Extrusion International 3-2020

30 Extrusion International 3/2020 SURFACE TREATMENT – INTERVIEW Why is surface treatment so important in the extrusion process? Giuseppe Rossi: It’s not so much important in the process itself, as afterwards. To ensure good adhesion of the inks and lacquers during downstream converting processes, the molecular structure of the filmsurface needs to bemodified, and it needs to be done immediately after the cooling phase of the melt before the polymer is completely post-crystal- lised. By applying the Corona charge at this point to the top layer (to 1-micron deep), we can break the molecular chains and addmore oxygen. This alters the surface tension and im- proves adhesion. The longer you leave it before treatment, the more difficult the molecular chains are to break – in fact, it’s often impossible, so timing is critical. Are there different requirements for blown and cast film extrusion? Rossi: Blown film is the more common use for Corona treatment. Because of the high incidence of LDPE in this process and the relatively slow production speed, com- pared with cast extrusion or any of the converting pro- cesses, the Corona system requires only low energy to achieve a good result. The technology in this sector is well consolidated and mature, and with good control allows consistently high-quality film to be produced and treated. Cast film is a far more demanding process because the PP material and higher line speeds require a more complex Corona system layout. Even a single-sided treater (unlike the double-sided in blown extrusion) will typically need higher power, a cooled backing roller, direct drive and a nip roller – effectively a proper pull set up. There is a third type of extrusion that applies to Biorient- ed Cast Films like BOPP, BOPET, BOPA, where the width of the line and the high output demands that the Corona unit is contained within the extruder. Are the requirements different dependingon thematerial being extruded? Rossi: Yes, they are. It very much depends on the material and its intended use. How it will be converted after manu- Surface treatment in the form of Corona is a well-known and acknowledged part of the printing, converting, and laminating sectors of the industry, but it has an even more fundamental part to play in the extrusion process. Giuseppe Rossi is Vetaphone’s specialist in this sector and explained the need for the process and how technology is responding to changes in market demand Surface Treatment for the Extrusion Market Giuseppe Rossi, Vetaphone’s extrusion specialist Vetaphone makes it simple Vetaphone Corona treaters were in action at the K 2019 expo in Düsseldorf