Hybrid Inks

[lynnic]

Hi All,
I am not a pressman, but this is a vague description of our dilemma if anyone cares to comment.
We are printing offset on Poly SBS using hybrid UV inks. This is a new substrate for us and are having difficulties such as maintaining consistent color, piling, ink drying on rollers.
Where to begin?
Thanks in advance!
Lynn

 

[chevalier]

Hybrids are a nightmare. The best but also the worst of UV and conventional printing combined. We also print them on metallic poly SBS and SBS.

Suggestions:

• First check the dyne of the foil and make sure your ink is able to bond to it. If there is not enough surface tension the ink cannot adhere even if it is curing enough. We've had bad batches of metallic poly come in and had to reject it. Every vendor seems to have their own secret sauce.
• If you don't maintain your UV curing lights or spot check them time to time now is the time to check and make sure they are producing sufficient UV light. Just because they make light does not mean they are emitting the correct spectrum. The spectrum does degrade over the lifetime of the bulbs which is why they have to be replaced after so many hours.
• If the other two variables check out you may need to work with the ink vendor increase the UV:conventional ratio. I suspect you probably have an in-plant. If you don't get somebody in the plant from the ink company pronto.

 

[Cornishpastythighs]

The Hybid inks around now are very good in my opinion, both Sun and Flint make excellent ink. True they do have a tighter operating window which means your printers have to be on their game and must pratice good operating procedures such as having all the rollers set correctly, fountain solution in good condition and running Hybrid blankets and inking rollers. Poly coated SBS is a non absorbant stock so I would actually run full UV on this type of substrate. Dynes need to be checked but this is more for ink adhesion. If the operators carry too much dampening it can be carried via the substrate(non absorbant) to the next print unit and cause issues such as colour control.
Lamps must be in good condition but the reflectors are the key to good ink cure, they must be cleaned to manufacturers recommendations and replaced if they are worn or dull.
If the ink is drying on the rollers it is either by too much heat or stray UV light from rollers or lamps, direct sunlight on the print units or there is far too much Photo initiator in the ink causing premature polymerization (thats not a sexual condition by the way)
You dont have to have a lamp after every unit and can wet trap UV or Hybrid only curing the high coverage inks and then curing end of print. This cuts down on the amount of heat on the blankets.
Hope this helps

 

[chevalier]

Cornish definitely covered some areas I overlooked...

We've had issues resolved by cleaning deflectors to get good curing. For whatever reason our operators didn't seem to think keeping them clean/tidy was important.

We also fought a drying issue for a week or two and the culprit turned out to be that the plant lightbulbs above the press had been replaced. The solution? Cut some board down and cover up the ink wells.

 

[Cornishpastythighs]

you can purchase covers for your lights that filter out the UV. These should be used anywhere there is UV ink open (ink fountains/rollers).

 

[lynnic]

Thank you all for your replies. We will take all this information and see what we can do.
I appreciate your input!