Coating colour is at its most troublesome at high solids. When calcium carbonate and clay sit in the same batch, flocculation starts and viscosity climbs with it. Coat weight becomes hard to hold, opacity swings, and the sheet looks different from one run to the next.
In paper coating, Chemi Tech's lead line is the polymeric dispersant range, matched to pigment type and solids content. Ground calcium carbonate, clay and mixed systems are all covered, from the KMT series.
Business Advantages
First, the viscosity drop is pronounced: raise the solids and the viscosity still holds. Once the particles are separated the colour flows better, pumping and feeding run smoother and line pressure stays steady.
Second, viscosity does not rebound. Flocculation is held back, so a batch that sits in the tank overnight is still usable and the line does not need re-tuning in the morning.
Third, opacity is consistent and coat weight is easy to control. With the colour in a stable state, coat thickness varies less, the sheet looks more even and reject rates on the coater come down.
Fourth, it is not fussy about partners: it sits stably in the same bath as conventional binders without interfering with the other additives in the system.
Boundary on these figures: a note from Chemi Tech. The behaviour described comes from machine trials. Change the pigment quality or the process water and the results move. Run a small-scale trial before switching.
Industry Pain Points and Solutions
Dispersing coating pigment comes down to three hard points: high solids, viscosity that rebounds, and opacity that still has to be delivered.
Pain point one: at high solids the viscosity will not stay down and pumping is a struggle. The answer is to work on dispersion itself and get the particles separated first.
Pain point two: the colour thickens after sitting a while and the shift keeps re-adjusting. The answer is better anti-flocculation so the number of mid-shift corrections comes down.
Pain point three: coat weight swings and opacity goes thick and thin. The answer is to adjust the dispersant together with the formulation rather than watching one number on its own.
What Chemi Tech does on site is a three-step reproduction: reproduce the solids and shear conditions on your own colour first, then run a pilot grind, and finally fix the type and the addition method.
Typical Conditions and Verification
Coating colour usually runs around seventy percent solids, with grinding and storage temperatures moving with the season. Viscosity shows up worst after the mill discharge and after long storage.
Failure signals come from four places: the viscometer reading climbs; pump pressure runs high; coat weight swings; the coating shows streaks and misses and the sheet develops cross-direction shade variation. Two of those and a pilot verification is due.
Pilot data at the same solids and the same formulation can be requested from Chemi Tech for comparison, with viscosity and coat weight checked side by side.
FAQ
Q1: Why is coating pigment so unforgiving about the wrong dispersant?
General-purpose products have limited tolerance for pigment type and tend to fail in mixed systems. The viscosity comes down and then climbs straight back, so the shift keeps topping up.
Q2: Will a dispersant affect coating strength and printability?
It has to be verified separately. Binder systems differ and the degree of effect differs with them, so the pilot run decides, with strength and print results judged together.
Q3: How many steps does replacing an imported dispersant take?
Record the original product's dosage and the colour viscosity as a baseline first, reproduce it equivalently on the same pigment batch, and only split the line over once the pilot has passed.