Ink train temp. for proper ink transfer

[Tarun Chopra]

Hi,

I want to know what should be the temp of ink rollers so that proper ink transfer can happen, as I understand high temp of ink rollers can adversely effect ink transfer properties.


Thanks

 

[HecTiK]

I think its supposed to be around 80 degrees. I know when my vibrator chill pack is about 85 it starts to tone in (streaks on the side).

 

[Deleted member 16349]

Hi,

I want to know what should be the temp of ink rollers so that proper ink transfer can happen, as I understand high temp of ink rollers can adversely effect ink transfer properties.


Thanks

Tarun,

In general, overall ink transfer down through the roller train to the paper is only related to the ink feed rate while printing at steady state conditions. Therefore, ink transfer is only indirectly related to temperature. It depends on the type of ink feed.

If you have a positive ink feed, then differences in ink temperature will have virtually no affect on the average steady state solid density.

Unfortunately, most offset presses have what I call an Equilibrium ink feed and what Goss calls a Passive ink feed. This means that the actual amount of ink being fed into the press is affected by conditions in the roller train, which temperature is one of those factors. So with any kind of equilibrium system, there are points where the equilibrium will be more stable. So in that context, there is probably an ink temperature range that promotes consistent ink transfer for presses with equilibrium ink feed systems .

I tend to think the advantage of having temperature controlled rollers and fountain solution is in the consistency of printing dots, etc. My view is that for consistent and predictable solid density one should go to positive ink feed but for quality of print one should think about the method of application of fountain solution and temperature control.

Lots of areas for potential improvement.

 

[RGPW17100]

Our chiller went out a couple of weeks ago and we had to run for two days without it cooling the fountain solution. What we experienced was mega consumptions of alcohol, constantly having to increase the water to the press and the ink emulsification into the water. After two days of running like this the water was very muddy. We run our chiller at 59 degrees F but have never measured the temp in the trays.

 

[Alois Senefelder]

Enlightenment

Enlightenment

A PDF ----- re Ink train Temperature


Regards, Alois

 

[Tarun Chopra]

Hi,

Would it be correct to ask ink companies at what temp. their ink would give best results?

Thanks

 

[Deleted member 16349]

Hi,

Would it be correct to ask ink companies at what temp. their ink would give best results?

Thanks

Yes, they should be able to provide that guidance. They may have more reasons for determining a temperature range than what might be experienced on press.

 

[Tarun Chopra]

Hi,

I was going through some documentations which state that "the maximum heat dispersion happens on the rollers when the machine stops." which means that the difference in the ink train temperature would change, the increased temperature would change the ink viscosity which also "gets reduced by 50% for every 8 degrees C (approx)" thereby changing ink transfer properties and various other aspects resulting in a non uniform print run.

Is the above information correct?

Because, I tried checking this on my press I did not see any difference in inktrain temperature during a print run and when the press stopped using an IR non contact thermometer!!!

The reason for this thread is to understand temperature as a factor for variations in ink transfer properties resulting is variation during a press run.

Thanks

 

[Deleted member 16349]

Hi,

I was going through some documentations which state that "the maximum heat dispersion happens on the rollers when the machine stops." which means that the difference in the ink train temperature would change, the increased temperature would change the ink viscosity which also "gets reduced by 50% for every 8 degrees C (approx)" thereby changing ink transfer properties and various other aspects resulting in a non uniform print run.

Is the above information correct?

Because, I tried checking this on my press I did not see any difference in inktrain temperature during a print run and when the press stopped using an IR non contact thermometer!!!

The reason for this thread is to understand temperature as a factor for variations in ink transfer properties resulting is variation during a press run.

Thanks

I would say that the document is correct. It should show a difference in temperature but this also depends on how long the press have been running. You also have to wait for the increase in temperature to come to the surface of the roller. Taking the temperature just after stopping will not show the greatest differences. The internal heat build up in the rollers is due to the continual cycles of compressing the rubber. The important temperature is not the one seen when the press stops since roller cooling and fountain solution cooling due its cooling control system and to to evaporation tend to maintain the ink temperature.

Most of my ink experience is with EB or UV inks but basically all inks are non Newtonian fluids and have a property called Thixotropic, which means that the viscosity decreases as the shear rate of the fluid increases. Also after stopping the shear rate, the lower viscosity will still be present for a while.

The lowering of viscosity due to the shearing of the ink and due to the addition of water into the ink has a much greater effect on the lowering of viscosity than the temperature changes.

If you are talking about density variation during the run, that is because you do not have volumetric control of the ink feed rate during the run.

This is propably one of the only industries that believes that not having positive control of a variable is better than having positive control of a variable.

 

[jlind]

I would direct you to a TAGA paper from the 90's, (best I can do) by a french student from EFPG Grenoble. Working with a Technotrans ink train temperature control unit, and a brand new SM102, she studied the effect of temperature on tone value increase. As I recall, the press was idled until each target temperature was achieved, and then a representative amount of paper was printed with a test form.

What the temperature IS is less important than that it remains the same. At one point, the temperature of the rollers was set too low, and water started to condense on the ink train, the dew point....

In another experiment on the Rotoman 38 inch web, which also had temperature controlled inking, the press didn't reach steady state temperature until it ran for 15 minutes.

According to Stefans equation, ink tack decreases as temperature increases. Ink transfer increases with increasing temperature. The TAGA paper reinforces this fact.

John Lind
Cranberry Township, PA
724-776-4718

 

[Deleted member 16349]

I would direct you to a TAGA paper

snip

In another experiment on the Rotoman 38 inch web, which also had temperature controlled inking, the press didn't reach steady state temperature until it ran for 15 minutes.

According to Stefans equation, ink tack decreases as temperature increases. Ink transfer increases with increasing temperature. The TAGA paper reinforces this fact.

John Lind
Cranberry Township, PA
724-776-4718

John,

Mixing the words "fact" and "TAGA" in the same sentence could lead to misunderstandings.

The statements and so called facts are too simple and out of context to be considered as knowledge.

An increase of ink temperature does not necessarily mean an increase in ink transfer. It is very dependent on the configuration of the components of the situation. An increase in ink transfer implies that more ink is transfered. Where does that extra ink come from? If the system is supplied with a fixed amount of ink feed then it can not create out of thin air, extra ink to satisfy the statement.

If you have just two inked rollers that are in contact and run at the same temperature, they do not transfer any ink from one roller to another. Change the temperature and again they do not transfer any ink from one to the other.

Ink transfer has more to do with the difference in ink film thickness on one roller surface compared to the other. In a press, the difference in ink films is a result of printing the ink on the substrate and the feed of the ink. This sets up an ink distribution in the roller train. Draw a line across the roller train in any location and the net amount of ink crossing that line wil be the same no matter where you draw the line.

Yes the ink on an Inkometer will show a drop in Tack when the temperature increases but add a bit of water and the Tack will drop like a rock. The Tack measurement on a Tackometer does not represent printing conditions.

Also the Stefans equations, though helpful, does not directly apply to rollers. It applies to the separation of plates. It is used as a rough idea of the relationships but I do not believe it can be used to describe accurately what happens in the splitting of ink in and after the nip, where there can also be cavitation and not just fluid flow.

 

[Alois Senefelder]

Rheology of Lithographic Emulsions

Rheology of Lithographic Emulsions

Hello fellow Lithographers,

A Pdf illustration of "Ink Cavitation"



Regards, Alois

 

[Wilco de Groot]

Ink transfer

Ink transfer

There are a numberof aspects affecting ink transfer, several are influenced also by temperature. There are two things called ink transfer, I assume that you mean ink transfer to the paper, not so much the transfer of the ink down to the blanket.
Ink splitting: amonst others, the temperature determines the ratio between the ink layer on the one and on the other roller, happens in the roller system but is in equilibrium.
Misting: Higher temperature results in finer mist, may not influence your image as it only happens in the ink train, but certainly the cleaning.
Evaporation: although not so much at these low temperatures, there is a difference related to ink temperature only in the roller system.
Water pick-up: strongly influenced by temperature, may result in over-emulsification or instability.
Tack: As the final effect you want to acheive is to lay down ink on the paper, or on top of a previous ink layer, here tack comes into the game. The resulting ink layer on paper is to a large extent determined by the tack of the ink on the blanket and the remaining tack of the ink after transfer to the paper.

Wilco de Groot, IGT testing Systems