Sun-proof yellow pigment preparation process and product thereof

Abstract

The invention relates to the technical field of yellow pigment processing, in particular to a sun-proof yellow pigment preparation process and a product thereof, and the process comprises the following steps: under the protection of nitrogen, preparing a diazonium solution from polyvinylpyrrolidone, hydrochloric acid, dichloroaniline and sodium nitrite; preparing a coupling solution from sodium hydroxide, phenyl methyl pyrazolone and hexadecyl trimethyl ammonium bromide; mixing the modified titanium dioxide with sodium dodecyl benzene sulfonate, rosin soap and ethylene diamine tetraacetic acid, carrying out four-stage pH regulation and gradient heating, finally adding the modified titanium dioxide, and carrying out heat preservation, filter pressing and drying. On the premise of not changing the traditional azo core reaction, the sun-proof grade of the pigment is improved to 7-8 grade from 4-5 grade through assistant synergy and crystal form regulation and control, and the pigment has high tinting strength, excellent dispersity and batch stability, is suitable for building exterior wall coatings, automobile plastic ornaments and high-end light-color ink, and thoroughly solves the problem of outdoor yellow color fading.

Description

Technical Field

[0001] This application relates to the field of yellow pigment processing technology, and more specifically, to a lightfast yellow pigment preparation process and its products. Background Technology

[0002] Yellow organic pigments are among the most widely used colorants in the plastics, inks, and coatings industries. Azo pigments, in particular, have long held a dominant position in the production of yellow pigments due to their chromatographic purity, high tinting strength, good processability, readily available raw materials, and excellent batch stability. They are used in formulations for everyday plastic coloring, gravure / offset printing inks, and high-quality industrial coatings.

[0003] However, azo pigments also have significant drawbacks in yellow applications, namely generally poor lightfastness and weather resistance. Most classic azo pigment varieties have a lightfastness rating of only 4-5, making them susceptible to fading due to light and environmental factors in light-colored products or outdoor use, resulting in insufficient product appearance stability. Currently, azo pigment varieties modified with special structures, such as condensation structures or benzimidazolone groups, can achieve a lightfastness rating of 7-8. However, the production process for these modified varieties is more complex and costly, making it difficult to completely replace the widespread use of classic varieties. This has become a key factor limiting the expansion of azo pigments into high-end outdoor applications. Summary of the Invention

[0004] To address the issues of lightfastness and weather resistance in yellow azo pigments, this application provides a lightfast yellow pigment preparation process and its product.

[0005] In a first aspect, this application provides a process for preparing a lightfast yellow pigment, employing the following technical solution: A process for preparing a lightfast yellow pigment includes the following preparation steps: Preparation of diazo liquid: Under nitrogen protection, water, polyvinylpyrrolidone, hydrochloric acid solution and dichloroaniline are mixed, slurryed, cooled to 0°C by adding ice water, and then sodium nitrite solution is added and stirred to obtain diazo liquid; Preparation of coupling solution: Mix water and sodium hydroxide solution, heat to 50-55℃, then add phenylmethylpyrazolone and hexadecyltrimethylammonium bromide and stir until dissolved, cool to 25-30℃, add water, let stand, and obtain coupling solution; Synthesis: The diazo solution, coupling solution and sodium dodecylbenzenesulfonate were stirred and mixed evenly. Rosin soap and disodium EDTA solution were added and stirred. The pH was adjusted to 3.5-4, then adjusted to 9.5-10 and stirred. The pH was then adjusted to 2-2.5, the temperature was raised to 80-85℃, the pH was adjusted to 6.5-7, the temperature was raised to 90-95℃, modified titanium dioxide was added, the mixture was kept at the temperature and stirred, cooled, filtered under pressure, and dried to obtain a lightfast yellow pigment.

[0006] By adopting the above technical solution, the process produces lightfast yellow pigments with good lightfastness and weather resistance, while meeting the requirements of 7-8 level lightfastness, high tinting strength and good processability. It can meet the weather resistance requirements of outdoor coatings, such as yellow paint for building exterior walls, which need to withstand long-term rain and sun exposure, and can also be used for outdoor plastic parts, such as yellow park seats and yellow exterior trim for cars. It can also be used in high-end light-colored inks.

[0007] This application achieves excellent lightfastness and weather resistance in lightfast yellow pigments by optimizing only the additives without altering the core reaction. The diazo solution uses dichloroaniline as the diazo component, and the coupling solution uses phenylmethylpyrazolone as the coupling component. This is the core of the high tinting strength of traditional azo yellow pigments. The azo structure formed by the reaction of these two components can efficiently absorb light and exhibit a bright yellow color, thus the tinting strength remains unaffected. Simultaneously, the addition of hexadecyltrimethylammonium bromide to the coupling solution and sodium dodecylbenzenesulfonate during the synthesis stage allows them to adhere to the pigment particle surface, reducing particle agglomeration and ensuring uniform dispersion of the pigment in plastic melts, ink resins, or coating bases, avoiding problems such as color spots and floating color. Furthermore, the nitrogen protection during diazo solution preparation prevents dichloroaniline from being oxidized by air, avoiding batch-to-batch color differences caused by raw material impurities and ensuring batch stability in industrial production.

[0008] Furthermore, in the synthesis stage, this application first adjusts the pH to 3.5-4 to allow the diazonium salt and coupling components to combine efficiently and directionally generate azo pigment intermediates, avoiding side reactions such as decomposition or self-coupling of the diazonium salt under unsuitable pH conditions; then it raises the pH to 9.5-10, and the alkaline conditions can dissolve the incompletely reacted coupling components, allowing them to fully react with the remaining diazonium salt to ensure a complete reaction, while simultaneously optimizing particle dispersibility and avoiding uneven crystal growth in the subsequent stages; finally, it lowers the pH to 2-2.5, and under a strongly acidic environment, the intermolecular forces of the pigment intermediate change, causing them to aggregate and grow into a more compact and regular crystal structure. The optimized crystal structure is more lightfast than traditional azo pigments; raising the temperature to 80-85℃ and then adjusting the pH to 6.5-7 can terminate the previous effects of acid and alkali on the crystal structure, allowing the formed regular crystal structure to stabilize. The addition of modified titanium dioxide further improves the sun resistance of the pigment. The active groups on the surface of modified titanium dioxide can form chemical bonds with pigment molecules, which is equivalent to wrapping a layer of anti-ultraviolet barrier on the pigment particles, directly blocking the damage of azo bonds by ultraviolet rays. Ultimately, the sun resistance level jumps from the traditional 4-5 level to 7-8 level, completely solving the fading problem of light-colored outdoor products.

[0009] Preferably, the modified titanium dioxide is prepared by the following method: 1) Mix 10g of titanium dioxide with 100-150ml of anhydrous ethanol to obtain a suspension; 2) Mix 0.5-2g of hexadecyltrimethylammonium bromide, 1-5ml of sodium hydroxide solution with 100ml of water, then add 4-6g of tetraethyl orthosilicate and the suspension, and stir continuously to obtain a mixture; 3) Mix 1-2g of silane coupling agent with 10ml of anhydrous ethanol, add the mixture dropwise to the liquid phase, stir continuously, pour out after the reaction is finished, centrifuge, wash, and obtain pretreated titanium dioxide. 4) Mix 1-2g of pretreated titanium dioxide, benzophenone-based ultraviolet absorber and 30ml of solvent, continue stirring, pour out, centrifuge, and obtain modified titanium dioxide.

[0010] By adopting the above technical solution, the modified titanium dioxide prepared can not only effectively exert its anti-ultraviolet effect to improve the pigment's lightfastness in the azo yellow pigment system, but also perfectly integrate into the pigment system without producing any negative effects.

[0011] Titanium dioxide itself possesses the ability to reflect and scatter ultraviolet (UV) light, which can initially block UV penetration. However, pure titanium dioxide has a narrow absorption range for UV light, resulting in limited UV protection efficiency. In this application, a benzophenone-based UV absorber is loaded onto the surface of pretreated titanium dioxide. This absorber actively absorbs UV light in the 290-400 nm wavelength range and converts the UV energy into harmless heat, filling the absorption gap of pure titanium dioxide. The combination of these two forms a dual barrier: titanium dioxide reflects some UV light, while benzophenone absorbs the remaining UV light, synergistically improving UV protection efficiency and ultimately helping the lightfastness rating of azo yellow pigment jump from level 4-5 to level 7-8. The silane coupling agent modification in steps 2 and 3 provides stable loading sites for benzophenone, preventing it from detaching during pigment processing or use and ensuring long-term effectiveness in UV protection.

[0012] Simultaneously, in step 2, cetyltrimethylammonium bromide modifies the surface of titanium dioxide to be oleophilic, while tetraethyl orthosilicate hydrolyzes to form a uniform silicon layer, providing a stable carrier for the subsequent loading of ultraviolet absorbers. Sodium hydroxide solution regulates the alkaline environment, ensuring sufficient silicon layer coating. In step 3, the active group of the silane coupling agent binds to the silicon layer on the titanium dioxide surface at one end, and provides an anchoring point for benzophenone-based ultraviolet absorbers at the other end, ensuring that the subsequent loading does not detach. Centrifugal washing in steps 3 and 4 removes impurities and reduces performance fluctuations; the steric hindrance formed by the surface-modified groups prevents particle aggregation, ensuring uniform dispersion during pigment and substrate processing, and guaranteeing uniform coloring and stable lightfastness.

[0013] Preferably, in step 2), the tetraethyl orthosilicate and the suspension are added by double dropwise addition, with the dropwise addition time controlled at 30-60 min and the dropwise addition temperature maintained at 25-35℃. After the dropwise addition is completed, stirring is continued for 1-3 h.

[0014] By adopting the above technical solution, the simultaneous droplet addition of tetraethyl orthosilicate and titanium dioxide suspension can avoid the violent local reaction caused by excessive amount of a single material, and ensure that the siloxane generated by the hydrolysis of tetraethyl orthosilicate is uniformly coated on the surface of each titanium dioxide particle, ensuring that the silicon layer is firmly attached and forming a silicon layer of uniform thickness, providing a stable substrate for subsequent loading of ultraviolet absorbers.

[0015] Preferably, the amounts of raw materials used in preparing the diazo solution are as follows: 400ml of water Polyvinylpyrrolidone 1-2g 62-70g of hydrochloric acid solution 40g of dichloroaniline 200-230ml of ice water 86-90g of sodium nitrite solution.

[0016] By adopting the above technical solution, a fixed amount of 400ml water and 40g dichloroaniline can stabilize the concentration of the diazo component, ensuring the formation of sufficient azo structures during the subsequent reaction with the coupling component. This is a key prerequisite for maintaining the high tinting strength of the pigment. 1-2g polyvinylpyrrolidone can help regulate the dispersibility of the system, avoiding particle agglomeration during the diazo reaction, laying the foundation for the uniform dispersion of the pigment in the substrate. 62-70g hydrochloric acid solution can provide a suitable acidic environment, ensuring that dichloroaniline is fully dissolved and the diazo reaction is completed, avoiding incomplete reaction due to insufficient acid or waste of raw materials due to excessive acid. 200-230ml ice water can precisely maintain the system at a low temperature of 0℃, preventing the decomposition of sodium nitrite, reducing side reactions, and ensuring the stability of the diazo solution. The amount of sodium nitrite solution used is matched with dichloroaniline, ensuring the complete diazo reaction and the formation of highly active diazonium salts, which is beneficial for the reaction with the coupling solution.

[0017] Preferably, the amounts of raw materials used in the coupling solution are as follows: 500ml of water 30-35g of sodium hydroxide solution Phenylacetylpyrazolone 43.5-45g 1.5-2g of hexadecyltrimethylammonium bromide.

[0018] By employing the above technical solution, 500ml of water as the base solvent can fully dissolve all raw materials, maintain system stability, and provide a suitable environment for subsequent reactions. 30-35g of sodium hydroxide solution can precisely adjust the alkalinity, ensuring complete dissolution of phenylmethylpyrazolone and creating suitable conditions for the coupling reaction, avoiding reaction inhibition. The matching amount of 43.5-45g of phenylmethylpyrazolone with 40g of dichloroaniline in the diazo solution ensures sufficient reaction to generate a sufficient amount of azo structure, which is the core of the pigment's high tinting strength. 1.5-2g of hexadecyltrimethylammonium bromide can adhere to the pigment particle surface in advance, reducing agglomeration and laying the foundation for uniform dispersion of the pigment in coatings, plastics, and other substrates, helping the product meet the processing needs of multiple scenarios.

[0019] Preferably, in the synthesis step, the amount of sodium dodecylbenzenesulfonate is 2-3g, the amount of rosin soap is 4-6g, and the amount of disodium ethylenediaminetetraacetate solution is 5-6ml.

[0020] By employing the above technical solution, sodium dodecylbenzenesulfonate, as an anionic surfactant, complements the cationic hexadecyltrimethylammonium bromide in the coupling solution, enhancing the surface repulsion of pigment particles through charge adsorption and reducing agglomeration. Rosin soap assists in regulating interfacial tension, improving the wettability of pigments in coatings and plastic melts, and optimizing processing dispersibility. Disodium ethylenediaminetetraacetate chelates trace metal ions in the system, preventing them from catalyzing the photo-oxidative decomposition of azo bonds and enhancing weather resistance. The appropriate dosage of these three components synergistically ensures uniform pigment dispersion, reduces color spot floating, and, combined with crystal form regulation and modified titanium dioxide, helps achieve a balance between 7-8 level lightfastness and high tinting strength.

[0021] Preferably, in the diazonium solution preparation step, the sodium nitrite solution is added at a uniform rate over 15-30 minutes, and stirring is continued at 0-2°C for 30-60 minutes.

[0022] By adopting the above technical solution, byproducts can be reduced, diazonium salt decomposition and raw material residues can be avoided, and the purity and stability of the diazonium solution can be improved, laying the foundation for the smooth progress of subsequent coupling reactions and the final pigment's tinting strength and batch stability. Adding sodium nitrite at a uniform rate avoids excessively high local concentrations: if added too quickly, it can easily lead to an excess of sodium nitrite in certain areas, generating byproducts such as diazonium amino compounds with dichloroaniline, thus reducing the purity of the diazonium salt; adding it at a uniform rate allows it to react evenly with hydrochloric acid and dichloroaniline, ensuring efficient diazonium salt formation.

[0023] Stirring at a low temperature of 0-2℃ serves two purposes: first, diazonium salts are more stable at low temperatures, preventing their thermal decomposition and thus avoiding interference with subsequent reactions; second, sufficient stirring time ensures that dichloroaniline is completely converted into diazonium salts, reducing unreacted raw material residues and preventing residual raw materials from interfering with the uniformity of subsequent coupling reactions.

[0024] Preferably, in the synthesis step, the temperature is raised to 80-85°C and then held for 30-45 minutes.

[0025] By adopting the above technical solution, the regular, dense, and defect-free high lightfast lattice generated by acid regulation is fully impurity removed, pressure released, and shaped, preventing subsequent high-temperature re-dissolution or phase inversion; at the same time, the surfactant is adsorbed in an orderly manner, providing a perfect interface for uniform bonding of TiO, ensuring batch stability, and achieving 78-level lightfastness.

[0026] Preferably, in the synthesis step, after adjusting the pH to 6.5-7 with ammonia, stirring is continued for 10-20 minutes, and then the temperature is increased to 90-95℃ at a rate of 1-3℃ / min.

[0027] By adopting the above technical solution, the pH of the system can be evenly distributed, avoiding uneven aggregation of pigment molecules caused by local pH fluctuations. At the same time, the pigment intermediates generated in the early reaction are fully dispersed, reducing particle agglomeration and ensuring that the crystal growth starting point is consistent during the subsequent heating process, forming a denser and more stable crystal structure and improving the lightfastness of the pigment itself.

[0028] Secondly, this application provides a lightfast yellow pigment, employing the following technical solution: A lightfast yellow pigment, wherein the lightfast yellow pigment is prepared by the lightfast yellow pigment preparation process described in the first aspect.

[0029] By adopting the above technical solution, the pigment produced by this process has a lightfastness rating of 7-8, which is a leap from the traditional 4-5 level; it has high tinting strength, excellent dispersion and no floating color; regular crystal form, good weather resistance, strong resistance to sun exposure; stable processing, small batch color difference, suitable for exterior wall coatings, automotive parts and high-end light inks, completely solving the problem of yellowing and fading outdoors.

[0030] In summary, this application has the following beneficial effects: 1. This process, without altering the core reaction of traditional azo yellow, achieves a leap in lightfastness rating from 4-5 to 7-8 through additive and process optimization. Nitrogen protection, hexadecyltrimethylammonium bromide, and sodium dodecylbenzenesulfonate synergistically reduce oxidation and agglomeration, ensuring high tinting strength, batch stability, and excellent dispersion in coatings, plastics, and inks. Three-stage pH control sequentially promotes the directional formation of azo bonds, thorough reaction, and dense, regular crystal structure, followed by gradient curing of the crystal structure at 80-95℃. Finally, modified titanium dioxide is introduced, with surface-active groups chemically bonded to the pigment, forming an anti-UV barrier to block UV damage to azo bonds. This process combines high weather resistance, high tinting strength, and easy processing, fully meeting the long-term non-fading requirements of outdoor construction, automobiles, public facilities, and high-end light inks. Detailed Implementation

[0031] Preparation Example Preparation Example 1 A modified titanium dioxide is prepared by the following method: 1) Mix 10g of titanium dioxide and 100ml of anhydrous ethanol to obtain a suspension; 2) Mix 0.5g of hexadecyltrimethylammonium bromide, 1ml of sodium hydroxide solution (mass fraction of 30%), and 100ml of water, then add 4g of tetraethyl orthosilicate and the suspension, and stir continuously to obtain a mixture; Tetraethyl orthosilicate and the suspension were added by double dropwise addition, with the addition time controlled at 30 min and the addition temperature maintained at 25 °C. After the addition was completed, stirring was continued for 1 h. 3) Mix 1g of silane coupling agent (γ-mercaptopropyltriethoxysilane) and 10ml of anhydrous ethanol, add the mixture dropwise to the liquid phase, stir continuously, pour out after the reaction is finished, centrifuge, wash, and obtain pretreated titanium dioxide. 4) Mix pretreated titanium dioxide, 1g of benzophenone-based ultraviolet absorber (2-hydroxy-4-methoxybenzophenone), and 30ml of solvent (ethanol), continue stirring, pour out, and centrifuge to obtain modified titanium dioxide.

[0032] The difference between Preparation Examples 2-3 and Preparation Example 1 lies in the types, amounts, and parameters of raw materials used to prepare the modified titanium dioxide. The specific differences are shown in Table 1. Table 1. Raw material types, dosages, and parameters for the preparation of modified titanium dioxide in Examples 1-3. Preparation Example 4 A modified titanium dioxide, the difference between this preparation example and preparation example 1 is that tetraethyl orthosilicate is not added in step S2.

[0033] Preparation Example 5 A modified titanium dioxide, the difference between this preparation example and preparation example 1 is that ethanol is used instead of benzophenone for ultraviolet absorption. Example

[0034] Example 1 A process for preparing a lightfast yellow pigment includes the following preparation steps: Preparation of diazo solution: Under nitrogen protection, 400 ml of water, 2 g of polyvinylpyrrolidone, 62 g of hydrochloric acid (mass fraction 37%) and 40.25 g of dichloroaniline (3,4-dichloroaniline, 0.25 mol) were mixed and stirred. 200 ml of ice water was added to cool to 0 °C, and then 86 g of sodium nitrite solution (0.25 mol, mass fraction 20%) was added and stirred to obtain diazo solution. Sodium nitrite solution was added at a uniform rate over 15 minutes, and stirring was continued at 0°C for 30 minutes. Preparation of coupling solution: Mix 300 ml of water and 33 g of sodium hydroxide solution (30% sodium hydroxide solution by mass), heat to 50 °C, then add 43.5 g of phenylmethylpyrazolone (1-phenyl-3-methyl-5-pyrazolone, 0.25 mol) and 1.5 g of hexadecyltrimethylammonium bromide and stir until dissolved. Cool to 25 °C, add 200 ml of water, and let stand to obtain the coupling solution; Synthesis: Diazo solution, coupling solution and 2g sodium dodecylbenzenesulfonate were stirred and mixed evenly. 4g rosin soap (50% potassium soap by mass) and 5ml disodium ethylenediaminetetraacetate solution (20% by mass) were added and stirred. Hydrochloric acid (10% hydrochloric acid solution) was added to adjust the pH to 3.5. Then, 30% sodium hydroxide solution was added to adjust the pH to 9.5 and stirred. The pH was then adjusted to 2 with hydrochloric acid (10% hydrochloric acid solution). The temperature was raised to 80℃ and held for 30min. The pH was adjusted to 6.5 with ammonia water and stirred for another 10min. The temperature was raised to 90℃ at a rate of 1℃ / min and held for 60min. 10g modified titanium dioxide (from preparation example 1) was added, and the mixture was kept warm and stirred. The mixture was then cooled, filtered under pressure, and dried to obtain a lightfast yellow pigment.

[0035] The difference between Examples 2-3 and Example 1 lies in the types, amounts, and parameters of raw materials used to prepare the lightfast yellow pigments. Specific differences are shown in Table 1. Table 1. Raw material types, dosages, and parameters for the preparation of lightfast yellow pigments in Examples 1-3. Example 4: A process for preparing a lightfast yellow pigment. The difference between this example and Example 1 is that the modified titanium dioxide is derived from Example 4.

[0036] Example 5 A process for preparing a lightfast yellow pigment. The difference between this embodiment and Example 1 is that the modified titanium dioxide is derived from Preparation Example 5.

[0037] Example 6 A process for preparing a lightfast yellow pigment. The difference between this embodiment and Example 1 is that in the synthesis step, the temperature is raised to 80°C and then held for 10 minutes.

[0038] Comparative Example Comparative Example 1 A process for preparing a lightfast yellow pigment. The difference between this comparative example and Example 1 is that titanium dioxide is used instead of modified titanium dioxide.

[0039] Comparative Example 2 A process for preparing a lightfast yellow pigment. The difference between this comparative example and Example 1 is that in the synthesis step, sodium hydroxide solution is first added to adjust the pH to 9.5, then hydrochloric acid is added to adjust the pH to 3.5, hydrochloric acid is added again to adjust the pH to 2, and the temperature is raised to 80°C to adjust the pH to 6.5.

[0040] Comparative Example 3 A process for preparing a lightfast yellow pigment. The difference between this comparative example and Example 1 is that sodium dodecylbenzenesulfonate is not added in the synthesis step.

[0041] Comparative Example 4 A process for preparing a lightfast yellow pigment. The difference between this comparative example and Example 1 is that cetyltrimethylammonium bromide was not added.

[0042] Comparative Example 5 A process for preparing a lightfast yellow pigment. The difference between this comparative example and Example 1 is that carbon nanotubes are used instead of modified titanium dioxide.

[0043] Test Method / Experimental Method for Lightfastness: The lightfast yellow pigments prepared in Examples 1-6 and Comparative Examples 1-5 were diluted with standard tap water at a ratio of 1:1. A 20mm wide and approximately 80mm long strip was drawn on 200g watercolor paper using a 0.10mm applicator. The strips were air-dried at room temperature for 24 hours, followed by drying at 50℃ for 30 minutes to remove residual moisture, thus obtaining the samples. One 30mm*30mm blue label of each grade 1-8 was cut out. The samples and the blue labels of grades 1-8 were placed side by side in a xenon lamp box, with half of the light blocked. The xenon lamp box was set to 42 minutes of light exposure + 18 minutes of spray exposure. The machine was stopped every 5 cycles for comparison with the gray card. When the color difference of the sample reached grade 3 on the gray card, the corresponding blue label grade was the lightfastness level.

[0044] Coloring performance test: 0.1g of the lightfast yellow pigments prepared in Examples 1-6 and Comparative Examples 1-5 were respectively mixed with 3.0g of white paste (60% R-706 titanium dioxide + 38% long-oil alkyd + 2% Ca-St, pre-dispersed to 10μm) and placed in a flat grinder. A 4.5kg weight was set on the grinder, and the process was repeated 4 times at 25 revolutions, with the scraper retracted every 50 revolutions for a total of 200 revolutions. Then, the two pigment pastes were scraped side-by-side onto black and white cardstock using a 150μm wet film preparation device. The mixture was dried at 25℃ for 24 hours. The Y value was read using a D65 / 10° colorimeter. Reference Ys and sample Yt were used to calculate the relative tinting strength = (Ys / Yt)*100%. Experimental data are shown in Table 3. Table 3. Experimental data of Examples 1-6 and Comparative Examples 1-5 Examples or comparative examples Sun resistance rating (level) Relative tinting strength (%) Example 1 8 102 Example 2 8 103 Example 3 8 101 Example 4 5 99 Example 5 5 98 Example 6 6 97 Example 7 6 99 Comparative Example 1 5 95 Comparative Example 2 5 94 Comparative Example 3 6 93 Comparative Example 4 6 90 Comparative Example 5 5 92 The experimental data above show that by incorporating the formulation and process described in this application, the lightfastness and tinting strength of lightfast yellow pigments can be greatly improved.

[0045] Comparing the experimental data of Example 1 and Comparative Examples 1-5, the sun resistance rating of Comparative Examples 1-5 is lower than that of Example 1, and the tinting strength is also lower than that of Example 1. Comparative Example 1 uses only unmodified titanium dioxide, and the sun resistance rating drops back to level 5, with the tinting strength falling to 95%. Comparative Example 2 reverses the pH order, increasing lattice defects, and the rating and tinting strength drop to level 5 and 94%, respectively. Comparative Example 3 omits sodium dodecylbenzenesulfonate, achieving a sun resistance rating of level 6 and a tinting strength of 93%. Comparative Example 4 lacks hexadecyltrimethylammonium bromide, achieving a rating of level 6, with a tinting strength of only 90%. Comparative Example 5 uses carbon nanotubes instead of modified titanium dioxide, achieving a sun resistance rating of level 5 and a tinting strength of 92%. The data differences prove that the absence of any element causes azo yellow to fail to break through level 6, and the tinting strength drops by 7-12 percentage points simultaneously. Example 1, through the synergy of the above components and processes, enables classic azo yellow to meet the long-term sun exposure and non-fading requirements of high-end outdoor scenarios such as exterior wall coatings and automotive parts, providing the industry with a low-cost, high sun resistance, and high tinting strength upgrade path.

[0046] A comparison of the experimental data from Examples 1 and 4-5 demonstrates that the modified titanium dioxide prepared by the method described in this application can increase the lightfastness of azo yellow from level 6 to level 8 while maintaining high tinting strength.

[0047] Comparing the experimental data from Example 1 and Example 6, it is shown that insufficient heat preservation time or excessive heating rate, even with the addition of fully modified titanium dioxide, resulted in a lightfastness rating dropping to level 7, and a corresponding decline in tinting strength. Sufficient heat preservation at 80°C and slow heating are necessary to form dense, low-defect, high-lightfastness crystals, thereby improving the lightfastness rating and tinting strength of lightfast yellow pigments.

[0048] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A process for preparing a lightfast yellow pigment, characterized in that, The preparation steps include the following: Preparation of diazo liquid: Under nitrogen protection, water, polyvinylpyrrolidone, hydrochloric acid solution and dichloroaniline are mixed, slurryed, cooled to 0°C by adding ice water, and then sodium nitrite solution is added and stirred to obtain diazo liquid; Preparation of coupling solution: Mix water and sodium hydroxide solution, heat to 50-55℃, then add phenylmethylpyrazolone and hexadecyltrimethylammonium bromide and stir until dissolved, cool to 25-30℃, add water, let stand, and obtain coupling solution; Synthesis: The diazo solution, coupling solution and sodium dodecylbenzenesulfonate were stirred and mixed evenly. Rosin soap and disodium EDTA solution were added and stirred. The pH was adjusted to 3.5-4, then adjusted to 9.5-10 and stirred. The pH was then adjusted to 2-2.5, the temperature was raised to 80-85℃, the pH was adjusted to 6.5-7, the temperature was raised to 90-95℃, modified titanium dioxide was added, the mixture was kept at the temperature and stirred, cooled, filtered under pressure, and dried to obtain a lightfast yellow pigment.

2. The process for preparing a lightfast yellow pigment according to claim 1, characterized in that, The modified titanium dioxide was prepared by the following method: 1) Mix 10g of titanium dioxide with 100-150ml of anhydrous ethanol to obtain a suspension; 2) Mix 0.5-2g of hexadecyltrimethylammonium bromide, 1-5ml of sodium hydroxide solution with 100ml of water, then add 4-6g of tetraethyl orthosilicate and the suspension, and stir continuously to obtain a mixture; 3) Mix 1-2g of silane coupling agent with 10ml of anhydrous ethanol, add the mixture dropwise to the liquid phase, stir continuously, pour out after the reaction is finished, centrifuge, wash, and obtain pretreated titanium dioxide. 4) Mix 1-2g of pretreated titanium dioxide, benzophenone-based ultraviolet absorber and 30ml of solvent, continue stirring, pour out and centrifuge to obtain modified titanium dioxide.

3. The process for preparing a lightfast yellow pigment according to claim 2, characterized in that: In step 2), the tetraethyl orthosilicate and the suspension are added by double dropwise addition, with the addition time controlled at 30-60 min and the addition temperature maintained at 25-35℃. After the addition is completed, stirring is continued for 1-3 h.

4. The process for preparing a lightfast yellow pigment according to claim 1, characterized in that, The amounts of raw materials used to prepare the diazo solution are as follows: 400ml of water Polyvinylpyrrolidone 1-2g 62-70g of hydrochloric acid solution 40g of dichloroaniline 200-230ml of ice water 86-90g of sodium nitrite solution.

5. The process for preparing a lightfast yellow pigment according to claim 1, characterized in that, The amounts of raw materials used in the coupling solution are as follows: 500ml of water 30-35g of sodium hydroxide solution Phenylacetylpyrazolone 43.5-45g 1.5-2g of hexadecyltrimethylammonium bromide.

6. The process for preparing a lightfast yellow pigment according to claim 1, characterized in that, In the synthesis steps, the amount of sodium dodecylbenzenesulfonate is 2-3g, the amount of rosin soap is 4-6g, the amount of disodium ethylenediaminetetraacetate solution is 5-6ml, and the amount of modified titanium dioxide is 10g.

7. The process for preparing a lightfast yellow pigment according to claim 1, characterized in that: In the preparation step of the diazonium solution, the sodium nitrite solution is added at a uniform rate over 15-30 min, and stirring is continued at 0-2℃ for 30-60 min.

8. The process for preparing a lightfast yellow pigment according to claim 1, characterized in that: In the synthesis step, the temperature is raised to 80-85℃ and then held for 30-45 minutes.

9. The process for preparing a lightfast yellow pigment according to claim 1, characterized in that: In the synthesis step, after adjusting the pH to 6.5-7 with ammonia, stirring is continued for 10-20 min, and then the temperature is increased to 90-95℃ at a rate of 1-3℃ / min.

10. A lightfast yellow pigment, characterized in that: The lightfast yellow pigment is prepared by the lightfast yellow pigment preparation process described in any one of claims 1-9.

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