Do it right, Treat it Right

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.








The decision to drive the treater roll is related to a number of primary parameters which can be influenced by still more secondary considerations. The simple rule of thumb on this question is any web, whether film or foil, that is 25um or less and will be run at 300 m/min or more should be treated on a driven roll. Note that converters should be aware of baggy edges or a baggy centre to ensure the material is consistent and free of defects. These conditions can contribute to wrinkles or trapped air between the material and backup roll.

Maintenance
Maintaining Corona surface treating equipment is necessary. One of the biggest causes of downtime on a corona treater is due to improper cleaning.

Most polymer materials tend to leach slip and other additives during the corona process. Corona treaters incorporate the use of exhaust blowers that tend to pull in the air, along with dirt from the surrounding area. All of this can get deposited on the electrodes and rollers.

Dirt build up can also contribute to producing unwanted backside treatment, by causing high and low spots on the treater roll, enabling air gaps to be created.

The three most important things are clean, clean, and clean. Clean often and keep the equipment clean, especially during the humid months. This will have a very significant impact on the reliability and function of their corona discharge treating equipment, and it is the most often overlooked, until problems occur.

However using the removable Quick Change electrode cartridges enable easy and effective off-line cleaning of all vital components.

In addition inspect all wiring and high-voltage connections should be done regularly. Power is often lost due to power bleeds caused by HP wire proximity to ground sources, and insulation breakdowns.

Assure proper exhaust/cooling air to eliminate issues associated with fugitive ozone emissions. Inspect and remove broken web or loose substrate near the exhaust capture ports of the station.

Keep the treater roll properly grounded and to replace the ground brush regularly, to prevent rollers and bearings from failing prematurely.

Conclusion
Properly designed Corona treaters and maintained treaters should last a long time. The right model according to application, use, and care of a treater will be the largest influencing factor on its performance from day to day and year to year.

Exhibitor Data Sheet