UV Gloss Varnish Turning Black areas Dull?

[jimvolkman]

I am printing 4-CP (UV Hybrid) plus UV Varnish inline on coated side of SBS. Have some pretty good solid black areas, black printing last before the UV.

Have run this order a fair amount over the past 2 years. In the last month or so I find that the areas with solid black seems to have a duller, almost pitted look after the UV Varnish is applied& cured, compared to the gloss over the other colors and the non-printed areas.

In fact, I found out by measuring the gloss level that it actually is declining (over the black only) by about 10-15 points when measured 24 hrs after printing.

I am looking into a number of possible causes, but has anyone heard of or dealt with this issue in the past and have any advise or cause so I might narrow my search.

I have tried changing paper, ink sequence, running faster, slower, putting trans white over final print (prior to varnish) and have not seen any dramatic improvement.

THX in advance for your support.
Jim

 

[Bob Peterson]

Jim,

Please answer the following questions:

1.) Are you inter deck curing?
2.) If no inter deck curing, what is the curing sequence?
3.) What is the TAC of the black build i.e. (240%, 280%, 320% etc.)
4.) What densities are you running on each of the 4/colors?

Based on the description of the problem what you are seeing is called gloss back. This is due to the ink film not being fully cured when the coating is applied. As the inks post cure the ink film contracts causing micro ruptures in the gloss coating which cause the dull effect.

The lack of cure can be attributed to many factors. If you can answer the above questions I should be able to provide you with a solution.

 

[Rhino]

UV Coating & Gloss back

UV Coating & Gloss back

Jim,

The "gloss back" or "dry back" you're experiencing is a commonly experienced problem in the industry. The not fully-cured black ink is migrating into the wet UV coating before it's cured resulting in poor gloss. I would recommend working with your ink supplier for a faster curing black ink and while you're at it, you may wish to test a new generation type of UV coating which we do offer that I believe will prove beneficial. Our RhinoFlexx series of UV coatings are environmentally-friendly, pressman-friendly and ODOR-FREE.

Visit our web site at Welcome To Rhino Performance Products or call 866-601-6241.

 

[Cornishpastythighs]

As you have run this job before without issues it could be your UV lamps/reflectors may need looking at. We had this very same issue running Hybrid, when we UV coated our gloss level was around 90, after a few hours it went down to 70. We had a very inefficient UV system on the press and had to let the job sit overnight to fully 'postcure' then UV coat the next day to achieve low 90's gloss levels.

 

[jimvolkman]

Thanks everone for their feedback. I will let you know how things turn out.

Jim

 

[Inks]

switch to a slower drying, stronger black. Despite common logic (as stated in other replies) it is the opposite of what they think. Let me know if you cannot solve this common issue.

 

[jimvolkman]

What is the theory behind the use of a slower (i'm assuming you mean slower curing UV) black ink?