Driers

Driers - (note spelling) Used to catalyze drying oil varnishes which “dry” by oxidative polymerization. Driers are only used in sheetfed printing.

Generally employ cobalt, manganese, cerium or zirconium salts of fatty acids (e.g. cobalt octonate, CoC₇H₁₅COOH).

Inorganic peroxides may also act as driers. Increasing the temperature increases the rate of drying by oxidative polymerization just as it speeds any chemical reaction.

However, increasing the temperature increases the fluidity and hence may adversely effect dot formation. Increased humidity increased the drying time.

Reducing the pH slows drying because it takes the metal ions out of the system, replacing them with hydrogen ions.

Driers work best in a pH range of 4.5 to 5.5. This is consistent with the conditions for best fountain solution performance in sheet fed offset printing.

Drier molecules may adsorb on pigment particles, which leads to drier dissipation.