When using aluminium pigments in aqueous coating systems, gas is often formed! How can this be avoided?
There are three possible causes for the formation of gas in aqueous metallic coatings. These three causes are as follows: • High shearing forces were applied when dispersing the aluminium pigments into the coating system; this damages the aluminium pigments. This means there are unprotected aluminium surfaces, which lead to the formation of gas. Usual conditions for dispersing aluminium pigments are to produce a pigment slurry consisting of the aluminium pigment, as well as a suitable solvent and possibly a dispersing additive. These components are then stirred carefully for approximately 20 minutes at shearing rates of 500 – 1000 rpm. Subsequent storage at room temperature can also be helpful. • As an amphoteric metal, aluminium reacts both in the acidic and alkaline range, it is therefore important that, when formulating the coating, the pH value is in the 7 – 8 range. DMEA, TEA or AMP from Angus Chemicals have proven useful as neutralising agents. • Despite all the described measure
