Just sprayed on, the surface was perfectly smooth, but after drying, it turned out covered with fine, dense pinholes? "Pinholes" and "blisters" are high-frequency quality defects in industrial coating application. As a professional manufacturer, we provide an in-depth analysis: why neglecting "flash-off time" traps solvents inside the film, and how to scientifically avoid these flaws.
In the spraying workshop, many applicators, in order to rush the schedule, spray the second coat immediately after the first, or push the workpieces directly into the high-temperature baking oven right after spraying. As a result, once the paint film dries, the surface is covered with dense, pinprick-like tiny holes (pinholes) or raised small bubbles.
As an industrial paint manufacturer, we must remind you: this is mostly because you skipped the critical flash-off time.
1. What is "flash-off"? Why is it indispensable? Flash-off refers to the natural drying process between two coats of spraying, or from the completion of spraying to before entering the oven.
- Solvent release: The wet paint film contains a large amount of solvent, and flash-off allows the surface solvent to evaporate steadily.
- Cause of bubbles: If the next coat is applied or heating is done in a hurry without flash-off, the surface will skin over first, "locking in" the solvent in the lower layer. As the internal solvent expands when heated and tries to break through the skin, bubbles will form; if the bubbles burst after the paint film has lost its flowability and cannot flow back to level out, pinholes are left behind.
2. The 3 Major Misconceptions That Cause Pinholes and Bubbles
- Wet-on-wet too fast: The first coat of paint is covered by the second coat before it has flashed off to the "touch-dry" state, and the thick paint film completely blocks the solvent escape channels.
- Baking temperature rising too rapidly: The wet paint film enters the high-temperature zone directly, causing the solvent to boil violently and "burst" the paint film.
- Wrong thinner used: A thinner that evaporates too quickly was used, causing the paint film surface to dry rapidly while the internal solvent had not yet begun to move.
3. Manufacturer's Recommendation: How to Achieve Precise Control?
- Allow 10-15 minutes: At room temperature, it is generally recommended to allow a 10-15 minute flash-off time between two coats of spraying.
- Observe the paint film status: Observe that the paint film changes from a "flowing state" to a "semi-matte" state, and that it is not sticky to the touch when lightly touched with a finger (touch-dry). This is the best time to spray the next coat.
- Forced ventilation assistance: In high-humidity environments, forced air circulation can be used to assist solvent flash-off.
Conclusion: Even good paint fears "rapid heating." Respect the natural law of solvent evaporation and allow sufficient flash-off time for the paint film to achieve a mirror-like, dense, and flawless professional coating.