Unusually low TVI (dot gain) on one unit

[Elton McAleer]

Hi all.

I am setting up ISO 12647-2 plate curves for paper type 1&2 on a komori Lithotrone 28. Whilst I am aware that komoris are said to print a 'sharp' dot, I am getting some very strange results when running linear plates to calculate the mechanical gain and then compensate to the desired TVI.

I have set up lots of presses over the last few months, and 'typically' the linear gain before compensation is in the region of 19 -25% at 50 (eg a 50%tint prints at 69-75). This is fine, and is easily corrected with a plate compensation curve to bring the TVI in line with the standard (In this case, 14.3% CMY and 16%K at 50%).

On the komori in question, I am seeing a strange linear result on Cyan in particular, (graphs attached) although all four colours are gaining less than i would usually expect to see.

NOTE: these curves are before any plate/press compensation is applied.

The Cyan is only gaining by a max of approx 8% and seems to be 'flat' from quarter tones to shadows - rather than the usual smooth, 'high' linear result.

I have checked blankets (packing and torque) roller settings and shore, fountain solution, alcohol, plate calibration, etc etc, but am still getting a 'poor transfer' of the dot. I suspect there may be a mechanical problem on the cyan unit but am not a press engineer so I don't really know where to suggest the customer starts.

Paper is 115gsm matte coated, ink conforms to ISO and is not thinned, pressroom and press temperatures are all within spec.

Has anyone seen this kind of 'flat curve' before? Care to suggest what might be causing it?

I use Kodak Tonal Curve Toolkit and GMG Print Control to establish my figures.

Curves are generated from 400 sheet (after make ready) run to wet densities to give dry LABs that meet PaperType 1, 5 sets of 10 sheets, 50 measurements averaged by TCT to smooth data over run and across sheet.

Thanks guys,

Elton

(Fogra PSO implementation partner)

 

[Tarun Chopra]

Ever thought of doing a re-run on a different manufacturer substrate of similar specifications? A lot depends on paper too.

I have seen considerable difference, will be waiting to hear your experience.

Tarun Chopra

 

[Paultheprinter]

hi there,

my opinion is to change all blankets, even though shore hardness is good you can never measure this accuratly and chemicals in wash system or a wash by hand does change the micro hardness resulting in poor transfer and low tvi ive seen it quite a few times and a quick five min change usually brings press back into tollerance.

Paul

 

[Elton McAleer]

Hi guys,

Thanks for your responses

I have tried a different substrate from different manufacturer - yes there was a slight difference - about 2% more gain on Everest 130 compared to Sumo 128 - both coated matte - but the 'Cyan' problem was still very pronounced compared to the other units.

I plan to do a complete wash up and switch the cyan and magenta units to run KMCY (just for testing) I know that running M before C will mean a colour shift and trapping change, but at least I will be able to see if it is an ink related issue or just related to the particular unit. I have to run KCMY when I'm done but this may help eliminate a variable i guess...

I also changed all the blankets before the test - I was suspicious that the original test results were caused by 'dodgy' blankets so we tried moving from a Servicom to a Coates (slightly more 'expensive') blanket. all 4 units were put on new, run for a day and then re-torqued.

hmmmm!

Anyone else got any ideas?!!

Cheers

Elton

 

[gordo]

Don't switch M and C units (two washups) just run M in the C unit (one wash up). If it runs the same as the M in the proper M unit does then you'll know that the C ink is the problem.

best, gordon p

Quality In Print current topics Print '09

 

[Elton McAleer]

thanks gordon - good idea.... it will save me a bit of time and keep the printer sweet..

Cheers

Elton

 

[tmason]

Elton,

Try to deep clean to rollers to be sure there is no calcium build up that may be causing this issue. Even if the rollers look clean, there still may be contamination.

We had the same issue with cyan several years ago and switched to another ink and the problem went away. We worked with our ink vendor, (who claimed no one else had the problem) for several months before we gave up. We had tried everything in the book but could not figure out how to make the cyan print.

Does the pressman have trouble getting the cyan up to standard density? Does the cyan begin to lighten up during the run? This is another sign of incompatible ink.

Also be sure the pressman finishes the wash up with water, every time. The water will flush any remaining solvent from the rollers and remove paper contamination.

Good luck.

 

[kseldridge1]

I am having some of the same issues with TVI. Did you solve your problem?

 

[BryanC]

We are having same issue but with all 4 colors. Our dot gain numbers are in the low to mid teens at normal density if we push the ink 20 to 30 points dot gain comes up closer to where it should be and we match proof.
We run linear plates, Superior Elite med. tack Black and Cyan low tack Magenta and Yellow in that order,
Prisco 2451 Fountain solution and Alkaless V sub 3oz and 2oz, Day 3000 blankets and Kodak Sword plates. Any suggestions would be appreciated.

 

[frank67]

frank67

frank67

Did you check the K value of the cyan!!!

 

[marktonk]

Bryan,

I think your problem is different. You are weak in all four colors but you can push ink to get closer to the proof. Where are your ink densities without pushing and where are they when you do?

If your densities are reasonably normal and you have to push to get closer, then this points to using linear plates. They do not meet the dot gain of your proof or any standards providing your proof is meeting the standard you want to print to. This is not unusual, linear plates are usually too open to match most standard dot gain (at least in the U.S.), you need to add a compensation curve to bring the dot gain on plate up to a point that once it is printed, you match your target and proof and not have to force ink densities to get the gain. Forcing ink can lead to other problems with drying, offsetting, etc.

Regards,

Mark

We are having same issue but with all 4 colors. Our dot gain numbers are in the low to mid teens at normal density if we push the ink 20 to 30 points dot gain comes up closer to where it should be and we match proof.
We run linear plates, Superior Elite med. tack Black and Cyan low tack Magenta and Yellow in that order,
Prisco 2451 Fountain solution and Alkaless V sub 3oz and 2oz, Day 3000 blankets and Kodak Sword plates. Any suggestions would be appreciated.