Commercial Printing: Thoughts on Added Paper Coatings

I received an email link to a commercial printing website this week. Being curious in matters of custom printing, I followed the link to a blog about this vendor’s options for cover coatings, or, more specifically, UV coating options.

This motivated me to do some more research into cover coating options. Here are a few things you might consider when specifying cover coatings.

Coated and Uncoated Paper

First of all, commercial printing paper can be categorized as either coated or uncoated. Coated paper has an extra transparent coating over its entire surface that is composed of such materials as calcium carbonate, kaolinite, and talc. This coating keeps printing ink up on the surface of the press sheet rather than allowing it to seep into the fibers of the paper. (This is called “ink holdout,” and it allows for crisp, heavily coated ink solids, precise type letterforms, and detailed photos.) Such paper coatings come in various surface textures: dull, matte, satin, and gloss. Gloss coating makes photos “pop.” Matte coating or dull coating makes text easy to read.

The other option, uncoated paper, is ideal for text-heavy print books or even annual reports, particularly if your goal is to present an environmentally friendly tone. Uncoated paper feels softer, and photos printed on uncoated paper will be a little less crisp (softer) than the same images printed on a coated press sheet. This is because the ink seeps into the underlying paper fibers.

So there are good reasons to choose both coated and uncoated printing paper. It all depends on your design goals.

Additional Paper Coatings

Once you have selected a press stock for your job, you can also choose to add an additional paper coating. For the most part, however, you would choose to do this only if you’re using a coated press sheet. This is because surface coatings seep into uncoated paper, leaving the surface either looking like it has no coating or looking unevenly coated.

(To understand this, think about what it would be like to paint on a sponge. You would not end up with an even, coated surface. The paint would just be absorbed into the cellulose fibers of the sponge.)

If you choose to add a paper coating to a press sheet, you have a number of surface textures to choose from and materials with which to do the coating, and you can produce a number of artistic effects with the coating.

To start with the goals, you would usually coat a press sheet to protect the printed ink. For instance, if you have heavy ink coverage on the cover of a print book, you might want to add a cover coating to protect the ink from scuffing. Scratches, or even fingerprints and other damage from the oils in your hands, can diminish the pristine quality of a printed piece. It can look old fast. A cover coating can minimize this damage, even over time and under heavy use.

Another goal might be to highlight elements of a design. For instance, if you print your job on a matte or dull press sheet and then “spot” coat the photos with a gloss coating, your photos will appear to jump off the page. You can do the same thing with type or a solid block of ink. (For instance, you might want to spot gloss coat a large initial capital letter on a page of your printed job.)

Regarding materials, you have a number of options for coating paper: varnishing, aqueous coating, UV coating, and laminating. In most cases you would choose one of these based on the surface texture you want, the overall cost (some options are more expensive), and the level of durability you need.

Varnish is similar to commercial printing ink without color. It is transparent. You would print a varnish using one of the printing units on your offset press. Therefore, you might choose to either flood the press sheet with the gloss or dull varnish (for protection or a particular sheen or smoothness), or you might choose to spot coat the sheet (to highlight only the photos, for instance).

On the downside, however, over time a varnish can yellow, changing the perceived color of the paper it covers. Varnish is the cheapest option, but it may be wise to use it primarily for items that do not need to last very long (such as a postcard that will be read and then discarded).

Your next option is liquid aqueous coating, which is applied with a coating tower at the end of a commercial printing press. (This is called “in-line coating,” as opposed to “off-line coating,” which refers to coating added after the job has been printed and has dried.) Being an aqueous product, aqueous coating is environmentally friendly. However, you would use aqueous coating primarily as a “flood coating,” in part because its application is not as precise as the application of a varnish. However, by using an aqueous coating, you avoid any problems with yellowing that varnish can present. Aqueous coating is also more durable than varnish.

UV coating is a third option. This liquid is usually applied “off line,” after the printed job has dried and on different coating equipment (sometimes by a different vendor altogether). It can be applied as a flood coating or a spot coating, and it can be one of the shiniest options you can choose (it can be glossier than varnish, for example). UV coating dries instantly (this is actually called “curing”) once it is exposed to UV light. Once cured, UV coating is inert (and therefore environmentally friendly).

A fourth option is lamination (think of menus in a pancake house, which must take a lot of abuse and be wiped clean with a wet sponge repeatedly). Lamination is applied off line. It comes in a number of thicknesses (from 1.2 mils to 10 mils or more). Lamination is expensive. (UV coating and aqueous coating are less expensive, and varnish is cheap.) If your print job has a long press run, lamination can add a considerable cost. It can also add considerable weight to a printed product, which can drive up mailing (i.e., postage) costs.

Things to Consider

Here are some things to keep in mind when selecting a paper coating:

1. 1. Varnish can be tinted with a little ink. This can provide a film of transparent color, which can be used for subtle, ghosted images. However, as noted before, it will yellow over time. The yellowing is more noticeable over unprinted paper than over process inks.

1. 1. Aqueous coatings have a higher abrasion resistance than varnish. They can also be smoother and shinier than varnish. Because they seal the underlying press sheet entirely, they can keep air away from metallic inks, keeping them from tarnishing. If your printer can specially formulate the aqueous coatings, you can write on them with a No. 2 pencil or overprint them with a laser printer. (Otherwise, you need to “knock out”–or omit varnish or aqueous coating from–any area that must be written on or mechanically addressed.) Finally, aqueous coatings are best on thicker press sheets. Thin press sheets (one article says less than 80# text) may curl or wrinkle.

1. 1. Aqueous and UV coatings can chemically interact with the underlying inks (certain hues like Reflex Blue and Rhodamine Violet have changed or burned out or bled, according to some of the articles I read). Time, heat, and exposure to light can cause these changes to occur, sometimes suddenly, up to months or years after the press run.

1. UV coatings come in a lot of different surface textures (as noted on the printer’s website I mentioned at the beginning of this article). The particular custom printing vendor who sent me the link includes “soft feel,” “rubber feel,” and “sandpaper” among their offerings. This can be especially exciting depending on how it is used. For instance, no online advertisement can be as dramatic as a print ad for an oceanfront property with a spot sandpaper UV coating over the sandy beach in the photo. That said, UV coatings can be tricky. Some printers want to only use them with UV inks; others require that the underlying inks be wax free and be allowed to dry completely before the application of the UV coating. Some recent ink developments involve hybrid inks that minimize drying problems and surface texture problems when used with UV coatings.

The Takeaway

Ask your commercial printing supplier for samples of any paper coatings you are considering. See exactly what they will look like before you commit to one coating or another.

Ask about any potential liabilities (drying problems, yellowing, etc.).

Ask about the potential for cracking if the print job folds and the coating extends across the folds.

Consider the cost (and the press run length). Choose an option that fits your budget.

Also consider any weight a thick coating (like laminating film) can add if you plan to mail your printed product.

This entry was posted on Monday, July 22nd, 2019 at 1:48 pm and is filed under Paper Coatings. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.