ink/water balance

[Deleted member 16349]

I've worked on quite a few webpresses, all lithographic and all big. To me, what you speak of is so far fetched it demands an explaination.

Your points about all the issues related to heatset etc. are very valid. My comment about 50 impressions basically starts from when the printing of the paper starts. It is OK if you think it is far fetched, that is actually good because if most think something is not possible then those that try to make a change can potentially benefit. No one succeeded by saying something can't be done.

It seems to me that your concern is that getting to colour so soon is just not possible for the press. Well think of your own press. It is running along nicely.

Why is the next impression basically the same as the one before?

Is it far fetched to think that consecutive impressions should print very similarly on your press?

Of course they will print the same because the conditions in the press and on the plate were right for the next impression to be similar.

Have a press that can preset those conditions and maintain them at the start and you will print close to the desired colour on the first couple of impressions and very quickly it will converge to the target values.

Other printing processes can have very short startups getting ink to paper. You mentioned letter press. There is also Flexo, Gravure and inkjet and anilox waterless ink systems such as Karat, Genius and conventional lithographic anilox systems such a Anicolor.

You comment about large presses and their difference to smaller presses. Yes there are differences but large presses do not print any more ink per length of paper than small presses. Large presses are large basically because they are wider.

Large presses do have more ink storage on their roller trains than small presses, which would suggest that they are slower to respond. That would take more paper. This is true. But 50 impressions is more paper on a large press than on a small press due to the repeat length difference. It is kind of relative.

I have done computer simulations of a web press at a change over from a high coverage to a low coverage. In the simulation the blanket and plate were cleaned. At the start up the press was within tolerance well before the 50 impressions.

One might say that a computer simulation is not a real press. I say, modify the press so it runs like the simulation. Mathematically definable.

 

[blazini]

Like I said, the 50 impressions thing doesn't exist in my world, but I'll play anyway

Why is the next impression basically the same as the one before?

Because nothing changed. The coverage along the circumference of the plate for each particular key zone is exactly the same. The roller train is at temp and the ink is fluid. plate cylinder temp is stable and dampening system is set to run at this speed.

Have a press that can preset those conditions and maintain them at the start and you will print close to the desired colour on the first couple of impressions and very quickly it will converge to the target values.

Well I thought we were talking about my existing press, now we're introducing a theoretical press. Either way, can it predict the difference in the surface temp of all of the rollers in the ink train when I just went from a job I ran on offset paper at 70,000iph to a coated paper job that I will makeready at 20,000iph? I already have temp controlled vibrators but a speed difference that great and the rubber will run cooler regardless. That's gonna change the fluidity of the ink, can it possibly account for this alone? If so does it know that I just ran low lack black in my first unit to stop the offset from picking and now am running regular tack black? Lord forbid if the rollers aren't set 100% correct. This new system is going to have to make alot of assumptions already, I'd hate to have to tell it that I'm running 872 gold in the unit I usually use for yellow. This is why automatic presets aren't even close now. It's not that the systems can't accurately read coverage, it's because there's entirely too many variables. By the time you weed out all those variables it's not offset litho anymore.

Other printing processes can have very short startups getting ink to paper. You mentioned letter press. There is also Flexo, Gravure and inkjet and anilox waterless ink systems such as Karat, Genius and conventional lithographic anilox systems such a Anicolor.

Well the first couple processes you mention are completely apples to oranges. A doctor blade totally negates the use of presetting period. There's no need for adjustment when there's no adjustabillity. The latter are sheetfed presses, can they pull this off at the speeds that a modern webpress will see? Once again, I thought we were talking about an existing commercial webpress.

You comment about large presses and their difference to smaller presses. Yes there are differences but large presses do not print any more ink per length of paper than small presses. Large presses are large basically because they are wider.

And with a wider web litho press comes register issues. Does it matter if I can get up to color in 50 impressions if my assistant can't get it in register in 50? The newest closed loop register can't cock a plate cylinder or bustle the web.

I have done computer simulations of a web press at a change over from a high coverage to a low coverage. In the simulation the blanket and plate were cleaned. At the start up the press was within tolerance well before the 50 impressions.

What press is this? Is this a 2 vibrator/ 2 ink form newspaper press, or a 3 vibrator 3 form commercial press? Going from solid coverage nearly the size of the cutoff to a couple lines of small type doesn't happen in 50 imps on a newspaper press let alone a commercial. Want color with no waste? rinse the inker and turn the ink feed on before the forms. But how good was the preset on that fountain, and did I run that ink feed for just the right amount of time? Now I just killed time washing the inker. Paper is (relatively) cheap, time is money. That's why they buy faster presses and love to see them run fast.

Say a unit just scummed out and it took me 1 minute to catch/fix it. At 1000fpm I just threw out 500 impressions. at 2000fpm I threw out 1000 impressions. That's assuming I caught it in the same amount of time cuz now I'm twice as busy. Do you think they want me to run 1000fpm, or would they rather me run at 2000fpm? Once again, does color in 50 impressions mean anything to a commercial webpress?

 

[Deleted member 16349]

Like I said, the 50 impressions thing doesn't exist in my world, but I'll play anyway

Because nothing changed. The coverage along the circumference of the plate for each particular key zone is exactly the same. The roller train is at temp and the ink is fluid. plate cylinder temp is stable and dampening system is set to run at this speed.

Nothing has changed? Are you kidding? On each cycle ink has come off the blanket and plate and has to be reapplied within one rotation. That is not a simple and smooth continuous process.

If you have a presettable method to apply the ink to the plate that satisfies the desired condition, then one has the capability to have very short makereadies. You don't know what is required and I believe I do.

I have never said that your press, in its present condition, can do this. Presses would have to be modified.

You have lots of experience with the problems in offset. Do you want to have those problems removed from the process or do you just like to talk about how you have to deal with them?

I would like to remove those problems and I have wanted to find other parties that would too. Press manufacturers are one major group that should be interested and could take action but so far they have not. It is not about the amount of investment because they were not interested in doing things when times were good. It is an attitude problem. They seemed to think they could sell printers that same press concept without the printers expecting more. If you believe that major improvements can not be made, it makes it so much easier for suppliers to meet that expectation.

I am trying to change that expectation. Ink water balance is the critical problem. I say the density variation problem related to it can be eliminated. You believe it can't. I don't think I can change your mind and will not try. Maybe some day you will change your view. We have to wait to see what happens in the future.

 

[Green Printer]

I can take the same press and ink and just change fountain solution and see ink density changes of up to 50%. Just by changing the ink fountain stroke I can change the density to meet density requirements. So ink transfer must also be a function of fountain solution and the subsequent ink water emulsion made and its ability to wet transfer from ink form to plate to blanket to substrate.

 

[Deleted member 16349]

I can take the same press and ink and just change fountain solution and see ink density changes of up to 50%. Just by changing the ink fountain stroke I can change the density to meet density requirements. So ink transfer must also be a function of fountain solution and the subsequent ink water emulsion made and its ability to wet transfer from ink form to plate to blanket to substrate.

Yes, your observations are right but the conclusions are not exactly right.

Changing fountain solution can change ink transfer to the substrate but what it also can change is ink transfer from the ink fountain roller to the high speed press rollers of the press. To determine if the change in fountain solutions has a permanent change in ink transfer to the substrate, one needs to make the ink transfer into the press independent of fountain solution.

One needs to look at the ink transfer question in the context of the whole process.

At steady state conditions, on average the ink transfer from the ink fountain into the press equals the ink transfer from the form rollers to the plate and equals the ink transfer from the plate to the blanket and equals the ink transfer from the blanket to the substrate.

If you have a diagram of the roller train and draw horizontal lines across the system (roller train) the ink transfer across all of those lines will be the same on average. If they would not be, there would be a continuous build up of ink between any set of lines.

If you have a system such as with conventional presses where the ink feed is not consistent then the ink transfer across all of those lines will not be consistent. On the other hand if you do have an ink feed that is consistent and independent of other variables, such as with a positive ink feed, then the ink transfer across any of those lines will also be consistent, on average.

Steady state problems are different than transient problems. If one does not solve the steady state problem, it is much harder to understand and solve the transient ones. Ink transfer due to changes in temperature, water, speed, etc are transient issues. Understanding the steady state issues requires looking at the whole system and not isolated phenomena in a particular location.

Observations are not explanations. Valid explanations should lead to better approaches. Hopefully.

 

[Green Printer]

I quit it isn't worth the time.

 

[Al Ferrari]

Perhaps you are not really interested in understanding the factors involved.

Al

 

[blazini]

Nothing has changed? Are you kidding? On each cycle ink has come off the blanket and plate and has to be reapplied within one rotation. That is not a simple and smooth continuous process.

If you have a presettable method to apply the ink to the plate that satisfies the desired condition, then one has the capability to have very short makereadies. You don't know what is required and I believe I do.

I have never said that your press, in its present condition, can do this. Presses would have to be modified.

You have lots of experience with the problems in offset. Do you want to have those problems removed from the process or do you just like to talk about how you have to deal with them?

I would like to remove those problems and I have wanted to find other parties that would too. Press manufacturers are one major group that should be interested and could take action but so far they have not. It is not about the amount of investment because they were not interested in doing things when times were good. It is an attitude problem. They seemed to think they could sell printers that same press concept without the printers expecting more. If you believe that major improvements can not be made, it makes it so much easier for suppliers to meet that expectation.

I am trying to change that expectation. Ink water balance is the critical problem. I say the density variation problem related to it can be eliminated. You believe it can't. I don't think I can change your mind and will not try. Maybe some day you will change your view. We have to wait to see what happens in the future.

I think you have far too many theories, you need to spend more time in a pressroom and add some practical knowledge to those theories. I figured you were selling something by the way you completely ignore certain points and dwell on changing the minds of printers. How is it you are going to solve my problems when none of them relate to the ink feed? Like I said I can already bring the press "up to color" in less impressions than it takes to set everything else up, so what are you going to do for me? What will it do for sheetfed printing when existing systems that you yourself mentioned can already do it faster?

 

[Deleted member 16349]

I think you have far too many theories, you need to spend more time in a pressroom and add some practical knowledge to those theories.

Maybe that would be good to do.

Sorry I can't help with all your other problems. The topic was ink/water balance and that is what I am interested in. Let's see if history supports my theories or your experience as being a better guide.

 

[BeauchampT]

Well, that got heated. Let's suffice it to say that we've come a long way from greasy crayons and limestone.

And we've got a lot further to go - while press variables are an issue, so much of ink/water balance is at the mercy of our ink suppliers. I firmly believe one thing that the entire printing industry needs is to get better educated about ink formulation and exactly what ink companies are using as their approach.

Take the press I work on: the ink we use works wonderfully at makeready speeds, but when you get to higher speeds, (800+ m/min) all sorts of oddity breaks loose - trapping issues, dot gain curves that I can only describe as malformed, and so forth. Nothing that makes running impossible - we run quite stable; all the same, it makes matching proofs and running to a standard quite interesting.

Where can we (actually, more specifically, I) start to grow in our understanding of these chemical complexities??

 

[blazini]

While it's great to know as much as you possibly can, I think the question is "What good will that knowledge do for you?" Ink, fountain solution, and paper are all consumable materials. Where they come from is a business decision. I'm sure every place is different but in my case when those materials cause more downtime and waste outweigh the cost/convenience of using those materials, then they will change. Personally I don't get paid for my chemistry skills , I get paid to run a press. I care to know only as much as I need to. You may be a printing chemical guru but does your company care when all is said and done it's still cheaper to use what they use?

For example, my company buys ink from a certain supplier because that one supplier can supply all of the plants with ink. I believe the fountain solution is the same deal, but it's a different supplier. The fountain solution wasn't specifically formulated to work with that ink but it was "tested" to work well enough on every press in the plant with that ink. The problem is that sometimes my press will form "dahlgren streaks" in screens. So now we run the same fountain solution out of a different supply with an alcohol substitute mixed in. The problem with the alcohol sub is that it causes counter-etching of the downstream plates when running a metallic. Another press will completely lose cyan screens out of nowhere running the same ink and fountain solution the rest of the presses do. My secret solution is that I found an old stash of cyan ink from a different supplier we tested a while ago. The only explaination I have is that it's a stronger bodied ink. The older guys still wonder how I killed them on those jobs they couldn't run on that press. The best solution is to use what works on each press, but that's not convenient or cheap, so it doesn't matter.

When I have an issue that I don't think is related to the press itself, I have a certain amount of time to play around before my supervisor starts asking questions. I've been know to make magic soup in an ink fountain once in a while. On a press that runs brush dampening there's no lateral control over the water, it's either up or down. If it starts to emulsify on one side and catch-up on the other, I know that putting a certain reducing oil in the ink will give me a wider ink/water window. Now I can run the press faster and produce better quality work, when all I did was find a jug of stuff and use it outside of it's intended purpose. I like to experiment, but I try not to get caught up in the hows or the whys.

 

[Ajax]

"all I did was find a jug of stuff and use it outside of it's intended purpose"

What was your jug of stuff?

 

[Richard]

You want just enough ink transferred for each sheet that passes. Set the dampener(s)correctly, thats it! Follow the fundamentals of setting an ink fountain: keys low, rotation variable. I have run alcohol and non alcohol damperning systems, they are both wet.
It is always good to work with a boss who has limited knowlege of lithography, they always see things from a simple logic point of view that is helpful. Put the stock in, water, and ink, and switch the machine on, as fast as you can.

 

[BeauchampT]

Legitimate....We don't need to know more than necessary to run a press. My particular plant essentially only runs one type of job and we try to perfect it to maximize production. So it is kind of unique to my job to try and know as much as possible so as to create better and more uniform results.

Frankly, I experiment too. But playing with a random "jug" of chemicals will eventually have limited results. End of day, if you want to achieve a high quality level with low waste you need to know what to ask your management for - if I need a better plate, I prove it and show it and ask for better supplies; if the ink sucks, I prove it and while I make it runnable I still keep asking for changes to the formulation.

I suppose messing with chemistry really depends on what you are producing. I assume that for the majority, constant changes in paper, ink, etc due to customer demands just requires flexibility. IMO though, this concept of 'just make it work' perpetuates the idea that ink/water balance is an 'art' and not a legitimate science.

Hope that didn't come out too harshly, but more knowledge will NEVER hurt anyone.

 

[Richard]

Lets get back to what this discussion started as: " How do you know you have the correct water balance?" Well, if doesn't look right, and you think it is because of dampening issues, than fix it. It is not an ART to have correct water balance,it is more of a juggling ACT.I can't afford an expensive device to measure conductuity, and PH. Use distilled water and have a reliable source on a regular basis. Practice the accepted printing realities of minimum ink, minumum water, and minimum pressure.

 

[WLprinter]

rogue unit

rogue unit

Hi,

We are experiencing a rather nasty problem which we cannot over come.
History: 5 colour CD UV press 2001 – all running well. Last week we put a sealer in unit 5the yellow unit. Since then blue on unit 4 is creeping forwards and contamination the yellow. We have change the rollers in unit 5, changed the water even though it cannot be that as all other units working well. We have swapped over motors. Changed blankets. All unit rollers heaters seem to be working ok. Nothing has worked so any ideas please.

We are not sure if it is just a coincidence with that we ran the sealer.
Could it unit 5 that is wrong or unit 4 as everything in unit 5 seems ok.
Any help appreciated.

Regards T

 

[D Ink Man]

Ask your inkmaker for a 20% stronger cyan or add 30% transparent white, extender to your yellow. The back trap should go away and you can decide on a long term plan for prevention. This will work.

 

[WLprinter]

Hi. We think the ink is ok as if we move back 1 unit and keep the sequence the same we dont the problem.
Regards t

 

[tmiller_iluvprinting]

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

Hi Gordo,
Of these nine scenarios, which scenarios would possibly contribute to low dot gain? Thank you.
Regards,
Todd

 

[gordo]

Hi Gordo,
Of these nine scenarios, which scenarios would possibly contribute to low dot gain? Thank you.
Regards,
Todd

What does your experience suggest?

Best Gordo