White pigments such as titanium dioxide (or titania) reflect and scatter all visible light wavelengths, making a pigmented product white and opaque. As the most used inorganic pigment by far and the most used colorant overall, titanium dioxide creates a dense whiteness in polymers at low cost when used in its rutile mineral form at an optimum 0.25-micron average particle size. TiO2 used in UV-exposed applications is commonly surface treated so that it is not reactive in the degradation processes of the polymer or with phenolic-based antioxidant additives. A coating may be composed of a layer of silica covered with a layer of alumina, which aids in dispersion and handling and is itself covered with an organic surface treatment creating wettability with the polymer. The silica in the coating helps suppress TiO2 catalyzing tendency in the production of free radicals when it is exposed to UV light. Moreover, by absorbing the near-UV light spectrum and blocking some UV radiation, titanium dioxide also imparts a degree of UV protection to the polymer.
Typical of TiO2
There are two commercially useful forms: rutile and anatase. Rutile has higher opacity and is considerably less photocatalytically active than anatase. It also has a slightly higher refractive index (2.70 as against 2.55), giving better light-scattering power. Rutile-type Ti02 also accepts surface treatments more readily, bonding better than anatase.
Anatase is used mainly in paper and elastomers: in thermosetting resin systems, it retards gel time and may prevent cure altogether. The pigment is extracted from crude ore, removing impurities such as iron oxide. There are two manufacturing processes:
- Sulphate (46% of production, and declining): a multi-stage wet chemical process, batch or continuous. Titanium dioxide is dissolved in the raw materials by concentrated sulphuric acid, precipitating the hydrous salt. This is then calcined to produce one of the two crystalline forms, anatase or rutile.
- Chloride (54% of production, and rising): a two-stage process, at high temperature. Titanium ore is reacted with coke and chlorine to produce titanium tetrachloride. Purified titanium tetrachloride is then reacted with oxygen to produce rutile titanium dioxide. The chloride produced is recycled to the first stage. The process cannot produce commercial quantities of anatase. It is a more modern process and is considered preferable on environmental grounds.
Other white pigment
Alternatively, other white pigments reflect some or all UV light; these include zinc sulfide (which absorbs some UV light) and barium sulfate (barytes or “blanc fixe,” which absorbs no UV light). These two pigments have lower refractive indices than rutile TiO2 (ZnS, 1.6; barytes, 2.4; and rutile, 2.7); this allows some flexibility for adjusting the shading or transparency of white resins. Moreover, ZnS, with its low Mohs hardness, is less damaging to glass fibers when used for pigmenting glass fiber-reinforced resins, in comparison with harder, abrasive TiO2. Other white pigments include antimony oxide (refractive index of 2.1-2.3), zinc oxide (index of 2.0), and the anatase form of TiO2 (2.5).
Examples of Relevant Organic and Inorganic Colorants:
|Most common pigment, in rutile form; some UV absorption
|Brighter, bluer whites; nonabrasive if used with glass fibers
Buy White Masterbatch
There are many industries that use white masterbatch. Some of the most commonly used industries are films with different thicknesses, food and pharmaceutical packaging, toys, sheets, cars, shoes, etc. Dan Polymer Company offers white Masterbatch with a combination of different percentages along with technical information for respectable manufacturers who are looking for white Masterbatch. You can contact our sales experts before buying white masterbatch.