Muddy Printing (Splotchy)

[nj_printer]

Forgive me if this is the wrong category for this question!

We're getting splotchy printing from our press. It's really been noticeable during the last week. I handle some prepress and I'm not sure if it's a pre or press issue. We're running a booklet with some large solid areas of color and it's coming out uneven. There are very tiny blotches in the solid, making everything muddy. I've been working with the press operator as to what it might be, but I'm out of ideas. We're running 80# gloss cover on a 28" press with Kodak Thermal Direct Plates.

So far, I've recalibrated our plate curve and made replacement plates. I don't think it's too much ink for the paper there is around 250% ink coverage max. The running density is within acceptable limits. The pressman has tried flushing the fountain solution, adjusting the squeeze, replacing a water form roller...I don't think they've changed brands of ink or house stock recently.

I'd point the finger at the Kodak system we had installed a few months ago, but the plates don't look splotchy before or after they are hung. I've had them here already and they seem to think the machine is operating correctly. Admittedly, I don't know enough about what happens in the press during printing. I'm at a loss as to what to examine next.

If you have any ideas, I'd appreciate the help. Thanks!

 

[Green Printer]

Are the ink batches or lot numbers different than the previously used ink that worked.?

 

[Prepress_Parasite]

Sounds to me like a coating problem with the sheet you are using. Does it show up on all stocks or just this one?

 

[Green Printer]

Does the ink have a different oder? Is the body the different? Is the mast tone different?

 

[gordo]

As Prepress_Parasite suggests, run a different stock - but equivalent paper stock to see if it's the paper (most likely culprit) Plate curves will not fix mottle "blochiness". Poor ink transfer can also exaggerate mottle. Does the mottle appear in solid ink areas or screened tint areas? It could be back trap mottle which is caused by small-scale nonuniformities in the absorptivity of the paper. The nonumiformities lead to differential ink film split as paper passes through the press, which causes variation in the color of the print. The lack of color uniformity is noticed visually as a mottle/blotchiness.

gordo

 

[nj_printer]

Thanks for all of your help. I spoke to Kodak about the issue and they mentioned that it may be an issue with the "processing" of the plate when it it on press. They want us to try either a longer or shorter water/ink cleaning procedure before the ink forms are engaged. They also said it may be an issue with too much water, both in the initial plate cleaning and the run.

As to the paper, we switched to an 80# gloss text job and had the same issue. Actually it looked worse. I'm wondering if we pull out out old plate processor and use that to clean the plate before the we hang it...

The mottle is most visible in large blocks of darker (but not black) solids. The main color we saw was a C17/M100/Y100/7K. Also, I don't believe there was a different ink batch.

Thanks.

 

[cosmo]

are you able to take a close up photo of the problem? scan it maybe? What unit is the problem on? CMYK?

I cant see the plates being the problem, more likely fountain solution, what press are you running?

 

[Paultheprinter]

After reading your thread the most probable culprit is as gordo suggested the paper, have a look at a plain sheet in a uv light and see how the sheet is, i use a torch i got from ebay and its amasing how much mottle in the surface of a sheet you can see. If this does not yeild any major discoveries what sequence are you running the inks, i assume K,C,M,Y ? If so it seems ok as the rule goes screen before solid. But it may be worth noting the issue of backtrap mottle, check ink tack ratings and if possible try running different sequences to see if the problem is wose or better, check ipa levels as too much alcohol can cause mottle, drop down to 8% and see if that helps. Last point is blankets, a harder blanket may smooth out any mottle, this sofftening may be caused by an over agressive blanket wash being used or a soft blanket being used. I have a PDF which notes some points on mottle, if your intrested e-mail me and ill send it you. If anybody else wants a copy post your email adress and i sort the rest, or email me off line.

Happy Printing Paul

 

[nj_printer]

We tried some different stocks and had the same issue. I hadn't heard of the term "Mottle" before, so I googled it and found a great PDF from the Sappi site explaining all about the different types of mottle, their causes and how to address it. I gave a copy to my pressman and he went to work. I'm not 100% we got it licked, but something (or things) he did has made a difference. That PDF was a great resource, but I would never have looked into it without the help of this board. I found it at:
http://www.sappi.com/NR/rdonlyres/451819EC-CC19-44EF-B3EC-6AA6DA283295/0/PrintMottle.pdf
I plan on reviewing the situation with our pressman next week to determine what the issue was and what he did that made a difference. Thanks again to everyone that posted.

 

[JP@mwv]

Could you send me the PDF that addresses print mottle problems?
[email protected]

 

[brycesteiner]

The link is there just click on it and it will show up in your web browser.

 

[turbotom1052]

without seeing a sample i tend to agree with gordo that its a back trap mottle. this is usually visable when you run k,c,m,y sequence and have solid images that are comprised of a cyan solid with magenta screen printing over the cyan solid. if these are in fact the solids your having problems with i would suggest you switch the cycan and magenta printing order. this is a very common issue and its the reason why i look for the potential for this with every job i put on press and change the sequence if i see this potential good luck and let us know how it works out