Ink doubling effect in varnish

[Lukas Engqvist]

Some time ago when we had dryinig trouble we decided to change our varnish plates to 80% ink. Twice we noticed moire effects on magenta once in black, imaging 100% varnish was a way to circumvent the problem.

Recently however we are getting a doubling effect. It is in all solid colours and at 20% dot... so we know it has to do with the non-printing areas of varnish. Right now we go back to imaging 100% plates for varnish, but curious if anyone can explain why the non printing varnish areas would create a doubling effect.

Going 100% does solve the moire problems but there is still a vertical smearing (control strip has vertical and horisontal lines, horisontal lines are significantly darker). We will test integrated dampening in the varnish as soon as we get a breathing space from production.

 

[Lukas Engqvist]

Additional information as we are researching is that we changed blankets to "Böttscher". Previously we had "Kinyo" or "Man Roland"

 

[tmason]

Without seeing a press sheet, it sounds like you are flood coating with varnish and the non image area (blank paper with varnish only) has an ink image in the varnish that mirrors the actual image.

If this is the case, it can be corrected by running more varnish, varnishing off line, reducing the tack of the varnish or running less ink.