Preparation method of improved quinacridone pigment

Abstract

The invention belongs to the technical field of organic pigment preparation methods, and particularly relates to an improved quinacridone pigment preparation method. The method comprises the steps of preparation of an anthraquinone solution and a cyanation solution, a cyanation reaction, synthesis of a target intermediate, aniline condensation, crystallization salting-out, chlorine trifluoride gas phase catalysis and subsequent oil milling and coating treatment. By controlling the proportion of anthraquinone, the cyaniding agent and the catalyst and optimizing the reaction temperature, pressure and time, the product purity and reaction selectivity are effectively improved, and the obtained quinacridone pigment has the advantages of small particle size, good dispersity, high thermal stability, strong solvent resistance and the like. By monitoring the reaction endpoint and adopting the surface coating technology, the application performance of the pigment is remarkably improved, and the method is suitable for the fields of plastics, coatings, printing ink and the like and has a good industrial application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of organic pigment preparation methods, and particularly relates to an improved preparation method of quinacridone pigment. Background Art

[0002] Quinacridone pigments are a class of high-performance organic pigments. Their vibrant colors, excellent lightfastness, strong heat resistance, and high chemical stability make them widely used in high-end coatings, plastics, inks, and textile printing and dyeing. Among these, red quinacridone pigments, particularly those from the red family, possess promising commercial value and industrial application prospects.

[0003] Currently, the traditional preparation process for quinacridone pigments primarily involves multiple steps, including the nitrilation of anthraquinone raw materials, aniline coupling, crystallization and purification, and surface coating. While this process is relatively mature, it still suffers from numerous deficiencies in actual industrial applications. First, the nitrilation reaction often utilizes liquid-phase catalysis, which results in demanding reaction conditions, a high concentration of intermediate impurities, and large yield fluctuations, making precise control difficult. Second, impurities are difficult to completely separate, often leading to unstable pigment color development, uneven particle size distribution, and poor dispersibility. Third, existing surface coating treatments generally utilize a single coating agent, lacking the ability to multi-dimensionally control the surface structure of the dye particles. This leaves room for improvement in key performance aspects such as thermal stability and migration resistance.

[0004] Furthermore, traditional preparation methods rely heavily on reaction conditions, such as high temperature, high pressure, and precipitation of strong acids, resulting in high energy consumption and a heavy environmental burden. Furthermore, the controllability and safety of the entire process flow also require urgent improvement. Therefore, developing an improved preparation method for quinacridone pigments that combines highly selective reaction steps, the ability to control high-purity products, and balances environmental performance with efficiency has become a pressing technical challenge in this field. Summary of the Invention

[0005] In view of the above problems, the present invention aims to provide an improved method for preparing quinacridone pigments, which specifically comprises the following steps: S1. Solution preparation: preparing a reaction solution, wherein the reaction solution includes an anthraquinone solution and a nitrilation solution; The anthraquinone solution consists of anthraquinone and N-methyl-2-pyrrolidone NMP; The mass proportion of anthraquinone is 10% to 20%, and the mass proportion of NMP is 80% to 90%; The cyaniding solution comprises a cyaniding agent, a palladium-carbon catalyst and NMP, wherein the mass proportion of the palladium-carbon catalyst is no more than 25% of the anthraquinone, and the cyaniding agent is an alkali metal cyanide, and the mass proportion is 2 to 4 times that of the anthraquinone; S2, nitrilation: transfer the nitrilation solution to a high-pressure reactor, and react at a temperature of 150-170° C. and a pressure of 1.8-2.2 MPa for 2-3 hours to obtain a nitrilation solution; S3. Combining: adding the anthraquinone solution to the nitrilation solution obtained in step S2, stirring the reaction under normal pressure, and collecting and recording the concentration changes of the standard compounds in the solution until the concentrations of all impurities reach the lowest and the concentration of 2,5-dicyano-3,6-dioxy-1,4-phenylenedipropylene begins to decrease, which is the reaction endpoint; S4, aniline reaction: to the reaction solution obtained in step S3, a n-butanol solution of aniline was added, and NMP was removed by distillation after reacting for 1 hour. The volume of the n-butanol solution was 10% of the volume of the reaction solution, and the mass concentration of aniline was 0.8 g / mL; S5, purification and salting out: deionized water is added to the solution obtained in step S4, diluted until crystals are formed, and then nitric acid solution is added for salting out; S6. Chlorine trifluoride gas-phase catalysis: The crystals obtained after salting out are dried and ground into powder, and chlorine trifluoride gas is introduced to carry out a gas-phase catalytic reaction in the presence of calcium fluoride catalyst; S7, grinding and coating: adding the product obtained in step S6 into an oil mill, adding a surface treatment agent for coating treatment, and obtaining the target quinacridone pigment.

[0006] In a preferred technical solution, in step S1, the alkali metal cyanide is potassium cyanide or sodium cyanide.

[0007] In a preferred technical solution, in step S5, the volume concentration of nitric acid in the nitric acid solution is 65%.

[0008] In a preferred technical solution, in step S6, the mass ratio of the calcium fluoride catalyst to the powder to be reacted is 0.1:100 to 1:100.

[0009] In a preferred technical solution, in step S7, the surface treatment agent is an oily resin composed of isocyanate derivatives.

[0010] In a preferred technical solution, in step S3, the stirring speed is controlled at 200-300 rpm to promote mixing uniformity and reaction sufficiency.

[0011] In a preferred technical solution, it is characterized in that: in the step S4, the addition temperature of the aniline solution is controlled at 40-60° C. to promote the condensation reaction.

[0012] In a preferred technical solution, the crystallization time in step S5 is 0.5 to 1 hour, and the salting-out time is 1 to 2 hours.

[0013] In a preferred technical solution, it is characterized in that: the gas phase catalytic reaction temperature in step S6 is controlled at 60-80° C., and the reaction time is 10-30 minutes.

[0014] In a preferred technical solution, it is characterized in that: the amount of the coating treatment agent in step S7 is 1% to 3% of the pigment mass, and the oil grinding time is controlled at 30 to 60 minutes.

[0015] Beneficial effects The present invention provides an improved method for preparing quinacridone pigments, which has the following beneficial effects: 1. Improve pigment purity: By introducing a standard compound concentration monitoring endpoint after nitrilation, the occurrence of side reactions can be effectively suppressed, the intensity of impurity peaks can be reduced, and the purity and hue consistency of the finished pigment can be significantly improved.

[0016] 2. Improve dispersibility and particle size control: Using N-methyl-2-pyrrolidone (NMP) as a solvent, combined with a reasonable anthraquinone mass ratio and oil grinding and coating steps, helps to obtain pigment particles with a concentrated particle size distribution and easy dispersion in the resin system, thereby improving hiding power and color uniformity.

[0017] 3. Enhanced thermal stability and solvent resistance: Under the synergistic effect of the aniline reaction and the chlorine trifluoride gas-phase catalysis step, the modified pigment molecular structure is more stable, showing a higher thermal decomposition onset temperature and stronger organic solvent tolerance, suitable for application scenarios in high temperature and harsh environments.

[0018] 4. Reduce the formation of by-products during the synthesis process: By optimizing the cyaniding agent addition ratio, catalyst content and reaction conditions (such as temperature, pressure, etc.), the formation of incomplete nitrilation and heterocyclic by-products can be effectively suppressed, thereby improving the yield of the target product and process repeatability.

[0019] 5. Improve product performance: The introduction of isocyanate oily resin as a surface treatment agent enhances the surface wettability and interfacial affinity of pigment particles, thereby improving the stability and processing adaptability of pigments in application systems such as coatings, plastics, and inks.

[0020] In summary, the present invention achieves a comprehensive improvement in the performance of quinacridone pigments by systematically optimizing each key step of the preparation process without significantly increasing the complexity of the process, and has significant industrial practical value and promotion prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the method flow of the present invention; Figure 2 This is a SEM photograph of the quinacridone prepared in Example 1 of the present invention; Figure 3Schematic diagram of comparative experimental results (dispersion-550nm transmittance) of the present invention; Figure 4 Schematic diagram of comparative experimental results (thermal stability) of the present invention; Figure 5 is a schematic diagram of comparative experimental results (solvent resistance score) of the present invention; Figure 6 Schematic diagram of comparative experimental results (average particle size) of the present invention; Figure 7 Schematic diagram of comparative experimental results (impurity peak intensity) of the present invention. DETAILED DESCRIPTION

[0022] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to the examples. The examples are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0023] Example 1 (T1) like Figure 1 As shown, this embodiment provides an improved method for preparing quinacridone pigment, and the specific steps are as follows: S1. Solution preparation Weigh 20 g of anthraquinone, add 180 g of N-methyl-2-pyrrolidone (NMP), and stir thoroughly to form an anthraquinone solution, in which the mass proportion of anthraquinone is 10% and the mass proportion of NMP is 90%.

[0024] Separately, 80 g of potassium cyanide (4 times the mass of anthraquinone) and 5 g of palladium-carbon catalyst (25% of the mass of anthraquinone) were weighed, added to 100 g of NMP, and stirred thoroughly to form a nitrilation solution.

[0025] S2. Nitrilation reaction The nitrilation solution was transferred into a high-pressure reactor, the reaction temperature was set at 160° C., the reaction pressure was controlled at 2.0 MPa, and the reaction time was maintained for 3 hours to form a nitrilation product solution.

[0026] S3. Combined reactions The anthraquinone solution prepared in the previous step was slowly added to the nitrilation solution, and the reaction was stirred continuously at 250 rpm under atmospheric pressure. During the reaction, the concentration of the target product, 2,5-dicyano-3,6-dioxo-1,4-phenylenedipropylene, was monitored using liquid chromatography (HPLC). The reaction endpoint was determined when its concentration began to decrease and the concentrations of other impurities reached a minimum level, and the reaction was terminated.

[0027] S4. Aniline reaction Dissolve aniline at a concentration of 0.8 g / mL in 50 mL of n-butanol to form an aniline n-butanol solution (its volume accounts for 10% of the reaction mixture). Add this solution to the reaction mixture at 50°C. Stir the reaction for 1 hour, then begin vacuum distillation to remove the NMP solvent.

[0028] S5. Purification and salting out The reaction mixture was diluted with 300 mL of deionized water and allowed to stand for approximately 45 minutes to form an orange-red crystalline precipitate. A 65% nitric acid solution (100 mL) was then added and the mixture was stirred for 1.5 hours to allow salting out, completing the precipitation and preliminary purification of the crude product.

[0029] S6, Chlorine trifluoride gas phase catalysis Dry the crystals obtained in the previous step in a hot air drying oven at 60°C for 12 hours, then grind them into a fine powder. Weigh 100 g of this powder, add 1 g of calcium fluoride as a catalyst, and mix thoroughly at a mass ratio of 1:100. Then, introduce chlorine trifluoride gas and conduct a vapor-phase catalytic reaction at 70°C for 20 minutes. After completion of the reaction, cool to room temperature.

[0030] S7, Grinding Coating The reaction product was placed in an oil mill, and 2% by weight of an isocyanate derivative oil resin (2 g) was added as a surface treatment agent. The product was oil-milled at 60 rpm for 45 minutes to complete the coating operation, ultimately obtaining a quinacridone pigment powder with uniform structure and excellent dispersion properties.

[0031] Take SEM photos of the prepared quinacridone pigment powder, such as Figure 2 shown.

[0032] Example 2 (T2) This embodiment provides an improved method for preparing quinacridone pigments, which is carried out according to the following steps: S1. Solution preparation Weigh 15 g of anthraquinone and add it to 135 g of N-methyl-2-pyrrolidone (NMP). Stir thoroughly to prepare an anthraquinone solution with a mass ratio of 10% anthraquinone to 90% NMP. Separately, weigh 45 g of sodium cyanide (3 times the mass of anthraquinone) and 3 g of palladium-carbon catalyst (20% of the mass of anthraquinone) and add them to 97 g of NMP to prepare a nitrilation solution.

[0033] S2. Nitrilation reaction The nitrilation solution was transferred to a high-pressure reactor and reacted at a temperature of 165° C. and a pressure of 2.1 MPa for 2.5 hours to form a nitrilation product.

[0034] S3. Combined reactions Slowly add the anthraquinone solution obtained in S1 to the nitrilation product. Stir the reaction at atmospheric pressure at 280 rpm. Monitor the concentration of the target product, 2,5-dicyano-3,6-dioxo-1,4-phenylenedipropylene, using liquid chromatography during the reaction. The reaction endpoint is determined when the product concentration reaches a decreasing inflection point and the impurity concentration reaches a minimum.

[0035] S4. Aniline reaction Aniline was dissolved in 45 mL of n-butanol at a concentration of 0.8 g / mL to obtain an aniline solution, approximately 10% of the reaction mixture. This solution was slowly added dropwise to the combined reaction products at 60°C. After stirring for 1 hour, the NMP was removed by distillation.

[0036] S5. Purification and salting out Dilute the reaction mixture with 250 mL of deionized water and allow it to stand for 40 minutes to produce an orange-red crystalline precipitate. Slowly add 80 mL of 65% nitric acid solution to allow for salting-out for 1 hour.

[0037] S6, Chlorine trifluoride gas phase catalysis The resulting salting-out crystals were dried in hot air at 65°C for 10 hours and ground into a fine powder. Weigh 80 g of this powder, add 0.4 g of calcium fluoride catalyst at a mass ratio of 0.5:100, mix evenly, and then introduce chlorine trifluoride gas in the presence of calcium fluoride. A gas-phase catalytic reaction was carried out at 75°C for 25 minutes.

[0038] S7, Grinding Coating The above product was put into an oil mill, and 3% (i.e., 2.4 g) of an oily resin composed of an isocyanate derivative was added thereto. The product was then coated within 45 minutes to complete the surface modification of the final pigment and obtain a quinacridone pigment product with good dispersion properties.

[0039] Example 3 (T3) This embodiment provides an improved method for preparing quinacridone pigment, and the specific process steps are as follows: S1. Solution preparation Weigh 20 g of anthraquinone and add it to 160 g of N-methyl-2-pyrrolidone (NMP). Stir thoroughly to dissolve the anthraquinone solution. Anthraquinone accounts for 11.1% of the total mass, and NMP accounts for 88.9%.

[0040] Separately, 60 g of potassium cyanide (3 times the mass of anthraquinone) and 2 g of palladium-carbon catalyst (10% of the mass of anthraquinone) were weighed and added to 100 g of NMP to prepare a nitrilation solution.

[0041] S2. Nitrilation reaction The nitrilation solution was poured into a high-pressure reactor and reacted at a temperature of 155° C. and a pressure of 1.9 MPa for 3 hours to obtain a nitrilation product.

[0042] S3. Combined reactions The anthraquinone solution obtained in S1 was added to the nitrilation product, and the reaction was stirred at 250 rpm under normal pressure for 6 hours. The reaction was terminated after the concentration of the target product 2,5-dicyano-3,6-dioxy-1,4-phenylenedipropylene decreased and stabilized after observing the peak value through online UV-Vis monitoring.

[0043] S4. Aniline reaction Prepare a aniline n-butanol solution: aniline concentration of 0.8 g / mL, about 50 mL (10% of the reaction volume), and slowly add it to the reaction mixture at 50°C. After 1 hour of reaction, remove the residual NMP solvent by vacuum distillation.

[0044] S5. Purification and salting out 300 mL of deionized water was added to the reaction solution to promote crystallization of the product. The crystallization time was controlled within 40 minutes to form a red crystalline precipitate. Then, 90 mL of 65% nitric acid solution was added for salting out. The salting out time was controlled within 1.5 hours.

[0045] S6, Chlorine trifluoride gas phase catalysis The crystals obtained by salting out were dried at 60°C for 12 hours and then ground into powder. 100 g of the powder was weighed and thoroughly mixed with 0.8 g of calcium fluoride catalyst (mass ratio of 0.8:100), and chlorine trifluoride gas was introduced at 70°C for gas-phase catalytic reaction for 20 minutes.

[0046] S7, Grinding Coating The catalytic product was added to an oil mill, and 2% (i.e., 2 g) of an oily resin composed of isocyanate derivatives was added thereto. The product was ground and coated at 60°C for 45 minutes to obtain a surface-modified and stable quinacridone pigment product.

[0047] Comparative Example 1 (C1) This comparative experiment aims to verify the rationality of the key parameter ranges in the technical solution of the present invention, and the following formula and process flow are used for the experiment: S1. Solution preparation 25 g of anthraquinone was weighed and dissolved in 125 g of N-methyl-2-pyrrolidone (NMP) to obtain an anthraquinone solution. The anthraquinone content by weight was >20%, exceeding the 10% to 20% range specified in the present invention.

[0048] Separately, 40 g of sodium cyanide (1.6 times the mass of anthraquinone, less than the lower limit of 2 times) and 10 g of palladium-carbon catalyst (40% of the mass of anthraquinone, **exceeding the limit of not more than 25%) were weighed and added to 100 g of NMP to obtain a nitrilation solution.

[0049] S2. Nitrilation reaction The nitrilation solution was transferred into a high-pressure reactor and reacted for 1.5 hours (less than 2 hours) at a temperature of 145°C (lower than 150°C) and a pressure of 1.5 MPa (lower than 1.8 MPa) to obtain a nitrilation product.

[0050] S3. Combined reactions The anthraquinone solution was added to the nitrilation product and the reaction was stirred at normal pressure at a stirring speed of 150 rpm (lower than the recommended lower limit of 200 rpm). The reaction time was controlled to 3 hours. It was observed that the impurity peak did not completely disappear and the concentration of the target product fluctuated violently.

[0051] S4. Aniline reaction Prepare an aniline n-butanol solution with an aniline concentration of 0.4 g / mL (lower than the recommended 0.8 g / mL) and a volume that accounts for 6% of the reaction volume (lower than the recommended lower limit of 10%). Add the aniline at 30°C (lower than the recommended temperature range of 40-60°C). Terminate the reaction after 30 minutes, then distill the NMP solvent.

[0052] S5. Purification and salting out Deionized water was added to the reaction solution, but no obvious crystallization was observed. A nitric acid solution with a volume concentration of 30% (lower than the recommended value of 65%) was further added for salting out. The salting out time was 0.5 hours (lower than the recommended lower limit of 1 hour), and the crystallization efficiency was low.

[0053] S6, Chlorine trifluoride gas phase catalysis After the salting-out crystals were dried and ground, 1.5 g of calcium fluoride catalyst (exceeding the recommended upper limit of 1:100) was added and mixed with 100 g of powder. The gas-phase catalytic reaction was carried out at a temperature of 95°C (higher than the recommended upper limit of 80°C) for 40 minutes (exceeding the recommended upper limit by 30 minutes).

[0054] S7, Grinding Coating Add 5% of the mass of an oily surface treatment agent to the above product (exceeding the recommended upper limit of 3%), and perform coating treatment at a high temperature of 90°C for 20 minutes (the time is lower than the recommended lower limit of 30 minutes).

[0055] Comparative Example 2 (C2) In order to further verify the technical effect of the improved process in the technical solution of the present invention, this comparative example selected a traditional and common quinacridone pigment preparation method for experiment, and the process flow is as follows: S1. Raw material mixing and melt condensation: Weigh 50 g of anthraquinone, 60 g of phthalamide, and 200 mL of chlorosulfonic acid, add them together into an enameled reactor, heat to 180°C under normal pressure, and maintain the reaction in a molten state for 3 hours to form an intermediate amide compound.

[0056] S2. Hydrolysis reaction: After cooling the intermediate, slowly pour it into 2 L of ice water, and add 20% sodium hydroxide solution for hydrolysis. Stir the reaction for 2 hours to allow the reactant to be hydrolyzed and precipitated.

[0057] S3. Filtration and drying: Filter the precipitate, wash with distilled water until neutral, and dry it at 80°C for 12 hours to obtain a powdery intermediate.

[0058] S4. Aniline coupling: The above powder was mixed with aniline in equal molar amounts, 150 mL of ethanol was added as solvent, and the mixture was refluxed for 6 hours to form a quinacridone skeleton structure.

[0059] S5, acid boiling and sealing: the reactants were treated with sulfuric acid boiling for 1 hour.

[0060] S6. Catalyst-free gas phase treatment: direct drying and crushing.

[0061] S7. Mechanical grinding: dry ball milling for 30 minutes.

[0062] Comparative experiment Purpose of the experiment: The primary objective of this experiment was to demonstrate that the proposed improved preparation method offers significant advantages over methods with inappropriate parameters or outdated processes in terms of pigment color intensity, thermal stability, dispersion stability, solvent resistance, and impurity control. By setting up appropriate experimental groups and comparative examples, and comparing performance using identical testing conditions, the innovative effects of this invention were quantified.

[0063] Experimental groups: T1 (Example 1): The preparation process was carried out precisely according to the recommended parameters.

[0064] T2 (Example 2): The ratio of anthraquinone to NMP was adjusted to 20:80.

[0065] T3 (Example 3): Increase the calcium fluoride catalyst ratio to 0.8:100 to optimize the gas phase reaction efficiency.

[0066] C1 (Comparative Example 1): The amount of cyaniding agent added exceeded the range of 4 times, and the amount of catalyst added was too low.

[0067] C2 (Comparative Example 2): A traditional wet coupling preparation method was used without nitrilation, chlorine trifluoride gas phase treatment and coating steps.

[0068] Experimental process description: All experimental groups prepared quinacridone pigments according to the designed plan, and after obtaining dry powder samples, the following performance tests were performed: 1. Dispersion stability test: Prepare dispersion: Disperse the pigment sample in a standard resin system at a fixed ratio (e.g., 5 wt%) and process in a high-speed disperser for 30 minutes. Static observation: let the sample stand in a transparent cuvette for 24 hours; Spectral detection: Take the upper liquid and measure the transmittance at a wavelength of 550 nm using a spectrophotometer.

[0069] 2. Thermal stability test: The pigment samples were tested using a thermogravimetric analyzer (TGA). Approximately 5 mg of dried pigment powder was placed in a platinum crucible and heated from room temperature to 600°C at a rate of 10°C / min in an air atmosphere. The mass change curve of the sample was simultaneously recorded. The temperature at which the sample experienced a 10% mass loss was determined to be the thermal stability onset temperature (T) of the pigment. 10 %), as a reference indicator for evaluating its thermal stability performance.

[0070] 3. Solvent resistance test: Soak the pigment sample in acetone and ethyl acetate for 24 hours, and visually observe whether there is discoloration, decomposition or structural change, and score. The scoring criteria are shown in Table 1: Table 1 Scoring criteria for visual evaluation of solubility resistance Observe the phenomenon Assessment Description Fraction No obvious changes, stable color, and intact surface Excellent, completely solvent resistant 10 Very slight discoloration or slight swelling, almost unnoticeable to the naked eye Excellent, extremely solvent resistant 9 Slight discoloration or slight structural changes Good, minimal solvent influence 8 Slightly faded, slightly blurred edges, and slightly loose grain Good, with certain solvent resistance 7 Noticeable fading and flaking in some areas Generally, there is a solvent penetration effect 6 Significant fading, partial shedding, loose structure Moderate, solvents are destructive 5 Large areas of fading, severe structural damage, and obvious color changes Deviation, solvent obviously destroys the structure 4 Almost completely faded, with a lot of grain peeling Poor, poor solvent resistance 3 Basically dissolved, the sample surface is severely damaged or falls off Very poor, basically no resistance to solvents 2 Complete dissolution, complete loss of color, or structural disintegration Very poor, completely ineffective 1 4. Particle size and uniformity test: Use a particle size analyzer to measure the mean particle size.

[0071] 5. Impurity residue test: Analyze the organic impurity peaks by gas chromatography-mass spectrometry (GC-MS).

[0072] Experimental data: The experimental data results are shown in Table 2: Table 2 Experimental data results on the performance of quinacridone pigments Group Dispersibility (550nm transmittance / %) Thermal stability (℃) Solvent resistance score (1-10) Average particle size (nm) Impurity peak intensity (AU) T1 28..3 285 8.9 115 0.12 T2 32.7 280 8.7 120 0.15 T3 29.5 288 9.1 112 0.11 C1 61.2 255 6.8 150 0.38 C2 67.8 260 6.5 145 0.41 Draw according to Table 2 Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 and Figure 7 , in order to visualize the experimental results.

[0073] Data Analysis: From the data in the table, it can be seen that the experimental groups T1, T2, and T3 all showed relatively good comprehensive performance indicators, while the comparative groups C1 and C2 had obvious disadvantages. The specific analysis is as follows: 1. Dispersion (550nm transmittance): The light transmittance of samples in group T (T1–T3) was significantly lower than that in group C (28.3%–32.7% vs. 61.2%–67.8%), indicating that the pigment particles in group T were evenly dispersed and stably suspended. The low light transmittance reflects the strong hiding power. The pigments in group C settled significantly, forming a supernatant, which resulted in increased light transmittance and poor dispersion stability.

[0074] 2. Thermal stability (10% mass loss temperature): The T group has excellent thermal stability, with an initial decomposition temperature above 280°C and a maximum of 288°C (T3); The temperature of group C was significantly lower, only 255℃ and 260℃, indicating that it is more susceptible to degradation under high temperature conditions and is not suitable for high temperature applications.

[0075] 3. Solvent resistance (score 1–10): Samples in group T scored between 8.7 and 9.1, indicating high solvent resistance, stable hue, and complete structure. The score of group C dropped significantly to only 6.5–6.8, indicating that it is prone to color change or particle structure destruction in the solvent.

[0076] 4. Average particle size (nm): The T group has a smaller particle size (112–120 nm), which helps the dispersion and tinting strength of the pigment; The particle size of group C is relatively large (145–150 nm), which is prone to sedimentation, affecting hiding power and storage stability.

[0077] 5. Impurity peak intensity (AU): The impurity peak intensity of group T was controlled between 0.11–0.15 AU, indicating that the product purity was high and the side reactions were well controlled; The impurity intensity of group C is as high as 0.38–0.41AU, indicating that significant by-products are generated under traditional or uncontrolled conditions, affecting the hue and stability of the pigment.

[0078] Summary: The improved preparation methods (T1–T3) provided by this invention outperform traditional methods (C1 and C2) in all five performance indicators, particularly in dispersibility, thermal stability, and solvent resistance. By optimizing nitrilation conditions and precisely controlling reaction concentration and post-processing steps, this method achieves a high-purity, high-performance preparation pathway for quinacridone pigments, demonstrating broad potential for practical applications.

[0079] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. An improved method for preparing quinacridone pigments, characterized in that: The specific steps include: S1. Solution preparation: preparing a reaction solution, wherein the reaction solution includes an anthraquinone solution and a nitrilation solution; The anthraquinone solution consists of anthraquinone and N-methyl-2-pyrrolidone NMP; The mass proportion of anthraquinone is 10% to 20%, and the mass proportion of NMP is 80% to 90%; The cyaniding solution comprises a cyaniding agent, a palladium-carbon catalyst and NMP, wherein the mass proportion of the palladium-carbon catalyst is no more than 25% of the anthraquinone, and the cyaniding agent is an alkali metal cyanide, and the mass proportion is 2 to 4 times that of the anthraquinone; S2, nitrilation: transfer the nitrilation solution to a high-pressure reactor, and react at a temperature of 150-170° C. and a pressure of 1.8-2.2 MPa for 2-3 hours to obtain a nitrilation solution; S3. Combining: adding the anthraquinone solution to the nitrilation solution obtained in step S2, stirring the reaction under normal pressure, and collecting and recording the concentration changes of the standard compounds in the solution until the concentrations of all impurities reach the lowest and the concentration of 2,5-dicyano-3,6-dioxy-1,4-phenylenedipropylene begins to decrease, which is the reaction endpoint; S4, aniline reaction: to the reaction solution obtained in step S3, a n-butanol solution of aniline was added, and NMP was removed by distillation after reacting for 1 hour. The volume of the n-butanol solution was 10% of the volume of the reaction solution, and the mass concentration of aniline was 0.8 g / mL; S5, purification and salting out: deionized water is added to the solution obtained in step S4, diluted until crystals are formed, and then nitric acid solution is added for salting out; S6. Chlorine trifluoride gas-phase catalysis: The crystals obtained after salting out are dried and ground into powder, and chlorine trifluoride gas is introduced to carry out a gas-phase catalytic reaction in the presence of calcium fluoride catalyst; S7, grinding and coating: adding the product obtained in step S6 into an oil mill, adding a surface treatment agent for coating treatment, and obtaining the target quinacridone pigment.

2. The method for preparing an improved quinacridone pigment according to claim 1, wherein: In the step S1, the alkali metal cyanide is potassium cyanide or sodium cyanide.

3. The method for preparing an improved quinacridone pigment according to claim 1, wherein: In step S5, the volume concentration of nitric acid in the nitric acid solution is 65%.

4. The method for preparing an improved quinacridone pigment according to claim 1, wherein: In step S6, the mass ratio of the calcium fluoride catalyst to the powder to be reacted is 0.1:100 to 1:

100.

5. The method for preparing an improved quinacridone pigment according to claim 1, wherein: In step S7, the surface treatment agent is an oily resin composed of isocyanate derivatives.

6. The method for preparing an improved quinacridone pigment according to claim 1, wherein: In step S3, the stirring speed is controlled at 200-300 rpm to promote mixing uniformity and reaction sufficiency.

7. The method for preparing an improved quinacridone pigment according to claim 1, wherein: In step S4, the temperature of adding the aniline solution is controlled at 40-60° C. to promote the condensation reaction.

8. The method for preparing an improved quinacridone pigment according to claim 1, wherein: The crystal formation time in step S5 is 0.5 to 1 hour, and the salting-out time is 1 to 2 hours.

9. The preparation method according to claim 1, wherein: The gas phase catalytic reaction temperature in step S6 is controlled at 60-80° C., and the reaction time is 10-30 minutes.

10. The method for preparing an improved quinacridone pigment according to claim 1, wherein: The amount of the coating treatment agent in step S7 is 1% to 3% of the pigment mass, and the oil grinding time is controlled to be 30 to 60 minutes.

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