All About Offset Coatings

The right coating can help protect the printed piece or add a creative dimension. The results will usually look best on coated paper because the hard, nonporous surface of coated paper holds the coating on the top of the paper rather than have it disappear by being absorbed into the paper. Even when trying to achieve an overall matte effect, a gloss coated sheet is usually the best paper choice and the gloss finish on the paper will provide superior printability. In general, uncoated papers do not benefit very much in appearance from coatings or varnishes, although either will help prevent rubbing in areas of heavy ink coverage. Matte or satin varnishes or coatings are the best choices for uncoated stocks.

Varnishes :Varnishes are applied on press like any other ink and can be tinted to create a special effect. Although gloss and matte varnishes are typically used as spot or overall coatings, they can also be incorporated in the process or spot color inks in order to provide a unique look to the presswork. They can be wet trapped (i.e. printed at the same time as the other inks) or dry trapped (i.e. printed as a second pass through the press after the other inks have dried). Dry trapping provides a superior result but is a more expensive process. Varnishes may yellow with age, however, this is usually not noticeable when the varnish is used over process colors, but it is noticeable when the varnish is applied over unprinted paper. They also require the use of offset spray powder on press to keep the printed sheets from sticking together before the varnish is completely cured. The powder left behind can adversely affect the look and feel of the finished piece.
Gloss varnish: This coating can be applied overall or in spot areas with high precision. A gloss varnish increases the saturation and depth of colors while improving image contrast. It provides good protection against rub-off but some fingerprinting will be apparent on dark or light colors. Because the gloss finish is highly reflective it creates glare on the surface of the print which may impair the readability of text. 

Matte varnish: This ink protects the sheet with a non-reflective coating which enhances the readability of text-heavy pages. Using a matte varnish over images tends to flatten and soften them, but it can provide a lush tactile quality to the paper surface. As with a gloss varnish the coating is printed with a litho plate, so it can also be spot applied with high precision. It is more resistant to fingerprinting than a gloss varnish however it will tend to scuff or gloss up with wear. If the presswork is packed for delivery it's a good idea to place blank paper between the printed items to prevent them rubbing against each other and scuffing.

Satin varnish: This coating is created by mixing gloss and matte varnishes together and offers an intermediate level of shine, with good scuff resistance.

Opaque varnish: Adding a small amount of opaque white to a varnish can give it a slight opacity which can help in creating a stronger separation between a gloss and a matte varnish. Adding a slight contamination with silver ink can accomplish the same effect on very dark colors. 

Strike-through matte varnish: A litho plate printed varnish that, when overprinted with an overall gloss UV or aqueous coating, will create a visual separation between areas of a press sheet. Gloss/matte effects work best on dark colors, or when enhance by the content of underlying graphics.

Aqueous coating: These water-based coatings are applied using a rubber blanket inline on a special dedicated press unit. among the most commonly used coatings available today and provide good protection from fingerprints and other blemishes. Aqueous coatings are less likely to yellow and are more environmentally friendly than varnishes. They dry faster than varnishes which translates into faster turnaround times on press. They don't require spray powder. Because they seal the ink from the air, they can help prevent metallic inks from tarnishing. Aqueous coatings can cause certain spot colors such as reflex blue, rhodamine, violet, purple, and PMS warm red to change color. Sometimes within a few minutes but also over time - months or even years later. Because the aqueous coating is water-based an typically applied over the entire sheet it is best to use at least an 80# text weight or heavier paper to prevent the paper from curling, distorted, or wrinkled.

Gloss aqueous: Usually applied as an overall coating, gloss aqueous offers better protection than gloss varnish. It is sometimes applied to a spot area however this requires cutting an expensive press blanket. It also results in edges that are not as sharp as a spot varnish and registration that is less precise. The surface dries instantly, making it an excellent choice for short run work-and-turn projects. Aqueous coatings help disguise surface flaws and roughness in the non-print areas of inexpensive papers. The gloss finish improves the apparent saturation of ink but somewhat reduces the readability of text.

Matte aqueous: A scuff resistant matte coating which, as with gloss aqueous, is generally applied overall. And like a matte varnish it will soften and flatten images slightly. 

Satin aqueous: A popular compromise between gloss and matte, offers a pleasing sheen and good sheet protection.

SoftTouch aqueous: A proprietary coating that is applied with a special metering roller to create a suede-like texture and extreme matte appearance.

Pencil receptive aqueous: This is a special matte aqueous coating that is designed to be pencil, ink and laser receptive. 

Dry erase aqueous coating: An inexpensive high gloss alternative to lamination to make any paper suitable as dry erase marker surface. 

Primer aqueous: A coating that is applied before lamination, or to difficult substrates to make them ink receptive. 

UV Coatings UV coatings are applied inline by printers or offline by finishers or converters. They are applied as a liquid, using a roller, screen or blanket, and then exposed to ultraviolet light to polymerize and harden the coating. Like aqueous coatings, UV coatings can cause certain spot colors to shift in hue. Some UV coatings may have a strong odor.

Gloss UV: Creates the highest printable overall gloss coating. Depending on the printer's equipment it can be applied to spot areas.

Matte UV: Depending on the printer's equipment it can be applied overall or just to spot areas. It is prone to fingerprinting.

Pearlescent UV: These gloss coatings include miniscule metal flecks in red, blue or silver, giving a pearlescent appearance. 

Orange peel UV: A slightly raised, textured finish, gives this coating a unique tactile and visual quality that is similar in appearance to thermography.