Rheology Control In Waterborne And Solventborne Coatings

The Same Chemistry, Two Systems

QK4100 and QK4200 are both modified polyurea solutions supplied at 50% non-volatile content, and they work the same way: stirred into the coating they build a three-dimensional network that is strongly shear-thinning. The difference is which continuous phase they are built for. QK4200 covers waterborne, dispersion and emulsion systems plus water/glycol-ether and alcohol-solvent blends. QK4100 covers solventborne and solvent-free systems, PVC plastisol and natural curing resins.

Why Polyurea And Not Fumed Silica

Fumed silica works, but it arrives as a dust that needs high-shear pre-dispersion, and loading enough of it to stop a sag usually costs gloss. A polyurea solution arrives as a pumpable liquid at 200-1600 cps, needs only moderate shear, and builds structure without the loading that dulls a finish. There is no pre-gel to prepare, which is the other reason bentonite gets replaced.

Anti-Settling And Anti-Sag Are Different Dosages

This is the part most often missed. QK4200 publishes 0.2-1% for anti-settling and 0.5-2% for anti-sag on the total formulation. QK4100 publishes 0.2-0.5% and 0.5-1% on resin for PVC. Deciding which problem you are solving comes before choosing a number, because dosing for sag when the problem is settling means paying for structure you do not need.

Give It Time Before You Judge It

Polyurea structure does not appear the moment stirring stops. QK4200 needs 2 to 24 hours after mixing before the rheology can be evaluated, and QK4100 needs 2 to 4 hours. Measuring immediately after the mixer switches off and concluding that the additive has failed is a common and expensive mistake.

Post-Addition Is A Real Option

Both grades are post-addable. A batch that has come out under-bodied can be corrected in the tank under moderate to medium shear instead of being reworked or blended away. No special temperature control is needed, and the additive can equally go in at the mill base stage.

The Cautions In The Data

Both grades are moisture sensitive and should be stored dry, and slight turbidity in storage does not affect the effect. If a drier is present, discoloration from metal complex formation is possible and the rheology should be re-evaluated. Pushing the dosage too high risks yellowing, which matters on whites and pastels. For QK4100, reactive, catalysed and nitrocellulose systems should be storage stability tested first.