Polymer Coatings
A polymer coating acts as a protective covering in corrosive environments by enhancing the abrasion resistance of the component's surface. The most common harmful elements that a polymer coating protects against are oxidization, scratches and deterioration. In addition, polymer coatings improve the aesthetic properties as well as preserving and smoothing the surface of the component. 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. Polymer coatings are utilized in industries such as pharmaceutical, electronics, transportation, aerospace, automotive, food processing, construction and chemical processing. Applications of polymer coatings include contact lenses, hood latches, feeding tubes, biological adhesives, soft tissue replacements, needle roller bearings, pill coatings and textile manufacturing rollers. Polymer materials used for coating applications include thermoplastics, HIPS, polyesters, polyvinyls, acrylics, polyamides, phenolics, polyethylene, polyesters, polyvinyls and polystyrenes. The most common polymer used in dip coating is plastisol, a polymer which is liquid at room temperature and solidifies permanently when heated.
Polymer coatings can be formed during the dip coating process, also referred to as immersion coating. Dip coating is the immersion of 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 process: 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 both 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. The cold dip coating process is much less widely known and used. Cold dip coating 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. The advantage of cold dip coating is that the viscosity of the paste in the dipping tank is not altered by any accumulation of partly gelled agglomerations.