Ink consistency problems

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Ink consistency problems

Postby barb » Wed Jul 19, 2017 12:32 pm

Hi guys, newbie here!

I'm a prepress operator but recently I figured there's really not much sense if my prepress is good if our pressrom has no standards and system for consistency.

So - I decided to dig into the density and ink mixing problems we have. I didn't notice we had THAT much of a problem until our customer ordered about 15 products with same design/same colors/same prepress/same plates. The situation is that we printed about 3-4 runs on Monday, fresh ink from dispenser, new doctors blades, etc., we finished at 3PM and started next day at 8AM and BAM - the first print is waay too off/too red (we focus on the part with the solid tone made of CMY).
Operator then goes ahead and tries to get the correct shade while loosing about one hour and repro material and also start loosing his mind. Last call was to change the doctor blade, so he does that and gets kiiiinda of a correct shade but still you can measure and see the difference.

I will use the search option for topics that interest me but I would still like to discuss my particular questions I'm trying to figure out...
1. How do you define when do you need to change the doctor blades? (currently I think they change it at about 100,000m or earlier if there's are problem like this one)
2. Is it possible to get the EXACT shade and density the next day with leftover ink as well as with the fresh one? (given that all other parameters stay intact)
3. If the material, design, viscosity and pressures are identical - does that mean that density should be automatically identical too?

Man, this is frustrating.... :x
barb
 
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Re: Ink consistency problems

Postby Frank Burgos » Wed Jul 19, 2017 1:18 pm

Hi Barb,

While I give this some thought, let me know whether your team strictly controls and associates anilox rollers used by serial number with each of the colors.
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Re: Ink consistency problems

Postby barb » Thu Jul 20, 2017 1:00 am

Hi Frank, thank you for the quick reply.

I just checked with my guys and yes, they always make sure it's always the same roller for each color.
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Re: Ink consistency problems

Postby Frank Burgos » Thu Jul 20, 2017 7:07 am

You're welcome, Bard.

I'll get back to this.
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Re: Ink consistency problems

Postby wilsontim » Thu Jul 20, 2017 2:53 pm

Hi newbie,

not sure if this will help you but it should,not sure if the doctor blade is plastic or metal ? looking down at the anilox roll while the press is running make sure the anilox roll does not look to wet or have lines you can see if so change the doctor blade if the blade wears to much it will let extra ink by and will change the shade your shooting for we run our press at 500 ft per min and change the anilox roll many times per day to keep from laying down to much ink hope this helps you
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Re: Ink consistency problems

Postby Frank Burgos » Thu Jul 20, 2017 3:11 pm

Excellent point, wilsontim,

As blades wear, it's common for inexperienced operators to compensate by applying too much blade pressure. The blade flexes and the ink hydroplanes under the blade, resukting in a shiny anilox surface. Check to see if that happens.
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Re: Ink consistency problems

Postby Fuzz » Thu Jul 20, 2017 3:55 pm

Hi Captain Obvious here...Are the plates tuned in the same? Maybe hitting harder than the night before. I'd suggest remounting the plates on fresh tape. How were the anilox rolls handled overnight? All rolls, from all colors, cleaned well, and delivering the same volume as the night before?
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Re: Ink consistency problems

Postby wilsontim » Thu Jul 20, 2017 4:11 pm

sorry newbie

i meant to say we change the doctor blades many times in one day
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Re: Ink consistency problems

Postby barb » Thu Jul 20, 2017 5:30 pm

Wilsontim & Frank - thanks, that makes sense. I'll look over next few runs and see how it behaves.

Our blades are metal and yes Frank, I've heard numerous times guys saying they'll 'loosen' or 'tighten' the blade to get a different shade and then somtimes end up changing it completely at the end.
Just recently we had an argument with our boss who always tells that the blade is either 1 or 0, it either works or not, yet our guys state that you can get more from it with changing the pressure.

Wilsontim, do you have an approx. meters you do in a shift? We have a new Comexi machine and most of the time for process jobs they run 220-250m/min yet they don't change the blades too often, it usually passes couple of days/shifts before they replace them as from what I saw.

Fuzz - how do you mean 'tuned the same'? I know they re-use the tape multiple times but I'll check tomorrow for detailed info. Also for the rolls.. I think they don't do a thourough cleaning after each shift but I'll try to inspect that more.

Thank you guys so much for you help, I'm just starting to get really afraid I'll find out that we do almost everything the wrong way...
barb
 
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Re: Ink consistency problems

Postby barb » Fri Jul 21, 2017 10:58 am

Random thought - what parameters are crucial to write down/monitor after a first run of a new job?
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Re: Ink consistency problems

Postby Fuzz » Mon Jul 24, 2017 10:21 am

I mean setting the impression. Is it the same today as yesterday? I'd bet if you have used sticky back you are hitting impression harder on day two.
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Re: Ink consistency problems

Postby barb » Mon Jul 24, 2017 4:48 pm

Eh guys, I'm sorry but my fear has come true and so it seems like I've wasted your time for nothing...

I started off thinking density/ink mixing was the main issue while I came to a conclusion today that indeed most of the things in process of print goes random.
I can't search for root of a problem and solution for it if our pressroom has no standards or quality control whatsoever.

That's why I asked the other day what are the most important parameters to track down from first run because after your replies I went over to the press and started watching how our guys prepare and run some random reprint. In this particular situation they did not have absolutely any detailed information from previous run neither did they monitor, measure or compare any parameter. I feel like everything they did was basically approximate match.

As for the impression Fuzz - that might actually be the biggest problem in the situation I described in my first post, not the blades not the density or something else but impression and mounting tape/sticky back. Because I looked closely over some samples and there weren't only differences day before and after, there were differences on the same day! I looked over with magnifier and what I saw was just confusing, two samples with same design next to each other - cmyk dots were completely different and randomly wrong. Over pressured, brigdes, different shapes, basically what I saw through samples I can use as 'how dots shouldn't look - the manual' :smile: :( ....

I'll try my best to get on track with each part of the process and see what can be done. I'll get back to you after we start managing some basic stuff first..
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Re: Ink consistency problems

Postby Gorilla Printer » Fri Jul 28, 2017 11:20 am

Hi Barb
That shouldn't have happened, something has changed.
I'm assuming the press, chambers and job were left set the same for the next day.
Even with the same worn chambers that were left from the afternoon before there should not have been a dramatic change in one colour.I'm thinking they didn't grab the same batch of ink that was used from the day before.Or they didn't restore inks to the same ink running viscosities they were.Especially the magenta.My pick is they used a different batch or both.
With regards to Frank's (Hi Frank!) and Wilsontim's comments, they are very valid points, but surely that would have been spotted when comparing the size of the process dots from the previous days print.
The clue is there would have been build up on the dots (dot gain).Actually even on solid plates if the ink is hydroplaning there will be some form of ink build up on an image and if there are multiple images the the shade of colour won't be consistent between images.

Ok thats my 2 cents worth
Good Luck
And Cheers
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