How To Choose A Wetting And Dispersing Agent

Start With The Binder System

This is the decision that cannot be corrected by dosage. Waterborne systems need QK3778, QK3770, QK3755, QK3740 or QK3730. Solventborne systems need QK3340 or QK3320. Epoxy and UV systems need QK3310, which the data sheet states will not cause resin crosslinking. A dispersant designed for the wrong continuous phase has nothing to anchor with, and the symptom shows up as colour strength that will not build no matter how long the grind runs.

Then Compare Active Content, Not Addition Level

Published dosages look wildly different across the range because active content does. QK3730 is 35% active, QK3770 and QK3755 are 40%, QK3778 is 60%, QK3320 is 80%, and QK3740 and QK3310 are 100%. What reaches the pigment surface is active polymer, so when comparing two grades, multiply the dosage by the active content before drawing a conclusion.

Read The Dosage By Pigment Class

Every dispersant page publishes four separate figures where the source data gives them: inorganic pigment, organic pigment, titanium dioxide and carbon black. The spread is large. QK3770 asks 5-10% on titanium dioxide and 60-120% on carbon black. All of these are percentages on pigment weight, not on the batch, which is the single most common misreading of an additive data sheet.

Get The Grinding Procedure Right

Where the dispersant goes in matters as much as how much goes in. QK3770 and QK3755 must be ground in water alone, with no resin, amine or co-solvent present, then let down. QK3740 has to be dissolved in water or a glycol solvent first. QK3730 is dispersed fully in water before it meets the pigment. QK3320 needs resin and solvent premixed, then the additive added slowly, then pigment. If the order goes wrong on QK3320, post-addition under high shear is the documented recovery.

Special Cases Worth Knowing

Three grades exist for reasons other than general performance. QK3730 is free of APEO-class substances, which is what clears a customer restricted substance list. QK3778 disperses anti-corrosive pigments and extenders that general-purpose grades struggle with. QK3310 is 100% active and non-crosslinking, which is what makes it usable in epoxy and UV without disturbing pot life.

How To Run The Trial

Hold the grind and the let-down constant and change only the dispersant. Run three dosage points across the published band. Measure grind fineness, mill base viscosity, colour strength against a reference, and a rub-out on a mixed shade. The rub-out is the test that catches flooding and flocculation while there is still time to react.