With corona treating the goal is to increase the material’s surface energy to provide wettability and adhesion. Treating a substrate can be ineffective when the system is not properly run and maintained.

Over / Undertreating
When a corona treating system transfers too much or too little energy to a substrate, a host of problems can occur. Attempting to obtain satisfactory printing results on undertreated materials can result in the use of excessive amounts of ink in an effort to try to make up for the inadequate treatment level, and doing so can have its own set of problems. Overtreatment can result in heat damage to the material itself, as well as problems with blocking of the material.

Poor adhesion, low dyne levels, and inadequate wettability can also occur. To get to the right watt density, set a beginning point for the watt density power level and work your way up on power until the anticipated dyne level is achieved. Test the adhesion through quality assurance checks of the film with dyne test pens. Once the watt density level is established for the given product, note the watt density level, re-use it next time, and you are assured of desired dyne repeatability.

Material type, material thickness, and even material suppliers are all variables which can impact the appropriate power level, but once determined, the appropriate watt density setting should become a permanent part of your job specification.

Web tension
Accurate Corona treatment depends on web tension, which, if not controlled properly, can hinder the process. With too much tension, the material can wrinkle or snap; whereas, a lack of tension creates air gaps between the material and the roll. In both cases, the material may be unevenly treated, resulting in backside treatment.

Materials that do not make close contact with the roll under the electrode or the backup roll can affect the treatment process. Wrinkles in the material or air trapped under the material will result in some treatment of the backside of the material which will reduce the treatment level in the respective areas on the top side, and may also cause the material to stick together, or block.

Consider nip rolls when running at speeds greater than 300 m/min, as this will eliminate concerns associated with developing an air boundary layer between the ground roll and the web. In some cases spreader rolls/crowned rolls are used to eliminate wrinkles. Although you never want to hear this, slowing down the line will minimize your web handling problems.