The need for coating additives
Advancements in printing technologies have placed greater demand on the surface of the paper sheet. To meet these requirements, paper surfaces are coated with pigment-rich formulations to impart a more ideal condition for the printing process.
The incorporation of coating additives into the coating formulation would serve the following purposes:
- Improve the coverage of the base paper fibres to give a uniform surface.
- Reduce the porosity of the base paper.
- Increase the paper whiteness.
- Contribute to paper opacity.
- Impart the desired finish (e.g. gloss, matt).
- Impart the desired optical & physical properties.
- Impart the desired printing properties.
Generally, all materials in a coating formulation excluding pigments and binders can be broadly classified as additives.
Coatings are typically applied at the coater section of the paper machine.
Amazon Papyrus has a range of coating additives including lubricants, insolubilizers, dispersants, WRRM and defoamers.
Lubricants and release agents are used to enhance smoothness and flow properties of the wet coating as well as the plasticity and gloss of the dried coating.
Lubricants can also reduce buildup of stalagmites in blade coatings and to reduce calender picking and dusting. These products are mostly calcium and ammonium stearates. Wax emulsions are mostly emulsions of paraffin waxes, microcrystalline waxes or polyethylene waxes.
Water-soluble binders tend to lose their binding power when in contact with water, and this leads to water sensitivity of the paper/board coating.
There are many different types of insolubilizers or crosslinkers though they all have the same primary function - to add water resistance to the finished coated paper or board.
Commonly used insolubilizers are glyoxal, glyoxal-urea resins and zirconium based products such as ammonium zirconium carbonate and potassium zirconium carbonate.
These are used to provide water retention and rheology control.
In the paper coating process, defoamers are applied to prevent buildup of foam and entrained air in the coating.
Oil-based defoamers are often used in the coating process. These defoamers are dispersible, water free formulations and typically contain various types of components.
Our team of professionals would work with you to select the most appropriate products to meet your specific needs.