PrintColor

Densitometry as a means of SPC

2008-11-03T17:20:00.000-05:00

http://www.flexoglobal.com/flexomag/08-November/flexomag-toc.htm

Density & Dot Gain

2008-07-08T17:43:00.001-04:00

Please, submit any comments on the article in this post.

http://www.gravurexchange.com/gravurezine/0804-ezine/ploumidis.htm
http://www.flexoglobal.com/flexomag/08-July/flexomag-ploumidis.htm

Quality Control & The Role of Color Management

2008-05-04T21:07:00.002-04:00

Hello all,
I throught to provide this area in case you would like to comment on my articles published on GravurEzine and FlexoGlogal.
http://www.gravurexchange.com/gravurezine/0803-ezine/ploumidis.htm and/or
http://www.flexoglobal.com/pdfs/01-May%202008.pdf

I chose the topic of Quality Control as a means to emphasize the importance on color management and to provide an outline of the topics i'll be discussing.

Regards,
-D

Inkjet Proofing

2007-10-16T00:19:00.000-04:00

Hello again,

The most interesting area I've been involved during these months of absence from the blogging community was inkjet proofing. There are plenty of variables involved in this process.

The simplest and most reliable way to inkjet proofing is continuous tone proofs. I am not very interested in discussing continuous tone proofs, as there are plenty of software packages that are able to provide a reliable proof with certain pre-engineered color management algorithms. They certainly need their mastery and a critical visual evaluation, but the calculations, after approximately three iterations of optimization, can provide results that are really close to a visual target. In that, either EFI's rip or ORIS Color Tuner, provide very good results (i'm not all inclusive here... this is just what i tried). Then, certain adjustments for visual match give a very good proof.

Where do the complications of inkjet proofing start?

1. The white point of the target paper and absolute colorimetric intent.
2. Banding.
3. Halftone proofs
4. Hexachrome proofing
5. The color of black

To begin with:
1. WHITE POINT
Mapping the white point of the target paper through absolute colorimetric intent is not always perfect. Introducing the LAB value of the target paper into the proofing media alters the color of the proof. This is obvious especially in the highlight regions where the yellowness or blueness is introduced in the light areas. This problem is dealt with certain software packages where the user is able to affect only a small region of the color gamut. Relative intent works much better, but at cases where the target white points differs significantly from the proofing medium, there is a discrepancy that might be confusing to the press/customer. It is nevertheless astonishing that the profiling software is not able to map the white point with relative ease. I could make a wild guess and say that this is being caused due to chromatic adaptation, but it would be wild and uneducated.

2. BANDING
I've seen certain banding problems that can only be associated with the color algorithms of certain packages or with the ICC profile itself. I would guess again that the more you tweak a profile the more likely it is banding to occur. Then again, the way the software packages work, by trying to minimize the color difference from the profiling target to the media profile, some clustering of the target LAB values is not unlikely.

3. HALFTONE PROOFS
This is where the party starts. The rest is manageable. There isn't a software that is able to effectively color manage halftone proofs. EFI's rip offers a color management option with halftoning, but my experience is that the moire you get is unsaleable! Then again, you can separate the digital file to 1-bit TIFFs and try to work them around. How is color management applied to four channels that are a. already separated into 1010101 dots and b. translated into 7 or 8 eight channels based on the proofer? Only solution that we came up with was through editing the source profile. Results were decent, but unless my vision is all messed up it takes about 40 iterations, and then again... at some point... you just cannot get any closer to the target, since the above-mentioned clustering that would bring all the colors closer to the target LAB values is impossible through the naked eye. This might be a thesis topic for my valuable friend Arvind (http://cias.rit.edu/printmedia/03_programs/grads/karthikeyan.html) who's been helping me with proofing.

4. HEXACHROME
Ha! Forget about it, especially if you want halftones or spot colors as 7th or 8th channels. Then again, even halftone offset printing is kind of weird...

5. BLACK INKS
This is a colorant issue. Again, depending on the software, the color of the black might be unmanageable. I don't think that EFI has a good solution, as I was getting the cast of the inkjet proofers inks, and that was different from that of the ink supplier. I haven't seen such an issue yet with ORIS software.

In conclusion, inkjet proofing can have very good results in continuous tone proofs. My belied is that inkjet is the way of the future though, and that film based proofs with significantly lose their value, even if they provide higher stability and larger gamut (plus halftoning!!!) at this point of time. It is up to smart color scientists and engineers though to come up wth the algorithms that would eliminate all or some of the factors I discussed above, and -my belief again- that this is only a matter of time.

-D

PS> I would like to mention and thank my friend Rob Seckendorf of Color Correct Solutions, who has been providing his support and expertise with inkjet proofing (www.colorcorrectsolutions.com)

It is what it is

2007-04-10T15:34:00.000-04:00

When I visited TAGA I saw lots of concern about the G7 method of calibration. I only saw some results, and one paper saying that ISO actually outperformed G7.
Still, I was frustated by the general feeling of discontent about the G7 process. Sometimes it sounded like unreasonable, and sometimes I was hearing people that I overall trust to say that it doesn't work; yet I saw no valid research.

There, I made up my mind: I would try it out for myself and see if it would work or not. And I did.

I setup my roller stripes, drained my fountain solution and cleaned up the 64" beastie and there we were: ready to run with our hybrid ink set... shooting for grey.

To make a long sorry short, the results were disappointing. As with everything in litho, there can be numerous reasons.
1) idealliance software on shadows
2) measuring devices & idealliance software
3) natural press variation
4) ink set

I'm going to proceed from bottom to top:
4) We used the hybrid process ink set and the hybrid hexachrome ink set. On the color analysis tab we were getting the LAB values for paper grade #1 stock and the respective solid CMY. However, is the hybrid ink set supposed to be matching the NPDC curve, and whatever calculation thereafter? My speculation would be that the curves and calculation thereafter were done based on press runs with conventional ink sets. I might be lacking in theoretical understanding of the G7 calibration, but how can we use one set of curves for all the processes when there is a significant difference in dot gain between hybrid process, hybrid hexachrome (just the CMYK out of it), and conventional process inks? Should I be expecting to get my gray balance? I didn't... and this might be one reason. Even still, wet trapping our inks would allow us to be close to conventional TVI, and thus the software should work.
3) You know ;-)
2) I was getting significant differences in the suggested plate curves when measuring the targets with different measuring devices. Does the idealliance software work only with DTP70 and Eye-One? What prohibits it from working with x-rite 530 or spectroscan. Why in this earth do i get a difference of 20% on the yellow midtones between different devices? Praise the Lord! I guess the problem is that x-rite bought Gretag or WHAT HAVE YOU (i admit... i'm frustrated).
1) OFF.

SO... after such knowledge what forgiveness...

There are consultants who vouche that it works. I believe them.
There are other people who vouche that it doesn't work. I believe them too.

Thing is, at about 11:00 pm yesterday (and after missing a girl's birthday due to working late), I decided to get rid off all the software, match my densities, and calculate the curves on my own. I got my gray balance nice and neat! Am I G7 certified? I am 'Dimitri' certified. Why? I didn't use the software. Is grey balance tied up to G7? We were using the Brunner system before G7 and we were grey balanced already.

There is a long way to standardization... a long damn way and billions of variables to take into account. There is no magic; there is no beauty! Even if someone comes up with the perfect solution, nothing assures that we have the variables of the process under control. We are drifting and misjudging the effect as the cause... basic human fallacious reasoning... the dream within the dream... (i used to read Nietzsche instead of doing my homework at highschool).

What is the main problem? Calibrating something for certain conditions, or fixing these conditions? And I mean ink-water balance...

Here's my frustated plan of action:
1) trust noone
2) set up ISO densities and possibly TVI
3) get grey balance
4) train our operators
5) get device link software or other software with smart color management options.
6a) and MOST IMPORTANTLY: prioritize press maintenance
6b) and optimize support systems and supplies.

-D

PS1> Good luck to all... let me know if I am easily getting frustated...
PS2> Some people don't like feta cheese even though they have never tried it.

The Devil and the Virus

2007-04-05T23:52:00.000-04:00

We've got an old saying in Greece -maybe people have it in other countries as well- that says that there is a devil in every printshop, meaning that there are countless things that can go wrong.

Funny or not, I'm feeling that in order to be a printer you've got to have religious feelings: they are forced into us, and there is a certain amount of give-and-take with a higher deity when we are setting up a job. Are my prayers going to be answered, I ask myself time and again? is it going to work? is there a God above? What NOW? Is there a secret cord that David played to please the Lord?

Am I being sarcastic? Kind of!

Has anyone heard of having a malicious virus hitting the press? It CAN happen if your windows 2000 server is connected to a network. I guess, I could pose this question in reverse order, asking what is the least likely cause of press downtime. A damn virus! Presses connected to a network need Spyware and Virus protection I guess.

So be warned my fellow printers: don't put your pin in your press, and don't pay your bills online through the press console, and first and foremost, don't visit adult content sites between the scans.

-D

And one more thing...

2007-03-25T22:51:00.000-04:00

... now that I think of it directed to TAGA administration peoples.

Please, publish the TAGA Proceedings online!!! Please!

This wealth of information is going to waste in this digital age and it is a shame not to utilize the technologies available to help researchers further their work and professionals get answers. I became a member hoping to be able to access these issues and I cannot (unless I am doing something wrong). Not even the abstracts!!!

I'm not strong with economics and market prices, but you could sell each article for like $12-15 to non members, and $8-10 to members... or something similar. IS&T has a model website for it, where we can review the abstract and go on and purchase the article.

I would love to have the TAGA proceedings online. Please do something about it. I volunteer to help.

-D

Summing up TAGA 2007

2007-03-25T01:35:00.000-04:00

Well... I had a nice time myself. The hotel bar was pretty good and I hit Pittsburgh on Saint Patrick's day!

Seriously now:
I would love to see more attendants next year in SF. We were about 170 people. We can be more. There are lots to learn. Technical people can have a serious benefit in attending this meeting: Networking! Not so much in terms of making friends, but in terms of meeting the people that can provide an answer to their questions when the need arises. As Mr. B. Blom put it, throughout his years at TAGA that was the main benefit: the people! Well, you got to be a printing nerd too to enjoy it.

The students were an enthusiastic crowd as well (getting lost in conversations about density at the bar is absolutely awesome). Compliments on Cal Poly on winning the brochure award - of which I am particularly proud since my company happened to design and produce their packages; which I only became aware at the conference, mainly because I am knee deep in our litho department at work.

Top topics of what I have retained:
#1 There is a lot of research going on on RFID. I hope it works out.
#2 There is another definite tendency to move to colorimetry for process calibration, and why not control. It shall need a huge effort on technical and managerial level, but it can work and provide solutions were density fails short (workflow solutions and color portability, as well as spot colors I would say on top of my head).
#3 I retain the research on the low VOCs. It is important to be prepared for it... if possible!
#4 The discussions and presentations on colorimetry issues and ICC profiling (including mine) however -I have to say- are falling short of the research that is going on in imaging and color conferences. We cannot expect the printing industry to lead in this field, but we can definitely expect to publish some research on the applied elements of ICC profiling and colorimetry for the printing processes.
#4a. we need to work on color difference equations
#4b. we need to establish a linear relationship between IFT, density, dot gain and CIELAB.
#5 Paper companies were criticised -and forgiven nonetheless since it is realized that they are bound to price demands- for UV brighteners, standardization of white point, and to a lesser extend paper properties that affect printability for various processes.
#6 G7... well... read previous post!
#7 Process variation issues discussed and researched and found awful. Well: welcome to litho... and as professor Chung would say: variation is the 'nature of the beast'. Pretty much: 0.10 density units is something very common as natural variation, and it results in about 5.0 DEab... reminding me of William Burroughs novels, where drunk and angry press-boys wonder on saliva and the loose limbs of grey crocodiles and pink elephants (huh?!?)

Farewell,
-D

G7 on TAGA

2007-03-25T01:19:00.000-04:00

There was lots of discussion regarding G7 on this years TAGA conference. There was a session devoted on it. Everyone could chip in a comment. Most of the comments were against it. Why? There was only one published paper on it. Apart from this, there was no published research to substantiate the unfavorable comments. The research community should be the first to know that we need to back up our claims with research.

Being on the field right now, I NEED to be able to read published results regarding any new technology that can help me be more productive, and I need it from this community. Going into endless discussions about how and why it doesn't work is totally worthless, if not damaging.

The main argument against G7 is that it doesn't take into account the color of the inks. Profiling does. Even more, device link profiling is able to calibrate the presses and in the same time take into account the colorants. I buy that. I have tested device link profiles and I know that they are able to do an amazing job. Within the next month, I will test out G7 as well and see for myself if it works.

I have to comment on Dave McDowell's efforts (who was awarded for his immense contribution to the industry) to close the gap between the group that is for and the group that is against G7. Dave, and the particular ISO committee are trying to put G7, ISO 12647 and device link profiles into agreement taking the strenghts of each method into account. I would love to see the ISO document and I hope that it comes out soon enough.

Characterization of Conductive Polymer Inks Based on PEDOT: PSS

2007-03-20T16:19:00.000-04:00

by Erika Hrehorova, WMU

Erika started her presentation commenting on the need to continue the research on printed electronics, stating that there is a future along the line.

The goal of printed electronics is to create structures and devices that are similar in functionality with conventional electronics, but at greater speed, lower cost and less production complexity.

Ink conductivity is achieved by mettalic or other conductive particles incorporated on a non-conductible polymer matrices, or by using intrinsically conductive polymers in suitable solvents.

PEDOT:PSS based polymer inks are water soluble polyelectrolyte systems with good film-forming properties, high visible light transmittance, and excellent stability and it commercially available as aqueous dispersions. The main problem is substrate wetting and ink spreading. In this work it was modified with addition of alcohols and non-ionic sirfactants.

It was found that ethylene glycol decreases the surface tension. Surfactants and alcoholic co-solvents were used as additives to further reduce the surface tension of water based systems. It was found that ethanol was more effective in the reduction of the surface tension, as well as in the improvementof the surface wetting under both dynamic and static conditions. Addition of ethylene glycol increases the conductivity and improves the uniformity of the polymer layer.

losing momentum towards the end

2007-03-20T16:11:00.000-04:00

So... someplace here the 'live' blogging sort of ends. I think I lost momentum today... missing a number of speeches, plus having to present my own paper.

I will make a couple of more summarizing posts within the next few days. I know that what I wrote was incomplete and most likely focuses only on the results... but that was the best I could do. To get more information: become a member... it's not that expensive and there is a wealth of knowledge available. Next year it's in SF.... providing an opportunity for me to get out of the Valley and family-oriented Modesto, and for those willing to come, to see SF. It's really a great city!

-D

Analysis of Color Rendering in Digital Cameras

2007-03-20T12:25:00.000-04:00

by Jason Lisi, Ryerson

Lack of standardization of raw data. Only the camera vendor knows what the camera is doing, and companies like adobe have to reverse engineer the images to find out what is going on.

so the path is: CCD Data -> Raw Data -> RGB rendered data

The question is: can this color rendering step be isolated, mapped and predicted?
They used 6 rendering s/w, 5 raw format and one JPEG and assigned the sRGB profile.

Neutral (as well as quandrant) rendering is good from different vendors, but color matching overall is not as good.

Wiggles

2007-03-20T12:01:00.000-04:00

by Franz Sigg, RIT

This is an experiment Franz run across while I was still in RIT. Apparently, what Franz found out by chance in a first press run intrigued him, and he repeated the test focusing only on the 'wiggles'. The days at RIT were really nice.... when I was working late at the labs, every other month would come to me, all excited at 10 or 11 in the night, needing to communicate what he found here or there, every time about something new and interesting.

in this experiement, he found large deviation from the target value of a large printed target across a target with small incremental value increases. He assumed it was press nonuniformity of the inking, or the press, I guess mostly on the circumefential direction of the printing cylinder, and even more specifically at the lead edge of the sheet. He suggested to use two randomized targets and average them.

And a final remark was that the tolerances for printing are very hard too keep.

Color Difference Equations and the Human Eye

2007-03-20T11:38:00.000-04:00

by Martin Habekost, Ryerson University

Discussion on the color difference equations. DEcmc introduced the weighting factors and was developed for the textile industry. It is used widely for color matching in the ink manufacturing industry.

Second revision was on 1994, again with weighting factors that are adjustable as well. It is even more realistic than cmc, but it has weaknesses in the blue and violet region.

So CIE made DE2000, which is considered to be the best and is recommended. It is not used in the industry though. What I have heard is that it moves the color space around and it creates a moving color target.

Martin suggests after the experiment that DE2000 or DEcmc are to be used, and preferably DEcmc because the data were more coherent.

Q&A
Important considerations were raised during the Q&A section. First, Dave McDowell focused on the need to establish the weighting factors that are more fitting for our processes. After all, the developers of these equations reccomend each user to develop the factors that suit their processes best. Why don't we do so? One might say: lack of awareness or knowledge, or time to test out what is more fitting. I've seen people using a DEcmc(2:2) as QC. You cannot imagine what comes through as OK with these factors. I have seen some others using factors that narrow down the variation of hue, but allow variation in chroma and lightness. This should be very useful for the ink making process, where hue is the most critical parameter. However, the variations during the printing process would be on IFT, and if C* (being sensitive to IFT variations) has a wide tolerance, it is likely to be very forgiving... more than what a customer can forgive.

Densitometric and Planimetric Measurement Techniques for Newspaper Printing

2007-03-20T11:21:00.000-04:00

by Maria Wroldsen, Peter Nussbaum, Jon Hardeberg

an investigation of the statistical relationship between densi and planimetric measurements on newsprint. Is it possible to convert planimetric to densitometric and vice versa?

They used regression analysis with 2nd order polynomials. Each color was studied individually. They used a training set to establish the model and a test set to evaluate its performance. They did all the repeatability tests as well.

The model is not good enough for prediction, since it exceeds 2% tolerance that is the target for dot area meters.

It's interesting that they did this experiement because of the increased use of measurements in Norway

Method for Calibration of a Printing System with digital Data using Near-Neutral Scales

2007-03-19T17:57:00.000-04:00

by Dave McDowell, Consultant

There is a change in the game, cause more than 95% of content data is exchanged digitally and there are many options to manipulate the data... BUT no standard method to do so.

Dave created a model workflow: we need to determine a stable operating position AND match both aim targets and overprints. The system should be adjusted for in-gamut colors.

so how can this be done: adjust the process parameters or adjust the data.

Platesetter curves, rip curves, TVI curves, NPDC curves, device link profiles...

At ISO TS 10128 calibration standard meeting the committee focused on agreeing on the last three. One point that Dave makes thepoint that in effect there are no densities that are defined outside a CIELAB color space that is not based on some other characterization data. There are no densities as standard targets that are device specific. As I quickly understand it, and I might be wrong, this TS will help narrow down the specs by standardizing the calibration and using the strenghts of these approaches.

A Theoretical and Experimental Comparison of GRACoL and ISO approaches to Press Characterization and the Data Set Produced.

2007-03-19T17:32:00.000-04:00

by Greg Radencic, PIA/GATF

There is admiteddly great discussion for different color controls on press. This paper attempts an objective evaluation.

ISO 12647-2 defines colorimetric values for CMYK solids and densitometric control of tone reproduction. Grey balance is a secondary control in ISO.
G7 is a calibration method for proofing and printing and uses colorimetry through grey balance measurements.

When they run the G7: the calibration software doesn't perform a good calibration to grey below 30% and above 60% dot areas. G7 has admitted the problem and they said they will fix it. (I jut bought the s/w by the way... a bit disturbing to know that I bought sthg that might be wrong!?!)
When they run the ISO: it was succesful with nice grey.

The Effect of Certain Process Parameters On Inherent Color Variations on Press

2007-03-19T17:15:00.000-04:00

by John MacPhee, Baldwin Technology Company Inc.

John asks the question what is the expected upper bound of inherent type density variations for the lithographic process and provides an answer.
Then he suggests to reduce the density variation by changes in substrate, screening, use of waterless process and use of gravure inks. His study showed that none of these 4 parameters made any difference.

The main cause of variation is random IFT variation due to transfer.
There are three types of density variation: a. factor or color (Y being the smallest), b. screen area with picks of shadows, and c. location in the sheet.
The answer to the question what causes the variation is that it is variations in IFT or slurring.

The Benefits of Concentric Screening for Offset Lithography

2007-03-19T16:47:00.000-04:00

by Mark Samworth, Artwork Systems

A concentric dot is a regular AM dot divided into rings.

Mark describes differences between AM, stochastic and concentric screening. Well... concentric has the best of both worlds... Organic (2nd generation stochastic by Artwork systems) has better registration, low visibility, fine detail, press stability, color saturation, ink savings..... disagrees however that has better registration. Mark claims it is actually worse than AM screening. Main difference is the savings in ink, because of the rings that decrease the amount of ink film that builds up on the surface.
The benefits of stochastic screening is the smaller dot size. And concentric screening has a smaller size.
The benefit of AM screening is that uniform patterns appear smoother visually.
So... concentric screening combines both.

Plus, concentric screening has higher chroma and is adjustable on press.

Effects of Rendering Intents in Color Management

2007-03-19T16:15:00.000-04:00

by Anthony Stanton, CMU and Mark Bohan, PIA/GATF

Focus is to compare the color renderings associated with the applications of different rendering intents in a color managed workflow.

4 vendors / 4 rend intents +1 with no color mgmt / 5 samples

Suggest the use of DeltaE2000 as a better, more accurate metric. The older DeltaEab overestimates color differences, and depends on hue, saturation and color levels (non uniform in CIELAB color space).

The study was mostly descriptive.

How many DeltaEs are there in a DeltaD?

2007-03-19T15:26:00.000-04:00

by John Seymour, QuadTech

Kind of attacks the ISO 12647-2 standard. There are three reqs:
The first req is that we make a proof and we have to match the target LAB values. Then, the second req is that the OK sheet must meet the LAB values of the proof. Then the press run is the same, having to match the LABs of the OK sheet.

John's thesis is that it is possible to maintain a given DeltaD throughout a press run and n this way maintain DeltaE.

L* and density have an almost linear relationship. You can predict L* based on density when paper is a given.
Another conclusion is that we cannot use density to compare proof and press run, mainly because of the impurity of the inks (plus different pigmentation).

The Impact of Changing Fountain Solution Chemistry and Press Consumables on the Runnability of a Web Offset Press

2007-03-19T15:06:00.000-04:00

by Dr. Mark Bohan, PIA/GATF

Need for standardized fountain solution with types of paper, inks, presses and printers (well.. of course)

The project evaluated impact of process variables on a web press when fountain solution chemistry changes.
They used a traditional NA fountain solution and made variations of it.

Well.... there were 42 press trials 'successfully' completed. The results are pretty much broad and hard to sum up here.
One I retained was that stochastic screening takes more time to stabilize. Water levels change throughout the press run, but do so rather consistently. The chemistry of fountain solution affects the performance of the press run and can be optimized per process.

The Printing Problems Created by the Use of Reduced VOC Washup Solvents and Their Effect on Press Conductivity

2007-03-19T14:45:00.000-04:00

by John MacPhee, PIASC Solvent Task Force

Regulations cause south CA printers (all of CA printers actually) to use solvents that contain low VOCs (no more than 100 grams/liter).
What are the problems:

1. Longer makeready times following a roller washup. Mostly due to print defects. The problems didn't show up immediately. Solvent accumulates on the rollers, then it would be released and dilute the ink. Terrible effect. Ink tack is dramatically reduced.
REMEDY: Follow normal washup with an aqueous fluid (???). But it takes more time to washup the rollers.
2. Some low VOC solvents become bonded to the rubber when absorbed, causing the rubber in the long term to swell and become harder. Swelling is not uniform.
3. Some older washup systems apply more solvents than needed, which results in drips of fugitive solvent that can cause print defects and/or produce a safety hazard. But with high VOC this evaporates. with low VOC the amount of 'fugitice solvent' it collects someplace and creates problems. The solution is a third generation of systems that we got the solvent applied on a pre-soaked cloth.

Conclusions
1. When less than 100 gram/liter the problems created are very real and involve productivity deficiencies and also equipment and material costs.
2. CA will have less productivity and will be less competitive.
3. It should be stopped before it goes all over the US.

Honestly, doing some research on my own... it is a horrible thing and I have to find a way to solve it for my company.

The Effect of Ink Film Thickness Variation on Color Control in the Circumferential Printing Cylinder Direction of Offset Presses

2007-03-19T14:15:00.000-04:00

by Manfred H. Breede, Ryerson University

'Imperfections of the ink system design' as an opening statement. It goes straight back to our discussions with Eric over previous posts of this blog.

Gravure has direct transfer... no ghosting.. less variation.... very uniform amount of ink in x and y directions.
Flexo is consistent as well, due to replenishment of anilox rollers.
Screen printing is extremely uniform as well.
In digital printing the digital file is electronically linked with the imaging device.

And then.... welcome to litho:

Large roller train creates variation. The problem lies in the ink free zone of the cylinder gap. Moreover, the form rollers need several revolutions in the circumferential direction, and it is not easy to deliver the same amount in every revolution. In addition, the ductor roller oscillates and disperses a very think and unequal ink film. Finally, disruptive factors also include the image area configuration.

They printed a test form (0-100 tints) four times, starting with G7 standard density values and decreasing them every press run. they compared it with electrophotography.

There is density variation is about 0.10 points for all the process colors. The DE measurements show that the less ink resulted in more color variation (up to .15), but when the standard was run at the standard densities it was pretty much within 5 DE.

Manfred claimed that this was due to problems of the colorimetric system.

Q&A
First the DI press was a bad press.
The test form might cause ink starvation.
These were serious objections to the results of the test.

Liberty Inks

2007-03-19T12:15:00.000-04:00

by Steve Miller, Sun Chemical

They require less water... I can say that they have a smaller ink/water balance tolerance. so true... Steve also mentions that they need to change the mentality of the printer.
Drainage to the surface of the substrate varies a lot due to the substrate properties.

The resin system requires less water... if you make it right it is more stable.