dotgain on highlight area not on shadow

[aymantu]

facing a problem with dotgain on cyan tower with roland 700 press where
dotgain is high from 0% to 50% and it is normal from 55% till 99%
as compared to ISO TVI

hope anyone has an explanation

 

[rstirpe]

dot gain in highlights

dot gain in highlights

Have you examined the plate prior to printing?

Have you turned the subsequent unit impressions off to see if conditions are the same

 

[Lukas Engqvist]

Do the curves look normal?

 

[aymantu]

hi

the plate is 100% linear
the press operator tried to lower the pressure between the plate and balnket cylinder ,and increased the pressure between blanket and paper but stil same result

the curve look normal but if look at the result in comparison with ISO TVI paper 1 and 2 the result is high dot gain on highlights.

 

[Lukas Engqvist]

This is a limit of linear plates. I would not strive after a linear plate. It is like trying to shoot an arrow at a target than must go through a noose half way to the target.
You have checked for slurring, and confirmed that you do not have corona effect on your dots?
It could be a "soft" focus on your plate, meaning that you are measuring the dot gain on plate, and then proximity of the dot is picking up ink. (Check your inked in plates to see if they are still linear) Could be your blankets. Are the dots sharp or blurred? Do you have any one else with the same/similar setup? Plates, blankets, press, ink, fount solution?
Have you had a good curve and it is now, without changing properties of the plate become this way?
Could be contamination of rollers…*(as prepress person I don't know the terminology for it)

I would add a TVI curve (actually I don't even believe in linear plates) to make the compensation so that the substrate has the target TVI.

 

[rapid3]

What dampening system is on the press? If it's an 'Epic Delta'
style system, your problem could be with that.

Regards

 

[Bob Peterson]

Has this always been an issue with the cyan? If not, have you changed to a different set of inks? If you haven't changed inks I would check the lot number on your cyan ink and see if you have a different lot and see if the problem still exists. If the problem goes away with a different lot the problem is with the body of the ink.

Here is some info pertaining to ink and how it effects dot gain providing the plate, press, and chemistry are all in order:

1.) 0-35% Dot is affected by the body / viscosity of the ink. For example, if the body is too soft the highlight area will print full causing you to decrease the density to reduce the dot size. Or is the body is too heavy the dot will be too sharp causing you to increase the density or blanket pressure.

2.) 35-65% dot area is effected by the strength of the ink. If the ink is too weak the mid-tones will print too full and if too strong they will print too sharp. Also, the strength of the ink will also affect how well the inks trap.

3.) 65-95% is almost always affected by mechanical induced or chemistry i.e. (poor ink water balance). However, ink water balance can be controlled by the body & strength of the ink. Therefore, if both body & strength are proportioned correctly so that items 1 & 2 above are evenly balanced. The gain is usually caused by running excessive water, too much blanket pressure, mechanical slur, and/or paper stretch.

I highly recommend getting away from printing with a linear curve. You will have much better control over your print quality using individual plate curves for each color providing all of your consumables are within spec and the press is set up correctly.

Regards
Bob

 

[inkinveins]

I would add a TVI curve (actually I don't even believe in linear plates) to make the compensation so that the substrate has the target TVI.

I think the only true standard is linear, It is the only way plates can be output on a level playing field, beyond that it is only consumables. It is my belief that we are going backwards trying to curve plates to accomodate an unlimited array of consumables and substrates to acheive the almighty unrealistic GB.

 

[gordo]

I think the only true standard is linear, It is the only way plates can be output on a level playing field, beyond that it is only consumables. It is my belief that we are going backwards trying to curve plates to accomodate an unlimited array of consumables and substrates to acheive the almighty unrealistic GB.

The purpose of applying curves (including linearization curves) to plates is to align presswork tone reproduction to a standard. Plates have always been curved - even in a film workflow.

Curving plates to achieve grey balance, as you suggest, may be problematic.

best, gordon p