color change between frames

Hello everyone,

I'm currently managing a metal sheet printing facility in Tunisia. We use a 6 unit KBA Rapida 142.

It seems that everytime we need to print a design with a framed logo (which happens quite often) the background color between the frames changes color along the whole sheet ( ).
We first thaught that the cause was the difference in thikness in the plates that caused a pressure differential. We switched to printing the background with a pantone, the result was worse.

Did any of you incountered such a problem?
If yes, what is the right diagnosis and how can we avoid this problem?

Thanks in advance

 

Is it possible to print it off square, that is to replate the image and skew it diagonally so as to get rid off the picture framing?

Then you will have to square up again on the cutter.

Other alternative is to let your forme rollers oscillate, although I feel this wont completely rid you of that effect.

 

First, thanks for your reply

your first suggestion is unfortunately not possible because we cut the printed metal sheets on circular slitters that cut only following square lines. In addition, this method would waste too much tin plate which is pretty expensive.

I'll have to ask my techs regarding your second option, I don't know what the forme roller is (I hope my techs do, Tunisia is a french speaking country...), but do you suggest to let it oscilate laterally? vertically?

Also, do you think our diagnosis is correct?

 

Yes laterally. In my opinion, this particular problem is inherent with this type of layout, all you can do is mitigate the problem using the suggestion I have offered, other people may have a different solution?

Good luck.

 

Unfortunately, the customeer cancelled the order.
My techs were already oscillating the forme rollers. The last trial was with two green pantone... it was not bad, but not good enough for the customer.
We were about to separate the background in two different plates: one for the top and bottom parts and the other for the in-between frames narrow rectangles.
This order is gone, but I will face this issue again and would like to find a solution to fix it...

Any help would be highly appreciated

Thanks