Coating

Introduction
Most polymeric glasses are sensitive to scratching and wear, coating is a common way of improving the scratch behavior of these materials.(Gauthier, Durier, Fond, & Schirrer, 2006) Increasing the scratch and wear resistance is equivalent to introducing an elastic contribution into a fully plastic behavior or to increasing the elastic component in an elastic–plastic behavior. Surface protection films are necessary to achieve mechanical properties similar to glass on soft substrates. The mechanical behavior, such as elastic modulus, hardness and fracture toughness are responsible for the coating resistance of the overall system(Al-kawaz et al., 2016).
Some methods for coating polymer
There are a lot of coating techniques such as spin coating, doctor blading, casting, spray coating, slot-die coating, slide coating and knife-overedge coating that are employed to form coating surfaces.(Krebs, 2009)
Casting
This is the simplest film-forming technique. The advantage is that no equipment is needed except a horizontal work surface. The procedure is to simply cast a solution onto a substrate followed by a drying step. While it is possible to prepare films of good quality and also thick films, the technique suffers from a lack of control over the film thickness and often picture framing effects are observed near the edges of the film or precipitation during drying. Moreover, in a case the surface tension of the liquid dominates, the drying is inhomogeneous. There is also a requirement that the material to be coated has a high solubility in the solvent used if crystallization and precipitation is to be avoided.