Successive Unit Mottling

We have a Heidelberg SM74 Six Color with coater and Alcolor Dampeners. When printing large areas of Pantone Colors on uncoated sheets the Pantone looks mottled with each successive unit. Such as when we print a solid in the last printing unit and don’t use the coater the Pantone color looks fine. But if we print the Solid Pantone color in the 4th unit then another color in the fifth and sixth units the Solid Pantone that was printed 4th unit seems to pull off on the fifth and sixth units and give a mottled appearance. It seems as though this began happening when we went away from film and started using Thermal Plates. Has anyone else experienced this problem and what did you do to remedy it. Any help would be appreciated.

 

We get the same problem so we set our PMS to print in the last unit on offset stocks. One of our customers switched from an offset to matte stock(on a particular job) due to this problem.
We haven't used film for several years now, but I can't see how that would be responsible for the problem.

 

It can affect, cuz there are more thing changing among with the plates. Thing such as fountain additives, percentage and IPA levels. Make sure that there are not scratches the things u see on the solid. If the ink does peel off, talk to your consumables guy.

 

I would also make sure you are using a high quality blanket. Day 3000 is pretty much top of the line blanket.

 

Sounds like the ink is being 'stripped' by the subsequent blankets. This can happen is the setting time of the ink is too quick.

I'd try adding some tint or trans white to the ink (say 10 - 15%) run the ink higher on the sweep and you should see an improvement.

Let us know how you go on.

 

trans white? is the same thing we use here.we call it "medium".use to reduce ink, more light so we can run the ink higher. help to reduce hickey on plate(delta system).

 

Trans(parent) white, tinting medium... both pretty much the same thing

 

Tinting medium, isn't that a psychic printer?

 

add some printing oil...

 

Are you sure you don't mean grease?

 

may b...