The major benefit of using CA, CAB or CAP in a coating is the control of viscosity properties. All cellulose esters are able to impart flow and leveling while controlling sag due to their Newtonian flow properties combined with a high molecular weight. CAP, which has lower solubility and compatibility and also less odor compared with CAB is used in inks, overprint varnishes, and nail lacquers. CA, which is only soluble in strong solvents and has a low tolerance for hydrocarbons, is used in solvent, chemical and grease resistant formulations, dopes and cements.
With only a small loss of solvent, cellulose esters hold the coating in place, preventing sag, enhancing pigment dispersion, orienting pigment flakes, and producing a hard dry-to-touch film even when significant amounts of solvent remain in the coating. This allows the rapid application of topcoats and the ability to sand and polish thermosetting coatings before the system is completely cured.
Ease of Application
Cellulose esters provide ease of application. When spraying, they improve atomization to reduce surface defects. In roll coat applications, they help to produce a uniform film. In curtain coatings, they reduce pin holes and maintain curtain coat integrity.
Viscosity Control
Cellulose esters build viscosity exponentially with evaporation of the solvents and this prevents:
Sag Resistance
The rheology of CABs is nearly Newtonian at low solids, but it becomes highly pseudo-elastic as the solids level increases. This explains why CABs are able to maximize flow and leveling while maintaining good sag resistance. In many thermosetting coating formulations, additions of 1% - 5% CAB (based on resin solids) can minimize sagging of the finish.
Enhanced Pigments Dispersion
Due to their rheological properties, cellulose esters enhance pigment dispersion in multi-pigmented systems (no color separation) and prevent pigment flooding and floating. Addition of CAB contributes to a flow behavior that allows coatings to flow and level, significantly reducing surface defects.
CAB helps prevent pigment separation and provide good pigment wetting. Because of good pigment wetting characteristics (particularly the higher hydroxyl types), CAB is used to enhance pigment dispersion without negative affects on coating performance.
As an illustration, 10% - 20% CAB (based on resin solids) is used with both thermoplastic and thermosetting acrylic resins as a pigment dispersion medium.
Outstanding Metal Finish
Used as viscosity control agents, cellulose esters provide excellent pigment flake orientation, and therefore coatings exhibit a brighter finish with more flop.
Moreover, CAB provides excellent redissolve resistance and prevents strike-in caused by solvents in the topcoat.
