An ink composition for benneli film printing and a preparation method thereof

Abstract

This invention belongs to the field of water-based ink technology, and discloses a printing ink composition for Baili film and its preparation method. The composition uses a cationic water-based polyurethane emulsion as a binder. The polyurethane molecular chain is covalently introduced with long-chain alkyl groups, bisquaternary ammonium-bridged cationic structures, and latent catechol structures through functionalized dihydroxy chain extenders. The catechol structure exists in an isopropylidene protected state during the polyurethane synthesis stage. After acetone removal, it undergoes acid-catalyzed hydrolysis in the aqueous phase, and the acetone generated by hydrolysis is removed by inert gas purging, achieving a deprotection rate of over 96%. The resulting ink, after coating, leveling at room temperature, and drying at 70°C for 5 minutes, achieves a cross-cut adhesion grade of 0-1, and exhibits resistance to wiping with 75% ethanol, scratching with 3% hydrogen peroxide, and immersion in water. Under accelerated testing conditions of light avoidance, nitrogen headspace replacement, and storage at 50°C for 14 days, the emulsion and ink did not show significant discoloration or flocculation.

Description

Technical Field

[0001] This invention belongs to the field of water-based ink technology, specifically relating to an ink composition and preparation method for printing on polyolefin film, and the application of the ink composition in surface printing on non-food direct contact surfaces of polyolefin film (commonly known as polyolefin film) for liquid food flexible packaging; this invention also relates to a functionalized dihydroxy chain extender and a cationic water-based polyurethane emulsion used as a binder in the ink composition. Background Technology

[0002] Pasteurized milk, UHT milk, and milk-containing beverages widely use pillow-shaped flexible packaging made primarily of polyethylene, commonly known in the industry as "Baili film." The printed surface of this type of film is a polyethylene layer, a typical low-surface-energy non-polar substrate (surface tension approximately 31 mN / m), and the film has poor heat resistance, drying only within minutes at 60–80°C after printing. Furthermore, during filling, storage, transportation, and consumption, the ink layer of dairy products must be subjected to wiping with disinfectant ethanol, contact with hydrogen peroxide disinfectant, and immersion and friction in condensate and ice water, placing high demands on the ink layer's interfacial adhesion, water resistance, and chemical resistance.

[0003] Currently, most of these films are printed using solvent-based inks, which poses problems such as organic solvent emissions, residual solvent odors, and food safety risks. Water-based inks are a clear alternative, but existing water-based systems have the following shortcomings when used for polyethylene surface printing:

[0004] Anionic waterborne polyurethane is the mainstream. Most commercially available waterborne polyurethane dispersions are achieved by neutralizing carboxylic acid monomers such as dimethylolpropionic acid with amines to form salts. Their ionic groups depend on the pH of the system and are prone to losing their stabilizing effect when the system is dry or when the pH of the environment changes. The residual carboxylic acid salts and volatile amines used for neutralization after film formation are hydrophilic and migratory, resulting in poor water resistance and strong odor of the ink layer.

[0005] Traditional cationic systems are also pH-dependent. Schemes that introduce cations by acid neutralization and protonation using tertiary amine chain extenders such as N-methyldiethanolamine have protonation degree and ionization state affected by the system pH, resulting in varying dispersion stability with pH changes. Furthermore, the lack of nonpolar structures compatible with polyolefins in the molecule limits adhesion to polyethylene.

[0006] The methods for bonding the interface are limited. Existing technologies mostly rely on substrate corona / plasma treatment or the addition of chlorinated polypropylene, adhesion promoters, etc. to improve adhesion. The activation effect of the former decays rapidly over time, while the latter exists in the form of physical blends, which are easy to migrate and be extracted by solvents or water, making it difficult to achieve long-lasting wet adhesion.

[0007] The introduction of dopamine / catechol-based adhesive functional agents is limited. Catechol groups have excellent interfacial hydrogen bonding and coordination adsorption capabilities, but their free phenolic hydroxyl groups are highly reactive to isocyanates, making them unsuitable for direct use in polyurethane synthesis. If added physically in the form of small molecules (such as catechol and dopamine), they are easily oxidized to form ortho-quinones, causing emulsion discoloration, flocculation, zeta potential decay, and ink clumping, resulting in poor storage stability. Furthermore, the small molecules themselves pose a risk of food contact migration.

[0008] Therefore, how to simultaneously and stably introduce non-polar structures compatible with polyolefins, pH-independent permanent ionization dispersion structures, and catechol structures that can play an interfacial adsorption role into the main chain of waterborne polyurethane binders, and solve the reaction conflict between catechol active groups and isocyanates and their oxidative stability issues, are technical problems that urgently need to be solved in this field. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to overcome the defects of existing water-based inks used in Peli film (polyethylene surface printing) such as insufficient adhesion to low surface energy substrates, poor wet water and chemical resistance, ionic stability dependent on system pH, and poor storage stability when the adhesive functional group is added in small molecule form. The present invention provides a water-based ink composition for Peli film printing and its preparation method, which can achieve excellent adhesion, resistance to 75% ethanol wiping, resistance to 3% hydrogen peroxide scratching, resistance to water immersion and rubbing, and storage stability of emulsion and ink under low temperature and short time drying conditions.

[0010] Specifically, it includes:

[0011] A functionalized dihydroxy chain extender is provided that can covalently introduce three functional structures—long-chain alkyl, bisquaternary ammonium bridging cation, and latent catechol—into the polyurethane backbone in a single step, thereby resolving the reaction conflict between the catechol phenolic hydroxyl group and the isocyanate group (by protecting it with isopropylidene to make it inert during the synthesis stage).

[0012] To resolve the process contradictions in protecting group removal: since ketal hydrolysis is a reversible reaction and acetone is a product, a sequential process needs to be provided, which involves first removing acetone, then acid-catalyzed deprotection in the aqueous phase, followed by purging to remove acetone, so that the deprotection rate is ≥96%;

[0013] Solve the problem of abnormal branching and gelation caused by the catalysis of isocyanate trimerization / urea carbamate by quaternary ammonium bromide;

[0014] Solve the charge compatibility problem between cationic binders, pigment dispersions, and additives to avoid flocculation, thickening, and demulsification;

[0015] Reduce volatile amines and residual solvents while taking into account food contact compliance verification pathways.

[0016] A printing ink composition for Baili film includes a cationic aqueous polyurethane emulsion, a pigment predispersant, additives, and water;

[0017] The polyurethane in the cationic aqueous polyurethane emulsion is obtained by addition polymerization of diisocyanate, polyether diol, functionalized dihydroxy chain extender and small molecule diol, and end-capped with n-butanol when necessary.

[0018] The functionalized dihydroxy chain extender has primary hydroxyl groups at both ends of the molecule and a bisquaternary ammonium salt structure bridged by alkylene groups in the middle of the molecule. Each quaternary ammonium nitrogen is connected to a C15-C18 long-chain alkyl group and a benzyl group containing an isopropylidene protected catechol structure.

[0019] The functionalized dihydroxy chain extender participates in the polyurethane chain extension reaction via its two primary hydroxyl groups, covalently introducing the long-chain alkyl group, the bisquaternary ammonium cationic structure, and the isopropylidene protected catechol structure into the polyurethane molecular chain. After the polyurethane is formed, it undergoes acid-catalyzed deprotection to form free catechol groups. The content of the free catechol groups, based on the deprotected polyurethane solid, is 0.30–0.60 mmol / g, and the quaternary ammonium nitrogen content is 0.30–0.60 mmol / g.

[0020] A printing ink composition for Baili film, by weight: 30-50 parts of cationic aqueous polyurethane emulsion with a solid content of 45 wt%, 10-30 parts of pigment pre-dispersion with a pigment content of 20 wt%, 0.1-2 parts of wetting and dispersing agent, 0.1-1 parts of defoamer, 0.5-2 parts of leveling agent, and 15-35 parts of water.

[0021] A printing ink composition for Baili film, wherein the amount of polyether diol is 1, the amount of functionalized dihydroxy chain extender is 0.3-0.7, the amount of small molecule diol is 0.3-0.7, and the sum of the two is 1, and the molar ratio of isocyanate group to total hydroxyl group NCO / OH is 1.00-1.05.

[0022] Preferably, the diisocyanate is selected from isophorone diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane diisocyanate; the polyether diol is polytetrahydrofuran glycol or polypropylene glycol with a number average molecular weight of 1000-2000; and the small molecule diol is selected from 1,4-butanediol, ethylene glycol, 1,6-hexanediol, and 1,4-cyclohexanediethanol.

[0023] A method for preparing a printing ink composition for Peli film includes the following steps:

[0024] S1 prepolymer: Diisocyanate and dehydrated polyether diol react in acetone in the presence of a catalyst to obtain NCO-terminated prepolymer;

[0025] S2 Stepwise Chain Extension: First, pre-extension is performed using the functionalized dihydroxy chain extender in a protected state with catechol, followed by further chain extension with a small molecule diol. When the theoretical residual NCO content is still not less than 0.10 wt% after the small molecule diol chain extension reaches the theoretical endpoint, the excess isocyanate groups are capped with n-butanol until the residual NCO content is <0.10 wt% and the infrared spectrum is 2270 cm⁻¹. -1 No obvious isocyanate characteristic absorption peaks were observed nearby;

[0026] S3 reverse emulsification: After emulsification with water, acetone is removed under reduced pressure until residual acetone is <0.5 wt%.

[0027] S4 Aqueous Deprotection: Add acid to the aqueous system after acetone removal, and react at 45-65°C, in the dark, with headspace purged by inert gas. Remove the acetone generated by hydrolysis while reacting to achieve a protecting group removal rate of ≥96% and obtain polyurethane containing free catechol groups.

[0028] S5 is neutralized and the solid content is adjusted to obtain a cationic aqueous polyurethane emulsion.

[0029] S6 Ink Preparation: After premixing the pigment pre-dispersion, dispersant and water, slowly add the emulsion in batches while stirring, then add the defoamer, leveling agent and the remaining water in sequence, and filter to obtain the ink.

[0030] Preferably, the acid in S4 is hydrochloric acid, and the dosage is 0.03–0.10 mmol H₂ per gram of polyurethane solid. + The pH of the system was adjusted to 1.5–2.5, the solid content of the system was adjusted to 20–30 wt% before deprotection, the reaction temperature was 55±5℃, and the time was 4–12 h.

[0031] Preferably, in S5, triethanolamine is used to neutralize the acid at 1.02 to 1.10 times the molar amount of the added acid, until the pH of the 1:9 dilution is 5.8 to 6.2.

[0032] Preferably, step S2 further includes a control step to suppress the side reaction of isocyanate catalyzed by quaternary ammonium bromide: the functionalized dihydroxy chain extender solution is added dropwise at 40±5℃, and after the addition is complete, the temperature is raised and the temperature of the entire chain extension reaction system is controlled at 50~58℃, and does not exceed 65℃ throughout the process; and in step S2, when the chain extender is not completely dissolved in acetone, acetonitrile equivalent to 10%~30% of the volume of acetone used to dissolve the chain extender is added as a co-solvent, wherein the water content of the co-solvent is <0.03wt%.

[0033] Application of a Baili film printing ink composition in surface printing of polyolefin films for flexible packaging of liquid food;

[0034] Preferably, the ink composition is printed on the non-food direct contact surface of a polyolefin film for flexible packaging of liquid food, wherein the printed surface layer of the film is a polyethylene layer with a total thickness of 40–120 μm; before printing, the printing surface is subjected to corona or atmospheric pressure plasma treatment to achieve a surface tension ≥38 mN / m, and the coating is applied within 30 min after treatment; after coating, it is dried at 60–80°C for 2–10 min, with a drying ink application rate of 3–8 g / m. 2 The total residual solvent in the resulting printed film is <5mg / m³. 2 .

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] First, by using a functionalized dihydroxy chain extender, long-chain alkyl groups, bisquaternary ammonium bridging structures, and catechol structures are simultaneously fixed onto the polyurethane main chain through a chain extension reaction. The measured cross-cut adhesion of samples I to III is grade 0 to 1, and the ink layer retention area is 99% to 100%. All samples passed the tests after being wiped with 75% ethanol 50 times, scraped with 3% H2O2 20 times, and rubbed 50 times after being immersed in water for 30 minutes. In contrast, the conventional cationic system (D1) without the above structures only had a grade 3 cross-cut adhesion and a retention area of ​​62%, and all of the above tests failed.

[0037] Second, after removing the catechol structure (D3), replacing the C18 long-chain alkyl with the C4 short-chain alkyl (D5), or replacing the bisquaternary ammonium bridging chain extender with the monoquaternary ammonium chain extender (D6), at least one wet property or adhesion property decreased, indicating that retaining the above three types of functional structures is beneficial to obtaining better overall interfacial adhesion and wet stability.

[0038] Third, based on the approximate matching of the theoretical molar concentration of catechol in Sample I and the physical addition of catechol D4, the mixed emulsion achieved a ΔEab of 18.5 after 50℃ / 14 days. 400 The concentration of the emulsion increased from 0.05 to 0.92, the Zeta potential decreased from +39mV to +13mV, the centrifugal sedimentation rate was 6.8%, and discoloration, flocculation, and ink clumping occurred; while the emulsion of this invention, under the same conditions, had ΔEab ≤ 1.4 and A 400 An increase of ≤0.03, a decrease in Zeta potential of ≤8%, and a centrifugal sedimentation rate of ≤0.2% were all deemed normal.

[0039] Fourth, the bisquaternary ammonium salt has a permanent ionization site, eliminating the need for acid / base neutralization to form a salt, resulting in an emulsion zeta potential of +38 to +52 mV. 50 It has a particle size of 65-85 nm, a PDI of ≤0.15, small particle size, narrow distribution, and stable storage.

[0040] Fifth, isopropylidene protection keeps catechol in a protected state during the prepolymerization and chain extension stages. After acetone is removed to <0.5 wt%, catalytic hydrolysis is performed in an aqueous phase at 55 °C and pH 1.5–2.5, followed by purging to remove the generated acetone. In the examples, the deprotection rate reached 96.5%–97.4%. In contrast, in D2 under essentially the same conditions but maintained at 25 ± 2 °C, the deprotection rate was only 3.2%, indicating that in this system and within the stated reaction time, heating plays a crucial role in achieving complete deprotection.

[0041] Sixth, the theoretical residual NCO calculation benchmark and endpoint criteria for each stage are given, along with a triple monitoring and anomaly handling scheme for quaternary ammonium salt catalytic side reactions based on temperature, viscosity, and infrared radiation. The viscosity gradually increases from approximately 35 mPa·s to approximately 210 mPa·s throughout the chain extension process, with no gel formation and a Mw of 5.2 × 10⁻⁶. 4 、Mw / Mn2.1.

[0042] Seventh, high-boiling-point triethanolamine is used to replace volatile amines for neutralization, resulting in residual acetone in the emulsion ≤0.15wt%, acetonitrile ≤7mg / kg, and volatile amine <10mg / kg; total residual solvent in the printed film is 1.8mg / m³. 2 Odor level 2; Total migration of sample I: 2.1 / 1.5 / 2.6 mg / dm³ 2 (4% acetic acid / 10% ethanol / 50% ethanol), primary aromatic amines, heavy metals, tin, and bismuth were not detected.

[0043] Eighth, it is suitable for low-temperature short-time drying and multi-color applications. Under the room temperature leveling and 70℃×5min drying conditions used in the examples, a high-performance ink layer can be formed. The five colors of ink, blue, red, yellow, black and green, all show good comprehensive printing performance. Under accelerated test conditions of light protection, nitrogen headspace replacement and 50℃ storage for 14 days, there is no flocculation or hard sedimentation, and the ink layer ΔE*ab≤1.1. Detailed Implementation

[0044] The Peli film described in this invention refers to a polyolefin-based film used in soft pillow-shaped packaging bags for liquid foods (pasteurized milk, room-temperature milk, milk-containing beverages, etc.). Its inner layer, which is in direct contact with the contents, is a polyethylene layer, while the printed surface (outer layer) is a white or natural-colored layer primarily composed of polyethylene, with a carbon black-colored opaque layer in the middle. The Peli film can be a single-layer polyethylene film or a multi-layer co-extruded film with polyethylene as the printed surface layer, with a total thickness of 40–120 μm. The ink composition described in this invention is printed on the non-food-contact surface (outer surface) of the Peli film, which is a surface printing application.

[0045] The latent catechol structure described in this invention refers to a structure in which the two phenolic hydroxyl groups of catechol are protected in the form of acetal (isopropylidene, i.e., 2,2-dimethyl-1,3-benzodioxane); this structure is inert to the isocyanate group during the polyurethane synthesis stage, and releases the free catechol group after acid-catalyzed hydrolysis.

[0046] Measurement Standards: Unless otherwise specified, NCO content, hydroxyl equivalent, etc., are calculated based on the mass of polyurethane resin solids. The mass of polyurethane resin solids refers to the sum of the masses of all reacting components that ultimately constitute the polyurethane resin solids up to this reaction stage, including diisocyanate, polyether diol, functionalized dihydroxy chain extender, small molecule diol, and end-capping agents that have reacted and covalently bonded during the end-capping process. It excludes components that do not constitute the polyurethane resin solids, such as acetone, acetonitrile, water, hydrochloric acid, and triethanolamine. The theoretical remaining NCO content at each stage is calculated using the following formula:

[0047] Theoretical remaining NCO content (%) = [n(NCO)0 - n(OH) already added] × 42 ÷ (1000 × m) × 100%;

[0048] In the formula: n(NCO)0 is the initial amount of isocyanate group, n(OH) added is the amount of hydroxyl group provided by all hydroxyl-containing components that have participated in the reaction up to this stage, and when n-butanol is used for end-capping, it also includes the amount of hydroxyl group provided by the n-butanol used for end-capping. Both are expressed in mmol; m is the solid mass of the resin at this stage, expressed in g; 42 is the molar mass of the isocyanate group, in g / mol; 1000 is the conversion factor between mmol and mol.

[0049] Verification criteria for hydroxyl content: All hydroxyl-containing components were verified by hydroxyl value determination before addition, not simply by conversion based on nominal number-average molecular weight. The measured hydroxyl value of polytetrahydrofuran glycol used in this paper was 112.2 mg KOH / g, corresponding to a hydroxyl equivalent of 500.0 g / mol and a number-average molecular weight of 1000; the measured hydroxyl value of chain extender M-C18 was 85.2 mg KOH / g. The amounts of substances listed throughout this paper were calculated based on theoretical molecular weights. The relative deviation between the measured and theoretical hydroxyl values ​​of each hydroxyl-containing component did not exceed 1.0%, and the resulting deviation in the NCO / OH molar ratio did not exceed 0.01, which did not affect the determination of the endpoints at each stage. The NCO / OH molar ratio in this paper was uniformly retained to two decimal places.

[0050] Solid content determination: Unless otherwise specified, the oven drying method is used. Weigh 1.0 ± 0.1 g of the sample into a pre-weighed aluminum dish and dry at 105 ± 2 °C until constant weight (the difference between two weighings should not exceed 0.001 g). The solid content is calculated as the percentage of residual solid mass to the sample mass. Two parallel determinations are performed, and the average value is taken. All solid content data in this application were determined under these uniform conditions. When the system contains semi-volatile components such as propylene glycol, the measured solid content may be lower than the theoretical solid content calculated based on the input.

[0051] Example 1:

[0052] Preparation of functionalized dihydroxy chain extender M-C18

[0053] 1.1 Structural Design

[0054] This embodiment provides a functionalized dihydroxy chain extender that simultaneously contains a long-chain alkyl structure, a latent catechol structure, and a bisquaternary ammonium salt structure. Its structural features are as follows:

[0055] The molecule contains primary hydroxyl groups at both ends, which can react with isocyanate groups to achieve covalent fixation of the functional structure in the polyurethane backbone;

[0056] The molecule contains a bis-quaternary ammonium salt structure bridged by hexamethylene, which provides a permanent ionization dispersion site for waterborne polyurethane that is independent of the system pH.

[0057] The molecule contains long-chain alkyl structures on both sides, which are used to improve the interfacial compatibility between polyurethane binders and low surface energy polyolefin films.

[0058] The molecule contains a catechol structure protected by isopropylidene, which forms a free catechol group after deprotection.

[0059] 1.2 Synthetic Route

[0060] Procedure 1: The catechol group of 3,4-dihydroxybenzaldehyde is protected with acetal; the resulting isopropylidene-protected 3,4-dihydroxybenzaldehyde is condensed with a long-chain alkylamine to form an imine intermediate, which is then reduced to obtain a long-chain alkyl secondary amine intermediate containing the isopropylidene-protected catechol group, the chemical structure of which is as follows:

[0061] ;

[0062] Step 2: The secondary amine intermediate undergoes N-alkylation with 6-bromo-1-hexanol to yield the tertiary amine intermediate, whose chemical structure is as follows:

[0063] ;

[0064] Step 3: The tertiary amine intermediate undergoes quaternization with 1,6-dibromohexane, bridging the two tertiary amine centers via a hexamethylene segment to obtain a functionalized dihydroxy chain extender with the following chemical structure:

[0065] ;

[0066] The long-chain alkylamine monomer is selected from one of n-pentadecanamine, n-hexadecamine, n-heptadecamine, and n-octadecamine. R is one of n-pentadecanyl, n-hexadecyl, n-heptadecyl, and n-octadecyl. Taking n-octadecylamine as an example, the resulting product is abbreviated as M-C18, and its chemical structure is as follows:

[0067] ;

[0068] The molecular formula of M-C18 is C 74 H 134 N2O6Br2 has a relative molecular mass of 1307.7 g / mol, a theoretical hydroxyl value of 85.8 mg KOH / g, and a theoretical bromine content of 12.22 wt%.

[0069] 1.3 Preparation steps of functionalized dihydroxy chain extenders

[0070] (1) Isopropylidene protected 3,4-dihydroxybenzaldehyde

[0071] Add 5.50 g (39.8 mmol) of 3,4-dihydroxybenzaldehyde and 60 mL of anhydrous acetone to a dry reaction flask and stir at room temperature until dissolved; add 0.50 g (2.9 mmol) of anhydrous p-toluenesulfonic acid and stir at room temperature for 10 min. Dissolve 6.00 g (57.6 mmol, 1.45 equivalent) of 2,2-dimethoxypropane in 50 mL of anhydrous acetone and transfer to a constant pressure dropping funnel.

[0072] The gas phase space of the apparatus was purged with nitrogen and nitrogen protection was maintained; the temperature was lowered to 0°C in an ice-water bath, and 2,2-dimethoxypropane-acetone solution was added dropwise at 1.5 mL / min with stirring; after the addition was complete, the mixture was stirred at 0°C for 30 min, the ice bath was removed and the temperature was allowed to rise naturally to room temperature (25°C) for 2 h, and the reaction was continued. Samples were taken every 0.5 h for TLC monitoring (ethyl acetate / petroleum ether = 1:3, V / V).

[0073] Saturated sodium bicarbonate solution was slowly added under ice-water bath to quench and neutralize p-toluenesulfonic acid until the pH of the aqueous phase was approximately 7 and no obvious bubbles were observed. Most of the acetone was removed by rotary evaporation under reduced pressure. The residue was extracted three times with ethyl acetate (30 mL each time). The organic phases were combined, washed once with saturated brine, dried over anhydrous sodium sulfate for 2 h, filtered, and rotary evaporated under reduced pressure. The crude product was purified by silica gel column chromatography (ethyl acetate / petroleum ether elution gradient 1:5 → 1:2), dried under vacuum, and yielded 5.82 g of a white to pale yellow solid, with a yield of 82%.

[0074] (2) Imine intermediate

[0075] Add 5.30 g (29.74 mmol) of the product from step (1) and 50 mL of anhydrous ethanol to a dry reaction flask and stir at room temperature for 10 min to dissolve. Add 2 g of 4 Å molecular sieve activated at 300 °C for 4 h and cooled to room temperature under dry conditions and 0.15 mL of glacial acetic acid and stir at room temperature for 10 min.

[0076] 8.20 g (30.43 mmol, 1.02 equivalents) of n-octadecylamine was added to 100 mL of anhydrous ethanol and dissolved by stirring at 50 °C. The solution was then transferred to a constant-pressure dropping funnel with a constant-temperature jacket (50 °C). The apparatus was purged with nitrogen and kept under protection. The system was heated to 50 °C, and the n-octadecylamine ethanol solution was added dropwise at 2 mL / min. During the addition, the feed solution was kept clear to avoid precipitation of n-octadecylamine. After the addition was complete, the temperature was raised to 60 °C and the reaction was carried out for 5 h. TLC (ethyl acetate / petroleum ether = 1:8, v / v) was taken every 1 h for monitoring.

[0077] The mixture was cooled to room temperature, filtered to remove the molecular sieve, and the filtrate was evaporated under reduced pressure to remove ethanol. The crude product was purified by silica gel column chromatography (elution with ethyl acetate / petroleum ether gradient 1:10 → 1:6, with the eluent containing 0.5% triethylamine by volume) to give 11.30 g of a white waxy solid, with a yield of 88%.

[0078] (3) Secondary amine intermediate

[0079] 5.00 g (11.64 mmol) of the imine intermediate was added to 50 mL of anhydrous ethanol in a dry reaction flask and stirred at room temperature for 10 min to dissolve. Nitrogen was used to purge and maintain the protective atmosphere. The mixture was then cooled to 0 °C in an ice-water bath. 0.661 g (17.5 mmol, 1.5 equivalents) of sodium borohydride was added in portions, with the system temperature controlled to not exceed 5 °C. After the addition was complete, the mixture was stirred at 0 °C for 30 min. The ice bath was removed, and the mixture was allowed to rise naturally to room temperature for 3 h. TLC (ethyl acetate / petroleum ether = 1:4, V / V, containing 0.5% triethylamine) was monitored every h.

[0080] The mixture was returned to an ice-water bath, and 5–10 mL of acetone was slowly added dropwise under effective venting and temperature control until no further significant gas escaped. 60 mL of water was slowly added, and most of the ethanol and acetone were removed by rotary evaporation under reduced pressure. The residue was extracted three times with dichloromethane (30 mL each time), and the organic phases were combined, washed once with saturated brine, dried over anhydrous sodium sulfate for 2 hours, filtered, and then rotary evaporated under reduced pressure. The crude product was purified by silica gel column chromatography (eluting with a gradient of ethyl acetate / petroleum ether 1:6 → 1:3, containing 0.5% triethylamine), dried under vacuum, and yielded 4.67 g of a white solid, with a yield of 93%.

[0081] (4) Tertiary amine intermediate

[0082] Add 4.30 g (9.96 mmol) of the secondary amine intermediate to 40 mL of anhydrous acetonitrile in a dry reaction flask and stir at room temperature for 10 min to dissolve. Add 2.06 g (14.9 mmol, 1.5 equivalents) of anhydrous potassium carbonate and stir at room temperature for 10 min. Dissolve 1.99 g (11.0 mmol, 1.10 equivalents) of 6-bromo-1-hexanol in 10 mL of anhydrous acetonitrile and transfer to a constant pressure dropping funnel. Connect a reflux condenser, purge with nitrogen, and maintain protection.

[0083] 6-Bromo-1-hexanol acetonitrile solution was added dropwise at 1 mL / min with stirring; after the addition was complete, the temperature was raised to 75 °C and the reaction was carried out for 12 h. Samples were taken every 2 h for TLC monitoring (ethyl acetate / petroleum ether = 1:3, V / V, containing 0.5% triethylamine), and ninhydrin colorimetric method was used to assist in the determination of secondary amine residue; the endpoint was determined when the secondary amine spots basically disappeared and the ninhydrin colorimetric method showed negative or only a weak residue.

[0084] The mixture was cooled to room temperature, filtered to remove inorganic salts, and the filter cake was washed with a small amount of acetonitrile. The filtrate and washings were combined, and acetonitrile was removed by rotary evaporation under reduced pressure. The residue was dissolved in 60 mL of dichloromethane and washed once each with deionized water and saturated brine. The organic phase was dried over anhydrous sodium sulfate for 2 h, filtered, and then rotary evaporated under reduced pressure. The crude product was purified by silica gel column chromatography (eluting with a gradient of ethyl acetate / petroleum ether 1:8 → 1:2, containing 0.5% triethylamine), and dried under vacuum to give 4.01 g of a pale yellow viscous substance, with a yield of 76%.

[0085] (5) Chain extender M-C18

[0086] Add 5.00 g (9.40 mmol) of tertiary amine intermediate to 40 mL of anhydrous acetonitrile in a dry reaction flask and stir at room temperature for 10 min to dissolve. Dissolve 1.10 g (4.51 mmol, tertiary amine / dibromohexane molar ratio 2.08:1) of 1,6-dibromohexane in 10 mL of anhydrous acetonitrile and transfer to a constant pressure dropping funnel. Purge with nitrogen and maintain protection.

[0087] 1,6-dibromohexane acetonitrile solution was added dropwise at 1 mL / min with stirring; after the addition was complete, the temperature was raised to 60 °C and the reaction was carried out for 15 h. Samples were taken every 3 h for TLC monitoring (dichloromethane / methanol = 10:1, V / V).

[0088] Cool to room temperature and remove acetonitrile by rotary evaporation under reduced pressure; dissolve the crude product in 20 mL of methanol, slowly add 200 mL of anhydrous diethyl ether with stirring, stir at room temperature for 30 min, let stand in an ice-water bath for 2 h, filter to collect the precipitated solid, dry under vacuum to obtain 5.01 g of white powdery bisquaternary ammonium salt type chain extender M-C18, yield 85% (based on 1,6-dibromohexane).

[0089] If the quaternization is incomplete (as indicated by the failure of the quality control items listed in Table 1), the quaternization temperature can be increased to 75-80℃ and the time extended to 24-36h, or the crude product can be repeatedly precipitated in a methanol / anhydrous diethyl ether system 2-3 times before testing.

[0090] 1.4 Structural Validation and Quality Control

[0091] 1 H NMR (DMSO-d6, 400MHz) δ:

[0092] 0.87~0.89 (t, 6H, 2×-CH3 of C 18 );

[0093] 1.24~1.33 (m, 60H, 2×C) 18 Chain C3 to C17 positions -CH2-).

[0094] 1.35–1.43 (m, 16H, 12H of hydroxyhexyl C3 / C4 / C5 position -CH2- and 4H of bridging hexyl C3 / C4 position -CH2-).

[0095] 1.62 (s, 12H, 2× isopropylidene-C(CH3)2-);

[0096] 1.71~1.77 (m, 12H, quaternary ammonium nitrogen ortho-β-CH2:C) 18 4H at the C2 position of the hydroxyhexyl group, and 4H at the C2 / C5 position of the bridging hexyl group.

[0097] 3.18~3.20 (m, 12H, 6×N⁺-CH2-);

[0098] 3.42~3.46 (m, 4H, 2×-CH2-OH);

[0099] 4.31~4.32 (t, 2H, 2×-OH);

[0100] 4.54 (s, 4H, 2×Ar-CH2-N⁺);

[0101] 6.98–7.07 (m, 6H, 2×aromatic ring 3H).

[0102] The total integral is 6 + 60 + 16 + 12 + 12 + 12 + 4 + 2 + 4 + 6 = 134H, which is the same as the molecular formula C. 74 H 134 N₂O₆Br₂ has the same number of hydrogen atoms. Among them, C... 18 The α-CH2 of the chain is attributed to N at δ 3.18–3.20. +-CH2 and β-CH2 belong to the δ1.71–1.77 range, therefore the δ1.24–1.33 range corresponds only to each C signal. 18 Fifteen methylene groups at positions C3 to C17 of the chain.

[0103] Elemental analysis (Vario EL Ⅲ): Theoretical values: C 67.97%, H 10.33%, N 2.14%; Measured values: C 67.88%, H 10.25%, N 2.10%.

[0104]

[0105]

[0106] M-C18 must meet all the requirements in Table 1 to be used in polyurethane synthesis. (Based on elemental analysis...) 1 The significant low-field shift of the benzylic methylene singlet at δ4.54 in HNMR, along with the determination of bromine content and residual tertiary amine, indicate that the bis-quaternary ammonium salt structure has been successfully constructed and the degree of quaternization meets the requirements.

[0107] Example 2:

[0108] Preparation of cationic aqueous polyurethane emulsion I

[0109] This embodiment employs a prepolymer (acetone) method: NCO-terminated prepolymers are prepared using IPDI (isophorone diisocyanate) and PTMG (hydroxyl value 112.2 mg KOH / g); pre-chain extension is performed using M-C18, followed by further chain extension using 1,4-butanediol (BDO); ​​emulsification is first performed by phase inversion and acetone is removed, then the catechol protecting group is removed by acid catalysis in the aqueous phase, and the solid content is adjusted after neutralization to obtain emulsion I.

[0110] The molar ratio of IPDI:PTMG:M-C18:BDO is 2.01:1:0.3:0.7.

[0111] Key Process Description (Necessity of the Deprotection Sequence): The acid-catalyzed removal of the isopropylidene protecting group is a reversible hydrolysis reaction, with acetone as the hydrolysis product. If deprotection is carried out directly in the acetone solution, the hydrolysis equilibrium is pushed to the protected state due to the large excess of acetone in the system, making effective deprotection difficult. Therefore, this invention requires deprotection to be carried out in the aqueous phase after the acetone has been substantially removed. During the deprotection process, the generated acetone is removed by heating and nitrogen purging, shifting the equilibrium towards deprotection.

[0112] Key process description (role of acid): In this invention, hydrochloric acid is a catalyst for ketal hydrolysis, not a stoichiometric reactant. Its role is to provide and maintain the required hydrogen ion concentration, and it is not consumed during deprotection. Therefore, the amount of acid added is based on the catalytic amount to maintain the pH of the system, not on the equivalent amount of the protecting group; correspondingly, the amount of neutralizing alkali required after deprotection is only corresponding to the amount of acid added.

[0113] (1) Raw material pretreatment

[0114] PTMG was dehydrated at 100℃ and a vacuum of -0.095 MPa for 2 hours, then cooled and sealed under nitrogen protection for later use. BDO and M-C18 were vacuum dried at 50℃ and -0.095 MPa, respectively, and the moisture content was determined by the Karl Fischer coulometric method. When the moisture content was below 0.10 wt%, the containers were cooled and sealed for later use. All reaction vessels, stirrers, dropping funnels, condensers, and feeding devices were dried at 105℃ and then cooled and placed in a dry nitrogen environment for later use.

[0115] (2) NCO-terminated polyurethane prepolymer

[0116] Add 4.47 g (20.1 mmol) IPDI, 10.00 g (10.0 mmol) PTMG and 100 mL anhydrous acetone to a dry reaction flask, stir at room temperature for 20 min, purge with dry nitrogen for 20 min to replace air and water vapor, and maintain a slight positive pressure nitrogen protection throughout the process.

[0117] Add 5.9 mg of bismuth neodecanoate catalyst (bismuth content 28.91 wt%), which is 5.9 mg × 28.91% = 1.71 mg based on metallic bismuth. The solid mass of the resin in this stage is 14.47 g, so the catalyst dosage based on metallic bismuth is approximately 118 mg / kg. The heating bath temperature is controlled at 60℃ to stabilize the acetone under reflux. Samples are taken every 30 minutes, and the NCO content is determined according to the di-n-butylamine back titration method (Method A) specified in HG / T 2409.

[0118] The theoretical remaining NCO content in this stage is (40.2−20.0)×42÷(1000×14.47)×100%=5.86%. When the measured NCO reaches this value and the difference between two consecutive measurements does not exceed 0.05 percentage points, the prepolymerization is considered complete. The reaction time is about 4.5 hours.

[0119] Optional catalysts: Bismuth octoate or zirconium-based catalysts can also be used, with a dosage of 100-150 mg / kg of resin solids based on metal content; or 50 μL of dibutyltin dilaurate (DBTDL) can be used, which can shorten the prepolymerization time to about 3 hours. However, due to the risks of migration and regulatory restrictions associated with organotin catalysts, bismuth-based catalysts are preferred for use in food packaging printing. It should be noted that non-tin catalysts have a weaker inhibitory effect on the trimerization side reaction of isocyanates than organotin catalysts. When using non-tin catalysts, the control measures described in step (3) should be strictly implemented.

[0120] (3) Stepwise chain extension reaction

[0121] Cool the prepolymer acetone solution to 40°C. Add 3.92 g (3.00 mmol) of M-C18 to 50 mL of anhydrous acetone and stir at 40°C for 30 min. If M-C18 is not completely dissolved (visible insoluble matter or turbidity), add 10%–30% of the volume of anhydrous acetonitrile (10 mL of anhydrous acetonitrile in this example) as a co-solvent, and continue stirring at 40°C until the system is clear. The co-solvent must be pre-dried using a 4 Å molecular sieve and have a moisture content of less than 0.03 wt%.

[0122] M-C18 solution was added dropwise to the prepolymer system at a rate of 1 mL / min with stirring, keeping the system clear during the addition. After the addition was complete, the temperature was raised to reflux with acetone (heating bath temperature 60℃, actual system temperature 56±2℃) to continue the reaction. At this stage, the resin solids mass was 18.39 g, and the theoretical remaining NCO content was 3.24%. NCO was measured every 30 min. Pre-chain extension was considered complete when the measured value reached the theoretical value and the difference between two consecutive values ​​did not exceed 0.05 percentage points. The reaction time was approximately 2.5 h.

[0123] The temperature was lowered to 40℃, and 5 mL of anhydrous acetone solution containing 0.63 g (6.99 mmol) BDO was added. The temperature was then raised again to reflux with acetone to continue chain extension. The resin solids content at this stage was 19.02 g, with a theoretical remaining NCO content of 0.048%. The NCO content was determined using HG / T 2409 Method A, and Fourier transform infrared spectroscopy was used to monitor the NCO content at 2270 cm⁻¹. -1 Characteristic absorption peaks of isocyanates in the vicinity.

[0124] When the NCO content drops to near the theoretical residual value, combined with the NCO content and 2270cm -1 The characteristic absorption peaks of nearby isocyanates indicate the reaction progress. For systems with a theoretical residual NCO content below 0.10 wt%, the reaction continues until the residual NCO content is <0.10 wt%, and the peak value at 2270 cm⁻¹ is reached. -1Nearby characteristic peaks basically disappeared; for systems where the theoretical residual NCO content is still not less than 0.10 wt% due to the NCO / OH ratio being greater than the stoichiometric ratio, after the small molecule diol chain extension reaches the theoretical endpoint, add n-butanol equivalent to 1.0 to 1.2 times the molar amount of excess NCO, and react at 50°C for about 1 hour to cap the chain until the residual NCO content is <0.10 wt% and the 2270 cm⁻¹ peak value is reached. -1 The nearby characteristic peaks have basically disappeared.

[0125] Side reaction control (necessary process conditions): The quaternary ammonium bromide in M-C18 has a potential catalytic effect on the trimerization and urea-formylation of isocyanates, which may cause unintended branching or even gelation under prolonged high temperature. Therefore, the following are specified: (a) Temperature control - the heating bath temperature during the chain extension stage shall not exceed 60℃, the actual measured temperature of the system shall be 56±2℃, and the temperature shall not exceed 65℃ throughout the process; (b) Viscosity monitoring - from the time M-C18 is dropped, samples shall be taken every 30 minutes simultaneously with the NCO determination, and the apparent viscosity shall be measured at 25℃ and 60r / min using a rotational viscometer (LV series No. 2 rotor). The following situations are considered abnormal branching signs: (c) Viscosity increase exceeding 50% of the previous measurement value within a single sampling interval; system wall adhesion, stringing, or a sudden increase in stirring torque; visible gel particles, insoluble matter, or the system changing from clear to turbid; (d) Abnormal handling—immediately remove heating and cool to below 40°C, add 20–50 mL of anhydrous acetone for dilution, and continue the reaction at 50–55°C until the endpoint after the system returns to clarity and viscosity stabilizes; (e) Infrared-assisted discrimination—monitor 1690–1710 cm⁻¹. -1 The carbonyl absorption peak of the nearby isocyanurate should not increase significantly; (e) Preferred option: the pre-expansion temperature of M-C18 can be reduced to 50-55°C and the time extended to 3-5 h.

[0126] After the above control, the resulting solution should remain clear and homogeneous, and no visible gel particles should be observed after filtration through a 100-mesh sieve; in this embodiment, the viscosity gradually increased from about 35 mPa·s to about 210 mPa·s throughout the chain extension process without any abnormalities.

[0127] Molecular weight controllability: In this example, the total hydroxyl content was 39.98 mmol, and the NCO / OH molar ratio was 1.01, close to the stoichiometric equivalent. The resulting polyurethane had a high molecular weight and was sensitive to stoichiometric accuracy and moisture content. To improve batch reproducibility and avoid gelation, one of the following measures can be adopted: (a) Control the NCO / OH ratio to 1.02–1.05. After the small molecule diol chain extension reaches the theoretical endpoint, add n-butanol equivalent to 1.0–1.2 times the excess NCO molar amount and react at 50°C for 1 hour to block the residual NCO; (b) Maintain the NCO / OH ratio at approximately 1.01, but add BDO in two batches: first add 80% of the amount and react until the NCO is close to the theoretical value, then measure the actual NCO and add the remaining BDO according to the measured value; (c) Before adding all hydroxyl-containing raw materials, the moisture content was determined by the Karl Fischer method, and the IPDI dosage was corrected according to the consumption of 2 mmol of NCO per 1 mmol of water. The weight-average molecular weight of the resulting polyurethane should preferably be 3 × 10⁻⁶. 4 ~1×10 5 g / mol (GPC method, DMF + 0.01 mol / L LiBr as mobile phase, polystyrene standard, 40℃). The measured Mw in this example is 5.2 × 10⁻⁶ g / mol (GPC method, DMF + 0.01 mol / L LiBr as mobile phase, polystyrene standard, 40℃). 4 Mw / Mn is 2.1.

[0128] (4) Conversely, emulsification and acetone removal

[0129] Cool to 25℃. Determine the residual NCO content and 2270 cm⁻¹ content using HG / T 2409 Method A and infrared spectroscopy, respectively. -1 Characteristic absorption peak; emulsification can only be carried out when the residual NCO is less than 0.10 wt% and the characteristic peak has basically disappeared.

[0130] Add 50 mL of acetone to reduce the viscosity of the system, transfer it to a mechanical stirrer, and slowly add 35 mL of deionized water dropwise at 0.8 mL / min under 1200 rpm to allow the system to gradually undergo phase inversion emulsification. With the addition of water, the system gradually transforms from a homogeneous transparent or semi-transparent organic phase into a homogeneous milky white aqueous dispersion. Phase inversion is considered complete when the system can be rapidly and uniformly dispersed in deionized water, the viscosity no longer increases significantly after adding small amounts of water, and there are no visible flocculants, gel particles, or phase separation.

[0131] Increase the rotation speed to 3000 r / min and continue high-speed shear emulsification for 30 min. Use the cooling jacket to control the system temperature below 35℃ to obtain cationic polyurethane crude emulsion.

[0132] Acetone and some water were removed by rotary evaporation under reduced pressure at 45℃ and -0.09MPa. The residual acetone was measured according to the following method, and the next step could only be carried out after the residual acetone was controlled to be below 0.5wt%. In this example, the residual acetone after removal was 0.15wt%.

[0133] (5) Acid-catalyzed removal of catechol protecting groups in aqueous phase

[0134] Add deionized water to adjust the total mass of the system to approximately 76g (solid content approximately 25wt%) to ensure good system flowability and provide a sufficient aqueous environment during the deprotection process.

[0135] Under mechanical stirring (600 rpm), nitrogen protection, and light-protected conditions, 2 mol / L hydrochloric acid aqueous solution was slowly added dropwise at a rate of 0.5 mL / min. The hydrochloric acid was added according to the catalytic dosage, with a dosage standard of 0.05 mmol HCl per gram of resin solid. In this example, the resin solid was 19.02 g, corresponding to approximately 0.95 mmol HCl; therefore, 0.50 mL of 2 mol / L hydrochloric acid aqueous solution (1.00 mmol HCl) was added. After the addition was complete, the pH of the system was measured; it should fall within the range of 1.5–2.5 (actual pH 1.8). If the pH was higher than 2.5, 2 mol / L hydrochloric acid was added in increments of 0.10 mL until the standard was reached, with the total added amount not exceeding 0.10 mmol HCl per gram of resin solid. The amount of hydrochloric acid added, calculated per gram of resin solids, can be 0.03–0.10 mmol H⁺. When the addition amount is below 0.03 mmol / g, the system pH is difficult to maintain stably below 2.5, and the deprotection rate decreases significantly. When the addition amount is above 0.10 mmol / g, residual acid increases, and the amount of neutralized alkali increases accordingly, which is detrimental to the oxidative stability of catechol. In this example, the addition amount is 0.05 mmol / g. The system temperature is controlled not to exceed 30°C during the dropping process.

[0136] The system was heated to 55±2℃ and stirred for 6 h under nitrogen protection, light avoidance, and weak nitrogen headspace purging. Samples were taken every 1 h, and after freeze-drying, the samples were dissolved in DMSO-d6. The deprotection rate was calculated by the integral change of the isopropylidene methyl single peak (12H, s) near δ1.58~1.66, using the aromatic ring proton peak as an internal reference. At the same time, the increase of catechol characteristic absorption near 280 nm was monitored by UV-Vis spectrophotometry as an auxiliary criterion.

[0137] Deprotection is considered complete when the deprotection rate reaches 96% or higher and the content of free catechol groups, calculated based on the solid mass of the deprotected polyurethane, reaches 0.30–0.60 mmol / g. If the deprotection rate is less than 96% after 6 hours, the generated acetone can be removed by short-term vacuum distillation at 45℃ and -0.09 MPa to promote equilibrium shift. The reaction can then continue at 55℃ for 2–4 hours, with a total reaction time not exceeding 12 hours. If necessary, the pH can be adjusted to 1.5–1.8.

[0138] After deprotection, the temperature was lowered to 25°C. Neutralization was then carried out by slowly adding a 10 wt% triethanolamine aqueous solution at a rate of 0.2–0.5 mL / min under mechanical stirring and nitrogen protection. The amount of neutralizing alkali was calculated as 1.02–1.10 times the molar amount of hydrochloric acid added. In this example, 1.00 mmol of HCl was added, corresponding to 1.02–1.10 mmol (0.152–0.164 g) of triethanolamine, i.e., 1.5–1.6 mL of a 10 wt% triethanolamine aqueous solution (1.5 mL in this example). During the addition, 1.00 g of the reaction solution was diluted with 9.00 g of deionized water, and the pH was measured. The addition was stopped when the pH of the diluted solution reached 5.8–6.2. Neutralization was used to reduce the adverse effects of residual acid on the stability of the polyurethane chain segments and the oxidative stability of the catechol groups.

[0139] Neutralizing agent selection guidelines: Triethanolamine has a high boiling point and is essentially non-volatile, which can prevent pH drop caused by the volatilization of alkaline components during subsequent vacuum concentration, and also avoid the residue and odor problems of volatile amines in the finished membrane. Triethylamine (5wt% aqueous solution, added at the same molar ratio) can also be used, but the pH should be monitored every 15 minutes during the concentration process. If the pH of the diluted solution drops below 5.5, neutralizing agent should be added to restore it.

[0140] (6) Post-processing

[0141] The mixture was concentrated under reduced pressure at 45℃ and -0.09MPa to a total mass of approximately 42g. The solid content was determined using a standardized method, and the solid content was adjusted to 45wt% by adding deionized water or by further concentration. After filtration through a 100-mesh sieve, cationic aqueous polyurethane emulsion I containing catechol and octadecyl structures was obtained.

[0142] Preferred embodiment (antioxidant protection): To inhibit the oxidation of free catechol during storage, one or more of the following adjuvants can be added after the solid content adjustment: 0.05-0.20 wt% of ascorbic acid or sodium isoascorbate (based on the total mass of the emulsion), 0.02-0.10 wt% of sodium metabisulfite, and 0.02-0.05 wt% of disodium ethylenediaminetetraacetate (used to chelate residual bismuth, iron, and other metal ions in the system). After addition, stir at 500 rpm for 20 min.

[0143] The resulting emulsion was purged with nitrogen headspace and then stored in a dark, sealed container, with the pH controlled at 5.5–6.5.

[0144] Application range of solid content: The solid content of the emulsion described in this invention can be 25-50 wt%; when the viscosity of the system is too high or it exhibits obvious thixotropy, the solid content can be adjusted to 30-40 wt%, and the weight parts of the emulsion and deionized water in the ink formulation of Example 5 can be adjusted accordingly to keep the resin solid content in the ink consistent.

[0145] The measurement basis for the free catechol group content and quaternary ammonium nitrogen content is calculated based on the mass of the polyurethane solids after deprotection. During the deprotection process, the mass of the resin solids decreases by 40.06 g / mol for each isopropylidene protecting group removed. In this example, the input resin solids were 19.02 g, containing 6.00 mmol of catechol structure and 6.00 mmol of quaternary ammonium nitrogen, with a deprotection rate of 96.5%. The mass reduction due to the removal of protecting groups was approximately 6.00 × 0.965 × 40.06 ≈ 0.23 g, resulting in approximately 18.79 g of polyurethane solids after deprotection. Therefore, the free catechol group content was 0.308 mmol / g, and the quaternary ammonium nitrogen content was 0.319 mmol / g.

[0146] Example 3:

[0147] The preparation of cationic aqueous polyurethane emulsion II differs from that in Example 2 in that:

[0148] The molar ratio of IPDI:PTMG:M-C18:BDO is 2.01:1:0.5:0.5.

[0149] 6.54g (5.00mmol) M-C18 replaced 3.92g M-C18; 0.45g (4.99mmol) BDO replaced 0.63g BDO; total hydroxyl content 39.99mmol, NCO / OH = 1.01;

[0150] The second stage resin solids weighed 21.01g, with a theoretical remaining NCO content of 2.04%; the third stage resin solids weighed 21.46g, with a theoretical remaining NCO content of 0.041%.

[0151] The amount of water used for phase inversion emulsification was adjusted to 40 mL (as the amount of M-C18 increases, the content of permanent cationic groups in the molecular chain increases, and the hydrophilicity and phase inversion behavior of the system change. At the same time, the increase in the amount of M-C18 increases the viscosity of the acetone phase in the system. In order to maintain the shear uniformity during the phase inversion process, the amount of water added needs to be increased accordingly. It should be noted that the amount of water required for phase inversion is not determined by hydrophilicity alone. Therefore, the amount of water used in the M-C4 system (17.85 g resin) in Comparative Example 5, which has strong hydrophilicity but low viscosity, is 30 mL, which does not contradict this example).

[0152] Before deprotection, add deionized water to adjust the solid content of the system to about 25 wt% (total system mass about 86 g); add 0.55 mL of 2 mol / L hydrochloric acid aqueous solution (1.10 mmol) based on 0.05 mmol HCl per gram of resin solids, so that the pH is between 1.5 and 2.5;

[0153] Neutralize by adding 1.7 mL of 10 wt% triethanolamine aqueous solution (approximately 1.14 mmol, which is 1.04 times that of HCl) until the pH of the diluted solution is 5.8–6.2.

[0154] The remaining raw materials, steps, and process conditions were the same as in Example 2. The resulting emulsion was designated as Emulsion II, with a deprotection rate of 97.1%.

[0155] According to the method in Example 2, the content of free catechol groups in this example is 0.461 mmol / g and the content of quaternary ammonium nitrogen is 0.475 mmol / g.

[0156] Example 4:

[0157] The preparation of cationic aqueous polyurethane emulsion III differs from that in Example 2 in that:

[0158] The molar ratio of IPDI:PTMG:M-C18:BDO is 2.01:1:0.7:0.3.

[0159] 9.15g (7.00mmol) M-C18 replaced 3.92g M-C18; 0.27g (3.00mmol) BDO replaced 0.63g BDO; total hydroxyl content 39.99mmol, NCO / OH = 1.01;

[0160] The second stage resin solids weighed 23.62g, with a theoretical remaining NCO content of 1.10%; the third stage resin solids weighed 23.89g, with a theoretical remaining NCO content of 0.037%.

[0161] Conversely, adjust the amount of water used for transemulsification to 45 mL;

[0162] Before deprotection, adjust the solid content of the system to approximately 25 wt% (total system mass approximately 96 g); add 0.60 mL of 2 mol / L hydrochloric acid aqueous solution (1.20 mmol), adjusting the pH to 1.5–2.5;

[0163] Neutralize by adding 1.9 mL of 10 wt% triethanolamine aqueous solution (approximately 1.27 mmol, which is 1.06 times that of HCl) until the pH of the diluted solution is 5.8–6.2.

[0164] Everything else was the same as in Example 2. The resulting emulsion was designated as Emulsion III, with a deprotection rate of 97.4%.

[0165] According to the method in Example 2, the content of free catechol groups in this example is 0.584 mmol / g and the content of quaternary ammonium nitrogen is 0.600 mmol / g.

[0166]

[0167]

[0168] Note: The viscosity listed in Table 2 is the viscosity of the final aqueous emulsion (solid content 45wt%); the viscosity of the polyurethane acetone solution in Example 2 (3) which increased from about 35 mPa·s to about 210 mPa·s is the viscosity of the chain extension stage. The two systems are different and are not comparable.

[0169] Range of optional raw materials and proportions:

[0170] With the amount of polyether diol as 1, the amount of functionalized dihydroxy chain extender is x, and the amount of small molecule diol chain extender is 1−x, where x is 0.3 to 0.7; and NCO / OH is 1.00 to 1.05.

[0171] The diisocyanate is preferably an aliphatic or alicyclic diisocyanate, and can be selected from hexamethylene diisocyanate (HDI) and dicyclohexylmethane diisocyanate (HMDI) in addition to IPDI. Aromatic diisocyanates such as toluene diisocyanate and diphenylmethane diisocyanate are not suitable because they easily cause yellowing of the ink layer, and the primary aromatic amines in the hydrolysis products are food contact migration controlled substances, which are not suitable for the application scenario of this invention.

[0172] The polyether diol can be selected from polytetrahydrofuran diol (PTMG) or polypropylene glycol (PPG) with a number average molecular weight of 1000-2000; PTMG with a number average molecular weight of 1000 (measured hydroxyl value 112.2 mg KOH / g) was used in all the above examples and comparative examples.

[0173] The small molecule diol chain extender, in addition to 1,4-butanediol, can be selected from ethylene glycol, 1,6-hexanediol, and 1,4-cyclohexanediethanol.

[0174] In the synthesis of chain extenders, dibromoalkane can be selected from 1,4-dibromobutane and 1,8-dibromooctane, in addition to 1,6-dibromohexane; bromool can be selected from 4-bromo-1-butanol and 8-bromo-1-octanol, in addition to 6-bromo-1-hexanol. The corresponding dichloro derivatives are not preferred because their alkylation activity is significantly lower than that of the brominated derivatives.

[0175] The implementation rules for using the above-mentioned alternative raw materials are as follows: (i) The amounts of diisocyanate and polyether diol are calculated based on their actual NCO equivalent and measured hydroxyl value, respectively, and measured in conjunction with the amount of hydroxyl provided by the functionalized dihydroxy chain extender and the small molecule diol, so that the molar ratio of isocyanate groups to all hydroxyl groups (NCO / OH) is maintained at 1.00–1.05; (ii) After the chain extender is replaced, the amount of small molecule diol is recalculated based on its measured hydroxyl value, so that the total hydroxyl content remains unchanged; (iii) The theoretical remaining NCO content at each stage is recalculated according to the formula listed in the measurement standard, and the endpoint criterion remains unchanged; (iv) The amount of acid used for deprotection is still calculated as 0.05 mmol HCl per gram of resin solids, with a pH of 1.5–2.5, and the amount of alkali neutralized is calculated as 1.02–1.10 times the amount of acid. After adjustments according to the above rules, the remaining process steps and judgment criteria can be directly used.

[0176] Example 5:

[0177] Water-based ink compositions for Baili film printing

[0178] 5.1 Compatibility requirements for additives (essential condition)

[0179] The waterborne polyurethane binder described in this invention is cationic, and its emulsion particles are positively charged. The pigment pre-dispersions, dispersants, and other additives used in conjunction with it should all be products that are stable by steric hindrance mechanisms, have no effect on pH-sensitive systems, or are explicitly recommended by the supplier for use in cationic base systems. Dispersants containing anionic groups such as carboxylates, sulfonates, and phosphates should not be used, nor should commercially available color pastes or commercially available waterborne polyurethane dispersions that are stable by anionic mechanisms be used (most commercially available waterborne polyurethane dispersions are anionic products that are neutralized by dimethylolpropionic acid to form salts), otherwise flocculation, thickening, or demulsification will occur due to the neutralization of opposite charges.

[0180] Compatibility pre-screening method: Mix the candidate additives with the cationic aqueous polyurethane emulsion of the present invention according to the actual formulation ratio, stir at 1000 r / min for 10 min, and let stand for 24 h. Visually, there should be no flocculation, layering, clumping, or obvious thickening; the Zeta potential of the mixed system should remain positive and not lower than +20 mV; the viscosity change rate before and after mixing should not exceed 30%. Only additives that pass the pre-screening can be used in the ink composition of the present invention.

[0181] It should be noted that the additives stabilized by anionic mechanisms are excluded in this invention. Some polymeric dispersants stabilized by steric hindrance mechanisms (such as DISPERBYK-2012 used in this invention, with an amine value of approximately 7 mg KOH / g and a small amount of acid value) may contain trace amounts of acidic groups, but their stabilization mechanism is steric hindrance rather than electrostatic repulsion. After passing the aforementioned compatibility pre-screening (the zeta potential of the mixed system remains positive and not lower than +20 mV, no flocculation occurs after 24 hours, and the viscosity change rate does not exceed 30%), they can be used. The specific active ingredient content, amine value, and acid value of the additives are subject to the supplier's current technical data sheet.

[0182] 5.2 Preparation of Pigment Predispersion (Self-made)

[0183] By weight: 20 parts pigment (phthalocyanine blue 15:3), 12 parts DISPERBYK-2012, 5 parts propylene glycol, 0.2 parts BYK-024, and 62.8 parts deionized water.

[0184] The following feeding method is used: first, deionized water and propylene glycol are mixed, and the dispersant is slowly added while stirring at 1000 r / min for 10 min until uniform; then, the pigment is slowly added and the speed is increased to 2000 r / min for pre-dispersion for 30 min; then, it is transferred to a horizontal sand mill and milled with 0.6-0.8 mm zirconia beads. During the sand milling process, the system temperature is controlled by cooling water to not exceed 35°C until the fineness measured by the scraper fineness gauge is ≤5 μm (in this example, the fineness is 3 μm after sand milling for 90 min); then, the defoamer is added and stirred at low speed for 10 min, and filtered through a 300 mesh sieve to obtain the blue pigment pre-dispersion.

[0185] The pigment content in the obtained predispersant was 20.0 wt%, the solid content measured by a unified method was 24.6 wt%, and the Zeta potential was −2 to +5 mV, which is sterically stable.

[0186] Using the same method, phthalocyanine blue 15:3 was replaced with equal parts by weight of pigment red 57:1, pigment yellow 74, and phthalocyanine green 7 to prepare red, yellow, and green pigment predispersions. When preparing the pigment carbon black predispersion, the amount of DISPERBYK-2012 was adjusted from 12 parts to 24 parts (based on 120% of the pigment mass), and the amount of deionized water was adjusted accordingly from 62.8 parts to 50.8 parts, while the pigment content remained at 20.0 wt%.

[0187] 5.3 Ink Formulation

[0188]

[0189] Except for Example 6, which used a different pigment pre-dispersant due to the different colors, the other ink components in ink compositions I-III and comparative examples D1-D6, excluding the resin binder, were kept consistent in terms of type, batch, and amount.

[0190] 5.4 Preparation method

[0191] Step 1: Preparation of the pigment pre-dispersion system

[0192] Add 20.0 parts by weight of blue pigment predispersant to 20.0 parts by weight of deionized water, and add 0.5 parts by weight of DISPERBYK-2012 while stirring. Stir and disperse at 1500 r / min for 20 min to form a homogeneous pigment premix system. The resulting system should be free of visible particles, flocculents, and obvious sedimentation; the fineness measured by a scraper fineness meter should be ≤5 μm.

[0193] Step 2: Preparation of the ink composition

[0194] To the system obtained in step one, slowly add 40.0 parts by weight of cationic aqueous polyurethane emulsion in batches under stirring at 1000 r / min (addition time not less than 10 min to avoid excessive local concentration causing flocculation). After the addition is complete, continue stirring at 1000 r / min for 30 min. Then reduce the speed to 500 r / min and add 0.3 parts by weight of BYK-024, 1.0 parts by weight of BYK-346 and 5.0 parts by weight of deionized water in sequence. Continue stirring at low speed for 20 min. Filter through a 200-mesh filter to obtain the water-based ink composition for Baili film printing.

[0195] The basic properties of the obtained ink are: pH 6.0, viscosity (Ford cup 4, 25℃) 22s, fineness ≤5μm, Zeta potential +30mV, solid content 27.6wt%, and pigment content 4.6wt%.

[0196] When emulsions I, II, and III are used, the resulting inks are respectively denoted as ink compositions I, II, and III.

[0197] Example 6:

[0198] Different color ink compositions

[0199] Based on ink composition I, keeping the proportions of other components and the preparation process unchanged, only the blue pigment pre-dispersion is replaced with equal parts by weight of red, yellow, black and green pigment pre-dispersions. The resulting inks are respectively denoted as ink compositions I-a, I-b, I-c and I-d.

[0200]

[0201] The fineness, viscosity, zeta potential, and appearance of each ink are comparable to those of ink composition I. Since the above four inks and ink composition I use the same batch of emulsion I, the emulsion storage stability of their binders is the same as that of emulsion I, and no further testing is required.

[0202] Example 7:

[0203] Application of ink compositions on non-food direct contact surfaces of Baili film

[0204] Step 1: Surface treatment of the Baili film

[0205] A 50μm thick liquid food flexible packaging film with a polyethylene printing surface was selected as the printing substrate.

[0206] The printed surface was activated using a corona treatment device. The gap between the electrode and the film surface was 1.0–2.0 mm (1.5 mm in this example), and the treatment power was 150 W. The treatment dose was adjusted to 20–60 W·min / m by adjusting the linear velocity of the film surface. 2 (In this embodiment, approximately 40 W·min / m 2 ).

[0207] After treatment, the surface wettability is evaluated using a dyne pen to ensure that the surface tension of the printed surface reaches at least 38 mN / m, preferably 40-44 mN / m (42 mN / m was measured in this embodiment).

[0208] Coating should be carried out within 30 minutes after corona treatment to reduce the impact of the decay of the surface activation effect of the polyolefin film.

[0209] If atmospheric pressure plasma jet equipment is used instead of corona treatment, the distance between the nozzle and the film surface can be 5-10 mm (8 mm in this embodiment), the treatment time is 10-20 s, and the surface tension after treatment should meet the above requirements.

[0210] Step 2: Ink Pretreatment

[0211] The ink composition was stirred at 500 rpm for 10 minutes to make the system homogeneous, and then filtered through a 200-mesh filter to obtain the ink to be printed.

[0212] Step 3: Coating (simulating printing)

[0213] The ink to be printed was uniformly coated onto the corona-treated Baili film surface using a bar coater, and the wet film thickness was controlled at 20μm.

[0214] After coating, allow it to stand at room temperature for 30 minutes to allow the coating to fully level; then lay it flat on a metal frame and dry it in a 70℃ electric thermostatic drying oven for 5 minutes to obtain a printed simulation sample with a water-based ink coating on the surface. The dry film thickness is approximately 5 μm, and the dry ink application is approximately 5.5 g / m³. 2 .

[0215] Drying conditions: Polyethylene surfaces are prone to softening, shrinkage, and curling under high temperature and prolonged conditions. Therefore, the specified drying temperature is 60–80℃, and the time is 2–10 minutes. For industrial continuous printing, gravure or flexographic printing can be used, with adjustments made to parameters based on printing speed, ink volume, hot air temperature, and airflow.

[0216] The samples obtained using ink compositions I, II, and III are designated as Sample I, II, and III, respectively; the samples obtained using ink compositions I-a to I-d are designated as Sample I-a to I-d, respectively.

[0217] Step 4: Food Contact Compliance Verification

[0218] The ink described in this invention is printed on the non-food direct contact surface of the Peli film, which is a surface printing application; the ink layer does not directly contact the contents. Given that the binder contains a quaternary ammonium bromide structure, the system may also contain residual bromide ions, chloride ions, triethanolamine, catalysts, and unreacted small molecules. All of these components are migration-sensitive substances. Therefore, before the resulting printed film is actually used for food packaging, it should undergo conformity verification according to currently effective national standards, covering aspects such as basic raw materials, additives, production and printing processes, final product migration, and characteristic substance process control.

[0219] (a) Basic Raw Material Level. According to GB 4806.14 regarding inks, except for colorants which are subject to its specific rules, the basic raw materials for inks (including the waterborne polyurethane binder of this invention and its synthesis diisocyanate, polyol, chain extender, etc.) should be basic raw materials approved for use in food contact materials and articles in my country. M-C18 described in this invention is a functionalized dihydroxy chain extender with a specific structure. When the ink of this invention is intended for use in printing food contact materials and articles, the compliance and applicability of M-C18, the waterborne polyurethane binder, and other components should be verified according to the currently effective food contact material regulations and related announcements. If the relevant substances or their scope of use are not covered by the current approved list, the corresponding compliance procedures should be completed in accordance with the applicable requirements for the management of new varieties of food-related products. Before the compliance of the relevant food contact use is confirmed, the ink of this invention can still be used in the field of polyolefin film printing that does not involve food contact regulations.

[0220] (b) Additives. In accordance with GB 9685 and relevant announcements from the National Health and Health Commission, verify whether the additives used in the ink (wetting and dispersing agents, defoamers, leveling agents and optional antioxidants, etc.) are permitted additives, and verify their scope of use and maximum usage.

[0221] (c) Production and printing process. The production, formulation, storage and printing processes of inks shall comply with the relevant requirements of GB 31603 General Hygiene Standard for the Production of Food Contact Materials and Products, and the safety risks from inks shall be controlled through measures such as raw material management, production process control, pollution prevention and control and product information transmission.

[0222] (d) Migration in the final product. According to the general safety requirements of GB 4806.1 and the general rules for migration testing specified in GB 31604.1, select applicable food simulants and determine test conditions based on the category of the actual packaged food. For milk and dairy products, food simulants including 50% ethanol (by volume) should be selected according to their respective categories, but not limited to 4% acetic acid, 10% ethanol, and water. Migration testing shall be conducted according to GB 31604.8 to determine the total migration amount and according to GB 31604.9 to determine the migration amount of heavy metals (as Pb) in the food simulant.

[0223] Contact method for migration testing: The printed film is made into a sample consistent with the actual packaging form, or a single-sided contact pool is used, so that the food simulant only contacts the food-contact inner surface of the film, with the printed ink layer on the other side of the sample. The side with the printed ink layer must not be directly immersed in the food simulant. The migration amount measured reflects the migration of ink components through the substrate, as well as the transfer of dirt caused by the ink layer adhering to the inner surface during the winding of the printed roll, which is consistent with the actual use of surface printing inks.

[0224] (e) Process control indicators. For the characteristic substances of the system of this invention, the content of residual triethanolamine, residual bismuth, residual solvent, and soluble bromide ions in the finished membrane were separately determined.

[0225] The above verification results should meet the limit requirements of the applicable standard; the specific scope of application, test conditions and limit values ​​of the referenced standard shall be based on the current effective text of the standard.

[0226] Validation results for Sample I: Total migration (4% acetic acid, 40℃ / 10d) 2.1 mg / dm³ 2 (10% ethanol) 1.5 mg / dm 2 (50% ethanol) 2.6 mg / dm 2 Heavy metals (as Pb) were not detected; primary aromatic amines were not detected (<0.01 mg / kg); tin was not detected; bismuth was not detected; soluble bromide ions were 0.8 mg / dm³. 2 ; 0.9 mg / dm³ of triethanolamine can be soluble. 2 .

[0227] Step 5: Control of residual solvents and volatile components

[0228] (a) Residual solvent in the emulsion: determined by headspace gas chromatography-flame ionization detection (HS-GC-FID). Weigh 1.0 g of the emulsion into a 20 mL headspace vial, add 4.0 g of deionized water and 1.0 g of sodium chloride, seal, equilibrate at 80 °C for 30 min, and inject. Quantify using the external standard method. The finished emulsion should contain: residual acetone <0.5 wt% (preferably <0.2 wt%), residual acetonitrile <50 mg / kg, and residual volatile amines (calculated as triethylamine) <100 mg / kg. Triethanolamine is non-volatile and should be determined by high performance liquid chromatography-evaporative light scattering. The total amount of triethanolamine (calculated as free amine and its salts) should be <0.5 wt%. If the residual acetone exceeds the limit, extend the reduced pressure evaporation time at 45 °C and -0.09 MPa, or add 20–30 mL of deionized water and repeat the reduced pressure azeotropic removal until it meets the requirements, then adjust the solid content.

[0229] (b) Residual solvent in the printed film: Take a 100cm sample of the printed simulation film. 2 Cut the sample into small pieces and place it in a headspace vial for testing under the conditions described above. The total residual solvent in the printed film after drying should be <5 mg / m³. 2 Acetone <3mg / m³ 2 The measured total residual solvent in sample I was 1.8 mg / m³. 2 .

[0230] (c) Odor evaluation: Take 100cm 2 The printed samples were placed in 1L stoppered glass bottles and kept at 60°C for 2 hours. They were then evaluated by at least three evaluators according to a rating of 1 to 6 (Rating 1: odorless; Rating 6: strong odor). The odor rating of the samples in each embodiment of this invention should not exceed level 3; Sample I was measured at level 2.

[0231] Comparative Example 1:

[0232] Ordinary cationic waterborne polyurethane ink

[0233] Prepared according to the preparation method of emulsion I, the difference being that M-C18 is not added, and N-methyldiethanolamine (NMDEA) and BDO are used as a composite chain extender instead.

[0234] The molar ratio of IPDI:PTMG:NMDEA:BDO was 2.01:1:0.3:0.7. Specifically, in the NCO-terminated prepolymer prepared from 4.47 g (20.1 mmol) IPDI and 10.00 g (10.0 mmol) PTMG, 0.36 g (3.02 mmol) NMDEA was added for pre-chain extension (resin solids mass at this stage: 14.83 g, theoretical remaining NCO content: 4.01%), followed by the addition of 0.63 g (6.99 mmol) BDO for further chain extension (resin solids mass at this stage: 15.46 g, theoretical remaining NCO content: 0.049%). The total hydroxyl content was 40.02 mmol, and the NCO / OH ratio was 1.00.

[0235] When the NCO content reaches the endpoint control requirement and 2270cm -1 After the characteristic peaks largely disappeared, 1.43 mL of 2 mol / L hydrochloric acid aqueous solution (2.86 mmol, 0.95 times the molar amount of the tertiary amine) was added to protonate the tertiary amine. In this comparative example, hydrochloric acid was a stoichiometric reactant for the salt formation of the tertiary amine, not a catalyst, and was added at a substoichiometric level. Since there was no free strong acid in the system, no additional alkali was added for neutralization; the measured pH of the diluted solution was 5.5.

[0236] Subsequently, it was processed according to the reverse emulsification and acetone removal method of Emulsion I, and subjected to the same thermal process as in Example 2 (55±2℃, nitrogen protection, stirring in the dark for 6 hours). Finally, the solid content was adjusted to 45wt% in the same way to obtain a common cationic waterborne polyurethane emulsion.

[0237] Emulsion I was replaced with this emulsion, and the amounts of other components, ink preparation methods and printing conditions were the same. The resulting ink and the printed sample were denoted as D1 ink and comparative example D1, respectively.

[0238] This comparative example is used to compare the overall differences in the comprehensive performance of inks using traditional cationic chain extenders and those using M-C18, and is not used to distinguish the independent effects of the three functional structures.

[0239] Comparative Example 2:

[0240] Catechol retains its isopropylidene protective state.

[0241] The preparation method of emulsion I was used, and all raw materials, feed amounts, chain extension processes, phase inversion emulsification, and acetone removal steps were exactly the same as in Example 2; the only difference was the temperature conditions of the deprotection step.

[0242] In the deprotection step, deionized water was added to adjust the system to a solid content of approximately 25 wt%. Similarly, 0.50 mL of 2 mol / L hydrochloric acid aqueous solution was added to bring the pH to 1.5–2.5. The mixture was stirred for 6 hours under nitrogen protection and in the dark, maintaining the system temperature at 25 ± 2 °C throughout the process without raising it to 55 °C. Subsequently, 1.5 mL of 10 wt% triethanolamine aqueous solution was added to neutralize the diluted solution to a pH of 5.8–6.2, and the solid content was adjusted to 45 wt% using the same method.

[0243] As described in Example 2 1 The H NMR method showed that the deprotection rate of this comparative example was 3.2%, meaning that the residual rate of isopropylidene protecting group was over 95%, and catechol was basically kept in a protected state.

[0244] Replace emulsion I with this emulsion, and keep all other aspects the same. The resulting ink and printing sample are respectively denoted as D2 ink and comparative example D2.

[0245] Design Description: This comparative example uses an equal amount of acid, an equal time period, and no temperature increase to inhibit deprotection, making it completely consistent with Sample I in terms of salt content, ionic strength, residual acid and neutralizing alkali amount, and total treatment time. This limits the difference variable to whether catechol is in a free state.

[0246] Comparative Example 3:

[0247] Control chain extender without catechol structure

[0248] Preparation of chain extender M-C18-Bn: Synthesized according to the route of Example 1, the only difference being that equimolar benzaldehyde was used instead of the isopropylidene-protected 3,4-dihydroxybenzaldehyde obtained in step (1), and directly condensed and reduced with n-octadecylamine to obtain N-benzyl-n-octadecylamine; the subsequent N-alkylation and quaternization steps were exactly the same as in Example 1.

[0249] M-C18-Bn molecular formula C 68 H 126 N2O2Br2 has a relative molecular mass of 1163.6 g / mol, a theoretical hydroxyl value of 96.4 mgKOH / g, and a theoretical bromine content of 13.73 wt%; the measured hydroxyl value is 95.8 mgKOH / g and the bromine content is 13.68 wt%.

[0250] Emulsion preparation: Following the method in Example 2, 3.49 g (3.00 mmol) of M-C18-Bn was used to replace 3.92 g of M-C18, and the amount of BDO remained at 0.63 g (6.99 mmol). The total hydroxyl content was 39.98 mmol, and the NCO / OH ratio was 1.01. The resin solids mass in the second stage was 17.96 g, with a theoretical residual NCO content of 3.32%; the resin solids mass in the third stage was 18.59 g, with a theoretical residual NCO content of 0.050%.

[0251] Because the system does not contain isopropylidene protecting groups, no deprotection reaction occurs in this comparative example; however, in order to keep the salt content, ionic strength, residual acid and neutralizing alkali, and thermal history of the system consistent with those in Example 2, the exact same acid treatment and neutralization process is still performed: after removing acetone, water is added to a solid content of about 25wt%, 0.50mL of 2mol / L hydrochloric acid aqueous solution is added, and the mixture is stirred at 55±2℃ under nitrogen protection and in the dark for 6h. Then, it is neutralized with 1.5mL of 10wt% triethanolamine aqueous solution to a pH of 5.8-6.2, and the solid content is adjusted to 45wt%.

[0252] The ink was prepared and coated using this emulsion instead of emulsion I. The resulting ink and the printed sample were respectively denoted as D3 ink and comparative example D3.

[0253] Design Notes: The structural difference between this comparative example and sample I is whether or not it contains a catechol group.

[0254] Comparative Example 4:

[0255] Physical addition of small molecule catechol

[0256] The emulsion obtained in Comparative Example 3 (i.e., the emulsion prepared with the control chain extender M-C18-Bn without catechol) was used as a binder, and catechol was physically added in small molecule form.

[0257] Measurement basis: Based on 40 parts by weight of emulsion with a solid content of 45 wt% (corresponding to 18.0 parts by weight of resin solids), the theoretical molar concentration of catechol structure in Example 2 was approximately matched. The theoretical feed amount of catechol structure in Example 2 is 6.00 mmol / 19.02 g resin solids, which is approximately 5.68 mmol per 18.0 g resin solids; based on the relative molecular mass of catechol of 110.11, approximately 0.63 parts by weight of catechol was added.

[0258] Dissolve 0.63 parts by weight of catechol in 4.37 parts by weight of deionized water and stir until completely dissolved under nitrogen protection and in the dark. Add the solution to the D3 emulsion and stir at 500 r / min under nitrogen protection for 20 min to mix evenly to obtain a mixed emulsion.

[0259] Emulsion I was replaced with this mixed emulsion, and the amount of deionized water in the formulation was reduced by 5.0 parts by weight (i.e., from 25.0 parts to 20.0 parts). The proportions of the remaining components, the preparation method, the printing and drying conditions were the same as those of ink composition I. The resulting ink and the printed sample were designated as D4 ink and comparative example D4, respectively. D4 ink was prepared under nitrogen protection and light-proof conditions, and was coated within 2 hours after preparation. The standing time from preparation to coating was kept consistent for all ink compositions.

[0260] Design Notes: Compared to Sample I, D4 is mainly used to examine the performance differences of catechol when it exists as a covalent structure of the polyurethane backbone versus as a physical blend of free small molecules.

[0261] Comparative Example 5:

[0262] Comparative chain extenders with short-chain alkyl substitution

[0263] Preparation of chain extender M-C4: Synthesized according to the route in Example 1, the only difference being that n-octadecylamine was replaced with an equimolar amount of n-butylamine, and the other steps were the same.

[0264] M-C4 molecular formula C 46 H 78 N2O6Br2, relative molecular mass 915.0 g / mol, theoretical hydroxyl value 122.6 mg KOH / g, theoretical bromine content 17.47 wt%; measured hydroxyl value 121.9 mg KOH / g, bromine content 17.40 wt%.

[0265] Emulsion preparation: Following the method in Example 2, 2.75 g (3.00 mmol) of M-C4 was used to replace 3.92 g of M-C18 in equal molar amounts, while the amount of BDO remained at 0.63 g (6.99 mmol). The total hydroxyl content was 39.98 mmol, and the NCO / OH ratio was 1.01. The resin solids mass in the second stage was 17.22 g, with a theoretical residual NCO content of 3.46%; the resin solids mass in the third stage was 17.85 g, with a theoretical residual NCO content of 0.052%.

[0266] Because M-C4 is highly hydrophilic, the amount of water used for emulsification was adjusted to 30 mL. For the deprotection step, based on 0.05 mmol HCl per gram of resin solids, 0.45 mL of 2 mol / L hydrochloric acid aqueous solution (0.90 mmol) was added, maintaining the pH at 1.5–2.5, and the reaction was carried out at 55 ± 2 °C for 6 h. For neutralization, 1.4 mL of 10 wt% triethanolamine aqueous solution (approximately 0.94 mmol) was added until the pH of the diluted solution reached 5.8–6.2. The deprotection rate was 96.8%. All other steps were the same.

[0267] The obtained ink and the printed sample are respectively designated as D5 ink and comparative example D5.

[0268] The only structural difference between this comparative example and sample I is the length of the long-chain alkyl chain (C4 vs. C18).

[0269] Comparative Example 6:

[0270] Monoquaternary ammonium salt type dihydroxy control chain extender

[0271] Preparation of chain extender S-C18: 4.32 g (10.0 mmol) of the secondary amine intermediate obtained in step (3) of Example 1 was added to a dry reaction flask along with 60 mL of anhydrous acetonitrile. 4.15 g (30.0 mmol) of anhydrous potassium carbonate was added, and under nitrogen protection, 4.35 g (24.0 mmol, 2.4 equivalents) of 6-bromo-1-hexanol dissolved in 15 mL of anhydrous acetonitrile was added dropwise at a rate of 1 mL / min. After the addition was complete, the temperature was raised to 80 °C and the reaction was carried out for 36 h. After the reaction was completed, the product was purified according to the precipitation method (methanol dissolution, anhydrous diethyl ether precipitation) in step (5) of Example 1, and dried under vacuum to obtain 4.63 g of monoquaternary ammonium salt type dihydroxy compound S-C18, with a yield of 65%.

[0272] S-C18 molecular formula C 40 H 74 NO4Br has a molecular weight of 712.9 g / mol, a theoretical hydroxyl value of 157.4 mg KOH / g, and a theoretical bromine content of 11.21 wt%; the measured hydroxyl value is 156.2 mg KOH / g, and the bromine content is 11.15 wt%. Its molecule contains one quaternary ammonium center, one isopropylidene protected catechol structure, one octadecyl group, and two hydroxyl groups.

[0273] Emulsion preparation: Following the method of Example 2, 4.28 g (6.00 mmol) of S-C18 was used to replace 3.92 g of M-C18, so that the quaternary ammonium nitrogen content (6.00 mmol) and catechol structure content (6.00 mmol) in the system were exactly the same as in Example 2.

[0274] S-C18 provides 12.00 mmol of hydroxyl groups, and PTMG provides 20.00 mmol. Therefore, the amount of BDO is adjusted accordingly to 0.36 g (4.00 mmol, providing 8.00 mmol of hydroxyl groups), so that the total hydroxyl groups remain at 40.00 mmol and the NCO / OH ratio remains at 1.01.

[0275] The second stage resin solids weighed 18.75g, with a theoretical remaining NCO content of 1.84%; the third stage resin solids weighed 19.11g, with a theoretical remaining NCO content of 0.044%.

[0276] For the deprotection step, based on 0.05 mmol HCl per gram of resin solid, 0.50 mL of 2 mol / L hydrochloric acid aqueous solution (1.00 mmol) was added, maintaining the pH at 1.5–2.5, and the reaction was carried out at 55 ± 2 °C for 6 h. Neutralization was achieved by adding 1.5 mL of 10 wt% triethanolamine aqueous solution until the pH of the diluted solution reached 5.8–6.2. The deprotection rate was 96.9%. All other steps were the same.

[0277] The obtained ink and printing sample are respectively designated as D6 ink and comparative example D6.

[0278] Design description and applicable scope of the conclusion: This comparative example and Sample I are matched in terms of the design feeding molar amounts of the long-chain alkyl structural unit, quaternary ammonium nitrogen and catechol structure, total hydroxyl amount and NCO / OH ratio. The main difference is that the cationic group is introduced into the main chain in the form of mono-quaternary ammonium rather than in the form of di-quaternary ammonium bridge. It should be noted that, limited by the structure of the compound itself, the two hydroxyl groups of S-C18 are connected to the same quaternary ammonium nitrogen, while the two hydroxyl groups of M-C18 are respectively connected to two quaternary ammonium nitrogen atoms and bridged by hexamethylene, and the connection modes between the hydroxyl groups and the ionic centers of the two are also different; therefore, the conclusion drawn from this comparative example is limited to the overall difference between the introduction in the form of mono-quaternary ammonium and the introduction in the form of di-quaternary ammonium bridge, and the respective contributions of the number of ionic centers and the connection mode of hydroxyl groups are not further distinguished.

[0279] Performance Test

[0280] Except for the accelerated storage stability test of emulsions and inks, all printed samples are prepared under the same substrate treatment, coating and drying conditions, and are conditioned for 24 hours in an environment with a temperature of 23±2°C and a relative humidity of 50±5% before testing. Five parallel specimens are set for each printing performance test, and the criterion for judging that the performance of this item is qualified is that all five parallel specimens meet the corresponding evaluation requirements.

[0281] Test 1: Ethanol Wipe Resistance Performance

[0282] The printed sample is cut into a 100mm×100mm test piece. A degreased cotton ball is fully immersed in a 75% volume fraction ethanol aqueous solution, taken out and gently pressed to remove excess liquid so that it is wet without dripping. The cotton ball is placed on the printed area, and wiped continuously for 50 times under a load of about 1N, with a reciprocating stroke of 100mm and a speed of about 60 times / min. After wiping, observe the coloring of the cotton ball and whether the ink layer has peeling off, color loss, obvious whitening or obvious scratches.

[0283] Evaluation criteria: After 50 times of wiping, the cotton ball has no obvious coloring, the ink layer has no obvious peeling, color loss or whitening, and the printed area remains intact, which is judged as qualified.

[0284] Test 2: Hydrogen Peroxide Scratch Resistance Performance

[0285] A 3% mass fraction hydrogen peroxide aqueous solution is uniformly coated on the printed area, and the test piece is allowed to stand at 23±2°C for 60s. The test is carried out by using a scratch resistance tester, the scratch head is covered with standard felt, the load is 500g, the reciprocating stroke is 50mm, the speed is 40 times / min, and the continuous scratching is performed 20 times. After the test, the test piece is rinsed with deionized water and naturally dried, and the coloring of the felt and the color loss, peeling, damage or obvious whitening of the ink layer are observed.

[0286] Evaluation criteria: After 20 times of scratching, the felt has no obvious coloring, the ink layer has no obvious color loss, peeling or damage, and the printed area remains intact, which is judged as qualified.

[0287] Test 3: Water Immersion and Kneading Performance

[0288] Immerse the sample completely in deionized water at 23±2℃ and let it stand for 30 minutes. After removing it, without drying, immediately rub the printed area back and forth while it is still wet, with a rubbing pressure of about 2N, for 50 consecutive times. Observe the coloring of the water and the ink layer peeling off, fading, bubbling or obvious whitening.

[0289] Evaluation criteria: After soaking in water for 30 minutes and rubbing 50 times, if the water shows no obvious coloring, and the ink layer does not fade, peel off, or bubble, and there is no obvious whitening, it is considered qualified; if only slight whitening occurs but no fading, peeling, or bubbling occurs, it is considered qualified and the slight whitening is recorded; if obvious whitening occurs or there is any degree of fading, peeling, or bubbling, it is considered unqualified.

[0290] Test 4: Adhesion strength and cross-cut adhesion performance

[0291] (1) Tape peeling method: Refer to GB / T 13217.7. Apply pressure-sensitive tape to the surface of the ink layer and press it firmly. Peel it off smoothly at an angle of about 60° within 0.5 to 1.0 seconds within 5 minutes. Measure and calculate the percentage of ink layer area retained after tape peeling.

[0292] (2) Cross-cut test: The test shall be conducted in accordance with GB / T 9286. A cross-cutting tool with a cutting spacing of 1 mm shall be used to make 6 parallel cuts along the first direction on the surface of the ink layer, and then 6 parallel cuts along the perpendicular direction. The cuts shall penetrate the ink layer to the surface of the substrate while minimizing damage to the substrate. During the test, the test piece shall be fixed flat on a rigid plate to avoid deformation of the flexible substrate. After the cross-cut test, loose ink film particles shall be removed, and the adhesive tape shall be applied and peeled off as described above. The test shall be rated according to the 0 to 5 grades specified in GB / T 9286. The lower the grade value, the better the peel resistance of the ink layer.

[0293] Test 5: Accelerated Storage Stability of Emulsion

[0294] This test is performed on emulsions to reflect the stability of the binder itself; different colored inks made from the same batch of emulsion will not be tested repeatedly in this test.

[0295] Sample preparation: Take 50g of the emulsion used to prepare each sample and put it into a 100mL brown glass bottle. After headspace nitrogen purging, seal the bottle and store it in a constant temperature incubator at 50±1℃ for 14 days in the dark. Take 10.0mL of each emulsion for centrifugation stability determination.

[0296] Test timing: Initial values ​​were measured before storage (within 24 hours after emulsion preparation, after equilibration at 23±2℃); after storage, the emulsion was removed, restored to 23±2℃ and equilibrated for 4 hours, and then sampled and measured after stirring at 500r / min for 5 minutes to make the system homogeneous.

[0297] Measurement items and conditions:

[0298] Appearance: Visually observe discoloration, flocculation, stratification, sedimentation, and gelation under natural diffused light;

[0299] Centrifugal sedimentation rate: Measure 10.0 mL of emulsion into a graduated centrifuge tube, centrifuge at 25℃ and 3000 r / min (centrifugation radius 120 mm, relative centrifugal force about 1200 × g) for 15 min, read the volume of sedimentation layer at the bottom of the tube V_s (mL), and calculate according to S=V_s / 10.0×100%;

[0300] Color difference ΔE*ab: Spectrophotometer, CIE 1976 L*a*b* color space, D65 light source, 10° standard observer, d / 8° integrating sphere geometry, including specular reflection (SCI), the sample is placed in a 10mm optical path quartz cuvette with a white standard plate as a backing, and the average is taken after 3 measurements.

[0301] Particle size and distribution: Dynamic light scattering method, diluted with deionized water to 0.10 wt%, equilibrated at 25.0 ± 0.5℃ for 120 s, and then D was measured. 50 For PDI, measure 3 times and take the average;

[0302] Zeta potential: Dilute with 1 mmol / L KCl aqueous solution to 0.05 wt%, adjust and confirm pH to 6.0 ± 0.2, equilibrate at 25.0 ± 0.5℃ for 120 s, and measure 3 times and take the average.

[0303] Viscosity: Rotational viscometer, LV series No. 2 rotor, 25.0±0.5℃, 60r / min, reading recorded after 30s of stabilization;

[0304] pH: Take 1.00g of emulsion, dilute it with 9.00g of deionized water, and measure it at 25±1℃;

[0305] Oxidation degree (auxiliary): Dilute to 0.020 wt% with deionized water, and immediately measure the absorbance A at 400 nm using a 10 mm quartz cuvette and deionized water as a blank. 400 It is used to characterize the formation of ortho-quinone oxidation products.

[0306] Evaluation criteria: Storage for 14 days is considered normal if all of the following conditions are met: no visual discoloration, flocculation, stratification, sedimentation, or gelation; centrifugal sedimentation rate ≤ 1.0%; ΔE*ab ≤ 3.0; D 50 Change rate ≤ 15% and PDI ≤ 0.30; absolute decrease in Zeta potential ≤ 20%; viscosity change rate ≤ 30%; A 400 The increase should be ≤0.05. If any condition is not met, the specific abnormal phenomenon and its corresponding value should be recorded accurately.

[0307] Explanation of test validity: The 50℃ / 14-day test is an accelerated storage test. Its results are used for cross-sectional comparison of samples under the same test conditions and are not directly equivalent to the actual shelf life under normal temperature conditions. If it is necessary to determine the shelf life, a separate long-term storage test at normal temperature should be conducted.

[0308] Test 6: Accelerated Storage Stability of Ink

[0309] This test is conducted on ink compositions to examine the stability of the complete ink system, including pigments, and is applicable to examples of different colors.

[0310] Sample preparation: Take 50g of each ink composition and place it into a 100mL brown glass bottle. After headspace nitrogen purging, seal the bottle and store it in a constant temperature incubator at 50±1℃ for 14 days, protected from light. The timing before and after storage, as well as the recovery and homogenization treatment methods, are the same as in Test 5.

[0311] Measurement items and conditions:

[0312] Appearance: Visually observe flocculation, clumping, stratification, sedimentation, and hard sedimentation; after storage, invert the glass bottle and observe whether there is any hard precipitate at the bottom that cannot be redispersed after stirring at 500 r / min for 5 min.

[0313] Fineness: Scraper fineness gauge, 25±1℃;

[0314] Viscosity: Fort-4 cup, 25.0±0.5℃, measured 3 times and averaged;

[0315] pH: Measured directly at 25±1℃;

[0316] Zeta potential: diluted to 0.05 wt% with 1 mmol / L KCl aqueous solution, under the same conditions as test 5;

[0317] The color difference of the printed ink layer ΔE*ab: The ink before and after storage was applied to the same batch of Baili film according to step three of Example 7. After conditioning for 24 hours, the color difference of the ink layer was measured under D65 light source, 10° standard observer, d / 8° geometry, and specular reflection conditions.

[0318] Evaluation criteria: After 14 days of storage, if all of the following conditions are met simultaneously, it is considered to be without abnormalities: no flocculation, clumping, stratification, or hard sedimentation that cannot be redispersed; fineness increase ≤2μm and absolute value ≤8μm; viscosity change rate ≤30%; pH change ≤0.5; Zeta potential remains positive and absolute value decrease ≤20%; ink layer ΔE*ab ≤3.0.

[0319] The test results are as follows:

[0320]

[0321]

[0322]

[0323] Samples I-a to I-d used the same emulsion I as sample I, so they are not listed again.

[0324]

[0325]

[0326] The results are analyzed as follows:

[0327] (I) Comparison with Comparative Example D1 – Overall Contribution of Functionalized Chain Extender. Comparative Example D1 used N-methyldiethanolamine and 1,4-butanediol as a composite chain extender, and did not contain the three functional structures of long-chain alkyl, bisquaternary ammonium salt and catechol introduced by the chain extender M-C18 of this invention. Its resistance to ethanol wiping, hydrogen peroxide, water immersion and rubbing, and adhesion performance were all poor (cross-cut adhesion grade 3, ink layer retention area 62%). Samples I, II, and III all showed significant improvement in the above tests (cross-cut adhesion grade 0-1, ink layer retention area 99%-100%).

[0328] (II) Comparison with Comparative Example D3 – The Influence of Catechol Structure. The only structural difference between the chain extender M-C18-Bn and M-C18 used in Comparative Example D3 is the absence of a catechol group; the remaining long-chain alkyl groups, bisquaternary ammonium salt structures, and all process conditions (including identical acid treatment, thermal history, and neutralization treatment) are completely identical. D3 exhibited satisfactory resistance to ethanol wiping and hydrogen peroxide, but showed slight discoloration after immersion in water and rubbing, with a cross-cut adhesion grade of 1. Sample I showed a cross-cut adhesion grade of 0, and only slight whitening without discoloration after immersion in water and rubbing. The above comparison demonstrates that, under the system and test conditions described in this invention, the free catechol group makes an independent contribution to wet interface stability and adhesion.

[0329] (III) Comparison with Comparative Example D5 – Effect of Alkyl Chain Length. The only structural difference between the chain extenders M-C4 and M-C18 used in Comparative Example D5 is the alkyl chain length (n-butyl vs. n-octadecyl). D5 failed the tests for ethanol wiping resistance, hydrogen peroxide resistance, and water immersion rubbing, with a cross-cut adhesion grade of 2 and an ink layer retention area of ​​85%, significantly inferior to Sample I. The above comparison results support the conclusion that, under the condition of corresponding process adjustments to address the phase inversion behavior of each system, C18 long-chain alkyl groups are more beneficial than C4 short-chain alkyl groups in improving the interfacial bonding and water resistance of the ink layer on the polyethylene surface.

[0330] (iv) Comparison with Comparative Example D6 – Overall Comparison of the Structures of Mono-quaternary Ammonium and Di-quaternary Ammonium Bridged Chain Extenders. D6 passed the tests for ethanol wiping and hydrogen peroxide resistance, but showed significant whitening after immersion in water and rubbing, thus failing the test, and its cross-cut adhesion was rated as Grade 1. The above results indicate that, under the system and test conditions described in this invention, the overall structure of the di-quaternary ammonium bridged chain extender represented by M-C18 results in better wet stability of the ink layer than that of the mono-quaternary ammonium chain extender represented by S-C18. Given the structural differences between the two in the number of ion centers and the connection method between hydroxyl groups and ion centers, this comparative example is not used to evaluate the independent contribution of each of the above structural factors.

[0331] (v) The performance is optimal when all three functional structures are present. The comparison results of D3, D5 and D6 show that, under the formulation and test conditions adopted in this invention, the ink layer exhibits the best overall interfacial adhesion and wet stability when the long-chain alkyl, free catechol and bisquaternary ammonium bridging structures are fully retained; after corresponding deletion or replacement of the above structures, at least one wet performance or adhesion performance decreases.

[0332] Regarding the mechanism of the above phenomenon, the applicant hypothesizes that: long-chain alkyl groups provide compatibility and anchoring to the polyethylene surface; free catechol provides interfacial hydrogen bonds and adsorption sites; and the bisquaternary ammonium salt bridging structure provides water dispersibility while allowing paired ion centers and paired long-chain alkyl groups to be integrally embedded in the main chain. This explanation is a hypothesis based on existing test data and has not been verified by direct microstructural characterization; therefore, it does not constitute a limitation on the scope of protection of this invention.

[0333] (vi) Effect of chain extender dosage. As the dosage of M-C18 increased from 0.3 (Sample I) to 0.5 (Sample II) and 0.7 (Sample III), the emulsion particle size decreased, the zeta potential increased, and the water-immersion kneading performance improved from acceptable and slightly whitened to acceptable. However, when the dosage was further increased to 0.7, the cross-cut adhesion decreased from grade 0 to grade 1 due to increased hydrophilicity of the system. This indicates that there is a suitable dosage range within the scope described in this invention, preferably 0.3–0.5.

[0334] (vii) Comparison with Comparative Examples D2 and D4 – Effect of Deprotection and Covalent Introduction Methods. D2 under essentially the same treatment conditions but maintained at 25±2℃, only underwent 3.2% deprotection and exhibited poor wet performance. Combined with the results of Sample I, this demonstrates that achieving sufficient deprotection in the system of this invention is beneficial for leveraging the interfacial role of the catechol structure and supports the deprotection step as an important process step for obtaining the target performance.

[0335] Comparative Example D4 used the D3 emulsion as a base, with catechol added in small molecule form at a molar concentration approximately matched to that of sample I based on the theoretical catechol structure. The main design difference between D4 and sample I was whether the catechol functional structure existed as a covalent bond in the polyurethane backbone or as a free small molecule physical blend. The designed addition amount of catechol in D4 was approximately matched to the theoretical molar concentration of the catechol structure in sample I, but the ink layer retention area further decreased from 94% in D3 to 88%, and the resistance to hydrogen peroxide and water immersion / rubbing remained unsatisfactory, with the cross-cut adhesion dropping to level 2. More significantly, the mixed emulsion used in D4, after being stored at 50℃ for 14 days, showed ΔE*ab reaching 18.5 and A... 400 The concentration increased from 0.05 to 0.92, the Zeta potential decreased from +39mV to +13mV, and the centrifugal sedimentation rate reached 6.8%, accompanied by significant discoloration and flocculation. Correspondingly, the ink also showed clumping and loss of fineness control. However, the emulsion used in the samples of this invention, under the same conditions, had a ΔE*ab value no greater than 1.4 and an A value of [missing value]. 400 The increase is no greater than 0.03, the decrease in Zeta potential is no more than 8%, and the centrifugal sedimentation rate is no greater than 0.2%. All indicators meet the requirements for the judgment of no abnormality.

[0336] Under the formulation and testing conditions adopted in this invention, the above comparative results support the covalent introduction of the catechol functional structure into the polyurethane backbone through chain extension reaction, which has significant advantages in terms of ink layer performance and system storage stability compared to physical addition in small molecule form.

[0337] In summary, this invention constructs a cationic waterborne polyurethane binder using a functionalized chain extender containing a long-chain alkyl structure, a bisquaternary ammonium salt structure, and a latent catechol structure. After acetone removal, the binder undergoes acid-catalyzed deprotection in the aqueous phase to form a free catechol structure. This results in a waterborne ink composition for Baili film printing exhibiting excellent comprehensive performance in terms of interfacial adhesion, water resistance, chemical resistance, and storage stability.

Claims

1. A printing ink composition for Peli film, characterized in that, Includes cationic aqueous polyurethane emulsion, pigment predispersant, additives and water; The polyurethane in the cationic aqueous polyurethane emulsion is obtained by addition polymerization of diisocyanate, polyether diol, functionalized dihydroxy chain extender and small molecule diol, and end-capped with n-butanol when necessary. The functionalized dihydroxy chain extender has primary hydroxyl groups at both ends of the molecule and a bisquaternary ammonium salt structure bridged by alkylene groups in the middle of the molecule. Each quaternary ammonium nitrogen is connected to a C15-C18 long-chain alkyl group and a benzyl group containing an isopropylidene protected catechol structure. The functionalized dihydroxy chain extender participates in the polyurethane chain extension reaction via its two primary hydroxyl groups, covalently introducing the long-chain alkyl group, the bisquaternary ammonium cationic structure, and the isopropylidene protected catechol structure into the polyurethane molecular chain. After the polyurethane is formed, it undergoes acid-catalyzed deprotection to form free catechol groups. The content of the free catechol groups, based on the deprotected polyurethane solid, is 0.30–0.60 mmol / g, and the quaternary ammonium nitrogen content is 0.30–0.60 mmol / g.

2. The ink composition for printing on Peli film according to claim 1, characterized in that, The functionalized dihydroxy chain extender has the structure shown in the following formula: ； Wherein, R is one of n-pentadecanyl, n-hexadecyl, n-heptadecyl, and n-octadecyl.

3. The ink composition for printing on Peli film according to claim 1, characterized in that, By weight: 30-50 parts of cationic waterborne polyurethane emulsion with a solid content of 45 wt%, 10-30 parts of pigment predispersant with a pigment content of 20 wt%, 0.1-2 parts of wetting and dispersing agent, 0.1-1 parts of defoamer, 0.5-2 parts of leveling agent, and 15-35 parts of water.

4. The ink composition for printing on Peli film according to claim 1, characterized in that, With the amount of polyether diol as 1, the amount of functionalized dihydroxy chain extender is 0.3 to 0.7, the amount of small molecule diol is 0.3 to 0.7, and the sum of the two is 1. The molar ratio of isocyanate group to total hydroxyl group, NCO / OH, is 1.00 to 1.

05.

5. The ink composition for printing on Peli film according to claim 1, characterized in that, The diisocyanate is selected from isophorone diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane diisocyanate; the polyether diol is polytetrahydrofuran glycol or polypropylene glycol with a number average molecular weight of 1000-2000; the small molecule diol is selected from 1,4-butanediol, ethylene glycol, 1,6-hexanediol, and 1,4-cyclohexanediethanol.

6. A method for preparing the ink composition for printing with Peli film according to any one of claims 1-5, characterized in that, Includes the following steps: S1 prepolymer: Diisocyanate and dehydrated polyether diol react in acetone in the presence of a catalyst to obtain NCO-terminated prepolymer; S2 Stepwise Chain Extension: First, pre-extension is performed using the functionalized dihydroxy chain extender in a protected state with catechol, followed by further chain extension with a small molecule diol. When the theoretical residual NCO content is still not less than 0.10 wt% after the small molecule diol chain extension reaches the theoretical endpoint, the excess isocyanate groups are capped with n-butanol until the residual NCO content is <0.10 wt% and the infrared spectrum is 2270 cm⁻¹. -1 No obvious isocyanate characteristic absorption peaks were observed nearby; S3 reverse emulsification: After emulsification with water, acetone is removed under reduced pressure until residual acetone is <0.5 wt%. S4 Aqueous Deprotection: Add acid to the aqueous system after acetone removal, and react at 45-65°C, in the dark, with headspace purged by inert gas. Remove the acetone generated by hydrolysis while reacting to achieve a protecting group removal rate of ≥96% and obtain polyurethane containing free catechol groups. S5 is neutralized and the solid content is adjusted to obtain a cationic aqueous polyurethane emulsion. S6 Ink Preparation: After premixing the pigment pre-dispersion, dispersant and water, slowly add the emulsion in batches while stirring, then add the defoamer, leveling agent and the remaining water in sequence, and filter to obtain the ink.

7. The preparation method according to claim 6, characterized in that, The acid mentioned in S4 is hydrochloric acid, and the dosage is 0.03–0.10 mmol H₂ per gram of polyurethane solid. + The pH of the system was adjusted to 1.5–2.5, the solid content of the system was adjusted to 20–30 wt% before deprotection, the reaction temperature was 55±5℃, and the time was 4–12 h.

8. The preparation method according to claim 6, characterized in that, In S5, triethanolamine is used to neutralize the acid at 1.02 to 1.10 times the molar amount of the added acid, until the pH of the 1:9 dilution is 5.8 to 6.

2.

9. The preparation method according to claim 6, characterized in that, S2 also includes a control step to suppress the side reaction of isocyanate catalyzed by quaternary ammonium bromide: the functionalized dihydroxy chain extender solution is added dropwise at 40±5℃, and after the addition is complete, the temperature is raised and the temperature of the entire chain extension reaction system is controlled at 50~58℃, and does not exceed 65℃ throughout the process; and when the chain extender is not completely dissolved in acetone in S2, acetonitrile equivalent to 10%~30% of the volume of acetone used to dissolve the chain extender is added as a co-solvent, and the water content of the co-solvent is <0.03wt%.

10. The application of the ink composition for printing on polyolefin films according to any one of claims 1-5 in surface printing of polyolefin films for flexible packaging of liquid food, characterized in that, The ink composition is printed onto the non-food direct contact surface of a polyolefin film used for flexible packaging of liquid food. The printed surface layer of the film is a polyethylene layer with a total thickness of 40–120 μm. Before printing, the printing surface is subjected to corona or atmospheric pressure plasma treatment to achieve a surface tension ≥38 mN / m, and the ink is applied within 30 minutes after treatment. After coating, the ink is dried at 60–80°C for 2–10 minutes, with a drying ink application rate of 3–8 g / m. 2 The total residual solvent in the resulting printed film is <5mg / m³. 2 .

Images