Blotchy printing

swp66

Active member
We are having some issues with print quality. We are trying to print a 60% black screen and what we are seeing is best described as blotchy or lighter and darker areas in the print. I have examined the dot with a microscope (see attached pics) and it looks nice and sharp on the plate but not so good on the press sheet. I am wondering if this could be coming from our Kodak Trendsetter 400? I have noticed this on 2 different presses. I have tried cleaning the plate processor, running job through a different profile, I have tried 175 line screen, 20 Micron Stacatto and I get the same result on everything. I just want to rule out anything in prepress that could cause this issue. We are seeing this in screens around the 40 to 60% range. The press is convinced the problem is in prepress, but I can't find the problem in any of the equipment. If the dot is good on the plate, shouldn't it be good on the press sheet? What am I missing? See attached pics for what we are seeing. Thanks in advance!
 

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Press operators will always blame Prepress. It's n15t a Prepress problem, apart from using too fine a screen for what appears to be an uncoated stock
Staccato will NEVER give you a smooth screen on single colour work. 175# is too fine for most uncoated stock. Use either 150# or 133# with conventional angles (Black 45°) and a round or elliptical dot.
 
Staccato will NEVER give you a smooth screen on single colour work.

I would disagree with that. That being said, it will resolve the issues of a poor substrate. So you see problems where you wouldn’t with a coarser screen.
 
I would disagree with that. That being said, it will resolve the issues of a poor substrate. So you see problems where you wouldn’t with a coarser screen.

I have never been able to get a flat screen to look smooth with FM screening, neither the early version with Brisque nor the newer version of Staccato on Prinergy, it always looks grainy. Photos look fantastic, that's the compromise you have to make.
 
I have never been able to get a flat screen to look smooth with FM screening, neither the early version with Brisque nor the newer version of Staccato on Prinergy, it always looks grainy. Photos look fantastic, that's the compromise you have to make.

I’m not an apologist for Staccato - that being said, when I did marketing for Creo, as much as possible we’d include large flat screen tint areas of either single color or multicolour builds specifically to show that it could produce smooth flat tints. And that was on every kind of substrate from #1 gloss to newsprint.
I haven’t got a clue about what Kodak has done with the screening. They never understood it when I was there.
 
Kodak don't seem to promote Staccato much any more, we only have a licence for 20µ so I don't know if 10µ yields superior results. We rarely use it apart from the occasional coffee table book. We did try a sort of home made hybrid screen for one book, imaging CMY in FM and K at 175# AM, that worked out very well.
 
Kodak don't seem to promote Staccato much any more, we only have a licence for 20µ so I don't know if 10µ yields superior results. We rarely use it apart from the occasional coffee table book. We did try a sort of home made hybrid screen for one book, imaging CMY in FM and K at 175# AM, that worked out very well.

They seem pretty quiet promoting everything. Like I said, Kodak didn’t understand staccato the way that creo did. Kodak just thought it was halftone screening. Creo understood what it really was from a corporate tactical and strategic point of view. But that’s all in the past now.

The cmy fm and k 175 combination was also used quite a bit for magazines in Latin and South America.

In any case there’s better screening in this class in production doing heat and coldest and even flexo.
 
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Hello swp66,


Without changing Press wise...... run 20/50 sheets each of a similar substrate stock, including coated paper - --

I suggest you do this by making a "Sandwich" of alternate substrates - see the printed results !!


Regards, Alois
 
We are printing on .26 mil pvc plastic stock. This is a new issue, we have printed successfully with Stacatto 20 and 175 line screens in the past. This issue just popped up last week.
 
Could this be an issue with the laser head on the Trendsetter 400? Anyone have any experience with what happens when the lens or mirror is dirty? What would I see if this was the case? I don't know, I just keep going back to the picture of the dots. I can't understand why the dot on the printed sheet looks like that when the dot on the plate looks clean.
 
Something I found during printing on plastic coated stock was that dampening solution from previous print units can have an adverse effect on subsequent print units, this is because the stock cannot absorb any excess dampening. The operators must carry as little dampening as possible and I have even seen air bars/air curtains installed between print units to eliminate the effect of dampening on downstream print units.

Have you researched this subject also [h=4]Corona Treatment of Plastic Substrates.[/h]
 
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Hello swp66,


It "DOES HELP" when you provide ALL the relevant information, not just a Pre-press view,

have you looked at the KCMY print control strips ?


Regards, Alois
 
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Could this be an issue with the laser head on the Trendsetter 400? Anyone have any experience with what happens when the lens or mirror is dirty? What would I see if this was the case? I don't know, I just keep going back to the picture of the dots. I can't understand why the dot on the printed sheet looks like that when the dot on the plate looks clean.

Unless they've made a radical design change the Trendsetter 400 does not have a mirror.
 
Something I found during printing on plastic coated stock was that dampening solution from previous print units can have an adverse effect on subsequent print units, this is because the stock cannot absorb any excess dampening. The operators must carry as little dampening as possible and I have even seen air bars/air curtains installed between print units to eliminate the effect of dampening on downstream print units.

Have you researched this subject also [h=4]Corona Treatment of Plastic Substrates.[/h]

Looking at the dots suggests (to me anyway) that they may be running too much water (ragged edges of dots and low K density).
 
Is it just me or is that the grainiest or most fibrous pvc ever? Great pics, btw. (and please excuse my ignorance; I have never printed on such a substrate, but we do occasionally print on credit cards and they are very smooth even when viewed at 100x)

But, seems like ink would look that way based on the close-up pic of it.

Anyway, also looks like press banding, as if from rollers.
Have never seen that "effect" from the Trendsetter or any other image setter. I'm assuming the top and bottom of press sheet pic is trailing and leading edge.
Issues from lasers on plates usually runs east to west, in the direction of laser travel. And usually the resulting pattern is quite uniform.

The pattern on this sheet is similar to a few things: roller chatter, bad stripes, and/or a few other things related to same.

Press always blames prepress (should have capitalized ALWAYS; and should probably exclude pressmen like Alois). And single color screens bring out the worst in every press too.
 
I have attached a picture of a job that was ran the day before this problem popped up. The gray screen is 50%, it looks nice and smooth. The only difference was this was ran on .06 mil. There was an issue with one of the files (some text was overprinting on the black card) and I had to remake the plates. When they put the revised plates on the next day, it looked blotchy like the other job in question. So this shows that we were printing cleaner, I just can't figure out what changed.
 

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1) have the plates previously had that slight blotchy look to them? Your picture shows an uneven colour on the plate dot.

2) Has the operator loaded fresh ink in, washed up and started water dials below scum point?

Your press sheet dot looks like serverly emulsified ink which can easily be done if water dials are left where they normally run on paper stocks or the ink has been left in the ink duct and continuously sprayed with anti skin each night.
 

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