Why Does Application Performance Change When the Additive Addition Sequence Changes?

Formula design in coatings and inks usually looks at raw material models, additive dosages and process parameters such as grinding and letdown. In real production, though, sometimes the formula has not changed and only the stage at which one additive is added has been adjusted, yet viscosity, foam or surface state of the final product differ.

This is not surprising. An additive does not act the same way simply by being mixed in; its effect also depends on the state of the raw materials when it is added, the dispersion environment and the later processing.

Take a dispersant. Added during pigment wetting and grinding, it can take part early in wetting and stabilizing the pigment surface. If the pigment has already formed large agglomerates, a dispersant added later may not achieve the same effect.

The reason is that a dispersant has to interact with the pigment surface, and its performance depends not only on dosage but also on pigment properties, resin composition, solvent environment and mechanical dispersion conditions. For color pastes or pigment systems that need grinding, the dispersant is usually placed at a suitable stage according to process requirements, rather than being added all at once after every raw material has been mixed.

A leveling agent mainly improves wetting and spreading of the coating on the substrate and affects the surface state during film formation. If it is added at an unsuitable stage, or later affected by other components and processing conditions, its real performance may differ from expectation.

A defoamer has to balance defoaming ability and system compatibility. Some systems suit adding part of the defoamer in the grinding or dispersion stage, while others need extra added at letdown. The arrangement depends on defoamer type, formula structure and production process. With unsuitable timing, even the same product may leave residual foam, surface defects or other appearance problems. The sequence therefore needs to be set according to each additive's characteristics.

A coating formula consists of resin, pigment, filler, solvent and many additives, and these components may interact through compatibility, adsorption competition or surface activity.

For example, when one additive enters the system first, it may act preferentially on the pigment or filler surface; if another additive is added afterwards, the competition and distribution in the system may change. These changes can further affect viscosity, foam stability and the surface of the film. So it cannot be assumed that all additives give identical results as long as they all end up in the formula. The sequence influences how the system forms, and the way it forms may influence final performance.

When viscosity change, uneven dispersion, residual foam or film defects appear, first confirm whether the production process has changed, including the stage of additive addition, stirring speed, grinding time and the sequence of feeding raw materials.

When troubleshooting, change only one major process factor at a time and keep the other conditions as consistent as possible, then compare viscosity, fineness, storage state, foam and application performance between schemes.

For dispersants, watch pigment wetting and the grinding process; for defoamers, evaluate against the stage where foam forms and the final film state; for leveling agents, observe compatibility after letdown and actual film formation.

Not all additives have a fixed, universal sequence. Different resin systems, pigment and filler types and production equipment can all affect the suitable process arrangement, which should still rely on product technical data and formula test results.