Corona treatment is a high frequency discharge that increases the adhesion of a plastic surface. Whether a liquid wets a material good or poorly depends primarily on the chemical nature of both the liquid and the substrate. Wetting is defined as the ratio between the surface energies of the liquid and substrate.
Surface energy of solid materials and the need for surface treatment of polymers. It is often necessary to bond plastic materials to metals or other plastic materials, or simply print on a plastic surface. In order to successfully accomplish this the liquid adhesive, or ink should be able to wet the surface of the material. And this is where Corona Treatment and Plasma Treatment technologies are necessary.
What Does Corona Discharge Do?
When atmospheric air is exposed to different voltage potentials, electrical discharge can develop. When this occurs, it results in an avalanche effect caused by the collision of neutral molecules and the electrically loaded molecules, which make up the voltage. Upon collision, the neutral molecules become electrically loaded, resulting in a heavily loaded zone or "lightening". This, in turn, creates a heavy oxide mixture of ozone and nitrogen oxides. To avoid this avalanche effect, an isolator is placed between two electrodes. The result is a cloud of ionized air - or the Corona discharge - which is then used for surface treatment of plastic substances.
When a plastic substance is placed under the corona discharge, the electrons generated in the corona discharge impact on the treatment surface with energies two to three times that necessary to break the molecular bonds on the surface of most substrates. The resulting free radicals react rapidly with the oxidation of products in the corona discharge, or with adjoining free radicals on the same or different chain, resulting in a cross-link. Oxidation of the solid surface increases the surface tension energy, allowing for better wetting by liquids and promoting adhesion. Though studies have shown that development of strong oxidants is not essential for adhesion to take place, wetting tension is most assuredly related to the oxidation of the polymer surface resulting in polar groups on the surface, primarily hydroxyl, carbonyl and amide groups.
Thermal Atmospheric Plasma Process
Thermal Atmospheric Plasma is created by combining reactive gas molecules and an electric field. This system uses one or more high voltage electrodes which charge the surrounding blown gas molecules, resulting in a highly ionized field that is forced onto the targeted surface. This highly ionized air stream creates a thermal property that reacts with the substrate (material) and breaks the existing hydrogen bonds, introducing oxygen which recreates the chemical properties of the surface. The Atmospheric Plasma process introduces an intensified reaction with the material which results in stronger bonding traits and eliminates the possibility for unwanted backside treatment.