Shortage of inks

[Evaldas Gu]

Hello all,

I work in a prepress. The part of job after we prepare designs for print, we calculate ink requirement per design (dry weight in gramms). In most cases this works pretty good, but in some cases, the shortage of ink in a print run is 30% and more. For calculation we use a Heidelberg PPI calculator. The most confusion comes when the same design is printed for several times with the same ink quantity, the same print run size and suddenly there is a shortage of ink... Printing on sheetfed Heidelbergs.
Has anyone encountered this? Is there a way to calculate ink requirement more precisely?
What might be the reasons and how much those could influence the shortage.

Thank you in advance.

 

[SteveSuffRIT]

I'm trying to better understgand the request?
You need this information for accounting costing and/or estimating?
Or to mix volume of spot color inks?
I assum it's not an issue for 4/c process (CMYK) becsue these inks are alwasys in available in inventory.
Have you correlated ink consumption with # printed press sheets, including make-ready (MR) and waste, not just good saved sheets?
Can historical data from previous runs be used to predict future ik consumption?

 

[Evaldas Gu]

I'm trying to better understgand the request?
You need this information for accounting costing and/or estimating?
Or to mix volume of spot color inks?
I assum it's not an issue for 4/c process (CMYK) becsue these inks are alwasys in available in inventory.
Have you correlated ink consumption with # printed press sheets, including make-ready (MR) and waste, not just good saved sheets?
Can historical data from previous runs be used to predict future ik consumption?

Yes, we have a CMYK colors available, but are calculating requirements of pantone colors and I want this quantity to be more precise. The requirement is calculated including make ready sheets and waste.
historical data is difficult to obtain. There are small requirements up to few kilogramms and if there are left 100-200 gramms it is not marked anywhere and thrown away, sometimes this waste may be 5% sometimes 20% and more. It is marked only there are shortage for print run up to 10%. It is difficult to solve a problem when not all the variables known, but this is what info I have...

 

[Magnus59]

The formula we learned many years ago was SPANKS
https://prezi.com/7n0-tav-iyu1/ink-mileage/

 

[D Ink Man]

Tried and true method as follows: 8.5 x 11" coated solid sheet will use 30 lbs. for 100,000 impressions That's 93.5 square inches. 8.5 x 11' uncoated solid sheet will use 45 lbs., again 100,000 impressions. You then can calculate any job, coverage based on total square inches and print run length.

Of course these numbers will vary somewhat depending on multiple factors. A couple are paper absorption and ink specific gravity. Don't get hung up on that however.

Using the aforementioned formula will get you where you want to go.

D Ink Man

 

[Evaldas Gu]

And does anyone know a simple way to check received ink quality? As I understand ink mixture received might vary from time to time and this may cause ink consumption to change.
And about SPANKS:
STOCK - we use cardboard as a substrate, in most cases this is not changed for different print runs, and I would like to reject this as a variable
PROCESS - there might be issues with this, the temperature and humidity may change a bit, but in general it is a controlled environment. Can this have a consumption to varry up to 30-50 %?
AREA - As I mentioned berore, this is calculated with Heidelberg PPI software, also may be calculated with ESKO in square milimeters.
NUMBER - usually we print on one side, but anyway, every time we calculate the requirement it is done for every side.
KIND - not sure what that is..
SPECIFIC GRAVITY - is there a way how to determine the specific gravity of one color or another?

 

[Alois Senefelder]

Hello Evaldas,

SALIENT POINTS:


I despair, that people in Pre-press are "Bamboozled" by software programmes !

1) The discrepancy with Ink volume usage is caused by variation in Ink Absorption of the substrate.

2) Your rejection of "Substrate Variation" shows you have a poor understanding of the Paper Making Process.

3) Ink Quality - buy the best you can, and don't go into the "Realms of Fantasy" that you can check Ink Quality!


Regards, Alois

 

[Evaldas Gu]

Hello Evaldas,

SALIENT POINTS:


I despair, that people in Pre-press are "Bamboozled" by software programmes !

1) The discrepancy with Ink volume usage is caused by variation in Ink Absorption of the substrate.

2) Your rejection of "Substrate Variation" shows you have a poor understanding of the Paper Making Process.

3) Ink Quality - buy the best you can, and don't go into the "Realms of Fantasy" that you can check Ink Quality!


Regards, Alois

1. We use software to calculate ink requirement and with 99 cases out of 100 those are correct, besides that, the software is a part of automation process, and I just want to find out, how to improve the results.
2. Yes, I might have a lack of knowledge in paper making process, that's why I'm here, to learn and gain knowledge. So please tell is there a posibility for paper to consume 30 or 50 % more ink during the run? In my practise, there were several cases, where 10+ print runs of 300.000 sheets. In those ink consumption varied for 2-5 % and then, suddenly in one print run of the same size grew to 35 %. All the pallets before print are measured for humidity and temperature, so my question is how to prevent it and is it possible to calculate/ measure for the future to avoid these problems?
3. I do understand that with best inks there are less problems, but in the company I work, this decision is not mine to make. Ofcourse the thing I can do is to advise to change ink supplier

 

[Alois Senefelder]

Hello Evaldas,

Google - Printing Ink Absorption Tests.



Regards, Alois


P. S - Try and visit Paper Mills and Ink Manufacturers

 

[OffsetStorefront]

You guys are being less than helpful...OP has observed a regular variation of 2-5% of ink usage across lots of jobs and then suddenly sees a 35% variation measurement. Are you saying that is normal and to be expected?

 

[Alois Senefelder]

Hello OSF,


Hopefully WE are trying to be "helpful" ------ NO... such a large variation is not normal is the "answer"


Time and Time again when I try and answer the questions posted - the "Pre- Press Brigade" appear to have a poor

knowledge of Lithographic Printing and its every facet.


Regards, Alois