PAINTING ON GALVANIZED STEEL
Conventional paints adhere poorly to hot-dip galvanized surfaces.
A conversion coat is necessary to ensure good adhesion of the paint and long term protection of the steel.
On industrial production lines, hot phosphating or chromating by dipping or spraying in different stages, offers satisfactory results only when the total treatment- phosphating or chromating followed by appropriated stoving paint- is carefully controlled.
A serious problem arises when such hot surface treatments cannot be applied as is the case for industrial maintenance and marine painting, structural steelwork, touch up work on coil coated surfaces and vehicle maintenance and repair work.
The usual polyvinyl butyral/phosphoric acid based wash primers and the modified short oil alkyd or epoxy ester primers do not normally ensure the expected adhesion improvement they offer on steel and other non ferrous metals.
The technical reasons for these failures are well known:
- Residual acidity in the cured film in the case of wash primers.
- Detrimental effect on adhesion of the zinc soaps formed by the presence of free fatty acids in alkyd primers.
T-wash or mordant solution is unsuitable where partial weathering has occurred.
Sweep blasting can damage irreparably the galvanized layer on vulnerable edges and corners.
ACTAN®GS is a water borne-VOC free- one component adhesion primer for non-ferrous metals.
It is an active resin system at quasi neutral pH that binds with the zinc surface without the disadvantages of gas formation, bubbling or cracking caused by the reaction of zinc or residual impurities at acid and alkaline pHs.
ACTAN®DU20 is an amine adduct in aqueous emulsion which is designed to optimise wet adhesion of two component water borne epoxy primers on non ferrous substrates such as galvanised steel, aluminium and its alloys.
With its specific amine functionality, it provides excellent wet and dry adhesion at a cross-linking degree of 100% and maintains the necessary water barrier to ensure long term protection with solid and liquid epoxy resins.
ACTAN®DU20 combinations with liquid epoxy resins provides the ability to develop VOC free coating systems for application on galvanised steel with long durability in various environments such as C5-I and C5-M as tested in accordance with International Standard ISO 12944-6.
In association with BPA/BPF epoxy resins, it is used to make waterborne adhesion primers for absorbing and non-absorbing substrates of construction materials.
Starting formulations are available with liquid and solid epoxy resins.