"Scratches" from front edge - to the middle

Hi, we have an XL 106 -2012 with carton package installed.
We are printing heavy cardboard (0,65 mm thick) with aluminium and laminate on the back.
For sure, its a stiff board but within HDM specs for rigidity.
We have a problem with some light "scratching" or touching of the sheet that we cannot find the reason for. What I find strange is that the "markings" are in the lead edge of the sheet up to the middle and not at all in tail edge. It would make a lot more sense to me if it was in the tail.

We did a test with only cyan & magenta and found that it happens on 0,65 mm board (picture 065_mm)

But not on 0,5 mm board (picture 050_mm)

These sheets were printed directly after each other with same plates.

We pressed the emergency stop to see where/when it was visible and our own conclusion is that its coming somewhere around the 5th unit. We could trace the sheets in the press backward until we found the last printed sheet with only cyan and from there we checked the previously printed sheets. As we found sheets without any markings printed with both Cyan & Magenta I concluded it must happen after these printing units.
When checking sheets after the Yellow unit they had markings.

We printed it in the following way:
PU1 Empty / impression on (to pickup dust)
PU2 Black / impression off
PU3 Cyan / impression on
PU4 Magenta / impression on
PU5 Yellow / impression off
PU6 Empty / impression off
PU7 Empty / impression off
PU8 Empty / impression off

Qestion: Is it correct that the press turns one complete revolution after hitting the emergency switch?

We run a lot of jobs with cyan screened backgrounds and now-days we have to move the cyan to unit 7 to get rid of this problem.

I would appreciate help on finding whats wrong.
This is how it looks in a microscope, not the same job but same problem.


Kr. Michael

 

On a sheet that rigid I'd be running ALL units with impression on.

I do agree though that I'd expect any marking to be more back half of the sheet, but worth a try as it will help with the sheet travel through the unused units.

Steve

 

Hi Steve,
Thank you for your reply.
Only the test-job was produced in this way. The every day jobs where we see this problem are always run with all units on impression, (non printing units are set to "dust off") and the result is the same.

 

Is the press an XL106 8P 4/4?

 

The press is a XL106 8 LYYLYYL X3 - 2012

 

Check the operating manual regarding the perfector marking in straight printing:

The freshly printed side of the sheet may get in touch with the reversing drum in straight printing. For this reason there are special cylinder jackets for the re‐ versing drum allowing you to obtain optimum printing quality. Use these cylinder jackets especially for thick printing materials.

It then gives solutions.

Steve

 

Normally we print only square artworks filling up the entire sheet, similar to the blue test sheets. But, a few days ago we printed a job on 0,40 material, with gluing flaps. In the waste & non printing/non varnished areas at the lead edge of the sheet, the printer detected polished markings, very similar in shape and position to the markings we see on the printed sheets shown in my original post.

The markings are in the lead edge up to the middle and nothing at the tail. Attaching pictures, maybe that can help in finding the root cause? What I find strange (again) is that this is happening on a sheet which is only 0,40 thick and has no backside laminate.

Lead edge: (colorbar for Inpress Control)


Tail:

Perhaps we are getting these polishing marks all the time but due to the fact that we completely varnish 99% of all sheets we don't see them until we print the jobs on thick board with the cyan screened areas. This board (0,65) is then so thick that whatever is creating the polishing will now be tighter/closer to the print surface and create the print defects we see.
Just thinking out loud....

I will ask the printer to print some sheets this afternoon without varnish just to see whats happening.

 

I have also seen this in the manual but disregarded it as we don't have a perfecting press, or am I missing something?

 

No you're not, it was me missing something
I'll have a think.

 

Thank you, its a tricky one

 

I remember having a similar issue years back turned out it was hard ink or coating on the decks that are under the the grippers only visible on heavy board no give in stock

 

Thoughts:
1.Could you change grain? -short to long and vice versa-
2.Magenta dots look ok
3.Exchange order Cyan and Magenta
4.Do you use Super blue net?

 

How long the press rotates after an emergency stop will depend on press speed.
To do a more accurate test using the emergency stop you could slow the press right down in production, but check you're still getting the marking, then press the stop button. That would give minimal rotation.

On your press all inter print unit sheet travel will be the the same and there's not really a lot there to mark the sheet.
I think there'll be a row of axial fans just above the sheet as it goes into the unit, but I don't see how a thick stock would hit them, more of a thin stock problem.

So from your test so far, it's marking going into PU5, in PU5, or as it comes out of PU5...

 

Dear Micheal,
First of all, Try to clean the infeed cylinder with IPA, because sometimes the slides of the cylinder surface could be contaminated.
Simultaneously, move out the cleaning brush above the infeed cylinder, and give me a try please.

 

I'd stick to asem - if it's 0n the top of the sheet and on the front edge that vely likely may be infeed cylinder or even more likely these guide wheels just over the front grippers. They may be seized and not turning, or there is some dried ink on them.

 

Good point I think you can loosen the guide rollers over infeed grippers and move them away from sheet .lift them up tighten finger nuts