Conductivity

[madjock]

Hi I was wondering if anyone can tell me what effect the addition of alcohol sub and fount has on the conductivity of fount solution.
I am running a 105XL CD and using Saphira fount at 3% and Saphira sub at 2.5%, the conductivity in the mixing tank measures around 2300 which seems really high, so my question is do the additives cause the high figures, or could it be that the water, which is filtered tap water that is causing the numbers to be so high?
I have spent the last 20 years using alcohol so I am not very experienced with alcohol free!

 

[turbotom1052]

2300 does seem awfully high. id begin by measuring your tap water over a period of 3 times a day for a week or so to determine what your starting point is. (tap water does vary). Take the average of your tap water readings for the week and then you can mix based on that. if you set the target point on your technotrans doser the unit should do the rest. Different conditions do require a sweet spot when it comes to conductivity and youll need to arrive at works for you. Id suggest a starting point of about 1200. Back in the old days of hand mixing alcohol free solution id be starting at about 1200 and dumping the tanks and mixing fresh at 2100.

 

[Dan Roll]

Conductivity readings of your fountain solution tell you the volume of dissolved salts in the mixture. All three of your components (water, FS & sub) will have some level of conductivity and you need to know what all three are. Typically, but not always, alcohol subs do not contain salts so their conductivity will be pretty low or non-existent. The suggestion to check the conductivity of your water regularly is a good one, and the manufacturer of your FS will usually have the conductivity/dose information on the product label. It is important to measure your fountain solution mixture before it is circulated so that you know you are measuring just the water/FS/sub mixture. The conductivity of the mixture will go up some (and sometimes a lot) when circulated, as contamination form ink, paper, plate finisher, plate cleaner, and who knows what else is usually ionic (meaning it will add to your conductivity).
As an alcohol user you are used to seeing a conductivity lower than you actually run, as alcohol acts as a resistor, lowering the reading of a solution. The salts are still in your mixture when running alcohol, the reading is lower because the meter just can't see them.

 

[Bob Peterson]

I third checking the conductivity of the incoming water source. When you mix the etch you want a starting conductivity 800-1200 mHos over the conductivity of the water. Furthermore, IMHO I wouldn't use any more then 1.5% of alcohol substitute. Using too much sub will slow down ink setting & dry times and break down the body of the ink quicker when running light coverage causing emulsification.

I recommend that you invest in a refractometer to measure and monitor the sub/glycol levels in your fountain solution. I find that the refractive index is less then 2.0. Here is a link where you can purchase a refractometer: Handheld Manual Refractometers And Brix Refractometers - Cole-Parmer Catalog

Drop me a PM if you have any questions.

 

[GJOHN]

While I agree with all posts above, I would like to ask what is happening to your prints at that conductivity number. If you have no print issues with it, why would you think that the conductivity is high. Perhaps you are just not used to seeing a conductivity of 2300 mmhos.

 

[madjock]

Thanks for your input guys, in answer to George John, I am not really having any print issues with the high numbers, it is just that conventional wisdom tells me it should be a lot lower than what we are getting, I will measure the tap water when we do a change.

 

[tmason]

When you dump the water tank be sure to flush with fresh water until the water in the tank reads the same as tap water, before you add the fountain solution.
We found that even though we were dumping every Friday, the conductivity shot up quickly after one day. After we started flushing our tanks the conductivity stabilized.

1900 seems to be our threshold for having color control issues on press.
When the conductivity gets too high, we notice tighter ink/ water balance and when it gets extreme we may see blinding or partial stripping, usually in the magenta first.
If you notice the "operating" window suddenly become very small between too much water, (washing out) and not enough water, (scumming) when you only change the setting slightly, it's time to flush the system
and do a calcium removal on the rollers.
Of course, I'm assuming all the rollers are set properly, etc...

 

[Lennyr]

conductivity

conductivity

Go out and get enough bottled distilled water to mix one batch of solution. Make sure you're unit is clean, and see how long it takes for the conductivity to significantly increase. I'm finding that some of these new chemicals we're having to use in California are making strange things happen.
Lenny r.

 

[rbailleu]

I little off topic, but we recently switched to alcohol sub as well. even with a fresh batch of water the balance window is much tighter than it was with alcohol. we tend to wash out quite a bit if the press shuts down frequently. to help this issue we set the pre and post damp settings to -5. it scum a few sheets but its better than washing out 50 or 100. now the question. Is this normal or should we look into it further. any suggestions?

 

[tmason]

Rob,

The first thing to do is make sure the water rollers are compatible with alcohol free printing. If you have used the press for any period of time with alcohol and then change the fount to use a sub, you most likely will have problems. You need to check the durometer of your rollers to make sure they are not too hard.
With alcohol you can get away with inferior rollers and settings but when you switch to a sub everything needs to be dialed in closely.

Next thing to do is experiment with the amount of sub. keeping in mind the more you add, the greater the ink breakdown may be and it will slow down drying. You can also try inks that will stand up to the water better.

If you have air bars that blow into the ink that may help as well, but expect to run overall higher water speeds than with alcohol.

 

[Dan Roll]

One thing to keep in mind when the inexperienced run alcohol free is that the delivery rate of your dampening system goes down without IPA, and goes up with it. This means when you run without IPA your dial speeds will be higher and your pressures need to be lower (this is very important) in order to get the same amount of water you got at a lower dial speed and higher pressure with IPA.
If you do not believe it, feel free to measure your liquid consumption with and without IPA on similar work. I have done this scores of times under a variety of circumstances (some better controlled than others) and have never failed to observe a considerable increase in the volume of fountain solution consumed when running IPA versus alcohol replacement chemistry.
The belief that one uses "less water" when running alcohol and "more water" when running ipa free is an illusion and has lead to many of the mistaken beliefs about running alcohol free.

 

[rbailleu]

we installed all new damp rollers. but we print alot of polypropylene stock and the window gets really narrow. not so bad on enamel and okay on offset.

 

[tmason]

Rob,
We throw in 5% alcohol and no sub when we run synthetic stocks. The sub retards the drying too much.

The alcohol helps the water evaporate quickly as the synthetic stock does not absorb water like paper, it pushes the water back into the ink train. Now I understand the original issue you were having.

This is the arena where the "less water" conversation may come alive..... Maybe not so much less water as "thinner" film of water and the amount of time it takes for the water to evaporate instead of attack the ink before it sets on the sheet. You want the water to wet the plate and not cause any excess emulsification of the ink in the ink train or on the substrate.