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Q&A: Corona Discharge Surface Treatment

by Bruce Stobbe

Corotec Corporation

SUBMITTED

A corona discharge treating system creates a molecular change in surface structure that is not visible, but causes the surface to be more chemically receptive to inks, coatings and adhesives.

How does corona discharge surface treatment work?

A corona discharge treating system utilizes a high-voltage discharge to effect a molecular change in the surface structure of the material being treated. This effect is not visible, but causes the surface to be more chemically receptive to inks, coatings and adhesives. Inks and coatings will more readily "wet" the surface and adhere after treatment, and the printing or coating process becomes far less variable with greatly improved adhesion, product quality and consistency.

What types of containers can be treated?

Virtually any type of material and container configuration can be treated with corona discharge. Cups, tubs, tubes, vials and other profiles, including closures of various types, are just a few common examples.

Can containers be treated right on the printing machine?

In most cases, yes. Surface treatment can take place at almost any open station on the machine.

How many containers per minute can be treated?

Typical production rates are up to 600 containers per minute or more, but higher rates are possible through the use of an appropriately sized power supply and, where required, multiple treatment stations. The maximum rate possible with a given system is a function of the container profile, dwell time, container material and desired treatment level – all of these factors play a role in proper system sizing.

How does the treating system interface with the machine?

A typical treating system accepts a signal from the machine controller to produce corona discharge as each container moves into the treatment position. The treating system monitors the process and then can provide an alarm output back to the machine controller to verify that treatment power was correct, that no faults occurred during the treating cycle and whether any defects in the container were detected. These containers then can be rejected downstream by the machine.

Can I treat the container all the way to the edges?

Yes, depending on the container profile and other factors, such as whether container defect sensing is desired.

How much energy does a treating system use?

The typical container-type treating system uses much less energy than even a small hand-held hair dryer.

What typically is involved in installing a corona discharge treating system?

The typical container treating system utilizes standard 120-volt power available from any outlet, and the power supply control cabinet can be located in any convenient area. The discharge electrode is mounted at the treatment station, and the high voltage transformer usually is mounted nearby to keep the length of the wire running from the transformer to the discharge electrode relatively short. All high voltage components are shielded or contained within an interlocked area for personnel protection. It also is good practice to provide an exhaust system in the area where the treatment is taking place to remove the ozone produced as a byproduct of the corona discharge process.

How do I know if corona discharge treatment will work on my products?

Corotec maintains a testing lab where sample containers can be run at specified production rates for system-sizing purposes; and treated samples then can be returned for processing and acceptance testing. In addition, Corotec facilitates in-plant equipment evaluation through a try-before-you-buy rental program, where a Corotec container treating system can be evaluated in-plant, on the production line and with specific products and processes.

Bruce Stobbe is president and chief electrical engineer of Corotec Corporation in Farmington, CT. He has been involved in the design and application of corona discharge surface treating systems and accessories for almost 40 years. For more information, email bstobbe@corotec.com, call 860.678.0038 or visit www.corotec.com.