Dot gain / TVI variation...

[Disappointed]

Hi all,

Considering the following....

Same paper,
same press speed,
same ink set,
same plate manuf,
same blankets

what sort of variation in TVI would you expect to see from job to job on a press?

I am guessing at it being very low <1-2% ???

Dave

 

[gordo]

But different day and different job.

+/- up to 3%

gordon p

 

[HachiZenki]

Don't forget the environmental factors as well. Is it hot and dry, humid, raining, cold, etc. will all affect your paper.

 

[J]

Day shift vs night shift.
Did the pressman have an argument with his wife that morning?

J

 

[printnewb]

Day shift vs night shift.
Did the pressman have an argument with his wife that morning?

J

Lol. Too many variables.

 

[Disappointed]

I can get rid of more variables...

Its in an air conditioned room so temp never varies, 22 degrees C 24/7,
Only one operator - me,
single day shift, same hours each day, mon-fri,
jobs are very similar as its a catalogue and all pages are similar,

any more??

Dave

 

[HachiZenki]

I can get rid of more variables...

Its in an air conditioned room so temp never varies, 22 degrees C 24/7,
Only one operator - me,
single day shift, same hours each day, mon-fri,
jobs are very similar as its a catalogue and all pages are similar,

any more??

Dave

Humidity also matters as it affects your paper. How long has that paper been sitting around? Have you given it time to normalize with the ambient conditions or did you use it right away after it's been delivered? Also time of year will affect your paper if you have a fast inventory turnover for paper because the wood pulp with be different from the summer harvest as opposed to the winter/spring harvest.

 

[Luther]

All things being equal or same ...start looking at the ink train chiller (settings and performance) and the cooling of the fountain solution.

 

[printnewb]

I can get rid of more variables...

Its in an air conditioned room so temp never varies, 22 degrees C 24/7,
Only one operator - me,
single day shift, same hours each day, mon-fri,
jobs are very similar as its a catalogue and all pages are similar,

any more??

Dave

If you are the press operator, that covers most of the variables.

 

[Disappointed]

Hi

all paper is stored in the press-room for a minimum of 24 hours before use, there is no fount solution, this is waterless printing, presume that the paper all came from the same pallet.

I am not looking for a cause or area to look in yet , i am merely trying to ascertain what a normal TVI variation between similar jobs would be.


Dave

 

[HachiZenki]

Well we use rolls that average 325 kg so to let them normalize you gotta let them sit for a lot more than 24 hours.

 

[Disappointed]

We're sheetfed. When i said 24hrs, thats an absolute minimum, usually 2-3 days.

Dave

 

[has-been]

Dissapointed:

You probably just gave the answer - waterless. 1 degree change in ink chiller can make a difference with some colours.

Was you gain in specific colours?

 

[has-been]

Dissapointed:

Sorry, I must have had a seniors moment.

There is one variable that you should consider.
Obviously a wash-up has taken place between the runs. It is possible for this to be a cause in the tonal change.
Most printers do not understand the problems that some press washes can cause.

Re-examine the printed work and see if the biggest change has ocurred in the magenta dots as this is the first ink affected by some washes. (Actually it happens with the yellow too -but you will have trouble seeing it.

hasbeen

 

[1Pressman]

TVI variations

TVI variations

Hi

all paper is stored in the press-room for a minimum of 24 hours before use, there is no fount solution, this is waterless printing, presume that the paper all came from the same pallet.

I am not looking for a cause or area to look in yet , i am merely trying to ascertain what a normal TVI variation between similar jobs would be.


Dave

What is the time lag?
Could be roller condition(durometer, contamination, settings) New good quality rollers will always print better then old or cheap rollers.
Clean versus dirty fountain solution is another possibility.
Plate processor just cleaned or old chemistry???
SOOO many variables!!!!
A 1-2% variation can be easily matched to proof via slight ink density adjustments. That is what is done on a daily basis through out the industry.
John

 

[eman]

dot gain/tvi

dot gain/tvi

3-4 percent

 

[danremaley]

dot gain

dot gain

The standard deviation for a sheetfed press is +/- 2% dot gain. With a +/- 4% color can still be ok as long as the gains are balanced, both lighter or heavier. The problem comes when Mag goes up and the cyan the same - or down - grey balance shifts and the color is off.
Felix Brunner says 80% of color problems on press are dot related. Only 20% of the problems are ink density related. So what does all the major press manufacturers measure?
20% of the problem!!! System Brunner, opens and closes the ink keys based on grey balance, best system in the world.
Dan Remaley
412.889.7643

 

[gordo]

Felix Brunner says 80% of color problems on press are dot related. Only 20% of the problems are ink density related. So what does all the major press manufacturers measure?
20% of the problem!!! System Brunner, opens and closes the ink keys based on grey balance, best system in the world.
Dan Remaley
412.889.7643

System Brunner does not measure color - it measures density.
Images do not have an intrinsic grey balance. Grey balance, or lack thereof, in the color bar is not an indicator of the correctness of the color in the live image area.

IMHO, as long as it measures a proxy and not the actual live image area it cannot be the best system in the world. We should be measuring what is being manufactured and delivered rather than something that will end up in the recycling bin.

But this issue has been covered several times already in this forum.


best, gordon p

 

[Disappointed]

Now we're getting somewhere, thanks.

It is a waterless DI press, so no plate or fount chemistry to worry about. The time lag is between jobs so anything from 30 mins to a couple of hours, no wash-ups as its all in the same day.

I have measured a wedge of 20 consecutive sheets within a job too and the variation is still there, it runs about 8% swing which is very noticeable, rollers and duct are temp controlled, room is temp controlled.

This is a change in behaviour as for the first six months of its life the press could not be faulted at all, 100% impressed. After that we have had trupble maintaing colour so we installed some measuring software and now monitor the 25/50/75% patches on all jobs and log the results, there is very little pattern to it. One job could have low cyan gain, the next could have high yellow, the next could have high magenta and low black, it goes on and on.

We cant pinpoint an event that triggered this. It has had new rollers.

Dave

 

[Deleted member 16349]

Now we're getting somewhere, thanks.

It is a waterless DI press, so no plate or fount chemistry to worry about. The time lag is between jobs so anything from 30 mins to a couple of hours, no wash-ups as its all in the same day.

I have measured a wedge of 20 consecutive sheets within a job too and the variation is still there, it runs about 8% swing which is very noticeable, rollers and duct are temp controlled, room is temp controlled.

This is a change in behaviour as for the first six months of its life the press could not be faulted at all, 100% impressed. After that we have had trupble maintaing colour so we installed some measuring software and now monitor the 25/50/75% patches on all jobs and log the results, there is very little pattern to it. One job could have low cyan gain, the next could have high yellow, the next could have high magenta and low black, it goes on and on.

We cant pinpoint an event that triggered this. It has had new rollers.

Dave

Dave,

Is it possible that you are doubling. One can get doubling between the plate and blanket. If possibly the plates are moving while the press is running, that could cause doubling and would show up as extra dot gain.

Is your difference in dot gain consistent for the run or does it change during the run?

Just an idea.