Iron oxide pigment with high chroma and stable oxidation and preparation method thereof

Abstract

The invention discloses a high-chroma oxidation-stable iron oxide pigment and a preparation method thereof, and relates to the technical field of iron oxide inorganic material enhanced coloring and stabilization. The invention relates to an iron oxide pigment with high chromaticity and oxidation stability. The iron oxide pigment with high chromaticity and oxidation stability comprises an alpha-Fe2O3 core, doping elements and a dispersion medium, the alpha-Fe2O3 core takes alpha-Fe2O3 as a core, and the surface of the core is sequentially coated with an aluminum oxide layer and a silane coupling agent modified layer. By optimizing the structure and the preparation process of the iron oxide pigment, the pigment disclosed by the invention has remarkable advantages in the aspects of initial chroma and chroma change after oxidation, the color stability is higher, and the color development purity is enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of enhanced coloring and stabilization of inorganic iron oxide materials, and in particular to an iron oxide pigment with high chroma and oxidation stability and a preparation method thereof. Background Art

[0002] Iron oxide pigments are a key class of inorganic pigments used in numerous applications, favored for their numerous advantageous properties. They exhibit excellent lightfastness, meaning their color remains stable even under prolonged exposure to light, resisting fading or discoloration. This ensures the consistent appearance of the product over its lifespan. Iron oxide pigments also possess excellent weather resistance, withstanding the erosion of diverse natural climates. Whether exposed to wind, rain, or sunlight, they maintain relatively stable performance, giving them significant advantages in outdoor applications.

[0003] In addition, iron oxide pigments have high chemical stability. Under normal usage and chemical conditions, their chemical structure is relatively stable and they are not prone to chemical reactions with other substances. This ensures that the pigment's color and performance are not easily affected by chemical factors. Furthermore, these pigments have strong hiding power, effectively covering the substrate at low dosages to achieve the desired coloring effect, thereby improving production efficiency and reducing costs. Iron oxide pigments also excel in tinting strength, achieving vibrant, uniform colors in the colored substrate with minimal addition. This has earned them a prominent position in the pigment market, with widespread application in many industries, including construction, coatings, plastics, and papermaking.

[0004] However, despite the numerous advantages already mentioned, existing iron oxide pigments still have areas for improvement. Certain specialized applications place even higher demands on the chromaticity and oxidative stability of iron oxide pigments. For example, in certain high-end coating applications, achieving more vibrant, bright, and long-lasting color effects requires pigments with higher chromaticity to enhance the product's visual appeal and market competitiveness. Furthermore, when applied in high-temperature, highly oxidizing environments or exposed to long-term adverse weather conditions, the pigment's insufficient oxidative stability becomes apparent, potentially leading to oxidative discoloration and impacting the appearance quality and service life of the product being colored.

[0005] Currently, various methods have been studied and attempted to improve the performance of iron oxide pigments. For example, various additives are added to improve certain pigment properties, or complex post-processing processes are used to modify the pigment surface. However, these methods often have limitations. For example, additives may react adversely with the pigment or other ingredients, affecting product quality; post-processing processes are complex and costly, making them unsuitable for large-scale industrial production. Therefore, developing an iron oxide pigment that can significantly improve chromaticity and enhance oxidative stability, while also having a simple and cost-effective preparation method, is of great significance for promoting the application of iron oxide pigments in more high-end fields and the development of related industries. Summary of the Invention

[0006] The present invention aims to provide a high-chroma and oxidatively stable iron oxide pigment by optimizing the preparation process and materials of iron oxide pigment, so as to solve the problems of insufficient chroma and poor oxidative stability of iron oxide pigments in the prior art and meet the demand for high-quality pigments in high-end application fields.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a high chroma oxidatively stable iron oxide pigment, wherein the high chroma oxidatively stable iron oxide pigment comprises an α-Fe2O3 core, a doping element and a dispersion medium; The α-Fe2O3 core is composed of α-Fe2O3 as the core, and the surface of the core is coated with an aluminum oxide layer and a silane coupling agent modified layer in sequence; The general formula of the silane coupling agent is ; Said R1 is a C1-C3 alkyl group; R2 is H or , The linking site.

[0008] Furthermore, the thickness of the aluminum oxide layer is 5-20 nm, and the thickness of the silane coupling agent modified layer is 2-10 nm.

[0009] Furthermore, the doping element accounts for 0.1%-2% of the molar percentage of the Fe element and is selected from zinc sulfate.

[0010] Furthermore, the average particle size of the α-Fe2O3 core is 100-300 nm, and the particle size distribution D90 / D10≤1.5.

[0011] Furthermore, the silane coupling agent is at least one of the compounds shown in the following structures: .

[0012] Furthermore, the dispersion medium is acrylic resin or alkyd resin.

[0013] Furthermore, the preparation method of the α-Fe2O3 core comprises the following steps: (a) reacting FeSO4 solution with alkaline solution to generate Fe(OH)2 precursor; (b) oxidative aging at 60-80° C. in an oxygen-containing atmosphere to form an α-Fe 2 O 3 suspension; (c) adding an aluminum salt solution to the α-Fe2O3 suspension, adjusting the pH to 4.0-5.0, and reacting at 85-95°C to form the aluminum oxide coating layer; (d) adding the alcohol solution of the silane coupling agent and the doping element, maintaining the pH at 8.0-9.0, carrying out a hydrolysis reaction at 70-85° C. for 1-2 hours, filtering, and drying to obtain α-Fe 2 O 3 cores.

[0014] Furthermore, in the step (c), the amount of aluminum salt added is 0.5-3% of the molar amount of Fe, and the aluminum salt is aluminum sulfate or aluminum nitrate.

[0015] Furthermore, in the step (d), the amount of the silane coupling agent added is 1.5-5% of the total mass of the high-chroma oxidation-stable iron oxide pigment.

[0016] Furthermore, during the oxidative aging in step (b), the temperature is raised to 75° C. at a rate of 2° C. / min and maintained at this temperature for 8-12 hours.

[0017] A method for preparing a high-chroma oxidatively stable iron oxide pigment comprises the following steps: mixing the α-Fe2O3 core and the dispersion medium at 60-80°C in a nitrogen atmosphere, stirring the mixture, and sieving the mixture to obtain a high-chroma oxidatively stable iron oxide pigment.

[0018] The present invention solves the problem of insufficient chroma and poor oxidation stability of iron oxide pigments by the following technical solution: with α-Fe2O3 with a particle size of 100-300nm and uniform distribution (D90 / D10≤1.5) as the core, the lattice is stabilized by doping Zn / Ti / Sn elements and the Fe 3+ Reduction, while optimizing the electronic band structure to enhance visible light absorption efficiency; constructing a 5-20nm dense aluminum oxide coating (Al2O3) on the core surface, Al 3+A physical barrier is formed by precipitation at a pH of 4.0-5.0, isolating oxygen, water vapor, and corrosive ions while passivating surface Fe active sites. A silane coupling agent is then used to form a 2-10 nm modified layer. Hydrolysis and condensation at alkaline pH 8.0-9.0 results in Si-O-Al bonds, strengthening the interface. The alkyl chains provide hydrophobic protection. Finally, chemical bonding between the silane organic groups and acrylic / alkyd resins enables uniform dispersion at 60-80°C under nitrogen. Precisely controlled oxidation aging yields a high-purity α-Fe₂O₃ crystalline phase. The coating density and monolayer coverage are optimized by adjusting the aluminum salt dosage (0.5-3% Fe molar weight) and silane dosage (1.5-5% total pigment weight). This triple-layer protective structure of "doped α-Fe₂O₃ core-alumina shell-silane interface" synergistically with the resin coating simultaneously enhances color purity and blocks oxidation pathways.

[0019] Compared with the prior art, the present invention has the following beneficial effects: Improved color stability: By optimizing the structure and preparation process of iron oxide pigments, the pigments of the present invention show significant advantages in initial chromaticity and chromaticity change after oxidation, with higher color stability and enhanced color purity.

[0020] Enhanced antioxidant capacity: In the oxidation stability test, the pigment of the present invention shows a smaller chromaticity change range, and the antioxidant stability is effectively improved, and can adapt to more harsh environmental conditions.

[0021] Optimized dispersion stability: The pigment of the present invention exhibits better dispersion stability in the dispersion medium, and no stratification occurs after long-term standing, and the dispersion system is more uniform and stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the NMR image of the silane coupling agent 1 described in the present invention. DETAILED DESCRIPTION

[0023] The following will clearly and completely describe the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] Preparation Example 1: Synthesis of silane coupling agent 1: ; Under nitrogen atmosphere, 15 g of raw material 1, 20.34 g of raw material 2, 13.58 g of potassium carbonate and 200 ml of toluene were sequentially added into the reaction system, the air in the reaction system was replaced with nitrogen for 3 times, 0.36 g of chloro[2-dicyclohexylphosphino-2',6'-bis(N,N-dimethylamino)biphenyl]palladium(II)(2'-amino-1,1'-biphenyl-2-yl) was added under nitrogen protection, the temperature was raised to 100°C, and the reaction was carried out under nitrogen protection for 6 hours. After the reaction was completed, it was cooled to room temperature, and the solvent was spin-dried. Finally, 21.63 g of silane coupling agent 1 was obtained by column chromatography (ethyl acetate and petroleum ether as eluent). Mass spectrum M / Z+1: 571. The nuclear magnetic chart of the silane coupling agent 1 is shown in Figure 1 .

[0025] Preparation Example 2: The synthesis of silane coupling agent 2, according to the synthesis method of Preparation Example 1, replacing the raw material 1 therein with , and the rest remains the same as Preparation Example 1, and the structure characterization test mass spectrum M / Z+1: 613.

[0026] Preparation Example 3: The synthesis of silane coupling agent 3, according to the synthesis method of Preparation Example 1, replacing the raw material 1 therein with , and the rest remains the same as Preparation Example 1, and the structure characterization test mass spectrum M / Z+1: 655.

[0027] Example 1: Preparation of a high-chroma oxidation-stable iron oxide pigment, comprising the following steps: 1. Synthesis of α-Fe2O3 nucleus: (1) 1.2 mol of FeSO4·7H2O was prepared into a 0.5 mol / L aqueous solution, and was mixed with an equal volume of 1.5 mol / L NaOH solution under nitrogen protection to generate Fe(OH)2 precursor (slurry); (2) The Fe(OH)2 precursor was transferred to the reaction kettle, and 25 vol% oxygen-containing nitrogen-oxygen mixed gas was introduced, and the temperature was raised to 75°C at a rate of 2°C / min, and the temperature was kept constant for 10 hours to obtain α-Fe2O3 suspension; (3) Al2(SO4)3 solution (containing Al 3+ 0.018 mol, accounting for 1.5% of the molar amount of Fe) was added to the α-Fe2O3 suspension, and the pH was adjusted to 4.5 with dilute H2SO4, and the reaction was carried out at 90°C for 2 hours to form an aluminum oxide coating layer with a thickness of 12 nm; (4) Add an ethanol solution of silane coupling agent 1 (concentration 20 wt%, amount added to 3% of the expected total mass of the pigment) and 0.015 mol of ZnSO4, maintain the pH at 8.5 with ammonia water, hydrolyze at 80 ° C for 1.5 hours, filter and dry at 110 ° C to form an α-Fe2O3 core covered with a silane coupling agent modified layer (thickness 5 mm).

[0028] 2. Under nitrogen atmosphere, α-Fe2O3 core and acrylic resin (solid content 40%) were mixed in a mass ratio of 1:1.5, stirred and dispersed at 70℃ for 3 hours, and passed through an 80-mesh sieve to obtain a high-chroma, oxidatively stable iron oxide pigment.

[0029] The acrylic resin was purchased from Shanghai Zhenlishi Network Technology Co., Ltd.

[0030] Example 2: A high-chroma oxidatively stable iron oxide pigment was prepared by referring to the preparation method of Example 1, except that the silane coupling agent 1 was replaced by the silane coupling agent 2, and the rest of the process remained the same as that of Example 1.

[0031] Example 3: A high-chroma oxidatively stable iron oxide pigment was prepared by referring to the preparation method of Example 1, except that the silane coupling agent 1 was replaced by the silane coupling agent 3, and the rest of the process remained the same as that of Example 1.

[0032] Comparative Example 1: A high-chroma oxidatively stable iron oxide pigment was prepared by referring to the preparation method of Example 1, except that the silane coupling agent 1 was replaced by the silane coupling agent KH550, and the rest of the process remained the same as in Example 1.

[0033] Comparative Example 2: A high-chroma oxidatively stable iron oxide pigment was prepared by referring to the preparation method of Example 1, except that the silane coupling agent 1 was replaced by the comparative compound 1, and the rest remained the same as in Example 1.

[0034] Comparative compound 1: .

[0035] Comparative Example 3: A high-chroma oxidatively stable iron oxide pigment was prepared by referring to the preparation method of Example 1, except that the silane coupling agent 1 was replaced by the comparative compound 2, and the rest remained the same as in Example 1.

[0036] Comparative compound 2: .

[0037] Performance testing: 1. Chromaticity test: Use a spectrophotometer (model: X-Rite Ci64) to measure the total color difference of the pigment (Δ The ΔE value represents the deviation from the standard sample (unaged state). The smaller the value, the better the color stability. The data is shown in Table 1.

[0038] 2. Oxidation stability test: Place the pigment in a constant temperature oven and bake it continuously at 80°C for 40 hours (simulating a long-term oxidation environment). After taking it out and cooling it to room temperature, measure the color coordinates and calculate the Δ The data are shown in Table 1.

[0039] 3. Dispersion stability test: Place the pigment in a constant temperature oven at 25°C for 500 hours and observe whether there is any stratification. The data is shown in Table 1.

[0040] Table 1 The examples (1-3) using the specific silane coupling agent of the present invention showed significant advantages in color stability, antioxidant capacity and dispersion uniformity. The values ​​are generally low, reflecting smaller color deviations and higher color purity. After treatment in a simulated oxidizing environment, the magnitude of the post-oxidation chromaticity change is also significantly smaller, indicating significantly enhanced antioxidant stability. In contrast, the comparative examples (using conventional silane coupling agents or comparative compounds) exhibit greater initial and post-oxidation chromaticity changes, suggesting that color is susceptible to environmental degradation. In dispersion stability testing, the example samples showed no delamination after long-term stabilization, indicating a highly uniform and stable dispersion. In contrast, the comparative examples exhibited varying degrees of stability issues, including slight or significant delamination tendencies. These trends highlight the key role of the silane coupling agent of the present invention in optimizing the pigment core structure, enhancing interfacial protection, and improving overall performance.

[0041] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A high chroma oxidatively stable iron oxide pigment, characterized in that: The high chroma oxidatively stable iron oxide pigment comprises an α-Fe2O3 core, a doping element and a dispersion medium; The α-Fe2O3 core is composed of α-Fe2O3 as the core, and the surface of the core is coated with an aluminum oxide layer and a silane coupling agent modified layer in sequence; The general formula of the silane coupling agent is ; Said R1 is a C1-C3 alkyl group; R2 is H or , The linking site.

2. The high chroma oxidation-stable iron oxide pigment according to claim 1, characterized in that: The thickness of the aluminum oxide layer is 5-20 nm, and the thickness of the silane coupling agent modified layer is 2-10 nm.

3. The high chroma oxidation-stable iron oxide pigment according to claim 1, characterized in that: The doping element accounts for 0.1%-2% of the molar percentage of the Fe element and is selected from zinc sulfate.

4. The high chroma oxidation-stable iron oxide pigment according to claim 1, characterized in that: The average particle size of the α-Fe2O3 core is 100-300 nm, and the particle size distribution D90 / D10 is ≤1.

5.

5. The high chroma oxidation-stable iron oxide pigment according to claim 1, characterized in that: The silane coupling agent is at least one of the compounds shown in the following structures: 。 6. The high chroma oxidation-stable iron oxide pigment according to claim 1, characterized in that: The dispersion medium is acrylic resin or alkyd resin.

7. The high chroma oxidation-stable iron oxide pigment according to claim 1, characterized in that: The preparation method of the α-Fe2O3 core comprises the following steps: (a) reacting FeSO4 solution with alkaline solution to generate Fe(OH)2 precursor; (b) oxidative aging at 60-80° C. in an oxygen-containing atmosphere to form an α-Fe 2 O 3 suspension; (c) adding an aluminum salt solution to the α-Fe2O3 suspension, adjusting the pH to 4.0-5.0, and reacting at 85-95°C to form the aluminum oxide coating layer; (d) adding the alcohol solution of the silane coupling agent and the doping element, maintaining the pH at 8.0-9.0, carrying out a hydrolysis reaction at 70-85° C. for 1-2 hours, filtering, and drying to obtain α-Fe 2 O 3 cores.

8. The high chroma oxidation-stable iron oxide pigment according to claim 7, characterized in that: In the step (c), the amount of aluminum salt added is 0.5-3% of the molar amount of Fe, and the aluminum salt is aluminum sulfate or aluminum nitrate; In the step (d), the amount of the silane coupling agent added is 1.5-5% of the total mass of the high-chroma oxidation-stable iron oxide pigment.

9. The high chroma oxidation-stable iron oxide pigment according to claim 7, characterized in that: During the oxidative aging in step (b), the temperature is raised to 75° C. at a rate of 2° C. / min and maintained at this temperature for 8-12 hours.

10. The method for preparing a high-chroma oxidatively stable iron oxide pigment according to any one of claims 1 to 9, characterized in that: The following steps are involved: The α-Fe2O3 core and the dispersion medium are mixed and stirred uniformly at 60-80° C. under a nitrogen atmosphere, and the mixture is sieved to obtain an iron oxide pigment with high chroma and oxidation stability.

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