ink/water balance

[bikozak]

Measuring ink/water balance window

Measuring ink/water balance window

You could start by measuring your ink and water window. Some ink and fountain solution combos will give you different results.

Try the suggestion at this site.

 

[BeauchampT]

"Productive" Ink Water Balance

"Productive" Ink Water Balance

I have several ink guys in our pressroom that all seem to have a different philosophy on this topic and I'm hoping to standardize the way the balance is achieved. The most "productive" method so far seems to be to balance everything according to the piling on the blankets. In other words, get the balance and then adjust the water to get the longest stretch without washing the blankets (btw, this is a MAN Lithoman 4 100k/hr doublewide). I appreciate any input from those that work with similar equipment.

I work on a Lithoman 4 as well and have found that the piling approach also works (especially from a productivity standpoint). However, it only works if you approach it from the right viewpoint - piling doesn't always mean a need for more water.

On the press I work on, we will get piling in our 4th unit (yellow) that actually originates from number 2 (cyan). Dropping water in cyan will actually reduce the piling in yellow. It really is a balance of looking at your units VERY closely in order to make intelligent adjustments of your waters, rather than just flooding them with more water.

The rule of thumb I've been using is: if it is reverse piling (non-image), raise water; if it is piling of ink and debris from another unit, lower water in the offending unit. Works quite well.

Also, on the subject of scum lines, etc... On a high speed press like a Lithoman 4, if you allow yourself even a slight scum line, you pile horribly, smash your blanket, and wear your plates fast. I've found that if you have a colour control strip with solid patches, use these as a reference point. If you have just a touch of scum wisping off them, you are at the very bottom of your window.

Then again, this is the perspective of someone using newer equipment; probably doesn't fully apply on older machines.

 

[blazini]

IMO water should be run just above catch up (scum), only going above that to reduce dot gain and sharpen up the image. I learned from some old school printers in both newspaper and commercial web presses. The most important part is when starting the press the first time on a new job. Every press is different in regards to the dampening system and the control you have over the width of the press, but it's the same idea regardless.

Before starting the press, there should be a little ink in the roller train and all waters should be set to scum out, but not wrap up. Once the press is started, water needs to be set *at the units* just until the plate runs clean. Looking at the gloss of a plate is the only way to set water IMHO. A plate should look slightly dull while running, never glossy unless it's been run over a few hundred thousand imps and has polished.

While running I expect to see slight scum once the press heats up and adjust water accordingly. Beyond that I really only raise the water to clean up a screen a little. AFAIC blanket pile is not the way to set dampening rate, with the exception of litho varnish. Ink tack, fountain solution and paper have more to do with that than dampening rate and throwing water at things like that lead to other problems. I will throw water at varnish for blanket pile from time to time since about the only defect varnish is ever really effected by is piled blankets.

 

[BeauchampT]

I agree with you in prinicple, however, not always the case.

For example, some very fine grained plates will look very shiny but still scum. The appearance is decieving. In this case, plate shine is not the ONLY way of setting ink water balance.

Also, piling is very much affected by dampening. In an intergrated dampening system, adding more water to your emulsion will help reduce reverse image piling, improve blanket 'lubrication' (for lack of a better term), keep temperatures lower, and, on the subject of tack, reduces the tack.

After quite a bit of observation, experimentation, etc. I have found that adjusting waters in one unit can help reduce piling in suceeding units (all to do with tack).

There is NO SINGLE approach to setting ink/water balance. Printing is a very complicated science that needs to be adapted to each set of circumstances (i.e. press, materials, product).

 

[Deleted member 16349]

There is NO SINGLE approach to setting ink/water balance. Printing is a very complicated science that needs to be adapted to each set of circumstances (i.e. press, materials, product).

With a positive ink feed, the ink is set and one can adjust the water to fit the various conditions one wants to control. The water levels wont affect the amount of ink printed to the substrate. This could be vary helpful to the press operator.

 

[Green Printer]

Very interesting read. Quite amazing all of the different view points.

 

[Deleted member 16349]

Very interesting read. Quite amazing all of the different view points.

It has always been my view that ink/water balance and its related density variation is THE most critical issue in offset printing. I could be wrong about that but that has been my view.

So understanding it, eliminating it if possible should be of value to printers.

 

[blazini]

I agree with you in prinicple, however, not always the case.

For example, some very fine grained plates will look very shiny but still scum. The appearance is decieving. In this case, plate shine is not the ONLY way of setting ink water balance.

Also, piling is very much affected by dampening. In an intergrated dampening system, adding more water to your emulsion will help reduce reverse image piling, improve blanket 'lubrication' (for lack of a better term), keep temperatures lower, and, on the subject of tack, reduces the tack.

After quite a bit of observation, experimentation, etc. I have found that adjusting waters in one unit can help reduce piling in suceeding units (all to do with tack).

There is NO SINGLE approach to setting ink/water balance. Printing is a very complicated science that needs to be adapted to each set of circumstances (i.e. press, materials, product).

A finer grained plate is still going to shine more with more water, It's just something you would get used to seeing. Even the specific press is going to run a film of water that looks different running the same fountain solution and same plates. In a place that runs 5 different manufacturers commercial webpresses and a few that are the same model yet have had the integrated dampening removed and retrofitted with spray dampening, I still base initial and running ink/water balance on the plate shine. In printing, nothing will be the "only" way of doing something but plate appearance is the most reliable AFAIC.

On the blanket piling scenario I will agree that dampening rate does reduce blanket piling in the non image area but I totally disagreee that more water "reduces ink tack". Fountain solution chemistry itself does affect ink tack, but not dampening rate. Adding water actually increases ink tack by bodying it up on the plate. How do you reduce picking?.....lower the water or reduce the ink tack(by adding oil). At the point that ink actually has lost tack form water, it's been broken down.

"After quite a bit of observation, experimentation, etc. I have found that adjusting waters in one unit can help reduce piling in suceeding units (all to do with tack)." That is actually somewhat correct but it has nothing to do with tack IMO. By adding water to the previous unit you increased the moisture content of the paper before it hit the next unit. On the other hand you just increased the amount of fan out and the register will suffer, how much depends on web width and paper type.

"There is NO SINGLE approach to setting ink/water balance. Printing is a very complicated science that needs to be adapted to each set of circumstances (i.e. press, materials, product)." I agree with that 100%, which is exactly why I take the most complicated part (ink/water balance) and apply the simplest approach. With every upwards push of that water button comes another possible consequence. I know that I could get away with alot more on a narrow 4-color press than I can on the 38" 7-unit presses that I do run. Hitting one web of paper with ink and water 7 times on each side can lead to alot of problems. I make it easy on myself by knowing that I'm not running any more ink or water in any one unit than I need to.

 

[Deleted member 16349]

On the blanket piling scenario I will agree that dampening rate does reduce blanket piling in the non image area but I totally disagreee that more water "reduces ink tack". Fountain solution chemistry itself does affect ink tack, but not dampening rate. Adding water actually increases ink tack by bodying it up on the plate. How do you reduce picking?.....lower the water or reduce the ink tack(by adding oil). At the point that ink actually has lost tack form water, it's been broken down.

Tack of course is not a fluid dynamic property but is a value that one gets from measuring an ink on an Inkometer. Tack is basically related to the force required to split the ink film. Tack is not directly related to the viscosity of the ink.

I have done some tests on an Inkometer with ink and how water affects tack. Running the unit with just ink, the tack is at one level. Add some water and the tack drops a lot but slowly returns to the initial value after the water has evaporated. At least that was what happened when I did a test. Other tests with other inks might show different results.

I have also done tests with a positive ink feed method and the print density was consistent with a normally dry looking plate and a soaking wet plate by just changing only the water feed rate.

There are a lot of interesting and important issues related to this topic

 

[Al Ferrari]

A very unfortunate typo.

I think Erik's next to last sentence ending with "by just changing the only water feed rate." Should instead end with "by just changing only the water feed rate.

Al

 

[Al Ferrari]

What are some examples of commercially available positive ink feed systems?

Al

 

[Deleted member 16349]

What are some examples of commercially available positive ink feed systems?

Al

There are at least two commercially available positive ink feed systems that I know about.

One is the DigiRail by Goss and the other is a system provided by Controls Group Inc. Both systems tend to be used for Newspaper presses which have low viscosity, low strength inks. Both are positive displacement pumping technology for each ink zone.

These systems have replaced the older versions which were called page packs. They have been around for quite some time. These newer systems are sometimes called digital inkers.

There is another system supplied by PPSI in the UK but from what I remember, the concept did not have a positive displacement pump for each ink zone but did have one for the total flow. I would not consider their approach a true positive ink feed concept although I did like it that their system fed ink directly onto the high speed rollers.

The problem with the Goss and CGI concepts is that they apply ink to a slow speed roller similar to an ink fountain roller. This is a problem because it introduces new problems of slow response times and allows more density variation about the average. Not such a problem for long runs and with inks that are weaker such as newspaper inks but it is a problem for higher strength and/or higher viscosity commercial and packaging inks and where very short makereadies are needed.

One of the Goss mottos was, "Set and Forget". Basically they are saying that once set, there is no reason to adjust. There would also be no need to have a closed loop colour control system on a press with a DigiRail system.

Of course I have my own concept, which unlike the Goss and CGI approaches, can be used with high viscosity inks and would cost a tenth of those other systems. I just need a press manufacturer to be interested.

 

[BeauchampT]

On the blanket piling scenario I will agree that dampening rate does reduce blanket piling in the non image area but I totally disagreee that more water "reduces ink tack". Fountain solution chemistry itself does affect ink tack, but not dampening rate. Adding water actually increases ink tack by bodying it up on the plate. How do you reduce picking?.....lower the water or reduce the ink tack(by adding oil). At the point that ink actually has lost tack form water, it's been broken down.

Fair enough. As I commented, this is observation of the press I work on, with the unique chemistry of paper, ink, dampening, and whatever other factors we can think of.

Really, this thread proves more and more to me that a good press operator has to be able to adjust his thinking to whatever new set of circumstances he finds himself in, since every situation leads to different solutions/conclusions.

And IMO, plate shine is definitely the easiest way to take care of your press - I do it every run of every day.

Loving all these comments.

 

[blazini]

One of the Goss mottos was, "Set and Forget". Basically they are saying that once set, there is no reason to adjust. There would also be no need to have a closed loop colour control system on a press with a DigiRail system.

The company I work for sent some people from an insert plant to the plant I work in for training (long story). I worked with a supervisor and lead operator. They were telling me about the "closed loop color" that was installed on one of the Goss presses they work on. Apparently they didn't know the difference between the separate Goss Digirail and closed loop control, they just referred to the whole thing as "closed loop color". I had to show them 4 presses with traditional closed loop color setups before they understood the difference. Anyway point being there is some installations being made with Digirail being controlled by closed loop. I'm not sure how Goss markets Digirail itself tho.

 

[Deleted member 16349]

Anyway point being there is some installations being made with Digirail being controlled by closed loop. I'm not sure how Goss markets Digirail itself tho.

Blazini,

This is very interesting and thanks very much for your comments. I have asked in the past for feedback about people's experience with Digirail but there were no direct responses.

Having an accurate ink feed device like the Digirail and a closed loop colour control system is problematic. I am an engineer and I know something about control theory and this is why I say there would be a problem with combining those technologies.

When a device like the Digirail is applying ink to the slow roller where there is a continuous ductor taking the ink away, this sets up a situation where the slow roller acts like a very large ink storage device. The ink transfer point between the slow roller and the continuous ductor, transfers ink related to the ink film thickness on the slow roller plus the transfer is affected by factors such as changes in water, press speed and temperature.

The transfer variations are only temporary since the long term ink transfer is directly related to the positive ink feed rate of the Digirail. What this means is that this causes very long response times and more variation than if the positive ink feed was directly introduced to the high speed rollers of the press.

Having a system with a slow response and that can have these temporary variation swings will be a real problem for any closed loop colour control system. The problem with any feedback system is that if the Gain, which is basically the magnitude of the correcting signal, is set too high, the system can become unstable and even have violent swings due to over correcting.

So my expectation would be that with a Digirail system that is used with a continuous ductor, the Gain on the closed loop control system would have to be set very low to avoid that unstable situation. On most feedback systems there are at least three gains that can be set. They are referred to as PID. Proportional, Integrative and Differential. I won't go into the details but these have to be tuned to how the physical system works. If these Gains have to be set very low, they really don't do the job that one hoped for them to do.

One useful advantage of having a closed loop control on a Digirail type system is at the start up. Not because the Digirail system but because the ink key (zone) presetting data is not accurate. A closed loop control would help with getting an inaccurate ink key setting to an accurate one but that takes the running of paper to get to the desired result. Wasteful.

Having a closed loop control to address an inaccurate ink key presetting algorithm is IMO technical overkill. Why not just develop an accurate algorithm? It would be much cheaper and would result in less waste since you would start at the right point from the beginning.

If you had a Digirail applying ink properly into the press, with an accurate presetting algorithm, going from one job to another at standard ink densities, you would be up to colour in about 50 impressions and without closed loop control. It would be steady as a rock for the whole run. There is a lot of potential for performance improvement but things have to be done properly. Details matter a lot.

Many issues related to this general problem were presented in my 1997 TAGA paper.

I love this topic. Just wish the industry would too.

 

[blazini]

Eric,

That was slightly over my head but I can't help but get the feeling you come from a sheetfed background. Your comment about "50 impressions" is what makes me say this. From my experience, nothing happens on a web press in 50 impressions. If you were to mount a plate with less coverage and start the press with the ink ball turned off, you still wouldn't run enough ink out of the roller train to bring the density down. I've never worked in sheetfed but I did interview once. I recall the guy telling me the biggest run they get is 5000 sheets. Honestly if I can makeready a commercial webpress in 5000 impressions I did pretty good that day.

I'm no engineer but I work with older GMI Colorquicks on Harris presses with swinging ductors and Man Rolands and Goss presses with newer Quadtechs and continuous ink feeds so I'm pretty familiar with their operation. Personally I can see closed loop color working fine with Digirail on a webpress. For one it you have the head of the closed loop color that scans back and forth checking the density, it scans from operator to gear then moves back to the operator and scans again and that's after it even finds the colorbar which is at least 400-500 impressions. I've never counted but I can't see one scan happening in less than 100 impressions moving at only 700fpm. (the slowest I'll ever makeready a decent webpress). Ink key movements are always relative to the density it scans, but it never moves any single key more than 5% at a time.

That's just to give you an idea of what I look at everyday. The only thing expected to move fast is the paper through the press. The time it takes the micrometric to scrape the excess ink off the ink ball is peanuts compared to the time it takes for the roller train to exhaust itself to the web. On that note an inkball on a press with a continuous ink feed actually tends to run pretty fast anyway.Where press with a swinging ink ductor never actually stops recieving ink from a keyzone that is at it's lowest point you tend to nurse the ink ball speed to keep the ink as low as possible in a low/no coverage zone. A continuous feed press can always have the keys ink film low enough to never touch the ink ball, so you can have that ink ball run much faster. AFAIK they don't even install Digirail on ductor fed systems. The guys I talked to told me that Goss actually retrofitted the press with micrometrics when they installed the Digirail.

In my experience, closed loop color is best used to maintain densities and help achieve a final result. On an older Harris with a GMI, it serves practically no purpose in makereadys. It's too slow to find a color bar and too slow at making corrections. My procedure on these presses is to adjust the presets, start the press, balance the water and shut it off. I look at it, make ink moves start it back up and begin running if it's up to color. At that point I set the GMI into closed loop to fine tune while I'm already running good copy. On a Man Roland which has the best fully segmented, deep pocket ink fountains I've ever seen I turn the Quadtech on from the start but I never expect it to bring the densities in by itself during a makeready. Ill watch the densities on the screen and make the big moves on the ink keys myself for a minute then shut the press down. Make the rest of the colormoves, start the press and begin running with it still in closed loop. In this environment I can easily see Digirail working fine the way it is. Wasteful? Absolutely, but it's what is expected in web printing

 

[Deleted member 16349]

Eric,

That was slightly over my head but I can't help but get the feeling you come from a sheetfed background. Your comment about "50 impressions" is what makes me say this. From my experience, nothing happens on a web press in 50 impressions. If you were to mount a plate with less coverage and start the press with the ink ball turned off, you still wouldn't run enough ink out of the roller train to bring the density down. I've never worked in sheetfed but I did interview once. I recall the guy telling me the biggest run they get is 5000 sheets. Honestly if I can makeready a commercial webpress in 5000 impressions I did pretty good that day.

I'm no engineer but I work with older GMI Colorquicks on Harris presses with swinging ductors and Man Rolands and Goss presses with newer Quadtechs and continuous ink feeds so I'm pretty familiar with their operation. Personally I can see closed loop color working fine with Digirail on a webpress. For one it you have the head of the closed loop color that scans back and forth checking the density, it scans from operator to gear then moves back to the operator and scans again and that's after it even finds the colorbar which is at least 400-500 impressions. I've never counted but I can't see one scan happening in less than 100 impressions moving at only 700fpm. (the slowest I'll ever makeready a decent webpress). Ink key movements are always relative to the density it scans, but it never moves any single key more than 5% at a time.

That's just to give you an idea of what I look at everyday. The only thing expected to move fast is the paper through the press. The time it takes the micrometric to scrape the excess ink off the ink ball is peanuts compared to the time it takes for the roller train to exhaust itself to the web. On that note an inkball on a press with a continuous ink feed actually tends to run pretty fast anyway.Where press with a swinging ink ductor never actually stops recieving ink from a keyzone that is at it's lowest point you tend to nurse the ink ball speed to keep the ink as low as possible in a low/no coverage zone. A continuous feed press can always have the keys ink film low enough to never touch the ink ball, so you can have that ink ball run much faster. AFAIK they don't even install Digirail on ductor fed systems. The guys I talked to told me that Goss actually retrofitted the press with micrometrics when they installed the Digirail.

In my experience, closed loop color is best used to maintain densities and help achieve a final result. On an older Harris with a GMI, it serves practically no purpose in makereadys. It's too slow to find a color bar and too slow at making corrections. My procedure on these presses is to adjust the presets, start the press, balance the water and shut it off. I look at it, make ink moves start it back up and begin running if it's up to color. At that point I set the GMI into closed loop to fine tune while I'm already running good copy. On a Man Roland which has the best fully segmented, deep pocket ink fountains I've ever seen I turn the Quadtech on from the start but I never expect it to bring the densities in by itself during a makeready. Ill watch the densities on the screen and make the big moves on the ink keys myself for a minute then shut the press down. Make the rest of the colormoves, start the press and begin running with it still in closed loop. In this environment I can easily see Digirail working fine the way it is. Wasteful? Absolutely, but it's what is expected in web printing

Thanks for all the comments from your experience. It is helpful as a reference.

I am not talking about only sheetfed. My major practical experience is with web presses although the science I have developed applies to both.

I can understand why this might be hard to believe but I still say that getting to colour in 50 impressions is still a practical target under the conditions I stated. It requires changes but if people accept long makereadies as being normal, that creates a huge problem just trying to get past that phycological barrier.

Think of a combination lock. If you know the combination, you can open it right away. If you don't know the combination it takes a lot longer and seems very difficult. Same problem for both situations but solving it depends of specific knowledge. That is the kind of knowledge I have developed related to the density control problem. It is very specific to that problem. There is a need for some press manufacturer to take it to the next level.

 

[stu]

Going back to the original post, as someone who has trained people with no offset experience on an offset sheetfed press with a closed loop colour control system, I tell people to stop the press for a few seconds, then start it up again. (the plate then dries) If the density goes up they've been running too much water, not the most definitive answer by any means, but it is an easy reference for the inexperienced.

 

[Greg Imhoff]

Closed Loop color as described in this thread is better than not. The question becomes application needs vs. costs. ROI must be present.

Erik's ideas are likewise progressive for production. Why then is there resistance to this is it because the industry is conservative to change? Or does it work but does not fit mathematically into applications for a reasonable ROI?

Greg Imhoff
President GRIPDigital, inc. & Director EPG Color Solutions
(708) 557 - 2021 cell
Essex Products Group | Integrated Color Control Systems
alt email: [email protected]
Skype: gregimhoff

Thanks for all the comments from your experience. It is helpful as a reference.

I am not talking about only sheetfed. My major practical experience is with web presses although the science I have developed applies to both.

I can understand why this might be hard to believe but I still say that getting to colour in 50 impressions is still a practical target under the conditions I stated. It requires changes but if people accept long makereadies as being normal, that creates a huge problem just trying to get past that phycological barrier.

Think of a combination lock. If you know the combination, you can open it right away. If you don't know the combination it takes a lot longer and seems very difficult. Same problem for both situations but solving it depends of specific knowledge. That is the kind of knowledge I have developed related to the density control problem. It is very specific to that problem. There is a need for some press manufacturer to take it to the next level.

 

[blazini]

Thanks for all the comments from your experience. It is helpful as a reference.

I am not talking about only sheetfed. My major practical experience is with web presses although the science I have developed applies to both.

I can understand why this might be hard to believe but I still say that getting to colour in 50 impressions is still a practical target under the conditions I stated. It requires changes but if people accept long makereadies as being normal, that creates a huge problem just trying to get past that phycological barrier.

Think of a combination lock. If you know the combination, you can open it right away. If you don't know the combination it takes a lot longer and seems very difficult. Same problem for both situations but solving it depends of specific knowledge. That is the kind of knowledge I have developed related to the density control problem. It is very specific to that problem. There is a need for some press manufacturer to take it to the next level.

What conditions exactly are you stating this is possible? You really didn't state exactly what type of press we are talink about here. Have you ever seen this actually happen? What form of printing? What type of press? It's not that it's hard for me personally to wrap my mind around it, it's that it doesn't seem remotely possible in any way shape or form. I'm just curious, what exactly is the procedure and what circumstances is that possible? I can't help but think that we are talking about some dinky little UV 2 color webpress or something, certainly hope so because not to
sound offensive, but this is losing credibility.

I can give any number of reasons why it isn't, but the most simple is that you can't even start a heatset webpress in 50 impressions. t takes at least that to bring the oven up to temp. You could start the press with the oven cold and wrap the chills up. The length of my press from the last unit to the rewinder is probably closer to 100 impressions so I couldn't even see what was printed until 100 impressions later. If I had a folder on the end of it it would be even longer. While everybody loves to save paper, why even be so concerned about color in 50 imps when it takes at least 250 to for the automatic blanket washers to wash blankets? 50 impressions is core waste from a mill roll. 50 impressions is the damage that comes on about half of the 1500-3000lb mill rolls before they enter the plant. I still can't help but think we are talking about 2 entirely different things here. The fact that I mentioned a 5000 imp makeready, and you referring to it as "long" says we're not on the same page. 5000 impressions at makeready speed on these presses is about 5 minutes after it starts printing.

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. It's funny that you mention "press manufacturers need to take it to the next level" I'm curious how they will do that when nobody is buying presses. The year before last there was a total of *ONE* brand new commercial webpresses purchased in the entire US. I look at it everyday because it sits right next to mine. It's obvious that Goss couldn't figure out how to do what you're suggesting, nor could the hundreds of years of combined printing experience that works with me, but you have?

There is 1 press that I've can think of that can do what you say...........It's a very old rotary letter press. No need for closed loop color when you don't have ink keys. No need to balance the water system out when you don't have one.