In a given system, there will be in the continuous polymer phase, into which TiO2 and extender are dispersed, efficiently yet randomly in the polymer. The TiO2 cannot occupy the same space as the extender, yet the extender is approximately the same refractive index as the polymer. As a result the TiO2 is compressed into the spaces between the extender, the random nature of its dispersion meaning that only about 30% of it is at the optimum 280 nm particle spacing for best TiO2 efficiency.
It is well documented that TiO2 is inefficient if too close together, or in lower concentrations if too far apart.
Since the extenders are the same refractive index as the polymer, they also effectively make “windows” in the film for light to pass through due to the lack of refraction, hence while a small amount of extender can be used to replace some of the TiO2 the effectiveness is limited to only a few % replacement before opacity drops.
By replacing a portion of the TiO2 with FP-Opacity Pigment™, we increase the average distance between TiO2 particles by the “dilution effect”, in addition to replacing the volume of TiO2 with TiO2 particles that are optimally spaced. The effect on the statistical particle spacing is clear.
Therefore in effect, and in many plastics and coatings applications FP-Opacity Pigment™ can be used to replace 10-30% of the TiO2 and not reduce the optics.