High-gloss titanium dioxide pigment is usually coated with one or more layers of metal oxides, such as silica, alumina, aluminum-silicon-zirconium or others, and mixed into pigment particles through oxidation or precipitation, and the addition amount is 0.5% ~ 3% of the total amount of titanium dioxide. The organic surface coating covers carboxylic acid, silane, siloxane, hydrocarbon wax and products that react with the surface of titanium dioxide, and the addition amount is 0.5 wt% ~ 1.5 wt% of the total pigment. Commercial products on the market, such as DuPont R-900, R700, Camilla RDI-S, DuPont R-706, Imperial Japanese Chemical Company W-6042 and Huntsman TR-52, among which TR-52 and RDIS have long occupied the high-end ink market in China.
1. 1 technology for improving the gloss and weatherability of titanium dioxide Andrejs Baidins and others invented a preparation method of titanium dioxide pigments with high gloss and high weatherability. The pigment surface is coated with porous alumina and dense alumina, in which the total mass concentration of alumina is (2-6)% of TiO2, and the mass ratio of dense alumina to boehmite alumina is 8: 1-65438. Compact alumina is an alumina containing sulfate ions, in which sulfate ions exist in alumina in the form of adsorption, and the mass ratio of alumina to sulfate ions is10:1~1.3:1. At (30 ~ 65)℃, bauxite is a crystalline form of alumina and contains adsorbed water. Water is randomly and regularly inserted into the octahedral layer of Al(OH)6. The surface of TiO2 pigment is coated with dense alumina to improve its durability, such as light resistance and pulverization resistance. However, coating the surface of titanium dioxide pigments with boehmite alumina layer improves its luster and dispersibility.
Brian Tear et al. provided another preparation method of titanium dioxide pigments with improved gloss and weatherability: treating titanium dioxide with various metal salts, such as 1.0% ~ 3.0% Al2O3 aluminum, zirconium and phosphorus compounds, at least one of which can provide monovalent anions. According to the wet treatment, the addition of aluminum compounds is generally1.0% ~ 3.0% Al2O3; According to the deposition amount on the surface of titanium dioxide, the addition amount of zirconium compound is 0.1%~ 0.4% ZrO2; The dosage of phosphorus compound is 0.1%~ 0.5% P2O5; Organic coating 0.2% ~ 0.4% of TMP, TME or pentaerythritol. It has been found that multivalent anions in soluble metal salts, such as SO42-, will attach to pigments during ion exchange in the coating process, but conventional water washing can not completely remove these multivalent anions, and these multivalent anion impurities will cause flocculation, reducing the dispersibility, whiteness, luster and weatherability of the final product. However, metal salts containing monovalent anions will reduce this trend.
Michael Hiew and others adopted a continuous process, and strictly controlled the pH value, temperature and adding time of silicon and aluminum to prepare titanium dioxide pigments with improved glossiness and weatherability. At 75℃, the silicon compound was added in three steps, namely, pH= 10.0, pH=9.4 and pH=4.9, with each step staying at least10 ~ 20min. Ph = 5.5 ~ 7.5, adding aluminum compound at 75℃. The addition of silica is 2.5% ~ 3.5% of the weight of titanium dioxide pigments, and the addition of alumina is 1.6% ~ 1.9% of the weight of titanium dioxide pigments. Finally, 0.2% ~ 0.8% TMP was coated organically. The deposition time of silicon and aluminum is 10 ~ 45 minutes, and the whole continuous process includes a residence time of no more than 120 minutes. The pigment has that advantage of excellent luster and good compatibility in paint, plastics and coatings. The data of tinting strength and Harrington instrument show that the titanium dioxide pigments prepared by this method has good dispersibility and will not agglomerate when used in coatings and plastics.
1.2 technology for improving the gloss and dispersibility of titanium dioxide John E.Halko et al. reduced the amount of dispersant in the surface treatment process and deposited at least one monoamine salt on the surface for treatment. Finally, the gloss and dispersity of the prepared titanium dioxide pigments are obviously improved. The amine salt can be one of DMPA+ triisopropanolamine TIPA, DMPA+TIPA+TME, DMPA+TIPA+TMP, DMBA+TIPA+TME, DMPA+TIPA+TMP. The molar ratio of DMPA or DMBA to TIPA is1:1~1:1.1,so that the neutral salt generated in this way does not contain excessive alkanolamine. The ratio of amine salt to TME or TMP is 95∶5 ~ 1∶ 1. The addition amount of amine salt is 0.2 wt% ~ 0.5 wt% of the mass of titanium dioxide. Compared with untreated titanium dioxide and pigments treated by TME or other amine salts, the titanium dioxide pigments prepared by this method has obvious improvement in dispersibility and luster, especially when it is used in waterborne coatings, which is its greatest advantage.
2. Domestic technical status of improving the gloss of titanium dioxide
At present, there are few reports about improving the gloss of titanium dioxide in China. In order to improve the hiding power and printing adaptability, some high-grade inks on the market still use a large number of imported chlorinated titanium dioxide, such as DuPont and Midland.
China patent publicationNo. CN 10 1880492A "Special Titanium Dioxide Pigment for Ink and Its Preparation Method", titanium dioxide pigment particles are coated with alumina to improve the gloss and dispersibility of its oily system application. Adding an alkaline aluminum compound and an acidic aluminum compound aqueous solution in sequence, wherein the total amount is 1wt%-4wt% of the titanium dioxide particles in the suspension, and the ratio of the addition amount of aluminum in the alkaline aluminum compound aqueous solution to that in the acidic aluminum compound aqueous solution is1:1:3. The method can be used for treating titanium dioxide pigments prepared in any form, and each step can be carried out intermittently or continuously.
3. Conclusion
The key to titanium dioxide selection is luster and durability. If the interior wall and ink coating require high gloss, ceramic grade titanium dioxide can be selected. If the exterior wall building coating requires high gloss (medium durability), you can choose high gloss general titanium dioxide. If automobile and pipeline coatings require high gloss (high durability), you can choose high gloss anti-pulverization titanium dioxide. There are many ways to improve the gloss of titanium dioxide, among which adding aluminum compound is essential and the most effective.