A sol-gel method for the preparation of cobalt violet pigments

Abstract

The application discloses a sol-gel preparation method of cobalt violet pigment, which comprises the following steps: (1) adding a cobalt source and a phosphorus source into water, mixing, and uniformly ultrasonic dispersing to obtain a mixed solution; (2) adding an auxiliary agent and a complexing agent into the mixed solution obtained in the step (1), adjusting the pH value to be acidic, heating and reacting, and drying to obtain a dry gel; and (3) placing the dry gel obtained in the step (2) in an inert atmosphere, calcining, cooling, and grinding to obtain the cobalt violet pigment. The cobalt violet pigment prepared by the method has the advantages of narrow particle size distribution, excellent dispersing performance, small average particle size, high crystal lattice stability, low dissolution, good light reflection consistency, color deviation avoidance, excellent color saturation, bright and persistent color, good stability, simple process, low energy consumption and environmental friendliness.

Description

Technical Field

[0001] The invention relates to the field of pigments, and in particular to a sol-gel preparation method for cobalt violet pigment. Background Art

[0002] Cobalt violet, due to its unique color and excellent stability, is widely used in coatings, inks, ceramics, and other fields. Traditional cobalt violet pigment preparation methods mostly use high-temperature solid-phase methods, where the raw materials are mixed and then directly calcined in the solid phase at high temperatures, usually above 1200°C. This leads to high energy consumption, coarse pigment particles, and uneven color.

[0003] In recent years, the preparation of pigments by the sol-gel method has received increasing attention. As a wet chemical preparation method, the sol-gel method can react at a lower temperature, achieve atomic-level mixing, and precisely control the chemical composition and microstructure of the product. The cobalt violet pigment used in modern industry is mainly Co3(PO4)2, which is green, environmentally friendly, non-toxic and harmless. However, it is difficult to control the crystal phase structure of the pigment with existing technology. The spinel phase of Co3(PO4)2 is bluish-purple, and the olivine phase is reddish-purple, which can easily lead to uncontrollable product color. At the same time, a single cobalt source system is difficult to form a stable purple crystal phase, which is often accompanied by blue or red impurities, and there is a lack of systematic methods for crystal phase regulation, resulting in poor color reproducibility.

[0004] Therefore, the method of preparing cobalt violet pigment using the sol-gel method and effectively controlling its crystal phase still needs further research and improvement. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a sol-gel preparation method for a cobalt violet pigment having a narrow particle size distribution, excellent dispersion performance, a small average particle size, high lattice stability, low dissolution amount, good consistency in light reflection, avoidance of color deviation, excellent color saturation, bright and long-lasting color, good stability, simple process, low energy consumption, and environmentally friendly cobalt violet pigment.

[0006] The technical solution adopted by the present invention to solve the technical problem is as follows: a sol-gel method for preparing cobalt violet pigment comprises the following steps:

[0007] (1) Add the cobalt source and the phosphorus source into water, mix them, and disperse them evenly by ultrasonication to obtain a mixed solution;

[0008] (2) adding an auxiliary agent and a complexing agent to the mixed solution obtained in step (1), adjusting the pH value to acidic, heating the mixture for reaction, and drying the mixture to obtain a dry gel;

[0009] (3) The dry gel obtained in step (2) is placed in an inert atmosphere, calcined, cooled, and ground to obtain a cobalt violet pigment.

[0010] The invention idea of ​​the method of the present invention is: the cobalt source and the phosphorus source are evenly dispersed by ultrasonication to ensure the uniformity of the gel network; under the action of the complexing agent, the pH value is adjusted to prevent PO4 3- Premature precipitation increases the crosslinking degree of the gel, effectively inhibiting grain growth, resulting in a narrow particle size distribution and excellent dispersibility. After calcination, grinding is performed to obtain a cobalt violet pigment. The method of the present invention utilizes a sol-gel method with a high conversion rate while effectively reducing energy consumption compared to traditional processes. The resulting cobalt violet pigment has excellent hiding power and good dispersibility. By adding metal ion dopants and varying calcination conditions to regulate the crystalline phase of Co3(PO4)2, the conversion of Co3(PO4)2 between two phases is achieved, resulting in excellent color saturation.

[0011] Preferably, in step (1), the molar ratio of the cobalt element in the cobalt source to the phosphorus element in the phosphorus source is 3:2.

[0012] Preferably, in step (1), the concentration of the cobalt source in the mixed solution is 240-250 g / L.

[0013] Preferably, in step (1), the cobalt source includes one or more of cobalt nitrate, cobalt acetate, cobalt chloride or cobalt sulfate.

[0014] Preferably, in step (1), the phosphorus source includes one or more of ammonium dihydrogen phosphate, phosphoric acid or disodium hydrogen phosphate.

[0015] Preferably, in step (2), the auxiliary agent is starch or a metal ion dopant.

[0016] Preferably, in step (2), the complexing agent includes citric acid, etc. Using citric acid as a complexing agent can effectively improve the uniformity of the pigment particle size, improve the color saturation, and improve the purity of the crystal phase.

[0017] Preferably, in step (2), the heating reaction temperature is 60-80° C. and the time is 12-24 hours.

[0018] Preferably, in step (2), the drying refers to: heating to 60-80°C at a rate of 1-5°C / min, and keeping the temperature until constant weight.

[0019] Preferably, when the auxiliary agent is starch, the amount of starch used is 5-10% of the mass of the cobalt element in the cobalt source. Using starch as an auxiliary agent can form a porous gel structure, reduce particle agglomeration, and improve the dispersibility of the pigment.

[0020] Preferably, after adding starch, the mixture is stirred and mixed at 80-90° C. for 20-40 minutes, and then the complexing agent is added.

[0021] Preferably, the pH value is adjusted to 3-5 with a complexing agent.

[0022] Preferably, the starch includes potato starch, etc. The gelatinization viscosity of the potato starch is 1000 mPa·s.

[0023] Preferably, when the auxiliary agent is a metal ion dopant, the molar ratio of the metal ions in the metal ion dopant to the cobalt element in the cobalt source is 0.05 to 0.20:1.

[0024] Preferably, the molar ratio of the complexing agent to the metal ions in the metal ion dopant is 1.5 to 2.5:1.

[0025] Preferably, a nitric acid solution with a mass concentration of 4 to 6% is added dropwise to adjust the pH value to 3 to 5.

[0026] Preferably, the metal ion dopant includes Al 3+ and / or Mg 2+ The method of the present invention uses Al 3+ Doping substitution Co 2+ Generate oxygen vacancies, reduce the olivine phase energy, and promote the formation of pure phase; Mg 2+ Doping can stabilize the spinel phase through solid solution and inhibit phase transformation.

[0027] Preferably, when it is desired to obtain a spinel phase Co3(PO4)2 product, the Mg-containing 2+ compounds as metal ion dopants, and Mg 2+ The molar ratio of the cobalt element to the cobalt source is 0.05 to 0.10:1.

[0028] Preferably, when it is necessary to obtain olivine phase Co3(PO4)2 product, the Al-containing 3+ compounds as metal ion dopants, Al 3+ The molar ratio of the cobalt element to the cobalt source is 0.15 to 0.20:1.

[0029] Preferably, when a mixed phase Co3(PO4)2 product of spinel phase and olivine phase is required, the Al-containing 3+ and Mg 2+ Compounds as composite metal ion dopants, Al 3+ With Mg 2+ The molar ratio of Al is 1 to 3:1. 3+ +Mg 2+ The molar ratio of the cobalt element to the cobalt source is 0.15 to 0.20:1.

[0030] Preferably, the metal ion dopant includes aluminum isopropoxide and / or magnesium acetate. The method of the present invention adds aluminum isopropoxide as a metal ion dopant, hydrolyzes it in an aqueous solution to generate Al(OH)3 colloid, and slowly releases Al3+ , has good compatibility with the sol-gel system and can form a uniform precursor; the method of the present invention adds magnesium acetate as a metal ion dopant, which can cooperate with citric acid to increase Mg 2+ The solid solubility rate is excellent, and it has excellent particle size control performance.

[0031] Preferably, in step (3), the calcination refers to: heating to 650-900°C at a rate of 3-12°C / min and keeping the temperature for 1-3 hours.

[0032] Preferably, in step (3), the grinding time is 30 to 50 minutes. The grinding is wet grinding, and the grinding medium is zirconium oxide.

[0033] Preferably, in step (3), the inert atmosphere includes a nitrogen atmosphere or the like.

[0034] Preferably, when it is necessary to obtain a spinel phase Co3(PO4)2 product, the calcination is carried out at a rate of 3-5°C / min, the temperature is raised to 680-720°C, and the temperature is kept for 1.5-2.5h. 2+ Oxidation of the cubic system, Co 2+ Occupying the tetrahedral voids, spinel phase Co3(PO4)2 is obtained.

[0035] Preferably, when it is necessary to obtain an olivine phase Co3(PO4)2 product, the calcination is carried out at a rate of 10-12°C / min, the temperature is raised to 800-900°C, the temperature is kept at this temperature for 1.5-2.5 hours, and the calcination is completed, followed by rapid cooling. The method of the present invention obtains an orthorhombic system by high temperature and rapid heating, which promotes the transformation to the olivine phase. 2+ Located in the octahedral voids, olivine phase Co3(PO4)2 is obtained.

[0036] Preferably, when a mixed phase Co3(PO4)2 product of spinel phase and olivine phase is required, the calcination is carried out at a rate of 5-10°C / min, heating to 700-800°C, keeping the temperature for 1.5-2.5h, and rapidly cooling after the calcination is completed.

[0037] The beneficial effects of the method of the present invention are as follows:

[0038] (1) The cobalt violet pigment obtained by the method of the present invention has a narrow particle size distribution, excellent dispersibility, and a small average particle size, which achieves a refined and uniform distribution of particle size; 2+ The dissolution amount is far below the EPA standard, indicating that the obtained cobalt violet pigment has high lattice stability and low dissolution amount. At the same time, the C* value is between 37.9 and 44.8, indicating that the uniform particles of the cobalt violet pigment have good light reflection consistency, avoid color cast, have excellent color saturation, bright and long-lasting color, and good stability.

[0039] (2) The method of the present invention has simple process, low energy consumption and is environmentally friendly. DETAILED DESCRIPTION

[0040] The present invention will be further described below with reference to the embodiments.

[0041] The gelatinization viscosity of the potato starch used in the examples and comparative examples of the present invention is 1000 mPa·s; the raw materials or chemical reagents used in the examples and comparative examples of the present invention, unless otherwise specified, were obtained through conventional commercial channels.

[0042] Example 1

[0043] (1) Cobalt acetate and ammonium dihydrogen phosphate were added to water at a molar ratio of 3:2, mixed, and ultrasonically dispersed to obtain a mixed solution (cobalt acetate concentration was 240 g / L);

[0044] (2) Add potato starch (the amount of Co 2+ 5% by mass), first stir and mix at 90°C for 30 minutes until uniform, then add complexing agent citric acid to adjust the pH value to 3, heat at 60°C for reaction for 24 hours, and then dry: heat to 80°C at a rate of 2°C / min, keep warm until constant weight, to obtain dry gel;

[0045] (3) The dry gel obtained in step (2) was placed in a nitrogen atmosphere and calcined: the temperature was raised to 650°C at a rate of 3°C / min, kept at this temperature for 3 hours, cooled, and wet-milled with zirconium oxide as a medium for 30 minutes to obtain a cobalt violet pigment.

[0046] Example 2

[0047] (1) Same as step (1) in Example 1;

[0048] (2) Add potato starch (the amount of Co 2+ 8% by mass), first stir and mix at 90℃ for 30min until uniform, then add complexing agent citric acid to adjust the pH value to 4, heat at 70℃ for reaction for 18h, and dry: heat to 80℃ at a rate of 2℃ / min, keep warm until constant weight, to obtain dry gel;

[0049] (3) The dry gel obtained in step (2) was placed in a nitrogen atmosphere and calcined: the temperature was raised to 750°C at a rate of 4°C / min, kept at this temperature for 2 hours, cooled, and wet-milled with zirconium oxide as a medium for 40 minutes to obtain a cobalt violet pigment.

[0050] Example 3

[0051] (1) Cobalt acetate and ammonium dihydrogen phosphate were added to water at a molar ratio of 3:2, mixed, and ultrasonically dispersed to obtain a mixed solution (cobalt acetate concentration was 250 g / L);

[0052] (2) Add potato starch (the amount of Co 2+ The mixture was stirred at 90°C for 30 minutes until uniform, and then citric acid was added as a complexing agent to adjust the pH value to 5. The mixture was heated at 80°C for 12 hours and then dried: the temperature was raised to 80°C at a rate of 2°C / min and kept warm until constant weight was obtained to obtain a dry gel.

[0053] (3) The dry gel obtained in step (2) was placed in a nitrogen atmosphere and calcined: the temperature was raised to 850°C at a rate of 5°C / min, kept at this temperature for 1 hour, cooled, and wet-milled with zirconium oxide as a medium for 50 minutes to obtain a cobalt violet pigment.

[0054] Example 4

[0055] (1) Same as step (1) in Example 1;

[0056] (2) Adding the metal ion dopant aluminum isopropoxide (Al 3+ With Co 2+ The molar ratio is 0.18:1) and the complexing agent citric acid (citric acid and Al 3+ The molar ratio of the mixture is 2:1), a 5% nitric acid solution is added dropwise to adjust the pH value to 4, and the mixture is heated at 70°C for 18 hours. The mixture is then dried by heating to 80°C at a rate of 2°C / min and keeping the temperature until constant weight is obtained to obtain a dry gel.

[0057] (3) The dry gel obtained in step (2) was placed in a nitrogen atmosphere and calcined: the temperature was raised to 850°C at a rate of 10°C / min, kept at this temperature for 2 hours, rapidly cooled, and wet-milled with zirconium oxide as a medium for 40 minutes to obtain cobalt violet pigment (olivine phase Co3(PO4)2).

[0058] Example 5

[0059] (1) Same as step (1) in Example 1;

[0060] (2) Adding metal ion dopant magnesium acetate (Mg 2+ With Co 2+ The molar ratio is 0.08:1) and the complexing agent citric acid (citric acid and Mg 2+ The molar ratio of the mixture is 2:1), a 4% nitric acid solution is added dropwise to adjust the pH value to 5, and the mixture is heated at 70°C for 18 hours. The mixture is then dried by heating to 80°C at a rate of 2°C / min and keeping the temperature until constant weight is obtained to obtain a dry gel.

[0061] (3) The dry gel obtained in step (2) was placed in a nitrogen atmosphere and calcined: the temperature was raised to 700°C at a rate of 3°C / min, kept at this temperature for 2 hours, cooled, and wet-milled with zirconium oxide as a medium for 40 minutes to obtain cobalt violet pigment (spinel phase Co3(PO4)2).

[0062] Example 6

[0063] (1) Same as step (1) in Example 1;

[0064] (2) Adding metal ion dopants aluminum isopropoxide and magnesium acetate (Al 3+ With Mg 2+ The molar ratio of Al is 2:1. 3+ +Mg 2+ With Co 2+ The molar ratio is 0.20:1) and the complexing agent citric acid (citric acid and Al 3+ +Mg 2+ The molar ratio of the mixture is 2:1), a nitric acid solution with a mass concentration of 6% is added dropwise to adjust the pH value to 3, and the mixture is heated at 70°C for 18 hours. The mixture is then dried by heating to 80°C at a rate of 2°C / min and keeping the temperature until constant weight is obtained to obtain a dry gel.

[0065] (3) The dry gel obtained in step (2) was placed in a nitrogen atmosphere and calcined: the temperature was raised to 750°C at a rate of 5°C / min, kept at this temperature for 2 hours, rapidly cooled, and wet-milled with zirconium oxide as a medium for 40 minutes to obtain a cobalt violet pigment (a mixed phase of spinel phase and olivine phase Co3(PO4)2).

[0066] Comparative Example 1

[0067] The only difference between this comparative example and Example 2 is that potato starch is not added in step (2), and the rest is the same as Example 2.

[0068] Comparative Example 2

[0069] The difference between this comparative example and Example 2 is that in step (2), the amount of potato starch added as an auxiliary agent is Co 2+ The rest are the same as in Example 2.

[0070] Comparative Example 3

[0071] The only difference between this comparative example and Example 5 is that no metal ion dopant is added in step (2), and the rest is the same as Example 5.

[0072] Comparative Example 4

[0073] The only difference between this comparative example and Example 5 is that in step (1), the molar ratio of cobalt acetate to ammonium dihydrogen phosphate is 2:1, and the rest is the same as Example 5.

[0074] Relevant performance tests were performed on Examples 1 to 6 of the present invention and Comparative Examples 1 to 4. The specific tests are as follows:

[0075] (1) Particle size test: Malvern laser particle size analyzer Mastersizer 3000 was used to analyze the particle size distribution of the samples. The dispersion medium was 0.1% sodium hexametaphosphate solution. Ultrasonic treatment was performed at 300W for 5 minutes. The refractive index of Co3(PO4)2 was 1.72 and the absorptivity was 0.1. The Span value was calculated. Each group was tested three times and the average value was taken. The particle size of the samples was tested using Hitachi high-resolution emission scanning electron microscope SU8010. The software was used for analysis and the average particle size was recorded. Each group was tested three times and the average value was taken.

[0076] (2) Heavy metal dissolution test: Based on the EPA 3060A method, the sample was mixed with 0.1 mol / L HCl at a ratio of 1:20 (g / mL), shaken for 24 h, filtered, and the Co in the dissolution solution was determined using an AAS atomic absorption spectrometer. 2+ Concentration, the limit is 0.1 mg / L, each group is tested three times and the average value is taken;

[0077] (3) Color saturation test: The test was conducted in an alkyd resin system, where the mass ratio of cobalt violet pigment to resin was 1:10. The samples were tested using a Datacolor 650 spectrophotometer with a D65 light source, an observation angle of 8°, and an aperture of ≥4 mm. Each group was tested three times and the average value was taken.

[0078] The above test results are shown in Table 1.

[0079]

[0080] Note: “-” in the table indicates that the dissolution amount exceeds the EPA limit of 0.1 mg / L and is not recorded.

[0081] As shown in Table 1, the Span values ​​of Examples 4 to 6 of the present invention are ≤0.72, indicating that the particle size distribution is narrow and the dispersion performance is excellent. In addition, the average particle size corresponding to Examples 1 to 6 of the present invention is small, which achieves the refinement and uniform distribution of the particle size. 2+ The dissolution amount is low, far below the EPA standard, indicating that the obtained cobalt violet pigment has high lattice stability and low dissolution amount. At the same time, the C* value is between 37.9 and 44.8, indicating that the uniform particles of the cobalt violet pigment have good light reflection consistency, avoid color deviation, and have excellent color saturation.

[0082] As can be seen from Table 1, the Span values ​​corresponding to Comparative Examples 1 to 4 are larger, the particle size distribution is wider, and there is agglomeration phenomenon, indicating that the absence of auxiliary agents or metal ion dopants in Comparative Examples 1 and 3 affects the particle size and distribution; the amount of starch used in Comparative Example 2 is too high, which will cause the gel structure to be excessively fluffy, the residual carbon impurities after calcination increase, the adhesion between particles is serious, the Span value increases, and the impurities affect the lattice stability, and the color saturation is reduced due to shading by impurities; in Comparative Example 4, after the molar ratio of cobalt to phosphorus deviates from 3:2, the raw material ratio is unbalanced, resulting in impure crystal phase, serious particle agglomeration, significant increase in Span value and average particle size, and a significant reduction in color saturation due to impurity interference, indicating that deviation from the parameters will lead to poor stability and color saturation of the cobalt violet pigment.

Claims

1. A sol-gel method for preparing cobalt violet pigment, characterized in that: The following steps are involved: (1) Add the cobalt source and the phosphorus source into water, mix them, and disperse them evenly by ultrasonication to obtain a mixed solution; The molar ratio of the cobalt element in the cobalt source to the phosphorus element in the phosphorus source is 3:2; the concentration of the cobalt source in the mixed solution is 240-250 g / L; the cobalt source includes one or more of cobalt nitrate, cobalt acetate, cobalt chloride or cobalt sulfate; the phosphorus source includes one or more of ammonium dihydrogen phosphate, phosphoric acid or disodium hydrogen phosphate; (2) adding an auxiliary agent and a complexing agent to the mixed solution obtained in step (1), adjusting the pH value to acidic, heating the mixture for reaction, and drying the mixture to obtain a dry gel; The auxiliary agent is starch or a metal ion dopant; the complexing agent includes citric acid; the temperature of the heating reaction is 60 to 80°C and the time is 12 to 24 hours; the drying comprises: heating to 60 to 80°C at a rate of 1 to 5°C / min and keeping the temperature until constant weight; When the auxiliary agent is starch, the amount of starch used is 5-10% of the mass of the cobalt element in the cobalt source; after adding the starch, stirring and mixing at 80-90° C. for 20-40 minutes, and then adding the complexing agent; adjusting the pH value to 3-5 with the complexing agent; the starch includes potato starch; When the auxiliary agent is a metal ion dopant, the molar ratio of the metal ion in the metal ion dopant to the cobalt element in the cobalt source is 0.05-0.20:1; the molar ratio of the complexing agent to the metal ion in the metal ion dopant is 1.5-2.5:1; a nitric acid solution with a mass concentration of 4-6% is added dropwise to adjust the pH value to 3-5; the metal ion dopant includes Al 3+ and / or Mg 2+ Compounds; (3) The dry gel obtained in step (2) is placed in an inert atmosphere, calcined, cooled, and ground to obtain a cobalt violet pigment.

2. The sol-gel method for preparing cobalt violet pigment according to claim 1, wherein: When it is necessary to obtain spinel phase Co3(PO4)2 product, Mg-containing 2+ compounds as metal ion dopants, and Mg 2+ The molar ratio of Al to cobalt in the cobalt source is 0.05 to 0.10:1; when it is necessary to obtain olivine phase Co3(PO4)2 product, select Al 3+ compounds as metal ion dopants, Al 3+ The molar ratio of cobalt to cobalt in the cobalt source is 0.15-0.20:1; when it is necessary to obtain a mixed phase Co3(PO4)2 product of spinel phase and olivine phase, select Al-containing 3+ and Mg 2+ Compounds as composite metal ion dopants, Al 3+ With Mg 2+ The molar ratio of Al is 1 to 3:

1. 3+ +Mg 2+ The molar ratio of the metal ion dopant to the cobalt element in the cobalt source is 0.15 to 0.20:1; the metal ion dopant includes aluminum isopropoxide and / or magnesium acetate.

3. The sol-gel method for preparing cobalt violet pigment according to claim 1 or 2, wherein: In step (3), the calcination refers to: heating to 650-900°C at a rate of 3-12°C / min and keeping warm for 1-3 hours; the grinding time is 30-50 minutes; and the inert atmosphere includes a nitrogen atmosphere.

4. The sol-gel method for preparing cobalt violet pigment according to claim 3, wherein: When it is necessary to obtain a spinel phase Co3(PO4)2 product, the calcination is carried out at a rate of 3-5°C / min, the temperature is raised to 680-720°C, and the temperature is kept at this temperature for 1.5-2.5 hours; when it is necessary to obtain an olivine phase Co3(PO4)2 product, the calcination is carried out at a rate of 10-12°C / min, the temperature is raised to 800-900°C, and the temperature is kept at this temperature for 1.5-2.5 hours, and after the calcination is completed, the product is rapidly cooled; when it is necessary to obtain a mixed phase Co3(PO4)2 product of spinel phase and olivine phase, the calcination is carried out at a rate of 5-10°C / min, the temperature is raised to 700-800°C, and the temperature is kept at this temperature for 1.5-2.5 hours, and after the calcination is completed, the product is rapidly cooled.

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