Usually materials are pre-treated at extrusion, but by the time passing before lamination they can loose the initial surface value. For this reason, a corona treatment installed on laminating lines is called “refreshing treatment”, as it reinstates the treatment value previously obtained during extrusion.
Material surface treatment is essential for guaranteeing a satisfactory bonding between substrates that have to be laminated. Lamination can be done between two, three or four materials in a single passage in order to obtain different multi-layers structures, depending on the technical features that the packaging requires.
Most common structures of laminated films
- Printed BOPP + PE
- Printed PET + PE
- Printed PET + AL + PE
- Printed OPP + metallised OPP
- Printed PET + PAPER + metallised OPP.
Adhesives that guarantee a perfect lamination between two materials can be solvent based, water based or “solventless”.
Solventless Laminating Line
In the last years we’ve seen a great increase of the use of solventless adhesives, as they have a minor environmental impact (solventless laminating lines grant remarkable energetic savings compared to solvent based laminating lines, as they avoid the drying oven).
In case of lamination with this type of adhesives, corona treatment is very important: the minimum requested surface tension value is at least 42 dyne/cm.
The perfect configuration for a solventless laminating line that laminates two materials (A and B) in a single passage is the one equipped with two corona treatments:
- a corona treatment for treating the material “A” that has to be coated with the adhesive
- a corona treatment for treating the material “B” that has to be laminated.
Combined Laminating Line
The perfect configuration of a combined laminating line, that can use different types of adhesives (solventless and solvent based) and that can laminate three materials (A, B and C) in a single passage, is the one equipped with four corona treatments:
- a corona treatment for treating the material “A” that has to be coated with the adhesive
- a corona treatment for treating the material “B” that has to be laminated
- a corona treatment for treating the laminated material A+B before the second coating
- a final corona treatment for the material “C” that has to be laminated.