Optical Brighteners show the desired effect as long as UV-light is present which delivers the energy needed for the method of action. Without UV-Radiation, the mechanism will not work.
Besides the intensity of the UV-radiation, there are three other factors which influence the efficiency of an optical brightener -. the initial color of the polymer (uncolored or solution dyed) itself, the presence of any matting agents and finally the loading of OB.
In determining the optimum concentration of OB. the effect of any other UV-absorbing component of the final formulation in the specific plastic material has to be considered.
In combinations with matting agents like TiO2 or BaSO4, brilliant white shades can be achieved, but such combinations require higher levels of optical brighteners.
On the contrary, the addition of UV-Absorbers can significantly reduce or even nullify the desired effect.
Optical brighteners are suitable for a wide selection of polymers; not just EPL’s but also for polyolefin.
Typical concentrations for optical brightener can range from as low as 5ppm up to about 1000ppm depending on polymer used, its application and the targeted effect.
In order to develop the desired effect, OB’s have to be dissolved in the polymer matrix. Since the addition levels are quite low and in order to make handling cleaner, they are normally prepared and added as master batch. This is usually achieved by extrusion under the processing conditions required for the carrier material.