PPI question

[rbailleu]

we just put in prepress interface. is it common to have to adjust the stroke of the ink ductor with the first installation or should I start messing with the tranfer graphs in ppi. it seems like ppi sets the keys right but the stroke of the ductor we have to cut in half

 

[janezl]

Talking of ink film thickness on the press, coming down to the plate, looking at historic development, presses could initially only regulate it by regulating the speed of ductor. Later on, possibility to regulate ink thickness zonally was added by manual and later servo driven ink keys.
Fact with modern presses: ink film thickness is regulated with combination of ductor speed and ink key opening.
On the market, there are different printing inks (pigmentation, rheology...) and printing substrates available.
Basic interaction between ink and paper can be observed by ink thickness remaining on the paper. Depending of area covered on the (flat) sheet, corresponding film thickness on (round) rollers, should be provided, to provide even ink film thickness everywhere on paper.
This interaction is not linear. It is defined by so called characteristic curve initially available in CPC 1-04 and later on in CP2000 and Prinect Press Center with much more options (database of characteristic curves, ColorAssistant option for automatic creation/editing of characteristic curves).
Short answer for you: instead of reducing ductor speed, you could close ink zones.
Proper answer: talk to your local Heidelberg on Print Color Management service. One of the activities, provided is also setting correct characteristic curve, which will correspond to your ink/paper/press combination.
Prior to that, take your time and read documentation/presentation from: Heidelberg - Color and Quality

Janez

PS.: You know, that you can define different paper qualities in the MetaDimension PrintManager Administration/Resources/Printing materials. By entering not only name and dimension (for creeping in Signa and press feeder setup) but also paper type (ISO 12647 style: PT1 glossy coated...). MDS enables transfer of this data from MD to Prinect Signa and Printready/PrepressManager. After you chose in Signa proper material, this information will travel back to MD, which can be effectively used for choosing proper calibration in Calibration manager. It will be written to CIP3 and travel through PPI and PresetLink/InstantGate (not Job memory card) to CP2000/Press Center, which will automatically select characteristic curve for chosen ink/paper combination.

 

[rbailleu]

thank you for the response. very nice. They said it would be very close. and the key setting were, but I had to cut the ductor number in half 57 % to be exact. I did finally just reduce the characteristic curve by 57% and that hit the mark. in press console of course. this seems like a big reduction to me. so why if it is a newish 2003 heidelberg press. a new ppi, a new meta, etc. is the setting this far off.

we ran our first job with the new setting and did not touch the console after loading the settings by the way. 5000 sheets. the pressman was singing a happy tune, and so was I. 5000 impression no changes. usually on a rush job he is just putting plates on when I get the paper to him. this time I get 1000 sheets cut and he is loading the paper already. by the time I get the rest of the paper cut he has 500 off. you have to love automation.

 

[janezl]

You wrote: so why if it is a newish 2003 heidelberg press...

Press came with built in curve, that was valid for ink/paper combination, that Heidelberg used in Germany in that production year, for you rough guess.
I am not pressman, but I happened to do some tests of different inks on IGT printability tester (per ISO 2846). Same amount of different ink on same type of paper, gave me very different results. No way to predict in advance, should you overall increase/reduce curve, or you had to change its shape. Only proper test upon proper methodology. Your goal should be to use 200 sheets of blank paper for press setup, achieving deltaE <5.

Janez

 

[rbailleu]

57% just seemed like a large move to me. I would not think we would need to make this big of a correction. I guess I was wondering what the average move that other people made.