The characteristics of pearlescent pigment and organic pearlescent pigment

Pearlescent pigment has beautiful metallic luster, non-toxic, high temperature resistance, and has been widely used in the coloring of decoration and car paint, paint printing, cosmetics, plastics, etc. Pearlescent pigment can be divided into two categories: mica titanium iron pearlescent pigment and organic dye coloring pearlescent pigment.

I. Pearlescent pigment

Pearlescent pigment (mica titanium pearlescent pigment) is a pigment with pearlescent luster made by coating the surface of scaly mica crystal with titanium dioxide or titanium dioxide and other oxides in appropriate thickness. In order to obtain the pearlescent pigment with excellent performance, appropriate process should be chosen to evenly deposit titanium dioxide onto the surface of mica crystal, and this "titanium plating" process can have three kinds as follows.

1、Adding alkali "titanium plating" method

Titanium salt such as titanium tetrachloride solution is added to the water suspension of mica, while alkali is added dropwise to neutralize the generated hydrochloric acid, Laizhou Color Source Pigment Technology Co. The pigments have the advantages of bright color, high coloring power and good dispersion, which are widely used in various industries. The pH value of the reaction system is controlled, and the generated metatitanic acid is precipitated on the surface of mica crystals. The suitable pH value is 2-2.5.

2、Buffering "titanium plating" method

In order to control the pH of titanate hydrolysis process, buffers (hydroxy organic acid and tartaric acid, citric acid, etc.) or metal (such as zinc, iron, aluminum, etc.), metal oxides (zinc oxide, cobalt oxide, copper oxide, etc.) can be used instead of alkali solution to neutralize the inorganic acid generated by the reaction.

This process is low cost, and the hydrated titanium dioxide is evenly distributed on the mica surface with good pearlescent effect.

3、Heating hydrolysis "titanium plating" method

Without adding alkali or buffer, titanium sulfate or titanium oxide sulfate is added to the mica suspension, and the temperature is rapidly increased to boiling, so that the hydrolyzed titanic acid is deposited on the mica crystal surface in the acidic medium. Obviously this method is simple and low cost, but the particles are coarse and the pearlescent effect is slightly poor.

Using the above coating method, the titanate (hydrated titanium dioxide) generated by the hydrolysis of titanium salts on the mica surface needs to be transformed into titanium dioxide by high temperature calcination, and has a specific crystal shape.

Usually, with the increase of calcination temperature, the anatase titanium dioxide will be gradually transformed into rutile titanium dioxide, and the latter has better temperature and weather fastness, which is suitable for the coloring of enamel and automobile paint.

Second, organic pearlescent pigment

In order to make the pearlescent pigment not only show the soft pearlescent characteristic, but also make different metal ions (such as Bi, Sb, As, Fe, Zn, Mn, etc.) deposited on the surface of mica titanium dioxide to get the pearlescent products with different colors, for example, FeCl3, FeSO4 deposited to make yellow and orange, Cr2(SO4)3, K4Fe(CN)6 deposited to make green and cyan pearlescent pigment. The colored pearlescent pigment made by inorganic salt deposition has excellent heat and weather fastness, but the color is not bright and the coloring intensity is low.

In recent years, organic pearlescent pigment has been developed, that is, organic dyes and pigments are used to implement surface coloring of mica titanium, and the specific implementation methods are as follows. One method is to mix mica titanium pearlescent pigment with dyes or pigments to make it evenly and stably dispersed in the pigment and dyes, for which the surface of mica titanium should be modified to reduce the polarity so that it is compatible with the colored coloring agent. For example, when producing color pearlescent paint or ink, silver white pearlescent powder can be mixed with organic pigment and resin linkage, usually the amount of mica titanium is 2%-10%, and the amount of pigment or dye is 0.1%-0.5%, in order to get the double effect with pearlescent and color. Another method is to use mica titanium as the substrate and adopt chemical-vapor-deposition method for precipitation. For example, β-type CuPc is firstly put in fluidized state, while titanium tetrachloride is passed into the reactor in gaseous state to react with water vapor. The generated titanium dioxide is deposited on the crystal surface of β-CuPc to obtain a blue product with pearlescent properties. The third method is the precipitation of organic dyes on the surface of mica titanium with the help of aluminum and calcium salts, such as first depositing Al(OH)3 envelope on the surface of mica titanium and then coloring it with specific dyes, so that water-soluble dyes form insoluble dye precipitates on the surface of mica titanium with aluminum hydroxide; or dispersing mica titanium in a certain concentration (e.g. 0.5%) of aqueous dye solution (pH=5.0), adding dropwise CaCl solution (20%) to carry out the color precipitation reaction to obtain colored pearlescent pigment.

Compared with the above inorganic metal ion coloring process, the colored pearlescent pigment colored by organic dyes has the advantages of simple process and bright color of the product, but the durability is a little worse. Some acidic mordant dyes, acid dyes and direct dyes can be colored with mica titanium by step-by-step method under the selected conditions, and also by one-step method.

Usually, acid dyes with small molecules and large solubility, such as acid red 35, do not easily form colored precipitates and do not bond well on the surface of mica titanium, so they are easily faded by washing and the coloring effect is not ideal. Certain direct dyes with larger molecular weight, such as direct blue 86, direct red 80 easy to form insoluble color precipitates with Al3+, Ca2+, on mica titanium can obtain more ideal coloring effect.

Acid-mediated dyes can form complexes with transition metal ions and form bonds with hydroxyl groups in mica molecules, thus making the dyes more firmly coated with the mica titanium surface.