Major set off

[GazKL440]

On monday mornin the next press over discovered that a job run on the weekend had set off worse than anything we had ever seen, about 5,000 sheets of 250gsm artboard that had been printed 5 col both sides then varnished 1 side to seal 877 silver.. it had plenty of drying time before varnishing(matt), and every precaution against set off had been taken(small stacks, PLENTY of spray powder and minimal varnish loading)

The stacks were absolute bricks from top to bottom, as little as the top 5 sheets had set off and even the sample sheets still on the console had set off... never seen set off of the like of it! We have only speculated so far but perhaps the varnish had reacted with the amount of powder on it(there was heaps) but nothing concrete was pinpointed.. it had set off over whole sheet even none image areas not just in the silver as first suspected The Job was done with Best One process and hostmann steinberg 877 silver and printlac, using nikkyala spray powder, on a Komori L526..

Thanks in advance for any ideas..

 

[REYES1377]

What was the load temp. ? to much heat can do this. Also if the pressman put any type of dryer in the varnish? To much dryer can have the opposite effect.

 

[GazKL440]

none of the above, just straight thru overprint varnish

 

[nhprinter]

Just a thought

Just a thought

Hi,

We had this happen once before with ink...not varnish, but the problem turned out to be a bad batch of ink.

Check the batch numbers on the varnish and see if this was the first time it was used in the shop.

Good luck,
Dave

 

[rathishvm1]

All metallic inks not drying faster and dryer addition.

All metallic inks not drying faster and dryer addition.

Hi,

We had this happen once before with ink...not varnish, but the problem turned out to be a bad batch of ink.

Check the batch numbers on the varnish and see if this was the first time it was used in the shop.

Good luck,
Dave

Ink film thickness required for metallic ink printing is debatable and when film thickness is more, tends to aggrevate the drying problem. Use ink dryer pastes from same manufacturer as ink to have a logical single source solution to the problem faced. Reduce pile heights, press room temperature, alcohol in dampener solution. Donot use pile turner!!!!

 

[otherthoughts]

Set-off just 5 sheets down from the top of the stack is way beyond powder settings, reasonable varnish feed rates and the usual suspects in my opinion.

I looked up PRINTLAC® and found this statement for all their varnishes,

Special remarks
Note should be taken of the following when using print varnishes In contrast with dispersion coatings and UV coatings, print varnishes are comparatively slow-drying. The mechanism of oxidative drying, which produces stable coating films in print varnishes as a result of the cross-linking of fatty acid chains, can occupy several hours or even days, depending on the drying conditions. Drying can be accelerated by the use of IR radiators. However, pile temperatures of more than 35 °C must always be avoided as there is a risk of blocking(emphasis mine). The use of inks in pre-printing that stay fresh can result in the delaying of varnish drying, especially on papers with low absorption capacity.
​

Whether you call it bricking or blocking, this seems to fit. It shouldn't be too difficult to confirm or eliminate pile temperatures with some simple follow up testing I would think?

For what it's worth.
Otherthoughts

 

[GazKL440]

The press is not equipped with dryers or coaters and the ambient temp was pretty low round 18-20deg c, with a relatively low run speed to avoid marking etc, and a pretty standard film of varnish applied... it did have a heap of spray prob more than average as it was to be de-sprayed.. this particular job has since been re run with a different varnish and it went thru no probs... one of those things hey?

 

[Lukas Engqvist]

We have found instances where varnishing a dry job means that the varnish wetts the inks rather than sealing them. Usually if the inks are surface dry rather than fully dry. Are you varnishing at 100%? We varnish at 80% to seal, but allow deep drying, unless we get moire with the varnish (has happened on 2 jobbs)

Is your spray corse enough? The spray is grains that are supposed to keep paper appart, so too fine grain can some times be a problem. A larger grain spray will have more effect than increasing the amount. (just a though, I am a prepress not a printer, but I listen to conversations)

 

[GazKL440]

the nikka spray generally gives excellent results and is a very fine, anti coagulating spray; to be honest its got us beat maybe just a bad batch of varnish it was reportedly like water pouring into duct.. the varnish run was done after the process + silver which was given enough drying time(over an hour) but the job set off across the whole sheet including non image areas after dry offset application so im guessing that discounts an ink and varnish reaction and leaves it at varnish+spray issue..

 

[otherthoughts]

It would seem that the unsatisfactory/bad-batch varnish might make an excellent glue

Regrds
Otherthoughts