Given the variables involved in the conformal coating process (e.g. coating formulation, viscosity, substrate variation, temperature, air mixing, contamination, evaporation, humidity, etc.), coating defect issues can often arise. Let’s take a look at some common problems that can arise when applying and curing paint, along with potential causes and what to do about it.
1. Dehumidification
This is caused by substrate contamination that is incompatible with the coating. The most likely culprits are flux residues, process oils, mold release agents, and fingerprint oils. Thorough cleaning of the substrate prior to applying the coating will resolve this issue.
2. Delamination
There are several common causes of this problem, where the coated area loses its adhesion to the substrate and can lift from the surface, one major cause is contamination of the surface. Typically, you will only notice delamination issues once the part is produced, as it is usually not immediately observable and proper cleaning can resolve the issue. Another reason is insufficient adhesion time between coats, the solvent does not have proper time to evaporate before the next coat, ensuring sufficient time between coats for adhesion is a must.
3. Bubbles
Air entrapment may be caused by the coating not evenly adhering to the substrate surface. As air rises through the coating, a small air bubble is created. Some of the bubbles collapse to form a crater-shaped concentric ring. If the operator is not very careful, the brushing action can introduce air bubbles into the coating, with the consequences described above.
4. More air bubbles and voids
If the coating is too thick, or the coating cures too quickly (with heat), or the coating solvent evaporates too quickly, all of these can cause the surface of the coating to solidify too quickly while solvent is still evaporating underneath, causing bubbles in the top layer.
5. Fisheye phenomenon
A small circular area with a “crater” protruding from the center, usually seen during or shortly after spraying. This can be caused by oil or water entrapped in the sprayer air system and is common when the shop air is cloudy. Take precautions to maintain a good filtration system to remove any oil or moisture from entering the sprayer.
6. Orange peel
It looks like the peel of an orange, an uneven mottled appearance. Again, there could be a variety of reasons. If using a spray system, if the air pressure is too low, it will cause uneven atomization, which can cause this effect. If thinners are used in spray systems to reduce viscosity, sometimes the wrong choice of thinner can cause it to evaporate too quickly, not giving the coating enough time to spread evenly.
Post time: May-08-2023