Auto impression settings on CI press

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Auto impression settings on CI press

Postby barb » Thu Oct 04, 2018 10:46 pm

Hi guys, need help with the impression settings on auto setup press.

So the operator prepares the job, start the run and the press automatically sets the impressions.
For example, on color is just black text and you can clearly see there's way too much impression (edges around letters). When I ask about it, the answer is - if we lower the impression then ink is missing one some parts so the only way to have full image is to print with squashed letters.

Couple of days ago we also had a full cmyk job, I checked the dot gain and see on the 3% control bar that magenta has way too much impression. Same thing, we pulled off the impression and the ink completely started missing on some parts.

How can this be avoided?

Also, since the press has auto settings for the impression, does the speed on which the job is started affect on how the press can set the impression? For example, if the job is started on 120m/min and then later it's set to 300m/min?
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Re: Auto impression settings on CI press

Postby longtimefan » Sat Oct 06, 2018 9:59 pm

So, you back off imp to get crisp print and anilox or inking misses?

Maybe a ink transfer issue
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Re: Auto impression settings on CI press

Postby guy de cafmeyer » Mon Oct 08, 2018 1:41 am

I would do tests with different cushion tapes first , before resetting the press settings .
On halftone it is quite incredible to see the different results using say , hard tape versus a soft tape .
( Maybe just print a step wedge ...? ) Generally speaking , one wants a kiss inker setting , with just a little more impression ; just to assist in keeping the print clean . Hard edges around spot colours may also be a result of too low viscosity . Post a pic , then we can all see ?
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Re: Auto impression settings on CI press

Postby barb » Mon Oct 08, 2018 4:34 am

Longtimefan - yes, by the time we pull the impression off to get a nice print it immediately starts missing ink on some parts.

Guy - I wouldn't say the viscosity is the problem in this particular case because I have experienced this issue on both minimum and maximum visc the ink supplier recommends. As for the stickyback/cushion - good thinking, Tesa has various types, we only used secure-x so far, would different bonding type affect impression settings?

I'll try to post some samples later this week..
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Re: Auto impression settings on CI press

Postby guy de cafmeyer » Tue Oct 09, 2018 3:54 am

The adhesion will not make a difference to the print result ..
The tape you are using is a "soft" tape , and therefor one would definitely do a trial with a medium , as well as hard tape .
An example of where one would use a different tape ; If a halftone pic is predominantly a "heavy" pic with plenty shadow areas , one would consider a harder tape to ensure "harder"/better transfer of shadow dots ... and similarly if a pic is filled with highlights , one would want to use a soft tape , ensuring the integrity of the minimum dot areas . Hope this makes sense ? Even applies to line work to a degree >>> Cheers !
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Re: Auto impression settings on CI press

Postby Frank Burgos » Tue Oct 09, 2018 6:38 am

Barb. A few possible causes/things to look into:

Plate mounting tape condition. I NEVER reuse mounting tape. Even over-impressing during set-up can deform the tape to where those defects you describe show up.

Burrs on plate cylinders.
Plate cylinder total indicated runnout (TIR).
Anilox roller TIR.
Dirty impression cylinder.
Stuff applied to the back of the plates (shellac) to allow for easier removal of plate from tape.

Looking forward to pics.

Frank
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Re: Auto impression settings on CI press

Postby iteachflexo » Tue Oct 09, 2018 5:21 pm

If you are just printing text and Impression looks heavy, change the anilox to a higher line. If running a 400 line, change to 550 or higher. Also, check the gear on the print cylinder. Make sure it is not damaged. Try another print cylinder and see if impression is better. Are plates analog or digital? Sometimes analog plates can have a low spot. Digital plates are more uniform. I assume plates have bearers. If bearers are printing, generally everything between the bearers should print cleanly. You can also add a slur patch to the bearer to check impression. Hope this helps.
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Re: Auto impression settings on CI press

Postby barb » Fri Nov 09, 2018 3:17 pm

Hi guys,

sorry been busy lately, so here are the pictures (it was a fast run, couldn't get better images).

First showing is a starting point - spot brown color with text and patch of soild, you can clearly see the heavy impression on the text.
Second showing is after adjusting just a little bit lower impression - text was better but still a bit squashed and already the solid patch started missing ink.

1.jpg
1.jpg (1.7 MiB) Viewed 3159 times

2.jpg
2.jpg (596.99 KiB) Viewed 3159 times


Frank, we do re-use the tapes sometimes, but this problem occurs with both new and reused tape. I googled TIR, I need to look more into that topic.
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Re: Auto impression settings on CI press

Postby Frank Burgos » Fri Nov 09, 2018 3:44 pm

Barb. Can you take a photo of multiple images, at a greater distance. I'm looking to see whether bounce is involved. Are you familiar with plate cylinder bounce and how it manifests on images?
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Re: Auto impression settings on CI press

Postby barb » Sat Nov 10, 2018 11:48 am

Frank, if I'm correct bounce effect is when the plate has larger non-printing spaces between print elements and so the cylinder bounces and you either have lines from bounce visible or/and you have to set stronger impression to get full ink coverage. I believe I heard somewhere that this is one of the troubles of CI presses in general, but we sometimes manage to save this problem by placing straight continuous lines outside design width.

I'll take couple of more shots when I see again this effect on full halftone images.
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Re: Auto impression settings on CI press

Postby longtimefan » Sun Nov 11, 2018 12:01 pm

Bearer bars is what your description is of lines out side the design
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Re: Auto impression settings on CI press

Postby Frank Burgos » Mon Nov 12, 2018 7:29 am

Yes. That's what I mean, Barb.

Aside from design, press speed, plate durometer, and tape durometer also factor in.

Looking forward to additional pics
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Re: Auto impression settings on CI press

Postby Bengalnation » Mon Nov 12, 2018 8:42 am

Good Morning Barb,
I'm coming a little late to the party! Without being there to watch the press run as i am sure everyone would agree it's hard to troubleshoot with a few pictures. I would like to see some pictures that aren't as up close as well, one thing i would look into would be to check what the undercut on your plate cylinder are as well as the thickness of your plates. It may be something as simple as you are using the wrong thickness mounting tape as well. I look forward to seeing more pics, I've learned there are some pretty sharp people on here that are a big help.
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Re: Auto impression settings on CI press

Postby guy de cafmeyer » Wed Nov 28, 2018 1:52 am

From what I see ,( if your viscosity is correct ) from pics is that
you have too much inker pressure , and too little impression .
One should always , after a set-up , reduce inker slightly , increase impression slightly .
This keeps the print clean during the run too ...
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Re: Auto impression settings on CI press

Postby Gorilla Printer » Tue May 07, 2019 4:09 am

Hi Barb
First of all, reusing tape is a false economy in my opinion.As a printer we have enough trouble with worn plates and worn presses,we don't need to add to the problem by reusing mounting tape.I'm wondering if the pics you gave had a plate mounted on reused tape.If so ,well that could have added to the problem.But just in case the tape being used is new lets move on.
The 2nd pic shows impression coming off,but I believe there is also an inkers miss because the the line under the barcode and the bars are printing.Yet the numbers aren't.So that leads me to believe there is bounce/play in the impression cylinder.
Since there are auto impression settings,I'm assuming the press is a later model and mounted cylinders slide onto shafts on press?
If so the operator side cylinder clamps would open .I'd open them all up and check for play on the shaft.There should be no give and the shaft should feel supported no matter which way you flex it.Compare all shafts.
Thats where I'd start checking,then move onto checking clamps and TIR.If all is good ,I'd move onto doing the same with the anilox shafts.
It looks as though you have a T.I.R problem?


Cheers
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