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Flexo spitting

Posted: Fri Jun 16, 2023 2:37 am
by Yow Ling
Hi we have a bit of a problem with spitting on one of our presses
Its a Comco Commander 18 with UV curing.
We have a range of aniloxes from 200 lpi to 800lpi mostly hex cell but a couple of tri helical which are less of a problem
doctor blades are steel lamella tip 1/2' in factory dr blade holders.
Standard ink tray setup with fountain roll geared off anilox.
If we run much ove 75fpm we get unacceptable amounts of spitting.

Is there a good baseline setup we can use , recommended dr blade , best practice anilox engraving etc


Re: Flexo spitting

Posted: Sun Jun 25, 2023 1:36 pm
by Frank Burgos
Hello Yow,

Most of the time that I, or my colleagues, have experienced spitting has been when the ink, especially UV, has built up over time on the "back" of the metering blade (the side away from the anilox surface). Until you find a more permanent solution, you might give the blade(s) a when the problem arises or during roll changes.

The buildup of ink on the back of the blade is known as "back-doctoring", and I am almost certain that it occurs more with UV inks, because they don't dry on the blade.

As the ink builds up, the bead of ink on the back of the blades gets big enough to start touching the anilox. The anilox touches and slings the excesses ink, giving you a little time before it builds up again, touches again, and "spits" again.

One line of thought is that the surface energy of the blade attracts the ink onto the back. It makes sense to me. I'm sure that the magnitude of the problem various with anilox roller surfaces, ink properties, ink, anilox and blade temperatures, press speeds, and blade material.

Re: Flexo spitting

Posted: Sun Feb 04, 2024 4:59 am
by TechnicsFlex
What material are you printing on? Is it thermal?

Re: Flexo spitting

Posted: Thu Feb 08, 2024 9:34 am
by dkelley
I have found a Lamella tip blade helps and lowering the ink viscosity with a UV viscosity reducer helps with ink spitting.

Re: Flexo spitting

Posted: Thu Jun 06, 2024 3:38 am
by sachpat79
Hello Yow,

The spitting problem is most common with high viscous ink (UV Inks). Spitting is a combination of many parameters like the ink, ink temperature, viscosity, blade, anilox screen, speed (worst at high speeds) etc. You can try GTT anilox from apex and are proved ones against spitting.