Research Progress of Colored Mica Titanium Pearlescent Pigments at Home and Abroad

Rong Jianfeng, Lang Jianfeng (College of Chemical and Biotechnology, Hebei Polytechnic University, Tangshan 063009, Hebei, China)

Jia Qianyi (School of Materials, Hebei Polytechnic University, Tangshan 063009, Hebei, China)

Abstract : This paper summarizes recent developments in research and development of titanium pearlescent pigments for colored mica at home and abroad. It is pointed out that broadening the chromatographic range of pigmented pearlescent pigments and developing sheet-like conductive pearlescent pigments will be the future direction of research and development.

Keywords: colored mica pearlescent pigments; rare earth oxides; functional materials

Pearlescent pigments are decorative pigments with a pearlescent luster. Mica titanium pearlescent pigments are based on mica and are coated on the surface with a transparent film of metal oxides with a high refractive index such as TiO2. It is widely used in coatings, decoration and cosmetics, inks, ceramics and other industries.

Mica titanium pearlescent pigments can be roughly classified into three types: silver-white, rainbow, and colored. Silver-white pearlescent pigments, because white light reflects on the titanium surface of mica and does not transmit light, can only present a single silver-white phase, but due to the difference in the particle size of mica and the coating rate of TiO2, it will appear as a visual angle Pearl-like mercerized changes. It is the most versatile pearlescent pigment, but it has poor hiding power. The rainbow type is coated with a layer of TiO2 or other metal oxides with higher refractive index, such as Fe2O3, Cr2O3, SnO2, etc., on the flaky mica substrate, and it is excellently produced through multi-level reflection and interference of light. Pearl effect and flop effect. Since this type of pigment both reflects light and transmits light, light at certain wavelengths is strengthened, while others are weakened to exhibit different hue. The biggest advantage of rainbow-type pearlescent pigments is that they can be matched like ordinary pigments, and the resulting complex color is bright and beautiful. The coloring type is based on two kinds of pearlescent pigments of silver white type and rainbow type, and then add a coloring pigment or a dye capsule. This kind of pigment can absorb some light in the visible spectrum. If the reflection color of the absorbing color and the oxide coated mica pigment have the same hue, then the absorption color increases, and the color can be seen at all angles; if the hue is different, it can only be The reflection color is seen at the mirror angle, and the color of the absorption pigment is seen at other angles. Between these two extremes, the transition color can be seen. The pigmented pearlescent pigments are optical pigments that utilize the pearlescent and colored materials of mica titanium to absorb some of the visible light and become a class of pigments with a full spectrum of color and a bright color.

This article briefly introduces the research and development status of titanium colored pearlescent pigments at home and abroad.

1 Research and Development Status of Colored Mica Titanium Pearlescent Pigments at Home and Abroad

1.1 Foreign R&D Status

Colored mica titanium pearlescent pigments are generally coated with mica titanium pearlescent pigments. According to the different coating layers can be roughly divided into two categories: (1) The inner coating layer is a colorless transparent metal oxide. The outer cladding is the same or different single metal oxide or other non-metal oxides that can absorb different wavelengths of light; (2) the outer cladding is a composite of multiple metal oxides.

1.1.1 outer coating is a single metal oxide or non-metal oxide

E. Merck developed a mica titanium pearlescent pigment coated with mica titanium as a substrate and coated with various non-ferrous metal oxides. For example, iron cyanide, Fe2O3, Fe3O4, alpha, gamma-FeOOH, Cr2O3, Mn(OH)2, etc. are coated. In addition, in order to improve the color and weather resistance of automotive finishes, Merck has also successfully developed a new type of gray pearlescent pigment that does not use carbon black, so that the Fe2O3-TiO2 coating on mica chemically reacts at high temperatures. Silver-gray FeTiO3 or titanium-iron spinel (FeTiO4) is generated; Fe2O3 in the iron oxide-coated mica titanium pearlescent pigment is converted to black Fe3O4 to obtain a black mica pearlescent pigment having a metallic texture.

The U.S. patent states that the exfoliation, discoloration, and other changes that occur as a result of long-term exposure to the external environment as a pigment for outdoor use are the result of the combined effects of ultraviolet light, moisture, and temperature in the sun. In order to obtain good weather resistance, titanium is used to pretreat mica and re-plating titanium. After filtering, washing, and then calcining, the crystal form of TiO2 is converted to rutile. Finally, the pigment is post-treated with Cr(OH)3 solution. Compared with the conventional pearlescent pigments, the weather resistance is significantly improved.

Because such pearlescent pigments are not only coated with a colorless transparent metal oxide film that produces pearlescent interference, but also have a colored metal oxide film, they have a strong pearl luster, a high hiding power, and a certain degree of hiding power. The coloring power.

1.1.2 The outer cladding is a composite of various metal oxides

With the increasing demand for pearlescent pigments, the relevant countries are actively exploring suitable outer coatings to achieve complete product chromatography, excellent performance, low price, and high practicality. KORPIT studied a pearlescent pigment. First, a high-refractive-index TiO2 film layer was coated on a substrate mica. The calcined mica titanium was suspended in an aqueous solution containing zinc nitrate, cobalt nitrate, nickel chloride, and urea, and heated. To a certain temperature, and then use the stage temperature control, and then use the potential difference layer by layer evenly full coating, the formation of Co-Ni-Zn composite oxide film, filtered and dried to obtain high-brightness green pearlescent pigments.

Kohei et al. coated Cr, Cu, and Mn composite metal oxides on the titanium surface of mica to obtain a black pearlescent pigment. The specific method is: mica titanium suspended in an aqueous solution containing urea, sulfuric acid, soluble Cu, Cr, Mn salts, heated at 70 ~ 100 °C for 3 ~ 4h, filtered, washed, dried, calcined and baked. Another Japanese patent reports that a complex oxide of Co-Ni-Sb is coated on the surface of mica titanium, thereby producing a gold-colored pearlescent pigment.

Václavötengl et al. reported on the preparation of a blue-green pearlescent pigment. The muscovite having a particle size of 10 to 60 μm is made into a suspension, and a certain concentration of TiCl4 solution and CoCl2, MgCl2 and CaCl2 aqueous solution are added under stirring at 95° C. and pH=1, and after stirring for a certain time, NaOH is used. The pH was adjusted to 6 and the precipitate was washed, dried and calcined to give a product.

MaileFJ reported on the preparation method of bright blue mica titanium pearlescent pigments: The aqueous suspension of mica powder was treated with titanyl sulfate and water to obtain TiO2 coated mica. Then, it was suspended in water, mixed with cobalt nitrate, aluminum nitrate and urea and coated at 100° C. The separated pigment was dried and calcined to obtain a product.

The composite pearlescent pigments coated with various metal oxides have higher hiding power and coloring ability, but the pearlescent effect is lower than that of the first type.

1.2 Domestic Development Status

The research and development of mica-titanium pearlescent pigments in China started later than those in Europe, the United States, Japan, and other economically developed countries. Research, production, and application are all in the primary stage of development, regardless of the level of production, quality, and application of the products. Compared with foreign countries, the gap is concentrated in the low gloss of the pigment, the color is not pure, brilliant, and the wettability and dispersibility are not ideal, resulting in the limited range of pigment applications. At present, the domestic research work mainly focuses on the exploration of coating technology, identifying and improving various technological factors and parameters that affect the quality of titanium pearlescent pigments for mica, and exploring how to improve the whiteness, color effect and pearlescent luster of mica titanium pearlescent pigments. method.

1.2.1 Ferric oxide coated mica titanium pearlescent pigment

There are many domestic reports on iron oxide coated mica titanium, mainly focused on the use of different coating processes, research and exploration of such colored pearlescent pigments. Hao Hong et al. prepared a diiron trioxide-coated mica titanium pearlescent pigment by boiling hydrolysis method. Experiments were conducted to examine the effect of different process conditions, ie, pH value, deposition amount, and reaction time on product quality. The optimum process conditions were as follows: pH 2~4, reaction time 1~1.5h, calcination temperature 670°C, Fe2O3 deposition amount were different, pearlescent pigments of different colors could be obtained.

Fu Xiansong et al. used mica titanium as a base material and coated the surface with Fe2O3 by a liquid-phase precipitation method to obtain a bronzed pearlescent pigment. The optimum process parameters of the coating process and the roasting process were studied, and the performance of the pigments was tested. The results were as follows: oil absorption was 30%, hiding power was 15.24 g/m2, and coloring power was 120.3% (800 °C samples as standard samples ), Munsell label HV/C is 5.0YR7.80/13.2.

Zhang Yujun et al. studied the process of preparing colored pearlescent pigments by metal organic chemical vapor deposition (MOCVD). It uses Ti(OC2H5)4 as the source, using high-purity nitrogen as the carrier gas under aerobic conditions, and when the deposition temperature is 300°C, the deposited TiO2 film is anatase, and the temperature rises to 500°C. The TiO2 film has a rutile crystal form and is densely covered. On this basis, controlling different coating times and then coating Fe2O3-based iron oxides can provide orange-red, gold-red and other luster-colored pearlescent pigments.

1.2.2 Other metal oxide and non-metal oxide coated mica titanium pearlescent pigments

Further coating of mica titanium with multiple layers of metal coating or repeated coating can enrich the titanium phase of mica titanium products, improving its weather resistance, water resistance, dispersibility, or other functions.

Zhong Shengwen et al. studied the composite coloration of cobalt oxide, cobalt oxide-aluminum oxide, and chromium oxide-tin oxide, respectively. It was found that the results of primary coating test of divalent cobalt were dark blue and light, and black after adding oxidant; the composite film of alumina-cobalt oxide was light blue-green; the composite film of chromium oxide and tin oxide was yellow. The color change also depends on the amount of colorant coating.

Hou Wenxiang et al. used mica as a substrate and added phthalocyanine blue-activated carbon to the liquid phase to coat phthalocyanine blue and activated carbon on the titanium surface of mica to obtain pearlescent pigments with blue to blue appearance.

Chen Jing et al. used a microemulsion method to prepare a cobalt blue mica pearlescent pigment. Co2+ and Al3+ were dissolved in oleic acid/n-butanol/sodium carbonate aqueous solution and oleic acid/sodium hydroxide aqueous solution respectively to make a microemulsion, and then two kinds of microemulsions were mixed to form a cobalt blue precursor. The reaction solution was added to a reactor containing water to fully wet the mica, and stirred for 30 minutes while being added. The reaction product was then filtered, washed, dried, and calcined to obtain a cobalt blue mica pearlescent pigment. The test results show that the prepared pigment is of spinel type, and the particle size of the cobalt blue particles is 10-30 nm, which is spherical and uniformly and densely coated on the surface of the mica substrate.

Shen Lazhen et al. used urea as a precipitator to prepare light gray nanocomposite mica titanium conductive pearlescent pigments using a homogeneous precipitation method. The relationship between process parameters such as different reaction matrices and matrix feeding methods and pigment conductivity and pearlescent effect was studied.

Du Haiyan, Chen Qirong et al. used mica titanium with an interference color as a substrate and colored them with chromium oxide and cobalt oxide films, respectively, to prepare mica titanium pearlescent pigments with flop function. The effects of experimental conditions on the pigmentation effects of pigments were investigated, and the effects of angle changes on the pigment brightness and the color change trends were analyzed.

1.2.3 Rare earth oxide coating

Due to the rich visible line region of the electronic structure of rare earth element 4f, rare earth oxides or rare earth metal compounds can display their respective colors, such as Nd2O3 is violet, Er2O3 is pink, CeO2 is orange, and Pr2O3 and Zr2O3 are yellow. The atomic structure of rare earth metals has the common feature that there are two electrons in the outermost layer and eight electrons in the outermost layer, so their chemical properties are similar. Due to the shielding effect of the electrons in the outer layer and the outer layer, the rare earth compounds are less influenced by the environment, and the coloration is more stable, which is superior to the filtration of metal element compounds. It is therefore an excellent colorant for pigmented pearlescent pigments. Moreover, the coloring rare earth oxides are softer, more pure, and have a newer color tone and smoother finish than other colorants. Domestic research reports on rare earth colored pearlescent pigments are as follows:
Zhong Shengwen et al. found that: pearlescent pigments with the increase in film thickness from dark green to dark green to black, cerium-zirconium composite pearlescent pigment is orange-red; germanium pearlescent pigment with coating thickness increases from light to pale orange yellow; Pigments are pale violet; pearlescent pigments are light pink.

Zhang Jian et al. used a hydrolysis method to prepare yttrium oxide-mica pearlescent pigments. The optimum process conditions were: using CeCl4 solution at a temperature of 70 to 80°C, a coating rate of 30% to 40%, and a pH value of 6.50 to 7.50. The pigment precursor was heated at a rate of 3~5°C/min and fired at 800°C.

Sun Jiayue et al. adopted the uniform precipitation method and used mica titanium with green interference color as the substrate and urea as the precipitant to prepare rare earth pearlescent pigments of Nd2O3/TiO2/Mica. The effects of different amounts of yttrium oxide added on the pearlescent effect and UV absorption performance were studied. The results show that the ultraviolet absorbing ability of mica titanium coated with 5% Nd2O3 is significantly higher than that of mica titanium itself, which plays a very good UV shielding effect. The pearlescent effect is the best, and it has the effect of green-purple violet with different colors.

2 Outlook

Mica titanium pearlescent pigments have a short history of development, but the prospects are very attractive. As a fine chemical product, mica titanium pearlescent pigments have high added value. The resources of natural mica and titanium in China are very rich, and they have the material basis for the development of mica titanium pearlescent pigments. At present, domestic silver-white and rainbow-type pearlescent pigment production technology has matured, but the research on the development of coloring and functional materials is not very complete. From the analysis of domestic and foreign preparation of colored mica titanium pearlescent pigments, the directions for future research and development are as follows:

(1) With the continuous improvement of people's appearance quality requirements, the application fields of titanium pearlescent pigments for mica are increasingly expanding, and higher requirements are placed on the chromatographic range of pearlescent pigments. Therefore, broadening the chromatographic range of pigmented pearlescent pigments is a research focus in the future.

(2) In view of various drawbacks of carbon-based, metal-based, and metal oxide-based conductive pigments, the development of sheet-like conductive composite functional materials with mica or mica titanium as the base material is another research focus in the field of pearlescent pigments.