Cure Terms Glossary

Drier

A drier is a substance which accelerates the air-drying process. Air drying is the mechanism of cure for traditional alkyd resins.

Driers are resin-soluble salts of redox metals which function as hydroperoxide decomposition catalysts. The action of Cobalt(II) illustrates this role.

 

ROOH + Co2+ → RO + OH + Co3+

ROOH + Co3+ → ROO + H+ + Co2+

 

Suitable solubility is provided by metal soaps - i.e. salts of longish-chain organic acids (naphthenic and the like). The metals are typically: cobalt, manganese, copper or zirconium

Sometimes these are used in conjunction with soaps of other metals such as: calcium, zinc or barium. These are considered as secondary driers, although their mode of action is unclear. Since alkyd resins are created by polyesterifications involving fatty acids, it is possible that their action is ionic crosslinking of residual acid.