Q.1024: How is paper colored?
Ans. Unbleached fibers are brown in color. If paper is to be colored dark, unbleached paper can be directly colored, otherwise fibers are bleached before coloring. Paper can be colored by any of the following methods;
- Adding dye/pigment in pulp before sheet is formed. This is most common way to color paper. It is most economical if frequent color changes are not made. Major disadvantage of this method of coloring is that paper machine effluent is also get colored.
- Adding color at sizing press while paper is still wet.
- Spraying color in post dryer section or at calender.
- Coating paper with colored pigment.