In the production and application of high-gloss coatings, many factories assume that greater spray area equals higher efficiency. In reality, the larger the spray area, the thinner the coating film, and the more the surface quality declines. This article explains the scientific reasons behind this relationship and how paint factories should balance film thickness, gloss, and coverage.
Ⅰ. Film Thickness: The Key Driving Force for High-Gloss Leveling
For high gloss paint to achieve a mirror-like finish, it must rely on the phenomenon of “leveling” that occurs during the drying process. The thickness of the paint film is the crucial factor driving this leveling process.
Core Principle: Surface Tension is Proportional to the Square of the Film Thickness.
- It provides a sufficiently strong surface tension driving force to promote the smooth secondary flow within the film. This powerful flow effectively eliminates minor imperfections caused by spraying, resulting in a smooth, level, and high-gloss surface finish.
- The leveling force drops significantly. The secondary flow becomes difficult and slow, failing to fill minor defects effectively. This often leads to an uneven surface, reduced gloss, and visible aesthetic flaws like “orange peel.”
Conclusion: Adequate film thickness is an absolute prerequisite for achieving outstanding high-gloss effects.
Ⅱ. The Inverse Relationship Between Coverage Area and Film Thickness
Coating area and film thickness are inversely constrained. Assuming a fixed total amount of paint used:
Greater Coverage Area implies — Less Paint per Unit Area implies — Thinner Film
If the coating area is over-extended, causing the dry film thickness (DFT) to drop significantly (e.g., from a healthy 30um to 15 um ), even a high-quality gloss paint will have its leveling performance compromised, failing to meet the required surface quality.
Ⅲ. Formulation Pitfall: The Trade-off Between Hiding Power and Performance
Blindly increasing the proportion of pigment paste in a high gloss formulation to achieve “greater coverage” (i.e., better hiding power), while keeping the ratio of binders and key additives constant, often leads to negative consequences:
- Applying the same amount of paint over a larger area inevitably leads to a sharp decrease in the dry film thickness.
- DFT is a key indicator for coating durability, anti-corrosion capability, and protective performance. A thinner film not only compromises the gloss effect but also significantly reduces overall protective performance.
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