Ink Strength

[CKL]

What is the best to test ink strengths head to head ?
Pigment load ?
Mileage ?

 

[Lukew]

Re: Ink Strength

CKL, we are about to do the same testing between two different suppliers process colours.
Our main supplier who feels there ink is better then the one we are currently using is going to do a mileage test with us
Get ink to proper density and run with a measured amount of ink in the ducts
If this is the best way for the test or not I do not know, but I am certainly interested in hearing what others have to say.

 

[jlind]

Re: Ink Strength

CKL:
Three methods, whether sheetfed or web fed.
Tinctorial strength, or pigment loading, is a laboratory test. The ink is mixed 50 to one or 100 to one with a white ink, and a trained technician draws down the two mixtures and from experience, determines that the darker of the two is stronger by x amount. He adds x amount of white to the darker color, repeats the drawdown, and judges whether his estimate was correct. The result would be expressed as "magenta A is 20% stronger than magenta B." This takes about 30 minutes per color. Some ink companies try to do this estimate with a spectrophotometer and claim success, but you still have to weigh the stuff out and mix the inks until uniform. Advantages, it's fast, and doesn't tie up a press. Disadvantages: sometimes the process colors are slightly different shades, making the guessing a little difficult. This works for sheet fed or web inks.

Density versus ink film thickness curves. This is another laboratory test using a small laboratory printing press where you can weigh the ink amount that is printed on a sheet of paper. You don't weigh the paper, but the disc or printing plate that makes the print. You let the ink dry and plot status T density versus ink film thickness. The stronger ink will hit a typical density at a lower film thickness. Advantages: Brings the paper into the equation, and it's instructive to do this with coated and uncoated paper. Disadvantages: It might take four hours to do this for two sets of ink, or longer. This is similar to an ISO 2846 ink test. You need a careful technician to do this test right. Once again, you aren't tying up a printing press, but this isn't cheap to perform. As a printer, you should ask to see this data first, since the ink company may have already done it, to hedge their bet on what will happen out in the press room.

Finally, as a last resort, mileage tests on press. Should this be a live job or a test form? If you have CIP3 data, you can determine the exact coverage of CMYK on each form, to compare apples and apples, if it's not a test form. Is there temperature control on the press and in the press room? If temperature increases over the run, ink consumption will increase considerably as the viscosity drops. This has been documented by the print research geeks.

For sheetfed, it's convenient if you have one of those ink dispensing systems like Accel Graphics. If you run long enough, it can display how much ink was consumed. Otherwise, you need to weigh a few pounds of ink and scrape it all carefully into the ink fountain; then carefully scrape it all out again, to determine the precision and repeatability of the process. Then you need to run enough sheets to consume at least half of the ink in the fountain, probably 5000-10,000 copies. This can be done, but you can see that it takes time and care in scraping and weighing of ink.

Web presses are easier sometimes, I guess because they use a LOT more ink in a hurry. Again, you can scrape and weigh, only it's a lot more work. You might be lucky and have ink totes that are on scales that would give a direct read out of pounds of ink consumed. Again, hard to put Ink B into the same tote, but you get the idea. Another technology that is pretty cool is from LinkTech. This can continuously measure how much ink is added to the fountain. Again, the ink in the lines is Ink A, and to measure Ink B, you need to scrape and weigh.

It's a big project, but you will learn a lot about your equipment and your temperment as you go through the exercise. You could learn that less ink will be consumed when you print higher screen rulings, including stochastic. You will learn that uncoated or SCA or SCB papers suck up the ink at an alarming rate compared to coated paper.

John Lind
Cranberry Township, PA
724-776-4718

 

[Deleted member 16349]

Re: Ink Strength

John,

Just a couple of comments.

Ink consumption and ink strength are tricky subjects but potentially they don't have to be.

If one had a positive ink feed system, comparing strength between inks would be quite easy. In tests I have done with my Ink Transfer Blade (ITB) technology, I have been able to obtain data in about 10 minutes that allows me to plot a relative density / ink volume curve for the whole printing range. With a positive ink feed system, the ink volumes and therefore the relative ink film thickness is a by product of the system which is feeding ink in a volumetric way.

One has to be careful of using CIP3 data for calculation of ink consumption when one is comparing different printed designs and for absolute values. Basically most CIP3 calculations are too simple and contain errors that can be as high as 40%.

The problem of consistency and predictability of density control on press is very much related to the accurate calculation of ink consumption and ink strength.

 

[jlind]

Re: Ink Strength

Erik:
Good comments, as usual. I may have spoken wrong about the CIP3 data, though I find it hard to believe that it is that inefficient. Seems like it helps printers get "close". What I was referring to was a point in the prepress work flow where the page is assembled and it's converted to a one bit tif file. At that point, at least in the Agfa system, you can draw a box around the image area and the percent coverage of color is calculated.

My thinking was that with this data, you can compare two inks with forms that are slightly different. If ink consumption was different between two inks, it could be explained by the fact that one form had 34% cyan coverage whereas the other had 20% coverage.

While this was easy to do in the Agfa system, I spent many phone calls with Prinergy people trying to find the same feature in their workflow. For the record, I don't know much about workflow, just what the Agfa system could do.

John Lind
Cranberry Township, Pa
724-776-4718

 

[Lukew]

Re: Ink Strength

Not sure how cip 3/4 is set up on say heidelbergs/ryobi's but on shinohara a bunch of nubers are entered to convert the digital data to ink key openings/sweep,from low-mid-high ink coverage.
It works somewhat okay, but the design of it is poor because there is no compensation for change
If its set up on a very dry day then you go to use it on a humid day, your densities WON"T even be close to what there ment to be.
There is no compensation for the amount of water your running any given day.
But surely if you are going to be doing the milage test you would expect to alter the duct keys manual to get an even density accross the entire sheet so it doesn't realy matter how accurat/inaccurat cip3 sets. only you bang your head on the wall if your the one that paid a fortune for something that doesnt deliver whats promised.. IE sellable sheets whithin 20 sheets,, give me a break.... the worst part is now im expected to not use say 100 sheets for make ready but use 50 sheets...

 

[Deleted member 16349]

Re: Ink Strength

John,

I guess it is wrong to blame CIP3 for the errors. As I understand, CIP3 is mainly about the transfer of ink key presetting data. The CIP3 group does not care about the accuracy of the data. The accuracy of the calculation should be incorporated in the software that feeds to the data transfer method. Transferring ink key presetting data to presses has been around since before the mid 1980's but having accurate data has not been available yet.

Inefficient is not the right word. It is just a matter of the wrong calculation algorithm. One day in 1995 I think, I realized how bad the calculation was. This was after I had spent over three years and a lot of money developing a concept that in many ways required an accurate ink key presetting calculation. For several months of running the technology, I was wondering why on some jobs the predictability was very good and on others it was just OK. In talking with the press trainer about another issue on press, the source of my predictability problem came to me in a flash. When I made a calculation on the possible amount of error, I was shocked at how big the error can be. I knew then that I had wasted a lot of time and resources.

Basically ink consumption is NOT directly related to the image area of the plate. If you think hard, you will know that this is true. Think about what affects the thickness of ink films and then do a calculation. I am pretty sure you even know the numbers to use.

The fact that ink consumptions is related to several factors that are not always in the same proportions on each job, plus the fact that ink feeds are not consistent and that it is impossible (when using a conventional ductor roller) to obtain an accurate zero set point, which is critically important as the datum for ink key settings, means that having a self learning system is not possible. When vendors say they have one it is more hype that fact. They don't even know that it is not possible. But a reasonably accurate calculation is possible and would be relatively cheap to develop.

Yes, printers now can get close. A poor presetting calculation is very much better than no presetting. But the question is "How hard is it to get within a tolerance?" Well it turns out that it is not so difficult and it is only because of the limitations in capability of the ink feed system and the poor presetting calculations that presses only get close and still require ink adjustments.

Now consider a great tool that is available to anyone. It can be used to evaluate how hard it is to preset a press with accuracy and also to maintain consistency. The tool is the density/ink volume curve you mentioned. Pick some point on the curve which matches your density target. Let's say 1.5 pts. Now pick a tolerance of +/- 0.05 pts. That means 1.45 to 1.55. Now look at the difference in ink volume at those points. I am guessing that most inks for commercial printing would have a strength that would show up as about a +/- 8% volume (or ink film) change relative to the 1.50 density target for +/- 0.05 limits. That is a total range of 16%. Do you think that 16% is tight? I don't think so. It is not a difficult target to hit. We don't hit the target now because of the lack of capability in the ink feed system and the problems with the presetting calculations.

I will add that aiming at a target density requires both the ink key setting and the ink fountain speed to be properly calibrated. It is not related to water. It should be that the ink keys are determined to show the relative ink feed of the ink keys to each other, while the ink fountain roller speed would be for overall ink feed that targets density. This can not be done with existing systems but it can be done with a properly designed positive ink feed system. It could be done with my ITB.

Edited by: Erik Nikkanen on Jun 10, 2008 8:36 PM

 

[jlind]

Re: Ink Strength

Luke and Erik:
Let's try to get back on track with the ink strength.....Whatever the shortcomings of the CIP3 presetting, and recall that I said I meant the one bit tif and not CIP3, and whatever the faults of the roller/ductor/ink feed, the mileage test is relative to a particular press. You will compare two or more inks on the same press. You need to run for a while to minimize all these inherent process variables and suck up enough ink to give you good repeatable numbers. Otherwise, just stick with the laboratory test numbers.

John Lind
Cranberry Township, PA
724-776-4718

 

[Deleted member 16349]

Re: Ink Strength

Sorry John, I guess I just got carried away......again.

 

[jlind]

Re: Ink Strength

Erik:
We are all print junkies here, and I, at least, understand and admire your persistence. I think William Blake said that "the fool that persists in his folly becomes wise."

John Lind
Cranberry Township, PA
724-776-4718

 

[Bob Peterson]

Re: Ink Strength

CKL & Lukew,

For the most part most lithographic printing inks based on the application i.e.(sheetfed, heatset, ect.) are within 5-10% of each other in pigment strength. Sure you will have some inks that might be a little more or less but those aren't the norm. An ink that is too heavily pigmented can actually yeild reduced mileage, poor press performance, excessive scuffing, and chalking on some substrates due to the lack of ink vehicle that provides the lithographic properties.

Mileage, press performance, and cost to use are the key areas that need to be scrutinized when evaluating inks from multiple suppliers. Most print shop owners and purchasing agents look strictly at price per pound and not cost to use. I will elaborate on this later.

When evaluating ink mileage on press you need to take into consideration that your plating curves are most likely calibrated to your current ink system. However, I have seen some shops that run linear curves on press. When you run a test ink on a press that has an existing plate curve, your press operator may determine that the test ink is either too weak or too strong based on where he has to set his keys and sweep versus his current inks to match the proof. In my experience what the operator is seeing is a visual difference caused by too little or too much TVI (dot gain) in the high light and mid tone range. Therefore, the operator will either push or reduce the amount of ink to compensate for the TVI difference.

The operator needs ignore his key and press settings and try to visually match the proof. When it looks acceptable use a densitometer to measure the solid KCMY patches. This will give you an idea as to whether or not the test ink is too strong or weak or if the transfer is better or worse. If the operator has to increase his keys and sweep compared to his current inks; when you read the density and it is higher then normal would indicate that the test ink is printing much sharper or could possibly printing ragged due to emulsification. On the other hand if the operator has to reduce his keys and or sweep and the density reads lower then normal would indicate that the test ink is printing with excessive TVI.

The above evaluation would be best performed using linear curves on a test form in order to match apples for apples.

Cost to use versus price per pound: Most printers, not all, today are looking to reduce their operating and consumables costs to make up for shrinking margins. Ink companies are no different as we are continually exploring new avenues to become more efficient. When a printer chooses to change to a lower priced ink set I would recommend that you run an extended trial for 2-4 weeks on various stocks, coverage, and reprint jobs. What you want to look for is an excessive number of wash ups through out the day. How many sheets does it take to come back up to color after shutting down during a make ready. How long does it take to dry. Is the scuff resistance in the bindery acceptable, ect. All of these issues mentioned should not be increased or troubling with a lower priced ink as any of these items mentioned will increase the operating costs and therefore any savings lost hundred fold.

Regards,
Bob

 

[turbotom1052]

the easiest and i believe best way of testing ink stenghth or mileage is as follows...
1) At the end of a longer run job that you know to have good ink water balance take note of the sweep settings on all 4 ink fountains.
2) remove all 4 inks from fountains and replace with the product you want to compare, filling fountains to same level. DO NOT WASH UP THE ROLLERS!!!
3) run a couple of hundred sheets and compare the images from one ink set to another.
4) get densities on the new ink to come as close to the old ink as possible using only the sweep setting of your fountains to arrive there.
5) take note of the sweep settings on all colors and compare them either up or down from the settings from the first ink set.
You will be able to arrive at a percentage either up or down from one ink set to another. Be aware that some colors may require more sweep and some colors will require less sweep to arrive at the same densities. This difference will tell the entire story!!!

 

[Lukew]

Turbotom:
This will not give you an accurate figure at all..
Some inks require lower/higher fount dials to give a smear free print... If your just swapping out inks and not finding the correct operating water window, then it can not be an accurate assesment.

I have tried one set of CMYK ink that runs 10 - 15 points lower on the fount dials then compared to two other ink sets I have trialed.
Now if I was to swap to this ink after a run and only used the ink sweep dial, to get to the correct density, the result would be so far from acurate its not funny..

Please Please Don't be fooled by your ink key and sweep settings. Many ink companies are using high levels of alkyds and other ingredients, to raise flow out of the duct = low ink key and sweep settings, which gives the impression the ink is highly pigmented.

There are other ways to achieve high ink mileage and one is to use a non solvent based fountain solution matched with the correct ink system...

 

[Deleted member 16349]

Please Please Don't be fooled by your ink key and sweep settings. ...

Very true. There is no direct relationship between ink key settings, sweep and the actual amount of ink that goes into the roller train.

Ink flows both ways at the ductor. The fact that water and backtrapped ink can end up in the ink fountain is one proof of this. This uncontrolled situation is "state of the art".

 

[mkulengosky]

CKL:
Tinctorial strength, or pigment loading, is a laboratory test. The ink is mixed 50 to one or 100 to one with a white ink, and a trained technician draws down the two mixtures and from experience, determines that the darker of the two is stronger by x amount. He adds x amount of white to the darker color, repeats the drawdown, and judges whether his estimate was correct. The result would be expressed as "magenta A is 20% stronger than magenta B." This takes about 30 minutes per color. Some ink companies try to do this estimate with a spectrophotometer and claim success, but you still have to weigh the stuff out and mix the inks until uniform. Advantages, it's fast, and doesn't tie up a press. Disadvantages: sometimes the process colors are slightly different shades, making the guessing a little difficult. This works for sheet fed or web inks.

Using a spectrophotometer and software such as X-Rite's (formery GretagMacbeth's) Color Quality, the ink / white mixture can be drawn down and measured using the software's 'Dye Strength' display for comparison. This calculation appears to be most accurate when used to compare single-pigment inks with the same spectral curve.

Press testing, key settings, etc. all get into other ink characteristics such as flow, tack, viscosity and while they may be a good indication of overall 'mileage', are not exactly indication of 'strength'.

 

[turbotom1052]

Forgive me for making the assumption that the adjustment of water was something that went without saying. As far as ink strenghth having no bearing on ink mileage, i must respectfully disagree. A weakly pigmented ink will ALWAYS require a higher flow rate into the inker, to acheive the same color as a strongly pigmented ink. I dont need to have an advanced degree in fluid dynamics to know what my eyes have seen on a daily basis, for the last 30 plus years running presses. And i certainly dont need to waste my bosses money with expensive lab testing, to tell me what a simple on press test can tell me for the cost of a few sheets of paper, and 10 minutes of press time.
I suppose if you wanted to get really technical, the above mentioned tests would have you arriving at some valid conclusions, but in the interest of simplicity and low cost, i offered a way to do a quick test that would offer some pretty conclusive results.
Clk began this thread with a question as to what was the best way to test ink strenghth and mileage. I suppose i misspoke when i suggested that mine was the best way, and for that i stand corrected. But in the interest of simplifying things, i offered a quick test, that could be performed, and observed right there on the press, without having to worry about finding, and incurring the expense of a neutral testing facility, or without worrying about your testers hidden agenda. Lets not loose sight of the fact that many of the posters on this forum do have an agenda, and use this forum as a way to plug their product. So much so in fact that some have been censored by the administrators.

 

[aqazi81]

I agree with Turbotom, as a pressman we can simply test the strength and mileage in a few minutes, rather than wasting money and time on lab tests.
May be its not the best method but it gives you a very good idea of the strength of the two inks.
As a press operator I have experienced many times that an ink set we are running and if we replace the ink with a stronger ink, within few hundred sheets we notice the difference in the ink fountain sweep.