N-propyl alcohol versus Isopropanol alcohol

[Lukew]

Have just been looking up the msds sheets for both n-propyl alcohol and Isopropanol alcohol . It seems that N-propyl alcohol would be a safer option with its lower vapour pressure and evaporation rate, Is there a reason that printers don't use it more frequently in fount solutions rather then Isopropanol ?
With the figures below, it would seem that you could run n-propyl at say 6% versus Isopropanol at 3% and you would effectivley be emmitiing similar VOC levels,
I have only come across one fount that has n-propyl already premixed in it, But if you were to dose it yourself the possibility to cut VOC levels even further would be great.

Anyone using this stuff?


N-propyl alcohol
% Volatiles by volume @ 21C (70F):
100
Boiling Point:
97C (207F)
Melting Point:
-127C (-197F)
Vapor Density (Air=1):
2.07
Vapor Pressure (mm Hg):
21 @ 25C (77F)
Evaporation Rate (BuAc=1):
1.3

Isopropanol
% Volatiles by volume @ 21C (70F):
100
Boiling Point:
82C (180F)
Melting Point:
-89C (-128F)
Vapor Density (Air=1):
2.1
Vapor Pressure (mm Hg):
44 @ 25C (77F)
Evaporation Rate (BuAc=1):
2.83

[jlind]

Luke:
I think it will work OK, but you are overlooking the point of using alcohol in the first place. You want the alcohol to increase the viscosity of the water so it follows the rollers at a thinner water film, and then evaporates as soon as possible. You don't want the alcohol to be too good of a solvent for the ink, or you get tinting in the non image area and slow drying.

With this said, one solvent that works even better than isopropyl alcohol is ethanol. Unfortunately, alcoholism among printers is already high enough, for good reason, all the aggravation of those pesky designers and customers. Also, ethanol is taxed and very expensive, at least in the US of A.

Isopropyl alcohol was a compromise. N-propanol will not work as well for a few reasons. It is slower to evaporate, and will act like the butyl cellosolves (not that slow) of the current alcohol substitutes. Also, I think it will be a better solvent for the ink vehicles and thus tend to cause emulsification issues. And finally, since it is slower than isopropyl alcohol to evaporate, it will stay in the printed ink film longer and lead to drying and blocking issues.

If you look at early studies of replacing isopropyl alcohol, done at the old GATF, you will surely find data for n-propyl alcohol. It was probably one of the first things they tried.

So, in conclusion, I'll bet vodka would work great. Kampei!

John Lind
Cranberry Township, PA
724-776-4718

[Lukew]

With the n-propyl having a slower evaporating rate then isopropanol, could this mabee be a benefit for polyester plates, which are notorious for not wanting to hold fount,, especially towards end of shift when there's a fair amount of heat in and around the machine.
If pressmen are having to run their IPA % higher to compensate for any evaporation before it reaches the plate, then could it not be possible that running with a lower % of n-proyl would give similar effects but with a substansial drop in VOC emmisions.

I'm sure I have read an article on the use of n-propyl alcohol in fount, but it was a long time ago, and at a time that I had little interest in the matter, If any one has any links to such articles it would be great. as I can't find any at the moment

Luke..

[Pressmanscooter]

FYI— IPA does not increase the viscosity (specific gravity) of water, it lowers it thus the reason hydrometers sink as IPA is added. Second IPA is the best choice for one reason, it reduces the surface tension of the water it is in. The short, short definition of surface tension is the force on a liquid that makes it bead up versus spread out. A drop of water with IPA will spread out and cover more area than a drop without. It does evaporate quickly too which is a nice benefit unless you are concerned about VOC. Other IPA alternatives all have the same problems, they do not lower surface tension as well as IPA, they do not evaporate as quickly and they all result in water speeds higher than what would be used if IPA was used.

[archetype]

I agree with scooter. IPA breaks down surface tension, essentially making your water wetter than it was before. Unfortunately alcohol also breaks down ink in the rollor train causing it to emulsify prematurely and eats away at pigments causing dryback and fading of the ink. Glycol and glycerin compounds in alcohol subs are still alcohol, just a different kind, more like what you would find in antifreeze and do not evaporate.

[Alois Senefelder]

Hello, both Archetype and Scooter are wrong, they need to know more about the "Chemistry of Lithography" 1 IPA reduces the surface tension of the Dampening Solution. The practical Advantages: the film of dampening solution is even, and the Ink/Water balance stabilizes immediately. 2 Evaporative Cooling, IPA evaporates quickly, thus cooling the plate and the Inking System. As a result, the Rheological properties of the Ink remain constant during the Print Run. AND #3 IPA DOES INCREASE "VISCOSITY"
Adding IPA to dampening solution increases its viscosity. This in turn stabilizes the dampening film on the plate and facilitates the transport and the metering of the solution.

Regards, Alois

[Pressmanscooter]

Alois,

1) The cooling of which you speak is almost completely the result of the refrigeration of the fountain solution and very little from the evaporation of the IPA. Anyone that has had a chiller go out on them quickly realizes the IPA was not what was cooling the plate.

2) The 5-7% IPA added to fountain solution has zero effect on its viscosity. Viscosity, or rheology if you prefer, are not even relevant to the discussion we are having. Surface tension is the issue, not viscosity.

[Lukew]

Pressmanscooter,, Have a read of the document bellow, you will soon see IPA does increase the viscosity of the fount soloution,

Also pour some IPA onto your hand,, as it evaporates it will feel cold,, not very technical I know, but it does indeed, help cool the plate,,

Also having your fount chilled it keeps the IPA in suspension,, and slows it's evaporation rate,,
for example,,and only an example,, If you could run your chiller at 2 deg you could run a much higher % IPA before you notice the foul smell of IPA , then compared to running the chiller at say 10-15 deg with a lower IPA % basically the lower the temp the higher the % you can get before a saturation point is achieved in which case the IPA would then readily evaporate, at a high rate, bascally becoming useless,,


http://www.pneac.org/sheets/litho/al...eeprinting.pdf


If the PDF doesn't work try this HTML document,, it just won't have the little diagrames..
Alcohol-Free Printing

[Alois Senefelder]

Hello, and thank you Lukew, hopefully "Scooter" will read the Gatf Technical Report !!! and he will see How wrong he is !!!

Regards, Alois

[carosp]

Hi there,

We use N-Propyl and Toyo HyUnity inks. Recently appear some troubles in drying and inks try to keep in blanket when print job used Magenta cover areas. Anyone can help me to solve this? I am using Agfa RC661 2/3%, N-Propyl 8-10%, Vulcan Reflection blankets on a Komori Lithrone. Thanks for help.