Silicone sleeves & Dielectric coatings
Which dielectric covering you choose will really depend on which application you have, blown film, cast film or wide web extrusion as well as factors such as which materials you are treating, line speeds, whether you have a nip roll or not and budget!
However, what is critical, is that the quality and integrity of the dielectric covering on the base roll plays a key role in the successful operation of the corona treater. The correct covering will give you years of trouble-free treating, but the wrong covering will give you many problems.
Silicone Sleeves
Corona Supplies Ltd supply a dielectric silicone sleeve manufactured from a very specific silicone rubber compound, providing excellent electrical, thermal and chemical resistance, making it ideally suited to the harsh environment that is the corona treatment process. Produced specifically as an electrical dielectric sleeve, it is manufactured to extremely close tolerances, ensuring reliable and consistent corona treatment performance.
Ceramic Coatings
Ceramic is a purpose designed dielectric coating used to provide a hard, wear resistant covering.
Ceramic coated base rolls - the definitive answer to dielectric roll problems.
The main advantage is durability. Because the Ceramic is inert, it cannot perish with long exposure to a high energy source and the highly oxidative environment. The coating is extremely tough and cannot be cut by knives: it is easy to remove any slip additive and
Corrosion Prevention
ST42 is an alumina/titanium conductive ceramic coating applied to base rolls for use in applications where conductive materials are being treated. Its main advantages over bare roll corona treaters is improved corrosion resistance against ozone, durability of the roll and treatment enhancement, sometimes referred to as high definition corona.
ST42 coating is especially recommended where treatment of various widths is being considered, as it will protect the roll from the direct corona discharge from the ceramic electrodes. This protection will aide in the prevention of oxides on the aluminium roller and therefore help maintain a constant air gap between the electrode and the film surface.
Vulcanised Coatings
Vulcanised silicone rolls are generally used in applications such as cast film extrusion and wide web extrusion, where large diameter and wider base rolls are used and where fitment of a sleeve becomes difficult. Vulcanised silicone provides an excellent treater roll dielectric that is harder wearing than a sleeve, and this is essential where high web tensions are specified, for a silicone sleeve under these conditions may come away from the roll core.
Corona Supplies covers the corona treater roll with 4mm thick silicone vulcanised rubber to 80 IRHD ±5 hardness. The covered roll is subsequently ground to the required dimensions and certificated for compliance, giving excellent tolerances on roll diameter and concentricity - essential at today’s high speeds.
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