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Coatings Application · Orange Peel · Leveling
Orange peel in coating is a common surface problem in spray application. Insufficient film spreading, high application viscosity, solvent evaporating too quickly, unsuitable film thickness, and drying condition changes can all cause the surface undulation to become fixed in the film. When this type of problem appears, leveling agent can be one direction for adjustment — but it cannot be the only lever, and simply increasing the dosage is not the solution.
1
Why Does the Film Look Flat Right After Spraying, Then Orange Peel Appears After Drying?
Many coatings look relatively flat right after spray application, but as solvent evaporates and the film gradually dries, small surface undulations that were originally minor become more obvious and ultimately form orange peel texture. This shows that orange peel does not necessarily form at the moment of spraying — it may gradually develop during film flow, solvent evaporation, and drying. Solving orange peel therefore requires analysis of the entire film formation process, not just the state immediately after spraying.
2
Why High Application Viscosity Makes Orange Peel More Likely
After coating is sprayed onto the substrate, it needs to flow and spread under its own mobility. If application viscosity is high, film flow speed slows — the small surface undulations formed do not have enough time to adjust, and as the coating dries, these textures are easily retained. Especially in high-solid, fast-dry, or thick-film application systems, this situation occurs more easily. So when orange peel appears, first check actual application viscosity, spray distance, gun pressure, and spray film thickness. If the application conditions themselves have a problem, even changing the leveling agent may produce poor results.
3
Leveling Agent Can Improve Orange Peel — But More Is Not Always Better
Leveling agent primarily improves coating spreading and film flow state on the substrate surface, giving the coating more opportunity to correct its surface state before drying. But different leveling agents do not all work the same way — some are more suited to improving surface spreading, others focus more on film flow and surface state. Simply increasing the leveling agent dosage may not continue to reduce orange peel, and may affect recoatability, interlayer bonding, or other surface performance. Therefore, practical application is better suited to a small-range gradient test based on the resin system, solvent system, and application method, seeking the appropriate addition ratio.
4
Fast Solvent Evaporation May Also "Fix" Orange Peel
From spray application to complete drying, the coating goes through a continuous flow process. If solvent evaporation speed is too fast, the film surface quickly develops higher viscosity before the inside has fully flowed — surface texture may become fixed prematurely. This is also why the same formulation may show different orange peel degrees at different temperatures, humidity levels, or baking conditions. If the surface effect difference between summer and winter, or between ambient and baking application, is large, drying conditions need to be included in the investigation.
5
Spray Film Thickness Affects Final Leveling
When film thickness is too low, the film's own flow space is limited and small surface textures are not easy to fill in. When film thickness is too high, solvent evaporation and internal flow are both affected, potentially also causing surface defects. Therefore, maintaining a relatively stable film thickness during spraying is needed, along with attention to spray gun distance, traverse speed, and overlap. If leveling agent is simply used to compensate for unstable spray film thickness, it is usually difficult to fundamentally improve the film state.
6
How to Approach Orange Peel Adjustment
When orange peel appears in a coating, check in this order: application viscosity → spray film thickness → spray pressure and distance → drying conditions → resin and solvent system → leveling agent selection and dosage. If application conditions are basically stable, targeted leveling agent screening becomes easier to judge. For different resin systems, it is also not recommended to directly replicate another formulation's leveling agent and addition ratio — the same additive in a different system may show obvious differences in performance.
Summary
Coating orange peel does not necessarily mean a leveling agent must be added or increased. Whether the film ultimately forms a flat surface is the combined result of formulation and application working together. Starting from application viscosity, film thickness, solvent evaporation, and drying conditions in the investigation, then combining leveling agent adjustment, typically leads to a more appropriate solution than simply increasing additive dosage. For actual production, specific resin, coating system, and application method must also be combined for targeted testing.
Frequently Asked Questions
Is there a practical way to determine whether orange peel is caused by formulation factors or application conditions without running full spray trials?
A film application test on a flat horizontal panel at controlled conditions provides useful information. Applying the coating by drawdown (Bird bar or similar) at the target film thickness on a horizontal surface eliminates spray atomisation and gun-distance variables. If the drawdown film shows good leveling and no orange peel, the issue is likely in the spray application process. If the drawdown film also shows orange peel, the formulation is contributing to the problem — directing investigation toward viscosity, solvent balance, and leveling system.
Why does the same spray gun setup produce different orange peel results on different substrate shapes?
Substrate geometry affects how the spray pattern deposits on the surface. On a flat panel, the spray distance and angle are consistent across the surface. On curved, indented, or contoured surfaces, the effective spray distance and angle vary — some areas receive different film thickness, different atomisation quality, and different solvent evaporation rates. Orange peel tends to be worst where the effective spray distance is greatest or where the angle is most oblique, as both factors reduce the effective film build and atomisation quality at that location.
