Low Dot Gain. Again

[cementary]

Ok, so we've bumped into it again:
We have 4 ManRoland 900 (4 sections, no coater)
All presses are ± same year same condition and same configuration.
We use same: blankets, plates, ink (with target densities), fountain solution (with IPA 10%), ro water other printing chemicals, temperature settings for technotrans.
All 4 presses print mostly same on uncoated stock.
But on coated one of them has low dot gain on 3 (M) and 4 (Y) sections always and somtimes on 2 (C) section.
Drop is around 6-8%. 3 presses print with 14-18% gain, but this machine prints 6-10%
It's just it - we print, see low gain, take plates off, mount them on another press and see normal dot gain.
What i can't get my head around is if i make excess packing, like plus 0.1-0.2 and also make maximum possible impresson on impression cylinder i don's see difference in dot gain, while it probably should be.
Any thoughts, recommendations what to check also?

P.S. we had a serviceman for full shift, he also checked everithing and his conclusion was like "this is how this press work" ¯\_(ツ)_/¯

 

[Asures]

This specifically would be a good time to implement some G7 curves, specific to each press.

This way, you eliminate the investigative work and can produce a predictable piece, regardless of the press.

 

[cementary]

Well, i'd rather not.
First of all i do not want to have 8 different curve sets (4 coated 4 uncoated) - i'll loose interchangeability between presses.
Second - i personally do not believe in G7 methodology. I think there is a lot of marketing and overthinking.
It's more than enougth to establish density for each ink where i have lowest dE to the standard lab's, then calculate compensation curves, and there you go - nice gray balance according to System Brunners methodology.

 

[Cornishpastythighs]

Is this press running the same ink density/ink film thickness as your other presses. I have never had much success trying to introduce dot gain by overpacking blankets or increasing squeeze, blanket techology is very good nowadays and I found any increase was not worth the trouble. I have sometimes seen extender used in the ink to increase ink film thickness and get a bit more gain but again such measures may not be appropiate if you are striving for consistancy. As you say the same plates on another press print fine and you have all your presses running the same ink, fountain solution, roller compound and ink train temperatures and I assume this low dot gain is not just for a particular operator I would still think there is something mechanically different about this press, Bearer pressures, temps. good luck

 

[cementary]

Of course densities are the same. We've even double checked by measure printed sheet on other presses. Bearer pressure same also, checked that with serviceman, temps also. Btw we print with bearers being in contact, so not much can be done wrong in upper pair of cylinders.

 

[cementary]

Operators also different. What I can't understand is why there is a problem only on coated stock. If printing uncoated - all presses shows almost same dot gain

 

[Cornishpastythighs]

Operators also different. What I can't understand is why there is a problem only on coated stock. If printing uncoated - all presses shows almost same dot gain

we had a different curve for coated vs uncoated if memory serves me, uncoated stock absorbed more ink, coated paper ink seemed to print sharper, Newsprint would be the extreme example of this I guess. If your press is mechanically sound I guess the only things you can vary are print curves and ink recipe

 

[realaqu]

Of course densities are the same. We've even double checked by measure printed sheet on other presses. Bearer pressure same also, checked that with serviceman, temps also. Btw we print with bearers being in contact, so not much can be done wrong in upper pair of cylinders.

Hope this will help

https://cdn-s3.sappi.com/s3fs-public/sappietc/Progressive%20Dot%20Sharpening%20and%20Image%20Loss_v1.pdf

 

[cementary]

Hope this will help

Thanks, but we've excluded all that and again, same plates on other press doing just fine

 

[cementary]

we had a different curve for coated vs uncoated if memory serves me, uncoated stock absorbed more ink, coated paper ink seemed to print sharper, Newsprint would be the extreme example of this I guess. If your press is mechanically sound I guess the only things you can vary are print curves and ink recipe

We too have different curves for coated and uncoated. Inks are literally same - all 4 presses fed from same barrels through technotrans ink transporting system

 

[Cornishpastythighs]

We too have different curves for coated and uncoated. Inks are literally same - all 4 presses fed from same barrels through technotrans ink transporting system

looks like you have the perfect set up. good luck

 

[cementary]

Looks like perfect, but far from it actually. Because just 1 year ago all 4 presses printed almost same (plus minus tolerances) but now 1 stands out and only on coated stock. Mystery

 

[Cornishpastythighs]

Looks like perfect, but far from it actually. Because just 1 year ago all 4 presses printed almost same (plus minus tolerances) but now 1 stands out and only on coated stock. Mystery

did this happen suddenly of has it been happening over time, trying to help someone who is possibly thousands of miles away and not being familiar with the history makes it difficult to offer suggestions. We used to make fishbone diagrams when we were trying to solve an issue that involved so many inputs and variables

 

[cementary]

Well, probably it happened over time, but while that time we had some issues with lots of different inks and fountain solutions, plates also. And this particular press most of the time prints uncoated stock. So if something happened we've probably missed it. If you're talking about big changes like ink train rollers replacement or any big maintenance with large subassembly replacement - there was nothing like that.

 

[cementary]

One more funny thing. Dots and slurs produced by this press on coated stock on M & Y sections looks super sharp with very defined edges (true round dot) as if the situation like all other sections and presses prints badly

 

[SteveSuffRIT]

Just to rule out some software setting in the densitometer/spectro, are you using the same device to measure, not the brand or model but the same device?

 

[gordo]

Could you post some photo micrographs of your dots at 30 or 40% of the 4 press sheets?

 

[Asures]

Please provide more information regarding the consumables you use.

Conventional ink? UV Ink? LED Ink? Brand? Blankets / Brand? Roller Material? Fountain Solution / Manufacturer and dosage? Blanket Packing / Undercut vs. other presses? Spectrophotometer used to measure color - hand held or scanning on press?

Just trying to help you from a whole other continent Sir.

 

[DeltaE]

Ok, so we've bumped into it again:
We have 4 ManRoland 900 (4 sections, no coater)
All presses are ± same year same condition and same configuration.
We use same: blankets, plates, ink (with target densities), fountain solution (with IPA 10%), ro water other printing chemicals, temperature settings for technotrans.
All 4 presses print mostly same on uncoated stock.
But on coated one of them has low dot gain on 3 (M) and 4 (Y) sections always and somtimes on 2 (C) section.
Drop is around 6-8%. 3 presses print with 14-18% gain, but this machine prints 6-10%
It's just it - we print, see low gain, take plates off, mount them on another press and see normal dot gain.
What i can't get my head around is if i make excess packing, like plus 0.1-0.2 and also make maximum possible impresson on impression cylinder i don's see difference in dot gain, while it probably should be.
Any thoughts, recommendations what to check also?

P.S. we had a serviceman for full shift, he also checked everithing and his conclusion was like "this is how this press work" ¯\_(ツ)_/¯

May I have answer that your issue happens with all thickness of paper or "Uncoated - thick and Coated - thin paper"?