A uv white inkjet ink, its preparation method and application

Abstract

This invention belongs to the field of industrial UV inkjet printing consumables technology, specifically relating to a UV white inkjet ink, its preparation method, and its application. The UV white inkjet ink contains aliphatic polyurethane acrylate, silane-modified epoxy polyester, reactive diluent monomer, photoinitiator, adhesion promoter, white pigment, and optional additives. The silane-modified epoxy polyester is prepared by the following method: esterification of a diol compound with itaconic acid, followed by a mercapto-olefin click reaction of the resulting unsaturated polyester polyol with mercaptosilane, and then a condensation reaction of the resulting silane-modified polyester polyol with halopropylene oxide to obtain the silane-modified epoxy polyester. The UV white inkjet ink provided by this invention has high adhesion to the substrate and is not easily peeled off after handling friction and outdoor exposure.

Description

Technical Field

[0001] This invention belongs to the field of industrial UV inkjet printing consumables technology, specifically involving a UV white inkjet ink, its preparation method and application, especially for metal substrates such as hot-rolled steel plates, cold-rolled profiles, and galvanized steel pipes, solving the industry problems of poor ink adhesion, easy clogging and poor color development of existing inks, and is suitable for high-speed continuous inkjet printing operations on steel production lines. Background Technology

[0002] In the steel metallurgy and deep processing industries, inkjet printing technology is a key means of marking the surfaces of products such as steel plates and coils, enabling traceability and digital management throughout the product lifecycle. This technology can directly create characters or barcodes on the product surface, providing a non-contact operation with advantages such as high efficiency, flexibility, and no damage to the substrate. UV inkjet inks, with their environmentally friendly, fast-drying, and wear-resistant properties, have become the mainstream consumable for marking on steel surfaces.

[0003] However, steel substrates exhibit low surface energy, non-absorbency, and high density. Whether it's hot-rolled steel with oxide scale, smooth cold-rolled steel, or galvanized steel, their surfaces lack the ideal interface required for conventional inks to form mechanical anchoring or chemical bonding. Conventional inks struggle to wet and spread on them, and the cured film layer only exhibits weak physical adsorption with the substrate, making it extremely susceptible to peeling under external force, posing a severe challenge to the adhesion of inkjet inks. Marked steel plates undergo handling, stacking, bending, and shearing processes, requiring the film layer to withstand continuous sliding friction and intense deformation stress. Insufficient adhesion can cause the film layer to crack rapidly or peel off entirely due to stress concentration. Furthermore, steel stored outdoors for extended periods is exposed to ultraviolet radiation, wind, rain, and salt spray corrosion. Poorly adhered ink films create penetration channels for corrosive media at their interfaces, causing the film layer to peel off from the edges, powder, and eventually detach over large areas.

[0004] Existing UV inkjet ink technologies mainly focus on two routes: phosphate ester modification and silane grafting modification. Although they have a certain effect on improving the adhesion of some metal substrates, they have drawbacks such as the easy hydrolysis of phosphate ester systems, poor storage stability, and inability to improve the adhesion of steel surfaces in the long term. Furthermore, the purpose of silane grafting modification is mainly to reduce viscosity and improve weather resistance, with limited effect on improving adhesion. Summary of the Invention

[0005] The primary objective of this invention is to provide a UV white inkjet ink that can improve adhesion to steel surfaces over a long period of time.

[0006] A second objective of this invention is to provide a method for preparing the aforementioned UV white inkjet ink.

[0007] A third objective of this invention is to provide the application of the aforementioned UV white inkjet ink in the protection of steel surfaces.

[0008] The UV white inkjet ink provided by this invention contains aliphatic polyurethane acrylate, silane-modified epoxy polyester, reactive diluent monomer, photoinitiator, adhesion promoter, white pigment, and optional additives; the silane-modified epoxy polyester is prepared by the following method: esterification reaction of a diol compound with itaconic acid, followed by mercapto-alkene click reaction of the resulting unsaturated polyester polyol with mercaptosilane, and then condensation reaction of the resulting silane-modified polyester polyol with halopropylene oxide to obtain the silane-modified epoxy polyester.

[0009] The method for preparing the UV white inkjet ink provided by the present invention includes mixing aliphatic polyurethane acrylate, silane-modified epoxy polyester, reactive diluent monomer, photoinitiator, adhesion promoter, white pigment, and optional additives evenly.

[0010] The key to this invention lies in simultaneously introducing aliphatic polyurethane acrylate, silane-modified epoxy polyester, reactive monomer diluent, and adhesion promoter into the inkjet ink. The silane-modified epoxy polyester is prepared by the following method: esterification reaction of polyol compounds with itaconic acid, followed by mercapto-alkene click reaction of the resulting unsaturated polyester polyol with mercaptosilane, and then alkylation reaction of the resulting silane-modified polyester polyol with halopropylene oxide. The resulting UV white inkjet ink has high adhesion to the substrate and is not easily peeled off after handling, friction, or outdoor exposure. The reasons for this are speculated to be as follows: Firstly, silanes in silane-modified epoxy polyesters possess amphiphilic properties, providing both hydrolytic condensation capabilities anchored to the substrate, forming strong covalent bonds, and enhancing affinity with the ink layer, thus promoting ink film adhesion. Simultaneously, silanes are generally used in the form of free small molecules. Due to their low interfacial free energy, silanes in the ink migrate to the surface within an extremely short time, leading to differences in silane content at different locations in the ink film—high silane content on the surface and low content inside—thus failing to effectively volatilize the high adhesion of silanes. Linking silanes to the polyester backbone prevents silane migration and precipitation, and multiple silanes can be bonded to the same polyester backbone, effectively improving ink film adhesion. Secondly, the epoxy at the ends of silane-modified epoxy polyesters... The groups can undergo ring-opening polymerization in the presence of a photoinitiator, forming an interpenetrating network structure with other active resins in the system. This enhances the cohesive strength of the interfacial bonding layer. Furthermore, the residual hydroxyl groups after epoxy curing can form hydrogen bonds with the substrate and achieve polar adhesion, thereby improving ink film adhesion. On the other hand, aliphatic polyurethane acrylates possess high flexibility and elasticity, buffering stress when the ink film is subjected to handling friction or thermal expansion and contraction, preventing interface detachment due to brittle fracture. Simultaneously, it can form interpenetrating or semi-interpenetrating network structures with silane-modified epoxy polyesters, maintaining overall rigidity while providing impact and scratch resistance. Adhesion promoters can further fill interfacial voids, coordinating with the substrate surface or forming hydrogen bonds. Reactive diluents can reduce curing volume shrinkage and lower interfacial stress, a common cause of ink film detachment. In summary, this invention transforms the physical adhesion of traditional UV inks into a multi-anchoring system involving chemical bonding, coordination / hydrogen bonding, and stress buffering effects, resulting in a qualitative improvement in adhesion. Detailed Implementation

[0011] The UV white inkjet ink provided by this invention contains aliphatic polyurethane acrylate, silane-modified epoxy polyester, reactive diluent monomer, photoinitiator, adhesion promoter, white pigment, and optional additives. The molar ratio of the silane-modified epoxy polyester to the aliphatic polyurethane acrylate is preferably (15~40):1, such as 15:1, 18:1, 20:1, 25:1, 30:1, 35:1, 40:1, or any value between them. The molar ratio of the reactive diluent monomer to the aliphatic polyurethane acrylate is preferably (25~75):1, such as 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, 55:1, 60:1, 65:1, 70:1, 75:1, or any value between them. The preferred molar ratio of the photoinitiator to the aliphatic polyurethane acrylate is (10~25):1, such as 10:1, 12:1, 15:1, 18:1, 20:1, 22:1, 25:1, or any value between them. The preferred molar ratio of the adhesion promoter to the aliphatic polyurethane acrylate is (0.04~0.125):1, such as 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, 0.11:1, 0.12:1, 0.125:1, or any value between them. The preferred molar ratio of the white pigment to the aliphatic polyurethane acrylate is (0.8~1.8):1, such as 0.8:1, 0.9:1, 1.0:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, or any value between them. The preferred molar ratio of the additive to the aliphatic polyurethane acrylate is (0.02~0.08):1, such as 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, or any value between them.

[0012] In a preferred embodiment, based on the total mass of the UV white inkjet ink, the content of the aliphatic polyurethane acrylate is 28%~36%, the content of the silane-modified epoxy polyester is 6%~10%, the content of the reactive diluent monomer is 10%~20%, the content of the photoinitiator is 4%~7%, the content of the adhesion promoter is 1.5%~3.5%, the content of the white pigment is 30%~50%, and the content of the additives is 0.8%~2.2%. Through the synergistic effect of these components, the UV white inkjet ink, after high-speed printing and UV curing, can form a white marking layer with high opacity, strong adhesion, and resistance to abrasion and weathering. Specifically, the content of the aliphatic polyurethane acrylate can be 28%, 30%, 32%, 34%, 36%, or any value between them. The content of the silane-modified epoxy polyester can be 6%, 7%, 8%, 9%, 10%, or any value between them. The content of the reactive diluent monomer can be 10%, 12%, 14%, 16%, 18%, 20%, or any value between them. The content of the photoinitiator can be 4%, 5%, 6%, 7%, or any value between them. The content of the adhesion promoter can be 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, or any value between them. The content of the white pigment can be 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, or any value between them. The content of the additives can be 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, or any value between them.

[0013] In the aforementioned UV white inkjet ink, the silane-modified epoxy polyester is prepared by the following method: an esterification reaction is performed between a diol compound and itaconic acid; then, the resulting unsaturated polyester polyol undergoes a mercapto-olefin click reaction with a mercaptosilane; subsequently, the resulting silane-modified polyester polyol undergoes a condensation reaction with a halopropylene oxide to obtain the silane-modified epoxy polyester. The preferred molar ratio of the diol compound to itaconic acid is (1.1~1.2):1, such as 1.1:1, 1.12:1, 1.14:1, 1.16:1, 1.18:1, 1.2:1, or any value between them. The preferred molar ratio of the mercaptosilane to itaconic acid is (1.05~1.1):1, such as 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.09:1, 1.1:1, or any value between them. The molar ratio of the halopropylene oxide to the unsaturated polyester polyol is preferably (2-3):1, such as 2:1, 2.2:1, 2.4:1, 2.6:1, 2.81, 3:1, or any value between them. The diol compound is preferably a C3-C10 diol, more preferably 1,4-butanediol and / or 1,6-hexanediol. The mercaptosilane may include at least one of 3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane. The halopropylene oxide may be epibromopropane and / or epichlorohydrin. The preferred conditions for the esterification reaction include a temperature of 90°C to 150°C, such as 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, or any value between them; and a time of 1 hour to 24 hours, such as 1 hour, 3 hours, 5 hours, 8 hours, 10 hours, 12 hours, 16 hours, 20 hours, 22 hours, 24 hours, or any value between them. The preferred conditions for the mercapto-olefin click reaction include a temperature of 50°C to 150°C, such as 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, or any value between these values; a pressure of 0.05 MPa to 1 MPa, such as 0.05 MPa, 0.1 MPa, 0.2 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa, 1 MPa, or any value between these values; and a time of 5 h to 24 h, such as 5 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, or any value between these values. The mercapto-olefin click reaction needs to be carried out in the presence of an initiator, which can be selected from at least one of azo initiators, peroxide initiators, and redox initiators.The azo initiator may be selected from one or more of dimethyl azobisisobutyrate, azobisisobutyramidine hydrochloride, azodicarbonamide, azobisisopropylimidazoline hydrochloride, azoisobutylcyanoformamide, azodicyclohexylformonitrile, azodicyanovalerate, azobisisopropylimidazoline, azobisisobutyronitrile, azobisisovalerate, and azobisisoheptanenitrile. The peroxide initiator may be selected from one or more of hydrogen peroxide, ammonium persulfate, sodium persulfate, potassium persulfate, benzoyl peroxide, and benzoyl tert-butyl peroxide. The redox initiator may be selected from one or more of sulfate-sulfite, persulfate-thiourea, persulfate-organic salt, and ammonium persulfate-aliphatic amine. Specifically, the sulfate-sulfite can be selected from one or more of sodium sulfate-sodium sulfite, potassium sulfate-potassium sulfite, and ammonium sulfate-ammonium sulfite; the persulfate-thiourea can be selected from one or more of sodium persulfate-thiourea, potassium persulfate-thiourea, and ammonium persulfate-thiourea; the persulfate-organic salt can be selected from one or more of sodium persulfate-potassium acetate, potassium persulfate-potassium acetate, and ammonium persulfate-ammonium acetate; and the ammonium persulfate-aliphatic amine can be selected from ammonium persulfate-N,N-tetramethylethylenediamine and / or ammonium persulfate-diethylamine. Furthermore, the mass ratio of the unsaturated polyester polyol to the initiator can be 100:(0.05~2), such as 100:0.05, 100:0.08, 100:0.1, 100:0.3, 100:0.5, 100:0.8, 100:1, 100:1.2, 100:1.5, 100:1.8, 100:2, or any value between them. The preferred method of the condensation reaction involves reacting the silane-modified polyester polyol with halopropylene oxide in the presence of a strong base at a temperature of 80℃~150℃ (such as 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, or any value between them) for 2h~10h (such as 2h, 4h, 6h, 8h, 10h, or any value between them). The strong base may be potassium hydroxide and / or sodium hydroxide.

[0014] In the aforementioned UV white inkjet ink, the reactive diluent monomer is preferably a complex of a monofunctional acrylate monomer and a polyfunctional acrylate monomer. The monofunctional acrylate monomer may include at least one of the following: butyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, isobornyl acrylate, tetrahydrofurfuryl acrylate, 2-phenoxyethyl acrylate, and ethoxyethoxyethyl acrylate (EOEOEA). The polyfunctional acrylate monomer may include at least one of the following: 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, 1,4-butanediol diacrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, polyethylene glycol diacrylate, pentaerythritol triacrylate, and trimethylolpropane triacrylate (TMPTA). The reactive diluent monomer is particularly preferably a complex of ethoxyethoxyethyl acrylate (EOEOEA) and trimethylolpropane triacrylate (TMPTA). This effectively reduces the system viscosity while ensuring the curing crosslinking density, improving the ink film's abrasion resistance, and preventing ink film shrinkage due to monomer volatilization. The molar ratio of ethoxyethoxyethyl acrylate (EOEOEA) to trimethylolpropane triacrylate (TMPTA) in the reactive diluent is preferably (1~1.5):1, such as 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, or any value between them.

[0015] In the aforementioned UV white inkjet ink, the photoinitiator preferably contains both a free radical photoinitiator and a cationic photoinitiator, and more preferably contains a mixture of ethyl 2,4,6-trimethylbenzoylphenylphosphonate (TPO-L), phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide (IRGACURE 819), and bis(4-(diphenylthionyl)phenyl)sulfide-bis(hexafluorophosphate) in a molar ratio of (0.5~1):(0.5~1):1. These photoinitiators are not prone to yellowing, have strong deep curing ability, can be completely cured under UV LED light source irradiation, are suitable for high-speed production lines, and are stable in dark storage without causing printhead drying.

[0016] In the aforementioned UV white inkjet ink, the adhesion promoter is a long-chain alkyl phosphonate compound.

[0017] In the aforementioned UV white inkjet ink, the white pigment can be titanium dioxide, preferably rutile nano-titanium dioxide with surface coating treatment, and more preferably rutile nano-titanium dioxide with a double-layer coating of silicon aluminum oxide. Selecting the above-mentioned preferred white pigment can effectively improve dispersion stability and weather resistance. The particle size of the white pigment is preferably 50nm~150nm, such as 50nm, 80nm, 100nm, 120nm, 150nm, or any value between them. The proportion of the white pigment in the UV white inkjet ink is preferably 42%~48%. A high content ratio can ensure the inkjet ink's coverage on dark steel surfaces, resulting in a whiteness ≥95, clean and full lettering, and no graying or show-through phenomenon.

[0018] In the aforementioned UV white inkjet ink, the additives are selected from at least one of polyacrylate superdispersants, polyether-modified siloxane leveling agents, silicone-free defoamers, and polymerization inhibitors. The polyacrylate superdispersants ensure long-term dispersion of nano-titanium dioxide without sedimentation. The polyether-modified siloxane leveling agents improve ink film smoothness and gloss. The silicone-free defoamers eliminate air bubbles during preparation and printing, improving ink film stability. The polymerization inhibitors improve ink dark area stability and prevent nozzle drying.

[0019] The method for preparing the UV white inkjet ink provided by this invention includes uniformly mixing aliphatic polyurethane acrylate, silane-modified epoxy polyester, reactive diluent monomer, photoinitiator, adhesion promoter, white pigment, and optional additives. The mixing method is not particularly limited; the above raw materials can be added and mixed in any order.

[0020] The present invention also provides the application of the UV white inkjet ink in the protection of steel surfaces.

[0021] The present invention will be described in detail below through examples and comparative examples.

[0022] Aliphatic polyurethane acrylate was purchased from Zhengzhou Alpha Chemical Co., Ltd., CAS No. 68987-79-1. Adhesion promoter was purchased from Shanghai Guangyi Chemical Co., Ltd., brand name Easepi 9051. White pigment was titanium dioxide with a particle size D90 of 1.8 μm. Dispersant was BYK-2055.

[0023] Preparation Example 1 1.1 mol of 1,4-butanediol, 1 mol of itaconic acid, 0.34 g of p-toluenesulfonic acid, and 0.65 g of hydroquinone were added to a four-necked flask equipped with a stirrer, thermometer, nitrogen inlet, and condenser. Nitrogen was introduced to replace the air, and the mixture was heated to 140 °C under stirring and refluxed. During the reaction, the generated water was continuously separated by the condenser. After 4 hours of reaction, almost no water was generated in the system. The mixture was then cooled to room temperature, and the reaction product was dissolved in chloroform. After precipitation with methanol and filtration, the solid product was placed in a vacuum drying oven and dried at 100 °C for 10 hours to obtain unsaturated polyester polyol.

[0024] All of the above unsaturated polyester polyols were added to a light-protected reactor, along with 300 mL of tetrahydrofuran and 1.05 mol of 3-mercaptopropyltrimethoxysilane. The mixture was stirred at 250 rpm for 20 min, and nitrogen gas was introduced for 10 min to remove oxygen from the system. Then, 0.23 g of azobisisobutyronitrile was added, and the mixture was stirred at 250 rpm for 5 min. The mixture was then heated to 80 °C and reacted at a pressure of 0.08 MPa for 10 h to obtain a solution of silane-modified polyester polyols.

[0025] Add 3 mol of epichlorohydrin and 12 g of potassium hydroxide to the above solution containing silane-modified polyester polyol, raise the temperature to 120°C and react for 8 h. After the reaction is complete, neutralize to weak acidity with a 0.01 mol / L dilute acid solution, then wash three times with hot water at 50°C. After that, vacuum at 90°C for 3 h to remove residual moisture and low-boiling-point impurities, thus obtaining silane-modified epoxy polyester.

[0026] Preparation Example 2 1.05 mol of 1,6-hexanediol, 1 mol of itaconic acid, 0.34 g of p-toluenesulfonic acid, and 0.65 g of hydroquinone were added to a four-necked flask equipped with a stirrer, thermometer, nitrogen inlet, and condenser. Nitrogen was introduced to replace the air, and the mixture was heated to 150 °C under stirring and refluxed. During the reaction, the generated water was continuously separated by the condenser. After 2 hours of reaction, almost no water was generated in the system. The mixture was then cooled to room temperature, and the reaction product was dissolved in chloroform. After precipitation with methanol and filtration, the solid product was placed in a vacuum drying oven and dried at 100 °C for 10 hours to obtain unsaturated polyester polyol.

[0027] All of the above unsaturated polyester polyols were added to a light-protected reactor, along with 300 mL of tetrahydrofuran and 1.1 mol of 3-mercaptopropyltriethoxysilane. The mixture was stirred at 250 rpm for 20 min, and nitrogen gas was introduced for 10 min to remove oxygen from the system. Then, 0.23 g of azobisisobutyronitrile was added, and the mixture was stirred at 250 rpm for 5 min. The mixture was then heated to 120 °C and the pressure was controlled at 0.1 MPa for 5 h to obtain a solution of silane-modified polyester polyols.

[0028] Add 2.2 mol of epichlorohydrin and 8 g of sodium hydroxide to the above solution of silane-modified polyester polyol, raise the temperature to 80°C and react for 10 h. After the reaction is complete, neutralize to weak acidity with a 0.01 mol / L dilute acid solution, then wash three times with hot water at 50°C, and then vacuum at 90°C for 3 h to remove residual moisture and low-boiling-point impurities, thus obtaining silane-modified epoxy polyester.

[0029] Preparation Example 3 1.05 mol of 1,4-butanediol, 1 mol of itaconic acid, 0.34 g of p-toluenesulfonic acid, and 0.65 g of hydroquinone were added to a four-necked flask equipped with a stirrer, thermometer, nitrogen inlet, and condenser. Nitrogen was introduced to replace the air, and the mixture was heated to 120 °C under stirring and refluxed. During the reaction, the generated water was continuously separated by the condenser. After 6 hours of reaction, almost no water was generated in the system. The mixture was then cooled to room temperature, and the reaction product was dissolved in chloroform. After precipitation with methanol and filtration, the solid product was placed in a vacuum drying oven and dried at 100 °C for 10 hours to obtain unsaturated polyester polyol.

[0030] All of the above unsaturated polyester polyols were added to a light-protected reactor, along with 300 mL of tetrahydrofuran and 1.08 mol of mercaptopropylmethyldimethoxysilane. The mixture was stirred at 250 rpm for 20 min, and nitrogen gas was introduced for 10 min to remove oxygen from the system. Then, 0.23 g of azobisisobutyronitrile was added, and the mixture was stirred at 250 rpm for 5 min. The mixture was then heated to 100 °C and the pressure was controlled at 0.05 MPa for 12 h to obtain a solution of silane-modified polyester polyols.

[0031] Add 2.5 mol epichlorohydrin and 10 g potassium hydroxide to the above solution containing silane-modified polyester polyol, raise the temperature to 150℃ and react for 2 h. After the reaction is completed, neutralize to weak acidity with a 0.01 mol / L dilute acid solution, then wash three times with hot water at 50℃, and then vacuum at 90℃ for 3 h to remove residual moisture and low-boiling-point impurities, thus obtaining silane-modified epoxy polyester.

[0032] Comparative Preparation Example 1 1.1 mol of 1,4-butanediol, 1 mol of itaconic acid, 0.34 g of p-toluenesulfonic acid, and 0.65 g of hydroquinone were added to a four-necked flask equipped with a stirrer, thermometer, nitrogen inlet, and condenser. Nitrogen was introduced to replace the air, and the mixture was heated to 140 °C under stirring and refluxed. During the reaction, the generated water was continuously separated by the condenser. After 4 hours of reaction, almost no water was generated in the system. The mixture was then cooled to room temperature, and the reaction product was dissolved in chloroform. After precipitation with methanol and filtration, the solid product was placed in a vacuum drying oven and dried at 100 °C for 10 hours to obtain unsaturated polyester polyol.

[0033] All of the above unsaturated polyester polyols were added to a light-protected reactor, along with 300 mL of tetrahydrofuran and 1.05 mol of 3-mercaptopropyltrimethoxysilane. The mixture was stirred at 250 rpm for 20 min, and nitrogen gas was introduced for 10 min to remove oxygen from the system. Then, 0.23 g of azobisisobutyronitrile was added, and the mixture was stirred at 250 rpm for 5 min. The mixture was then heated to 80 °C and reacted at 0.08 MPa for 10 h. After precipitation with methanol, the mixture was filtered, and the solid product was placed in a vacuum drying oven and dried at 100 °C for 10 h to obtain silane-modified polyester polyols.

[0034] Comparative Preparation Example 2 1.1 mol of 1,4-butanediol, 1 mol of itaconic acid, 0.34 g of p-toluenesulfonic acid, and 0.65 g of hydroquinone were added to a four-necked flask equipped with a stirrer, thermometer, nitrogen inlet, and condenser. Nitrogen was introduced to replace the air, and the mixture was heated to 140 °C under stirring and refluxed. During the reaction, the generated water was continuously separated by the condenser. After 4 hours of reaction, almost no water was generated in the system. The mixture was then cooled to room temperature, and the reaction product was dissolved in chloroform. After precipitation with methanol and filtration, the solid product was placed in a vacuum drying oven and dried at 100 °C for 10 hours to obtain unsaturated polyester polyol.

[0035] All of the above unsaturated polyester polyols were added to a light-protected reactor, along with 300 mL of tetrahydrofuran, 3 mol of epichlorohydrin, and 12 g of potassium hydroxide. The temperature was raised to 120 °C and the reaction was carried out for 8 hours. After the reaction was completed, the mixture was neutralized to a weakly acidic state with a 0.01 mol / L dilute acid solution. The mixture was then washed three times with hot water at 50 °C. After that, the mixture was vacuumed at 90 °C for 3 hours to remove residual moisture and low-boiling-point impurities, thus obtaining epoxy polyester polyols.

[0036] Example 1 Based on the total mass of the UV white inkjet ink, 28% aliphatic polyurethane acrylate, 10% silane-modified epoxy polyester (obtained from Preparation Example 1), 10% reactive diluent monomer, 4% photoinitiator, 3% adhesion promoter, 43% white pigment, and 2% dispersant were stirred and mixed evenly to obtain the UV white inkjet ink. The reactive monomer diluent was a mixture of ethoxyethoxyethyl acrylate (EOEOEA) and trimethylolpropane triacrylate (TMPTA) in a molar ratio of 1:1. The photoinitiator was a mixture of ethyl 2,4,6-trimethylbenzoylphenylphosphonate (TPO-L), phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide (IRGACURE 819), and bis(4-(diphenylthionyl)phenyl)sulfide-bis(hexafluorophosphate) in a molar ratio of 0.5:1:1.

[0037] Example 2 Based on the total mass of the UV white inkjet ink, 36% aliphatic polyurethane acrylate, 6% silane-modified epoxy polyester (obtained from Preparation Example 2), 20% reactive diluent monomer, 5% photoinitiator, 1.5% adhesion promoter, 30% white pigment, and 1.5% dispersant were stirred and mixed evenly to obtain the UV white inkjet ink. The reactive monomer diluent was a mixture of ethoxyethoxyethyl acrylate (EOEOEA) and trimethylolpropane triacrylate (TMPTA) in a molar ratio of 1.5:1. The photoinitiator was a mixture of ethyl 2,4,6-trimethylbenzoylphenylphosphonate (TPO-L), phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide (IRGACURE 819), and bis(4-(diphenylthionyl)phenyl)sulfide-bis(hexafluorophosphate) in a molar ratio of 1:0.5:1.

[0038] Example 3 Based on the total mass of the UV white inkjet ink, 32% aliphatic polyurethane acrylate, 8% silane-modified epoxy polyester (obtained from Preparation Example 3), 15% reactive diluent monomer, 7% photoinitiator, 2% adhesion promoter, 35.2% white pigment, and 0.8% dispersant were stirred and mixed evenly to obtain the UV white inkjet ink. The reactive monomer diluent was a mixture of ethoxyethoxyethyl acrylate (EOEOEA) and trimethylolpropane triacrylate (TMPTA) in a molar ratio of 1.2:1. The photoinitiator was a mixture of ethyl 2,4,6-trimethylbenzoylphenylphosphonate (TPO-L), phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide (IRGACURE 819), and bis(4-(diphenylthionyl)phenyl)sulfide-bis(hexafluorophosphate) in a molar ratio of 0.8:0.8:1.

[0039] Example 4 UV white inkjet ink was prepared according to the method of Example 1, except that the amount of aliphatic polyurethane acrylate was adjusted to 40% and the amount of silane aliphatic polyurethane acrylate was adjusted to 2%, while the other conditions were the same as in Example 1, and UV white inkjet ink was obtained.

[0040] Example 5 UV white inkjet ink was prepared according to the method of Example 1, except that ethoxyethoxyethyl acrylate (EOEOEA) was used as the active monomer diluent, and the other conditions were the same as in Example 1, resulting in UV white inkjet ink.

[0041] Comparative Example 1 UV white inkjet ink was prepared according to the method of Example 5, except that the silane aliphatic polyurethane acrylate was replaced with the same amount of aliphatic polyurethane acrylate by weight, and the other conditions were the same as in Example 5, to obtain UV white inkjet ink.

[0042] Comparative Example 2 UV white inkjet ink was prepared according to the method of Example 5, except that the silane aliphatic polyurethane acrylate obtained from Preparation Example 1 was replaced by the same amount of silane-modified polyester polyol obtained from Comparative Preparation Example 1, and the other conditions were the same as in Example 5, to obtain UV white inkjet ink.

[0043] Comparative Example 3 UV white inkjet ink was prepared according to the method of Example 5, except that the silane aliphatic polyurethane acrylate obtained from Preparation Example 1 was replaced by the same amount of epoxy polyester polyol obtained from Comparative Preparation Example 2, and the other conditions were the same as in Example 5, to obtain UV white inkjet ink.

[0044] Test case (1) Initial adhesion: The initial adhesion was determined according to the national standard GB / T13217.7-2009 "Test Method for Adhesion Fastness of Liquid Ink", that is, to examine the degree to which the inkjet ink, after being sprayed onto the substrate and cured, was adhered to by the adhesive tape. Specifically: The UV white inkjet inks obtained in the above embodiments and the reference UV white inkjet inks obtained in each comparative example were sprayed onto coated paper and cured by UV light for 5 seconds. Then, the adhesion of the resulting ink film on the coated paper was tested according to the national standard GB / T13217.7-2009 "Test Method for Adhesion Fastness of Liquid Ink", with a tape pulling speed of 0.8 m / s. The results are shown in Table 1.

[0045] (2) UV resistance: The UV white inkjet inks obtained in the above embodiments and the reference UV white inkjet inks obtained in each comparative example were respectively sprayed onto coated paper and cured by UV irradiation for 5 seconds. Then, the resulting ink film was subjected to aging treatment under complex environments such as natural outdoor light, humidity and thermal shock, in accordance with the international automotive industry standard SAE J2527-2017 "Automotive Exterior Materials Performance Requirements". The irradiation intensity was 0.55 W / m 2 @340nm, blackboard temperature controlled at 70°C±2°C, humidity set to 95%±2% relative humidity in the condensation section, and cycling method of 102min irradiation + 18min condensation cycle. After aging treatment for 500h, the adhesion of the obtained ink film on coated paper was tested according to the national standard GB / T13217.7-2009 "Test Method for Adhesion Fastness of Liquid Ink", with the tape pulling speed at 0.8m / s. The results are shown in Table 1.

[0046] Table 1

[0047] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A UV white inkjet ink, characterized in that, The UV white inkjet ink contains aliphatic polyurethane acrylate, silane-modified epoxy polyester, reactive diluent monomer, photoinitiator, adhesion promoter, white pigment, and optional additives; the silane-modified epoxy polyester is prepared by the following method: esterification reaction of a diol compound with itaconic acid, followed by mercapto-alkene click reaction of the resulting unsaturated polyester polyol with mercaptosilane, and then condensation reaction of the resulting silane-modified polyester polyol with halopropylene oxide to obtain the silane-modified epoxy polyester.

2. The UV white inkjet ink according to claim 1, characterized in that, Based on the total mass of the UV white inkjet ink, the content of the aliphatic polyurethane acrylate is 28%~36%, the content of the silane-modified epoxy polyester is 6%~10%, the content of the reactive diluent monomer is 10%~20%, the content of the photoinitiator is 4%~7%, the content of the adhesion promoter is 1.5%~3.5%, the content of the white pigment is 30%~50%, and the content of the additives is 0.8%~2.2%.

3. The UV white inkjet ink according to claim 1, characterized in that, In the preparation of silane-modified epoxy polyester, the molar ratio of the diol compound to itaconic acid is (1.1~1.2):1; Preferably, the molar ratio of the mercaptosilane to itaconic acid is (1.05~1.1):1; Preferably, the molar ratio of the halo-oxidized propylene oxide to the unsaturated polyester polyol is (2~3):1; Preferably, the diol compound is a C3-C10 diol, preferably 1,4-butanediol and / or 1,6-hexanediol; Preferably, the mercaptosilane is selected from at least one of 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and mercaptopropylmethyldimethoxysilane; Preferably, the halopropylene oxide is epibromopropane and / or epichlorohydrin.

4. The UV white inkjet ink according to claim 1, characterized in that, In the preparation of silane-modified epoxy polyester, the esterification reaction conditions include a temperature of 90℃~150℃ and a time of 1h~24h. Preferably, the conditions for the mercapto-olefin click reaction include a temperature of 50°C to 150°C, a pressure of 0.05 MPa to 1 MPa, and a time of 5 h to 24 h. Preferably, the condensation reaction conditions include a temperature of 80℃~150℃ and a time of 2h~10h.

5. The UV white inkjet ink according to any one of claims 1 to 4, characterized in that, The reactive diluent monomer is a complex of ethoxyethoxyethyl acrylate and trimethylolpropane triacrylate; Preferably, the molar ratio of ethoxyethoxyethyl acrylate to trimethylolpropane triacrylate in the reactive diluent is (1~1.5):

1.

6. The UV white inkjet ink according to any one of claims 1 to 4, characterized in that, The photoinitiator contains a mixture of ethyl 2,4,6-trimethylbenzoylphenylphosphonate, phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, and bis(4-(diphenylthionyl)phenyl)sulfide-bis(hexafluorophosphate) in a molar ratio of (0.5~1):(0.5~1):

1.

7. The UV white inkjet ink according to any one of claims 1 to 4, characterized in that, The adhesion promoter is a long-chain alkyl phosphonate compound.

8. The UV white inkjet ink according to any one of claims 1 to 4, characterized in that, The additive is selected from at least one of polyacrylate superdispersants, polyether-modified siloxane leveling agents, silicone-free defoamers, and polymerization inhibitors.

9. A method for preparing the UV white inkjet ink according to any one of claims 1 to 8, characterized in that, The method involves uniformly mixing aliphatic polyurethane acrylate, silane-modified epoxy polyester, reactive diluent monomer, photoinitiator, adhesion promoter, white pigment, and optional additives.

10. The application of the UV white inkjet ink according to any one of claims 1 to 8 in the protection of steel surfaces.

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