Water-based formaldehyde-free painting pigment and preparation method thereof

Abstract

The invention relates to the technical field of pigments, in particular to a water-based formaldehyde-free painting pigment and a preparation method thereof. The method is realized by the following steps: firstly, grafting an initiator on the surface of amino mesoporous silica, and then grafting a zwitter-ion / hydrophobic copolymer brush on the surface of the amino mesoporous silica through purple light initiated polymerization; then preparing an acrylate pre-emulsion containing the functional nanoparticles, and carrying out semi-continuous emulsion polymerization to obtain a self-crosslinking emulsion; then introducing adipic dihydrazide as a latent cross-linking agent; and finally, adding functional nano-particles in multiple stages, mixing the functional nano-particles with pigments, auxiliaries and the like, and sanding and blending to obtain a final product. Formaldehyde is completely abandoned, a unique organic-inorganic composite structure and a latent cross-linking technology are utilized, the water resistance, scrubbing resistance, adhesive force and color stability of the pigment are synergistically improved, and meanwhile, the pigment has good environment-friendly safety and easy-to-clean performance and is particularly suitable for the fields of children painting and the like.

Description

Technical Field

[0001] This invention relates to the field of pigment technology, and in particular to a water-based formaldehyde-free painting pigment and its preparation method. Background Technology

[0002] With increasingly stringent environmental regulations and heightened consumer health awareness, water-based paints, as environmentally friendly products, are finding wider application in children's art education, artistic creation, and home decoration. Compared to traditional solvent-based paints, water-based systems, using water as the dispersion medium, theoretically offer advantages such as low toxicity, low odor, and easy cleaning. However, in practical applications, to achieve sufficient film strength, scrub resistance, and durability, most commercially available water-based paints still rely on formaldehyde-containing or formaldehyde-releasing crosslinking agents, such as urea-formaldehyde resin and melamine-formaldehyde resin. These crosslinking agents enhance the film by forming a three-dimensional network structure, but they continuously release free formaldehyde during the curing process, resulting in a pungent odor and potential health risks such as carcinogenicity and allergic reactions, especially for children with weaker immune systems. Furthermore, formaldehyde release is a long-term process, causing continuous environmental pollution during storage and use, making it difficult to meet modern environmental standards.

[0003] Besides safety concerns, the use of formaldehyde-based crosslinking agents also introduces a series of performance defects. On one hand, the formaldehyde crosslinking reaction is often too rapid or difficult to control, easily leading to stress concentration within the coating film, resulting in increased brittleness and decreased adhesion. Under thermal expansion and contraction of the substrate or external forces, the coating is prone to micro-cracks or even peeling, affecting its service life. On the other hand, excessive crosslinking sacrifices the polymer's flexibility, making the coating film hard and brittle, lacking the necessary toughness and ductility, which is detrimental to its application on flexible substrates (such as paper and fabrics). Simultaneously, formaldehyde residue can also react with pigments or additives, causing yellowing or discoloration, reducing color vibrancy and durability, and affecting artistic expression.

[0004] Existing water-based paints face significant challenges in terms of water and stain resistance. Water-based systems are inherently hydrophilic; insufficient cross-linking leads to swelling and softening of the coating upon contact with water, resulting in poor scrub resistance and susceptibility to contamination. However, increasing cross-linking often requires increasing the amount of formaldehyde-based cross-linking agents, which not only exacerbates environmental issues but also makes the coating overly rigid, losing its ability to encapsulate the pigment and adapt to the substrate. Furthermore, there is a contradiction between pigment dispersion stability and the cross-linking network: good color performance requires highly dispersed pigment particles fixed within the polymer matrix, but high cross-linking restricts polymer chain movement, hindering pigment orientation and color development, resulting in uneven color, low gloss, and difficulty in simultaneously achieving deep gamuts and high durability.

[0005] Interface compatibility is another major challenge. In aqueous systems, the large differences in density and polarity between organic film-forming agents (such as acrylic emulsions) and inorganic pigments (such as titanium dioxide and phthalocyanine blue) easily lead to phase separation, causing pigment sedimentation and clumping, which affects product storage stability and application leveling. To improve compatibility, dispersants, wetting agents, and other additives are often added, but these small-molecule additives may migrate to the coating surface, increasing VOC emissions and reducing stain resistance. Although the industry has developed some formaldehyde-free crosslinking technologies (such as aziridine and carbodiimide), they suffer from problems such as comparable toxicity, high cost, or harsh reaction conditions, making large-scale application difficult. They also often have shortcomings in film-forming efficiency and low-temperature curing properties.

[0006] Overall, existing water-based paints still face multiple bottlenecks in eliminating formaldehyde dependence and improving overall performance: insufficient safety, poor water resistance, weak color expression, and low interface stability. These problems are intertwined, making the development of truly environmentally friendly, efficient, and multifunctional formaldehyde-free water-based paints a technical challenge, urgently requiring an innovative design to achieve a balance between safety and performance. Summary of the Invention

[0007] In view of this, the purpose of this invention is to propose a water-based formaldehyde-free painting pigment and its preparation method, so as to solve the problems that existing water-based painting pigments generally rely on formaldehyde-containing crosslinking agents to improve film-forming performance, resulting in harmful substance residues and health hazards. At the same time, the water resistance, scrub resistance and color brightness of the coating are difficult to optimize in a coordinated manner, and the interface stability is insufficient, affecting the service life and safety.

[0008] To achieve the above objectives, the present invention provides a method for preparing water-based formaldehyde-free painting pigments, comprising the following steps: (1) Preparation of mesoporous silica nanoparticles containing initiating groups: acylation reaction of 2-bromoisobutyryl bromide and amino groups on the surface of amino mesoporous silica nanoparticles was carried out to obtain mesoporous silica nanoparticles containing initiating groups. (2) Preparation of zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles: Mesoporous silica nanoparticles containing initiating groups were dispersed in a mixed solvent of N,N-dimethylformamide and water, and 2-methacryloyloxyethyl phosphocholine, itaconic acid and lauryl methacrylate were added in sequence. Nitrogen gas was introduced for deoxygenation in the presence of 10-phenyl-10H-phenothiazine and triethylamine, and surface-initiated free radical polymerization was carried out under ultraviolet light irradiation to obtain zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles. (3) Preparation of acrylate preemulsion containing nanoparticles: Add methyl methacrylate, butyl acrylate, α-methacrylic acid, hydroxyethyl methacrylate and diacetone acrylamide to deionized water containing emulsifier, stir to form a monomer mixture, then add zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles, and disperse by shearing to obtain acrylate preemulsion containing nanoparticles. (4) Preparation of self-crosslinking acrylate emulsion: Ammonium persulfate was used as an initiator to carry out semi-continuous emulsion polymerization of acrylate pre-emulsion containing nanoparticles to obtain a self-crosslinking acrylate emulsion with a solid content of 40 wt%. (5) Preparation of self-crosslinking emulsion containing latent crosslinking agent: Dissolve adipic acid dihydrazide in deionized water to obtain adipic acid dihydrazide aqueous solution. Add the adipic acid dihydrazide aqueous solution dropwise to the self-crosslinking acrylate emulsion while stirring. After the addition is completed, continue stirring and adjust the pH of the emulsion to 8-9 to obtain a self-crosslinking emulsion containing latent crosslinking agent. (6) Preparation of water-based painting pigment paste containing functional nanoparticles: Glycerin, 1,2-propanediol, pigment and mesoporous silica nanoparticles grafted onto zwitterionic / hydrophobic copolymer are added to an aqueous solution of deionized water and dispersant. After mechanical stirring and dispersion, a self-crosslinking emulsion containing a latent crosslinking agent and an aqueous organosilicon defoamer are added and milled to obtain water-based painting pigment paste containing functional nanoparticles. (7) Preparation of water-based formaldehyde-free painting pigments: In the aqueous phase composed of deionized water and humectant, add a self-crosslinking emulsion containing a latent crosslinking agent and water-based painting pigment paste containing functional nanoparticles, and further add water-based organosilicon defoamer and mesoporous silica nanoparticles grafted with zwitterionic / hydrophobic copolymer. After stirring evenly, let stand to defoam and filter to obtain water-based formaldehyde-free painting pigments.

[0009] Preferably, in step (1), the amino-mesoporous silica nanoparticles have a specific surface area of ​​350-450 m². 2 / g, amino content 1.5-2.5mmol / g.

[0010] Preferably, in step (1), the mass ratio of 2-bromoisobutyryl bromide to amino mesoporous silica nanoparticles is 2:1.

[0011] Preferably, in step (2), the mass ratio of the mesoporous silica nanoparticles containing the initiating group, 2-methacryloyloxyethyl phosphocholine, itaconic acid, and lauryl methacrylate is 10:3-7:2-4:10-14.

[0012] Preferably, in step (2), the ultraviolet light irradiation conditions are: wavelength 405nm, light intensity 15mW / cm². 2 The reaction was carried out under continuous light and with stirring for 6 hours.

[0013] Preferably, in step (3), the mass ratio of emulsifier, deionized water, methyl methacrylate, butyl acrylate, α-methacrylic acid, hydroxyethyl methacrylate, diacetone acrylamide, and zwitterionic / hydrophobic copolymer-grafted mesoporous silica nanoparticles is 4:200:60:65:10:10:10-20:6-10.

[0014] Preferably, in step (3), the emulsifier is sodium dodecyl sulfate.

[0015] Preferably, in step (5), the mass ratio of adipic acid dihydrazide to self-crosslinking acrylate emulsion is 10-20:400.

[0016] Preferably, in step (6), the mass ratio of deionized water, dispersant, glycerol, 1,2-propanediol, pigment, zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles, self-crosslinking emulsion containing latent crosslinking agent, and aqueous organosilicon defoamer is 20:2:10:5:30:1-3:30:1.

[0017] Preferably, in step (6), the dispersant is sodium polyacrylate and the pigment is Pigment Blue 15:3.

[0018] Preferably, in step (6), the sand milling is performed by using a horizontal sand mill filled with 1.0mm zirconium oxide grinding beads, and circulating the sand mill for 60 minutes under the conditions of a sand milling speed of 1500r / min and a discharge temperature control of 30℃.

[0019] Preferably, in step (7), the mass ratio of deionized water, humectant, self-crosslinking emulsion containing latent crosslinking agent, water-based painting pigment paste containing functional nanoparticles, water-based organosilicon defoamer, and mesoporous silica nanoparticles grafted with zwitterionic / hydrophobic copolymer is 15:4:40:40:1:1.

[0020] Preferably, in step (7), the moisturizer comprises 3 parts by weight of glycerin and 1 part by weight of polyethylene glycol 400.

[0021] Preferably, in steps (6) and (7), the water-based silicone defoamer is defoamer BYK-024.

[0022] Furthermore, the present invention also provides a water-based formaldehyde-free painting pigment, which is obtained by the above-described method for preparing water-based formaldehyde-free painting pigment.

[0023] The beneficial effects of this invention are: This invention relates to a water-based formaldehyde-free painting pigment that incorporates mesoporous silica nanoparticles grafted with a zwitterionic / hydrophobic copolymer brush, constructing an organic-inorganic synergistically reinforced composite structure. This copolymer brush, with phosphocholine zwitterionic units and hydrophobic alkyl segments as side chains, forms a flexible brush layer on the surface of mesoporous silica. This not only improves the dispersion stability of the nanoparticles in acrylic emulsions but also acts as an internal plasticizer and interfacial bridging agent in the coating film. On one hand, the zwitterionic units enhance the adhesion between the coating and the substrate through electrostatic interactions and hydration, and impart good stain resistance and easy cleaning properties to the surface. On the other hand, the hydrophobic segments have good compatibility with the polymer matrix, reducing interfacial porosity and improving the density and water penetration resistance of the coating film. This structural design enables the coating film to possess both high strength and flexibility, overcoming the shortcomings of traditional coating films that are either hard and brittle or soft and sticky.

[0024] This invention uses diacetone acrylamide as a functional monomer, introducing it into the acrylate copolymer chain, and adding adipate dihydrazide as a crosslinking agent in the post-emulsion polymerization stage. This design ensures that the crosslinking reaction mainly occurs during the coating drying and curing process, avoiding the risk of pre-crosslinking during emulsion storage. During film formation, latex particles are first driven by capillary forces and surface tension to densely pack and fuse together, forming a continuous phase; subsequently, at ambient temperature or under slight heating, the hydrazide groups undergo efficient condensation with the ketone carbonyl groups, forming a hydrazone crosslinking network. This stepwise crosslinking mechanism ensures a uniform internal structure and no stress concentration in the coating, thus exhibiting excellent scrub resistance, abrasion resistance, and creep resistance. Simultaneously, the dynamic reversible nature of the hydrazone bonds helps alleviate stress concentration, improve microcrack development, and extend service life.

[0025] This invention employs a multi-stage strategy of adding functionalized nanoparticles to achieve a spatial gradient distribution of nanomaterials in the coating. Nanoparticles added during the acrylic pre-emulsion preparation stage are encapsulated within or on the surface of the emulsion particles, acting as a reinforcing phase to improve the mechanical stability of the emulsion. Nanoparticles added during the pigment paste preparation stage can adsorb onto the surface of pigment particles, preventing pigment flocculation through steric hindrance and improving tinting strength and color uniformity. Nanoparticles added during the final paint formulation stage preferentially distribute on the coating surface, forming alternating hydrophobic and hydrophilic regions within the micro / nano structure, thus achieving a balance between low surface energy anti-adhesion and high surface cleanliness. This hierarchical addition method maximizes the functionality of nanoparticles at different levels, avoiding the aggregation or uneven distribution problems caused by single additions.

[0026] Furthermore, the entire system completely eliminates formaldehyde-based crosslinking agents, employing biocompatible raw materials such as zwitterionic phosphate and itaconic acid, thus preventing the release of harmful substances at the source. The introduction of zwitterionic polymers also reduces the amount of traditional surfactants and dispersants, lowering the content of migratable organic matter in the system and ensuring the product meets the most stringent environmental standards. The abundant hydrophilic groups on the coating surface also make it easy to clean with water or neutral detergents, making it particularly suitable for painting scenarios frequently used by children. Ultimately, this solution achieves a comprehensive improvement in safety, durability, functionality, and environmental friendliness through the synergy of molecular structure design, crosslinking control, and multi-scale composite processes. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0028] Example 1: Step 1: Preparation of mesoporous silica nanoparticles containing initiating groups In a three-necked flask equipped with a mechanical stirrer, a constant-temperature oil bath, a condenser, and nitrogen inlet and outlet, add 200g of N,N-dimethylformamide and 20g of deionized water. After stirring evenly, add 10g of amino-mesoporous silica nanoparticles (amino-modified monodisperse porous mesoporous silica microspheres produced by Shaanxi Xingbei Aike Biotechnology Co., Ltd., with a specific surface area of ​​392m²). 2 (Amino content 2.1 mmol / g), dispersed for 30 min to obtain a uniform suspension, placed in an ice-water bath to cool to 0-5℃ and purged with nitrogen. Prepare a solution in a dropping funnel: add 20 g of 2-bromoisobutyryl bromide and 30 g of N,N-dimethylformamide, stir to dissolve and set aside. Prepare another solution in a dropping funnel: add 15 g of triethylamine and 30 g of N,N-dimethylformamide, stir to dissolve and set aside. Keep the system temperature no higher than 10℃, and simultaneously add the above two solutions dropwise over 60 min, maintaining nitrogen protection and stirring during the addition. After the addition is complete, remove the ice bath, raise the system temperature to 25℃, and continue stirring under nitrogen protection for 4 h. After the reaction, wash three times with deionized water, then twice with anhydrous ethanol, and vacuum dry at 40℃ for 12 h to obtain mesoporous silica nanoparticles containing initiating groups. Step 2: Preparation of zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles In a quartz reaction flask equipped with a magnetic stirrer and nitrogen inlet / outlet, 10g of mesoporous silica nanoparticles containing initiating groups, 150g of N,N-dimethylformamide, and 50g of deionized water were added and ultrasonically dispersed for 30min. Then, 3g of 2-methacryloyloxyethyl phosphocholine, 2g of itaconic acid, and 10g of lauryl methacrylate were added sequentially and stirred for 20min. Next, 1g of 10-phenyl-10H-phenothiazine and 4g of triethylamine were added, and the mixture was bubbled and deoxygenated for 30min under nitrogen protection. The reaction flask was placed at 25°C, and an array of 405nm ultraviolet light-emitting diodes was arranged externally, with the light intensity controlled at 15mW / cm². 2 The reaction was continuously irradiated and stirred for 6 hours. After the reaction was completed, the mixture was centrifuged at 12000 r / min for 10 min, the supernatant was discarded, the precipitate was resuspended in a mixed solution of 20 g methanol and 80 g deionized water and centrifuged, washed 5 times, washed 2 times with deionized water, and dried under vacuum at 40 °C for 24 h to obtain mesoporous silica nanoparticles brush-grafted with zwitterionic / hydrophobic copolymer. Step 3: Preparation of acrylate preemulsion containing nanoparticles In a beaker, add 200g of deionized water and 4g of sodium dodecyl sulfate, and disperse at 800r / min for 15min to form an emulsifier aqueous solution. Then, add 60g of methyl methacrylate, 65g of butyl acrylate, 10g of α-methacrylic acid, 10g of hydroxyethyl methacrylate, and 10g of diacetone acrylamide in sequence, and stir at 800r / min for 20min to form an oil phase monomer mixture. Then, add 6g of zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles, increase the stirring speed to 1200r / min, and disperse for 30min to obtain an acrylate preemulsion containing nanoparticles. Step 4: Preparation of self-crosslinking acrylate emulsion In a stainless steel reactor equipped with a mechanical stirrer, thermometer, nitrogen inlet and outlet, and dropping funnel, 240g of deionized water and 1g of sodium dodecyl sulfate were added. After stirring for 30 minutes, nitrogen gas was introduced for 30 minutes, and nitrogen protection was maintained throughout the process. The temperature was raised to 78°C, and 20g of acrylate pre-emulsion containing nanoparticles was added dropwise. In a separate beaker, an initiator solution was prepared: 2g of ammonium persulfate and 20g of deionized water were added, stirred and dissolved, and then added dropwise to the reactor within 10 minutes. The system temperature was maintained at 80°C for 30 minutes to form a stable emulsion seed. Subsequently, 352g of acrylate pre-emulsion containing nanoparticles and 1g of ammonium persulfate dissolved in 20g of deionized water were added dropwise. The addition time was controlled at 2 hours, and the temperature was maintained at 80°C and nitrogen protection was maintained throughout the process. After the addition was completed, continue stirring at the temperature for 60 minutes, then stop heating and cool to below 40°C. Adjust the pH of the emulsion to 8.5 with sodium hydroxide aqueous solution, filter to remove a small amount of gel, concentrate under reduced pressure to obtain a self-crosslinking acrylate emulsion with a solid content of 40 wt%. Step 5: Preparation of a self-crosslinking emulsion containing a latent crosslinking agent Add 80g of deionized water to a beaker and place it at 50℃. Add 12g of adipic acid dihydrazide and stir for 15min to obtain an aqueous solution of adipic acid dihydrazide. Take 400g of self-crosslinking acrylate emulsion and place it in a stirred beaker. Cool it to 25℃ and add the above aqueous solution of adipic acid dihydrazide dropwise over 30min using a constant-rate titration device while stirring at 300r / min. During the dropwise addition, use a cold water bath to control the emulsion temperature to not exceed 30℃. After the dropwise addition is completed, continue stirring for 60min. Then adjust the pH of the system to 8.5 with ammonia to obtain a self-crosslinking emulsion containing a latent crosslinking agent. Step Six: Preparation of Water-Based Painting Pigment Containing Functional Nanoparticles In a stainless steel dispersion tank equipped with a high-speed disperser, add 20g of deionized water and 2g of sodium polyacrylate (provided by Shanghai Aladdin Biochemical Technology Co., Ltd., item number P434408, weight average molecular weight 5100), and stir at 800r / min for 15min to form a dispersion solution. Then, add 1g of zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles, 10g of glycerol, and 5g of... 1,2-Propanediol was stirred at 800 r / min for 10 min, followed by the addition of 30 g of Pigment Blue 15:3. The stirring speed was gradually increased to 1500 r / min and dispersed for 30 min to obtain a primary pigment paste. 30 g of a self-crosslinking emulsion containing a latent crosslinking agent and 1 g of organosilicon-based water-based defoamer BYK-024 were added to the system. The mixture was stirred at 1500 r / min for 10 min to form a homogeneous mixture. The mixture was then fed into a horizontal sand mill filled with 1.0 mm zirconia grinding beads and circulated for 60 min at a sand milling speed of 1500 r / min and a discharge temperature of 30 °C to obtain a water-based painting pigment paste containing functional nanoparticles. Step 7: Prepare water-based formaldehyde-free painting pigments In a beaker equipped with a paddle stirrer, add 15g of deionized water, 3g of glycerin and 1g of polyethylene glycol 400, and stir at 300 rpm for 5 min to obtain a humectant mixture. Then, add 40g of a self-crosslinking emulsion containing a latent crosslinking agent and 40g of water-based painting pigment paste containing functional nanoparticles in sequence, and maintain stirring at 300 rpm for 20 min. Then, add 1g of water-based silicone defoamer BYK-024 and 1g of zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles, and continue stirring for 10 min. Finally, let the system stand to defoam for 30 min, and filter through a 100-mesh filter to obtain water-based formaldehyde-free painting pigment.

[0029] Example 2: Step 1: Preparation of mesoporous silica nanoparticles containing initiating groups In a three-necked flask equipped with a mechanical stirrer, a constant-temperature oil bath, a condenser, and nitrogen inlet and outlet, add 200g of N,N-dimethylformamide and 20g of deionized water. After stirring evenly, add 10g of amino-mesoporous silica nanoparticles (amino-modified monodisperse porous mesoporous silica microspheres produced by Shaanxi Xingbei Aike Biotechnology Co., Ltd., with a specific surface area of ​​392m²). 2 (Amino content 2.1 mmol / g), dispersed for 30 min to obtain a uniform suspension, placed in an ice-water bath to cool to 0-5℃ and purged with nitrogen. Prepare a solution in a dropping funnel: add 20 g of 2-bromoisobutyryl bromide and 30 g of N,N-dimethylformamide, stir to dissolve and set aside. Prepare another solution in a dropping funnel: add 15 g of triethylamine and 30 g of N,N-dimethylformamide, stir to dissolve and set aside. Keep the system temperature no higher than 10℃, and simultaneously add the above two solutions dropwise over 60 min, maintaining nitrogen protection and stirring during the addition. After the addition is complete, remove the ice bath, raise the system temperature to 25℃, and continue stirring under nitrogen protection for 4 h. After the reaction, wash three times with deionized water, then twice with anhydrous ethanol, and vacuum dry at 40℃ for 12 h to obtain mesoporous silica nanoparticles containing initiating groups. Step 2: Preparation of zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles In a quartz reaction flask equipped with a magnetic stirrer and nitrogen inlet / outlet, 10g of mesoporous silica nanoparticles containing initiating groups, 150g of N,N-dimethylformamide, and 50g of deionized water were added and ultrasonically dispersed for 30min. Then, 5g of 2-methacryloyloxyethyl phosphocholine, 3g of itaconic acid, and 12g of lauryl methacrylate were added sequentially and stirred for 20min. Next, 1g of 10-phenyl-10H-phenothiazine and 4g of triethylamine were added, and the mixture was bubbled and deoxygenated for 30min under nitrogen protection. The reaction flask was placed at 25°C, and an array of 405nm ultraviolet light-emitting diodes was arranged externally, with the light intensity controlled at 15mW / cm². 2 The reaction was continuously irradiated and stirred for 6 hours. After the reaction was completed, the mixture was centrifuged at 12000 r / min for 10 min, the supernatant was discarded, the precipitate was resuspended in a mixed solution of 20 g methanol and 80 g deionized water and centrifuged, washed 5 times, washed 2 times with deionized water, and dried under vacuum at 40 °C for 24 h to obtain mesoporous silica nanoparticles brush-grafted with zwitterionic / hydrophobic copolymer. Step 3: Preparation of acrylate preemulsion containing nanoparticles In a beaker, add 200g of deionized water and 4g of sodium dodecyl sulfate, and disperse at 800r / min for 15min to form an emulsifier aqueous solution. Then, add 60g of methyl methacrylate, 65g of butyl acrylate, 10g of α-methacrylic acid, 10g of hydroxyethyl methacrylate, and 15g of diacetone acrylamide in sequence, and stir at 800r / min for 20min to form an oil phase monomer mixture. Then, add 8g of zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles, increase the stirring speed to 1200r / min, and disperse for 30min to obtain an acrylate preemulsion containing nanoparticles. Step 4: Preparation of self-crosslinking acrylate emulsion In a stainless steel reactor equipped with a mechanical stirrer, thermometer, nitrogen inlet and outlet, and dropping funnel, 240g of deionized water and 1g of sodium dodecyl sulfate were added. After stirring for 30 minutes, nitrogen gas was introduced for 30 minutes, and nitrogen protection was maintained throughout the process. The temperature was raised to 78°C, and 20g of acrylate pre-emulsion containing nanoparticles was added dropwise. In a separate beaker, an initiator solution was prepared: 2g of ammonium persulfate and 20g of deionized water were added, stirred and dissolved, and then added dropwise to the reactor within 10 minutes. The system temperature was maintained at 80°C for 30 minutes to form a stable emulsion seed. Subsequently, 352g of acrylate pre-emulsion containing nanoparticles and 1g of ammonium persulfate dissolved in 20g of deionized water were added dropwise. The addition time was controlled at 2 hours, and the temperature was maintained at 80°C and nitrogen protection was maintained throughout the process. After the addition was completed, continue stirring at the temperature for 60 minutes, then stop heating and cool to below 40°C. Adjust the pH of the emulsion to 8.5 with sodium hydroxide aqueous solution, filter to remove a small amount of gel, concentrate under reduced pressure to obtain a self-crosslinking acrylate emulsion with a solid content of 40 wt%. Step 5: Preparation of a self-crosslinking emulsion containing a latent crosslinking agent Add 80g of deionized water to a beaker and place it at 50℃. Add 16g of adipic acid dihydrazide and stir for 15min to obtain an aqueous solution of adipic acid dihydrazide. Take 400g of self-crosslinking acrylate emulsion and place it in a stirred beaker. Cool it to 25℃ and add the above aqueous solution of adipic acid dihydrazide dropwise over 30min using a constant-rate titration device while stirring at 300r / min. During the dropwise addition, use a cold water bath to control the emulsion temperature to not exceed 30℃. After the dropwise addition is completed, continue stirring for 60min. Then adjust the pH of the system to 8.5 with ammonia to obtain a self-crosslinking emulsion containing a latent crosslinking agent. Step Six: Preparation of Water-Based Painting Pigment Containing Functional Nanoparticles In a stainless steel dispersion tank equipped with a high-speed disperser, add 20g of deionized water and 2g of sodium polyacrylate (provided by Shanghai Aladdin Biochemical Technology Co., Ltd., item number P434408, weight average molecular weight 5100), and stir at 800r / min for 15min to form a dispersion solution. Then, add 2g of zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles, 10g of glycerol, and 5g of... 1,2-Propanediol was stirred at 800 r / min for 10 min, followed by the addition of 30 g of Pigment Blue 15:3. The stirring speed was gradually increased to 1500 r / min and dispersed for 30 min to obtain a primary pigment paste. 30 g of a self-crosslinking emulsion containing a latent crosslinking agent and 1 g of organosilicon-based water-based defoamer BYK-024 were added to the system. The mixture was stirred at 1500 r / min for 10 min to form a homogeneous mixture. The mixture was then fed into a horizontal sand mill filled with 1.0 mm zirconia grinding beads and circulated for 60 min at a sand milling speed of 1500 r / min and a discharge temperature of 30 °C to obtain a water-based painting pigment paste containing functional nanoparticles. Step 7: Prepare water-based formaldehyde-free painting pigments In a beaker equipped with a paddle stirrer, add 15g of deionized water, 3g of glycerin and 1g of polyethylene glycol 400, and stir at 300 rpm for 5 min to obtain a humectant mixture. Then, add 40g of a self-crosslinking emulsion containing a latent crosslinking agent and 40g of water-based painting pigment paste containing functional nanoparticles in sequence, and maintain stirring at 300 rpm for 20 min. Then, add 1g of water-based silicone defoamer BYK-024 and 1g of zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles, and continue stirring for 10 min. Finally, let the system stand to defoam for 30 min, and filter through a 100-mesh filter to obtain water-based formaldehyde-free painting pigment.

[0030] Example 3: Step 1: Preparation of mesoporous silica nanoparticles containing initiating groups In a three-necked flask equipped with a mechanical stirrer, a constant-temperature oil bath, a condenser, and nitrogen inlet and outlet, add 200g of N,N-dimethylformamide and 20g of deionized water. After stirring evenly, add 10g of amino-mesoporous silica nanoparticles (amino-modified monodisperse porous mesoporous silica microspheres produced by Shaanxi Xingbei Aike Biotechnology Co., Ltd., with a specific surface area of ​​392m²). 2(Amino content 2.1 mmol / g), dispersed for 30 min to obtain a uniform suspension, placed in an ice-water bath to cool to 0-5℃ and purged with nitrogen. Prepare a solution in a dropping funnel: add 20 g of 2-bromoisobutyryl bromide and 30 g of N,N-dimethylformamide, stir to dissolve and set aside. Prepare another solution in a dropping funnel: add 15 g of triethylamine and 30 g of N,N-dimethylformamide, stir to dissolve and set aside. Keep the system temperature no higher than 10℃, and simultaneously add the above two solutions dropwise over 60 min, maintaining nitrogen protection and stirring during the addition. After the addition is complete, remove the ice bath, raise the system temperature to 25℃, and continue stirring under nitrogen protection for 4 h. After the reaction, wash three times with deionized water, then twice with anhydrous ethanol, and vacuum dry at 40℃ for 12 h to obtain mesoporous silica nanoparticles containing initiating groups. Step 2: Preparation of zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles In a quartz reaction flask equipped with a magnetic stirrer and nitrogen inlet / outlet, 10g of mesoporous silica nanoparticles containing initiating groups, 150g of N,N-dimethylformamide, and 50g of deionized water were added and ultrasonically dispersed for 30min. Then, 7g of 2-methacryloyloxyethyl phosphocholine, 4g of itaconic acid, and 14g of lauryl methacrylate were added sequentially and stirred for 20min. Next, 1g of 10-phenyl-10H-phenothiazine and 4g of triethylamine were added, and the mixture was bubbled and deoxygenated for 30min under nitrogen protection. The reaction flask was placed at 25°C, and an array of 405nm ultraviolet light-emitting diodes was arranged externally, with the light intensity controlled at 15mW / cm². 2 The reaction was continuously irradiated and stirred for 6 hours. After the reaction was completed, the mixture was centrifuged at 12000 r / min for 10 min, the supernatant was discarded, the precipitate was resuspended in a mixed solution of 20 g methanol and 80 g deionized water and centrifuged, washed 5 times, washed 2 times with deionized water, and dried under vacuum at 40 °C for 24 h to obtain mesoporous silica nanoparticles brush-grafted with zwitterionic / hydrophobic copolymer. Step 3: Preparation of acrylate preemulsion containing nanoparticles In a beaker, add 200g of deionized water and 4g of sodium dodecyl sulfate, and disperse at 800r / min for 15min to form an emulsifier aqueous solution. Then, add 60g of methyl methacrylate, 65g of butyl acrylate, 10g of α-methacrylic acid, 10g of hydroxyethyl methacrylate, and 20g of diacetone acrylamide in sequence, and stir at 800r / min for 20min to form an oil phase monomer mixture. Then, add 10g of zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles, increase the stirring speed to 1200r / min, and disperse for 30min to obtain an acrylate preemulsion containing nanoparticles. Step 4: Preparation of self-crosslinking acrylate emulsion In a stainless steel reactor equipped with a mechanical stirrer, thermometer, nitrogen inlet and outlet, and dropping funnel, 240g of deionized water and 1g of sodium dodecyl sulfate were added. After stirring for 30 minutes, nitrogen gas was introduced for 30 minutes, and nitrogen protection was maintained throughout the process. The temperature was raised to 78°C, and 20g of acrylate pre-emulsion containing nanoparticles was added dropwise. In a separate beaker, an initiator solution was prepared: 2g of ammonium persulfate and 20g of deionized water were added, stirred and dissolved, and then added dropwise to the reactor within 10 minutes. The system temperature was maintained at 80°C for 30 minutes to form a stable emulsion seed. Subsequently, 352g of acrylate pre-emulsion containing nanoparticles and 1g of ammonium persulfate dissolved in 20g of deionized water were added dropwise. The addition time was controlled at 2 hours, and the temperature was maintained at 80°C and nitrogen protection was maintained throughout the process. After the addition was completed, continue stirring at the temperature for 60 minutes, then stop heating and cool to below 40°C. Adjust the pH of the emulsion to 8.5 with sodium hydroxide aqueous solution, filter to remove a small amount of gel, concentrate under reduced pressure to obtain a self-crosslinking acrylate emulsion with a solid content of 40 wt%. Step 5: Preparation of a self-crosslinking emulsion containing a latent crosslinking agent Add 80g of deionized water to a beaker and place it at 50℃. Add 20g of adipic acid dihydrazide and stir for 15min to obtain an aqueous solution of adipic acid dihydrazide. Take 400g of self-crosslinking acrylate emulsion and place it in a stirred beaker. Cool it to 25℃ and add the above aqueous solution of adipic acid dihydrazide dropwise over 30min using a constant-rate titration device while stirring at 300r / min. During the dropwise addition, use a cold water bath to control the emulsion temperature to not exceed 30℃. After the dropwise addition is completed, continue stirring for 60min. Then adjust the pH of the system to 8.5 with ammonia to obtain a self-crosslinking emulsion containing a latent crosslinking agent. Step Six: Preparation of Water-Based Painting Pigment Containing Functional Nanoparticles In a stainless steel dispersion tank equipped with a high-speed disperser, add 20g of deionized water and 2g of sodium polyacrylate (provided by Shanghai Aladdin Biochemical Technology Co., Ltd., item number P434408, weight average molecular weight 5100), and stir at 800r / min for 15min to form a dispersion solution. Then, add 3g of zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles, 10g of glycerol, and 5g of... 1,2-Propanediol was stirred at 800 r / min for 10 min, followed by the addition of 30 g of Pigment Blue 15:3. The stirring speed was gradually increased to 1500 r / min and dispersed for 30 min to obtain a primary pigment paste. 30 g of a self-crosslinking emulsion containing a latent crosslinking agent and 1 g of organosilicon-based water-based defoamer BYK-024 were added to the system. The mixture was stirred at 1500 r / min for 10 min to form a homogeneous mixture. The mixture was then fed into a horizontal sand mill filled with 1.0 mm zirconia grinding beads and circulated for 60 min at a sand milling speed of 1500 r / min and a discharge temperature of 30 °C to obtain a water-based painting pigment paste containing functional nanoparticles. Step 7: Prepare water-based formaldehyde-free painting pigments In a beaker equipped with a paddle stirrer, add 15g of deionized water, 3g of glycerin and 1g of polyethylene glycol 400, and stir at 300 rpm for 5 min to obtain a humectant mixture. Then, add 40g of a self-crosslinking emulsion containing a latent crosslinking agent and 40g of water-based painting pigment paste containing functional nanoparticles in sequence, and maintain stirring at 300 rpm for 20 min. Then, add 1g of water-based silicone defoamer BYK-024 and 1g of zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles, and continue stirring for 10 min. Finally, let the system stand to defoam for 30 min, and filter through a 100-mesh filter to obtain water-based formaldehyde-free painting pigment.

[0031] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that 2-methacryloyloxyethyl phosphocholine, itaconic acid, and lauryl methacrylate are not added in step 2, nor are 10-phenyl-10H-phenothiazine and triethylamine. Instead, 10g of the mesoporous silica nanoparticles containing initiating groups obtained in step 1 are dispersed in 150g of N,N-dimethylformamide and 50g of deionized water. After being uniformly stirred by ultrasound and mechanical stirring, they are directly centrifuged, washed, and vacuum dried to obtain mesoporous silica nanoparticles with only initiating groups on the surface and without zwitterionic / hydrophobic copolymer brush structures. In steps 3, 6, and 7, all the mesoporous silica nanoparticles grafted with zwitterionic / hydrophobic copolymer brushes used in Example 2 are replaced by the above-mentioned mesoporous silica nanoparticles containing only initiating groups, and the other conditions are the same as in Example 2.

[0032] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is as follows: In step two, the amount of mesoporous silica nanoparticles containing initiating groups (10g), N,N-dimethylformamide (150g), and deionized water (50g) remains unchanged. The amount of 2-methacryloyloxyethyl phosphocholine is adjusted from 5g to 0g, while the amount of lauryl methacrylate is increased from 12g to 17g. The amount of itaconic acid remains at 3g. Surface polymerization is carried out under nitrogen protection and the same light conditions, so that the surface of the resulting mesoporous silica nanoparticles is only grafted with a hydrophobic copolymer brush composed of itaconic acid and lauryl methacrylate, without the zwitterionic structure of phosphocholine. In subsequent steps three, six, and seven, the mesoporous silica nanoparticles grafted with this type of polymer brush are added according to the addition sequence and total amount in Example 2, and the other conditions are the same as in Example 2.

[0033] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that: in step three, the amount of zwitterionic / hydrophobic copolymer-grafted mesoporous silica nanoparticles added was adjusted from 8g to 11g, and in steps six and seven, zwitterionic / hydrophobic copolymer-grafted mesoporous silica nanoparticles were no longer added, so that all 11g of zwitterionic / hydrophobic copolymer-grafted mesoporous silica nanoparticles were added at once in the acrylate pre-emulsion stage, and the total amount of nanoparticles added remained the same as in Example 2, and the other conditions were the same as in Example 2.

[0034] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that in step four, the timing of adding adipic acid dihydrazide was changed from post-crosslinking after the emulsion polymerization to simultaneous addition during the emulsion polymerization process. Specifically, 16g of adipic acid dihydrazide was dissolved in 80g of deionized water to prepare an aqueous solution, which was then added dropwise at 80°C simultaneously with the acrylate pre-emulsion containing zwitterionic / hydrophobic copolymer-grafted mesoporous silica nanoparticles and the ammonium persulfate initiator solution. The dropwise addition time was 2 hours, and after holding at the temperature for 1 hour, it was cooled to room temperature. Only the pH was adjusted to 8.5, and the adipic acid dihydrazide aqueous solution was not prepared and added separately in step five. The other conditions were the same as in Example 2.

[0035] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that: in step three, the amounts of methyl methacrylate, butyl acrylate, α-methacrylic acid and hydroxyethyl methacrylate monomers are kept constant, and 15g of diacetone acrylamide is completely replaced with 15g of butyl acrylate so that the total mass of acrylate monomers remains unchanged and the self-crosslinking polymer does not contain diacetone acrylamide structural units. In step five, the mixture is prepared in the same manner as in Example 2, and an aqueous solution containing 16g of adipate dihydrazide is added dropwise to 400g of self-crosslinking acrylate emulsion at a temperature not exceeding 30°C and the pH is adjusted to 8.5. The remaining conditions are the same as in Example 2.

[0036] Comparative Example 6: The difference between Comparative Example 6 and Example 2 is that no zwitterionic / hydrophobic copolymer-grafted mesoporous silica nanoparticles are added in steps three, six, and seven. Correspondingly, 8g of zwitterionic / hydrophobic copolymer-grafted mesoporous silica nanoparticles are removed in step three, 2g of zwitterionic / hydrophobic copolymer-grafted mesoporous silica nanoparticles are removed in step six, and 1g of zwitterionic / hydrophobic copolymer-grafted mesoporous silica nanoparticles are removed in step seven. The remaining formulation components, order of addition, and operating conditions are the same as in Example 2.

[0037] Performance testing: Sample preparation: Cold-rolled steel plates with dimensions of 150mm × 70mm × 0.5mm, treated with degreasing, rust removal, and phosphating according to GB / T 9271-2008, were selected as standard test plates for mechanical property and durability testing, and as substrates for simulated painting. Test plates were prepared using the scraping method according to GB / T1727-2021. The samples of the examples and comparative examples were scraped onto the surface of the steel plates using a stainless steel wet film preparation tool, with the wet film thickness controlled at (100±5)μm and the scraping direction consistent. After the test plates were placed in an environment of 23℃±2℃ and relative humidity of (50±5)% for 24 hours to dry to the touch, they were cured under the same conditions for 7 days to serve as test specimens for subsequent performance tests.

[0038] Viscosity determination: The viscosity was determined according to GB / T 1723-1993 using a Forte-4 cup at (23.0±0.5)℃. Each sample was tested three times and the average value was taken. The results are shown in Table 1.

[0039] Water resistance of the coating film: The immersion method in GB / T 1733-1993 was used. Grade III water conforming to GB / T 6682-2008 was added to the glass tank and the water temperature was controlled at (23±2)℃. The steel plate sample was suspended vertically so that the coating film was completely immersed in the water. After immersion for 24 hours, the sample was removed and dried. The coating film was observed under a standard light source to see if it blistered, cracked, peeled, or discolored. The observation was repeated every 24 hours until obvious loss of gloss or blistering occurred. The total immersion time from when the coating film remained intact to when obvious failure occurred characterized the water resistance. The results are shown in Table 1.

[0040] Coating wet scrub resistance and cleanability: According to GB / T 31410-2015, a paint film was prepared on a standard cement fiberboard. After drying and curing for 7 days, the coating was repeatedly scrubbed on a dedicated wet scrub resistance tester with a specified brush, load, and detergent solution with a pH of 10.0. The number of scrubs required for the paint film to be worn through to expose the substrate was recorded. At the same time, the cleanability level of the coating after contamination and cleaning was evaluated according to the standard method. According to the contamination-cleaning procedure in the standard, the coating was contaminated with standard contaminant, dried, and then scrubbed 200 times with a neutral detergent and sponge under a specified load. The color difference ΔE of the coating before and after contamination was measured. The results are shown in Table 1.

[0041] Coating adhesion: The coating was tested on steel plate specimens according to GB / T 5210-2006. An aluminum pull-out head of specified diameter was used. After the coating was completely dry, epoxy adhesive was applied. After 24 hours, the coating was pulled off on a pull-out tester at a stress rise rate of (1±0.1) MPa / s. The maximum pull-out force at failure was recorded and the adhesion strength was calculated. The results are shown in Table 1.

[0042] Mirror gloss of coating: The gloss was measured on steel plate samples under 60° geometric conditions according to GB / T 9754-2007. A gloss meter conforming to the standard was used and calibrated according to the standard. The gloss was measured at three different positions on each sample and the average value was taken. The results are shown in Table 1.

[0043] Volatile organic compounds (VOCs): The VOC content of each pigment sample was determined according to GB / T 23985-2009, and evaluated with reference to the relevant limits in GB 18581-2020 "Limits of Hazardous Substances in Wood Coatings". During the test, each pigment sample was placed in an aluminum box and kept at constant weight at a specified temperature. The mass loss was calculated and the moisture and non-volatile matter fractions were deducted to obtain the VOC mass fraction. The results are shown in Table 1.

[0044] Paper colorfastness and evenness of application: Tested on medium-rough watercolor paper conforming to QB / T 2204-1996 and GB / T 22830-2020, with a basis weight of 230 g / m². 2 The whiteness and absorbency meet the above-mentioned standards for watercolor paper used by middle school students and art students. For each sample, 0.20g of painting pigment was evenly applied to a 5cm×5cm area using a specified brush (wolf hair liner brush, 2mm width). The application was controlled by three unidirectional strokes. After application, the paper was dried for 24 hours at (23±2)℃ and (50±5)% relative humidity. Then, according to GB / T 9761-2008 and GB / T 11186.2-2012, the Lab* value of the coated area was measured using a benchtop spectrophotometer under a standard light source D65. The color difference ΔE and relative tinting strength K / S value compared to the blank paper were calculated. K / S and color difference uniformity were used to characterize the coloring performance and application uniformity of the paper. The results are shown in Table 1.

[0045] Table 1 Performance Test Results

[0046] Data Analysis: As can be seen from the data in Examples 1-3 of Table 1, the water-based formaldehyde-free painting pigments prepared by this invention exhibit a general trend of moderate construction rheology, synergistic enhancement of coating density and interface stability under different grafting amounts and crosslinking degrees. With the systematic adjustment of the amount of zwitterionic / hydrophobic copolymer brush on the mesoporous silica surface and the amounts of diacetone acrylamide and adipate dihydrazide in the emulsion, the coating maintains good spreadability and feel, while exhibiting high levels of water resistance, wet scrubbing resistance, surface cleanability, and adhesion. At the same time, the migratable organic components remain in a low range, and the color difference control and relative tinting strength also show stable pigment dispersion and coating effects. When the crosslinking and inorganic content are increased to an appropriate level, a multi-scale network composed of a self-crosslinking acrylic resin skeleton, graft copolymer brush, and nano-silica is formed inside the coating film, providing a flexible and durable bonding layer at the interface between the paper base and pigment particles, and forming a hydration interface rich in phosphocholine and carboxyl groups on the surface, thus taking into account the safety, durability, easy cleaning, and color stability of the painting pigments in children's application scenarios.

[0047] As can be seen from the data in Table 1 for Example 2 and Comparative Example 1, when only unmodified silica particles are used without the zwitterionic / hydrophobic copolymer brush layer, the system's application viscosity is significantly higher, the coating gloss and wet scrub resistance decrease, the cleanability and color difference increase, and the adhesion and relative tinting strength also deteriorate to varying degrees. The main reason is that the exposed silica surface is highly hydrophilic and prone to aggregation, making it difficult to form a flexible transition layer compatible with the self-crosslinking acrylic emulsion. This hinders the rearrangement of latex particles during film formation, resulting in discontinuous rigid inorganic aggregates within the coating film. This weakens the coating and fixation of pigment particles and creates rough micro-regions on the surface, easily trapping dirt and causing stress concentration. In contrast, the copolymer brush grafted with phosphocholine and hydrophobic segments in Example 2 provides a gradual polarity and flexibility between the inorganic core and the organic matrix, achieving a synergistic effect of mechanical enhancement, pigment stability, and easy surface cleaning, exhibiting a significant synergistic effect of 1+1>2.

[0048] As can be seen from the data in Table 1 for Example 2 and Comparative Example 2, while maintaining the presence of nano-silica, the coating gloss is improved to some extent when only carboxyl groups and long-chain hydrophobic monomers are grafted without the presence of phosphocholine-type zwitterionic structures. However, the improvement in water resistance, wet scrubbing resistance, and surface cleanability is limited, and the adhesion and color stability are also lower than in Example 2. The main reason is that with only hydrophobic segments, the polar shielding of the particle surface is strong. Although this is beneficial for reducing surface energy and improving initial gloss, the hydration layer is insufficient, the electrostatic stability is weakened, and the reagglomeration of pigments and fillers during high-shear dispersion and drying is more likely to occur, leading to local pigment accumulation and micropore formation, making it difficult to improve durability and cleanability simultaneously. In Example 2, after introducing phosphocholine zwitterionic units, the particle surface maintains moderate hydrophobicity and forms a stable hydration shell and ion association network. This synergistic effect with the hydrophobic segments in pigment wetting, slurry rheology control, and dry coating antifouling results in comprehensive optimization of gloss, durability, and easy-to-clean properties.

[0049] As can be seen from the data in Table 1 for Example 2 and Comparative Example 3, when nano-silica is added only once in the pre-emulsion stage and not replenished in subsequent pigment pastes and finished paints, the coating's water resistance, wet scrub resistance, and adhesion are better than the system without any nanoparticles, but still significantly lower than Example 2. Surface cleanability and tinting strength also show differences. The main reason is that the single-stage addition causes most of the grafted nanoparticles to be fixed inside the emulsion particles or near the substrate, making it difficult to form a continuous inorganic / organic synergistic interface structure around the pigment particles and on the coating surface. This results in insufficient spatial hierarchy for pigment coating, surface densification, and anti-fouling regulation. Example 2, by introducing grafted nano-silica in three stages—pre-emulsion, pigment paste, and finished paint—creates a gradient distribution of particles along the thickness direction, from bottom reinforcement and middle coating to surface regulation. This significantly amplifies the durability and easy-to-clean effect under the same nanoparticle dosage, demonstrating the synergistic effect between the multi-stage addition process and the grafted structure.

[0050] As can be seen from the data in Table 1 for Example 2 and Comparative Example 4, when adipic acid dihydrazide is added simultaneously with the monomer during the emulsion polymerization process, the system viscosity is significantly higher, and the coating gloss, water resistance, and wet scrub resistance all decrease. Cleanability and adhesion are also inferior to those in Example 2. The fundamental reason is that the crosslinking agent participates in the emulsion polymerization prematurely, causing the diacetone acrylamide units to crosslink before the particles have fully formed a film and interdiffused. This generates a large number of unevenly distributed microgel particles, disrupting the fusion and rearrangement between latex particles, resulting in hard particles and interface defects within the coating film. On the one hand, this premature crosslinking weakens the continuity and stress relief capacity of the overall network, making it difficult to achieve the expected scrub resistance and water resistance. On the other hand, the obstructed surface leveling and increased micro-roughness also simultaneously reduce gloss and cleanability. In contrast, Example 2 employs a latent crosslinking strategy by adding adipic acid dihydrazide after polymerization, which allows the crosslinking reaction to mainly occur during the film formation and post-curing stages. This is more conducive to building a uniform and dense crosslinked network while ensuring sufficient interdiffusion of latex particles, thus exhibiting significant structure-process synergistic advantages.

[0051] As can be seen from the data in Example 2 and Comparative Example 5 in Table 1, when the diacetone acrylamide monomer is completely removed and replaced only with a more flexible alkyl acrylate while maintaining the addition of adipic dihydrazide, the coating viscosity is significantly reduced and the initial gloss is improved. However, the water resistance, wet scrubbing resistance, adhesion, cleanability, and color stability are all significantly reduced. This is because, without active carbonyl sites, adipic diamide is difficult to effectively condense with the emulsion backbone. The coating can only maintain its structure through physical entanglement and weak polarity, resulting in insufficient network strength and weak swelling resistance. On the one hand, the high proportion of soft segments makes the coating prone to plastic deformation and pigment migration during wet scrubbing and repeated washing, causing surface residue and color difference accumulation. On the other hand, the lack of chemical crosslinking points also makes it easier for migratable small molecules and additives to precipitate under heating and scrubbing conditions, increasing the risk of VOC content and surface contamination.

[0052] As can be seen from the data in Table 1 for Example 2 and Comparative Example 6, when the mesoporous silica and its graft copolymer brush were completely removed, the system's application rheology was at a moderate level. However, the coating gloss, water resistance, wet scrub resistance, cleanability, and relative tinting strength were all lower than those of Example 2 containing grafted nanoparticles, and the VOC content was also difficult to further reduce. The main reason is that it is difficult to obtain a multi-scale structure with high density, high strength, and excellent surface control capabilities by relying solely on self-crosslinking acrylic emulsions and pigment / filler systems. On the one hand, the lack of a nano-inorganic framework makes the coating more prone to plastic flow and local wear under long-term immersion and repeated scrubbing, resulting in insufficient water resistance and scrub resistance. On the other hand, without the interfacial strengthening and surface rearrangement effect of the graft copolymer brush, pigment particles are more likely to recombine during the drying process, forming microscopic spots and rough areas, which reduces the K / S tinting strength and color difference control capability.

[0053] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing a water-based formaldehyde-free painting pigment, characterized in that, Includes the following steps: (1) Preparation of mesoporous silica nanoparticles containing initiating groups: acylation reaction of 2-bromoisobutyryl bromide and amino groups on the surface of amino mesoporous silica nanoparticles was carried out to obtain mesoporous silica nanoparticles containing initiating groups. (2) Preparation of zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles: Mesoporous silica nanoparticles containing initiating groups were dispersed in a mixed solvent of N,N-dimethylformamide and water, and 2-methacryloyloxyethyl phosphocholine, itaconic acid and lauryl methacrylate were added in sequence. Nitrogen gas was introduced for deoxygenation in the presence of 10-phenyl-10H-phenothiazine and triethylamine, and surface-initiated free radical polymerization was carried out under ultraviolet light irradiation to obtain zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles. (3) Preparation of acrylate preemulsion containing nanoparticles: Add methyl methacrylate, butyl acrylate, α-methacrylic acid, hydroxyethyl methacrylate and diacetone acrylamide to deionized water containing emulsifier, stir to form a monomer mixture, then add zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles, and disperse by shearing to obtain acrylate preemulsion containing nanoparticles. (4) Preparation of self-crosslinking acrylate emulsion: Ammonium persulfate was used as an initiator to carry out semi-continuous emulsion polymerization of acrylate pre-emulsion containing nanoparticles to obtain a self-crosslinking acrylate emulsion with a solid content of 40 wt%. (5) Preparation of self-crosslinking emulsion containing latent crosslinking agent: Dissolve adipic acid dihydrazide in deionized water to obtain adipic acid dihydrazide aqueous solution. Add the adipic acid dihydrazide aqueous solution dropwise to the self-crosslinking acrylate emulsion while stirring. After the addition is completed, continue stirring and adjust the pH of the emulsion to 8-9 to obtain a self-crosslinking emulsion containing latent crosslinking agent. (6) Preparation of water-based painting pigment paste containing functional nanoparticles: Glycerin, 1,2-propanediol, pigment and mesoporous silica nanoparticles grafted onto zwitterionic / hydrophobic copolymer are added to an aqueous solution of deionized water and dispersant. After mechanical stirring and dispersion, a self-crosslinking emulsion containing a latent crosslinking agent and an aqueous organosilicon defoamer are added and milled to obtain water-based painting pigment paste containing functional nanoparticles. (7) Preparation of water-based formaldehyde-free painting pigments: In the aqueous phase composed of deionized water and humectant, add a self-crosslinking emulsion containing a latent crosslinking agent and water-based painting pigment paste containing functional nanoparticles, and further add water-based organosilicon defoamer and mesoporous silica nanoparticles grafted with zwitterionic / hydrophobic copolymer. After stirring evenly, let stand to defoam and filter to obtain water-based formaldehyde-free painting pigments. In step (2), the mass ratio of the mesoporous silica nanoparticles containing initiating groups, 2-methacryloyloxyethyl phosphocholine, itaconic acid and lauryl methacrylate is 10:3-7:2-4:10-14. In step (3), the mass ratio of emulsifier, deionized water, methyl methacrylate, butyl acrylate, α-methacrylic acid, hydroxyethyl methacrylate, diacetone acrylamide, and zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles is 4:200:60:65:10:10:10-20:6-10. In step (5), the mass ratio of adipate dihydrazide and self-crosslinking acrylate emulsion is 10-20:400; In step (6), the mass ratio of deionized water, dispersant, glycerol, 1,2-propanediol, pigment, zwitterionic / hydrophobic copolymer brush-grafted mesoporous silica nanoparticles, self-crosslinking emulsion containing latent crosslinking agent and waterborne silicone defoamer is 20:2:10:5:30:1-3:30:

1. In step (7), the mass ratio of deionized water, humectant, self-crosslinking emulsion containing latent crosslinking agent, water-based painting pigment paste containing functional nanoparticles, water-based organosilicon defoamer, and mesoporous silica nanoparticles grafted with zwitterionic / hydrophobic copolymer is 15:4:40:40:1:

1.

2. The method for preparing water-based formaldehyde-free painting pigments according to claim 1, characterized in that, In step (1), the specific surface area of ​​the amino-mesoporous silica nanoparticles is 350-450 m². 2 / g, amino content 1.5-2.5mmol / g.

3. The method for preparing water-based formaldehyde-free painting pigments according to claim 1, characterized in that, In step (1), the mass ratio of 2-bromoisobutyryl bromide to amino mesoporous silica nanoparticles is 2:

1.

4. The method for preparing water-based formaldehyde-free painting pigments according to claim 1, characterized in that, In step (3), the emulsifier is sodium dodecyl sulfate.

5. The method for preparing water-based formaldehyde-free painting pigments according to claim 1, characterized in that, In step (6), the dispersant is sodium polyacrylate and the pigment is Pigment Blue 15:

3.

6. The method for preparing water-based formaldehyde-free painting pigments according to claim 1, characterized in that, In step (6), the sand milling is carried out by using a horizontal sand mill filled with 1.0mm zirconium oxide grinding beads, and circulating the sand mill for 60 minutes under the conditions of sand milling speed of 1500r / min and discharge temperature control of 30℃.

7. The method for preparing water-based formaldehyde-free painting pigments according to claim 1, characterized in that, In step (7), the moisturizer includes 3 parts by weight of glycerin and 1 part by weight of polyethylene glycol 400.

8. The method for preparing water-based formaldehyde-free painting pigments according to claim 1, characterized in that, In steps (6) and (7), the water-based silicone defoamer is defoamer BYK-024.

9. A water-based, formaldehyde-free painting pigment, characterized in that, It is obtained by the preparation method of water-based formaldehyde-free painting pigment according to any one of claims 1-8.

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