ink/water balance

[jbeniston]

The simplest and most practical method is to adapt the one described by Albert Noel

[Erik Nikkanen]

Originally Posted by gordo

Ink is designed to take up a certain amount of fountain solution (water).
Too much water - solid ink densities drop, solids become orange peel looking, dot edges or other hard ink/non ink transitions become soft or fuzzy, small areas of ink ma wash away/go blind, trapping is poor
Not enough water - the non-image area of the plate will start to take ink resulting in scumming in the presswork.
Solids and dots in your color bar or live image areas as well as non-printing areas are what you use to check ink/water balance.

It's a bit more complicated since there are 9 different combinations possible:
1 Not enough ink, not enough water
2 Not enough ink, water just right
3 Not enough ink, too much water
4 Ink just right, not enough water
5 Ink just right, water just right
6 Ink just right, too much water
7 Too much ink, too much water
8 Too much ink, water just right
9 Too much ink, not enough water

best, gordo

What Gordon has stated is basically true for the existing conditions of offset presses but it does not have to be as complicated as what exists now. The 9 combinations is not the basic problem but the fact that on existing presses the adjustment of either ink or water will affect the other. It is the effort to balance the two interrelated variables of ink and water that is the big problem.

In Gordon's example he states that too much water will result in solid ink densities dropping. This condition is not directly related to the chemistry of the ink or the water but to the design of the press. The increase in water affects the ink feed into the roller train at the ductor resulting in the change of density on the sheet. The interrelationship of the ink and water can be broken by providing a positive ink feed that is not affected by changes in the water on the roller train. When this is done, you can not wash the density out, even with very high water settings.

For the lithographic process to work, the ink and water must be emulsified. The percentage of emulsification on press goes way past the laboratory water take up percentage and it requires to be higher so that some of the water can come out of the super emulsified ink as free water. This free water is then available to wet the plate.

If one can have a positive ink feed as is possible with my Ink Transfer Blade (ITB) technology or any other properly designed positive ink feed system, then the adjustment of ink and water are made independent of each other. This greatly simplifies the problem with the interrelated 9 combinations.

With the positive ink feed, one sets the ink for the desired density and one sets the water feed to obtain the desired quality of print. Adjusting the water up or down will have virtually no affect on the density. Changing press speed will have no affect on density. Starting up after a long stop will have no affect on print density. Changes in press temperature will have no affect on the print density.

One will find that the water window is much greater than thought possible. This does not suggest that one should run with lots of water but it becomes less critical and much easier to set to the desired level since it will have no affect on print density.

The conventional ductor, which is on almost all modern presses, has been on presses for over 150 years. It is the fundamental cause of the ink water balancing problem and average steady state density variation. The reason for ink water balancing problems to still exist is because the technology that causes it is still used. Change the technology and the performance will change.

[Al Ferrari]

"For the lithographic process to work, the ink and water must be emulsified. The percentage of emulsification on press goes way past the laboratory water take up percentage and it requires to be higher so that some of the water can come out of the super emulsified ink as free water. This free water is then available to wet the plate."

Hi Erik,

Can you please explain why this emulsification is necessary? After all, except on integrated dampening systems, there already is a water form roller supplying water to the non image areas of the plate surface.

Thanks,

Al

[Erik Nikkanen]

Originally Posted by Al Ferrari

"For the lithographic process to work, the ink and water must be emulsified. The percentage of emulsification on press goes way past the laboratory water take up percentage and it requires to be higher so that some of the water can come out of the super emulsified ink as free water. This free water is then available to wet the plate."

Hi Erik,

Can you please explain why this emulsification is necessary? After all, except on integrated dampening systems, there already is a water form roller supplying water to the non image areas of the plate surface.

Thanks,

Al

Al,

Even with a separate water form that wets the plate directly, the ink will still get emulsified. It will pick up the water from the plate and work it into the ink on the roller train. Having water worked into the ink can not be avoided. In the case of the separate water form method, the word "necessary" might not be totally correct but the emulsification is unavoidable.

For the lithographic process, which is mainly the separation of the inking of image areas from non image areas, water can be introduced into the system at any point. It can be introduced directly to the plate with the separate water form as you have stated or with water going to the first form roller by a dampening roller or sprayed into the roller train a bit higher up or even premixed into the ink in the ink fountain. With all the other methods emusification is necessary.

Each of these methods of introducing water has its own requirements and issues. My personal view is that introducing the water right at the plate or on the first form roller is difficult because the application is sensitive. The water film needs to be very well controlled and there is less time for water to be worked into the ink evenly and this may tend to cause print problems.

My preference is to apply the water higher up in the press, which gives it time to be worked into the ink more evenly. But to do this well requires a positive ink feed that will not have the ink feed be affected by the water being applied up so high in the roller train. Much less costly and less sensitive methods of applying water can be developed for this approach.

From reports and technical papers on these other methods ( single fluid ink; water-in-ink and spray dampening) to apply water into the system there were very few comments on negative print quality issues but I hear often about problems with the existing dampening systems causing problems with print quality due to mechanical issues which affect the consistency of the water film being applied.

Environmentally I like the idea of applying water higher up in the press. Since it is easier to make it so the fount solution goes one way only and does not return to the supply, there is no issue about maintaining and dumping a tank of solution.

Going to positive ink feed allows other less expensive methods of applying water which will also work better. Of course this will not happen until the industry gets out of its narrow thinking mode.

The view of the need for the ink to be emulsified with water is not my own but is in the literature.

[Neil Meggitt]

Originally Posted by Sfdp2300

Your best bet is when starting a Make ready start out with low water and ink . It is easier to add ink and water than to get ink and water out. Take water out till you scum and then add the water back till the scum cleans up.

The tint line one the lead edge of the plate works well as an indicator. Also if you are picking up the press from another operator and the job is in process of running. Look at all of your plates while running. If your plates look wet and shiny you have to much water. The plates should look dull and flat with no shine in your non image area while you are running.

Assuming all roller settings and fount mix are correct you cannot go wrong with this method. The shine on the plate whilst running is a great indicator and tends to be forgotten by many, everything else comes with experiance and as mentioned the temperature increasing during the day, the press speed, etc are all going to effect the need for dampening changes but the shine on the plate should always look the same.

[Tarun Chopra]

Hi,

In many documents it has been stated that there should be 1mm ink appearing uniformly across the plate width in the lead edge of the plate.... indicating a good ink water balance across the plate.

Experience might prove it correct but the question is why should there be a ink in an area where there should be "No Ink". what actually happens at the lead edge of the plate that the 1mm ink strip is formed (which technically is a non image area) and is not cleaned by dampening solution?

I am confused on this aspect!!!

Thanks

[Alois Senefelder]

Hi Tarum Chopra,

This is due to the "Mechanics of the Press" ---- as the Plate Cyl. rotates it's contacted first by the "Dampening Rollers" which apply an even film of enriched Fountain Solution + Water to the Plate ----- NEXT are the Plate Inkers which come into contact with the Plate, in doing so they "Rupture" the film of water at the "Leading Edge of the Plate" so forming a "SCUM LINE" --- approx 1 mm wide.

ALL ROLLER (INK/ DAMPENING) settings MUST be correct.

Again the "Scum Line" is only a Indication !!!!!!!!!

Regards,

Alois

[erictoray]

Another method to reduce the ink and water ballance issues is to remove the water from the equation!
We at Toray have been producing waterless lithographic plates for over 20 years with many customers having great success with the process. Granted when waterless printing was first introduced there were issues with ink temperature controls and ink suppliers and the simple fact that retrofitting the press was expensive. In todays press market, almost every press over 26" comes with ink temperature control as a standard feature with the press. If not, almost every press manufacturer offers it as an option. Waterless CTP uses the same 830NM thermal devices that conventional "wet" plates are imaged on and use 80% less processing chemicals than conventional plates. Ink suppliers are on top of the waterless offerings and many of them are producing UV waterless inks for plastics and non porous applications as well as traditional stocks.
Over the past 3 years we have seen a large number of printers going with waterless and UV waterless printing in order to not only differentiate themselves but to offer a more environmentally friendly approach to printing by cutting down the waste stream (make ready and liquids) along with VOC reductions.
If anyone would like additional information regarding this, feel free to contact me @ e.friedman@toray-intl.com.

Best regards to all and happy new year

Eric Friedman
No. American Sales Manager; Waterless
Toray International America, Inc.