The Problem with Second Coats
Applying multiple different layers to create a multi-layer film is a major advantage of dip coating. However, many engineers hit a frustrating wall here. You dip your part for the second coat, and the perfect first layer completely melts away.
This happens because the solvent in the new liquid (like alcohol or thinner) attacks and dissolves the binder in your base coat. To stop this cross-dissolving, you need to attack the problem from two angles.
Fix 1: Fully Cure the Base Coat
The first rule is to make sure your first layer is 100% cured. Just because it feels dry to the touch does not mean it is fully hardened inside. If there is any unreacted solvent or soft resin left underneath, the second liquid will instantly dissolve it.
Do not rely on air drying alone. Use an oven to bake the part thoroughly, or use a UV light to fully cross-link the polymers. Once the base coat forms a strong chemical network, it becomes much harder for the second solvent to break it down.
Fix 2: Minimize Time in the Liquid
Even a fully cured base coat will start to melt if you leave it in the second liquid for too long. This is why controlling your “dwell time” (how long the part sits in the tank) is critical.
The golden rule for multi-layer coating is: get in and get out fast. You need to dip the part quickly, hold it at the bottom for zero seconds, and pull it out smoothly before the base coat has time to dissolve.
Precise Control with SDI Equipment
Doing this by hand is impossible. You cannot manually dip a part fast and then perfectly transition to a slow, steady withdrawal speed.
SDI dip coaters solve this. Our machines let you program the downward dipping speed, the dwell time, and the upward withdrawal speed completely independently. You can drop the part in fast, set a zero-second wait, and pull it out precisely. This minimizes damage to your base coat while giving you perfect multi-layer films every time.
▼ Check SDI’s Product Lineup for Precise Speed Control
https://www.sdicompany.com/en/products/