Stable dispersed iron oxide pigment paste and preparation method thereof

Abstract

The invention discloses stably dispersed iron oxide pigment paste and a preparation method thereof, and belongs to the technical field of coating chemical industry. The pigment paste is prepared from iron oxide pigment, a composite dispersing agent, a wetting agent, a defoaming agent, a preservative and deionized water; the preparation method comprises the following steps: dissolving the composite dispersant and the deionized water, slowly adding the iron oxide pigment under high-speed stirring, carrying out preliminary dispersion, transferring into a sand mill, carrying out fine grinding, adding the rest of the auxiliary agent and the deionized water, adjusting to a specified solid content, and uniformly stirring. According to the invention, specific anionic and nonionic surfactants are compounded as the composite dispersant, so that the charging sequence and the grinding process are optimized, and the problems of poor storage stability, sedimentation, thickening and the like of the traditional iron oxide pigment paste are effectively solved. The prepared pigment slurry is uniform in dispersion, good in flowability and extremely high in stability (no hard settlement is generated after more than 6 months), can be directly used in the fields of water-based coatings, emulsion paints, papermaking coloring and the like, and is excellent in application performance.

Description

Technical Field

[0001] This invention belongs to the field of coating chemical technology, and particularly relates to a stable and dispersed iron oxide pigment paste and its preparation method. Background Technology

[0002] With sustained economic growth and rapid infrastructure development, concrete, with its environmentally friendly, strong, durable, and easy-to-process characteristics, has become one of the most widely used building materials. Traditional concrete is a single shade of gray, but as living standards improve and aesthetic demands increase, people have higher expectations for the aesthetics and visual experience of their living environment, which is particularly evident in urban architecture and transportation facility design. Therefore, colored concrete has emerged. The pigment-addition method, due to its simple preparation process, good durability, and low cost, has become the most common approach. It involves using white, gray, or colored cement as a base material and adding coloring materials in specific proportions. This replaces traditional paints, which are mostly chemical substances, easily pollute the environment, and are prone to fading and peeling over time, requiring high maintenance and repair costs. This material upgrade not only responds to people's aesthetic needs but also embodies the people-oriented philosophy of modern urban construction, creating a warmer, more aesthetically pleasing, more convenient, and more efficient living environment, and injecting new vitality into the sustainable development of cities.

[0003] However, iron oxide pigments, especially nano-sized transparent iron oxide, have a high specific surface area. This makes the pigment particles prone to spontaneous aggregation due to their high surface energy, forming flocculation. Even with the use of superdispersants to maintain kinetic stability, thermodynamic aggregation is still an inevitable trend towards reducing surface energy, leading to problems such as stratification and sedimentation in pigment pastes during storage and use. Furthermore, when the iron oxide pigment content exceeds 20%, the viscosity of the dispersion system increases exponentially, causing transportation difficulties. Some methods to improve the performance of iron oxide pigment pastes involve surface modification with phosphorus-containing compounds. While this can improve the tinting strength and stability of water-based pigment pastes, phosphorus-containing compounds can easily cause eutrophication of water bodies, which is inconsistent with the trend of green chemistry. Summary of the Invention

[0004] To address the problems of poor stability, easy sedimentation and flocculation, and poor media compatibility in existing iron oxide pigment slurries, this invention proposes a stable and dispersed iron oxide pigment slurry and its preparation method. To achieve the objectives of this invention, the following technical solution is adopted: This invention provides a stable and dispersed iron oxide pigment slurry, comprising the following raw materials in parts by weight: The composition includes 200-250 parts of iron oxide pigment, 159-177 parts of composite dispersant, 5-8 parts of wetting agent, 2-4 parts of defoamer, 3-5 parts of preservative, and 1000 parts of deionized water. The composite dispersant includes the following raw materials: 37-40 parts of amino silicone oil; 42-47 parts of benzotriazole-grafted polysiloxane; and 80-90 parts of polysiloxane grafted with long ether chains.

[0005] The preparation process of the composite dispersant is as follows: S1. Polysiloxane-grafted benzotriazole S101. Synthesis of Amino Silicone Oil Octamethylcyclotetrasiloxane was added to a dry four-necked flask equipped with a reflux condenser, stirrer, and separatory funnel. Potassium hydroxide was used as a catalyst. The mixture was heated, stirred, and purged with nitrogen. When the temperature reached 65°C, hydrolyzed N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane was added dropwise into the flask through the separatory funnel. The temperature was then slowly increased to 135°C and the reaction was maintained at this temperature in an oil bath for 3 hours. After the reaction, unreacted and low-boiling substances were removed by vacuum distillation to obtain a colorless, transparent, viscous liquid, i.e., amino silicone oil. Due to ring strain, the Si-O bonds in octamethylcyclotetrasiloxane are highly polar, and oxygen has a higher electronegativity than silicon, becoming the main active site. When the temperature reached 65°C, the (OH) groups of potassium hydroxide... - The attack on positively charged Si generates a linear polysiloxane oxygen intermediate. The hydrolyzed N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane with two hydroxyl groups (-OH) undergoes dehydration condensation with the hydroxyl groups (-OH) of the polysiloxane oxygen intermediate, and is connected by (Si-O-Si) bonds.

[0006] S102. Grafting of benzotriazole The amino silicone oil obtained from S101 was cooled to 50°C. Under stirring, a 1-chloromethylbenzotriazole solution was added dropwise to a flask using a separatory funnel. The reaction was carried out at a constant temperature for 3 hours. After the reaction was completed, heating was stopped, and unreacted and low-boiling substances were removed by vacuum distillation using a water ring vacuum pump to obtain benzotriazole-grafted polysiloxane. At 50°C, the primary amino groups on the side chains of the amino silicone oil maintained high activity. The nitrogen atom in the primary amino group contains a lone pair of electrons, and the electronegativity of the nitrogen atom is greater than that of the adjacent hydrogen atom, making the amino group a strong nucleophilic site. The electronegativity of the chlorine atom is much greater than that of the carbon atom, making the carbon atom in the chloromethyl group carry a partial positive charge, thus becoming an electrophilic active site. Furthermore, the C-Cl bond is highly polar and easily broken, so the amino group attacks the carbon atom in the chloromethyl group with its lone pair of electrons to form a CN bond for connection.

[0007] S2. Grafting of long ether chains Add 100 mL of anhydrous toluene to a four-necked flask, then add anhydrous sodium sulfate and stir for 30 min. Filter the mixture through a Buchner funnel and pour it back into the four-necked flask. Add the benzotriazole-grafted polysiloxane obtained in S1 to the four-necked flask and stir at medium speed. Heat the oil bath to 80°C, add p-toluenesulfonic acid, and stir for 10 min, maintaining the solution pH at 3-4. Add polyethylene glycol to the dropping funnel slowly. After the addition is complete, heat to 110°C, turn on the water separator and condenser, and drain the lower layer of water every 30 min. Continue the reaction for 4-6 h until the water separator no longer produces water. When the layer and solution are stable and transparent, stop heating and stirring. After the reaction solution cools to room temperature, add 5% sodium carbonate solution and stir for 20 min. Remove toluene by rotary evaporation and vacuum dry at 60℃ for 2 h to obtain polysiloxane grafted with long ether chains. Use anhydrous toluene as solvent to dissolve benzotriazole-grafted polysiloxane and anhydrous sodium sulfate as desiccant to prevent polyethylene glycol hydrolysis. At 80℃, p-toluenesulfonic acid is used as a catalyst to form a hydroxyl protonated intermediate in polyethylene glycol, which dehydrates and condenses with the terminal hydroxyl groups of the benzotriazole-grafted polysiloxane to form ether chains linked by Si-OC bonds.

[0008] S3. Anion loading Add the grafted long-chain polysiloxane obtained from S2 to a dry 250mL three-necked flask, followed by anhydrous ethanol. Install a stirrer and reflux condenser, heat the water bath to 50℃, and stir at medium speed until completely dissolved, yielding a pale yellow transparent solution. Slowly add NaOH aqueous solution to the flask using a pipette, adjusting the pH to 9-10. Slowly add an ethanol solution of chloroacetic acid to the three-necked flask, raise the water bath temperature to 70℃, and reflux for 3 hours, monitoring the pH during this process. Add NaOH aqueous solution if the pH falls below 9. After the reaction is complete, remove the ethanol by rotary evaporation to obtain the anion-loaded polysiloxane graft, which is the composite dispersant. In the alkaline environment created by sodium hydroxide, the amino group is deprotonated to form a negatively charged N-terminal nanoparticle. - The density of lone pair electrons of nitrogen atoms is significantly increased, and the nucleophilicity is greatly enhanced, which enables them to efficiently attack the C-Cl bond of chloroacetic acid. The C-Cl bond breaks, and acetic acid is successfully grafted onto the main chain. HCl may be generated during the reaction, so pH needs to be monitored and replenished with 1 mol / L NaOH aqueous solution as needed to control the pH between 9 and 10.

[0009] Preferably, the molar ratio of raw materials used in S101 is: octamethylcyclotetrasiloxane : N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane = 1 : 0.9-1.1; the amount of potassium hydroxide added is 0.2-0.4% of the system; and the N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane used is commercially available silane coupling agent 602.

[0010] Preferably, the raw materials used in S102 are: 24-25 parts amino silicone oil and 18-19 parts 1-chloromethylbenzotriazole.

[0011] Preferably, the polyethylene glycol used in S102 has a molecular weight of 400.

[0012] Preferably, the mass fractions used in S2 are: 37-40 parts of benzotriazole-grafted polysiloxane; 0.5 parts of anhydrous sodium sulfate; and 40 parts of polyethylene glycol.

[0013] Preferably, the raw materials used in S3 are: 75-85 parts by weight of grafted long ether chain polysiloxane and 70-75 parts by weight of chloroacetic acid; the concentration of the NaOH aqueous solution used is 1 mol / L.

[0014] This invention also proposes a method for preparing a stable and dispersed iron oxide pigment paste, comprising the following steps: 1) Preliminary dispersion: Add deionized water to a three-necked flask equipped with a stirrer and start stirring; slowly add the composite dispersant obtained from S3 and stir for 10-15 minutes to ensure that the dispersant is completely dissolved and forms a uniform and transparent dispersion; while stirring, slowly add the iron oxide pigment in 3-5 portions, stirring for 10 minutes after each addition to obtain a preliminarily dispersed pigment slurry. 2) Grinding and refining: Transfer the coarse pigment slurry to a sand mill and grind it at 2000 rpm and 25-40℃ for 2-4 hours. Take samples every 30 minutes and detect the pigment particle size distribution using a laser particle size analyzer: the target particle size is controlled at 50-200 nm. After filtration, pour it back into a three-necked flask, stir at medium speed, add wetting agent, defoamer and preservative and stir for 20 minutes; heat to 50-60℃, keep warm and stir for 1 hour, and cool naturally to room temperature to obtain a stable dispersed iron oxide pigment slurry.

[0015] Preferably, the grinding media used in step 2) are 0.4-0.8 mm zirconia beads or ceramic beads; the filtration is carried out using a 200-mesh nylon filter.

[0016] The beneficial effects of this invention are as follows: 1. The composite dispersant synthesized in this invention uses polysiloxane as the main chain. Due to its excellent high and low temperature resistance, chemical stability and low surface energy, the composite dispersant has good substrate adaptability. It can maintain stable performance under different working conditions such as high temperature coating baking and low temperature textile finishing. At the same time, the flexibility of the main chain can reduce the risk of cracking of the dispersant on the substrate surface. Meanwhile, the low surface energy characteristic can improve the fluidity of the dispersion system and avoid the agglomeration of dispersed particles.

[0017] 2. This invention grafts benzotriazole onto the main chain. The benzotriazole group can specifically absorb the 280-380nm ultraviolet band, giving the composite dispersant both dispersing and ultraviolet protection functions. When used in water-based coatings, textile finishing agents, and other systems, it can disperse pigment and filler particles in the system and protect the substrate, such as fabric fibers and coating substrates, from ultraviolet radiation aging. It can play the role of a specific functional group and reduce the types of functional additives in the system.

[0018] 3. This invention utilizes grafted long ether chains, specifically polyethylene glycol segments, which are nonionic surfactants. This allows for precise adjustment of the hydrophilicity and solubility of the composite dispersant, solving the problem of traditional polysiloxane dispersants being highly hydrophobic and difficult to integrate into aqueous systems. This enables the dispersant to be stably dispersed in mainstream systems such as water-based coatings and water-based adhesives. Simultaneously, the linear structure of the long ether chains enhances the encapsulation of the dispersant and dispersed particles, prolonging the storage stability of the dispersion system and reducing sedimentation.

[0019] 4. This invention uses carboxyl anions as the loading agent. Most pigments have negative ions on their surface groups such as hydroxyl and carboxyl groups. Therefore, this invention loads anions into the composite dispersant to enhance its electrostatic repulsion and prevent it from agglomerating and flocculating. The anionic groups can form hydrogen bonds with water molecules in the aqueous medium or interact with the polar groups of the polar solvent, so that the dispersant molecules can be stably dissolved or dispersed in the medium. Attached Figure Description

[0020] Figure 1 The 1H NMR spectrum of the amino silicone oil prepared in Example 2; Figure 2 The 1H NMR spectrum of the benzotriazole-grafted polysiloxane prepared in Example 2; Figure 3 The image shows the 1H NMR spectrum of the polysiloxane grafted with long ether chains prepared in Example 2. Detailed Implementation

[0021] The technical solution and its effects of the present invention will be further described below with reference to the accompanying drawings in the embodiments of the present invention. The following embodiments are only for illustrating the content of the present invention and are not intended to limit the scope of protection of the present invention. Simple modifications made to the present invention based on the concept of the present invention are all within the scope of protection claimed by the present invention.

[0022] The sources of the materials used in the following examples and comparative examples are as follows: Iron oxide pigment: Shenglong Chemical Company; 2018 Water-based Wetting Agents: Guangzhou Houhuan Chemical Additives Co., Ltd.; Propiconazole: Jiangsu Huifeng Bio-Agriculture Co., Ltd.; Octamethylcyclotetrasiloxane: Shanghai Maclean Biotechnology Co., Ltd.; Potassium hydroxide: Shanghai Maclean Biotechnology Co., Ltd.; N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane: Hangzhou Jessica Chemical Co., Ltd.; 1-Chloromethylbenzotriazole: Shanghai Aladdin Technology Co., Ltd.; Anhydrous toluene: Shanghai Aladdin Technology Co., Ltd.; Anhydrous sodium sulfate: Shanghai Maclean Biotechnology Co., Ltd.; p-Toluenesulfonic acid: Shanghai Aladdin Technology Co., Ltd.; Polyethylene glycol: Shanghai Aladdin Technology Co., Ltd.; 5% sodium carbonate solution: Shanghai Maclean Biotechnology Co., Ltd.; Chloroacetic acid: Shanghai Maclean Biotechnology Co., Ltd.; Iron oxide pigment: Tianjin Guangcheng Chemical Technology Co., Ltd.; Zirconia beads or ceramic beads: Tianjin Guangcheng Chemical Technology Co., Ltd.; Diethylene glycol: Shanghai Aladdin Technology Co., Ltd.; Deionized water: homemade.

[0023] Examples 1-3 and Comparative Examples 1-5 all consistently employ the synthesis method of the stably dispersed iron oxide pigment paste described in the invention. Example

[0024] The preparation process of the composite dispersant is as follows: S1. Polysiloxane-grafted benzotriazole S101. Synthesis of Amino Silicone Oil In a dry four-necked flask equipped with a reflux condenser, stirrer, and separatory funnel, 17.5 g of octamethylcyclotetrasiloxane and 1.5 g of potassium hydroxide were added. The mixture was heated, stirred, and purged with nitrogen. When the temperature reached 65 °C, 5.0 g of hydrolyzed N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane was added dropwise into the flask through the separatory funnel. The temperature was then slowly raised to 135 °C and the mixture was kept at a constant temperature in an oil bath for 3 hours. After the reaction was completed, unreacted substances and low-boiling substances were removed by vacuum distillation to obtain a colorless, transparent, viscous liquid, namely amino silicone oil. S102. Grafting of benzotriazole 24.5 g of amino silicone oil obtained from S101 was cooled to 50 °C. Under stirring, 18.5 g of 1-chloromethylbenzotriazole solution was added dropwise into a flask using a separatory funnel. The reaction was carried out at a constant temperature for 3 h. After the reaction was completed, heating was stopped. Unreacted substances and low-boiling substances were removed by vacuum distillation using a water ring vacuum pump to obtain benzotriazole-grafted polysiloxane. S2. Grafting of long ether chains Add 100 mL of anhydrous toluene to a four-necked flask, then add 0.5 g of anhydrous sodium sulfate and stir for 30 min. Filter the mixture through a Buchner funnel and pour it back into the four-necked flask. Add 38.5 g of the benzotriazole-grafted polysiloxane obtained from S1 to the four-necked flask and stir at medium speed. Heat the oil bath to 80 °C and add 2.2 g of p-methylbenzenesulfonic acid. Stir for 10 min, maintaining the pH of the solution at 3-4. Add 40 g of polyethylene glycol to the dropping funnel and slowly add it dropwise. After the addition is complete, heat the mixture to 110 °C, turn on the water separator and condenser, and drain the lower layer of water every 30 min. Continue the reaction for 4-6 h. When the water separator no longer produces a water layer and the solution is stable and transparent, stop heating and stirring. After the reaction solution cools to room temperature, add 5% sodium carbonate solution and stir for 20 min. Remove toluene by rotary evaporation and vacuum dry at 60 °C for 2 h to obtain the grafted long ether chain polysiloxane. S3. Anion loading Add 80g of the grafted long-ether chain polysiloxane obtained from S2 to a dry 250mL three-necked flask, then add anhydrous ethanol. Install a stirrer and reflux condenser, heat the constant temperature water bath to 50℃, and stir at medium speed until completely dissolved to obtain a pale yellow transparent solution. Use a pipette to slowly add NaOH aqueous solution to the flask and adjust the pH to 9-10. Slowly add 10mL of 1mol / L chloroacetic acid ethanol solution to the three-necked flask, raise the water bath temperature to 70℃, and reflux for 3h. Monitor the pH value during the process, and add NaOH aqueous solution when it is lower than 9. After the reaction is complete, remove the ethanol by rotary evaporation to obtain the anion-loaded polysiloxane graft, which is the composite dispersant. A method for preparing a stable and dispersed iron oxide pigment paste includes the following steps: 1) Preliminary dispersion: Add deionized water to a three-necked flask equipped with a stirrer and start stirring; slowly add the composite dispersant obtained from S3 and stir for 10-15 minutes to ensure that the dispersant is completely dissolved and forms a uniform and transparent dispersion; while stirring, slowly add the iron oxide pigment in 3-5 portions, stirring for 10 minutes after each addition to obtain a preliminarily dispersed pigment slurry. 2) Grinding and refining: Transfer the coarse pigment slurry to a sand mill and grind it at 2000 rpm and 25-40℃ for 2-4 hours. Take samples every 30 minutes and detect the pigment particle size distribution using a laser particle size analyzer: the target particle size is controlled at 50-200 nm. After filtration, pour it back into a three-necked flask, stir at medium speed, add wetting agent, defoamer and preservative and stir for 20 minutes; heat to 50-60℃, keep warm and stir for 1 hour, and cool naturally to room temperature to obtain a stable dispersed iron oxide pigment slurry. Example

[0025] The preparation process of the composite dispersant is as follows: S1. Polysiloxane-grafted benzotriazole S101. Synthesis of Amino Silicone Oil In a dry four-necked flask equipped with a reflux condenser, stirrer, and separatory funnel, 17.5 g of octamethylcyclotetrasiloxane and 1.5 g of potassium hydroxide were added. The mixture was heated, stirred, and purged with nitrogen. When the temperature reached 65 °C, 6.0 g of hydrolyzed N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane was added dropwise into the flask through the separatory funnel, and the temperature was slowly raised to 135 °C. The reaction was carried out at this constant temperature in an oil bath for 3 hours. After the reaction was completed, unreacted and low-boiling substances were removed by vacuum distillation to obtain a colorless, transparent, viscous liquid, namely amino silicone oil. Its 1H NMR spectrum is shown in the attached diagram in the instruction manual. Figure 1 As shown: peaks with chemical shifts around 0-1.5 ppm may correspond to saturated alkyl hydrogens such as methyl-Si(CH3)3 bonded to silicon in the compound; peaks around 2.5-3.5 ppm may correspond to amino groups. (-NH3) or hydrogen on the methylene group bonded to a heteroatom, whose chemical shifts to lower fields are influenced by the electronegativity of the heteroatom; peaks at around 4.5 ppm and higher may involve hydroxyl (-OH) groups or hydrogen influenced by strong electron-withdrawing groups; S102. Grafting of benzotriazole 24g of the amino silicone oil obtained from S101 was cooled to 50℃. Under stirring, 17g of 1-chloromethylbenzotriazole solution was added dropwise to the flask using a separatory funnel. The reaction was carried out at a constant temperature for 3 hours. After the reaction was completed, heating was stopped, and unreacted and low-boiling substances were removed by vacuum distillation using a water ring pump to obtain benzotriazole-grafted polysiloxane. Its 1H NMR spectrum is shown in the attached figure in the specification. Figure 2 As shown: the peaks with chemical shifts around 7.0-8.5 ppm may correspond to the aromatic hydrocarbon region in the compound, indicating successful grafting of benzotriazole; the peaks with chemical shifts around 0-5.0 ppm correspond to the aliphatic hydrocarbon region in the compound. S2. Grafting of long ether chains Add 100 mL of anhydrous toluene to a four-necked flask, then add 0.5 g of anhydrous sodium sulfate and stir for 30 min. Filter the mixture through a Buchner funnel and pour it back into the four-necked flask. Add 37 g of the benzotriazole-grafted polysiloxane obtained in S1 to the four-necked flask and stir at medium speed. Heat the oil bath to 80 °C and add 2.2 g of p-methylbenzenesulfonic acid. Stir for 10 min, maintaining the pH of the solution at 3-4. Add 40 g of polyethylene glycol to the dropping funnel and slowly add it dropwise. After the addition is complete, heat to 110 °C, turn on the water separator and condenser, and drain the lower layer of water every 30 min. Continue the reaction for 4-6 h. When the water separator no longer produces a water layer and the solution is stable and transparent, stop heating and stirring. After the reaction solution cools to room temperature, add 5% sodium carbonate solution and stir for 20 min. Remove toluene by rotary evaporation and dry under vacuum at 60 °C for 2 h to obtain the grafted long ether chain polysiloxane. Its 1H NMR spectrum is shown in the attached figure in the instruction manual. Figure 3As shown: Different from Figure 2 There are many peaks in the aliphatic chain hydrogen region of about 1-4 ppm, indicating the successful grafting of long ether chains. S3. Anion loading Add 85g of the grafted long-ether chain polysiloxane obtained from S2 to a dry 250mL three-necked flask, then add anhydrous ethanol. Install a stirrer and reflux condenser, heat the constant temperature water bath to 50℃, and stir at medium speed until completely dissolved to obtain a pale yellow transparent solution. Use a pipette to slowly add NaOH aqueous solution to the flask and adjust the pH to 9-10. Slowly add 8mL of 1mol / L chloroacetic acid ethanol solution to the three-necked flask, raise the water bath temperature to 70℃, and reflux for 3h. Monitor the pH value during the process, and add NaOH aqueous solution when it is lower than 9. After the reaction is complete, remove the ethanol by rotary evaporation to obtain the anion-loaded polysiloxane graft, which is the composite dispersant. A method for preparing a stable and dispersed iron oxide pigment paste includes the following steps: 1) Preliminary dispersion: Add deionized water to a three-necked flask equipped with a stirrer and start stirring; slowly add the composite dispersant obtained from S3 and stir for 10-15 minutes to ensure that the dispersant is completely dissolved and forms a uniform and transparent dispersion; while stirring, slowly add the iron oxide pigment in 3-5 portions, stirring for 10 minutes after each addition to obtain a preliminarily dispersed pigment slurry. 2) Grinding and refining: Transfer the coarse pigment slurry to a sand mill and grind it at 2000 rpm and 25-40℃ for 2-4 hours. Take samples every 30 minutes and detect the pigment particle size distribution using a laser particle size analyzer: the target particle size is controlled at 50-200 nm. After filtration, pour it back into a three-necked flask, stir at medium speed, add wetting agent, defoamer and preservative and stir for 20 minutes; heat to 50-60℃, keep warm and stir for 1 hour, and cool naturally to room temperature to obtain a stable dispersed iron oxide pigment slurry. Example

[0026] The preparation process of the composite dispersant is as follows: S1. Polysiloxane-grafted benzotriazole S101. Synthesis of Amino Silicone Oil In a dry four-necked flask equipped with a reflux condenser, stirrer, and separatory funnel, 17.5 g of octamethylcyclotetrasiloxane and 1.5 g of potassium hydroxide were added. The mixture was heated, stirred, and purged with nitrogen. When the temperature reached 65 °C, 6.0 g of hydrolyzed N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane was added dropwise into the flask through the separatory funnel. The temperature was then slowly raised to 135 °C and the mixture was kept at a constant temperature in an oil bath for 3 hours. After the reaction was completed, unreacted substances and low-boiling substances were removed by vacuum distillation to obtain a colorless, transparent, viscous liquid, namely amino silicone oil. S102. Grafting of benzotriazole 25g of amino silicone oil obtained from S101 was cooled to 50℃. Under stirring, 19g of 1-chloromethylbenzotriazole solution was added dropwise into the flask using a separatory funnel. The reaction was kept at a constant temperature for 3h. After the reaction was completed, heating was stopped. Unreacted substances and low-boiling substances were removed by vacuum distillation using a water ring vacuum pump to obtain benzotriazole-grafted polysiloxane. S2. Grafting of long ether chains Add 100 mL of anhydrous toluene to a four-necked flask, then add 0.5 g of anhydrous sodium sulfate and stir for 30 min. Filter the mixture through a Buchner funnel and pour it back into the four-necked flask. Add 37 g of the benzotriazole-grafted polysiloxane obtained from S1 to the four-necked flask and stir at medium speed. Heat the oil bath to 80 °C and add 2.2 g of p-methylbenzenesulfonic acid. Stir for 10 min, maintaining the pH of the solution at 3-4. Add 40 g of polyethylene glycol to the dropping funnel and slowly add it dropwise. After the addition is complete, heat the mixture to 110 °C, turn on the water separator and condenser, and drain the lower layer of water every 30 min. Continue the reaction for 4-6 h. When the water separator no longer produces a water layer and the solution is stable and transparent, stop heating and stirring. After the reaction solution cools to room temperature, add 5% sodium carbonate solution and stir for 20 min. Remove toluene by rotary evaporation and dry under vacuum at 60 °C for 2 h to obtain the grafted long ether chain polysiloxane. S3. Anion loading Add 75g of the grafted long-ether chain polysiloxane obtained from S2 to a dry 250mL three-necked flask, then add anhydrous ethanol. Install a stirrer and reflux condenser, heat the constant temperature water bath to 50℃, and stir at medium speed until completely dissolved to obtain a pale yellow transparent solution. Use a pipette to slowly add NaOH aqueous solution to the flask and adjust the pH to 9-10. Slowly add 7.5mL of 1mol / L chloroacetic acid ethanol solution to the three-necked flask, raise the water bath temperature to 70℃, and reflux for 3h. Monitor the pH value during the process, and add NaOH aqueous solution when it is lower than 9. After the reaction is complete, remove the ethanol by rotary evaporation to obtain the anion-loaded polysiloxane graft, which is the composite dispersant. A method for preparing a stable and dispersed iron oxide pigment paste includes the following steps: 1) Preliminary dispersion: Add deionized water to a three-necked flask equipped with a stirrer and start stirring; slowly add the composite dispersant obtained from S3 and stir for 10-15 minutes to ensure that the dispersant is completely dissolved and forms a uniform and transparent dispersion; while stirring, slowly add the iron oxide pigment in 3-5 portions, stirring for 10 minutes after each addition to obtain a preliminarily dispersed pigment slurry. 2) Grinding and refining: Transfer the coarse pigment slurry to a sand mill and grind it at 2000 rpm and 25-40℃ for 2-4 hours. Take samples every 30 minutes and detect the pigment particle size distribution using a laser particle size analyzer: the target particle size is controlled at 50-200 nm. After filtration, pour it back into a three-necked flask, stir at medium speed, add wetting agent, defoamer and preservative and stir for 20 minutes; heat to 50-60℃, keep warm and stir for 1 hour, and cool naturally to room temperature to obtain a stable dispersed iron oxide pigment slurry.

[0027] Comparative Example 1 It is basically the same as Example 1, except that polysiloxane is not used as the main chain, that is, step S101 is missing.

[0028] Comparative Example 2 Essentially the same as Example 1, except that benzotriazole is not grafted, i.e., step S102 is missing. Comparative Example 3 It is basically the same as Example 1, except that the long polyether chain is not grafted; that is, step S2 is missing.

[0029] Comparative Example 4 It is basically the same as Example 1, except that it does not use anion loading; that is, step S3 is missing.

[0030] Comparative Example 5 Composite dispersants sold by Nantong Hantai Chemical Co., Ltd.

[0031] Comparative Example 6 It is basically the same as Example 1, except that the amount of polysiloxane added in step S1 is changed to 8.75g, so that the degree of polymerization a=2.

[0032] Comparative Example 7 It is basically the same as Example 1, except that the amount of polysiloxane added in step S1 is changed to 13.13g, so that the degree of polymerization a=3.

[0033] Comparative Example 8 It is basically the same as Example 1, except that the amount of polysiloxane added in step S1 is changed to 21.38g, so that the degree of polymerization a=5.

[0034] Comparative Example 9 It is basically the same as Example 1, except that the amount of polysiloxane added in step S1 is changed to 26.25g, so that the degree of polymerization a=6.

[0035] Comparative Example 10 It is basically the same as Example 1, except that the amount of polyethylene glycol added in step S2 is changed to 36.36g, so that the degree of polymerization n=10.

[0036] Comparative Example 11 It is basically the same as Example 1, except that the amount of polyethylene glycol added in step S2 is changed to 32.72g, so that the degree of polymerization n=9.

[0037] Comparative Example 12 It is basically the same as Example 1, except that the amount of polyethylene glycol added in step S2 is changed to 29.10g, so that the degree of polymerization n=8.

[0038] Comparative Example 13 It is basically the same as Example 1, except that the amount of polyethylene glycol added in step S2 is changed to 47.27g, so that the degree of polymerization n=13.

[0039] Comparative Example 14 It is basically the same as Example 1, except that the amount of polyethylene glycol added in step S2 is changed to 50.90g, so that the degree of polymerization n=14.

[0040] The stable dispersed iron oxide pigment pastes obtained in Examples 1-3 and Comparative Examples 1-14, as well as their preparation methods, were tested as follows; the test results are shown in Tables 1 and 2.

[0041] 1. Stability Testing (1) High temperature resistance test Iron oxide pigment with added dispersant was mixed with the base material and uniformly coated onto the substrate to prepare a standard sample. The sample was placed in a normal temperature and humidity environment for 24 hours to ensure complete drying and curing of the coating. The pigment, dispersant, and deionized water were mixed and stirred at 3000 rpm for 30 minutes using a high-speed disperser, followed by treatment with a 300W ultrasonic disperser for 15 minutes to obtain a uniform slurry. This slurry was then placed in a high-temperature forced-air drying oven and heated at a rate of 5-10℃ / min for 2-4 hours, followed by natural cooling to room temperature. The coating was visually inspected for cracking, peeling, discoloration, fading, blackening, or blistering of the iron oxide pigment. A magnifying glass was used to further examine for minute defects. The particle size (D50) was measured using a laser particle size analyzer. 初始 D50 after insulation 最终 By comparing the changes in D50 values ​​before and after heat preservation, the particle size change rate was calculated. Particle size change rate = D50 初始 -D50 最终 / D50 初始 ×100% (2) Acid and alkali resistance test Take 20 mL of the test sample into a test tube, and slowly add hydrochloric acid / sodium hydroxide solution dropwise while stirring with a glass rod, while monitoring the pH in real time with a pH meter until the pH stabilizes at the target value of pH=2. Record the volume of reagent added to avoid excessive dilution of the system. Incubate at a constant temperature: Place the pH-adjusted test tube into a constant temperature water bath, set the temperature to the actual operating temperature of 40℃, seal it, and let it stand for 48 hours, avoiding vibration during this period. Detect the potential using a Zeta potentiometer.

[0042] (3) Longest life test Choose room temperature (23±2℃) and extreme storage temperatures (40±2℃ / 5±2℃), clearly labeled; place the sample in an opaque cabinet or wrap it in aluminum foil to prevent light exposure from causing pigment degradation or dispersant inactivation. Place it on a stable surface, avoiding frequent movement or vibration, and tighten the container lid to prevent sample evaporation, water absorption, or contamination. Test hard sedimentation and supernatant height, and other stability parameters, every two weeks, recording the time when the composite dispersant begins to fail.

[0043] (4) UV resistance test Take 50 mL of homogeneous sample and place it in a transparent glass container to simulate actual use conditions, with 3 parallel samples per group; mix the pigment paste with the base material, coat it onto a polyester film, and after drying and curing, cut it into 50 mm × 50 mm test pieces to evaluate the UV resistance in practical applications. Parameters were set according to the test standard GB / T 16422.3: UV band UV-B 313 nm to simulate a strong UV environment; irradiation intensity 0.71 W / m². 2 (UV-B) Blackboard temperature: 60±3℃; Humidity: 50±5% RH; Cumulative irradiation time: 21 days, cycle mode: 8 hours of irradiation + 4 hours of darkness, simulating day and night alternation; L (lightness), a (red-green hue), and b (yellow-blue hue) of the sample were measured using a colorimeter, and the color difference ΔE between the sample and the reference sample was calculated. ΔE=√[(ΔL) 2 +(Δa) 2 +(Δb) 2 ] 2. Dispersion performance test (1) Viscosity test Take 5 mL of slurry and pour it into a 50 mL beaker. Dilute it with deionized water to a transmittance of 80%-90%. Disperse it ultrasonically for 2 min to eliminate air bubbles. Place it in a 25℃ constant temperature water bath for 10 min. Use an RV5 rotor and test it at 60 rpm and 300 rpm respectively. Take the reading after each speed stabilizes.

[0044] (2) Anti-flocculation test Take 50 mL of slurry and put it into a sealed bottle. First, use a Mastersizer 3000 laser particle size analyzer to measure its D50. 初始The D50 value was determined by shaking the sample at 200 rpm for 2 hours at 30℃ using a shaker; 10 mL of the upper layer of slurry was then taken and the D50 was measured according to the test method. 静置后 Calculate the rate of change: Rate of change = (D50) 静置后 -D50 初始 ) / ×100% (3) Anti-settlement test Take 100 mL of slurry and pour it into a graduated transparent cylinder with a diameter of 2 cm. Record the initial volume V0. Let it stand at room temperature, and record the settling layer height H at 1 day, 7 days, and 30 days. Calculate the settling rate. Settlement rate = H / V0 × 100% Table 1. Test results of stable dispersed iron oxide pigment pastes prepared in Examples 1-3 and Comparative Examples 1-14

[0045] As shown in Table 1, the dispersants exhibited by Examples 1-3 demonstrate superior performance compared to the comparative examples. Example 1 showed the smallest color difference change and the longest service life under simulated strong summer UV conditions, likely due to the highest benzotriazole content. The benzotriazole molecule's structure, containing a 1,2,3-triazole ring and an o-hydroxyphenyl group, is key to its UV resistance. Under UV irradiation, it undergoes rapid and reversible tautomerism. An intramolecular hydrogen bond OH…N exists between the hydrogen atom of the o-hydroxyl group (-OH) and the N atom of the triazole ring, forming a stable six-membered ring chelate structure. Under UV light, especially UV-B / UV-A irradiation, the OH bond absorbs UV energy and is activated, causing hydrogen atom transfer—from the O atom to the N atom. After this hydrogen atom transfer, the molecule instantly transforms into a ketoimine structure, at which point the molecule is in a high-energy excited state. However, this ketone structure is unstable and immediately returns to the initial hydroxyl structure, the ground state, via reverse hydrogen transfer. During this process, the absorbed ultraviolet energy is released as low-energy heat or extremely weak visible light (wavelength >400nm), invisible to the naked eye, rather than causing molecular chain breakage and thus avoiding degradation. Furthermore, the ultraviolet absorption spectrum of benzotriazole highly overlaps with the sensitive absorption spectra of polymeric substrates (such as PVC and polyurethane), both concentrated in the 280-360nm range, the main aging bands of UV-B and UV-A. However, the molar absorptivity of benzotriazole is approximately 10. 4 L / mol·cm -1 The C / C bond density is much higher than that of the substrate, with an ε≈10. 2 L / mol·cm -1 ，It's like equipping ultraviolet light with an energy converter, turning it into heat. Besides, most UV protectants, such as benzophenones, gradually degrade and become ineffective after absorbing ultraviolet light. However, the mechanism of action of benzotriazole, as mentioned above, is completely reversible due to phototautomerism. During the entire process, the triazole ring + phenyl molecular skeleton of benzotriazole is not destroyed; only hydrogen atoms are transferred. No small molecule degradation products are generated, thus enabling it to be recycled and having a longer UV protection lifespan.

[0046] As shown in Table 1, Example 3 exhibited the smallest particle size change rate under high-temperature conditions and the smallest mass change rate under strong acid and alkali conditions. This is likely because Example 3 used the most polysiloxane chains. The core mechanism involves the condensation reaction between the alkoxy groups of silane molecules and the hydroxyl groups (-OH) on the surface of iron oxide, forming covalent bonds (-Fe-O-Si-), thus constructing a dense siloxane Si-O-Si network coating on the pigment particle surface. The siloxane bond energy is approximately 460 kJ / mol, significantly higher than the C / C bonds (347 kJ / mol) or ester bonds (351 kJ / mol) of organic dispersants. It is not easily broken at high temperatures (300-600°C), preventing pigment particles from agglomerating due to surface hydroxyl dehydration. The spatial structure of the siloxane network is stable, and chain segment movement or decomposition is not easily observed at high temperatures, effectively isolating pigment particles from external factors such as oxidation of the resin matrix and high-temperature reactions like crystal transformation. Untreated iron oxide particles exhibit enhanced surface atomic activity at high temperatures, making them prone to sintering and agglomeration through van der Waals forces. Grafted silane molecules form an insulating layer between particles through steric hindrance, preventing direct contact between particle surfaces. The organic functional groups in the silane molecules can crosslink with surrounding resin molecules, further fixing the particle spacing and preventing particle migration and aggregation at high temperatures. The flexible segments of the silane molecules, such as the long polyether chains grafted in this invention, can absorb some stress through segmental stretching at high temperatures, reducing crack formation. At low temperatures, the viscosity of liquid media increases sharply, even freezing, causing pigment particles to settle due to weakened Brownian motion. The polar siloxane segments of the grafted silane can form hydrogen bonds with water molecules, lowering the freezing point of water, similar to an antifreeze mechanism. Simultaneously, the organic segments of the silane, such as long-chain alkyl groups, can weaken the hydrogen bonds between water molecules, reducing ice crystal formation at low temperatures. The steric hindrance layer formed by silane on the particle surface reduces van der Waals attraction between particles, maintaining particle dispersion even in low-temperature, high-viscosity systems and preventing sedimentation and agglomeration.

[0047] As shown in Table 1, regarding the high-temperature and acid / alkali resistance of Comparative Examples 1-14, except for Comparative Example 5 which showed poor performance in all aspects, Comparative Examples 6 and 7 exhibited significantly larger rates of change, indicating a deterioration in both high-temperature and acid / alkali resistance. Comparative Example 7 was slightly better than Comparative Example 6, possibly due to changes in the degree of polymerization of the polysiloxane, thus demonstrating the importance of polysiloxane in high-temperature and acid / alkali resistance. However, Comparative Examples 8-9 showed that with further increases in the amount of polysiloxane grafting, the performance of the iron oxide pigment paste in this aspect did not meet expectations, but rather decreased. This is because the molecular weight of the polysiloxane is too large, and excessive grafting leads to insufficient material dispersibility, premature coagulation and sedimentation, resulting in an increased rate of change in particle size as measured in the experiment. This demonstrates the precise control of the grafting amount in this invention. Furthermore, Comparative Example 2 had the shortest failure time, primarily because it lacked benzotriazole grafting, thus losing its ability to resist UV aging. The mechanism has been explained in detail in the first paragraph and will not be repeated here. This comparative example further demonstrates the indispensability of grafting benzotriazole.

[0048] Table 2 shows the tests conducted on the stable dispersed iron oxide pigment pastes prepared in Examples 1-3 and Comparative Examples 1-14.

[0049] As shown in Table 2, the performance of Examples 1-3 is superior to that of the comparative examples. Among them, Example 2 shows the best performance in anti-settling and anti-flocculation functions. The core reason is that the polyether chain, as a nonionic surfactant, achieves anti-settling and anti-flocculation effects on iron oxide pigment paste through steric hindrance and interfacial affinity. Iron oxide pigment particles are inorganic rigid particles, which are easily agglomerated due to van der Waals forces, forming flocs, and eventually settle because their density is greater than that of the dispersion medium. The polyether chain breaks this process through physical adsorption and steric barrier. One end of the polyether chain molecule usually contains polar groups such as hydroxyl and amino groups, which form hydrogen bonds or van der Waals forces with the hydroxyl groups (-OH) on the surface of iron oxide particles to achieve anchoring adsorption; the nonpolar polyoxyethylene / polyoxypropylene chain segment at the other end, due to its compatibility with the dispersion medium, such as water and solvent, spontaneously extends into the medium to form a stable structure of particle-polyether chain-dispersion medium. The polyether chains adsorbed on the particle surface form a flexible polymer film, typically tens to hundreds of nanometers thick. When two adjacent iron oxide particles approach each other, the polyether chains on the particle surface undergo conformational changes due to spatial compression, leading to a decrease in entropy and an increase in osmotic pressure in the local area. This generates entropy repulsion and osmotic repulsion. Without the addition of polyether chains, the flocculated iron oxide particle clusters are dense and large, settling rapidly under gravity. However, after stabilization with polyether chains, the particles exist as monodisperse or small aggregates. The polyether chain film on the surface increases the contact area between the particles and the dispersion medium, enhancing the medium's encapsulation force on the particles, such as viscous resistance, slowing down the settling velocity, and preventing small particles from re-aggregating due to collisions, thus achieving long-term anti-settling. These two repulsive forces counteract the van der Waals attraction between particles, preventing them from further approaching to form flocs and avoiding agglomeration at its source. In addition, the polyoxyethylene-O-CH2-CH2- segments in the polyether chain have strong hydrophilicity and can form hydrogen bonds with water molecules, changing the particle surface from hydrophobic to hydrophilic, reducing particle aggregation caused by hydrophobic effects. This can improve the interfacial compatibility between iron oxide particles and the dispersion medium, and indirectly enhance the anti-settling / anti-flocculation effect.

[0050] As shown in Table 2, the pigment exhibited in Example 3 had the best flowability (lowest viscosity in the table). This is because the polysiloxane molecule has a -Si-O-Si- structure in its main chain, which has high bond energy and strong chain segment flexibility. The side chains are mostly non-polar groups such as methyl (-CH3), resulting in an overall extremely low surface energy of about 20-25 mN / m, which is much lower than that of water and most resins. The polysiloxane molecules will spontaneously adsorb onto the surface of the iron oxide pigment particles and form hydrogen bonds with the hydroxyl groups on the particle surface through intermolecular van der Waals forces or silanol groups, thus orienting the low surface energy methyl side chains toward the dispersion medium. This process significantly reduces the interfacial tension between pigment particles and the dispersion medium, decreasing the resistance of the medium to particle encapsulation and making the particles easier to slide in the system. Macroscopically, this manifests as a decrease in system viscosity and an increase in flowability. The polysiloxane segments (-Si-O-Si-) adsorbed on the particle surface possess extremely high flexibility. When particles approach each other or move within the system, these flexible segments can adjust their conformation, such as curling up or expanding, to buffer direct collisions between particles, replacing the high friction caused by rigid contact and further reducing the flow resistance within the system. One of the core driving forces behind the agglomeration of iron oxide pigment particles is the minimization of interfacial energy—the higher the particle surface energy, the more inclined the particles are to reduce their exposed surface area through agglomeration to lower their total energy. After polysiloxane adsorption, the particle surface is covered with low-surface-energy methyl groups, significantly reducing the interfacial energy difference between particles and between particles and the medium. This thermodynamically weakens the spontaneous tendency of particle agglomeration and reduces the occurrence of initial agglomeration. As shown in Table 2, the viscosity of the iron oxide pigment paste prepared in Comparative Examples 6-7 increased at both 600 and 3000 rpm. This is because the reduced content of polysiloxane led to a corresponding decrease in material fluidity, demonstrating the importance of polysiloxane for viscosity. However, in Comparative Examples 8-9, the excessive amount of polysiloxane resulted in an increase in viscosity. This is because although polysiloxane has a low surface energy, its relative molecular mass is high. Simply increasing its content is not beneficial for the pigment paste, as its large molecular weight causes premature sedimentation and flocculation. Therefore, it is evident that the amount of polysiloxane backbone added is not necessarily better the more it is added, further demonstrating the precise control of the functional group raw material ratio in this invention.

[0051] As shown in Table 2, in terms of anti-flocculation and anti-settling, except for Comparative Example 5 which is at the bottom in all aspects, Comparative Example 1 has slightly lower performance in these aspects. This indicates that in addition to increasing the fluidity of the material, polysiloxane can also play a certain role in the anti-flocculation ability of the system due to its low surface energy. Furthermore, Comparative Examples 10-12 and 13-14 showed varying degrees of performance degradation. The gradient decrease in Comparative Example 10-12 was due to insufficient steric hindrance, failing to counteract particle attraction. The polymer film formed after short-chain polyethers adsorbed onto the surface of iron oxide particles was extremely thin. When adjacent particles approached, the chain segments could not effectively compress space, resulting in entropy and osmotic repulsion forces far less than the van der Waals attraction between particles, failing to prevent particle aggregation and ultimately leading to flocculation and sedimentation. The short-chain polyethers also had few polar anchoring groups, such as hydroxyl groups, resulting in weak hydrogen bonding with the hydroxyl groups on the surface of iron oxide particles. Simultaneously, the short-chain non-polar segments lacked compatibility with the dispersion medium, easily detaching from the particle surface due to poor interfacial compatibility, losing their stabilizing effect, and causing particle re-aggregation. The increased viscosity of the system in Comparative Example 13-14 is also due to the large molecular weight, strong steric hindrance, and chain entanglement. The excessively long polyether chains form a very thick flexible polymer film on the particle surface, with strong steric repulsion, which can effectively prevent particle aggregation. However, at the same time, the excessively long polyether chains on the surfaces of adjacent particles are prone to chain entanglement, resulting in a significant increase in the overall viscosity of the dispersion system. The increase in viscosity directly slows down the particle settling rate, making its short-term anti-settling effect better. However, in the long run, the entangled chain segments may indirectly connect multiple particles to form loose aggregates, which will reduce the dispersion stability.

[0052] In summary, the embodiments, by grafting functional groups, precisely proportioning the ingredients, and selecting a specific combination of anionic and nonionic surfactants as a composite dispersant, optimized the feeding sequence and grinding process, effectively solving the problems of poor storage stability, sedimentation, and coarsening of traditional iron oxide pigment pastes. The resulting pigment paste is uniformly dispersed (flocculation rate <2.5%; sedimentation rate <2.0%) and has good flowability (viscosity <540 MPa·s at 60 rpm). -1 It has excellent UV resistance and extremely high stability (no hard settling after more than 6 months), and can be directly used in water-based coatings, latex paints, paper coloring and other fields. It has excellent application performance, and all indicators are within the high-performance optimization range. Moreover, each comparative example proves that removing any core component will lead to a significant deterioration in a certain performance dimension. Changing the raw material ratio of the core component will also lead to a large deviation in performance, which verifies the irreplaceability of the solution of this invention.

[0053] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A stable and dispersed iron oxide pigment paste, characterized in that, Including the following parts by weight of raw materials: 200-250 parts iron oxide pigment, 159-177 parts composite dispersant, 5-8 parts wetting agent, 2-4 parts defoamer, 3-5 parts preservative, and 1000 parts deionized water; The preparation process of the composite dispersant includes the following steps: S1. Polysiloxane-grafted benzotriazole S101. Synthesis of Amino Silicone Oil Octamethylcyclotetrasiloxane was added to a dry four-necked flask equipped with a reflux condenser, stirrer, and separatory funnel. Potassium hydroxide was used as a catalyst, the mixture was heated, stirred, and nitrogen gas was introduced. When the temperature reached 65°C, the hydrolyzed N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane was added dropwise into the flask through the separatory funnel, and the temperature was slowly raised to 135°C. The mixture was reacted at a constant temperature in an oil bath for 3 hours. After the reaction was completed, unreacted substances and low-boiling substances were removed by vacuum distillation to obtain a colorless, transparent, viscous liquid, namely amino silicone oil. S102. Grafting of benzotriazole The amino silicone oil obtained from S101 was cooled to 50°C. Under stirring, the 1-chloromethylbenzotriazole solution was dropped into the flask using a separatory funnel. The reaction was kept at a constant temperature for 3 hours. After the reaction was completed, heating was stopped. Unreacted substances and low-boiling substances were removed by vacuum distillation using a water ring vacuum pump to obtain benzotriazole-grafted polysiloxane. S2. Grafting of long ether chains Add 100 mL of anhydrous toluene to a four-necked flask, then add anhydrous sodium sulfate and stir for 30 min. Filter the mixture through a Buchner funnel and pour it back into the four-necked flask. Add the benzotriazole-grafted polysiloxane obtained in S1 to the four-necked flask and stir at medium speed. Heat the oil bath to 80 °C, add p-toluenesulfonic acid, and stir for 10 min, maintaining the solution pH at 3-4. Add polyethylene glycol to the dropping funnel slowly. After the addition is complete, heat to 110 °C, turn on the water separator and condenser, and drain the lower layer of water every 30 min. Continue the reaction for 4-6 h. When the water separator no longer produces a water layer and the solution is stable and transparent, stop heating and stirring. After the reaction solution cools to room temperature, add 5% sodium carbonate solution and stir for 20 min. Remove toluene by rotary evaporation and vacuum dry at 60 °C for 2 h to obtain the grafted long ether chain polysiloxane. S3. Anion loading Add the grafted long-ether chain polysiloxane obtained from S2 to a dry 250mL three-necked flask, then add anhydrous ethanol. Install a stirrer and reflux condenser, heat the constant temperature water bath to 50℃, and stir at medium speed until completely dissolved to obtain a pale yellow transparent solution. Use a pipette to take NaOH aqueous solution and slowly add it dropwise to the flask to adjust the pH to 9-10. Slowly add the ethanol solution of chloroacetic acid dropwise to the three-necked flask, raise the water bath temperature to 70℃, and reflux for 3 hours. Monitor the pH value during the process, and add NaOH aqueous solution when it is lower than 9. After the reaction is complete, remove the ethanol by rotary evaporation to obtain the anion-loaded polysiloxane graft, which is the composite dispersant.

2. The stably dispersed iron oxide pigment paste according to claim 1, characterized in that, The raw material molar ratio used in S101 is: octamethylcyclotetrasiloxane : N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane = 1 : 0.9-1.1; the amount of potassium hydroxide added is 0.2-0.4% of the system; the N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane used is commercially available silane coupling agent 602.

3. The stably dispersed iron oxide pigment paste according to claim 1, characterized in that, The raw materials used in S102 are: 24-25 parts amino silicone oil and 18-19 parts 1-chloromethylbenzotriazole.

4. The method for preparing a stable and dispersed iron oxide pigment according to claim 1, characterized in that, The polyethylene glycol used in S102 has a molecular weight of 400.

5. The stably dispersed iron oxide pigment paste according to claim 1, characterized in that, The mass fractions used in S2 are: 37-40 parts of benzotriazole-grafted polysiloxane; 0.5 parts of anhydrous sodium sulfate; and 40 parts of polyethylene glycol.

6. The stably dispersed iron oxide pigment paste according to claim 1, characterized in that, The raw materials used in S3 are: 75-85 parts by weight of grafted long ether chain polysiloxane and 70-75 parts by weight of chloroacetic acid; the concentration of the NaOH aqueous solution used is 1 mol / L.

7. The method for preparing a stable dispersed iron oxide pigment paste according to any one of claims 1-6, characterized in that, Includes the following steps: 1) Preliminary dispersion: Add deionized water to a three-necked flask equipped with a stirrer and start stirring; slowly add the composite dispersant obtained from S3 and stir for 10-15 minutes to ensure that the dispersant is completely dissolved and forms a uniform and transparent dispersion; while stirring, slowly add the iron oxide pigment in 3-5 portions, stirring for 10 minutes after each addition to obtain a preliminarily dispersed pigment slurry. 2) Grinding and refining: Transfer the coarse pigment slurry to a sand mill and grind it at 2000 rpm and 25-40℃ for 2-4 hours. Take samples every 30 minutes and detect the pigment particle size distribution using a laser particle size analyzer: the target particle size is controlled at 50-200 nm. After filtration, pour it back into a three-necked flask, stir at medium speed, add wetting agent, defoamer and preservative and stir for 20 minutes; heat to 50-60℃, keep warm and stir for 1 hour, and cool naturally to room temperature to obtain a stable dispersed iron oxide pigment slurry.

8. The method for preparing a stable and dispersed iron oxide pigment paste according to claim 7, characterized in that, The grinding media used in step 2) are 0.4-0.8mm zirconia beads or ceramic beads; the filtration is carried out using a 200-mesh nylon filter.

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