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Technical // Frequently asked questions

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  I can't reach my desired dyne level - Why?
If you have been successful in treating to your desired level, and now you cannot reach the required level, something must have changed. What has changed? Look at film type, is it the same, or has resin type changed. What about additive levels, like slip, have they changed without your knowledge. Film type changes will have an effect on the performance of your treater. Also consider line speed and film width changes. Faster running film will not treat as well as a slower running film. Same applies to a larger film width, this will not treat as well as a narrow web. Have the settings on your corona system been changed? If so, re-set to original settings and re-check treat levels.
On a more basic level, check that your dyne inks or pens are correctly labeled, have not cross contaminated or are past their use by date. If in doubt use completely new pens or ink from a reliable source, contact Corona Supplies.

  Is over treatment possible and what are the symptoms?
Over treatment is possible on most materials, but some are more susceptible than others. Films such as PET and low slip LDPE’s that are generally easier to treat, need little power, are the ones where over-treatment is possible. But other films such as BOPP, CPP, HDPE, can show the signs of over-treatment, high surface tension reading, but low adhesion level. Over-treatment causes the destruction of very top surface layer of the film, and the creation of low-molecular weight debris (small dust like particles) on the film surface, it is these particles that the printing ink or coating adhere to not the actual film surface, thus providing a much weaker bond.

  Why is air gap adjustment important?
Accurate air-gap setting has a 2 fold function. Firstly it allows control of cross-web treatment levels. For accurate even treat level across a film / web width a uniform air-gap is required. Un-even air-gap will result in different treatment levels across the web.
Secondly the air-gap forms a key part the equation of a balanced / matched corona system. For a reliable high performance corona system there must be a balance or match between the electrical high frequency generator and the mechanical discharge station. The corona air-gap forms part of this matching equation. A matched system means optimum performance and efficient running of the corona system, with best treatment levels for the lowest power. It will also mean your corona system will run trouble-free for long periods. Set your air-gap accurately and check that your generator and corona station are correctly matched and you will enjoy trouble-free treatment.

  My generator won`t work, why?
Please refer to our troubleshooting section which should answer these questions.

  The ceramic electrodes on my treater keep breaking, why?
There are 2 possible causes for Ceramic Electrode failure. Mechanical impact and over-heating. If you are suffering mechanical impact damage then you must find the source, lumps on your extruded film, a poor join or loose edge on your film reel. If your electrode holder pivots away from the treat position make sure this can still happen freely, and that the electrode movement is in the same direction of travel as the film.
Over-heating of the electrodes, ceramic electrodes are designed to run at temperatures approaching 200°C, but poor extraction flow or dirt/contamination or too much power, on the electrode will cause this to be exceeded and lead to electrode cracking or pin-holing and premature failure. Check you ozone extraction system is operating correctly with the recommended air flow rate and ducting size. Keep your ceramic electrodes clean, remove periodically and clean debris/oils from electrode and electrode holders. Do not run a low number of electrodes, if some electrodes are removed, then reduce the corona power accordingly. Running high power and with too few electrodes will stress them and lead to failure.

  What factors influence the cost of corona treatment?
The important factors are;
  • the types of films to be treated,
  • the location of the treater, ie type of production line, is this location hazardous/ solvent laden?
  • the film / treat width,
  • the number of sides to be treated,
  • the line speed,
  • the desired treat level,
  • the web tension range, will the treater roll need to be driven?
  • Is a particular roll coating required?
  • Is a particular type of discharge electrode specified, say do we need to stripe treat?
  • Are conductive films to be treated, such as aluminum foil, metalized films?

  What types of materials can be treated?
This will depend upon the type of corona station you have. A dielectric covering on the treater roll, ie ceramic, rubber, glass mean you have a covered roll treater system and thus can ONLY treat NON-CONDUCTIVE products, ie plastic films, paper, foam etc. A bare roll or Universal treater, ie dielectric coating on discharge electrode not on the roller, means you can treat conductive AND non-conductive products. Recommended for converting lines where all types of materials could be run.
To find out more about type of roll covering available and their differences please click here.

  What regular maintenance should I give my Corona Treater?
The key to successful corona treating is to keep your corona treater CLEAN. Corona is a high voltage electrical discharge process, so dirt and contamination within your station can cause un-wanted arcing / short circuits and premature failure.
Inspect all electrical insulators, clean if dirty, replace if cracked/broken or showing signs of electrical tracking.
Check all electrical connecting cables, make sure they are sound and clean. Replace worn or damaged cables with new ones.
Inspect all dielectric materials, roll coverings, electrodes for signs of wear or electrical weakness ensure that all surfaces are clean and free of debris build-up.
Check your ozone extraction system is still working efficiently, ozone ducting is still sound and free from holes and leaks. Ozone flow reduction can lead to over-heating of the electrodes and rolls within discharge station resulting is premature failure.
Your corona power supply / control panel will have internal cooling fans fitted, check and clean all fan filters and check cooling fans are still working.
Check you electrode air-gap and reset as necessary. The air-gap setting will have an optimum position to ensure the correct match / balance between power supply and station, see operator manual. In-correct air-gap setting can lead to internal stress and component over-load leading to premature failure.

  What is reverse back side treatment and how can it be avoided?
Unwanted treatment on the back side or reverse treatment, can lead to sealing problems and other undesirable features associated with pressure sensitive end usage.
In many instances therefore in the manufacture of cast film, a guarantee of "no back side treatment" may be required. Back-side treatment is as a result of the film lifting from the roll surface and air being trapped between the film and the roller surface. Where there is no air there can be no corona. Therefore, if we eliminate the air from behind the web, in the corona discharge area, we eliminate back-side treatment.
Please click here to download technical article on Nip Rolls or Lay-On Rolls.

  Ozone extraction fan and ducting, is it really necessary?
A primary concern in corona treater design has long since been ozone extraction. For many years electrodes have been enclosed in either fabricated housings or integrated into individual ozone extraction ducts which additionally act to keep the electrodes at an optimum operational temperature. Provided the extraction fans are sized correctly, both types will effectively and efficiently exhaust the ozone contaminated air away from the station.
Please click here to download information on correct ozone extraction information.

  How can I measure dyne level?
Please visit our dyne pens and inks page, which has information on dyne levels and download our instructions on how to use dyne pens and inks which should answer this question.

  How can I eliminate ozone gases from my corona treatment process?
Ozone, as a by product of corona treatment, can be eliminated by use of ozone destruction or elimination systems. Please visit our ozone destruct page for further information.

If you have any other questions which may not have been answered in this section, please contact Corona Supplies and we will be happy to help