The Influence of Corona Treatment on Surface Tension of Polyolefin Surfaces

Many industrial applications of polyolefin films require good adhesion properties such as adhesion by printing ink, paints and coatings. The presence of polar groups on the film surfaceplays a very important role for improving adhesion. Polyolefin films are non-polar materials with low surface tension. Treating the polymer with corona discharge is one method to enhance the surface adhesion. The corona discharge is anelectrical discharge between two electrodes under atmospheric pressure by high voltage. The electrical field generated, excites the gas molecules (air) and dissociates some of them. These charged active gas molecules may react with polymer molecules and may cause breaking of molecular bonds on thesurface and adding polar oxygen atoms. The functional groups produced on the surface are mainly COH, C=O and C-O [1].This mechanism only involves oxygen as a reactive species butother possibilities exist for the introduction of oxygen functionalities into the surface through reaction with water,nitrogen oxides and derived from them, but these groups are present at very low levels [1]. It is possible to determine the surface tension of a solid by aliquid in touch with it having certain surface tension. When a drop of liquid lies on the surface of a solid, a specific anglewill be created at the interface of them. The following equation is established to describe the relation between the surfacetension of three materials that are in contact with each other. Where the , and are the free energies of the liquid and solid against their saturated vapor and of the interface betweenliquid and solid respectively, is the equilibrium pressure of the absorbed vapor of the liquid on the solid and Ө is theequilibrium contact angle. Using liquids for determination of surface tension is more available than tensiometer equipments and easy to use. Also, itis possible to use this test method in production line without pause the production process. In this research, the treat level of polyolefin surfaces by corona discharge has been studied.