The adhesion process is affected by the following factors:
- mechanical interconnection between the substrate surface and the layer of ink, coating or adhesive
- chemical bonds, such as ionic bonds and Van der Waals forces (common in the polymers on which plastic materials, inks, coatings and adhesives are based).
The topography of the substrate creates mechanical connection points. If organic or inorganic particles prevent the contact between the polymeric surface of an ink/coating/adhesive and that of the substrate, adhesion is inhibited.
Contaminant particles come from the external environment (dust, hair, fibres and micro metal fragments, fingerprints), and contaminant agents create a layer on the surface (oil, fats, chemical residues, oxides).
In addition to blocking the points that might otherwise ensure a good anchoring effect, this extremely thin layer of dirty reduces the wettability of the materials and weakens the bond of intermolecular forces between the surface and the applied material.
Cleaning + adequate surface tension = optimal adhesion
Preparing the surfaces is crucial to ensuring a good level of adhesion and to preventing coatings, paints or adhesives from detaching from the support.
Atmospheric plasma is the most effective method for removing organic contaminant agents from plastic surfaces. The flow of atoms and ions toward the substrate:
- breaks up, removes and vaporizes contaminant particles
- alters the chemical composition of the plastic surface by replacing inert molecules with more reactive ones (which increases surface tension and hence improves adhesion).
Several tests confirmed that plasma treatment is an effective method for cleaning surfaces and increasing surface tension.
Advantages of plasma treatment
- Safe, environmentally-friendly and easy-to-use method
- Practical and efficient solution for surface cleaning in industrial processes (plastic or metal products)
- Removal of contaminant residues from plastic surfaces
- After treatment, the surfaces remain stable for at least some days
- Better results than other cleaning methods, such as cleaning with detergent solutions or solvents.