Titanium dioxide as a kind of high quality coating with white pigment, its whiteness is very important, is one of the key quality indicators of coating requirements, titanium dioxide whiteness is poor, will directly affect the appearance of the film.
(1) Impurities
The main factor affecting the whiteness of titanium dioxide is the type and content of harmful impurities, because titanium dioxide is very sensitive to impurities, especially rutile titanium dioxide, so even a small amount of impurities, will have a significant impact on the whiteness of titanium dioxide.
In titanium dioxide process, especially sulfuric acid titanium dioxide process, most of the operation is to remove impurities in the product, because impurities seriously affect the application performance of titanium dioxide, especially whiteness.
Usually chlorination process in the production of titanium white white degree often is better than sulfuric acid process production of titanium white, this is mainly because of the raw materials used by the chlorination process titanium pigment titanium tetrachloride is distilled, itself is less impurity content, and high content of impurities of the raw materials used by the sulfuric acid method, only by washing and bleaching technology to remove impurities.
(2) Crystal form of titanium dioxide
Rubinite crystal type of titanium dioxide is easier to absorb short wave light than anatase type, if there is too much rutile crystal mixed in anatase type titanium dioxide, titanium dioxide absorption coefficient of light K value will increase, the whiteness and gloss of the finished product will be worse.
(3) Particle size and particle size distribution
Particle size and particle size distribution are the main factors affecting the whiteness of titanium dioxide, which is mainly affected by the phenomenon of light reflection and scattering of titanium dioxide particles.
According to the existing measurement data, within a certain size range, the smaller the particle size of titanium dioxide, the higher the whiteness value, which is mainly due to the smaller the particle size of titanium dioxide, the increase of the surface area, the reflection of light, diffuse reflection.
(4) Particle shape
Particle shape refers to the existence of titanium dioxide particles, can be divided into spherical, rod-shaped and layered.
According to the existing measurement data show that the whiteness of layer titanium dioxide is slightly lower, the whiteness of the ball and rod is very close, therefore, titanium dioxide particle shape although can slightly affect the whiteness.
(5) Titanium content
Titanium content refers to the total content of titanium dioxide in titanium dioxide, the content of titanium dioxide in pigment grade titanium dioxide is generally more than 90%, specifically in 92% ~ 98%, other substances are mainly film coating agent and a small amount of impurities.
According to the existing measurement data, the whiteness value increases with the increase of the content of titanium dioxide.
(6) various auxiliaries
In the production, often use a lot of additives, such as filter aid, lubricants, these additives may contain long carbon chain organic compounds, high temperature will carbonize, make titanium dioxide hue dimming, even with obvious red brown.
