Plasma is ideal for treating plastics prior to adhesive bonding. Loose boundary films are removed and truly hyper-clean surfaces remain. In addition to cleaning, plasma is capable of to removing a few hundred angstroms of the bulk material. 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.
Organic mold release agents are readily removed using oxidizing plasmas. Si containing mold release agents need to be removed using chemical plasma. The bar chart below shows a case study for removing Si mold release agent from golf ball dimples comparing sandblasting with plasma cleaning. Even without pre-wash plasma performed better than the sand blasting method.
