75DI Set-Off Issues

[75DI]

Hi All,

We are running a 4/0 75DI. This was a brand new install, with no known issues at the time.

Our house-stocks are 70# Offset and 100# Gloss Cover. We are using Toyo MZ Aqueous inks, Infrared Dryer, and Varn 27 un-coated spray powder.

We have acclimated the press-room to 72 Fahrenheit with an RH of 35%, allowing any new deliveries to acclimate before we go to press.

Given the above information, from the time we started rolling sheets off the press we had no set-off, nothing changed, however now, we are experiencing intermittent set-off only on the 70# Offset stock.

The powder unit is clear, there are no blockages, the delivery fans are not set to push the sheets down hard, and our press is GRACoL G7 calibrated to density.

Would anyone out there have an idea as to what may be causing the set-off on the 70# Offset stock?

We haven't changed stock, ink, powder vendors, neither have we had a swing in acclimation conditions...

Any ideas would be greatly appreciated.

 

[Greg_Firestone]

Hi 75DI,

Just wondering what the Total Ink Limit is on the artwork. It could be too much for the 70# stock. I believe the GRACoL ICC profile allows 320% max.

Greg

 

[75DI]

Hi Greg,

We are running with a total ink coverage average of 270%. This has us perplexed...

 

[Greg_Firestone]

Hi 75DI,

Is it average 270% or max 270%?

This is a tricky one ... especially since none of your materials have changed and things used to work.

Greg

 

[75DI]

Hi Greg,

Max 270%...

 

[ryobidave]

Before you attempt anything, I would suggest going to a larger micron powder. This will give you more separation between the sheets, which is why powder is utilized.

Are you also aqueous coating? I noticed you mentioned aqueous inks. If so, you may be pushing too much heat into the sheet or not evacuating enough moisture from the delivery.

If you meant aqualess inks, then again maybe the dryer is too high. You should measure your stack temperatures during your runs. measure about 4-6 inches from the top each time. Your temps should be somewhere around 95 degrees on the first pass.