Aluminium Pigment Orientation In Waterborne Basecoats

Why Water Makes This Harder

In a solventborne basecoat, fast solvent loss shrinks the film quickly and pushes aluminium flakes parallel to the substrate. Water evaporates more slowly and less predictably, so the film stays mobile longer and flakes settle at whatever angle they happened to arrive at. The result reads as cloud patches, mottling and spotting, worst where film build varies.

The Two Routes Available

QK8521 is a non-ionic modified EVA copolymer wax emulsion at 20% active in water, with no VOC below 1500 ppm, dosed at 5-10% on the total formulation. QK8330 is a modified polyamide salt at 20% non-volatile content in propylene glycol methyl ether and water, dosed at 1-5%. Both improve orientation and reduce cloud patches; they differ in dosage, handling and what else they do to the system.

The pH Condition Nobody Reads Twice

Both products are acidic and will pull system pH down. QK8521 requires the system to be brought to pH 9 to 9.5 before addition, and the higher the co-solvent content of the formulation, the more headroom is needed. QK8330 is slightly acidic and is pre-blended with water at a 4:1 ratio before it goes in. Skipping the pH step is the most common reason a first trial of QK8521 disappoints.

Where In The Process They Go

QK8521 goes in at low shear after the effect pigment has been added, and it must not be pre-diluted with water. QK8330 can be added at any stage once pre-blended, and amine already present in the system helps it disperse without any dissolution step. Getting the addition point wrong costs orientation even when the dosage is right.

Measuring The Result

Viscosity cannot be judged with a flow cup on these systems. The QK8521 data sheet is explicit: final viscosity has to be read on a rotational viscometer such as a Brookfield. Orientation itself is graded on sprayed panels under controlled light, looking at flop and at the uniformity of the cloud, not in the can.

What Else Each One Brings

QK8521 reduces settling during storage and processing, is less sensitive to co-solvent than a polyurethane thickener, and arrives ready to use where bentonite and acrylic thickeners need preparation. QK8330 raises the brightness of solvent-free effect pigment slurries and has notably little effect on system viscosity compared with polyurethane and acrylic agents, which is useful when the spray window is tight.