TiO2 PERFORMANCE | PIGMENTS
equipment, reducing the lifetime of extruder screws by wearing the flight tips or increasing the amount of metal pick-up when using a high-speed mixer to prepare a dry-blend or pre-mix (with consequences for colour). In some applications where minimal abrasivity is required, softer anatase pigments can be used.
Although the optimum crystal size for TiO2 pigments for opacity is about 0.25 microns, TiO2 pigments made for plastics applications are often
intentionally made with a crystal size of 0.20 microns or less because this promotes scattering of blue light and imparts a more aesthetically pleas- ing “clean, blue” tone to white plastic articles, which can otherwise have a slightly yellow tone. The properties of the TiO2
pigment are further
modified by the application of coating materials to the surface of the TiO2
particles, applied dispersed
as an aqueous colloid. For pigments intended for use in plastics, alumina only, or silica with alumina (to improve durability) are the most common types of hydrous oxide coatings. In the final stages of pigment manufacturing, the
nature of the pigment surface is modified by application of a surfactant, commonly referred to as the “organic.” This is intended to compatibilise the pigment surface with the polymer. Siloxanes are widely used in the production of general-purpose plastics pigments. More recently, reactive C-8 surfactants have been used to make TiO2
pigments
with superior dispersibility. These types of pig- ments allow users to operate production lines at higher throughput rates, while providing excellent pigmentation of plastics materials. �
www.lomonbillions.global
Figure 2: Refractive index of rutile and anatase TiO2 compared to common thermoplastics. The difference in refractive index between pigment and polymer determines effective reflectivity Source: Lomon Billions
Figure 1: Refractive indices of rutile and anatase TiO2 compared to other potential white pigments
the extrusion specialist for mono- and multi- layer pipe coating
Engineering for Extrusion
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