Varnish Film Thickness

[bmoflaz]

I am trying to document a procedure to ensure that we are applying enough varnish to our sheetfed press sheets. It is based on using a Starrett ink-film thickness gauge and reading the results. The gauge goes from 0 to 2 thousandths of an inch. What should I be shooting for?

-OR-

Is there a better way to ensure that we are applying the proper amount of varnish?

 

[Jim Klann]

Varnish Film Thickness

Measurements of the film of inks, varnishes or coating are usually measured in mils.

1.5 mils is usually considered safe, anything close to 2 mils takes some consideration to the stock surface and weight, the coverage of the ink on the side you are varnishing and the coverage of the back side of the sheet.

You might think that you could put a rookie on it, seems simple but that might be a mistake, it takes good judgement for when it will need to be winded (most always necessary) and how high to run your loads.

Ink Train aqueous coatings are a great way to go if it fits to the job needs but they can be tricky too.

If you don't have to worry about yellowing when using varnish on a job, consider adding China Wood Oil to your varnish, it will help with the bricking or sticking issues.

If you don't already, pull out your water form roller, when varnish or coating dries on them, its not nice.

Good Luck

Jim Klann
Foothill Printing & Graphics

 

[nhprinter]

IMHO the proper amount of varnish is what looks best to you and your customers. If you're getting the look you want and the protection you want then you're running the proper amount.

If you have a console on your press like we do you can put the same amount of varnish on every job by creating a formula with the ink keys by measuring the length of the varnish area and opening the keys a certain amount per inch and keeping the stroke the same for every varnish job.

 

[meddington]

A gloss meter could potentially be used to regulate the amount of varnish or coating via gloss diffrential.

 

[jlind]

I like NHPrinter's approach, but verify first with the gloss meter. I wouldn't use any more thickness than the largest yellow ink key setting. And this would vary with the paper surface and paper variety.

John Lind
Cranberry Township, PA
724-776-4718

 

[bmoflaz]

There is a lot of great information here. I appreciate all of your responses. I'll go over all of this and formulate something that we can incorporate into our routine that we can keep as a quality record.

 

[Richard]

Hi, try downloading Van Sons printers digest, there is suggestions there.

 

[Robilious]

Knowing how much to use
Overprint Varnish is clear when its printed. So how do you
know if your running too much or too little? Most printers
can judge this without any problem because they have done
it numerous times and have just developed a sense about it.
However, if this is your first time, there is a method that is
not really scientific, but works very well.
Adjust the ink and water balance to your normal
settings if spot varnishing. If varnishing entire sheets, adjust
the ink fountain keys evenly across so that a normal flow of
varnish feeds through. Using about a hundred sheets of
waste stock, begin running through the press. After running
about 50 sheets at the film thickness you feel is correct, stop
the press. Reach into the receiver tray and place your hand
on the top sheet. It should feel a little sticky. Place the palm
of your hand flat on the sheet and apply a little pressure.
Lift your hand gently. The sheet should stick to your palm
momentarily and then drop off. If it sticks to your palm and
doesn’t drop off, you’re running too much varnish, if it
doesn’t stick to your hand you’re not running enough. (Told
you it wasn’t scientific.)

 

[Brian.B]

In the metal sheet-fed industry we measure varnish by mils or by weight. Usually by weight. 10 - 12 mg/4sqin