magenta ink going off in the duct

[maas]

We have an issue with DIC magenta newspeed ink going hard in the duct ( Goss HT70), seems to stay fresh in the 200ltr drum but after 2-3 days in the duct a solidified mass starts to build up mainly in the corners of the duct and progressively working its way to the middle, we run a Q7 neutral fount and do not have this issue with CYK by the same manufacturer, any similar experiences or suggestions welcome

regards
maas

 

[Bob Peterson]

Maas,

The solidifying / backing away in the corners is due to fountain solution traveling back up the ink train. More water tends to be run on the outside edges of the plate, this water overtime transfers back up the ink train to the ink fountain. Since the ink in the corners of the ink fountain doesn't get used, in most cases, it takes up the water and becomes emulsified. When magenta ink emulsifies it will loose its flow and body up. I would avoid, at this point, adjusting the ink to take up less water as this might create a different set of problems.

You may be able to eliminate some of the problem. I recommend that you check the durometer of your ink and water form rollers. If they are within the manufacturers specification, check and adjust the rollers to the manufacturers specification.

I am not familiar with the Q7 fountain solution so I can't comment on it. Also, you state that the solution is neutral. When you say neutral do mean that the mixed fountain solution measures a pH of 7.0 ?

In my experience magenta ink will perform best at a pH of 4.5 - 5.5.

Good Luck!
Bob

 

[Alois Senefelder]

Sleeping on the Job ......

Sleeping on the Job ......

...... INK that is !

Maas,

It's a common problem to find areas asleep especially at the ends of the duct on Web Offset Presses. Flocculate is the correct term.

In a conventional ink duct the only forces acting on the ink are gravity and the rotation of the duct roller.

The answer is to Agitate the ink by mechanical means or in the short-term use -
human agitators to stir all the ink in every duct being used, at least once during the print run. My choice of FS concentrate when running TMP Newsprint was a Acid Type running at between -- pH 4.5 - 5.5

Regards, Alois

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[maas]

Gents

Thank you both for your input, i really appreciate it, if i am correct the mild acid fount your both mention etches the plate aluminiuim and coats the surface with a gum, while the neutral fount we currently use acts like a detergent and interacts with the magenta pigment ( which essentially is a calcium salt)in terms of reduced solubility of this calcium salt in the alkaline solution and therefore when the water feeds up the ink train as mentioned in Bob's post the ink bodies up.

Ink am not a printer and therefore my synopses is speculative and i welcome discussion, the common denominator in both your replies is a mild acidic fount, so a batch test is in order.

again thank you for your input

regards
Maas