A paperboard printing ink and a process for its preparation

Abstract

The application relates to the technical field of inks, and discloses a paperboard printing ink and a preparation process thereof. The ink comprises a rosin-modified amide resin solution, an amidated dispersant, organic pigments, modified microcrystalline cellulose and an additive. Firstly, the rosin-modified amide resin solution with rigidity, flexibility and crosslinking sites is synthesized by reacting rosin with maleic anhydride, diethanolamine, epoxy soybean oil and gamma-aminopropyl triethoxysilane; secondly, the modified microcrystalline cellulose is prepared by surface grafting modification of microcrystalline cellulose with zinc oxide and gamma-aminopropyl triethoxysilane; in the film forming process, the resin and the modified microcrystalline cellulose form a dense interpenetrating network structure through chemical bonding, so that the ink has excellent adhesion, wear resistance, folding resistance and water resistance, is low in fineness, environment-friendly, and suitable for high-speed paperboard printing.

Description

Technical Field

[0001] This invention relates to the field of ink technology, specifically to a paperboard printing ink and its preparation process. Background Technology

[0002] Paperboard printing inks are widely used in the packaging industry, and their performance directly affects the visual effect, durability, and adaptability of printed materials to subsequent processing. With increasingly stringent environmental regulations, water-based inks, with water as the main dispersion medium, have become an important development direction. However, traditional water-based inks often face key technical bottlenecks when applied to porous paperboard with low surface energy: on the one hand, acrylic and styrene-acrylic resins, which are commonly used to pursue environmental protection and fast drying, have insufficient wetting and penetration of paperboard fibers, resulting in poor adhesion and easy peeling of the ink layer after friction, folding, or moisture absorption; on the other hand, inorganic fillers (such as silica powder and calcium carbonate) added to improve abrasion resistance are prone to agglomeration in the system, which not only increases grinding energy consumption and causes printing plate blockage, but also causes stress concentration due to weak bonding with the resin matrix, seriously damaging the flexibility and folding resistance of the ink layer, making it difficult to meet the stringent requirements of high-speed forming of cartons and frequent bending during circulation.

[0003] Therefore, developing an environmentally friendly paperboard printing ink that can simultaneously achieve excellent adhesion, superior abrasion resistance, good flexibility, and stable processing performance remains a pressing technical challenge in this field. Summary of the Invention

[0004] (a) Technical problems to be solved: To address the shortcomings of existing technologies, this invention provides a paperboard printing ink and its preparation process, solving the problem that paperboard printing inks cannot simultaneously possess excellent folding toughness, high abrasion resistance, and good water resistance.

[0005] (II) Technical Solution: In a first aspect, the present invention provides a paperboard printing ink comprising the following components: 35-45 parts by weight of rosin-modified amide resin liquid, 5-8 parts by weight of amidating dispersant, 18-25 parts by weight of organic pigment, 2-4 parts by weight of polyethylene wax emulsion, 0.5-2 parts by weight of modified microcrystalline cellulose, 0.2-0.5 parts by weight of defoamer, 0.3-1 parts by weight of pH adjuster, and 20-35 parts by weight of deionized water.

[0006] As a preferred embodiment of the present invention, the preparation method of rosin-modified amide resin liquid is as follows: Step (1): Under a nitrogen atmosphere, add rosin to the reaction vessel, heat to 160-170℃ and maintain for 2-3 hours to isomerize the rosin into L-piperidine, which can undergo an addition reaction. Then heat to 190-200℃, add maleic anhydride, stir the reaction for 3-4 hours, and after the reaction is completed, cool to 120-130℃ and maintain under vacuum for 0.5-1 hours to obtain maleic rosin anhydride.

[0007] Step (2): Under a nitrogen atmosphere, add maleic rosin anhydride to the reaction vessel, heat to 130-140℃, slowly add diethanolamine dropwise, controlling the dropwise addition time to 30-50 min, stir the reaction for 40-60 min after the dropwise addition is complete, then add epoxidized soybean oil, heat to 150-160℃, stir the reaction for 2-3 h, then cool down to 110-120℃, add ethylene glycol monobutyl ether and zinc oxide, stir for 20-30 min, finally add γ-aminopropyltriethoxysilane, continue stirring the reaction for 1-2 h until the system is transparent and uniform, and obtain rosin modified amide resin.

[0008] Step (3): Add rosin-modified amide resin to the reaction vessel, heat to 85-95℃, add 20-25% ammonia solution to adjust the pH to 8-8.5, add deionized water to adjust the solid content to 40-50%, stir evenly, filter, and obtain rosin-modified amide resin solution.

[0009] As a preferred technical solution of the present invention, the mass ratio of rosin to maleic anhydride in step (1) is 100:(20-25).

[0010] As a preferred technical solution of the present invention, the mass ratio of maleic rosin anhydride, epoxidized soybean oil, diethanolamine, ethylene glycol monobutyl ether, zinc oxide and γ-aminopropyltriethoxysilane in step (2) is 100:(15-25):(18-22):(8-12):(0.5-1.5):(0.5-2).

[0011] As a preferred technical solution of the present invention, the preparation method of the amidation dispersant is as follows: 30-35 parts by weight of styrene-maleic anhydride-acrylamide terpolymer and 10-15 parts by weight of isopropanol are added to a reaction vessel, mixed evenly, heated to 50-60°C, and a 20-25% ammonia solution is slowly added dropwise to carry out a neutralization reaction, so that the pH of the system is maintained at 8.5-9 until the resin is completely dissolved and the solution becomes transparent. Finally, 50-60 parts by weight of deionized water are added to dilute the solution to obtain the amidation dispersant.

[0012] As a preferred technical solution of the present invention, the method for preparing modified microcrystalline cellulose is as follows: at room temperature, 0.5-3 parts by weight of zinc oxide are dispersed in 50-60 parts by weight of an ammonia solution with a concentration of 20-25%, and stirred until a zinc-ammonia complex solution is formed. Then, 0.5-3 parts by weight of γ-aminopropyltriethoxysilane are added, and the mixture is stirred and hydrolyzed for 10-20 minutes. Then, 10-15 parts by weight of microcrystalline cellulose with a particle size of 5-10 μm are added, and the mixture is ultrasonically treated for 1-2 hours. The mixture is filtered, washed with deionized water until the washing solution is neutral, and dried to obtain modified microcrystalline cellulose.

[0013] As a preferred embodiment of the present invention, the pH adjuster is any one of 2-amino-2-methyl-1-propanol or monoethanolamine.

[0014] Secondly, the present invention also provides a method for preparing a paperboard printing ink and its preparation process, wherein the preparation process of the paperboard printing ink is as follows: S1. Preparation of color paste: Stir the organic pigment and the amidation dispersant for 20-30 minutes to make them evenly mixed, and then grind them with a sand mill until the fineness is ≤15μm to obtain the color paste.

[0015] S2. Ink preparation: Add rosin-modified amide resin solution to the mixing tank, and slowly add color paste at a speed of 600-800 rpm, stirring for 15-20 minutes.

[0016] S3. Functional modification: Add polyethylene wax emulsion and modified microcrystalline cellulose in sequence, increase the speed to 900-1200 rpm, and stir and disperse for 20-30 minutes.

[0017] S4. Post-treatment: Add defoamer and pH adjuster to maintain the pH of the system at 8.5-9. Then add deionized water to adjust the viscosity, filter, and obtain paperboard printing ink.

[0018] (III) Beneficial technical effects: 1. This invention first involves preparing maleic anhydride by Diels-Alder addition of rosin and maleic anhydride, followed by ring-opening amidation with diethanolamine to introduce hydrophilic hydroxyl and amide groups, thereby imparting good water solubility and wettability to the resin. Subsequently, epoxidized soybean oil is introduced, and its epoxy groups undergo ring-opening polymerization with carboxyl or amine groups on the resin backbone, grafting long-chain aliphatic flexible segments onto the rigid rosin skeleton, acting as an internal plasticizer to effectively improve resin brittleness and enhance ink layer folding resistance. Finally, γ-aminopropyltriethoxysilane is added and neutralized to form a salt, imparting moisture-curing crosslinking ability and water dispersion stability to the resin. Simultaneously, zinc oxide added to the system reacts with the carboxyl groups in the resin to form zinc soap, further improving film hardness and drying speed.

[0019] 2. This invention utilizes a zinc-ammonia complex formed by zinc oxide in ammonia water to activate the surface of microcrystalline cellulose, thereby activating and slightly swelling its hydroxyl groups. Subsequently, pre-hydrolyzed γ-aminopropyltriethoxysilane is added. Under ultrasonic assistance, its silanol groups undergo dehydration condensation with the active hydroxyl groups on the cellulose surface, achieving covalent grafting. During this process, zinc ions act as coordination anchors, significantly reducing the hydrophilicity and agglomeration tendency of cellulose, allowing it to be uniformly dispersed in the ink system with an extremely fine particle size. This not only helps reduce ink fineness and prevent plate clogging but also forms a uniformly distributed reinforcing skeleton within the ink film, thereby significantly improving abrasion resistance.

[0020] 3. The rosin-modified amide resin and modified microcrystalline cellulose of the present invention can be chemically bonded through active groups (such as silanol, amino, epoxy, etc.) to form a dense "organic-inorganic" interpenetrating network structure. This structure not only enhances the cohesive strength and adhesion of the ink film, but also effectively blocks water penetration, giving the ink excellent water resistance.

[0021] 4. The ink formulation provided by this invention has moderate viscosity, good leveling properties, and excellent resolubility, making it suitable for high-speed flexographic or gravure printing processes. Furthermore, this ink uses water as the main solvent and incorporates environmentally friendly additives, resulting in extremely low VOC content, meeting the environmental requirements for green packaging materials and possessing broad market application prospects. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Styrene-maleic anhydride-acrylamide terpolymer was prepared according to the method described in the journal "Journal of Shenyang Institute of Chemical Technology", 2003, (03): 201-203, "Development of Pour Depressant for Styrene-Maleic Anhydride-Acrylamide Terpolymer".

[0024] The defoamer listed below is model HR-8424, purchased from Dongguan Hongrui Chemical Co., Ltd.

[0025] Example 1:

[0026] A preparation process for paperboard printing ink: Step (1): Under a nitrogen atmosphere, add 100 parts by weight of rosin to the reaction vessel, heat to 160°C and maintain for 3 hours to isomerize the rosin into L-piperidine, which can undergo an addition reaction. Then heat to 190°C, add 23 parts by weight of maleic anhydride, stir and react for 3 hours. After the reaction is completed, cool down to 130°C, and maintain under vacuum for 0.5 hours to obtain maleic rosin anhydride.

[0027] Step (2): Under a nitrogen atmosphere, add 100 parts by weight of maleic rosin anhydride to the reaction vessel, heat to 130°C, slowly add 20 parts by weight of diethanolamine, control the addition time to 40 min, stir the reaction for 50 min after the addition is complete, then add 20 parts by weight of epoxidized soybean oil, heat to 160°C, stir the reaction for 2 h, then cool down to 120°C, add 10 parts by weight of ethylene glycol monobutyl ether and 1 part by weight of zinc oxide, stir for 30 min, finally add 1.4 parts by weight of γ-aminopropyltriethoxysilane, continue stirring the reaction for 2 h until the system is transparent and uniform, and obtain rosin modified amide resin.

[0028] Step (3): Add rosin-modified amide resin to the reaction vessel, heat to 90°C, add 25% ammonia solution to adjust the pH to 8.5, add deionized water to adjust the solid content to 40%, stir evenly, filter, and obtain rosin-modified amide resin solution.

[0029] Step (4): Add 35 parts by weight of styrene-maleic anhydride-acrylamide terpolymer and 15 parts by weight of isopropanol to the reaction vessel, mix evenly, heat to 50°C, and slowly add 20% ammonia solution for neutralization reaction, so that the pH of the system is maintained at 8.5 until the resin is completely dissolved and the solution becomes transparent. Finally, add 55 parts by weight of deionized water to dilute and obtain the amidated dispersant.

[0030] Step (5): At room temperature, 1.8 parts by weight of zinc oxide were dispersed in 55 parts by weight of a 20% ammonia solution and stirred until a zinc-ammonia complex solution was formed. Then, 2 parts by weight of γ-aminopropyltriethoxysilane were added and stirred for hydrolysis for 20 min. 12 parts by weight of microcrystalline cellulose with a particle size of 8 μm were added and ultrasonically treated for 1 h. The mixture was filtered, washed with deionized water until the washing solution was neutral, and dried to obtain modified microcrystalline cellulose.

[0031] Step (6), color paste preparation: Stir 21 parts by weight of organic pigment and 6 parts by weight of amidation dispersant for 20 minutes to make them evenly mixed, and then grind them with a sand mill until the fineness is 12μm to obtain color paste.

[0032] Step (7), Ink preparation: Add 40 parts by weight of rosin-modified amide resin liquid to the mixing tank, slowly add the color paste at 700 rpm, and stir for 15 minutes.

[0033] Step (8), Functional modification: Add 3 parts by weight of polyethylene wax emulsion and 1.3 parts by weight of modified microcrystalline cellulose in sequence, increase the speed to 900 rpm, and stir and disperse for 30 min.

[0034] Step (9), Post-processing: Add 0.3 parts by weight of defoamer and add 0.7 parts by weight of monoethanolamine to maintain the pH of the system at 9. Then add 30 parts by weight of deionized water to adjust the viscosity. Filter to obtain paperboard printing ink.

[0035] Example 2:

[0036] A preparation process for paperboard printing ink: Step (1): Under a nitrogen atmosphere, add 100 parts by weight of rosin to the reaction vessel, heat to 170°C and maintain for 2 hours to isomerize the rosin into L-piperidine, which can undergo an addition reaction. Then heat to 200°C, add 25 parts by weight of maleic anhydride, stir and react for 3 hours. After the reaction is completed, cool down to 120°C, and maintain under vacuum for 1 hour to obtain maleic rosin anhydride.

[0037] Step (2): Under a nitrogen atmosphere, add 100 parts by weight of maleic rosin anhydride to the reaction vessel, heat to 140°C, slowly add 22 parts by weight of diethanolamine, control the addition time at 50 min, stir the reaction for 60 min after the addition is complete, then add 15 parts by weight of epoxidized soybean oil, heat to 150°C, stir the reaction for 3 h, then cool down to 110°C, add 8 parts by weight of ethylene glycol monobutyl ether and 1.5 parts by weight of zinc oxide, stir for 20 min, finally add 0.5 parts by weight of γ-aminopropyltriethoxysilane, continue stirring the reaction for 1 h until the system is transparent and uniform, and obtain rosin modified amide resin.

[0038] Step (3): Add rosin-modified amide resin to the reaction vessel, heat to 95°C, add 20% ammonia solution to adjust the pH to 8, add deionized water to adjust the solid content to 45%, stir evenly, filter, and obtain rosin-modified amide resin solution.

[0039] Step (4): Add 30 parts by weight of styrene-maleic anhydride-acrylamide terpolymer and 10 parts by weight of isopropanol to the reaction vessel, mix well, heat to 60°C, slowly add 25% ammonia solution for neutralization reaction, keep the pH of the system at 9 until the resin is completely dissolved and the solution becomes transparent, and finally add 50 parts by weight of deionized water to dilute and obtain amidated dispersant.

[0040] Step (5): At room temperature, 0.5 parts by weight of zinc oxide are dispersed in 50 parts by weight of a 20% ammonia solution and stirred until a zinc-ammonia complex solution is formed. Then, 0.5 parts by weight of γ-aminopropyltriethoxysilane are added and stirred for hydrolysis for 10 min. Then, 10 parts by weight of microcrystalline cellulose with a particle size of 10 μm are added, and the mixture is ultrasonically treated for 1 h. After filtration, the mixture is washed with deionized water until the washing solution is neutral and dried to obtain modified microcrystalline cellulose.

[0041] Step (6), color paste preparation: Stir 18 parts by weight of organic pigment and 8 parts by weight of amidation dispersant for 25 minutes to make them evenly mixed, and then grind them with a sand mill until the fineness is 15μm to obtain color paste.

[0042] Step (7), Ink preparation: Add 35 parts by weight of rosin-modified amide resin liquid to the mixing tank, slowly add the color paste at 800 rpm, and stir for 15 minutes.

[0043] Step (8), Functional modification: Add 4 parts by weight of polyethylene wax emulsion and 0.5 parts by weight of modified microcrystalline cellulose in sequence, increase the speed to 1200 rpm, and stir and disperse for 20 min.

[0044] Step (9), Post-processing: Add 0.2 parts by weight of defoamer and add 0.3 parts by weight of 2-amino-2-methyl-1-propanol to maintain the pH of the system at 8.5. Then add 20 parts by weight of deionized water to adjust the viscosity. Filter to obtain paperboard printing ink.

[0045] Example 3:

[0046] A preparation process for paperboard printing ink: Step (1): Under a nitrogen atmosphere, add 100 parts by weight of rosin to the reaction vessel, heat to 170°C and maintain for 3 hours to isomerize the rosin into L-piperidine, which can undergo an addition reaction. Then heat to 190°C, add 20 parts by weight of maleic anhydride, stir and react for 4 hours. After the reaction is completed, cool down to 120°C, and maintain under vacuum for 1 hour to obtain maleic rosin anhydride.

[0047] Step (2): Under a nitrogen atmosphere, add 100 parts by weight of maleic rosin anhydride to the reaction vessel, heat to 130°C, slowly add 18 parts by weight of diethanolamine, control the addition time to 30 min, stir the reaction for 40 min after the addition is complete, then add 25 parts by weight of epoxidized soybean oil, heat to 160°C, stir the reaction for 3 h, then cool down to 120°C, add 12 parts by weight of ethylene glycol monobutyl ether and 0.5 parts by weight of zinc oxide, stir for 30 min, finally add 2 parts by weight of γ-aminopropyltriethoxysilane, continue stirring the reaction for 2 h until the system is transparent and uniform, and obtain rosin modified amide resin.

[0048] Step (3): Add rosin-modified amide resin to the reaction vessel, heat to 85°C, add 25% ammonia solution to adjust the pH to 8, add deionized water to adjust the solid content to 50%, stir evenly, filter, and obtain rosin-modified amide resin solution.

[0049] Step (4): Add 30 parts by weight of styrene-maleic anhydride-acrylamide terpolymer and 15 parts by weight of isopropanol to the reaction vessel, mix evenly, heat to 55°C, and slowly add 25% ammonia solution for neutralization reaction to maintain the pH of the system at 8.5 until the resin is completely dissolved and the solution becomes transparent. Finally, add 60 parts by weight of deionized water to dilute and obtain the amidated dispersant.

[0050] Step (5): At room temperature, 3 parts by weight of zinc oxide are dispersed in 60 parts by weight of a 25% ammonia solution and stirred until a zinc-ammonia complex solution is formed. Then, 3 parts by weight of γ-aminopropyltriethoxysilane are added and stirred for hydrolysis for 20 min. 15 parts by weight of microcrystalline cellulose with a particle size of 5 μm are added and ultrasonically treated for 2 h. The mixture is filtered, washed with deionized water until the washing solution is neutral, and dried to obtain modified microcrystalline cellulose.

[0051] Step (6), color paste preparation: Stir 25 parts by weight of organic pigment and 5 parts by weight of amidation dispersant for 30 minutes to make them evenly mixed, and then grind them with a sand mill until the fineness is 13μm to obtain color paste.

[0052] Step (7), Ink preparation: Add 45 parts by weight of rosin-modified amide resin liquid to the mixing tank, slowly add the color paste at 600 rpm, and stir for 20 minutes.

[0053] Step (8), Functional modification: Add 2 parts by weight of polyethylene wax emulsion and 2 parts by weight of modified microcrystalline cellulose in sequence, increase the speed to 1000 rpm, and stir and disperse for 20 min.

[0054] Step (9), Post-processing: Add 0.5 parts by weight of defoamer and add 1 part by weight of monoethanolamine to maintain the pH of the system at 8.5. Then add 35 parts by weight of deionized water to adjust the viscosity. Filter to obtain paperboard printing ink.

[0055] Comparative Example 1: The difference from Example 1 is that in step (2), γ-aminopropyltriethoxysilane is not added when preparing rosin-modified amide resin.

[0056] Step (2): Under a nitrogen atmosphere, add 100 parts by weight of maleic rosin anhydride to the reaction vessel, heat to 130°C, slowly add 20 parts by weight of diethanolamine, control the addition time to 40 min, stir the reaction for 50 min after the addition is complete, then add 20 parts by weight of epoxidized soybean oil, heat to 160°C, stir the reaction for 2 h, then cool down to 120°C, add 10 parts by weight of ethylene glycol monobutyl ether and 1 part by weight of zinc oxide, stir for 30 min, continue stirring the reaction for 2 h to obtain rosin-modified amide resin.

[0057] The remaining steps are the same as in Example 1.

[0058] Comparative Example 2: The difference from Example 1 is that in step (2), epoxidized soybean oil is not added when preparing rosin-modified amide resin.

[0059] Step (2): Under a nitrogen atmosphere, add 100 parts by weight of maleic rosin anhydride to the reaction vessel, heat to 130°C, slowly add 20 parts by weight of diethanolamine, control the addition time to 40 min, stir the reaction for 50 min after the addition is complete, then cool to 120°C, add 10 parts by weight of ethylene glycol monobutyl ether and 1 part by weight of zinc oxide, stir for 30 min, and finally add 1.4 parts by weight of γ-aminopropyltriethoxysilane, continue stirring the reaction for 2 h until the system is transparent and uniform, and obtain rosin modified amide resin.

[0060] The remaining steps are the same as in Example 1.

[0061] Comparative Example 3: The difference from Example 1 is that ordinary microcrystalline cellulose is used instead of modified microcrystalline cellulose.

[0062] Comparative Example 4: The difference from Example 1 is that zinc oxide was not added during the preparation of the modified microcrystalline cellulose.

[0063] Step (5): At room temperature, 55 parts by weight of a 20% ammonia solution and 2 parts by weight of γ-aminopropyltriethoxysilane were stirred and hydrolyzed for 20 min. Then, 12 parts by weight of microcrystalline cellulose with a particle size of 8 μm were added, and the mixture was sonicated for 1 h. After filtration, the mixture was washed with deionized water until the washing solution was neutral and dried to obtain modified microcrystalline cellulose.

[0064] The remaining steps are the same as in Example 1.

[0065] The inks of Examples 1-3 and Comparative Examples 1-4 were subjected to the following tests: Ink adhesion test: The adhesion of ink is tested in accordance with GB / T 13217.7-2023 "Ink Adhesion Test Method".

[0066] Ink viscosity test: The viscosity of the ink was tested in accordance with GB / T 13217.4-2020 "Ink Viscosity Test Method" and measured using a Forte 4 cup at 25°C.

[0067] Ink fineness test: The fineness of the ink was tested in accordance with GB / T 13217.3-2022 "Ink Fineness Test Method".

[0068] Ink abrasion resistance test: Use an ink abrasion tester, set the pressure to 4 pounds, use standard white paper for abrasion, and record the number of abrasions when the ink layer is exposed or there is obvious color loss.

[0069] Water resistance test of ink: After the printed sample is dried, it is completely immersed in water for 24 hours. After it is taken out and dried, observe whether there is bubbling, discoloration or peeling of the ink layer.

[0070] Ink folding endurance test: After the printed sample dries, fold it back and forth 180° 20 times along the fold line and observe whether the ink layer at the fold line cracks or peels.

[0071] Table 1

[0072] As shown in Table 1, the inks of Examples 1-3 exhibit good adhesion, abrasion resistance, water resistance, folding endurance, and low fineness. The rosin-modified amide resin solution in Examples 1-3 is rich in amide bonds and hydroxyl groups, endowing the system with excellent hydrophilicity and film-forming properties, and significantly improving the resin's wetting ability on the substrate and the dispersion stability of pigments and fillers, thereby effectively reducing ink fineness and improving adhesion. Simultaneously, the epoxidized soybean oil flexible segments introduced into the resin molecular chain effectively reduce the internal stress after film formation, giving the ink layer excellent folding toughness; while γ-aminopropyltriethoxysilane provides hydrolyzable crosslinking silicon sites, enhancing water resistance. Furthermore, the silanol and amino groups grafted onto the surface of the modified microcrystalline cellulose chemically bond and physically entangle with the resin matrix during film formation and curing, forming a dense interpenetrating network structure, significantly improving the cohesive strength and mechanical hardness of the ink layer, thus enabling the ink to exhibit excellent abrasion resistance.

[0073] The difference between Comparative Example 1 and Example 1 is that in step (2), γ-aminopropyltriethoxysilane was not added when preparing the rosin-modified amide resin, resulting in poor water resistance and low adhesion of the ink. This is mainly because the hydrolyzable silicon functional groups provided by the silane coupling agent are missing. When the resin dries and forms a film, it cannot form a dense Si-O-Si cross-linked network, which makes it easy for water to penetrate the ink layer and weaken the chemical bond between the resin and the paper fiber.

[0074] The difference between Comparative Example 2 and Example 1 is that in step (2), epoxidized soybean oil was not added when preparing the rosin-modified amide resin, resulting in poor folding resistance of the ink. This is because the rosin skeleton itself is rigid and brittle, and the lack of the flexible chain segment of epoxidized soybean oil means that the ink layer cannot effectively dissipate stress when subjected to folding force, thus causing brittle fracture.

[0075] The difference between Comparative Example 3 and Example 1 is that ordinary microcrystalline cellulose was used instead of modified microcrystalline cellulose, resulting in a larger ink fineness and a significant decrease in abrasion resistance. This is because the surface of unmodified cellulose contains a large number of hydrophilic hydroxyl groups, which have poor compatibility with hydrophobic resin systems, making them prone to aggregation and easy to detach from the ink layer during friction.

[0076] The difference between Comparative Example 4 and Example 1 is that zinc oxide was not added during the preparation of modified microcrystalline cellulose, which led to a decrease in wear resistance. This is because the zinc-ammonia complex formed by zinc oxide helps to promote the grafting efficiency and orderly arrangement of silane on the cellulose surface. The lack of coordination and anchoring effect of zinc oxide weakens the interfacial bonding force between microcrystalline cellulose and the resin matrix.

[0077] The present invention has been described in detail above with reference to the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A paperboard printing ink, characterized in that, The paperboard printing ink comprises the following components: 35-45 parts by weight of rosin-modified amide resin liquid, 5-8 parts by weight of amidation dispersant, 18-25 parts by weight of organic pigment, 2-4 parts by weight of polyethylene wax emulsion, 0.5-2 parts by weight of modified microcrystalline cellulose, 0.2-0.5 parts by weight of defoamer, 0.3-1 parts by weight of pH adjuster, and 20-35 parts by weight of deionized water.

2. The paperboard printing ink according to claim 1, characterized in that, The preparation method of the rosin-modified amide resin solution is as follows: Step (1): Under a nitrogen atmosphere, add rosin to the reaction vessel, heat to 160-170℃ and maintain for 2-3 hours to isomerize the rosin into L-piperidine, which can undergo an addition reaction. Then heat to 190-200℃, add maleic anhydride, stir and react for 3-4 hours. After the reaction is completed, cool down to 120-130℃, and maintain under vacuum for 0.5-1 hours to obtain maleic rosin anhydride. Step (2): Under a nitrogen atmosphere, add maleic rosin anhydride to the reaction vessel, heat to 130-140℃, slowly add diethanolamine dropwise, control the dropwise addition time to 30-50 min, stir the reaction for 40-60 min after the dropwise addition is completed, then add epoxidized soybean oil, heat to 150-160℃, stir the reaction for 2-3 h, then cool down to 110-120℃, add ethylene glycol monobutyl ether and zinc oxide, stir for 20-30 min, finally add γ-aminopropyltriethoxysilane, continue stirring the reaction for 1-2 h until the system is transparent and uniform, and obtain rosin modified amide resin; Step (3): Add rosin-modified amide resin to the reaction vessel, heat to 85-95℃, add 20-25% ammonia solution to adjust the pH to 8-8.5, add deionized water to adjust the solid content to 40-50%, stir evenly, filter, and obtain rosin-modified amide resin solution.

3. The paperboard printing ink according to claim 2, characterized in that, In step (1), the mass ratio of rosin to maleic anhydride is 100:(20-25).

4. The paperboard printing ink according to claim 2, characterized in that, In step (2), the mass ratio of maleic rosin anhydride, epoxidized soybean oil, diethanolamine, ethylene glycol monobutyl ether, zinc oxide, and γ-aminopropyltriethoxysilane is 100:(15-25):(18-22):(8-12):(0.5-1.5):(0.5-2).

5. The paperboard printing ink according to claim 1, characterized in that, The preparation method of the amidated dispersant is as follows: Add 30-35 parts by weight of styrene-maleic anhydride-acrylamide terpolymer and 10-15 parts by weight of isopropanol to the reaction vessel, mix well, heat to 50-60℃, and slowly add 20-25% ammonia solution for neutralization reaction, maintaining the pH of the system at 8.5-9 until the resin is completely dissolved and the solution becomes transparent. Finally, add 50-60 parts by weight of deionized water to dilute and obtain the amidated dispersant.

6. The paperboard printing ink according to claim 1, characterized in that, The method for preparing the modified microcrystalline cellulose is as follows: At room temperature, 0.5-3 parts by weight of zinc oxide are dispersed in 50-60 parts by weight of a 20-25% ammonia solution and stirred until a zinc-ammonia complex solution is formed. Then, 0.5-3 parts by weight of γ-aminopropyltriethoxysilane are added and stirred for hydrolysis for 10-20 min. Then, 10-15 parts by weight of microcrystalline cellulose with a particle size of 5-10 μm are added and ultrasonically treated for 1-2 h. The mixture is filtered, washed with deionized water until the washing solution is neutral, and dried to obtain modified microcrystalline cellulose.

7. The paperboard printing ink according to claim 1, characterized in that, The pH adjuster is either 2-amino-2-methyl-1-propanol or monoethanolamine.

8. The paperboard printing ink according to claim 1, characterized in that, The preparation process of the paperboard printing ink is as follows: S1. Preparation of color paste: Stir the organic pigment and the amidation dispersant for 20-30 minutes to make them evenly mixed, and then grind them with a sand mill until the fineness is ≤15μm to obtain the color paste; S2. Ink preparation: Add rosin-modified amide resin solution to the mixing tank, and slowly add color paste at a speed of 600-800 rpm, stirring for 15-20 minutes. S3. Functional modification: Add polyethylene wax emulsion and modified microcrystalline cellulose in sequence, increase the speed to 900-1200 rpm, and stir and disperse for 20-30 minutes; S4. Post-treatment: Add defoamer and pH adjuster to maintain the pH of the system at 8.5-9. Then add deionized water to adjust the viscosity, filter, and obtain paperboard printing ink.

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