Paper Coating OBA Carriers
Optical brighteners work only when they are fixed to a carrier. A good carrier is linear and contains OH- or other hydrophilic groups. Linearity increases the con¬tact between the carrier and OBA so that physical bonds (such as hydrogen bonds and van der Waals forces) can be formed between the OBA and the hydrophilic groups of the carrier. Carriers in a coating color are, among others, starch, CMC, or PVA. By adding one of these products in coating color, higher brightness can be achieved.
UV exposure causes yellowing of brightened paper, but a good carrier increases the light stability. Furthermore the carrier has an influence on the migration of OBA; the more efficient the carrier, the better the resistance of OBA to the mi¬gration.