ABSTRACT
The majority of commercially available polymers have amphoteric hydrophobicity/ hydrophilicity and surfaces are not hydrophilic, i.e., the contact angle of water is higher than 45 degrees (see Chapters 26 and 27), and water does not spread on the surface. Consequently, when a water-borne coating is applied on the surface, the coating does not spread well on the surface. Such an unprintable or uncoatable surface could be made printable or coatable by increasing the surface energy by various means. Aggressive chemicals could be used to partially oxidize the surface to increase the surface energy; however, the remaining chemicals causes increase of volatile organic content (VOC), which is a growing problem in recent years with respect to the environmental pollution. Plasma treatment, such as oxygen plasma treatment, does not cause a VOC problem and has been widely used in modifying the surface of rather hydrophobic polymers.
