Abstract
Many paint, ink and coating formulations contain alkyd-based resins which cure via autoxidation mechanisms. Whilst cobalt-soaps have been used for many decades, there is a continuing and accelerating desire by paint companies to develop alternatives for the cobalt soaps, due to likely classification as carcinogens under the REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) legislation. Alternative driers, for example manganese and iron soaps, have been applied for this purpose. However, relatively poor curing capabilities make it necessary to increase the level of metal salts to such a level that often coloring of the paint formulation occurs. More recent developments include the application of manganese and iron complexes with a variety of organic ligands. This review will discuss the chemistry of alkyd resin curing, the applications and reactions of cobalt-soaps as curing agents, and, subsequently, the paint drying aspects and mechanisms of (model) alkyd curing using manganese and iron catalysts.
Highlights
Many paint and ink formulations contain alkyd resins as binders to obtain solid coatings after curing [1,2]
2 (μ-O)3 (Me3 TACN)2 ](PF6 )2 with alkyd paints, that radical based autoxidation chemistry will be operative for the Mn-Me3 TACN complexes or mixtures discussed in different patents, further detailed investigations would be needed to elucidate the nature of the catalytically active species involved in alkyd paint drying using different sources of Mn-Me3 TACN and whether different sources of Mn-Me3 TACN would lead to the same mechanistic pathways of radical-based alkyd resin curing
Besides the iron alkyd paint drying catalysts that were presented in some detail above, another iron catalyst with a pentadentate nitrogen donor ligand was exemplified in a patent by Unilever [40]: the iron complex with the pentadentate ligand MeN4Py (N,N-bis(pyridin-2-yl-methyl-1,1-bis(pyridin-2-yl)-1-aminoethane) (Figure 4)
Summary
Many paint and ink formulations contain alkyd resins as binders to obtain solid coatings after curing [1,2]. The paint or ink formulations can either contain organic solvents to dissolve the alkyd resin or water as the solvent. The chemistry of radical curing processes in relation to alkydstudies based paints and soap inks inks will be discussed first in some detail. Several of the mechanistic studies on cobalt soap driers will driers will be discussed, after which publications and patent applications dealing with various classes be after which based publications and patent with various classes of paint of discussed, paint drying catalysts on manganese andapplications iron will bedealing highlighted. For example, evaporation of the solvent as the names could suggest
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