Smoother Solids versus Mottled Solids

[D Ink Man]

Smoother laying solids will get better ink mileage versus Mottled laying solids if everyting else in the lithographic print process is the same.

True or False?

Let us discuss.

 

[Cornishpastythighs]

I believe if you have a minimum ink and minimum water situation then your solids are smoother and your ink is being allowed to do its job. Your dot gain will be better also (dots are just tiny islands of solid ink anyway) If on the other hand you have the opposite situation over emulsified ink then you need to keep supplying more ink to maintain your print and more water to keep your non image clean and well I dont have to tell you the rest.

 

[D Ink Man]

Cornishpastythighs,

You are a lithographic master and a credit to your trade.

D

 

[Alois Senefelder]

Salient Point

Salient Point

Gentlemen,


The Ink transferred via the blanket onto the substrate is not the same Ink that left

the Ink Duct. It as become a Water in Ink micro emulsion ---- lithography depends on ink's

ability to emulsify the dampening solution.


Regards, Alois

 

[Cornishpastythighs]

Agreed, but the emulsion has to be stable, too much water in ink results in Emulsification

 

[gordo]

Agreed, but the emulsion has to be stable, too much water in ink results in Emulsification

Not emulsification. Over emulsification.

Best gordo

 

[Deleted member 16349]

Not emulsification. Over emulsification.

Best gordo

Can someone define or describe over emulsification.

Curious about how people define such a commonly used term.

 

[D Ink Man]

Can someone define or describe over emulsification.

Curious about how people define such a commonly used term.

I am curious too Erik.

 

[Cornishpastythighs]

Mottled solids caused by 'over emulsification' and plugged screens would more often than not result in the job being Re-Run at my place of work so there goes your ink mileage.

The Challenge of Emulsification - Ink World
For you Erik

 

[D Ink Man]

Very nice Cornishpastythighs. You answered two major topic questions with a brief reply. Killed two birds with one small stone. Good job sir. D

 

[TheProcessIStheproduct]

yes but you can get mottled look from blankets and/or sequence issues, which would have no impact on ink consumption?

 

[Cornishpastythighs]

It will if you have to reprint the order

 

[Deleted member 16349]

Mottled solids caused by 'over emulsification' and plugged screens would more often than not result in the job being Re-Run at my place of work so there goes your ink mileage.

The Challenge of Emulsification - Ink World
For you Erik

Cornish, I have read the article quite a while ago and I would say that it is faulty. Only my opinion.

The implication of the comments about mottled solids and plugging are that printers define over emulsification based on what they see in the print. This is understandable but it is not the kind of scientific definition I tend to look for.

I am not too happy with comments about lab tests trying to relate how the ink will run on the press. From what I have read, many researchers don't see a good correlation between many lab tests and press performance but they do them anyway.

As I understand it, there are two kinds of emulsification. The first kind is where the ink will take up water and is stable. The second kind is not stable and it is where ink takes up additional water by being forced into the emulsion by higher rates of shear. Once the shear stops, the additional water comes out of the emulsion. I seem to remember one researcher saying that on press the emulsion could be as high as 600% (water to ink).

Also from what I have read, inks that take up low amounts of water or high amounts of water in the first kind of stable emulsion, can perform well on press.

An ink that does not have an unstable emulsification part of its emulsification curve, where the ink just continually takes ink up in a stable way, will not perform well on press.

As many know, I am trying to get people to rethink these kinds of issues. I have stressed that ink feed is critical for density control but water feed is critical for print quality.

On the water feed side, given that the chemistries are correct, I see two issues. One is the amount of water and the other is the mechanical method of introducing water to the press.

My view is that with a positive ink feed, the amount of water will not be so critical to print density but of course it is better to put it in a range that provides good print quality.

I think that the addition of water into the press with a dampening system is causing problems because it is so close to the plate that if more water is applied, some of that water does not have much time to be emulsified into a fine distribution of ink and water in the film on the form rollers. Also with the existing dampening systems, ghosting issues due to the gap in the plate and uneven water feed due to many reasons can show up in the print.

My view is that it would be better to apply the water farther up in the roller train so there is more time for the fine emulsification of the unstable state can be developed. This can only be done with positive ink feed because with the water higher up in the roller train will be a problem with conventional ink feeds.

So if I can get the positive ink feed established, I think there are very interesting potential improvements in operating performance by changing the way we think about water feed and emulsification. Only time will tell.

Mottling may actually be a result of a lack of the proper emulsification due to not enough shear time and not over emulsification.

As I see it, there are chemical issues and there are mechanical issues. Fixing up the mechanical issue should help make it easier for the developers of inks, fount solution etc. to refine their technologies.

I think there is lots of potential for operational performance improvement but I have to say, when printers say the ink is over emulsified, that tells me nothing helpful. It doesn't mean anything that one can use to think about the problem.

That is why I tend to stay away for these kind of ink discussions. Partially because I don't know enough about the problem and also because I don't think one will get better knowledge until the mechanical issues are corrected.

These are important issues but right now it is like having discussions about the details of a flat earth. A lot is imagined resulting myths about that model to support it. Like falling off the edge. Later when one finds that the earth is round one has to throw out a lot of the myths and so called knowledge and start over. In the offset printing process, we have not fully gotten away from the flat earth thinking stage.

 

[Dan Roll]

One of my favorite subjects. One of the printing companies around the corner from my first job ran magazines heat-set web letterpress (a huge slow ATF) and their only problem, according to them anyway, was an inability to run solids that could not be described as 'mottled, snowflaked, alligatored, or grainy'. Sometimes they would spray a little water (sometimes oil, other times varnish, once I saw them dump a box of corn starch into the ink rollers) into the ink to 'solve' the problem.
Imagine my surprise when I was told the exact same problem on the offset litho web I was working on was due to 'emulsification'. I am sure that emulsification is to blame sometimes, but I am equally sure it is not the entire story.

 

[D Ink Man]

So we really need this Nanography business when it seems we are only scratching the surface in our own galaxy of Lithography? Interesting.... D

 

[Dan Roll]

As a fountain solution guy I have done a lot of investigating in the area of emulsion forming/breaking, particle size, etc over the last thirty years. The only thing I have been able to demonstrate as always true is when you stabilize the ink/water emulsion it is not a good thing. Keeping the ink/water emulsion unstable is critical but not always easy, as there are a lot of emulsion stabilizers lurking in the pressroom environment.

 

[Deleted member 16349]

Keeping the ink/water emulsion unstable is critical but not always easy, as there are a lot of emulsion stabilizers lurking in the pressroom environment.

This is how I understand it too. The emulsion must be in the unstable range for the process to work.

My view is that this will not be a problem when the ink feed is positively controlled. The exact amount of water will not be so important because it will not affect the ink amount which is the important part. This should make production much easier. This is hopefully what will come out of my testing.

 

[Alois Senefelder]

PDF from PIRA

PDF from PIRA

Gentlemen,


re - Unstable Lithographic Ink Emulsions and Fountain Solutions. - PDF "Taking the Waters"


read page 4 comment


Regards, Alois

 

[Dan Roll]

I got involved (against my better judgment) with a press manufacturer working on methods to determine when (or if) the ink volume in the ink rollers stabilized at a particular volume. Only indirect methods were used and the project predictably went nowhere. The only conclusion I was able to draw was the chance of project success looks to be inversely proportionate to the number of engineers involved.
I can see the volume of water to ink being heavily influenced by how this ink is fed into the system. A long time ago there was a project outfitting a M110 (an eight page web press for those not familiar with it) with an ink train consisting of just a few rollers, one being pretty big around. The theory was the inker would respond more quickly to changes in ink feed and that less ink in the ink system would require less water to be used. I lost contact with this project before it was completed (if it ever was) and only remember that water consumption was indeed measurably lower when compared to units with conventional inkers. At that time this unit didn't print worth a hoot either, but that may not have been the goal at the time.

 

[Deleted member 16349]

The only conclusion I was able to draw was the chance of project success looks to be inversely proportionate to the number of engineers involved.

Here seems to be a relationship that will hold up.

When engineers are working trying to advance a process into a new level of performance, they need valid science.

If they have no valid science as a guide, they are just guessing at what might happen and their efforts will be just as bad or even worse than what anyone else would get. Often a little or incomplete knowledge is worse than no knowledge, because it make an engineer think they are doing the right thing but in fact they keep doing the wrong things.

The fault is not so much with the engineers, although they could have done a better job, but with the quality of the science. One should be striving for better science that gives predictable results. That is not being done properly now.