**Misting**

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**Misting**

Postby Niek PD » Wed Nov 06, 2019 10:54 am

Hello everybody,

We recently bought a new flexo printing press which can run much higher speeds then we used to.
We print with sleeves with a big circumference (up to 1400mm) on LDPE film up to 600 meters a minute.
Because of the business we are in (garden products- and substrates, wood- strawfibre) we need a particular thickness of the ink layer to guarantee a good resistance against the weather etc.
We use 120L / 12 grams anilox rollers with a conventional / hexagonal "grid"for our full tones in the PMS colors.

If we run 400 mpm and up we have problems with "misting".
Because of the centrifugal force the ink comes out of the anilox roller, on the printing plates etc.
I did some tests with different doctor blades etc. but it doesnt help.
Because of the ink layer thickness we need, i cant really go back in volume with the aniloxes.

Does somebody have a simular experience with this problem or have some good ideas i can try to fix this?

Thanks in advance!
Niek.
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Re: **Misting**

Postby longtimefan » Wed Nov 06, 2019 2:37 pm

Water or solvent?

Ph good?

Viscosity good?

Try any types of solvents?
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Re: **Misting**

Postby Frank Burgos » Wed Nov 06, 2019 2:48 pm

That's a tough one. Gonna just think out loud:

Experimenting with a different ink occurs to me. Also, I believe that the blue Tesa is medium-hard. Can you get away with medium? I'm wondering whether impact at speed might contribute.

Finally, and not appealing, could you produce the same ink film thickness with two bumps over lower volume?
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Re: **Misting**

Postby Niek PD » Thu Nov 07, 2019 3:59 am

longtimefan wrote:Water or solvent?

Ph good?

Viscosity good?

Try any types of solvents?


Solvent ink, allready reduced the viscosity from 21 to 18 sec. din 4.
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Re: **Misting**

Postby Niek PD » Thu Nov 07, 2019 4:09 am

Frank Burgos wrote:That's a tough one. Gonna just think out loud:

Experimenting with a different ink occurs to me. Also, I believe that the blue Tesa is medium-hard. Can you get away with medium? I'm wondering whether impact at speed might contribute.

Finally, and not appealing, could you produce the same ink film thickness with two bumps over lower volume?


Hi Frank,

Because we need the restistance against the wheater etc. we have a custom Technical Compound in the ink. I contacted our ink supllier to test with a diffent TC, hope this will work!
I did some tests with medium tape. But this was more to standerdize, i did not give any extra attention whether this affected the misting. Could try this i guess.
Two bumps over lower volume is really difficult production wise. A 6 color job will be a 7 or 8 color job, longer changeover times, twice as much ink on stock etc.

If really nothing works i could maybe try to arrange this for particular customers, but this is really the last thing i would like to do :smile:

Thanks for the imput!!
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Re: **Misting**

Postby Frank Burgos » Thu Nov 07, 2019 7:49 am

OK, Niek. If I think of anything else, I'll post. In the meantime, there are a lot of knowledgeable and helpful people on this forum. Hopefully someone has other ideas.

Have a nice day!
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Re: **Misting**

Postby longtimefan » Thu Nov 07, 2019 9:01 am

Two bumps wouldn't necessarily be extra ink..

If your using a120 12? Maybe can use 2 aniloxes at 200 and separate by few decks for drying...

I've ran solid black and had to use 2 aniloxes.

If you are only doing 400 mom now, the change over and clean up and etc. Should be out weighed if you can go up to 600 mpm?

I also ran jobs that went outside and we used ink called weather tuff..I think was from siegwerk or at the time cci..
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Re: **Misting**

Postby Gory » Fri Nov 08, 2019 8:17 am

Niek PD wrote:
longtimefan wrote:Water or solvent?

Ph good?

Viscosity good?

Try any types of solvents?


Solvent ink, allready reduced the viscosity from 21 to 18 sec. din 4.


Occurs to me that running the ink thinner might be counter productive, thicker should be less prone to aerosolize
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Re: **Misting**

Postby just Andy » Fri Nov 08, 2019 4:24 pm

Niek PD wrote:Hello everybody,



Hi Dr. Niek (Simpsons joke, sorry had to)

Anyway...

Looking at the picture:
The size of the sleeve, relative to the Tesa logo, this is a big sleeve, if I had to guess it's repeat is 900-1000mm (40 inch)?. I also see it's one-around and very clearly this is a big solid plate.

So there's quite a few things that could contribute to this: anilox pressure, ink, plate type, plate bounce, and speed:

That gap of tape on the top of the sleeve looks far too wide. If there is such a big gap on the tape, you would probably need a lot of extra impression to get it to print out (particularly anilox pressure).
Ink is also a contributor and as Gory mentioned, the higher viscosity should be better than lower, however 21-18 DIN4 (32-27 Zahn2) is still a reasonable range. On top of that, if the ink is drying too slowly, the remaining ink on the plate is still wet enough to travel down to form the "mist". But mainly talk to your ink supplier about their pigment selection. If they are supplying you a permanent red for your weather resistance and lightfastness, they need to be careful with their formulation for good printability.
Plate type may play a role. Looking the shade of the plate I'm guessing it's ACE, it's a good plate but not textured. Textured plate surfaces typically give a better transfer of ink, so there's not much ink left on the plate when printed.
Plate bounce. That plate is one-around and a big solid plate. There's also a significant area of no print, which shows that there a possibility of bounce you may encounter. A turbulent design makes 600m/min quite a challenge then.
If the above are all in play, forcing it to run with speed may compound to the issues that you're describing.

Looking forward, while there are multiple possibilities, the quick ones to do is to close the gap on the mounting tape. Perhaps the plate is already indented, which means next time you may need set to kiss (for most of it) and pack the indented sections on the plate. Also talk to the ink guys about their formulation, considering you have a specific requirement on the red pigment used. And also remove the excess tape; it's just making cleaning the plate a lot harder and messier.

Hope these help and do keep us posted on what was the main cause. Cheers,
Andy
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