Plasma is ideal for treating plastics, metals, ceramics, and glass prior to adhesive bonding. In each case, loose boundary films are removed and truly hyper-clean surfaces remain.
For plastics, there is an additional advantage in that a few hundred angstroms of the bulk material can be removed after the loose boundary film is stripped. This final surface is roughened on an atomic scale, providing more surface binding sites for optimal adhesion.
Also, the surface is altered chemically by the reactive atoms present in the plasma. New chemical functional groups are formed with strong chemical bonds to the bulk of the material. These extra polar bonds help both water and adhesives wet into every crevice of the material. The net effect is a tremendous improvement in bonding. In some cases, up to a 50X bond strength improvement is observed.
It is also possible to alter the surface chemistry of a polymer to bond with a particular adhesive of choice. Gases other than oxygen can be used to create the type of surface needed. This greatly broadens the options for material engineers in product design.
