A gravure printing white ink and a method of preparing the same

Abstract

This invention belongs to the field of printing materials technology, specifically relating to a white gravure printing ink and its preparation method. The method involves dissolving polyvinyl alcohol and polyvinyl chloride in a specific ratio in a mixed solvent, mixing and grinding them with rutile titanium dioxide, zinc gallium silicon composite oxide-coated modified titanium dioxide particles, nitrogen-doped cerium zirconium composite oxide particles, and a dispersant, and then adding a modified polyurethane binder and an antifoaming agent. The modified polyurethane binder is obtained from cashew nut shell oil polyester glycol, hydroxyl-terminated silicone resin, and other raw materials through a multi-step reaction. Two key inorganic modifying compounds are prepared via sol-gel coating hydrothermal crystallization and urea co-precipitation nitriding methods, respectively. This invention, through the synergistic effect of the two modified compounds and the composite resin system, significantly improves the whiteness and hiding power of the ink, and exhibits excellent dispersion stability and adhesion, making it suitable for high-performance gravure printing.

Description

Technical Field

[0001] This invention belongs to the field of printing materials technology, specifically relating to a gravure printing white ink and its preparation method. Background Technology

[0002] Gravure printing, as one of the mainstream processes in the packaging printing industry, relies heavily on the performance of white inks for its printing quality. White inks not only need to provide excellent undercoating power to ensure the vibrancy and purity of colored patterns, but also must possess high whiteness, good leveling properties, storage stability, and strong adhesion to various plastic film substrates. During gravure printing, the ink undergoes high-speed shearing and rapid leveling and drying on the substrate, thus requiring strict control over its fineness, viscosity stability, and resolubility. Currently, the industry's demand for high-performance white inks is increasing, especially in high-end product packaging and flexible packaging. Traditional white ink formulations face severe challenges in terms of overall performance, making the pursuit of the optimal balance between optical properties, printability, and durability a key direction for technological research and development.

[0003] Currently, commercially available gravure printing white inks generally rely on the addition of large amounts of rutile titanium dioxide as the main pigment to achieve sufficient opacity and whiteness. However, this technical approach has several inherent drawbacks. First, titanium dioxide is expensive, and its dosage directly affects the final cost of the ink, placing a heavy economic burden on manufacturers. Second, excessive pigment addition can disrupt the rheological balance of the ink system, leading to increased viscosity, decreased dispersion stability, and a tendency for hard sedimentation during storage, potentially causing printing defects such as doctor blade lines and dot clogging during use. To alleviate these problems, existing technologies mostly focus on improving the resin binder or dispersant system, such as using multiple resin blends to improve film-forming properties and adhesion, or using highly efficient dispersants to enhance pigment wettability. Nevertheless, these improvements often focus on optimizing physical and mechanical properties or processing performance, with limited effect on improving ink whiteness and opacity. They fail to fundamentally overcome the limitations of the optical properties of traditional pigments, thus limiting further upgrades to ink performance.

[0004] In-depth analysis reveals that the limitations of existing technologies lie in their reliance on a physical mixing paradigm of "resin encapsulating pigments," failing to proactively design and regulate the light scattering and absorption behavior of pigments at the optical mechanism level. Specifically, traditional methods struggle to enhance opacity by altering the interaction between light and matter without increasing titanium dioxide usage; they also lack effective conversion and utilization of harmful spectra such as ultraviolet light to compensate for and improve visual whiteness. Furthermore, the interfacial compatibility between ordinary inorganic pigments and organic resins is typically poor, easily leading to interfacial defects that affect film density and adhesion. Therefore, the industry urgently needs a novel technological concept that breaks away from traditional formulation thinking. This involves creating novel pigment materials with unique structures and functions, and synergistically designing them at the molecular level with matching resin systems. This would comprehensively address multiple technical challenges at their source, including high opacity, high whiteness, stable dispersion, and strong adhesion, driving the development of gravure printing white inks towards high performance, low cost, and environmental friendliness. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a gravure printing white ink and its preparation method.

[0006] In a first aspect, the present invention provides a method for preparing a white gravure printing ink, comprising the steps of:

[0007] By weight, 1-5 parts of polyvinyl alcohol and 0.5-3 parts of polyvinyl chloride are dissolved in a mixed solvent of 30-60 parts of ethanol and ethyl acetate to obtain a resin solution; 15-40 parts of rutile titanium dioxide, 1-10 parts of zinc gallium silicon composite oxide-coated modified titanium dioxide particles, 0.5-5 parts of nitrogen-doped cerium zirconium composite oxide particles and 0.5-3 parts of dispersant are added to the resin solution, ground, and then 10-25 parts of modified polyurethane binder and 0.05-0.5 parts of defoamer are added, stirred and mixed, and filtered.

[0008] In this invention, the synthesis of modified polyurethane binder in gravure printing white ink embodies a multi-component precise construction and cross-linking strengthening mechanism. Cashew nut shell oil polyester diol, after rigorous dehydration, reacts with isophorone diisocyanate; the terminal hydroxyl groups add to the isocyanate groups to form urethane bonds, constructing a flexible backbone. The introduction of dimethylolbutyric acid anchors the carboxyl groups in the chain, enhancing polarity and adhesion. Terminal hydroxyl organosilicon resin participates in the reaction, embedding flexible siloxane segments into the polymer network, significantly improving high and low temperature resistance and film elasticity. The addition of branched diols optimizes the distribution of hard segments and improves cohesive strength. During the chain extension stage, the primary amine groups of isophorone diamine react rapidly with the prepolymer end groups, and the organotin catalyst precisely controls the reaction rate, forming a high-molecular-weight linear backbone. Subsequently, the amino groups of the silane coupling agent combine with the residual isocyanate groups, and its siloxane ends hydrolyze and condense under trace moisture, constructing an organic-inorganic hybrid cross-linked network. The resulting binder combines the environmental friendliness of bio-based materials, the weather resistance of organosilicon, and the strong interfacial bonding of silane crosslinking. It is highly compatible with pigments such as zinc gallium silicon composite oxide-coated modified titanium dioxide and nitrogen-doped cerium zirconium composite oxide particles, ensuring excellent leveling and rapid drying during ink printing. After film formation, it exhibits high hiding power, strong abrasion resistance, and long-lasting gloss, fully meeting the stringent requirements of high-end gravure printing for ink performance.

[0009] According to a preferred embodiment of the present invention, the preparation steps of the modified polyurethane binder include: by weight, under nitrogen protection, dehydrating 25-35 parts of cashew nut shell oil polyester diol under reduced pressure at 118-122°C, mixing it with 7-12 parts of isophorone diisocyanate, reacting at 84-86°C, then adding 1-3 parts of 2,2-dimethylolbutyric acid, and continuing the reaction to obtain prepolymer A; reacting 5-12 parts of hydroxyl-terminated silicone resin with 7-10 parts of isophorone diisocyanate at 74-76°C, then adding 1-3 parts of 2,2-dimethylolbutyric acid to obtain prepolymer B; and reacting 3-5 parts of cashew nut shell oil polyester diol with 7-10 parts of isophorone diisocyanate to obtain prepolymer B. 2,4-Diethyl-1,5-pentanediol and 9-10 parts of isophorone diisocyanate were reacted at 84-86℃ to obtain prepolymer C; prepolymer A, prepolymer B and prepolymer C were mixed, ethyl acetate was added, and the mixture was cooled to 30-34℃ to obtain a mixed prepolymer solution; under stirring, the mixed prepolymer solution was added to an anhydrous ethanol solution containing 6-10 parts of isophorone diamine, and 0.05-0.15 parts of dibutyltin dilaurate were added to carry out a chain extension reaction; 1-3 parts of N-aminoethyl-3-aminopropyltriethoxysilane were added to continue the reaction; finally, a mixed solvent of ethanol and ethyl acetate was added.

[0010] According to a preferred embodiment of the present invention, the reaction time at 74-76°C is 2-4 hours.

[0011] According to a preferred embodiment of the present invention, the method for preparing the zinc gallium silicon composite oxide coated modified titanium dioxide particles includes:

[0012] A1. By weight, 18-22 parts of rutile nano-titanium dioxide are dispersed in anhydrous ethanol and sonicated under nitrogen protection to obtain suspension A. 5-8 parts of zinc nitrate hexahydrate, 15-22 parts of gallium nitrate, and 4-6 parts of tetraethyl orthosilicate are dissolved together in a mixed solvent composed of anhydrous ethanol, 30-50 parts of deionized water, and acetylacetone, and stirred to obtain solution B. Solution B is added dropwise to suspension A under nitrogen purging and a water bath at 58-62℃ with stirring. After the addition is complete, the temperature is raised to 78-82℃ for reaction.

[0013] A2. After the reaction is completed, centrifuge to obtain a solid product. Wash the solid product with anhydrous ethanol and deionized water to obtain a washed solid product. Redisperse the washed solid product in deionized water with pH=8.8-9.2, transfer it to a high-pressure reactor, and hydrothermally crystallize it at 175-185℃ to obtain a hydrothermal product. After filtering, washing, and drying, place the hydrothermal product in a muffle furnace and calcine it at 598-602℃ in an air atmosphere.

[0014] In this invention, the core mechanism in the preparation of zinc gallium silicon composite oxide-coated modified titanium dioxide particles lies in the synergistic deposition process of sol-gel and interface. First, rutile titanium dioxide nanoparticles are uniformly dispersed in anhydrous ethanol to form a stable suspension phase. Zinc nitrate, gallium nitrate, and tetraethyl orthosilicate are dissolved in a mixed solvent of aqueous ethanol and acetylacetone. Acetylacetone regulates the release rate of metal ions through chelation, preventing excessively rapid local hydrolysis. During the dropwise addition, tetraethyl orthosilicate gradually hydrolyzes under the action of water molecules to generate silanol, which then condenses to form a silicon-oxygen network framework. Simultaneously, zinc and gallium ions hydrolyze in a weakly alkaline microenvironment, and the resulting hydroxides and silicon-oxygen network are directionally deposited on the surface of the titanium dioxide particles, constructing a dense amorphous coating layer. Subsequent hydrothermal treatment promotes lattice rearrangement of the amorphous layer, transforming it into a crystalline zinc gallium silicon composite oxide, whose multiphase structure forms a strong interfacial bond with the titanium dioxide matrix. Finally, calcination further optimizes the integrity of the crystal phase and the uniformity of the coating. This coating effectively passivates the active sites on the titanium dioxide surface, significantly inhibits photocatalytic side reactions, and improves the dispersion stability, weather resistance, and optical durability of particles in the ink system.

[0015] According to a preferred embodiment of the present invention, in step A1, the reaction time is 4-6 hours after heating to 78-82°C.

[0016] According to a preferred embodiment of the present invention, in step A2, the calcination time at 598-602°C is 2-4 hours.

[0017] According to a preferred embodiment of the present invention, the method for preparing the nitrogen-doped cerium-zirconium composite oxide particles includes:

[0018] B1. By weight, dissolve 21-25 parts of cerium nitrate hexahydrate and 15-17 parts of zirconium oxychloride octahydrate in deionized water and stir to obtain solution C; mix 18-30 parts of urea with deionized water to obtain solution D; add solutions C and D dropwise to a reactor containing deionized water while stirring and at 84-86℃. After the addition is complete, keep the reaction at 84-86℃, filter under vacuum to obtain a precipitate, wash the precipitate with anhydrous ethanol, and dry at 78-82℃ to obtain a dried precursor.

[0019] B2. Place the dried precursor in a quartz boat in a tubular furnace and nitrid it at 698-702℃ in an ammonia atmosphere, then cool it to room temperature.

[0020] In this invention, the synthesis of nitrogen-doped cerium-zirconium composite oxide particles relies on a urea pyrolysis-driven homogeneous co-precipitation and gas-phase doping mechanism. Cerium nitrate and zirconium oxychloride dissolve to form a homogeneous metal ion solution, and urea solution is added concurrently to the weakly alkaline reaction system as a slow-release precipitant. Under continuous heating, urea slowly hydrolyzes to generate ammonia and carbonate ions, steadily increasing the alkalinity of the system and promoting the synchronous and homogeneous precipitation of cerium and zirconium ions into a hydroxide co-precipitate. During the dropwise addition, the acid-base environment is dynamically adjusted by ammonia water to ensure no local concentration abrupt changes during precipitation, resulting in a precursor with uniform composition and particle size. The dried precursor undergoes high-temperature heat treatment in a flowing ammonia atmosphere, where the active nitrogen species generated by the cracking of ammonia molecules diffuse into the cerium-zirconium oxide lattice, partially replacing oxygen atom positions and forming a stable nitrogen-doped structure. This doping reconstructs the electronic band structure of the material, enhancing visible light response and thermochemical stability, while also increasing surface polarity. This allows it to synergistically optimize pigment dispersion and enhance ink film density in inks, giving printed products excellent environmental adaptability and long-term color retention.

[0021] According to a preferred embodiment of the present invention, in step B1, the reaction time at 84-86°C is 4-6 hours.

[0022] According to a preferred embodiment of the present invention, in step B2, the nitriding treatment time at 698-702°C is 3-6 hours.

[0023] A second aspect of the present invention provides a gravure printing white ink prepared according to the method for preparing gravure printing white ink.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) This invention achieves a breakthrough improvement in the core optical properties of whiteness and hiding power. By introducing zinc gallium silicon composite oxide to coat modified titanium dioxide particles, a more complex core-shell structure is constructed on the surface of classic high-refractive-index rutile titanium dioxide. This composite coating layer not only has excellent light scattering ability itself, but also produces an optical synergistic effect with the core titanium dioxide, greatly enhancing the reflection and scattering efficiency of pigment particles on light, thus contributing higher hiding power per unit amount of pigment. At the same time, the original nitrogen-doped cerium zirconium composite oxide particles play a unique optical control function. The defect centers generated by nitrogen doping in its lattice can effectively absorb ultraviolet light and partially convert it into emission in the visible light region (such as blue light). This "light conversion" effect compensates for the absorption in the short-wavelength region in an optical sense, significantly improving the visual whiteness of the ink and making it present a purer and brighter white appearance.

[0026] (2) The ink of the present invention exhibits excellent performance in terms of processing applicability and storage stability. A composite polyurethane binder specifically designed for modified inorganic pigments plays a crucial role. The cashew nutshell oil segments in the binder's molecular structure provide excellent flexibility and wettability, the organosilicon segments contribute slip properties and low surface energy, while the silane coupling agent structural units can form strong chemical bonds with hydroxyl groups and other groups on the surface of the inorganic pigments. This structure ensures perfect encapsulation and anchoring of the pigment particles, especially the two novel modified compounds, by the resin, achieving efficient and stable bridging from the hydrophilic inorganic surface to the oleophilic resin phase. Therefore, the pigment particles in the ink system can maintain a uniformly dispersed state for a long time, effectively preventing hardening and performance degradation caused by particle agglomeration and sedimentation.

[0027] (3) This invention has outstanding advantages in terms of comprehensive application performance and environmental and economic benefits. Due to the strong interfacial bond formed between the modified compound and the resin, the ink exhibits excellent adhesion on a variety of commonly used plastic film substrates, achieving the highest level in the cross-cut adhesion test, effectively solving the industry pain point of insufficient adhesion of traditional inks on some low surface energy substrates. At the same time, the close combination of organic and inorganic components in the system also endows the paint film with excellent abrasion resistance and flexibility. From a global perspective, this technical solution significantly reduces the dependence on expensive titanium dioxide through material innovation, which not only directly reduces the cost of raw materials, but also indirectly improves the overall rheological properties of the ink due to the optimization of pigment dosage, reducing losses during the printing process. In addition, the core innovative raw materials used can all be synthesized through conventional chemical processes. All raw materials are commercially available, the process route is mature and reliable, no special equipment is required, and it is easy to carry out large-scale industrial production, with significant economic benefits and promotional value. In summary, this invention provides a gravure printing white ink solution that combines ultra-high optical performance, excellent stability, wide applicability and good economy, with significant comprehensive technical effects that surpass the level of existing technology. Detailed Implementation

[0028] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0029] Example 1

[0030] This embodiment provides a method for preparing white ink for gravure printing, the steps of which include:

[0031] Preparation of zinc gallium silicon composite oxide coated modified titanium dioxide particles:

[0032] Step A1: Disperse 20.0 g of rutile nano-titanium dioxide (average particle size 50 nm) in 200 mL of anhydrous ethanol. Under nitrogen protection, treat with an ultrasonic cell disruptor at 400 W for 30 min to form a homogeneous suspension A. Dissolve 6.0 g of zinc nitrate hexahydrate, 18.0 g of gallium nitrate hydrate, and 4.5 g of tetraethyl orthosilicate in a mixed solvent consisting of 150 mL of anhydrous ethanol, 35.0 g of deionized water, and 50 mL of acetylacetone. Stir magnetically at 500 rpm for 30 min until completely clear to form precursor solution B. Under continuous nitrogen purging (flow rate 50 mL / min) and heating in a 60 °C water bath while maintaining mechanical stirring at 500 rpm, add solution B slowly and uniformly to suspension A over 2 h using a constant pressure dropping funnel. After the addition is complete, heat the reaction system to 80 °C and install a reflux condenser. Continue stirring at 500 rpm at this temperature for 4 h.

[0033] Step A2: After the reaction is complete, transfer the mixture to a centrifuge tube and centrifuge at 8000 rpm for 10 min to separate the solid product. Discard the supernatant, disperse and wash the solid with 100 mL of anhydrous ethanol, centrifuge, and discard the washing liquid; repeat the above washing operation with 100 mL of deionized water, for a total of three washes. Redisperse the washed solid product in 200 mL of deionized water with pH=9.0 (adjusted with 25% ammonia), transfer the suspension to a 100 mL high-pressure reactor lined with polytetrafluoroethylene, tighten it, and place it in an oven for hydrothermal crystallization at 180℃ for 18 h. After the reactor cools naturally to room temperature, remove the hydrothermal product and perform vacuum filtration. Wash the filter cake with deionized water until the filtrate is neutral, and then place the filter cake in an 80℃ forced-air drying oven for 12 h. The dried powder was placed in an alumina crucible and then placed in a muffle furnace. Under an air atmosphere, the temperature was programmed to rise to 600°C at a heating rate of 5°C / min, and then calcined at this temperature for 2 hours. After calcination, the powder was allowed to cool naturally to room temperature in the furnace, removed, and ground to obtain zinc gallium silicon composite oxide-coated modified titanium dioxide particles.

[0034] Preparation of nitrogen-doped cerium-zirconium composite oxide particles:

[0035] Step B1: Accurately weigh 21.7g of cerium nitrate hexahydrate and 16.1g of zirconium oxychloride octahydrate, dissolve them together in 200mL of deionized water, and stir magnetically at 500rpm for 30min until completely transparent to obtain solution C. Separately weigh 12.0g of urea, dissolve it in 100mL of deionized water, and stir until clear to obtain urea solution D with a concentration of 2mol / L. Add an appropriate amount of ammonia to a three-necked flask containing 100mL of deionized water preheated to 85℃ to adjust the initial pH to 10.0. Place this flask in an 85℃ constant temperature water bath equipped with a mechanical stirrer. Under vigorous mechanical stirring (800rpm) and maintaining 85℃, add solutions C and D dropwise to the three-necked flask in parallel using two constant flow pumps, controlling the dropping rate to ensure a total dropping time of 1h. During the dropwise addition, dilute ammonia (5% v / v) was continuously added using a pH meter to precisely maintain the pH of the reaction system at 10.0 ± 0.2. After the addition was complete, the reaction was maintained at an 85°C water bath temperature and a stirring speed of 800 rpm for 4 hours.

[0036] Step B2: After the reaction, the mixture was vacuum filtered while hot, and the precipitate was collected. The precipitate was washed three times with 100 mL of anhydrous ethanol preheated to 60 °C. The washed filter cake was transferred to a watch glass and dried in an 80 °C oven for 12 h to obtain a dried cerium-zirconium composite hydroxide precursor. The dried precursor was ground and placed in a quartz boat, which was then placed in the isothermal zone of a tube furnace. High-purity ammonia gas (purity >99.9%) was introduced into the tube furnace at a flow rate of 100 mL / min to replace the air for 30 min. Subsequently, under the condition of continuous ammonia gas flow, the temperature of the tube furnace was programmed to reach 700 °C at a heating rate of 3 °C / min, and nitrided at this temperature for 3 h. After the treatment, heating was stopped, and the furnace was allowed to cool naturally to room temperature (below 50 °C) while maintaining the ammonia gas flow rate. The quartz boat was removed, yielding nitrogen-doped cerium-zirconium composite oxide particles.

[0037] Preparation of modified polyurethane binder:

[0038] Step S1: In the first dry reaction flask equipped with a stirrer, thermometer, nitrogen inlet, and condenser, after purging the air with nitrogen, add 30.0 g of cashew nut shell oil polyester diol (hydroxyl value 85 mg KOH / g). Under continuous nitrogen purging, raise the temperature inside the reaction flask to 120°C and turn on the vacuum pump to dehydrate under reduced pressure at -0.095 MPa (gauge pressure) for 1 hour. After dehydration, turn off the vacuum, restore the nitrogen atmosphere, and cool the system to 85°C. Add 12.0 g of isophorone diisocyanate (IPDI) to the reaction flask, maintain the temperature at 85°C and stir at 500 rpm, and react for 2.5 hours. Then, add 1.5 g of 2,2-dimethylolbutyric acid and continue reacting at 85°C for 1 hour to obtain prepolymer A. In another dry reaction flask, 8.0 g of hydroxyl-terminated silicone resin (hydroxyl value 80 mg KOH / g) was added, and dehydrated under reduced pressure at 120 °C and -0.095 MPa for 1 h under the same conditions as above. After dehydration, the temperature was lowered to 75 °C, and 9.0 g of IPDI was added, reacting at 75 °C for 2 h. Then, 2.0 g of 2,2-dimethylolbutyric acid was added, and the reaction continued for 1 h to obtain prepolymer B. In a third dry reaction flask, 4.0 g of 2,4-diethyl-1,5-pentanediol was added, and dehydrated under reduced pressure at 120 °C and -0.095 MPa for 1 h under the same conditions as above. After dehydration, the temperature was lowered to 85 °C, and 9.0 g of IPDI was added, reacting at 85 °C for 2 h to obtain prepolymer C.

[0039] Step S2: Transfer prepolymers A, B, and C to a clean, dry beaker, add 50g of ethyl acetate, and stir at 300rpm for 15min to form a homogeneous mixed prepolymer solution. Then place the beaker in an ice-water bath to cool until the solution temperature drops below 35°C. In a three-necked flask equipped with a mechanical stirrer, add 8.0g of isophorone diamine (IPDA) and 100mL of anhydrous ethanol, and stir until dissolved to obtain a chain extender solution. Pour the cooled mixed prepolymer solution into a constant-pressure dropping funnel and slowly add it dropwise to the chain extender solution while stirring at high speed (1000rpm), keeping the system temperature below 40°C during the addition. Before the addition begins, add 0.08g of dibutyltin dilaurate catalyst to the chain extender solution. After the addition is complete, continue stirring at 1000rpm at 35°C for 30min to carry out the chain extension reaction. Subsequently, 2.0 g of N-aminoethyl-3-aminopropyltriethoxysilane was added to the reaction system, and the mixture was stirred at 35 °C for 1 h. Finally, a mixed solvent of ethanol and ethyl acetate was added to the system to adjust the total mass to 300.0 g. At this point, the solid content of the binder was 38.0%, yielding a transparent modified polyurethane binder.

[0040] Preparation of white ink for gravure printing:

[0041] 10.0 g of polyvinyl alcohol (PVA-1788) and 5.0 g of polyvinyl chloride (low degree of polymerization) were added to a sealed container equipped with a stirrer, followed by a mixed solvent of 200.0 g of ethanol and 200.0 g of ethyl acetate (mass ratio 1:1). The mixture was stirred at 300 rpm for 2 hours in a 45°C water bath until the resin was completely dissolved, yielding a clear resin solution. Under high-speed stirring at 800 rpm, 200.0 g of rutile titanium dioxide, 20.0 g of zinc gallium silicon composite oxide-coated modified titanium dioxide particles obtained in steps A1-A2, 5.0 g of nitrogen-doped cerium zirconium composite oxide particles obtained in steps B1-B2, and 6.0 g of hydroxysulfobetaine dispersant (short chain:long chain mass ratio = 1:3) were added sequentially to the resin solution. After the addition was complete, the stirring speed was increased to 1500 rpm, and high-speed pre-dispersion was continued for 1 hour to obtain a preliminary mixed slurry. The slurry was transferred to a basket mill, and zirconia beads with a particle size of 0.6 mm were added as grinding media (media filling rate 70%). The mill was circulated and ground at 1200 rpm for 5 hours until the slurry fineness was ≤10 μm. After grinding, 150.0 g of the modified polyurethane binder (based on solids) obtained in steps S1-S2 and 0.5 g of polydimethylsiloxane defoamer were added to the slurry. The stirring speed was reduced to 400 rpm, and stirring was continued for 1 hour to ensure thorough mixing and defoaming. Finally, the ink was filtered through a 200-mesh (approximately 75 μm pore size) nylon filter cloth and then filled into containers to obtain the high-whiteness gravure printing white ink product.

[0042] Example 2

[0043] The difference between this embodiment and Embodiment 1 is that zinc gallium silicon composite oxide coated modified titanium dioxide particles are prepared:

[0044] Step A1: Disperse 19.0 g of rutile nano-titanium dioxide in 200 mL of anhydrous ethanol and sonicate under nitrogen protection (400 W, 30 min) to obtain suspension A. Dissolve 5.5 g of zinc nitrate hexahydrate, 16.0 g of gallium nitrate hydrate, and 4.0 g of tetraethyl orthosilicate in a mixed solvent consisting of 150 mL of anhydrous ethanol, 30.0 g of deionized water, and 50 mL of acetylacetone, and stir until clear to obtain solution B. Under nitrogen purging and stirring in a 59 °C water bath, add solution B dropwise to suspension A over 2 h. After the addition is complete, reflux at 79 °C for 5 h.

[0045] Step A2: After the reaction, the solid product was centrifuged and washed three times each with anhydrous ethanol and deionized water. The washed solid was redispersed in 200 mL of deionized water with pH=8.9 (adjusted with ammonia), transferred to a high-pressure reactor, and hydrothermally crystallized at 178℃ for 18 h. The hydrothermal product was filtered, washed, dried at 80℃ for 12 h, and then placed in a muffle furnace. The temperature was increased to 599℃ at 5℃ / min under air atmosphere and calcined for 3 h to obtain the target particles.

[0046] Preparation of nitrogen-doped cerium-zirconium composite oxide particles;

[0047] Step B1: Dissolve 22.0 g of cerium nitrate hexahydrate and 15.5 g of zirconium oxychloride octahydrate together in 200 mL of deionized water to obtain solution C. Dissolve 10.0 g of urea in 100 mL of deionized water to obtain solution D. Under stirring and a constant temperature water bath of 84 °C, add solutions C and D dropwise in parallel to 100 mL of deionized water (initial pH = 9.9, adjusted with ammonia), maintaining the pH at 9.9 ± 0.2 during the addition process. After the addition is complete, maintain the reaction at 84 °C for 5 h. The precipitate is vacuum filtered, washed three times with anhydrous ethanol, and dried at 79 °C for 12 h to obtain the dried precursor.

[0048] Step B2: Place the dried precursor in a quartz boat in a tubular furnace and nitrid it at 699℃ for 4 hours under an ammonia flow of 100 mL / min at a rate of 3℃ / min. Then cool it to room temperature in an ammonia atmosphere to obtain the target particles.

[0049] Preparation of modified polyurethane binder:

[0050] Step S1: 28.0 g of cashew nut shell oil polyester diol was dehydrated under reduced pressure at 119℃ and -0.095 MPa for 1 h. After dehydration, it was reacted with 10.0 g of IPDI at 84℃ for 2.5 h, and then 2.0 g of 2,2-dimethylolbutyric acid was added and the reaction was continued for 1 h to obtain prepolymer A. 6.0 g of hydroxyl-terminated silicone resin was dehydrated and reacted with 8.0 g of IPDI at 74℃ for 3 h, and then 1.5 g of 2,2-dimethylolbutyric acid was added and the reaction was continued for 1 h to obtain prepolymer B. 3.0 g of 2,4-diethyl-1,5-pentanediol was dehydrated and then reacted with 10.0 g of IPDI at 84℃ for 2 h to obtain prepolymer C.

[0051] Step S2: Mix prepolymers A, B, and C, dilute with ethyl acetate, and cool to below 33°C. While stirring, add the mixed prepolymer solution to an anhydrous ethanol solution containing 7.0 g IPDA, add 0.1 g dibutyltin dilaurate, and proceed with the chain extension reaction for 30 min. Add 1.5 g N-aminoethyl-3-aminopropyltriethoxysilane and continue the reaction for 1 h. Finally, add the mixed solvent to adjust the total mass to 300.0 g (solid content approximately 37%), obtaining the linker material.

[0052] Preparation of white ink for gravure printing:

[0053] 3.0 g of polyvinyl alcohol and 2.0 g of polyvinyl chloride were dissolved in a mixed solvent of 150.0 g of ethanol and 150.0 g of ethyl acetate to obtain a resin solution. 100.0 g of rutile titanium dioxide, 8.0 g of the zinc-gallium-silicon composite oxide-coated modified titanium dioxide particles prepared above, 3.0 g of the nitrogen-doped cerium-zirconium composite oxide particles prepared above, and 3.0 g of dispersant were added, and the mixture was ground to a fineness ≤10 μm. 80.0 g of the modified polyurethane binder prepared above and 0.2 g of defoamer were added, and the mixture was stirred and mixed for 1 h, then filtered to obtain the ink.

[0054] Example 3

[0055] The difference between this embodiment and Embodiment 1 is that zinc gallium silicon composite oxide coated modified titanium dioxide particles are prepared:

[0056] Step A1: Disperse 21.0 g of rutile nano-titanium dioxide in 200 mL of anhydrous ethanol and sonicate under nitrogen protection (400 W, 30 min) to obtain suspension A. Dissolve 7.0 g of zinc nitrate hexahydrate, 20.0 g of gallium nitrate hydrate, and 5.5 g of tetraethyl orthosilicate in a mixed solvent consisting of 150 mL of anhydrous ethanol, 45.0 g of deionized water, and 50 mL of acetylacetone, and stir until clear to obtain solution B. Under nitrogen purging and stirring in a 61 °C water bath, add solution B dropwise to suspension A over 2 h. After the addition is complete, reflux at 81 °C for 4.5 h.

[0057] Step A2: After the reaction, the solid product was centrifuged and washed three times each with anhydrous ethanol and deionized water. The washed solid was redispersed in 200 mL of deionized water with pH=9.1 (adjusted with ammonia), transferred to a high-pressure reactor, and hydrothermally crystallized at 182℃ for 18 h. The hydrothermal product was filtered, washed, and dried at 80℃ for 12 h, then placed in a muffle furnace and calcined at 601℃ at a rate of 5℃ / min in air atmosphere for 2.5 h to obtain the target particles.

[0058] Preparation of nitrogen-doped cerium-zirconium composite oxide particles:

[0059] Step B1: Dissolve 23.0 g of cerium nitrate hexahydrate and 16.5 g of zirconium oxychloride octahydrate together in 200 mL of deionized water to obtain solution C. Dissolve 15.0 g of urea in 100 mL of deionized water to obtain solution D. Under stirring and a constant temperature water bath of 86 °C, add solutions C and D dropwise in parallel to 100 mL of deionized water (initial pH = 10.1, adjusted with ammonia), maintaining the pH at 10.1 ± 0.2 during the addition process. After the addition is complete, maintain the reaction at 86 °C for 4.5 h. The precipitate is vacuum filtered, washed three times with anhydrous ethanol, and dried at 81 °C for 12 h to obtain the dried precursor.

[0060] Step B2: Place the dried precursor in a quartz boat in a tubular furnace, and nitrid it at 701℃ for 5 hours under an ammonia flow of 100 mL / min at a rate of 3℃ / min. Then cool it to room temperature in an ammonia atmosphere to obtain the target particles.

[0061] Preparation of modified polyurethane binder:

[0062] Step S1: 32.0 g of cashew nut shell oil polyester diol was dehydrated under reduced pressure at 121℃ and -0.095 MPa for 1 h. After dehydration, it was reacted with 11.0 g of IPDI at 86℃ for 2.5 h, and then 2.5 g of 2,2-dimethylolbutyric acid was added and the reaction continued for 1 h to obtain prepolymer A. 10.0 g of hydroxyl-terminated silicone resin was dehydrated and reacted with 8.5 g of IPDI at 76℃ for 2.5 h, and then 2.5 g of 2,2-dimethylolbutyric acid was added and the reaction continued for 1 h to obtain prepolymer B. 5.0 g of 2,4-diethyl-1,5-pentanediol was dehydrated and then reacted with 10.0 g of IPDI at 86℃ for 2 h to obtain prepolymer C.

[0063] Step S2: Mix prepolymers A, B, and C, dilute with ethyl acetate, and cool to below 32°C. While stirring, add the mixed prepolymer solution to an anhydrous ethanol solution containing 9.0 g IPDA, add 0.12 g dibutyltin dilaurate, and proceed with the chain extension reaction for 30 min. Add 2.5 g N-aminoethyl-3-aminopropyltriethoxysilane and continue the reaction for 1 h. Finally, add the mixed solvent to adjust the total mass to 300.0 g (solid content approximately 39%), obtaining the linker material.

[0064] Preparation of white ink for gravure printing:

[0065] 5.0 g of polyvinyl alcohol and 1.5 g of polyvinyl chloride were dissolved in a mixed solvent of 180.0 g of ethanol and 180.0 g of ethyl acetate to obtain a resin solution. 300.0 g of rutile titanium dioxide, 15.0 g of the zinc-gallium-silicon composite oxide-coated modified titanium dioxide particles prepared above, 8.0 g of the nitrogen-doped cerium-zirconium composite oxide particles prepared above, and 5.0 g of dispersant were added, and the mixture was ground to a fineness ≤10 μm. 120.0 g of the modified polyurethane binder prepared above and 0.4 g of defoamer were added, and the mixture was stirred and mixed for 1 h, then filtered to obtain the ink.

[0066] Comparative Example 1

[0067] The difference between this comparative example and Example 1 is that zinc gallium silicon composite oxide coated modified titanium dioxide particles and nitrogen-doped cerium zirconium composite oxide particles are not prepared and added; otherwise, they are the same as in Example 1.

[0068] Comparative Example 2

[0069] The difference between this comparative example and Example 1 is that only zinc gallium silicon composite oxide coated modified titanium dioxide particles are added, and nitrogen-doped cerium zirconium composite oxide particles are not added; otherwise, it is the same as Example 1.

[0070] Comparative Example 3

[0071] The difference between this comparative example and Example 1 is that only nitrogen-doped cerium-zirconium composite oxide particles are added, and zinc gallium-silicon composite oxide coated modified titanium dioxide particles are not added; otherwise, it is the same as Example 1.

[0072] According to relevant national and industry standards, the performance of the gravure printing white inks provided in the above embodiments and comparative examples was tested. The test methods are as follows: all tests on the ink samples were conducted in a standard environment with a temperature of 23±2℃ and a relative humidity of 50±5%, and the samples were equilibrated for 24 hours before testing.

[0073] Whiteness Test: Measurements were performed using a spectrophotometer equipped with d / 8° geometry, a D65 light source, and a 10° field of view. Ink samples were uniformly coated onto standard black and white cardstock with a wet film thickness of 30 μm using a precision wire bar coater. The coating was then horizontally dried for 24 hours at 23±2℃ and 50±5% relative humidity to form a film. Optical opacity verification: The tristimulus values ​​Y of the film layer on both black and white cards were measured, and the contrast ratio (Yblack / Ywhite) was calculated. A contrast ratio ≥ 0.98 was considered optically opaque. Spectral reflectance data were obtained from the film layer on the verified opaque white card area, and the CIE whiteness index was calculated as the core criterion (a higher value indicates better visual whiteness). All measurements were repeated three times, and the arithmetic mean was taken as the final result.

[0074] Contrast ratio test: On the same film layer, the reflectance values ​​of the coating on a black background and a white background are measured respectively, and the ratio of the two (black background reflectance / white background reflectance) is calculated. The obtained value is the contrast ratio, which is used to evaluate the hiding power.

[0075] Initial viscosity test: Measured using a rotational viscometer under constant temperature conditions of 25.0 ± 0.5℃. Based on the estimated sample viscosity range, select a rotor and speed combination that ensures the torque reading is within 20-80% of the instrument's full scale during measurement. For samples with an estimated viscosity in the range of 300-400 mPa·s, a Brookfield LV series rotor No. 2 (LV-2) at 60 rpm can be used for measurement. Start the instrument and, after the reading at this speed stabilizes, record the viscosity value in mPa·s. Repeat the measurement three times for the same sample, and take the arithmetic mean as the reported result.

[0076] Viscosity change rate test after heat storage: Take approximately 200g of ink sample, seal it in a clean iron can, and place it in a constant temperature drying oven at 50±1℃ for continuous static storage for 30 days. After the expiration date, remove it, restore it to the standard environment for 24 hours, and measure the viscosity again under the initial viscosity test conditions. The viscosity change rate is calculated using the formula (viscosity after heat storage - initial viscosity) / initial viscosity × 100%.

[0077] Fineness test after heat storage: For the same ink sample that has completed the heat storage viscosity test, a scraper fineness meter is used for measurement. Take a small amount of sample and place it at the deepest end of the groove of the fineness meter. Scrape it across at a uniform speed with a scraper. Immediately observe the scale value at the point where the particle stripes appear at a 30° angle. This value is the fineness, in μm.

[0078] Low-temperature storage stability test: Take another 200g of ink sample, seal it, and store it in a refrigerated environment at 5±1℃ for 30 days. After the expiration date, take it out and restore it to a standard environment for 24 hours. Visually observe and record the state of the sample, such as whether there is layering, precipitation, or skin formation. Assess the ease of redispersing the precipitate by manual stirring.

[0079] For PET adhesion testing: Ink was applied to an untreated polyethylene terephthalate (PET) film using a bar coater, with a wet film thickness of 15 μm, and dried at room temperature for 24 hours. Using a single-edged cutter, 11 horizontal and 11 vertical grids were drawn on the film at 1 mm intervals, cutting down to the substrate. 3M 610 pressure-sensitive adhesive tape was tightly adhered to the grid area and then quickly peeled off at a 60° angle within 1-2 seconds. Under illumination, the paint film peeling in the grid area was examined using a 10x magnifying glass and compared with a standard rating chart: Grade 0: Completely smooth cut edges, no peeling; Grade 1: Peeling area ≤ 5%; Grade 2: Peeling area > 5% to ≤ 15%; Grade 3: Peeling area > 15% to ≤ 35%; Grade 4: Peeling area > 35% to ≤ 65%; Grade 5: Peeling area > 65%.

[0080] Print transferability test: Using a laboratory gravure proofing machine, a test plate of 175 lines per inch was selected, and proofing was performed at a constant printing pressure and a speed of 50 meters per minute. The prints were visually evaluated and under a 20x magnifying glass to check the uniformity of solid areas, the presence of squeegee lines or haze, and the clarity and completeness of the reproduction of highlight dots.

[0081] Dry rubbing resistance test: The print sample obtained from the print transfer test is cut and fixed on the base of the rubbing resistance tester. The rubbing head is wrapped with a standard dry cotton cloth, and a load of 500g is applied to the test area. The area is rubbed back and forth at a speed of 60 times / minute for 100 cycles. After the rubbing is completed, the test area is visually inspected and observed under a light box to evaluate whether the paint film shows signs of wear, peeling, whitening, or exposure of the substrate.

[0082] The performance test data above are shown in Table 1.

[0083] Table 1 Performance Test Results

[0084] ;

[0085] As can be seen from the above, the technical solutions provided by Embodiments 1-3 of the present invention effectively and systematically solve the key technical problems that have long existed in the field of white ink for gravure printing.

[0086] First, regarding the most crucial optical performance, the whiteness and contrast ratio data of the embodiment significantly and consistently surpassed all comparative examples, which directly confirms the indispensable synergistic effect of zinc gallium silicon composite oxide-coated modified titanium dioxide and nitrogen-doped cerium zirconium composite oxide.

[0087] Specifically, compared to Comparative Example 1, which did not use any modified compounds, the whiteness CIE value of the examples increased by more than 4 units, a improvement of more than 0.03. This breaks through the performance ceiling achievable solely by increasing the amount of titanium dioxide used in the traditional approach. Even Comparative Examples 2 and 3, which used only one of the modified compounds, did not show a performance improvement as significant as the examples. This clearly demonstrates that only the synergy of both compounds can achieve dual optimization of light scattering efficiency and spectral absorption conversion capability, thereby fundamentally solving the core industry problem of insufficient ink whiteness and hiding power while ensuring or even reducing the amount of titanium dioxide used.

[0088] Secondly, the examples demonstrated excellent performance in terms of storage stability, a key industrial indicator. After accelerated heat storage at 50°C for 30 days, the viscosity of the examples increased by only 3-5%, the fineness did not become coarser, and they were easily redispersed after low-temperature storage; while Comparative Example 1 showed a viscosity increase of more than 15% accompanied by gelation and hardening, and Comparative Example 3 also showed obvious precipitation.

[0089] This stark contrast demonstrates that the strong interfacial interaction between the two modified compounds and the special modified polyurethane binder effectively anchors the pigment particles, inhibiting their agglomeration and sedimentation tendencies caused by the weakening of Brownian motion. This solves the common technical pain points of high pigment content inks, such as poor storage stability, easy coarsening, and easy sedimentation.

[0090] Finally, the examples also demonstrated a decisive advantage in adhesion and film durability, which directly affect printing quality and end-use performance. All examples achieved the optimal adhesion rating of Grade 0 in tests on difficult-to-adhere PET films, and the film remained intact after dry rubbing tests; while the comparative examples generally showed adhesion peeling at Grades 1-2 and significant whitening due to friction. This is attributed to the strong chemical bonds formed between the silane coupling agent and other components in the modified binder and the surface of the inorganic modified particles and the plastic substrate, significantly enhancing the cohesive strength and interfacial adhesion of the paint film, thus effectively solving the common technical problems of insufficient adhesion and poor abrasion resistance of traditional inks on various plastic films.

[0091] In summary, the test data fully demonstrates that the technical solution of this invention, through the synergistic design of two innovative modified compounds and a composite resin system, not in a singular but systematic manner, simultaneously overcomes multiple technical bottlenecks in the optical performance, storage stability, and application performance of gravure printing white ink, achieving a leapfrog improvement in overall performance.

Claims

1. A method for preparing a gravure printing white ink, characterized by the steps of include: By weight, 1-5 parts of polyvinyl alcohol and 0.5-3 parts of polyvinyl chloride are dissolved in a mixed solvent of 30-60 parts of ethanol and ethyl acetate to obtain a resin solution; 15-40 parts of rutile titanium dioxide, 1-10 parts of zinc gallium silicon composite oxide-coated modified titanium dioxide particles, 0.5-5 parts of nitrogen-doped cerium zirconium composite oxide particles and 0.5-3 parts of dispersant are added to the resin solution, ground, and then 10-25 parts of modified polyurethane binder and 0.05-0.5 parts of defoamer are added, stirred and mixed, and filtered. The preparation steps of the modified polyurethane binder include: by weight, under nitrogen protection, dehydrating 25-35 parts of cashew nut shell oil polyester diol under reduced pressure at 118-122°C, mixing it with 7-12 parts of isophorone diisocyanate, reacting at 84-86°C, then adding 1-3 parts of 2,2-dimethylolbutyric acid, and continuing the reaction to obtain prepolymer A; reacting 5-12 parts of hydroxyl-terminated silicone resin with 7-10 parts of isophorone diisocyanate at 74-76°C, then adding 1-3 parts of 2,2-dimethylolbutyric acid to obtain prepolymer B; and reacting 3-5 parts of 2,4-diethyl... 1,5-Pentanediol was reacted with 9-10 parts of isophorone diisocyanate at 84-86℃ to obtain prepolymer C; prepolymer A, prepolymer B and prepolymer C were mixed, ethyl acetate was added, and the mixture was cooled to 30-34℃ to obtain a mixed prepolymer solution; under stirring, the mixed prepolymer solution was added to an anhydrous ethanol solution containing 6-10 parts of isophorone diamine, and 0.05-0.15 parts of dibutyltin dilaurate were added to carry out a chain extension reaction; 1-3 parts of N-aminoethyl-3-aminopropyltriethoxysilane were added to continue the reaction; finally, a mixed solvent of ethanol and ethyl acetate was added. The preparation method of the zinc gallium silicon composite oxide coated modified titanium dioxide particles includes: A1. By weight, 18-22 parts of rutile nano-titanium dioxide are dispersed in anhydrous ethanol and sonicated under nitrogen protection to obtain suspension A. 5-8 parts of zinc nitrate hexahydrate, 15-22 parts of gallium nitrate, and 4-6 parts of tetraethyl orthosilicate are dissolved together in a mixed solvent composed of anhydrous ethanol, 30-50 parts of deionized water, and acetylacetone, and stirred to obtain solution B. Solution B is added dropwise to suspension A under nitrogen purging and a water bath at 58-62℃ with stirring. After the addition is complete, the temperature is raised to 78-82℃ for reaction. A2. After the reaction is complete, centrifuge to obtain a solid product. Wash the solid product with anhydrous ethanol and deionized water to obtain a washed solid product. Redisperse the washed solid product in deionized water with pH=8.8-9.2, transfer it to a high-pressure reactor, and hydrothermally crystallize it at 175-185℃ to obtain a hydrothermal product. After filtration, washing, and drying, place the hydrothermal product in a muffle furnace and calcine it at 598-602℃ in an air atmosphere. The preparation method of the nitrogen-doped cerium-zirconium composite oxide particles includes: B1. By weight, dissolve 21-25 parts of cerium nitrate hexahydrate and 15-17 parts of zirconium oxychloride octahydrate in deionized water and stir to obtain solution C; mix 18-30 parts of urea with deionized water to obtain solution D; add solutions C and D dropwise to a reactor containing deionized water while stirring and at 84-86℃. After the addition is complete, keep the reaction at 84-86℃, filter under vacuum to obtain a precipitate, wash the precipitate with anhydrous ethanol, and dry at 78-82℃ to obtain a dried precursor. B2. Place the dried precursor in a quartz boat in a tubular furnace and nitrid it at 698-702℃ in an ammonia atmosphere, then cool it to room temperature.

2. The method for preparing a gravure printing white ink according to claim 1, characterized by, The reaction time at 74-76℃ is 2-4 hours.

3. The method of preparing a gravure printing white ink according to claim 1, characterized by, In step A1, the temperature is raised to 78-82℃ and the reaction time is 4-6 hours.

4. The method of preparing a gravure printing white ink according to claim 1, characterized by, In step A2, the calcination time at 598-602℃ is 2-4 hours.

5. The method of preparing a gravure printing white ink according to claim 1, characterized by, In step B1, the reaction is kept at 84-86℃ for 4-6 hours.

6. The method for preparing gravure printing white ink according to claim 1, characterized in that, In step B2, the nitriding treatment at 698-702℃ takes 3-6 hours.

7. A white ink for gravure printing, characterized in that, The gravure printing white ink is prepared by the method for preparing gravure printing white ink according to any one of claims 1-6.