Scumming at Lead Edge Corners...

[kdw75]

We have a 4 color GTO 52 with Crestline Altra dampeners on it. Originally the press was run with 15% alcohol but after we put new rollers in it I quit adding the alcohol. It worked out fine except that after running about 8,000 impressions I start getting scumming at the lead edges of the plates that gets into the sheet over an inch. All units share the same fountain solution but the last two units seem to do it much worse. We do have an infrared dryer which tends to heat up the rollers and ink on the last unit especially.

We use Toyo Hyplus inks and FC1000 fountain solution mixed 4 oz to the gallon. We are using tap water and the PH of our fountain solution is 4.0. The fountain solution is kept at 60 degrees.

Does anyone have any ideas where to start as far as getting rid of this problem?

[CD102]

RO water and an alcohol substitute? Do you measure your conductivity?

[madjock]

Well I have been getting this problem for about a year now on a 6 col 105XL, it seems to me to be a chemistry problem perhaps linked to the conductivity, it doesn't make sense though as there should be an excess of water down the edges of the plate where there is no paper, hence in the old days fans and air bars to help evaporate the excess.
I can be running all day and then it just suddenly starts to scum, and if you try and bump up the water to get rid of it, it floods out in the middle of the sheet, this can be a real problem when I am running max sheet size, can anyone explain this because I can't!!

[Cornishpastythighs]

I guess my suggestions wont be anything new to anyone who has switched from alcohol to non alcohol printing. We changed all of our rollers including dampening metering. We went to a softer durometer and paid much closer attention to rollers settings to plates and vibrators. Plate/Blanket squeeze was checked to make sure all was ok and checking blanket tightness. We introduced a good press cleaning regime especially with regards cleaning and gumming of chrome rollers. Good roller wash up procedures with frequent flushes. increased the filtration of our fountain solution system and went to a 2 step fountain solution with alcohol sub. All these things of course we should pay attention to every day but we used to rely on alcohol to help solve many issues both in and out of the plant.
my 0.02 pence
Good luck

[kdw75]

We haven't checked conductivity. We are only checking PH.

It also seems that we can run until the scumming starts then shut down the press and let it sit overnight and the next morning the scumming won't happen for another 6,000 sheets or so. It seems to reset things.

[RGPW17100]

Crestlines tend to have a problem with ink piling. We used to use alcohol substitute not as an alcohol replacement but as an anti piling agent. Sub is prone to emulsify the ink better. Try adding an ounce per gallon and see if that helps

[kdw75]

We don't seem to have any piling on the Crestline rollers. They have a very thin film of ink on them but it is smooth and doesn't look emulsified. We tried a Varn product called PAR that said it was an alternative to IPA. It actually made things drastically worse so I flushed it out and went back to straight fountain solution. Do you think it would be worth trying another fountain solution? We ordered a Hannah 98130 Conductivity and PH tester and we are thinking of going back to distilled water which we used to use several years ago. The tap water in our city is no longer directly from the river. They are now getting it out of deep wells.

[Al Ferrari]

"we are thinking of going back to distilled water which we used to use several years ago. The tap water in our city is no longer directly from the river. They are now getting it out of deep wells."

Bingo!

By trying various fountain concentrates and additives, you may hit on something that combats the problem. But by going to pure water, the main component of the fountain solution, you may remove the source of the problem. I would try this first.

Al

[mazengh]

i think distilled water has a very low conductivity, don't u need water to be at a certain conductivity level to make it print ready?

[Al Ferrari]

My suggestion to try distilled water is not intended as a final solution, and is based on my reading of the OP's reports to the effect that the onset of the problem coincides with the city's change in the source of the water. Also I did not mean for it to be used without additives, but to continue using the traditional additives, which on their own may impair some conductivity, before mucking around with new ones.

All of the other constructive suggestion can be tried afterwards.

Al