Titanium dioxide is currently the world’s whitest white pigment, its industrial production began in 1923.Before 1956, the industry mainly adopted sulfuric acid production. In 1956, Dupont began to industrialize the production method of titanium dioxide, which is more environmentally friendly.
So far sulfuric acid and chlorination are still the main industrial production methods.The chlorination method is energy-saving and environmentally friendly, with high degree of automation but high production cost, and is widely used in developed countries.
Sulfuric acid is relatively polluting, but the investment is small, so it has been used in industry.
Rutile titanium dioxide is widely used in various high-end pigments due to its high whiteness, strong hiding power and stable properties.
In order to perfect the properties of titanium dioxide, whether produced by sulfuric acid or chloride, titanium dioxide is treated to reduce the photochemical activity of titanium dioxide (enhance the weather resistance) and improve its dispersion.
I. core process of post-treatment of titanium dioxide – envelop
The coating of titanium dioxide is the core part of the post-treatment process.Envelope is also known as surface treatment, its purpose is to improve the application performance of titanium dioxide, especially rutile titanium dioxide, so that it has excellent application effect in different applications.
The envelop can be divided into inorganic envelop and organic envelop according to the properties of the materials needed to be coated on the surface of titanium dioxide.According to the coating method, it can be divided into dry method and wet method.In general, the film formed by inorganic oxides is wet film, that is, inorganic film.For adding organic surfactant to improve the performance of the product is generally dry envelop, the use of wet envelop.
Ii. Titanium dioxide post-treatment process
1. Inorganic treatment process
Mechanism: a uniform colorless or white inorganic oxide film was formed on the surface of particle titanium oxide to block the photoactivation point of TiO2 and improve the weather resistance.
Process: inorganic coated titanium dioxide after beating, under the environment of serous, join soluble salts, and by adjusting the pH value of slurry, the soluble salt deposition on the surface of titanium dioxide particles, forming a layer of oxide film coated, cut off from both titanium dioxide contact with air, at the same time as the membrane is thin and transparent, improves the performance of the titanium dioxide pigment.Treatment purpose: mainly to improve weather resistance.
Inorganic surface treatment agents: aluminum sulfate, sodium metaluminate, sodium silicate, etc.Zirconium sulfate, titanium sulfate (increase the oil absorption value, gradually eliminated), zinc sulfate and antimony, tin and so on.With primary particles as the core, it is coated with a thin film of hydrated oxide, generally several nanometers thick.Aluminum coating is the most widely used inorganic coating. There are many products treated with single aluminum, and many products treated with silicon and titanium.
2. Organic treatment process
Mechanism of action: when TiO2 is coated with a layer of organic oxide film or surfactant, when the organic coating agent is combined with the surface of pigment particles, the van der Waals force between pigment particles is not enough to make them adsorb together again, so the pigment is given good dispersion.At the same time, the group of organic coating agent gives the pigment particles good compatibility with the solution system.
Treatment process: generally, organic surface treatment agent can be added into the slurry before drying after inorganic surface treatment, or into the final airflow crushing. The additive amount generally accounts for 0.1%~1%(quality) of titanium dioxide, and the usual dosage is 0.2%~0.6%.In industry, organic surface treatment agents are usually added during the final crushing stage of titanium dioxide production, which is the air crushing.
Objective: to improve the dispersibility and compatibility of titanium dioxide in different media, and to improve the gloss, rheology and wettability.
Organic surface treatment agents: there are three major categories, namely polyols such as neopentyl glycol and trihydroxymethyl propane, organic amines such as triethanolamine and trimethylamine, and organic silicones such as silicone resin.
Post time: Jun-28-2019