FM Screening and Ink film thickness

[nilay]

Is there any article published for the FM screening and ink film thickness on the ink rollers ?

We have goss colorliner coldset newspaper printing presses.

 

[gordo]

Is there any article published for the FM screening and ink film thickness on the ink rollers ?
We have goss colorliner coldset newspaper printing presses.

AFAIK, ink film thickness on the substrate yes, but not anywhere else.

What is your concern?

best, gordon p

 

[nilay]

AFAIK, ink film thickness on the substrate yes, but not anywhere else.

What is your concern?

best, gordon p

Ink splitting for the AM and FM should be different on the ink rollers of the press. It is said that the ink film thickness should be lower on FM. I try to collect data before starting test on our press: specially the ink film thickness on the rollers, splitting of ink and fount solution volume.

 

[gordo]

Ink splitting for the AM and FM should be different on the ink rollers of the press. It is said that the ink film thickness should be lower on FM. I try to collect data before starting test on our press: specially the ink film thickness on the rollers, splitting of ink and fount solution volume.

Just to be clear, the lower ink film thickness with FM only happens on screen tint areas.

For example. Here is a photo of a 175 lpi AM and 20 micron FM screened to the same measured tone along with a solid patch of Cyan.

Using 3D mapping software to render density to height you can see the height of the AM and FM dots relative to the solid in these 4 views:

For the same final tone value on the press sheet, it's clear that the FM dots carry less ink than the solids and the AM screen.

best, gordon p

 

[nilay]

Just to be clear, the lower ink film thickness with FM only happens on screen tint areas.

For example. Here is a photo of a 175 lpi AM and 20 micron FM screened to the same measured tone along with a solid patch of Cyan.

Using 3D mapping software to render density to height you can see the height of the AM and FM dots relative to the solid in these 4 views:

For the same final tone value on the press sheet, it's clear that the FM dots carry less ink than the solids and the AM screen.

best, gordon p

Thanks Gordon,

Now how about fount solution ? If ink film thickness is lower then could we lower the fount solution too on the press ? Logic behind is that the paper is less wet and more on drier side and resultant low fan out .

 

[gordo]

Thanks Gordon,

Now how about fount solution ? If ink film thickness is lower then could we lower the fount solution too on the press ? Logic behind is that the paper is less wet and more on drier side and resultant low fan out .

There are no set rules about fountain solutions and FM that I am aware of. Also the relative thinness of the ink film on a FM dot is also related to the actual dot size being used - i.e. if it's FM on newsprint you'd be using a larger FM dot than if your printing FM on #1 sheetfed paper and hence less thinning of the film of ink on the dots.
While FM microdots are less sensitive to physical dot gain from over-inking, they are more sensitive than
larger AM dots to surrounding water levels and fountain conditions. Therefore, it is important to control pH,
temperature, conductivity, and contamination in the dampening system.
Theoretically you'd be right (less water = drier paper=less fan out) but practically speaking you may not notice a significant difference as far as that is concerned with newsprint application.

best, gordon p

 

[nilay]

We are using 1200 SPI so @42 Micron would be the spot on the newsprint (as we are resolving 2x2 checkerboard pattern). I just afraid about linting because of the ink splitting: which should be different then the AM screeing.

 

[gordo]

We are using 1200 SPI so @42 Micron would be the spot on the newsprint (as we are resolving 2x2 checkerboard pattern). I just afraid about linting because of the ink splitting: which should be different then the AM screeing.

In general, with a 1200 dpi device and a typical 2nd order FM screen you would use a 35/36 micron screen for newspaper work. The highlight dot is 30 microns (equal to a 2.25% dot @ 120 lpi or 3% @ 133 lpi). The midtones will be 43 micron dots and the AM screen equivalent will be about 205 lpi
For a 40 micron FM, the highlight dot is 40 microns (equal to a 3.5% dot @ 110 lpi), the midtones will be 48 micron dots and the AM screen equivalent will be about 190 lpi.

If you can run 133 lpi screens then you should be able to run a 36 micron or coarser FM screen without troubles.

As I'm sure you know, there are several causes for linting in newspaper presswork. But there is one cause in particular that may be exacerbated by FM screening (or high lpi AM/XM screening for that matter).

As ink film thickness gets thinner the effective tack increases which in turn can increase linting. Also, many newspaper printers use stiff inks to try and compensate for dot gain - which also causes ink transfer issues when using high frequency screening. The black ink used is basically soot and can react quite differently than the C, M, and Y.

To be successful you may need to engage professional services if you do not have the expertise in-house.

best, gordon p

 

[jlind]

Gordo:
Those are fascinating "mappings". Thanks for sharing that.
Very wise to not commit on the fountain solution. Of course there will be linting, which is the same as non-image piling as I recall. Some blankets have better release. The stochastic phenomena related to screens during the GATF work was non-image area piling, where there was more non-image area than ink. When the piling debris was studied, it was found to contain mostly ink. The ink was emulsifying into the fountain solution (tinting) as well as the fountain solution into the ink. A best case scenario might be an ink and water compatibility that is just barely acceptable, ie. if the ink can emulsify a lot of the fountain solution, then the converse is true and non-image piling is a possibility. I wonder if there is any anecdotal evidence that the FloClear recirculating and filtration system, usually on web presses, helped to minimize this issue?

John Lind
Cranberry Township, PA
724-776-4718

 

[Alois Senefelder]

I F T and Ink Transfer Theory

I F T and Ink Transfer Theory

Gentlemen,

COLD-SET WEB OFFSET PRINTING

The ink transfer within the printing nip in CSWO printing is dependent upon the properties of the printing surface; nip pressure and geometry; ink rheology and the amount on the blanket; blanket properties and the printing speed. This is a very complex situation.


I enclose a PDF as per NORM !!!!!!!!!

Regards, Alois

 

[gordo]

The thing of it is that printers are successful doing FM screening on heatset, coldset, sheetfed and even flexo. There may be issues in any implementation - or there may not. I know a printer in Toronto that went directly from 150 lpi film to 10 micron FM without any issues. I also know a printer in Miami that struggles with 20 micron FM and 175 lpi AM.

If there is an ROI to the printer for making a change to their process that is higher than the cost of implementation then, IMHO, they should make the investment in that change.

Don't be afraid. gordon p

 

[Alois Senefelder]

Fountain Solution Transfer

Fountain Solution Transfer

FAO Mr. Nilay

This topic should be in the Sheetfed/Web Offset Forum, but a few salient points for you.

Important to remember that F/S also acts as a Lubricant and a Cooling Effect on heat generated by the press. e.g. Roller Train Nips.

Fountain Solution Consumption on average equals a sheet of water about 0.4 Microns thick, the width of the press, running at press speed.

In addition to remaining on the paper surface, water also transfers into the paper. The penetration or absorption of water into the paper structure can occur in several different ways. 1) Filling of the pores and roughness pits at the surface. 2)Penetrationof liquid through capillaries,pores and cavities in the sheet. 3) Migration along Fiber surfaces.
4) Absorption into and diffusion inside fibers.

Regards, Alois - 2 more PDFs for you

 

[nilay]

Thanks a lot for all replies. I was out for four days and tried to keep myself far from the net. Reading all comments, I have now one more quick question;

We are using high GCR (GCR4): in that case black ink would be little bit higher then the normal setup. Does it affect the ink splitting from blanket to paper while using higher GCR ?

Other then that is it ture that old blanket becomes more tackier then the new blanket ?

 

[gordo]

We are using high GCR (GCR4): in that case black ink would be little bit higher then the normal setup. Does it affect the ink splitting from blanket to paper while using higher GCR ?

Other then that is it ture that old blanket becomes more tackier then the new blanket ?

What ink sequence are you running? (KCMY or YCMK or?)

best, gordon p

 

[nilay]

CMYK ink sequence

 

[gordo]

CMYK ink sequence

Methinks an unusual ink sequence for newspaper. In my experience YCMK is typically preferred for best quality.

With heavy GCR black ink would have more coverage and hence potentially be more affected by the next ink units in sequence (assuming it was first down) Printing K last is a good strategy especially if you are using the poor quality black that is so often seen in that market. Heavy GCR shouldn't affect ink splitting.

I don't know if it is true that old blankets become tackier than new blankets, but a slight increase seems possible if an old blanket has been "polished" somewhat because of usage. A smoother blanket makes the ink harder to release. E.g. if you hold two pieces of rough sand paper together it is easy to separate them. If you hold two sheets of smooth glass together they "stick" together making it hard to separate them.

best, gordon p

 

[nilay]

black we are using last may be due to no doubling for the last ink setup. On the new printing press (GOSS: cold set) we observe much more linting in cyan color: do you think we should check the tack of cyan ink or try to contact the ink company and find the reason that whether the tack is the factor for linting?

 

[gordo]

black we are using last may be due to no doubling for the last ink setup. On the new printing press (GOSS: cold set) we observe much more linting in cyan color: do you think we should check the tack of cyan ink or try to contact the ink company and find the reason that whether the tack is the factor for linting?

You're there. You're in a much better position to know what you should do than me.

best, gordon p

 

[Alois Senefelder]

Linting

Linting

FAO Mr. Nilay


PDF on Linting - I hope you will find it of interest and value.


Regards, Alois

 

[Alois Senefelder]

Linting # 2

Linting # 2

One more PDF



Regards, Alois