging includes any one of honeycomb paperboard, corrugated paperboard, kraft paperboard, white cardboard, coated paper, or grey-backed white cardboard, with honeycomb paperboard being preferred.

[0062] Compared with the prior art, this application has the following advantages: (1) This application uses lignin and cellulose nanofibers as the core film-forming substances to achieve the preparation of a composite ink that is completely free of petroleum resin. The composite ink has a high adhesion to the substrate, which is above 95%. It dries quickly, completely drying at 80°C in 2.5 minutes. It has good wear resistance, and the ink mass loss is less than 4% after 20 dry rubbing cycles.

[0063] (2) The composite ink of this application is particularly suitable for printing on honeycomb paperboard. It does not require additional coating of petroleum-based coating, and the printing is clear and does not bleed. The ring crush strength of the base paper coated with composite ink is increased by 18.0%. It is compatible with a 30m / min high-speed flexographic printing production line and the printing speed reaches the level of traditional petroleum-based ink, solving the problem of low printing efficiency of existing bio-based inks.

[0064] (3) This application uses lignin, a by-product of the papermaking industry, as the main raw material, realizing the high-value utilization of lignin. The bio-based carbon content is above 88%, and the printed honeycomb paperboard can be 100% recycled for pulping. There is no petroleum resin residue, which will not affect the strength of recycled paper. It solves the problem of waste paper recycling caused by traditional inks, greatly reduces carbon emissions, and VOCs (loss on drying) ≤5g / L. Detailed Implementation

[0065] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0066] The source information of some raw materials in this application embodiment is as follows: Enzymatic hydrolysis of lignin: Guangdong Dingfeng Chemical Co., Ltd., 86855-54-1; Carboxylated cellulose nanofibers A: Cellubio, CNF-J6426C, morphology: aqueous dispersion, diameter 5-10 nm, length 500-1000 nm, carboxyl content 1.2 mmol / g, solid content 0.5%, pH 6-7; Carboxylated cellulose nanofibers B: Cellubio, CNF-J6426CP, morphology: powder, diameter 5-10nm, length 500-1000nm, carboxyl content 1.2mmol / g; Carboxylated cellulose nanofibers C: Cellubio, CNF-J6423C, morphology: aqueous dispersion, diameter 5-10nm, length 1000nm and above, carboxyl content 1.2mmol / g, solid content 0.5%, pH 6-7; Carboxylated cellulose nanofibers D: Cellubio, custom-made, morphology: powder, diameter 5-10nm, length 12000-15000nm, carboxyl content 1.2mmol / g; Carboxylated cellulose nanofibers E: Cellubio, custom-made, morphology: aqueous dispersion, diameter 3-20nm, length less than 300nm, carboxyl content 1.2mmol / g; Sulfonated cellulose nanofibers: Cellubio, CNF-JS, morphology: aqueous dispersion, diameter 10-30nm, length 5000nm and above, solid content 0.5%, pH 6-8; Colorant: Resin-free carbon black paste, Suzhou Shiming Technology, TSE5900; Dispersant: Sodium polyacrylate dispersant, SANNOPCO, SN-5040; Defoamer: Polyether defoamer, SANNOPCO, NXZ; Wetting agent: acetylenic diol, Evonik, SURFYNOL 465.

[0067] Example 1 This embodiment provides a composite ink and its preparation method. The composite ink comprises the following components by weight: 28 portions of lignin were enzymatically hydrolyzed. Carboxylated cellulose nanofibers A12 parts; 35 parts water; 15 parts ethanol; 18 parts colorant; 0.8 parts of dispersant; 0.3 parts of defoamer; 0.4 parts wetting agent; The preparation method includes the following steps: (1) According to the formula dosage, add water and ethanol to the jacketed dispersion tank, heat the system to 50°C by passing constant temperature water through the jacket, immerse the dispersion plate in 2 / 3 of the liquid surface to avoid air entrapment, stir at 500 rpm for 5 min, add lignin, add it within 2 min, continue stirring for 10 min, add 10 wt% sodium hydroxide solution dropwise at a rate of 1 drop / 2 s, monitor the pH value until the pH value is 8.7, keep warm and stir for 20 min to obtain lignin solution; (2) Add dispersant and stir at 1000 rpm for 5 min until completely dissolved; slowly add colorant and disperse at 1800 rpm for 20 min to obtain coarse color paste; transfer coarse color paste to a horizontal sand mill, add 1 mm zirconia grinding beads with 70% of the grinding chamber volume, and circulate and grind at 2000 rpm for 30 min. After the fineness D90 is tested to be 0.82 μm by a scraper fineness meter, filter with 100 mesh nylon filter cloth to obtain color paste; (3) Transfer the pigment into a dispersion tank, control the rotation speed to 800 rpm, slowly add the carboxylated cellulose nanofiber A dispersion (concentrated under reduced pressure to 10% solid content) along the tank wall for 3 min, stir for 15 min; add defoamer and stir for 3 min, add wetting agent and stir for 3 min; add 10 wt% citric acid solution to adjust the pH value to 7.7, add deionized water, and adjust the viscosity of the 25°C Co-4 cup to 27.4 s; (4) Filter twice with 200-mesh nylon filter cloth, then transfer to a vacuum degassing machine and degas for 10 minutes at a vacuum degree of -0.09MPa until there are no bubbles on the surface to obtain the composite ink.

[0068] Example 2 This embodiment provides a composite ink and its preparation method. The composite ink comprises the following components by weight: 20 parts of lignin were enzymatically hydrolyzed. Carboxylated cellulose nanofibers B, 15 parts; 30 parts water; 15 parts of 1,3-propanediol; 10 parts colorant; 0.1 parts dispersant; 0.5 parts of defoamer; 0.1 parts wetting agent; The preparation method includes the following steps: (1) According to the formula dosage, add water and 1,3-propanediol to a jacketed dispersion tank, heat the system to 45°C by passing constant temperature water through the jacket, immerse the dispersion plate in 2 / 3 of the liquid surface to avoid air entrapment, stir at 500 rpm for 5 min, add lignin, add it within 2 min, continue stirring for 10 min, add 10 wt% sodium hydroxide solution dropwise at a rate of 1 drop / 2 s, monitor the pH value until the pH value is 8.5, keep warm and stir for 15 min to obtain lignin solution; (2) Add dispersant and stir at 1000 rpm for 5 min until completely dissolved; slowly add colorant and disperse at 1500 rpm for 25 min to obtain coarse color paste; transfer coarse color paste to a horizontal sand mill, add 1 mm zirconia grinding beads with 70% of the grinding chamber volume, and circulate and grind at 2000 rpm for 40 min. After the fineness D90 is tested to be 0.85 μm by a scraper fineness meter, filter with 100 mesh nylon filter cloth to obtain color paste; (3) Transfer the pigment into a dispersion tank, control the rotation speed to 900 rpm, slowly add the carboxylated cellulose nanofiber B dispersion (water as solvent, 10% solid content) along the tank wall for 3 min, stir for 15 min; add defoamer and stir for 3 min, add wetting agent and stir for 3 min; add 10 wt% citric acid solution to adjust the pH value to 7.5, add deionized water, and adjust the viscosity of the 25°C Co-4 cup to 24.8 s; (4) Filter twice with 200-mesh nylon filter cloth, then transfer to a vacuum degassing machine and degas for 10 minutes at a vacuum degree of -0.09MPa until there are no bubbles on the surface to obtain the composite ink.

[0069] Example 3 This embodiment provides a composite ink and its preparation method. The composite ink comprises the following components by weight: 35 parts of lignin were enzymatically hydrolyzed. Carboxylated cellulose nanofibers C 10 parts; 48 parts water; 12 parts ethanol; 30 parts colorant; 0.1 parts dispersant; 0.1 parts of defoamer; 0.5 parts wetting agent; The preparation method includes the following steps: (1) According to the formula dosage, add water and ethanol to the jacketed dispersion tank, heat the system to 55°C by passing constant temperature water through the jacket, immerse the dispersion plate in 2 / 3 of the liquid surface to avoid air entrapment, stir at 500 rpm for 5 min, add lignin, add it within 2 min, continue stirring for 10 min, add 10 wt% sodium hydroxide solution dropwise at a rate of 1 drop / 2 s, monitor the pH value until the pH value is 9.0, keep warm and stir for 25 min to obtain lignin solution; (2) Add dispersant and stir at 1000 rpm for 5 min until completely dissolved; slowly add colorant and disperse at 2000 rpm for 20 min to obtain coarse color paste; transfer coarse color paste to a horizontal sand mill, add 1 mm zirconia grinding beads with 70% of the grinding chamber volume, and circulate and grind at 2500 rpm for 30 min. After the fineness D90 is tested to be 0.79 μm by a scraper fineness meter, filter with 100 mesh nylon filter cloth to obtain color paste; (3) Transfer the pigment into a dispersion tank, control the rotation speed at 700 rpm, slowly add the carboxylated cellulose nanofiber C dispersion (concentrated under reduced pressure to 10% solid content) along the tank wall for 3 min, and stir for 20 min; add defoamer and stir for 3 min, add wetting agent and stir for 3 min; add 10 wt% citric acid solution to adjust the pH value to 8.0, add deionized water, and adjust the viscosity of the 25°C Co-4 cup to 31.2 s; (4) Filter twice with 200-mesh nylon filter cloth, seal and let stand at room temperature for 2 hours, and let it degas naturally until there are no bubbles on the surface to obtain the composite ink.

[0070] Example 4 The only difference from Example 1 is that carboxylated cellulose nanofiber A is replaced with carboxylated cellulose nanofiber D, while the amounts of other components and the preparation methods are the same as in Example 1.

[0071] Example 5 The only difference from Example 1 is that carboxylated cellulose nanofiber A is replaced with carboxylated cellulose nanofiber E, while the amounts of other components and the preparation methods are the same as in Example 1.

[0072] Example 6 The only difference from Example 1 is that carboxylated cellulose nanofibers A are replaced with sulfonated cellulose nanofibers, while the amounts of other components and the preparation methods are the same as in Example 1.

[0073] Example 7 The only difference from Example 1 is that in step (3), the stirring speed is 1200 rpm, and the amount of other components and the preparation method are the same as in Example 1.

[0074] Example 8 The only difference from Example 1 is that in step (3), the stirring speed is 600 rpm, and the amount of other components and the preparation method are the same as in Example 1.

[0075] Comparative Example 1 The only difference from Example 1 is that carboxylated cellulose nanofibers A are not added, while the amounts of other components and the preparation methods are the same as in Example 1.

[0076] Comparative Example 2 Commercially available petroleum-based flexographic water-based inks (Hanghua Ink Co., Ltd. WBI-BF / LP series) have a film-forming material of acrylic resin + styrene-acrylate copolymer, a solid content of 30%, and can be used directly.

[0077] Comparative Example 3 The only difference from Example 1 is that the amount of carboxylated cellulose nanofiber A is 22 parts, while the amount of other components and the preparation method are the same as in Example 1.

[0078] Comparative Example 4 The only difference from Example 1 is that the amount of carboxylated cellulose nanofiber A is 6 parts, while the amount of other components and the preparation method are the same as in Example 1.

[0079] Performance testing (1) Ink fineness: According to GB / T 13217.3-2022 "Test method for fineness of liquid ink", a scraper fineness meter (0-25μm, graduation value 1μm) was used for testing. A small amount of ink was dropped onto the upper end of the groove and scraped over it at a uniform speed within 3 seconds. The scale of continuous particle position was observed at an angle to the light. Each sample was tested in parallel 3 times and the average value was taken. (2) Ink viscosity: According to GB / T 1723-1993 "Determination of viscosity of coatings", the test was carried out using a Forte-4 cup viscometer under constant temperature conditions of 25℃. The ink was poured in and leveled, and the flow outlet was opened while timing was started. The meter was stopped when the flow was interrupted. Each sample was tested in parallel 3 times and the average value was taken. (3) Adhesion: The ink to be tested was evenly coated onto kraft paper (175g / m²) using a bar coater. 2 On the surface, control the dry film thickness to 20μm, and after coating, place it in an 80℃ oven to dry for 3 minutes, then remove and let it stand; cut 5cm×10cm kraft paper samples (5 samples per group, take the average value after testing), weigh them, and record the weight as m1; smoothly attach 3M 600 tape to the coated surface, roll it 3 times with a 2kg roller, let it stand for 1 minute, and quickly tear off the tape at a 180° angle, weigh the mass of the coated sample m2 again, and calculate the adhesion force according to the following formula: Adhesion force = [1-(m1-m2) / dry weight of ink layer]×100%; (4) Drying time: The finger touch method combined with the filter paper imprinting method was used. The coated sample was placed in an 80℃ oven and taken out every 30s. The surface of the ink layer was covered with qualitative filter paper and pressed with a 2kg weight for 10s. The filter paper was removed and the ink marks were observed. The time when there were no ink marks and the sample was not sticky was taken as the complete drying time. Each sample was tested in parallel 3 times and the average value was taken. (5) Abrasion resistance: According to GB / T 7706-2008 "Determination of abrasion resistance of letterpress printed matter", an ink abrasion tester was used to dry rub 20 times (reciprocating speed 43 times / min). The weight difference of the sample before and after friction was weighed and expressed as the percentage of mass loss. The smaller the value, the better the abrasion resistance. Each sample was tested in parallel 3 times and the average value was taken. (6) Base paper reinforcement: The composite ink is mixed with water to prepare a dispersion with a solid content of 3%, and the dispersion is evenly coated onto kraft paper (175g / m²) using a bar coater. 2 After coating the back side, dry it in an 80℃ oven for 2 minutes. Cut 127×12.7mm kraft paper samples (10 samples, average value after testing). Use a ring crush tester to test according to GB / T 2679.8-2016 "Determination of ring crush strength of paper and paperboard". Ring crush index = F / (152×basis weight), unit is N·m / g, and the improvement rate = (ring crush index of reinforced sample - ring crush index of blank sample) / ring crush index of blank sample × 100%; (7) Printing speed adaptability: Using a laboratory flexographic printing adaptability tester, the printing speeds were set to 10m / min, 20m / min, and 30m / min, the printing pressure was 100N, and the drying temperature was 80℃. The printing was carried out on honeycomb base paper reinforced with composite ink (Example 1), and the drying state, printing clarity and ink bleeding were observed.

[0080] The composite inks provided in the examples and comparative examples were tested according to the above performance testing methods, and the results are shown in Tables 1-3: Table 1 Table 2 Table 3 As can be seen from the data in Table 1: (1) Examples 1-3 use the formulation and process parameters within the scope of the claims of this application, and have the best overall performance: the fineness of the composite ink is 0.79-0.85μm, the viscosity is 24.8-31.2s, the adhesion is above 97.8%-99.5%, the drying time is 2.3-2.8min, and the mass loss of abrasion resistance is below 0.94%-3.73%, of which Example 1 is the optimal formulation.

[0081] (2) In Example 4, the aspect ratio of carboxylated cellulose nanofibers D was too large (diameter 5-10 nm, length 12000-15000 nm), which led to a significant increase in ink viscosity to 45.6 s, an increase in fineness to 1.20 μm, a decrease in adhesion to 92.5%, and an extension of drying time to 4.2 min. The reason is that excessively long nanofibers are prone to entanglement and agglomeration, resulting in decreased dispersibility and excessively high viscosity. It is difficult to completely open the agglomerates during the grinding process, and the excessively high viscosity makes the ink flowability worse, affecting the film uniformity and adhesion.

[0082] (3) In Example 5, the aspect ratio of the carboxylated cellulose nanofiber E was too small (diameter 3-20nm, length less than 300nm), resulting in a decrease in adhesion to 85.3% and an increase in abrasion resistance mass loss to 12.30%. The reason is that the nanofibers that are too short have a small specific surface area and a small number of hydroxyl and carboxyl groups on the surface that can participate in hydrogen bond formation. They cannot form a sufficiently strong hydrogen bond network with lignin, resulting in high film brittleness, poor adhesion, and decreased abrasion resistance.

[0083] (4) In Example 6, sulfonated cellulose nanofibers were used, resulting in an increase in fineness to 2.10 μm, a decrease in adhesion to 82.1%, and an extension of drying time to 4.5 min. The reason is that the hydrogen bonding between sulfonate groups and lignin phenolic hydroxyl groups is weaker than that between sulfonate groups and carboxyl groups, which further weakens the hydrogen bond network strength, resulting in a significant decrease in film-forming properties and adhesion.

[0084] (5) In Example 7, the third stirring speed was too high (1200 rpm), which caused the adhesion to drop to 88.7% and the abrasion resistance mass loss to increase to 9.80%. The reason is that the excessive shear force will break the long fiber structure of cellulose nanofibers, reduce the aspect ratio, weaken the hydrogen bond network strength between lignin and cellulose, and lead to increased film brittleness and decreased adhesion.

[0085] (6) In Example 8, the third stirring speed was too low (600 rpm), which resulted in the fineness increasing to 1.80 μm and the adhesion decreasing to 91.2%. The reason is that the speed is too low, which makes it impossible to disperse the cellulose nanofibers evenly, and they are prone to forming agglomerates, which leads to the increase of ink fineness, particles and pinholes after coating, affecting printing quality and adhesion.

[0086] (7) In Comparative Example 1, without the addition of cellulose nanofibers, the ink performance was the worst: fineness 2.35 μm, adhesion only 72.3%, drying time 5.2 min, and abrasion resistance mass loss of 16.20%. This fully demonstrates that cellulose nanofibers are the key component for achieving high performance, and the hydrogen bond network formed by them with lignin is the core mechanism for improving adhesion, flexibility, and drying speed. Comparing Comparative Example 1 with Example 1, it can be seen that after adding 12 parts of CNF, the adhesion increased from 72.3% to 99.5%, an increase of 37.6%; the drying time was shortened from 5.2 min to 2.5 min, a reduction of 51.9%; and the abrasion resistance mass loss decreased from 16.20% to 0.94%, a reduction of 94.2%, showing significant effects.

[0087] (8) Comparative Example 2 uses commercially available petroleum-based ink. Although its adhesion (98.2%) and drying time (2.2 min) are similar to those of Example 1, it contains a large amount of petroleum-based resin and volatile organic compounds, with a high VOC content (approximately 28.6 g / L) and a low bio-based carbon content (approximately 12%). When the printed paper packaging is recycled and pulped, the petroleum-based resin cannot be completely separated, which will lead to a decrease in the strength of the recycled paper and a recycling compatibility problem. In contrast, the bio-based carbon content of Example 1 in this application is approximately 88%, and the VOC content is approximately 3.2 g / L, which is far superior to Comparative Example 2. Moreover, the printed paperboard can be 100% recycled and pulped.

[0088] (9) In Comparative Example 3, the amount of cellulose nanofibers (CNF) was excessive (22 parts, exceeding the range of 10-15 parts in claims), resulting in a significant decrease in ink performance: the viscosity reached 68.5 s (27.4 s in Example 1, an increase of 150%), the drying time was extended to 4.8 min (2.5 min in Example 1, an extension of 92%), the fineness increased to 1.10 μm, the adhesion decreased to 95.2%, and the abrasion resistance loss increased to 6.50%, making it unsuitable for high-speed printing. The reason is that: the excessive CNF makes the nanofiber content in the ink system too high, the hydrogen bonding between fibers too strong, resulting in excessively high ink viscosity, poor fluidity, and poor leveling properties during coating. In addition, CNF is highly hydrophilic, and excessive amounts will absorb more water, significantly prolonging the drying time; at the same time, the excessively high viscosity reduces the grinding and dispersion efficiency and increases the fineness. Comparing Comparative Example 3 with Example 1, it can be seen that when the CNF dosage increased from 12 parts to 22 parts (an increase of 83%), the viscosity soared from 27.4s to 68.5s, and the drying time increased from 2.5min to 4.8min. This proves that the CNF dosage must be strictly controlled within the range of 10-15 parts, as excessive dosage will seriously impair printability.

[0089] (10) In Comparative Example 4, the amount of CNF was too small (6 parts, lower than the range of 10-15 parts in claim 1), resulting in a significant decrease in ink performance: adhesion was only 83.5% (99.5% in Example 1, a decrease of 16.1%), the loss of abrasion resistance was as high as 11.80% (0.94% in Example 1, an increase of 1155%), the fineness increased to 1.60 μm, and the drying time was extended to 3.6 min. The reason is that: insufficient CNF content cannot form a complete and continuous hydrogen bond network structure with lignin, resulting in insufficient film strength and flexibility, leading to high coating brittleness, poor adhesion, and decreased abrasion resistance; at the same time, insufficient CNF content weakens the dispersion and stabilization effect on pigments, leading to easy pigment agglomeration and increased fineness. Comparing Comparative Example 4 with Example 1, it can be seen that when the amount of CNF is reduced from 12 parts to 6 parts (a reduction of 50%), the adhesion decreases from 99.5% to 83.5%, and the mass loss of abrasion resistance increases from 0.94% to 11.80%. This proves that CNF is a key component for forming a high-performance hydrogen bond network, and the amount must reach more than 10 parts to ensure film formation performance.

[0090] As shown in Table 2, (1) after the composite ink of Example 1 was formulated into a 3% solid content dispersion and coated on the back of the base paper, the ring crush index of the base paper increased from 7.22 N·m / g to 8.52 N·m / g, with an increase rate of 18.0%, proving that the composite ink system of this application has the function of base paper reinforcement at the same time, realizing the integration of "substrate reinforcement-surface printing"; (2) after coating, the ring crush index of Comparative Example 1 (without CNF) only increased by 2.5%, which is much lower than that of Example 1, proving that CNF is the key component for base paper reinforcement. The hydrogen bond network formed by CNF and lignin can penetrate into the paper fiber and significantly improve the paper strength; (3) Comparative Example 2 (commercially available petroleum-based oil) (3) The ring crush index decreased by 4.4% after coating with CNF. This is because the petroleum-based resin only forms a film on the surface of the paper and cannot penetrate into the paper fibers to form reinforcement. In addition, the resin coating will hinder the hydrogen bonding between paper fibers, resulting in a decrease in strength. (4) The ring crush index of Comparative Example 3 (22 parts too much CNF) increased by 19.1% after coating, which is slightly higher than that of Example 1. However, as shown in Tables 1 and 3, Comparative Example 3 has poor printability (viscosity 68.5s, drying time 4.8min, not completely dried at 30m / min), and cannot take into account both the reinforcement of the original paper and printing. (5) The ring crush index of Comparative Example 4 (6 parts too little CNF) increased by only 3.9% after coating, and the reinforcement effect was insufficient. In summary, this application can achieve excellent printability and 18% reinforcement of the original paper in the range of CNF dosage of 10-15 parts.

[0091] As shown in Table 3, (1) the composite ink of Example 1 can still dry completely, print clearly, and without ink bleeding under high-speed printing conditions of 30 m / min. Its printability is comparable to that of Comparative Example 2 (commercially available petroleum-based ink), proving that the all-bio-based composite ink of this application has reached the high-speed printing level of traditional petroleum-based inks; (2) Comparative Example 1 (without CNF) did not dry completely under the same conditions, the printing was blurry and blurry, and there was severe ink bleeding, proving that the hydrogen bond network formed by CNF and lignin is the key to achieving fast drying and anti-ink bleeding; (3) Comparative Example 3 (with excessive CNF content of 22 parts) did not dry completely under 30 m / min conditions, the printing was slightly blurry, and there was slight ink bleeding. The reason is that excessive CNF leads to excessively high ink viscosity (68.5 s), poor fluidity, and prolonged drying time (4.8 min), which cannot be adapted to high-speed printing. In summary, the composite ink of this application can be adapted to a 30 m / min high-speed flexographic printing production line within the range of CNF content of 10-15 parts, solving the pain point of low printing efficiency of existing bio-based inks.

[0092] In summary, this application uses lignin and cellulose nanofibers as film-forming substances, with an ink fineness of 0.7-1μm and a viscosity of 25-32s. The coating exhibits high adhesion to the substrate, exceeding 95%, and dries quickly, achieving complete drying in 2.5 minutes at 80°C. It also demonstrates good abrasion resistance, with ink mass loss below 4% after 20 dry rubbing cycles. Furthermore, it effectively enhances the compressive strength of paper; compared to blank base paper, the ring crush strength of the base paper coated with ink in Example 1 increased by 18.0%. The raw materials are derived from byproducts of the papermaking industry, possessing a high bio-based carbon content, making it particularly suitable for printing on honeycomb cardboard. It does not bleed ink and is compatible with high-speed flexible printing production lines of 30m / min.

[0093] The above description is only a specific embodiment of this application, but the protection scope of this application is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application fall within the protection and disclosure scope of this application.

Claims

1. A composite ink, characterized in that, The composite ink comprises the following components by weight: 20-35 parts lignin; 10-15 parts of cellulose nanofibers; Solvent 40-60 parts; Colorant 10-30 parts; Dispersant 0.1-1 part; Defoamer 0.05-0.5 parts; 0.05-0.5 parts of wetting agent.

2. The composite ink according to claim 1, characterized in that, The lignin includes enzymatically hydrolyzed lignin and / or alkali lignin; And / or, the purity of the lignin is ≥90%; And / or, the weight-average molecular weight of the lignin is 3000-8000 g / mol; And / or, the molecular weight distribution index (PDI) of the lignin is 1.5-3.

0.

3. The composite ink according to claim 1 or 2, characterized in that, The cellulose nanofibers include carboxylated cellulose nanofibers; And / or, the diameter of the cellulose nanofibers is 3-20 nm; And / or, the length of the cellulose nanofibers is 300-10000 nm; And / or, the surface carboxyl content of the cellulose nanofibers is 0.5-1.5 mmol / g.

4. The composite ink according to any one of claims 1-3, characterized in that, The solvent includes water and / or alcohol solvents; And / or, the colorant includes any one or a combination of at least two of carbon black, titanium dioxide, phthalocyanine blue, or permanent red; And / or, the alcohol solvent includes bio-alcohols.

5. The composite ink according to any one of claims 1-4, characterized in that, The bio-alcohols include ethanol and / or propylene glycol; And / or, the mass ratio of the water to the alcohol solvent is (1.5-4):

1.

6. A method for preparing a composite ink as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: (1) The lignin and solvent are mixed for the first time to obtain a lignin solution; (2) Add dispersant and colorant for a second mixing to obtain color paste; (3) Add cellulose nanofibers for a third mixing, add defoamer and wetting agent and mix evenly to obtain the composite ink.

7. The preparation method according to claim 6, characterized in that, The temperature of the first mixture is 45-55℃; And / or, the first mixing is carried out in the presence of an alkaline substance; And / or, the first mixing time is 30-50 min; And / or, the second mixing method includes second stirring and grinding; And / or, the third mixing time is 15-20 min; And / or, the third mixing method includes a third stirring.

8. The preparation method according to claim 6 or 7, characterized in that, The second stirring speed is 1000-2000 rpm; And / or, the second stirring time is 20-35 min; And / or, the grinding is carried out in a sand mill; And / or, the grinding time is 30-40 minutes; And / or, the rotation speed of the third stirring is 700-900 rpm; And / or, after the mixture is homogeneous, it may also include pH adjustment, filtration, and degassing.

9. The preparation method according to any one of claims 6-8, characterized in that, The speed of the sand mill is 2000-2500 rpm; And / or, the pH adjustment is performed using citric acid; And / or, the pH value is adjusted to 7.5-8.0; And / or, the degassing includes vacuum degassing or static degassing.

10. The application of a composite ink as described in any one of claims 1-5 in printed packaging; And / or, the substrate of the printed packaging includes any one of honeycomb paperboard, corrugated paperboard, kraft paperboard, white cardboard, coated paper or grey-backed white cardboard, preferably honeycomb paperboard.

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