askralph

Victor asks:

We have been experiencing print variations when we print full coverage. The best way to describe this is that it looks like bands of light then dark print that run horizontally, across the entire width of the press. Similar to when an anilox is hitting the plate too hard, but is not. Sometimes it’s not as obvious at the beginning of the run, but becomes more noticeable after 200 to 300 sheets. Other times it’s obvious from the start. Have you heard of this happening and/or do you have any suggestions?

I reached out to Jack Fulton at Printron and through his sources he offers this info.

There are a number of variables that can create banding or striping when printing.

If the plate is larger than the sheet you will not transfer all of the ink from the plate to the sheet. So the remaining ink will cause uneven printing on subsequent sheets.

Banding or bumping can be caused by several things in combination with each other. If pH or viscosity is out of control it can make the problem worse. If using plastic doctor blades and 60 degree cell anilox rolls you can get a phenomenon like stripping a screw. If you put a screw into a piece of wood and turn it too tight you can strip it. It feels tight then all at once slips. The same thing happens here, the blade is tight against the roll, then slips and re-seats which causes the uneven inking or banding. Ink with more lubrication works best in this situation.

Some converters have reported experiencing banding on diecutters when the doctor blade angle was set at 60 degrees. When changing to a new doctor blade system with the blade angle at 32 degrees the problem went away. If you measure the opening between the two blades in chamber and it’s the same as the distance between the bands you are printing, then this may be the issue.

Also if your chamber moves laterally, or oscillates, stopping the chamber from moving laterally may help this issue.

You may also want to make sure the anilox roll pressure, not the impression but the pressure engaging the roll, is correct. If this is too low it can cause bouncing even with very light impression. You may want to contact your OEM for the correct specs and test procedures.

This entry was posted on January 17, 2013 at 1:28 pm and is filed under Printing. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.