Important things to consider with polymer coatings include the molecular structure of polymer types, their correlation with electrical and physical properties and functions, deposition processes, applications and testing. Plastic coatings are utilized in industries such as pharmaceutical, electronics, transportation, aerospace, automotive, food processing, construction and chemical processing.
Polymer materials used for coating applications include thermoplastics, polyesters, polyvinyls, acrylics, polyamides, phenolics, polyethylene and polystyrene. The most common polymer used in dip coating is plastisol, a polymer which is liquid at room temperature and solidifies permanently when heated. Applications of plastisol coating includes contact lenses, hood latches, feeding tubes, biological adhesives, soft tissue replacements, needle roller bearings, pill coatings and textile manufacturing rollers.
Polymer coatings are formed during the dip coating process, also referred to as immersion coating. Dip coating is the process of immersing a substrate into a tank containing a liquid polymer coating material, removing the piece from the tank, and allowing it to drain. The process is a three-step procedure: immersion, dwell time and withdrawal. During immersion stage, the substrate is immersed in the liquid polymer at a constant speed. In the dwelling stage, the substrate stays motionless and fully immersed in order for the liquid polymer to gel and apply to the substrate. Lastly, in the withdrawal stage the substrate is removed, again at a constant speed. How quickly the substrate is removed from the tank determines the thickness of the polymer coating material applied to the board.
There are two types of dip coating processes: hot dip coating and cold dip coating. The hot dip coating process is much more common and is used for most polymer coating applications. During this process the polymer material is kept in a liquid state while heated and primed substrates are dipped into the polymer from an overhanging rack. The polymer on the substrate is heat-treated, as most polymers’ properties are improved with some heat processing. Cold dip coating is not as common and is used mostly for thin coatings of polymers. In this process, the object is dipped in a liquid polymer without preheating, and then placed in the heated chamber for final fusion.