The following steps may be done during manufacturing in order to prevent rough coatings: I. If roughness is caused by partial spray drying, reduce atomizing conditions and/or reduce drying conditions to minimize this effect. II. Reduce coating solids if viscosity is too high for effective atomization. III. If roughness is caused by overwetting, improve drying conditions in the process. IV. Increase solids content to decrease viscosity.

• A. All statements are correct
• B. Only ONE statement is correct
• C. Two statements are correct
• D. Three statements are correct

Answer: (D)

Coating roughness comes from how droplets form, how they dry, and how the liquid flows and wets the surface. If droplets dry too early in flight, you get a crusty, irregular surface; if the liquid is too thick, atomization suffers and rough droplets land; if there’s too much liquid on the surface, drying is slowed and pooling leads to roughness.

Regarding partial spray drying, lowering the energy of atomization or slowing the drying can keep moisture from evaporating too quickly in flight. That means droplets stay more uniform when they reach the surface, reducing the crinkled, rough areas that form from premature drying.

If the coating is too viscous for effective atomization, dialing back the coating solids lowers viscosity, making it easier to generate uniform, fine droplets. Better atomization translates to a smoother coat with less roughness.

When overwetting is the problem, improving drying conditions helps remove excess solvent and prevents droplets from spreading too much or pooling. A properly dried layer lands more evenly, decreasing rough patches.

Increasing solids content to decrease viscosity doesn’t hold water in typical coating behavior—adding solids generally raises viscosity, making atomization harder and roughness more likely. So that adjustment isn’t effective.

Thus, three practical adjustments align with reducing roughness: manage partial spray drying through atomization and drying conditions, adjust solids to achieve workable viscosity for atomization, and optimize drying to control overwetting.