PH and Conductivity in the Pressroom... Does it really matter?

[EyeTech]

The suggested conductivity relates to press conditions in the Uk and Spain (I've worked in both countries) and it's pretty much the same levels.

I can't see it being much different in the States - the technology is the same after all.

[Aaron]

Thanks for the info Eyetech!

Does you info pertain to the fountain solution I am using (Prisco 2351) or is that a general idea for what to shoot for on any fountain solution system?

[EyeTech]

The interaction of fount additive/water/inks is down to basic chemistry, I guess.

The figures I mention should hold good wherever you print in the world. But they are only guidelines, a starting point for the printing conditions in your pressroom.

Let's say you had the incoming supply tested and you've detected high concentration of calcium, as can happen when water supply reservoirs are low, if you filter that supply with an RO unit then effectively you're bringing the supply within the necessary parameters to print clean ie without tinting or emulsification. Then you need to have a stable and slightly acidic fount to catalyze the ink setting process.

If you still have issues then it's time to look at the roller condition. Are they glazed for example, are all the inker/dampener stripes
settings correct?

Bottom line - if you don't address the basics then you can expect to have issues. 

Does your pressroom have problems with colour variation for example? Or wild fluctuations when there is a feeder stoppage and then a restart?

[Aaron]

Color variation, absolutely. Startup fluctuation, yup.

The Plant Manager as checked the stripes and we have fresh rollers in the units. The only unchecked element out there is the fountain solution system and ink tak and consistency. or is it tac?

[EyeTech]

It's tack

Startup fluctuation is an indicator of excess damp in the ink. When you're running the balance is probably geared towards preventing tinting (we call it catch-up in the UK), so when there's a stoppage, then the ink is milling on the rollers and the damp is evaporating out. When you start the press running again then you get a highly colour saturated 20 - 50 sheets before the balance is restored. To minimise this effect you need to carry out a heavy duty appraisal of all that i mentioned before. In the short term see if your pressman will drop his water down til it begins to pickup in the non-image areas, then up the damp til it clears and see if that improves matters.

Is this press a Komori?

[Aaron]

Nope. Mitsi 28" 1F-something. About 9 years old now.

[EyeTech]

Ok - let's see, does it have a facility for linking the speed of the water pan roller to the rotational speed of the press?

[Aaron]

yup. We do have delta unit as well though. They are all off except for the first unit so it can grab anything coming off the sheet.

[EyeTech]

Wait a sec, are those delta units Mitsi' or Dahlgren/Epic (retro-fitted)?

[Aaron]

Third party so I would say Dahlgren/Epic. Funny story about those things. We could never figure out what to set them at. We called Epic and they said ask Mitsi, we called Mitsi and they said ask Epic. Amazing.

We have them set at 0.5% whatever that means...

[EyeTech]

I used Epic on an old Planeta and it wasn't too bad. Can you adjust from the console?

Ok here's what I was getting at, the diagram attached shows a water/press speed compensation ramp. Based on Komori Ratio controls.

When you start to print around 3,500iph the ink/damp should be in balance but physics demands that the faster you go the more damp you need. (What kind of run lengths/speeds do you run at?)

So it sounds to me like your damp is overcompensated at higher speeds so when you stop all the 'almost' emulsified ink makes itself known when you start up again. Try lowering the amount of compensation at the higher speed and see if that helps. I'd suggest trying this when you're on a longish run where you can drop the compensation until the point of tinting and then up it until the tinting clears.

Does that make sense?

[Aaron]

What's tinting?

Average run length: 10,000
Average speed: 10,000iph

[EyeTech]

It's where the non-image area on the plate picks up ink due to insufficient damp. Catch-up is what we call it in the UK.

[Aaron]

Oh. Dry up?

[EyeTech]

I guess that would be it.

I hope that info helps - let me know how it goes.

Gotta go now there's a beer with my name on it.