Tip 1: Coating the print job
There are a number of reasons to coat the cover paper of a book, folder or a poster, but the primary ones involve appearance and durability. If you want the book, for instance, to endure heavy use or last a long time (or if you want to protect heavy ink coverage from fingerprinting), consider coating the sheet. Or, if you want to contrast various dull or gloss effects against one another to highlight the printed images, you may also want to add an additional coating.
Here are four options to consider when choosing a protective coating. (Remember that this is in addition to the gloss or dull surface of a coated sheet. Protective coatings go on top of the printed, dried press sheets.)
The simplest and least expensive paper coating is a machine varnish. Essentially varnish is ink without its colorant (or the ink vehicle with no pigment). We add this coating by using one of the ink units on the press.
Perhaps you could coat the photos with the gloss varnish to make them stand out, and coat the background with a dull varnish to make it recede. Using both varnishes together would make the contrast more striking, and would cause anything covered with gloss varnish to “jump” off the page.
Varnish is the least durable coating, and it may yellow over time, so it’s wise to consider how long your printed product will be in use. It also can darken the inks over which it is printed. And it is not particularly useful when printed on an uncoated sheet, since it will be absorbed into the paper fibres like any other ink, potentially rendering it useless for both protection and any aesthetic effect.
UV (ultraviolet) coating “cures” under ultraviolet light. It is more expensive than machine varnish and is completed off-line (as a separate finishing step).
Since UV coating “cures” instantly when exposed to light (rather than drying when exposed to heat), no solvents are necessary and no VOCs (volatile organic compounds) are released into the atmosphere during its application.
Even more durable than UV coating is lamination. This comes as a film coating. Since it seals the press sheet completely, you might wind up with book covers that curl. In this case, the uncoated interior of the book cover absorbs moisture (humidity) and expands, while the coated side does not. You can avoid this problem by specifying “lay-flat laminate,” which is permeable and allows air to pass through the polyester coating.
Things to Remember
If you will need to write on a portion of your print job with a ballpoint pen, or if you will need to inkjet information (like addresses) onto the printed press sheet, you will need to leave an unprinted area with no protective coating. Otherwise, the ink (particularly ballpoint pen ink) will smear.